2007 thomas the behavioural ecology of shellfish gathering in micronesia, 1, prey choice.pdf

8/11/2019 2007 Thomas The Behavioural ecology of shellfish gathering in micronesia, 1, prey choice.pdf

1/16

The Behavioral Ecology of Shellfish Gathering in Western

Kiribati, Micronesia 1: Prey Choice

Frank R. Thomas

Published online: 29 November 2006# Springer Science + Business Media, LLC 2006

Abstract Focusing on contemporary shellfish exploitation

among several atoll communities in Kiribati, Micronesia,

this paper examines the relationship between human

foragers and their invertebrate prey via the prey choice or

diet breadth model derived from optimal foraging theory.

Shellfish, like many other reef organisms, are relatively

sedentary and predictable, but these characteristics make

them susceptible to over-harvesting. The research reveals

that shellfish gatherers are foraging in a manner that

matches the predictions of optimal foraging theory. The

work adds to our understanding of optimal foraging

decisions in atoll settings by critically evaluating the

depiction of atoll dwellers as conservationists.

Key words Prey choice . shellfish gathering . conservation .

Kiribati . Micronesia

Introduction

Research into the behavioral ecology of food acquisition,

better known as optimal foraging theory (OFT), has

blossomed in recent years. Despite important ethnographic

and archaeological applications of foraging models, there

have been relatively few case studies of fishing strategies,particularly among tropical intertidal gatherers and fishers

(but see Aswani, 1998; Beckerman, 1983; Begossi, 1995;

Bn and Tewfik, 2001; Bird and Bliege Bird, 1997; De

Boer et al., 2002; Sosis, 2002). This two-part study of

shellfish gathering in a contemporary Pacific atoll setting

aims to test several models derived from OFT. This paper

focuses on the prey choice or diet breadth model. A second

article in this series will examine patch switching, patch

sampling, and risk.

Western Kiribati (formerly the Gilbert Islands) consists

of 16 atolls and table reefs spread over 640 km on both

sides of the equator in the west-central Pacific Ocean

between N330 and S245 and E17230 and E17700.

The area is considered part of Micronesia, a set of diverse

archipelagoes, which includes Nauru, the Marshall, Caroline,

and Mariana Islands.

There may be more than 1,000 species of shellfish in

Kiribati, based on estimates recorded in the neighboring

Marshall Islands to the north. Among the open atolls,

high biomass occurs together with relatively high diversity

due to the influence of the nutrient-rich waters of the

equatorial upwelling area (Paulay, 2001). As a result,

shellfish gathering is an important component of daily

subsistence activities among I-Kiribati (indigenous Gilbert

Islanders), with some species targeted for sale in local

markets.1

Hum Ecol (2007) 35:179194

DOI 10.1007/s10745-006-9066-5

F. R. Thomas (*)

University of the South Pacific, Pacific Studies Program,

PIAS-DG, Suva, Fiji

e-mail: [email protected]

e-mail: [email protected]

1

Compared to most finfish catches large quantities of shellfish areusually required to prepare a meal for a typical household. In that

respect, patterns of marine resource exploitation in Kiribati correspond

to the Pacific-wide focus on finfish as the major source of protein.

However, shellfish gathering increases during periods of daytime low

tides at new or full moon (spring tides). A significant rise in shellfish

consumption has occurred on South Tarawa, the administrative and

commercial center of Kiribati; a phenomenon linked to changes in

water circulation when causeways were built in the 1960s, encourag-

ing the establishment of certain species and increased fertilization by

sewage-driven nutrients (Paulay,2001). With growing populations and

internal migrations from the outer islands to the capital, there has been

more demand for cheap, easily gathered resources, such as shellfish.


2/16

Prey Choice

Optimal foraging theory postulates that all organisms select

food or prey types that maximize their short-term harvest

rate. An increased availability of food increases fertility and

survivorship. Minimizing time spent foraging allows the

pursuit of other fitness enhancing activities. Consequently

natural selection would favor individuals that are moreefficient foragers (Kaplan and Hill,1992). The optimal diet

is usually determined by comparing the amount of energy

acquired to energy expended, as well as time required to

search and process (handle) each prey type.

The prey choice or diet breadth model reveals the set of

resources that should be targeted by an efficient forager.

This model characterizes foraging behavior in a fine

grained environment where prey types are encountered at

random (i.e., in the same relative proportion throughout the

foraging area). A prey or resource type, which provides the

highest amount of energy acquired to energy expended per

unit time invested in pursuit and handling should always be

included in the diet on-encounter. It follows that when there

is a general increase in environmental productivity (result-

ing in frequent encounters with high-ranked resources), the

variety of food types falling into the optimal diet should be

more restricted than in situations where the environment is

less productive. Thus the inclusion of a prey type in the diet

should depend only on the availability of high-ranked prey

types, and not on its own availability (Emlen, 1966;

MacArthur and Pianka, 1966). In sum, the optimal diet

constitutes a trade-off between search costs and handling

costs (i.e., prey types are added in descending order until

the return rate per unit foraging time is maximized). A more

rigorous algebraic version of this model was developed by

Charnov and Orians (1973), which states that any prey jis

in the optimal diet set if its net energy return (Ej) per unit

handling time (hj) is greater than, or equal to, the average

return rate (including search time) for all prey types of

higher rank:

Ej=hjX

Li:Ei.X

Li:hi 1

Where Li is the rate at which each prey type is

encountered. To determine the optimal diet, three variables

must be known for each prey type: (1) the average expected

net energy gain after encounter with prey type i; (2) the

handling time with an individual of type i after encounter;

and (3) the rate of encounter with prey type i. It is assumed

that a forager knows, on the basis of past experience, the

mean encounter rate, average energy returns, and handling

costs associated with each prey type. Despite certain

methodological problems (for reviews and summaries of

case studies see Kaplan and Hill, 1992; Smith, 1983), the

prey choice model has shown its utility in structuring

questions and predicting the outcome of a number of

foraging decisions (Bettinger, 1991; Krebs and McCleery,

1984; Maynard Smith, 1978; Pyke et al., 1977; Smith and

Winterhalder,1992).

I-KIRIBATI Shellfish Patches

In most real life situations, resources are not randomly

distributed. Instead, they are clumped, so that their

distribution is said to be patchy or coarse-grained.

Environments that are markedly discontinuous (heteroge-

neous) consist of a patchwork of different resources, in

contrast to uniform or homogeneous environments contain-

ing similar or well-mixed resources (MacArthur and

Pianka, 1966). Where resources occur in patches, the key

assumption of the prey choice model, which states that

search time is equally shared among all prey types, would

seem inappropriate as the forager perceives resource

concentrations, often knows their location, and can accord-

ingly choose an itinerary, in violation of the random

encounter assumption of the model. While the prey choice

model cannot be applied to a set of prey types drawn from

different patches, within a patch, prey types will be

encountered randomly and the prey choice model is

appropriate. In sum, a forager must decide which set of

patches to forage in and how long to forage in each. These

issues will be addressed in a subsequent paper.

Shellfish gathering remains essentially a spatially

bounded activity. The I-Kiribati have long recognized that

specific areas (patches) of the lagoon and ocean habitats

tended to yield different resources or similar kinds of

resources but varying in density (Table I; Fig. 1). The

classification used in this study closely matches the patch

types recognized by the I-Kiribati.

The nearshore patch is primarily exploited for two shell

taxa: Smooth Beach Clam, Atactodea striata, and Pacific

Asaphis, Asaphis violascens. Women and children who

search for food visit this patch at low tide, digging into the

sand matrix. Being closest to shore, this patch is accessible

for relatively long periods of time, although the use of

beach latrines has limited exploitation near densely popu-

lated areas. The sand flat is the most extensive patch on the

lagoon reef flat. Resources there vary according to water

depth, size of sand particles, wave energy, and sand depth.

Several epibenthic, semi-infaunal, infaunal, and sessile

shellfish inhabit this zone. The sand flat supports the

economically important Burnt-end Ark, Anadara uropigi-

melana, Strawberry Conch, Strombus luhuanus, and Pecti-

nate Venus, Gafrarium pectinatum. The lagoon border of

sand flats may support extensive beds of seagrass along the

low intertidal and subtidal regions. Seagrass beds are

productive grounds for a variety of shellfish and are also

180 Hum Ecol (2007) 35:179194


3/16

important in fishing because of the high concentration of

nutrients. Beyond the seagrass, the lagoon slope was best

known for its fishing and commercial exploitation by divers

of A. uropigimelana on Tarawa Atoll. Spear fishing and

Giant Clam (Tridacnidae) gathering may take place along

the leeward reef platform in the vicinity of islets. Divers

often take the smaller species of Giant Clam, Tridacna

maxima, and collect the meat for sale in local markets.

Fishing and limited shellfish gathering also occur on the

ocean side of the atolls. As with the lagoon shore, the ocean

side is bordered by a nearshore patch. The reef flat extends

to the reef crest where Giant Clams and a variety of

gastropods can be found.

Methods

Field Methodology

Investigations were carried out intermittently between 1993

and 1998 and focused on communities living on five atolls:

Abaiang, Tarawa, Maiana, Abemama, and Tabiteuea. Data

on various aspects of shellfish gathering were obtained in

three ways: by participant observation (focal follows),

foraging diaries, and from the Shellfish Gatherer Survey

of the Tarawa Lagoon Project, a major interdisciplinary

environmental study of the lagoon (Abbott and Garcia,

1995). The following analysis is based primarily on

observed, quantitative data.

Data were recorded during 73 foraging expeditions

covering 69 days, for a total of 139.63 hours of direct

observation (286.92 forager-hours). Mean group size was

2.6 foragers (SD=0.9, N=146). A total of 59 different

individuals took part in these activities. Foragers were

generally members of the households where the investigator

resided and their neighbors. In addition, 65 foraging trips

were recorded from interviews over a period of 51 days, for

an estimated total of 88.5 h of foraging effort (161 forager-

hours). Mean group size was 3.1 foragers (SD=0.7,N=148).

A total of 19 different individuals were interviewed. A third

source of information was derived from data sheets made

available by personnel of the Tarawa Lagoon Project. This

information greatly expanded the sample size of foraging

events with 83 foraging trips covering 26 days and

approximately 191 h of foraging time (257 forager-hours).

Mean group size was 1.3 foragers (SD=0.7), involving 112

individuals. Although not originally conducted for measur-

ing foraging input and output, the survey nevertheless

included data to assess foraging efficiency, while providing

for an independent check of the harvesting patterns noted

through direct observation.

Analytical Methodology

Foraging activities were measured with a digital stopwatch.

Obtaining complete timemotion records for central-place

handling often proved difficult because processing activities

could be carried out at any time of the day or night. Similar

difficulties were encountered in attempts to measure costs

of acquiring firewood in preparation for boiling shellfish to

facilitate extraction of the animal. It was decided to exclude

the latter costs, while attempting to sample the various costs

of culling inedible parts of prey items. In the present

analysis, energy is assumed to be the maximized currency.

As will be demonstrated, observations are generally

consistent with the predictions of net energy maximization.

In other words, local shellfish gatherers appear to maximize

their overall returns within this particular food class, as

opposed to total caloric production. Although not addressed

in this study, more accurate assessments of the nutritional

value of shellfish can be achieved by examining the entire

range of I-Kiribati foraging patterns. Suffice it to say that

the bulk of energy requirements are derived from carbohy-

drate-rich foods, such as breadfruit, rice, and flour (Pargeter

et al., 1984).

Timemotion records (Nydon and Thomas, 1989) were

converted into estimates of energy expenditure. Energy

levels (kcal/minute/forager) for different age and sex

classes were derived from published sources (Durnin and

Passmore, 1967; Norgan et al., 1974; Ulijaszek, 1995).

Table I Main Shellfish Patches and Resources Found on a Typical Kiribati Atoll

Patch Resource

Lagoon nearshore Atactodea striata; Asaphis violascens

Sand flat Anadara uropigimelana; Strombus luhuanus; Gafrarium pectinatum

Seagrass Anadara uropigimelana; Strombus luhuanus; Gafrarium pectinatum; Trachycardium angulatum; Timoclea marica

Lagoon slope Anadara uropigimelana

Leeward reef platform Tridacna maxima; Hippopus hippopus; Lambis lambisOcean nearshore Atactodea striata; Asaphis violascens; Nerita spp.

Reef flat Tridacna maxima; Hippopus hippopus; Turbo setosus; Vasum turbinellum

Reef crest Turbo setosus

Hum Ecol (2007) 35:179194 181


4/16

Activity categories specific to shellfish gathering were

matched to their closest published equivalents, corrected

for tropical basal metabolic rate reductions of 10.3% for

males, 3.8% for females, and 7.4% for subadults (cf. Henry

and Rees,1991).

The values in TableII refer to the activities of an average

adult male and female weighing 68 kg and 58 kg,

respectively. The average weights are derived from a

sample of 18 males and 40 females from Ontong Java

Atoll in the Solomon Islands aged between 20 and 29 years,

reported by Friedlaender and Rhoads (1987) and applied to

this study. The weight of a reference subadult (10

12 years of age) is 35 kg (FAO/WHO/UNU,1985, p. 136).

Measurements from this PolynesianMicronesian popu-

lation are used in the absence of local data on weights 2. In

cases where published values are not available, the activity

Fig. 1 Lagoon and ocean

patches from a section of Tar-

awa Atoll (courtesy South Pa-

cific Applied Geoscience

Commission).

2 Although Ontong Java is commonly classified as one of the

Polynesian Outliers in Melanesia, it was shown to have consider-

able PolynesianMicronesian affinities(Mitchell et al.,1987, p. 51).

182 Hum Ecol (2007) 35:179194


5/16

specific expenditure rate for a woman weighing 60 kg, agedbetween 18 and 30 years, and a subadult weighing 35 kg,

aged between 10 and 12 years, is estimated at 85% and 71%

of the adult male value, using a 70 kg male reference

individual, aged between 18 and 30 years, and a basal

metabolic rate of 22.4 kcal/kg/day (cf. FAO/WHO/UNU,

1985, pp. 133134, 136; Henry and Rees, 1991). Mean age

for observed males was 22.2 years (SD= 10.4,N=19), while

the mean for females was 28.9 years (SD=9.1, N=20). A

mean of 11 years old (SD=4, N=20) was obtained by

combining both male and female subadults under the age

of 18.

Fossil fuel and equipment inputs were excluded forcomparability with extant analyses of foraging efficiency.3

The energy acquired per harvest was determined by

weighing the total edible portion for each prey type, using a

dial scale in the field (5 g increments) and applying the

appropriate caloric values. In circumstances where it was

not possible to measure meat weights separately, conver-

sion actors (ratio of edible soft parts/total weight), obtained

from various sources, were utilized (cf. Bird, 1996, p. 168;

Salvat, 1972; Yamaguchi et al., 1993). Twenty-four

shellfish prey types locally regarded as edible were

analyzed for proximate composition (Table III). Amino

and fatty acid profiles followed the methods described by

Tamaru et al. (1992), with methionine determined as thesulfone. Energy was then calculated. All analyses are single

trial, except for Gafrarium pectinatum, where the values

represent the average of two trials.

Average productivity of each prey type was established

by calculating on-encounter profitability per bout (load)

E/h (kcal/min) and overall efficiency E/T (kcal/min), where

T is total foraging time (sum of the time spent searching Ts

and handling Th). The number of observations N listed in

the subsequent tables refers to the number of distinct

foraging bouts where a particular prey type was harvested.

For group foraging (when several foragers contributed to

one bag or basin and proceeds were expected to be shared),a simplifying assumption was made in that time spent in

search and handling was equally shared among foragers,

particularly in situations where relatively dense resources

occurred, with search and handling following each other in

quick succession. While this assumption may be tenuous

among groups possessing different foraging abilities (e.g.,

adults vs. young children cf. Bird and Bliege Bird,

2000), subadults who participated in shellfish gathering

activities essentially confined themselves to searching and

harvesting easily accessible resources (i.e., epifaunal or

shallow, infaunal taxa), and thus probably tended to match

adult performance in terms of foraging efficiency.

Results

Prey Choice

A foraging bout usually takes place within a single patch

type, for example, a sand flat, seagrass bed, or nearshore

biotope. Most households are concentrated on the lagoon

3 It is methodologically feasible to calculate the caloric value of fossil

fuels, but as argued by Smith (1991), this approach significantly

reduces the validity of correlating adaptive costs and benefits with

energetic ones. While the monetary cost of fossil fuels can be

incorporated into labor time and energy measures, there are method-

ological dilemmas arising from the analysis of mixed economies

where currencies such as money and energy are used, or where

overhead costs such as equipment maintenance must be divided

among different productive activities.

Table II Activity Categories and Energy Expenditure Rates for I-Kiribati Shellfish Foraging Time/Energy Budgets

Activity category Published equivalent Male (kcal/min) Female (kcal/min) Subadult (kcal/min)

Process shellfish Sitting working1 1.2 1.0 0.9

Gather shellfish Standing working2 1.4 1.2 1.0

Dig in soft sand Dusting3 3.0 2.6 2.1

Dig in gravelly sand Clear light bush4 3.4 2.9 2.4

Underwater gathering Underwater swimming

5

5.4

3.8Breaking Lambis shell Cut tree6 6.2 5.3

Underwater swimming with load Walking uphill at own pace at 1,800 m7 7.2

Pry shellfish Husk coconuts8 6.2 5.2

1 Ulijaszek,1995: 382 Ulijaszek,1995: 393 Ulijaszek,1995: 364Norgan et al., 1974: 3395 Durnin and Passmore, 1967: 706Norgan et al., 1974: 3427 Ulijaszek,1995: 398Norgan et al., 1974: 341

Hum Ecol (2007) 35:179194 183


6/16

side of the islets and harvest shellfish and other resources

from this habitat. Where seagrass occurs, it becomes the

focus of the most intensive gathering pressure. Women and

children concentrate on resources in the intertidal andsubtidal areas of the lagoon where they can easily locate the

telltale signs of their prey. Lagoon slope and leeward reef

platform diving is an activity carried out by males only. The

higher in-patch returns in lagoons compared to ocean

patches is the reason why lago onal gath ering is of

considerable importance. Although foragers are quite

willing to walk relatively long distances on the exposed

intertidal lagoon flat (often in excess of overland distances

from a central-place to the ocean side), they also have more

opportunity to increase their net energy acquisition rate

across the various lagoon patches as the tide comes in andthey are compelled to move closer to shore to the less

productive patches (but still more productive relative to the

intertidal ocean patches) (Thomas,2002).

Seagrass and Sand Flat Table IV illustrates average

productivity of observed seagrass resources. As landings

from the Tarawa Lagoon Project indicate, species compo-

Table IV Seagrass Foraging: Profitability and Overall Returns

Prey type Gross kcal Net kcal Encounter rate/min E/h (kcal/min)

1

Rank

Trachycardium angulatum N=1 181 179.7 0.1 179.7 1

Anadara uropigimelanaN=10 141.1 SD=213.6 138.7 SD=210 0.8 SD=1.5 61.8 SD=15.6 2

Strombus luhuanus N=7 721.8 SD=716.8 689.4 SD=684.4 5.4 SD=6.7 19.6 SD=3 3

Gafrarium pectinatum N=3 8.3 SD=0.9 7.5 SD=0.4 0.2 SD=0.1 14.4 SD=1 4

E/T (kcal/min)2

5.3

SD=3.5

1 Values used to calculate E/h can be found in Thomas (1999).2 E/T refers to the overall returns for this patch. Details about whether it is optimal to include any item amongst the ranked resource types in

descending E/h beyond the highest-ranking item are discussed throughout the text and in Thomas (1999).

Table III Summary of Biochemical Analyses (g/100 g and kcal/100 g raw, wet edible weight)

Taxon Amino acids Fatty acids Glycogen Kcal

Nerita plicata 21.8 0.548 1.55 98.3

Cymatium muricinum 19.7 0.473 1.91 90.7

Strombus luhuanus 19.5 0.419 0.82 85.0

Polinices melanostomus 18.2 0.400 2.06 84.6

Nerita polita 18.2 0.542 1.62 84.1Vasum turbinellum 17.3 0.431 1.91 80.7

Lambis lambis 17.6 0.288 1.77 80.1

Pitar prora 16.5 0.563 1.64 77.6

Tridacna maxima 14.5 1.112 1.90 75.6

Atactodea striata 15.6 0.807 1.44 75.4

Gafrarium pectinatum 13.3 1.475 1.64 73.0

Barbatia foliata 14.6 0.600 2.18 72.5

Polices tumidus 14.5 0.331 2.63 71.5

Strombus variabilis 13.9 0.408 1.19 64.0

Timoclea marica 12.7 0.681 1.49 62.9

Turbo setosus 12.7 0.723 1.23 62.2

Oliva miniacea 12.7 0.482 1.46 61.0

Hippopus hippopus 9.6 1.256 1.72 56.6

Anadara uropigimelana 11.9 0.373 1.26 56.0

Tridacna gigas 7.9 0.733 3.38 51.7

Spondylus squamosus 10.3 0.491 0.81 48.9

Trachycardium angulatum 9.5 0.533 0.91 46.4

Quidnipagus palatam 6.9 0.289 2.75 41.2

Asaphis violascens 7.7 0.423 1.16 39.2

184 Hum Ecol (2007) 35:179194


7/16

sition in seagrass and sand flats is roughly comparable,

except for overall density, which is higher in the former

(Paulay, 2001). Sand flats are more accessible than

seagrass-covered areas, which are basically subtidal, be-

cause they occupy large sections of the mid- to low

intertidal zone. With the exception of Tarawa Atoll,

seagrass is either absent or distributed in small patches on

the outer islands, so that foragers spend most of their time

in sand flats. Despite their seemingly barren appearance,

sand flats provide both shelter and suitable algal foods for

S. luhuanus in areas with mixed soft sand and hard

substrata, while the mid-intertidal is often the focus of G.

pectinatum harvesting.

Table V summarizes sand flat harvests. More hours of

direct observation (42.17) were recorded than in seagrass

patches (20.73) because more time was spent with house-

holds living adjacent to areas largely devoid of seagrass.

It is useful to examine the implications of incorporating

central-place handling or postharvest processing costs.Anthropologists have for some time considered the appli-

cation of central-place foraging models (Stephens and

Krebs, 1996, pp. 5460) to determine the way in which a

maximum load will affect the ranking of resources located

at a distance from a home base and to establish under what

circumstances resources should be brought whole or be

processed prior to transport (Barlow and Metcalfe, 1996;

Bettingeret al., 1997; Bird, 1996, 1997; Bird and Bliege

Bird,1997; Jones and Madsen,1989; Metcalfe and Barlow,

1992; Thomas, 2002). The issue has potential significance

in the analysis of decision-making in whether or not the

comparative difficulty of handling a prey type once

harvested affects its rank order.

TableVIcompares E/h and rank order for seagrass prey

types with and without postharvest processing. Inclusion of

postharvest processing does not alter the ranking. However,

in the sand flat (Table VII), only Trachycardium angula-

tum, Barbatia foliata, andA. uropigimelana have unaltered

rankings.

Whether or not postharvest processing is included, T.

angulatum is the highest ranking prey type, but compared

to A. uropigimelana, its apparent density is low. Although

no quantitative data on density are available, this prey is

apparently harvested in equal proportion to its abundance

Table V Sand Flat Foraging and Overall Returns

Prey type Gross kcal Net kcal Encounter rate/min E/h (kcal/min) Rank

Trachycardim angulatum N=1 7.3 7.2 0.01 180 1

Barbatia foliata N=2 29 SD=25.6 21.1 SD=14.6 0.5 SD=0.6 71.8 SD=89 2

Anadara uropigimelanaN=16 172.3 SD=345.5 165.6 SD=329.1 1.2 SD=2.1 56.7 SD=20 3

Pitar prora N=1 1.3 1.26 0.01 31.5 4

Polinices melanostomus N=1 33.8 32.4 0.7 24.4 5Strombus luhuanus N=13 449 SD=402.8 433.7 SD=390.7 3.3 SD=2.5 21.8 SD=4 6

Gafrarium pectinatum1 N=1 91.3 88 1.4 16.4 7

Oliva miniacea N=1 24.4 22.4 0.4 10.3 8

Spondylus squamosus N=1 92.9 58.3 0.5 9 9

Polinices tumidus N=2 70.3 SD=118.7 66.8 SD=112.9 0.3 SD=0.5 9 SD=9.4 9

Cymatium muricinum N=2 32.9 SD=36.9 30.4 SD=34.4 0.7 SD=0.8 6.2 SD=1.5 10

Strombus variabilis N=1 2.1 1.9 0.02 5.0 11

Gafrarium pectinatum N=8 317.2 SD=112 131 SD=91.8 27.7 SD=52.4 3.3 SD=3.1 12

Gafrarium pectinatum/Pitar prora N=2 198.8 SD=33 70.1 SD=19.9 13.3 SD=14.1 1.4 SD=1 13

Gafrarium pectinatum/Timoclea marica N= 2 158.7 SD =75.3 53.7 SD =24.5 28.2 SD =11.1 1.3 SD =0.1 14

Barbatia foliata2 90.6 214.8 10.7 4.5 15

E/T (kcal/min)

3.6

SD=3

1 With digging considered search.2 Experimental harvest.

Table VI Seagrass Foraging: Comparison of Profitability and Prey

Type Rank Order Before and After Postharvest Processing

Prey type E/h without

postharvest

processing

Rank E/h with

postharvest

processing

Rank

Trachycardium

angulatum

360.5 1 179.7 1

Anadara

uropigimelana

124.4

SD=31.2

2 61.8

SD=15.6

2

Strombus

luhuanus

89.2

SD=1.5

3 19.6

SD=3

3

Gafrarium

pectinatum

29.3

SD=2

4 14.4

SD=1

4

Hum Ecol (2007) 35:179194 185


8/16

(expected encounter rate) in both patches.T. angulatumwas

harvested on only 10% of all foraging trips (N=146

combined observed, interview, and Shellfish Gatherer

Survey samples), and the mean number of specimens

gathered per bout was 4.3 (SD=6.9). A. uropigimelana is

a prey type that is both high ranked (always taken on-

encounter) and relatively abundant (therefore common in

the diet, unlike T. angulatum).

S. luhuanus(ranked fourth and sixth in sand flats before

and after postharvest processing), is an interesting prey typeprecisely because of the contrast in handling time and its

implications for selectivity. Moreover, the behavioral

attribute of this gastropod to aggregate violates the models

assumption of random encounter of available prey types:

encountering one item increases the probability of encoun-

tering another. Aggregation appears to be a feature of all

members of the genus Strombus (Catterall and Poiner,

1983). Here we have the equivalent of a patch, which can

influence the profitability of the prey type.

Excluding the firmly attached B. foliata and Spondylus

squamosus, G. pectinatum and other infaunal bivalves are

the lowest ranking prey. In a sense, the rank of G.pectinatum is seemingly at odds with its position as a

targeted prey. Taken at face value, the fact that it is sought

after may very well give credence to the notion that sheer

abundance alone is a determinant of collecting rate. Closer

examination of this prey types characteristics and

extrinsic factors, however, shows that when it is targeted

or otherwise harvested, foragers are indeed behaving

efficiently.

The clumped or patchy distribution of several infaunal

prey, similar to Strombidae, may be instructive here.

Because of their density, it is not uncommon for a forager

to dig up two or more prey items at once. Second, prey may

lie so close to the surface that they are visible to a forager

walking in either seagrass or sand flat. Field handling is

thus reduced, and is comparable to the costs incurred while

harvesting semi-infaunal or epibenthic prey. Some of the

observed variability in E/h for G. pectinatum can be

attributed to whether the prey was buried or lying near the

surface. The third aspect influencing foraging decisions is

the tidal cycle that repels or attracts efficient foragers to andfrom the mid-intertidal where overall returns may be

maximized under a different set of constraints. These

migrations are important for understanding the wider

problem of patch switching. With the exception of two

foraging trips, G. pectinatum was targeted when relatively

high water levels, often accompanied by windy conditions,

would undoubtedly have prevented efficient foraging in the

low intertidal because of reduced visibility. The exceptions

include one observed and one interview case. In both

instances, the presence of small children, who needed to be

supervised while adults collected, probably would have

reduced foraging efficiency in the deeper sections of thesand flat.

The remaining prey types were not specifically targeted,

either because their overall density precluded a focused

harvest or that environmental conditions effectively limited

the duration of the foraging process, such as for shallow

burrowing Polinices spp. and Oliva miniacea whose

characteristic trails in the sand can be spotted only at

extreme low tide. On-encounter, however, they are fre-

quently taken, because they differ little in terms of field

handling costs compared to the other prey types.

Table VII Sand Flat Foraging: Comparison of Profitability and Prey Type Rank Order Before and After Postharvest Processing

Prey type E/h without postharvest processing Rank E/h with postharvest processing Rank

Trachycardium angulatum 361.1 1 180 1

Barbatia foliata 140.3 SD=184.3 2 71.8 SD=89 2

Anadara uropigimelana 121.6 SD=30.3 3 56.7 SD=20 3

Strombus luhuanus 94.1 SD=16.2 4 21.8 SD=4 6

Oliva miniacea 80.2 5 10.3 8Pitar prora 64.1 6 31.5 4

Polinices melanostomus 58 7 24.4 5

Strombus variabilis 52.2 8 5 11

Cymatium muricinum 49.8 SD=11.7 9 6.2 SD=1.5 10

Polinices tumidus 43 SD=37.7 10 9 SD=9.4 9

Gafrarium pectinatum1 31.1 11 16.4 7

Spondylus squamosus 9.3 12 9 9

Gafrarium pectinatum 4.6 SD=5.1 13 3.3 SD=3.1 12

Gafrarium pectinatum/Pitar prora 1.8 SD=1.2 14 1.4 SD=1 13

Gafrarium pectinatum/Timoclea marica 1.6 SD=0.1 15 1.2 SD=0.1 14

Barbatia foliata2 4.5 16 4.5 15

1 With digging considered search2

Experimental harvest.

186 Hum Ecol (2007) 35:179194


9/16

Prey that are avoided on-encounter includeB. foliataand

S. squamosus, unless they are detached from their matrix or

weakly fastened. As in the case for the occasional infaunal

bivalve lying close to the surface, a weakly attached bivalve

may be considered a different prey type than one firmlyembedded even if they are the same taxon. This encounter

variability is an example of partial preferences, and

underscores the importance of context when analyzing prey

choice (Stephens, 1985). Given the fact that foragers

seldom venture into the lagoon with a cutting implement,

some opportunities to increase E/T are probably missed

when one encounters weakly attached prey.

In most observed cases and the assessment of other data

sources, the addition of prey types increased overall returns.

Apparent departure from optimal foraging was noted in

nine cases, including six observations. All involved the

gathering of infaunal prey (mostly G. pectinatum) from themid-intertidal when foragers decided to move closer to

shore with the rising tide. But as previously noted, this

behavior is suboptimal only when compared to favorable

gathering conditions in the low intertidal and shallow

subtidal areas of the lagoon, and a sufficiently high

encounter rate with high ranking prey. To some extent, this

resembles patch switching, even if the sand flat was defined

as a single patch type. When these two sets of activities are

combined (i.e., searching and harvestingS. luhuanusand A.

uropigimelana lagoonward, and digging in the mid-

intertidal), E/T is depressed. However, because of changed

constraints linked to the rising tide and its attendant

influence on foraging efficiency and possible risk, foragers

are in fact maximizing their returns. Although one cannot

say that foraging in the mid intertidal is in strict violation ofthe simultaneous search assumption (there is still the

possibility of encountering other prey types, including the

occasional A. uropigimelana and S. luhuanus), an efficient

forager should harvest infaunal bivalves and forego the

benefits of searching and handling other prey. Therefore,

under different sets of constraints as reported here, the fine

grained assumption is only weakly supported. Another

example of changed constraints resulted in what appeared

to be a further illustration of suboptimal harvest. In this

instance, foragers left the low intertidal because of

approaching nightfall, which would have hampered the

search for both epibenthic and semi-infaunal prey, anddelayed the return home. Harvesting continued closer to

shore by digging forG. pectinatum.

There were several cases from the Tarawa Lagoon

Project seemingly at odds with the idea of foraging

efficiency. Although the quality of the data prevented a

better assessment, conditions analogous to those described

above are suggested, such as harvestingG. pectinatumfrom

seagrass, possibly because they were visible from the

surface, or gathering S. squamosus that might have been

detached from their matrix.

Table IX Nearshore Foraging: Comparison of Profitability and Prey Type Rank Order Before and After Postharvest Processing


Nerita plicata1 21.8 1 2.6 1

Asaphis violascens 5 SD=7.9 2 1.3 SD=2.3 2

Nerita polita 1.9 SD=1.1 3 0.7 SD=0.6 3

Atactodea striata 1.2 SD=0.6 4 0.6 SD=0.4 4

Asaphis violascens/Quidnipagus palatam 0.9 SD=0.1 5 0.7 SD=0,04 3

Quidnipagus palatam2 0.2 SD=1.2 6 0.4 SD=1.2 5

1 Experimental harvest.2 Experimental harvest.

Table VIII Nearshore Foraging: Profitability and Overall Returns


Nerita plicata1N=1 126.3 101.1 45.7 2.6 1

Asaphis violascens N=9 263.3 SD=115.1 81 15.1 SD=20.6 1.3 SD=2.3 2

Asaphis violascens/Quidnipagus

palatam N=2

178.8 SD=214 145.6 SD=44.6 7.6 SD=4.5 0.7 SD=0.04 3

Nerita polita N=2 172.4 SD=77.4 74.5 SD=73.5 64.8 SD=35.3 0.7 SD=0.6 3Atactodea striata N=2 118.4 SD=60.8 21 SD=4.6 272.8 SD=179.9 0.6 SD=0.4 4

Quidnipagus palatam 2 N=3 191.4 SD= 201 18.3 SD=189.2 73.3 SD=73.3 0.4 SD= 1.2 5

E/T (kcal/min)

0.6

SD=0.5

1 Experimental harvest.2 Experimental harvest.

Hum Ecol (2007) 35:179194 187


10/16

Lagoon and Ocean Nearshore Unlike seagrass and sand

flats, nearshore patches on both lagoon and ocean sides

support a limited variety of prey types, although densities

may be locally abundant. Because of the restricted number

of observations, returns for A. violascens (the most often

targeted nearshore prey type) from both lagoon and ocean

patches were combined, because they are essentially

similar. TableVIIIshows the results of observed nearshore

harvests, while Table IX compares profitability and prey

type rank order with and without postharvest processing.

While A. violascens is the primary focus of nearshore

harvesting, it is probably not by virtue of being more

abundant than other nearshore prey types, such as the

smallerNerita plicata orA. striata. In fact, on the basis of

the inverse correlation between abundance and meat yield

(McNab, 1963), smaller prey are expected to be more

abundant. Consequently, there is compelling reason to

believe that A. violascens is gathered because of its

profitability. Of course, new constraints, such as increasing

levels of nearshore pollution associated with the use of

public latrines, may be determining factors in foragingdecisions4 A. striata can be a focal prey, but nearly always

for a segment of the human population (i.e., infants who

can easily digest small bivalves). The constraint here lies in

the infants ability to digest larger prey, so that a forager

may decide to focus on A. striata even if it means that

overall returns could be depressed.

Most foraging bouts within nearshore patches (N=40,

combined samples) involved the harvesting of a single prey

type, mainly A. violascens. In the few cases where more

than one prey was included in a catch (N=7, five

observations and two interviews), the addition of lower

ranking prey increased overall returns, except in one instance

where the focus shifted from gathering A. violascens to A.

striata. Not surprisingly, the adult male was planning to

secure a meal for his infant son. Otherwise, he may very

well have continued to forage forA. violascens.

Lagoon Slope Over a decade ago, the lagoon slope on

South Tarawa became the focus of an intensive A.

uropigimelana fishery. It is possible that these offshore

beds were new and made more attractive by declining fish

stocks, which prompted commercial fishermen to exploit

the largely undisturbed A. uropigimelana shellfish beds.

The year 1993 coincided with the rapid expansion of this

fishery. Two years later, however, few divers were seen. A

number of informants claimed that because of a tuna

surplus, the price of fish had dropped, thus contributing to a

decline in shellfish harvesting. Other informants stated that

lagoon slope gathering was no longer profitable because of

stock declines, presumably as a result of overharvesting.Table X shows profitability and overall returns for this

patch. Because all divers were men (who do not generally

process their catch after harvesting) E/h only reflects field

handling. At any rate, a prey destined for sale, as was the

case for most shellfish gathered from the lagoon slope,

obviously frees foragers from postharvest processing costs.

From the consumers point of view, T. angulatum and A.

uropigimelana obviously provide large meat packages and

minimal processing compared to S. luhuanus.

In 80% of the cases from South Tarawa (N=10), divers

specifically targeted A. uropigimelana for sale. The two

remaining divers collected for subsistence, and on bothoccasions, gathered the lower ranking S. luhuanus as well.

In both cases, however, E/T was raised.

While overall returns exceed those calculated for

seagrass and sand flats, major constraints facing foragers

include the need to secure a canoe or a floating device to

travel to the patch and hold their catch, as well as the

strenuous nature of the work: divers commonly free dive to

36 m for many hours each day to gather marketable

shellfish. A less obvious constraint may relate to gender

roles. Shellfish gathering is primarily a female activity, but

4 Although N. plicata is the highest ranked resource in the nearshore

patches, it may be avoided to a greater extent than A. violascensbecause of its proximity to the surface and evidence of pollution. This

highlights the type of patch classification used in this study, which

could benefit from greater refinements to take into account horizontal

and vertical differences among various benthic biotopes with variable

geomorphology and, consequently, species assemblages. As it stands,

the present classification can be said to violate random cropping

(Anderson, 1979; Sutherland, 1982) for the above resources, as they

are not strictly handled simultaneously. Because N. plicata occurs at

shallower depths than A. violascens, a forager is faced with the

decision to either handle the former by simply gathering this prey

type from the surface or expend greater effort by digging into the

gravelly matrix where the latter are concentrated.

Table X Offshore Foraging: Profitability and Overall Returns

Prey type Gross kcal Net kcal Encounter rate E/h (kcal/min) Rank

Trachycardium angulatum N=2 19.9 SD= 17.8 19.7 SD=17.7 0.03 SD= 0.02 446.9 SD= 126.5 1

Anadara uropigimelana N= 10 2,257.1 SD = 1,028.4 2,206.4 SD = 1,1005.3 2.7 SD = 1.3 217.9 SD = 0.7 2

Strombus luhuanus N=2 877.7 SD=598.1 829.4 SD=565.2 23.5 SD=31.3 86 SD=0 3

E/T (kcal/min)

15.4SD=9.6

188 Hum Ecol (2007) 35:179194


11/16

it is considered improper for women to dive, and so they

must restrict their work to intertidal and shallow subtidal

patches.

Leeward Reef (Diving) When the I-Kiribati from the more

populated windward islets venture out to the leeward reef

and adjacent islets, they often targetT. maxima. Additional

prey encountered include Hippopus hippopus and Lambis

lambis, whose profitability is illustrated in Table XI.

In calculating E/T, the costs of search and handling non-

shellfish resources were also incorporated5. Profitability

and corresponding rank for each prey type before and after

postharvest processing are shown in TableXII.

The addition of prey types, including fish and octopus,

among the observed foraging bouts raised overall returns,

except in one instance where E/h forT. maxima (16.6 kcal/

min) the lowest ranking prey reduced E/T from 29.6 to

27.6 kcal/min. However, because the primary motivation

was to collect for income, one cannot say that divers were

foraging suboptimally6.

Leeward reef (Walking) Many leeward reef islets currently

do not support permanent settlements. However, some are

temporarily occupied by fishermen who may process fish,

holothurians (seaslugs), and T. maxima. Although most

shellfish resources gathered from the leeward reef require

simple diving gear and a canoe, foraging on foot at low tide

in the intertidal zone at appropriate localities may yield a

similar range of prey types, including T. maxima, H.

hippopus, and L. lambis.

In the process of searching for resources at low tide,

foragers often encounter H. hippopus distributed in what

appeared to be two distinct patterns: the bivalves occur

either singly or in clumps. In the latter case, clumping is

sometimes associated with fish traps, suggesting the

presence of Giant Clam gardens (Thomas, 2001b).

Consequently, the relative high density of H. hippopus is

sometimes explained by deliberate introductions, with

humans responsible for the distribution of this particular

resource. Return rates for pedestrian leeward reef foraging

are presented in Tables XIIIand XIV.

Energy expenditure rates and field handling time differ

from leeward reef diving. Because the reef platform

between islets is searched at low tide by walking, gathering

is comparable to standing working (see Table II). In all

instances, at least one group member carried a knife in

anticipation of locating Giant Clams. When more than one

prey type was harvested, overall returns increased for all

observed cases.

Deeply embedded T. maxima (usually small specimens)

were often bypassed because foragers judged them too

Table XI Leeward Reef Foraging (Diving): Profitability and Overall Returns


Hippopus hippopus N=4 494.3 SD=364.3 482 SD=361.2 0.01 SD=0.01 152.2 SD=88.4 1

Lambis lambis N=5 1,036 SD=1,338.2 1,015 SD=1,318 0.1 SD=0.1 85.1 SD=34.8 2

Tridacna gigas N=2 898.3 SD=747.6 859.6 SD=736.5 0.01 SD=0.04 55.5 SD=78 3

Tridacna maxima N=6 586.2 SD=452.2 532.9 SD=410.7 0.3 SD=0.2 27.5 SD=26.1 4

E/T (kcal/min)16.3

SD=11.5

6 Money and energy currencies are kept distinct in this analysis. It is

sometimes difficult to separate artisanal fisheries into commercial and

subsistence operations (Adams et al., 1999). The FAO (1998) reports

that the nearshore commercial fish catch in Kiribati is principally

made up of reef- and deep-slope fish (54%), shellfish (25%), and

pelagic species (21%).

5 Because shellfish gathering is not the primary focus of fishing

activities in the leeward reef patch (except for T. maxima), all non-

shellfish prey types needed to be taken into account in determining

overall efficiency. Published data (Leung et al., 1972; Murai et al.,1958; Sidwellet al.,1974) were used for gross caloric values, and the

categories underwater swimming and sitting working from

TableII were applied to calculate energy expenditure associated with

non-shellfish resources, including octopus, eel, and several varieties of

reef fish. TableXI lists only the Latin binomials for the shellfish prey

types.

Table XII Leeward Reef Foraging (Diving): Comparison of Profit-

ability and Prey Type Rank Order Before and After Postharvest

Processing

Prey type E/h without

postharvest

processing

Rank E/h with

postharvest

processing

Rank

Lambis

lambis

525.7 SD =254.6 1 85.1 SD =34.8 2

Hippopus

hippopus

287.2 SD =136.6 2 152.2 SD =88.4 1

Tridacna

gigas

169.2 SD=119.6 3 55.5 SD=78 3

Tridacna

maxima

64 SD=69.3 4 27.5 SD=26.1 4

Tridacna

gigas112.5 5

1 Experimental harvest (failed pursuit).

Hum Ecol (2007) 35:179194 189


12/16

difficult to extract. Up to eight H. hippopus concentrated

inside a fish trap were left in place, as these were

considered off limits because fish traps and resources found

adjacent to them were said to belong to an individual or

extended family. However, a Tridacna gigas specimen,

located about 20 m from the shoreline, was promptly

harvested. Although it is clear that it had been carried to

this location, the absence of a fish trap meant that it couldbe collected in accordance with the open access regime

governing nearshore environments and their resources.

Reef FlatCompared to the nearshore ocean patch, which is

sometimes visited when tides or weather prevent efficient

foraging elsewhere, the reef flat does not seem to be the

focus of much shellfish gathering, even during the most

favorable low tides. On occasion, one sees small groups of

fishermen casting their line, but the windward section

remains largely devoid of human subsistence activities. A

notable exception is the presence of fish traps. Neverthe-

less, the reef flat is recognized as a distinct patch where T.

maxima or H. hippopus may be gathered if they are

encountered in the course of fishing trips. There are also

several other shellfish resources that are considered edible.

Results of foraging efforts are presented in Tables XVand

XVI.

The addition of lower ranked prey increased overall

returns among all observed bouts. The experimental

handling of T. maxima was the notable exception: in 48.9

minutes of search, one female forager encountered 0.02 H.

hippopusand 0.1T. maxima/min. Net energy per encounter

was 80.5 kcal and 0.3 kcal for each prey type, while

handling time per encounter was 1.41 min and 2.88 min.

Profitability for H. hippopus was 57.1 kcal/min, which

resulted in an overall rate of 1.6 kcal/min. Because

profitability for T. maxima was 2 kcal/min (E/h


13/16

most favorable conditions, returns from the reef crest would

still remain below the average for the other patches,

especially since T. setosus is a vulnerable species (Villiers

and Sire,1985). Repeated forays, accompanied by brief, butintensive harvesting could drastically reduce the number of

T. setosus, thus making reef crest foraging a relatively

unproductive venture.

Implications for Conservation

The prey choice model offers a simple way to assess the

hypothesis of short-term costs and gains in food acquisi-

tion, assumed by OFT, and to help better understand

alleged conservation practices by contemporary indigenoussocieties. As illustrated by Alvard (1993; 1994; 1995) in

work among an Amerindian community in Peru, a

behavioral ecological approach provides the framework to

distinguish between conservation behavior per se from its

effects, the latter defined as epiphenomenalconservation.

It follows that conservation can be seen as accepting short-

term costs for long-term gains. Whereas other criteria can

be used (Ruttan and Borgerhoff Mulder, 1999; Smith,

1995), this definition of conservation is sufficiently

rigorous to assess deviation from short-term harvest rate

maximization. While conservation of natural resources

among I-Kiribati might take place in other contexts subject

to testing, this case study of shellfish gathering hasdemonstrated that foragers are behaving according to the

predictions of the prey choice model.

The previous discussion of foraging decisions by

patches, includ ing instances where prey types were

avoided, supports the idea that foragers are seeking to

maximize their short-term energy gains by adding prey

types to increase overall return rates. High ranking prey

such as A. uropigimelana are always taken on-encounter.

Moreover, there seems to be no size/age discrimination in

harvesting within prey categories: smaller/subadult speci-

mens ofS. luhuanus, for instance, are harvested to the same

degree as mature individuals. Such behavior is inconsistentwith a conservation strategy. For S. luhuanus at least, it

clearly does not pay to refrain from taking juveniles with

the aim of reaping benefits in the future because these

gastropods are highly mobile, and therefore, an opportunity

lost today is probably lost forever, even though foragers can

be generally assured of abundant supplies of this resilient

type.

A prey which is seldom or never considered a focal or

targeted resource in no way implies that it is given special

Table XV Reef Flat Foraging: Profitability and Overall Returns


Spondylus squamosus N=1 24.5 24.3 0.1 121.3 1

Tridacna maxima N=2 119.1 SD=152.4 116.7 SD=150.5 0.02 SD=0.10 43.7 SD=44.2 2

Hippopus hippopus N=3 185.2 SD=237.3 177.1 SD=228.6 0.05 SD=0.1 28.9 SD=27 3

Turbo setosus N=1 9.3 8.6 0.1 10.1 4

Strombus variabilis N=2 141.4 SD=162.1 127.2 SD=149.2 1.6 SD=2 4.9 SD=0.4 5Vasum turbinellum N=4 72.6 SD=69.2 47.3 SD=49.5 1.7 SD=2 1 SD=0.3 6

Tridacna maxima1N=1 79.4 40.6 0.1 2 7

E/T (kcal/min)

1.2

SD=1.2

1 Experimental harvest.

Table XVI Reef Flat Foraging: Comparison of Profitability and Prey Type Rank Order Before and After Postharvest Processing


Hippopus hippopus 2,269.1 SD=1,839.7 1 28.9 SD=27 3

Spondylus squamosus 243.4 2 121.3 1

Turbo setosus 115.5 3 10.1 4

Tridacna maxima 107 SD=103.2 4 43.7 SD=44.2 2

Strombus variabilis 52.8 SD=0.1 5 4.9 SD=0.4 5

Vasum turbinellum 28.5 SD=1.7 6 1 SD=0.3 6

Tridacna maxima1 1.9 7 2 7

1Experimental harvest.

Hum Ecol (2007) 35:179194 191


14/16

consideration, for instance to assist in conserving existing

stocks for some future reward. Thus, the high ranked T.

angulatum, occurring in both seagrass and sand flat

patches, is not mentioned as a focal prey (unlike A.

uropigimelana) because it is relatively uncommon, not

because it should be avoided. From what could be

observed, the relative rarity of this prey type in the harvests

does not appear to be linked to the need to restrict

gathering: T. angulatum is the highest ranking prey in both

lagoon patches and is thus predicted to alwaysbe harvested

on-encounter.The case forS. squamosus and B. foliataunderscores the

concept of encounter variability and partial preferences.

Firmly attached S. squamosus and B. foliata have different

return rates than detached or weakly attached specimens. If

a forager bypasses prey types in the former state, the

behavior should be entirely consistent with return rate

maximization. Moreover, the lack of an appropriate extrac-

tive technology, such as a knife or crowbar, is a constraint

that limits the foragers ability to efficiently harvest a

resource, which would otherwise increase overall returns.

Knowing the full range of constraints imposed upon

foraging decisions is further illustrated by nearshoreresources: A. violascens, Nerita spp., and A. striata are

sometimes avoided to prevent pathogenic transmission.

Technological constraints, together with unfavorable tidal

conditions, could prevent specimens of Giant Clams from

being efficiently harvested. Given that T. maxima is a

vulnerable prey type (Alcazar and Solis, 1986), how are we

to interpret occasional avoidance? Again, foraging behavior

shows that small, deeply embedded specimens are

bypassed, while more easi ly accessible bivalves are

harvested. The case for H. hippopus discovered in the

vicinity of a fish trap poses an interesting problem, because

it did appear to involve a short-term cost, but not in the

sense of hoping to derive a long-term gain from the

resource. The bivalves had been placed next to a fish trap,

suggesting they were off limits to outsiders. In other

circumstances involving transported Giant Clams, T. gigas

andH. hippopus, pilferage was common. However, because

foragers in the above instance were searching on the reef in

broad daylight in an open setting where fishermen could

monitor each other, the foraging party decided to leave the

shells in place for fear of retribution.

Atolls are often described as marginal habitats for human

existence, as reflected in the size of habitable landmass and

in the distribution of resources. Compared to terrestrial

ecosystems, the lagoon and reef environments surrounding

the islets provide a wide range of resources. The key to this

high level of productivity is the rapid internal recycling of

nutrients within the ecosystem (Marsh, 1987). However,

even atoll marine environments do not match the level of

productivity found near continental margins or around most

volcanic high islands (Wiens, 1962). Intuitively, therefore,

several authors have suggested that because of these factorsatoll societies were more keenly aware of resource

limitations and, as a result, devised various conservation

strategies. In effect, they would epitomize, at least prior to

Western contact, the idea of the ecologically noble savage

(Redford, 1991). While debate over the effectiveness of

alleged precontact conservation strategies will likely con-

tinue, contemporary observations may assist in critically

evaluating some long-held beliefs and assumptions about

the relationship between humans and their environment on

small, resource poor islands or in other marginal habitats.

Indigenous societies undoubtedly possess a vast knowledge

of their respective environments, which often rivalsWestern scientific understanding. However, such knowl-

edge does not necessarily entail a concern for the

environment beyond what it can provide for the immediate

benefit of those extracting resources (Healey, 1993;

Pernetta and Hill, 1984). Moreover, it remains to be

demonstrated whether such knowledge is linked to a

conservation ethic or a user-oriented conservation strat-

egy (McNeelyet al.,1995; Ruddleet al.,1992).7 As Dwyer

(1994) argued, the modern conservation movement is often

at odds with the social and economic reality facing many

indigenous peoples, and as the local political elite often

relies on exclusionary rules that prevent segments of a

population from accessing resources in an increasingly

crowded world. In effect, such communal systems tend to

conserve, but only in terms of incidental outcomes

Table XVII Reef Crest Foraging: Profitability and Overall Returns

Prey type Gross kcal Net kcal Encounter rate/min E/h

Turbo setosus N=2 57.5 SD=19.8 52.8 SD=19.5 0.2 SD=0.1 11.7 SD=3.2

E/T (kcal/min)

0.2

SD=0.1

7 A conservation ethic is synonymous with the philosophical under-

pinnings of Deep Ecology, whereby all living things are considered to

possess an inherent value (Sessions, 1998). A user-oriented

conservation strategy, in contrast, is rooted in anthropocentric ethical

norms (Zimmerman,1998).

192 Hum Ecol (2007) 35:179194


15/16

stemming from social inequalities (Brower, 1983). For

Kiribati, however, with its more egalitarian social structure,

the major challenge stems from the erosion of customary

marine tenure, which together with high human population

growth, urban crowding, more efficient extractive technol-

ogies, and expanding market opportunities, has undermined

recent attempts to help conserve resources (Thomas,2001a;

2001b).

Acknowledgment This paper draws on doctoral fieldwork in

Kiribati between 1993 and 1998. My thanks go to Douglas Bird for

sharing his data and thoughts on shellfish gathering from the

perspective of human behavioral ecology, Margo Wilson and Martin

Daly for suggestions to improve this manuscript, and the many I-

Kiribati for their patience and hospitality. The manuscript also

benef ited from comments by three anonym ous reviewers. The

research was supported by Sigma Xi (Grant-in-Aid of Research

# 2719 and # 8326), Conchologists of America, Inc., The Hawaiian

Malacological Society, and the University of Hawaii Arts & Sciences

Advisory Council.

References

Abbott, R. R., and Garcia, J. (eds.) (1995). Management Plan for

Tarawa Lagoon, Republic of Kiribati: Volume III. Management

Plan, BioSystems Analysis, Santa Cruz, California.

Adams, T., Dalzell, P., and Ledua, E. (1999). Ocean resources. In

Rapaport, M. (ed.), The Pacific Islands: Environment & Society,

Bess, Honolulu, pp. 366381.

Alcazar, S. N., and Solis, E. P. (1986). Spawning, Larval Development

and Growth of Tridacna maxima (Rding) (Bivalvia: Tridacni-

dae). Silliman Journal33: 5673.

Alvard, M. S. (1993). Testing the Ecologically Noble Savage

Hypothesis: Interspecific Prey Choice among Piro Hunters ofAmazonian Peru. Human Ecology 21: 355387.

Alvard, M. S. (1994). Conservation by Native Peoples: Prey Choice in

a Depleted Habitat. Human Nature 5: 127154.

Alvard, M. S. (1995). Intraspecific Prey Choice by Amazonian

Hunters.Current Anthropology 36: 789818.

Anderson, A. (1979). Prehistoric exploitation of marine resources at

Black Rocks Point, Palliser Bay. In Leach, B. F., and Leach, H.

M. (eds.), Prehistoric Man in Palliser Bay, National Museum of

New Zealand Bulletin, No. 21, Wellington, pp. 4965.

Aswani, S. (1998). The Use of Optimal Foraging Theory to Assess the

Fishing Strategies of Pacific Island Artisanal Fishers: A Meth-

odological Review. Traditional Marine Resource Management

and Knowledge 9: 1926.

Barlow, K. R., and Metcalfe, D. (1996). Plant Utility Indices: Two

Great Basin Examples. Journal of Archaeological Science 23:351371.

Beckerman, S. (1983). Carpe diem: an optimal foraging approach to

Bari fishing and hunting. In Hames, R., and Vickers, W. (eds.),

Adaptive Strategies of Native Amazonians, Academic, New York,

pp. 269299.

Begossi, A. (1995). Fishing Spots and Sea Tenure: Incipient Forms of

Local Management in Atlantic Forest Coastal Communities.

Human Ecology 23: 387408.

Bn, C., and Tewfik, A. (2001). Fishing Effort Allocation and

Fishermens Decision-making Process in a Multi-species Small-

scale Fishery Analysis of the Conch and Lobster in Turks and

Caicos Islands. Human Ecology 29: 157186.

Bettinger, R. L. (1991). Hunter-Gatherers: Archaeological and

Evolutionary Theory, Plenum, New York.

Bettinger, R. L., Malhi, R., and McCarthy, H. (1997). Central Place

Models of Acorn and Mussel Processing. Journal of Archaeo-

logical Science 24: 887899.

Bird, D. W. (1996). Intertidal Foraging Strategies among the Meriam

of the Torres Strait Islands, Australia: An Evolutionary Ecolog-

ical Approach to the Ethnoarchaeology of Tropical Marine

Subsistence, Doctoral dissertation, University of California,

Davis.

Bird, D. W. (1997). Behavioral ecology and the archaeological

consequences of central place foraging among the Meriam. In

Barton, C. M., and Clark, G. A. (eds.), Rediscovering Darwin:

Evolutionary Theory and Archaeological Explanation, Archaeo-

logical Papers of the American Anthropological Association No.

7, Arlington, pp. 291306.

Bird, D. W., and Bliege Bird, R. (1997). Contemporary Shellfish

Gathering among the Meriam of the Torres Strait Islands,

Australia: Testing Predictions of a Central Place Foraging Model.

Journal of Archaeological Science 24: 3963.

Bird, D. W., and Bliege Bird, R. (2000). The Ethnoarchaeology of

Juvenile Foragers: Shellfishing Strategies among Meriam Chil-

dren. Journal of Anthropological Archaeology 19: 461476.

Brower, K. (1983). A Song for Satawal, Harper Row, New York.

Catterall, C. P., and Poiner, I. R. (1983). Age and Sex-dependent

Patterns of Aggregation in the Tropical Gastropod Strombus

luhuanus. Marine Biology 77: 171182.

Charnov, E. L., and Orians, G. H. (1973). Optimal Foraging: Some

Theoretical Explorations. Manuscript on file, Department of

Biology, University of Utah, Salt Lake City.

De Boer, W. F., Blijdenstein, A.-F., and Longamane, F. (2002). Prey

Choice and Habitat Use of People Exploiting Intertidal Resour-

ces. Environmental Conservation 29: 238252.

Durnin, J. V. G. A., and Passmore, R. (1967). Energy, Work and

Leisure, Heinemann, London.

Dwyer, P. D. (1994). Modern Conservation and Indigenous Peoples:

In Search of Wisdom. Pacific Conservation Biology 1: 9197.

Emlen, J. M. (1966). The Role of Time and Energy in Food

Preference. American Naturalist 100: 611

617.FAO (1998). Fishery Country Profile: Kiribati, FAO, Rome.

FAO/WHO/UNU (1985). Energy and Protein Requirements, Techni-

cal Report Series No. 724, World Health Organization, Geneva.

Friedlaender, J. S., and Rhoads, J. G. (1987). Longitudinal anthropo-

metric changes in adults and adolescents. In Friedlaender, J. S.

(ed.),The Solomon Islands Project: A Long-term Study of Health,

Human Biology, and Culture Change, Clarendon, Oxford, pp.

283306.

Healey, C. (1993). The significance and application of TEK. In

Williams, N. M., and Baines, G., Traditional Ecological

Knowledge: Wisdom for Sustainable Development, Centre for

Resource and Environmental Studies, Australian National Uni-

versity, Canberra, pp. 2126.

Henry, C. J., and Rees, D. G. (1991). New predictive equations for the

estimation of basal metabolic rate in tropical peoples. EuropeanJournal of Clinical Nutrition45: 177185.

Jones, K. T., and Madsen, D. B. (1989). Calculating the Cost of

Resource Transportation: A Great Basin Example. Current

Anthropology30: 529534.

Kaplan, H., and Hill, K. (1992). The evolutionary ecology of food

acquisition. In Smith, E. A., and Winterhalder, B. (eds.),

Evolutionary Ecology and Human Behavior, Aldine de Gruyter,

New York, pp. 167201.

Krebs, J. R., and McCleery, R. H. (1984). Optimization in behavioural

ecology. In Krebs, J. R., and Davies N. B. (eds.), Behavioural

Ecolo gy: An Evolu tionary Approach, 2nd ed., Blackwell,

London, pp. 91121.

Hum Ecol (2007) 35:179194 193


16/16

Leung, W.-T., Butrum, R. R., and Chang, F. H. (1972). Proximate

composition, mineral and vitamin contents of East Asian foods.

In Food Composition Table for Use in East Asia, U. S.

Department of Health, Education, and Welfare, Bethesda, pp.

1187.

MacArthur, R. H., and Pianka, E. A. (1966). On Optimal Use of a

Patchy Environment. American Naturalist100: 603609.

Marsh, J. A., Jr. (1987). Reef processes: Energy and materials flux. In

Devaney, D. M., Reese, E. S., Burch, B. L., and Helfrich, P.

(eds.), The Natural History of Enewetak Atoll: Volume I. TheEcosystem: Environments, Biotas, and Processes, U. S. Dept. of

Energy, Office of Energy Research, Office of Health and

Environmental Research, Ecological Research Division, Oak

Ridge, pp. 159179.

Maynard Smith, J. (1978). Optimization Theory in Evolution. Annual

Review of Ecology and Systematics9: 3156.

McNab, B. K. (1963). Bioenergetics and the Determination of Home

Range Size. American Naturalist97: 133140.

McNeely, J. A., Houston, A. I., and Weisser, W. W. (1995). Human

influences on biodiversity. In Heywood, V. H., and Watson, R. T.,

Global Biodiversity Assessment, Cambridge University Press,

Cambridge, pp. 715821.

Metcalfe, D., and Barlow, K. R. (1992). A Model for Exploring the

Optimal Trade-off Between Field Processing and Transport.

American Anthropologist94: 340356.

Mitchell, D., Nash, J., Ogan, E., Ross, H., Bayliss-Smith, T., Keesing

R., and Friedlaender, J. S. (1987). Profiles of the survey sample.

In Friedlaender, J. S. (ed.),The Solomon Islands Project: A Long-

term Study of Health, Human Biology, and Culture Change,

Clarendon, Oxford, pp. 2864.

Murai, M. Pen, F., and Miller, C. D. (1958). Some Tropical South

Pacific Foods: Description, History, Use, Composition, and

Nutritive Value, University of Hawaii Press, Honolulu.

Norgan, N. G., Ferro-Luzzi, A., and Durnin, J. V. G. A. (1974). The

Energy and Nutrient Intake and the Energy Expenditure of 204

New Guinean Adults. Philosophical Transactions of the Royal

Society of London, Series B, 268: 309348.

Nydon, J., and Thomas, R. B. (1989). Methodological procedures for

analyzing energy expenditure. In Pelto, G. H., Pelto, P. J., and

Messer, E. (eds.),Research Methods in Nutritional Anthropology,

United Nations University, Tokyo, pp. 5781.

Pargeter, K, Taylor, R., King, H., and Zimmet, P. (1984), Kiribati: A

Dietary Study, Noumea, South Pacific Commission.

Paulay, G. (2001). Benthic Ecology and Biota of Tarawa Lagoon:

Influence of Equatorial Upwelling, Circulation, and Human

Harvest.Atoll research Bulletin 487: 141.

Pernetta, J. C., and Hill, L. (1984). Traditional Use and Conservation

of Resources in the Pacific Basin. Ambio 13: 359364.

Pyke, G. H., Pulliam, H. R., and Charnov, E. L. (1977). Optimal

Foraging: A Selective Review of Theory and Tests. Quarterly

Review of Biology 52: 137154.

Redford, K. H. (1991). The Ecologically Noble Savage.Orion9: 2429.

Ruddle, K., Hviding, E., and Johannes, R. E. (1992). Marine

Resources Management in the Context of Customary Tenure.Marine Resource Economics7: 249273.

Ruttan, L. M., and Borgerhoff Mulder, M. (1999). Are East African

Pastoralists Truly Conservationists? Current Anthropology 40:

621652.

Salvat, B. (1972). La faune benthique de lAtoll de Reao (Tuamotu,

Polynsie). Cahiers du Pacifique 16: 31110.

Sessions, G. (1998). Introduction. In Zimmerman, M. E. (ed.),

Environmental Philosophy: From Animal Rights to Radical

Ecology, 2nd ed., Prentice Hall, Upper Saddle River, N. J., pp.

165182.

Sidwell, V. D., Foncannon, P. R., Moore, N. S., and Bonnet, J. C.

(1974). Composition of the Edible Portion of Raw (Fresh or

Frozen) Crustaceans, Finfish, and Mollusks. I. Protein, Fat,

Moisture, Ash, Carbohydrate, Energy Value, and Cholesterol.

Marine Fisheries Review 36(3): 2135.

Smith, E. A. (1983). Anthropological Applications of Optimal

Foraging Theory: A Critical Review. Current Anthropology 24:

625651.Smith, E. A. (1991). Inujjuamiut Foraging Strategies: Evolutionary

Ecology of an Arctic Hunting Economy, Aldine de Gruyter, New

York.

Smith, E. A. (1995). Comments on Intraspecific Prey Choice by

Amazonian Hunters by M. Alvard. Current Anthropology 36:

810811.

Smith, E. A., and Winterhalder, B. (1992). Natural selection and

decision making: Some fundamental principles. In Smith, E. A.,

and Winterhalder, B. (eds.), Evolutionary Ecology and Human

Behavior, Aldine de Gruyter, New York, pp. 2560.

Sosis, R. (2002). Patch Choice Decisions among Ifaluk Fishers.

American Anthropologist104: 583598.

Stephens, D. W. (1985). How Important are Partial Preferences?

Animal Behaviour33: 667689.

Stephens, D. W., and Krebs, J. R. (1996). Foraging Theory, Princeton

University Press, Princeton.

Sutherland, W. J. (1982). Do Oystercatchers Select the most Profitable

Cockles? Animal Behaviour30: 857861.

Tamaru, C. S., Ako, H., and Lee, C.-S. (1992). Fatty Acid and Amino

Acid Profiles of Spawned Eggs of Striped Mullet, Mugil

cephalus L. Aquaculture 105: 8394.

Thomas, F. R. (1999). Optimal Foraging and Conservation: The

Anthropology of Mollusk Gathering Strategies in the Gilbert

Islands Group, Kiribati. Doctoral dissertation, University of

Hawaii, Honolulu. University Microfilms International, Ann

Arbor.

Thomas, F. R. (2001a). Mollusk Habitats and Fisheries in Kiribati: An

Assessment from the Gilbert Islands. Pacific Science 55: 7797.

Thomas, F. R. (2001b). Remodeling Marine Tenure on the Atolls: A

Case Study from Western Kiribati, Micronesia. Human Ecology

29: 399423.

Thomas, F. R. (2002). An Evaluation of Central-place Foraging

among Mollusk Gatherers in Western Kiribati, Micronesia:

Linking Behavioral Ecology with Ethnoarchaeology. World

Archaeology34: 182208.

Ulijaszek, S. J. (1995). Human Energetics in Biological Anthropology,

Cambridge University Press, Cambridge.

Villiers, L., and Sire, J-Y. (1985). Growth and Determination of

Individual Age ofTurbo setosus(Prosobranchia Turbinidae), Hao

Atoll (Tuamotus, French Polynesia). Proceedings of the Fifth

International Coral Reef Congress5: 165170.

Wiens, H. J. (1962). Atoll Environment and Ecology, Yale University

Press, New Haven.

Yamaguchi, M., Yeeting, B., Toyama, K., Tekinaiti, T., and Beiatau, T.(1993).Report on a Preliminary Study of Molluscan Resources in

Tarawa Lagoon, with Special Reference to te bun (Anadara

maculosa [sic]), Department of Marine Sciences, University of

the Ryukyus, Okinawa.

Zimmerman, M. E. (1998). General introduction. In Zimmerman, M.

E. (ed.), Environmental Philosophy: From Animal Rights to

Radical Ecology, 2nd ed., Prentice Hall, Upper Saddle River, N.

J., pp. 16.

194 Hum Ecol (2007) 35:179194

2007 thomas the behavioural ecology of shellfish gathering in micronesia, 1, prey choice.pdf

Documents