forage of some eastern pacific midwater fishes

Forage of Some Eastern Pacific Midwater FishesAuthor(s): Sneed B. CollardSource: Copeia, Vol. 1970, No. 2 (Jun. 1, 1970), pp. 348-354Published by: American Society of Ichthyologists and Herpetologists (ASIH)Stable URL: http://www.jstor.org/stable/1441657 .

Accessed: 29/04/2014 04:28

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

American Society of Ichthyologists and Herpetologists (ASIH) is collaborating with JSTOR to digitize,preserve and extend access to Copeia.

http://www.jstor.org

This content downloaded from 86.2.149.152 on Tue, 29 Apr 2014 04:28:21 AMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=asih

http://www.jstor.org/stable/1441657?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


COPEIA, 1970, NO. 2 COPEIA, 1970, NO. 2

made specimens available. Harvey R. Bullis, Jr., Bureau of Commercial Fisheries, Pasca- goula, Miss., was responsible for collection of study specimens. Herbert Gordy, U. S. Bureau of Commercial Fisheries, Biological Laboratory, Beaufort, N. C., prepared Figs. 4 and 6.

LITERATURE CITED

DAWSON, C. E. 1969. Citharichthys abbotti, a new flatfish (Bothidae) from the southwestern Gulf of Mexico. Proc. Biol. Soc. Wash. 83: 355-372.

GUTHERZ, E. J. 1967. Field guide to the flatfishes of the family Bothidae in the western North Atlantic. U. S. Fish Wildl. Serv., Circ. 263, 47 pp.

made specimens available. Harvey R. Bullis, Jr., Bureau of Commercial Fisheries, Pasca- goula, Miss., was responsible for collection of study specimens. Herbert Gordy, U. S. Bureau of Commercial Fisheries, Biological Laboratory, Beaufort, N. C., prepared Figs. 4 and 6.

LITERATURE CITED

DAWSON, C. E. 1969. Citharichthys abbotti, a new flatfish (Bothidae) from the southwestern Gulf of Mexico. Proc. Biol. Soc. Wash. 83: 355-372.

GUTHERZ, E. J. 1967. Field guide to the flatfishes of the family Bothidae in the western North Atlantic. U. S. Fish Wildl. Serv., Circ. 263, 47 pp.

NORMAN, J. R. 1934. A systematic monograph of the flatfishes (Heterosomata). Vol. 1. Pset- toididae, Bothidae, Pleuronectidae. Brit. Mus. (Nat. Hist.), London.

PARR, A. E. 1931. A practical revision of the western Atlantic species of the genus Citha- richthys (including Etropus). Bull. Bingham Oceanogr. Coll. 4 (art. 1):1-24.

STARCK, W. A., II. 1968. A list of fishes of Alligator Reef, Florida with comments on the nature of the Florida reef fish fauna. Under- sea Biol. 1(1):5-40.

U. S. BUREAU OF COMMERCIAL FISHERIES BIO-

LOGICAL LABORATORY, BRUNSWICK, GEORGIA

31520 AND U. S. BUREAU OF COMMERCIAL

FISHERIES BIOLOGICAL FIELD STATION, GULF

BREEZE, FLORIDA 32561.

NORMAN, J. R. 1934. A systematic monograph of the flatfishes (Heterosomata). Vol. 1. Pset- toididae, Bothidae, Pleuronectidae. Brit. Mus. (Nat. Hist.), London.

PARR, A. E. 1931. A practical revision of the western Atlantic species of the genus Citha- richthys (including Etropus). Bull. Bingham Oceanogr. Coll. 4 (art. 1):1-24.

STARCK, W. A., II. 1968. A list of fishes of Alligator Reef, Florida with comments on the nature of the Florida reef fish fauna. Under- sea Biol. 1(1):5-40.

U. S. BUREAU OF COMMERCIAL FISHERIES BIO-

LOGICAL LABORATORY, BRUNSWICK, GEORGIA

31520 AND U. S. BUREAU OF COMMERCIAL

FISHERIES BIOLOGICAL FIELD STATION, GULF

BREEZE, FLORIDA 32561.

Forage of Some Eastern Pacific Midwater Fishes

SNEED B. COLLARD

Analysis of the stomach contents of 1087 specimens of 42 species of midwater fishes collected in the eastern Pacific indicate that these fishes have diverse diets and are nonpreferential in their selection of prey. The apparent prey specificity observed in lanternfish species by other workers may have resulted from limited sampling. Various crustaceans (principally copepods and euphausiids) are the major dietary constituents, and com- prised the forage of 95% of all specimens with identifiable stomach contents. There are both geographical and seasonal differences in the forage of the lanternfish, Stenobrachius leucopsarus. Larger specimens of S. leucopsarus feed on a wider variety of invertebrates than do smaller, younger individuals. Differences observed in the diets of sympatric species may be an example of niche diversification.

Forage of Some Eastern Pacific Midwater Fishes

SNEED B. COLLARD

Analysis of the stomach contents of 1087 specimens of 42 species of midwater fishes collected in the eastern Pacific indicate that these fishes have diverse diets and are nonpreferential in their selection of prey. The apparent prey specificity observed in lanternfish species by other workers may have resulted from limited sampling. Various crustaceans (principally copepods and euphausiids) are the major dietary constituents, and com- prised the forage of 95% of all specimens with identifiable stomach contents. There are both geographical and seasonal differences in the forage of the lanternfish, Stenobrachius leucopsarus. Larger specimens of S. leucopsarus feed on a wider variety of invertebrates than do smaller, younger individuals. Differences observed in the diets of sympatric species may be an example of niche diversification.

INTRODUCTION

ALTHOUGH the predators of some mid-

depth pelagic fishes are known (Mead and Taylor, 1953; Haedrich and Nielsen, 1966; Rofen, 1966; Maul, 1959; summarized for lanternfishes by Paxton, 1967a), and the economic and general ecological importance of midwater fishes in the open ocean econ- omy is recognized, relatively little is known about the feeding habits of these abundant fishes.

Paxton (1967b), in a study of the feeding habits of lanternfishes (family Myctophidae) from southern California waters, concluded that five of nine species collected in the San Pedro Basin were "highly specific feeders," and that feeding occurred in lanternfish pop- ulations with about equal intensity during the day and night. In addition to the five

INTRODUCTION

ALTHOUGH the predators of some mid-

depth pelagic fishes are known (Mead and Taylor, 1953; Haedrich and Nielsen, 1966; Rofen, 1966; Maul, 1959; summarized for lanternfishes by Paxton, 1967a), and the economic and general ecological importance of midwater fishes in the open ocean econ- omy is recognized, relatively little is known about the feeding habits of these abundant fishes.

Paxton (1967b), in a study of the feeding habits of lanternfishes (family Myctophidae) from southern California waters, concluded that five of nine species collected in the San Pedro Basin were "highly specific feeders," and that feeding occurred in lanternfish pop- ulations with about equal intensity during the day and night. In addition to the five

highly specific feeders, two species were considered possibly to be preferential feeders and only two species were thought to be non- specific in their forage. Because the fishes examined by Paxton are diel vertical migra- tors (Lavenberg, 1964; Paxton, 1967a), his results also implied that (at least) five of nine species fed with equal intensity (efficiency?) throughout their depth ranges.

Another study of the feeding habits of Triphoturus mexicanus collected in the nearby, and oceanographically similar, Cata- lina Basin indicated, however, that this fish was not selective in its forage and fed most intensively during the hours of darkness (Anderson, 1967). Anderson's results also indicated, by inference, that T. mexicanus feeds most intensively at the shoaler end of its diel depth range.

highly specific feeders, two species were considered possibly to be preferential feeders and only two species were thought to be non- specific in their forage. Because the fishes examined by Paxton are diel vertical migra- tors (Lavenberg, 1964; Paxton, 1967a), his results also implied that (at least) five of nine species fed with equal intensity (efficiency?) throughout their depth ranges.

Another study of the feeding habits of Triphoturus mexicanus collected in the nearby, and oceanographically similar, Cata- lina Basin indicated, however, that this fish was not selective in its forage and fed most intensively during the hours of darkness (Anderson, 1967). Anderson's results also indicated, by inference, that T. mexicanus feeds most intensively at the shoaler end of its diel depth range.

348 348



COLLARD-FORAGE OF PACIFIC MIDWATER FISHES

TABLE 1. COLLECTION DATA. Letters indicate general geographic area of collections (Table 2) at

approximate latitudes and longitudes shown. Specific data have been presented by Collard (1968).

Symbol Area Lat. Long.

A Antarctic 610 i'S 100? 21'W B Peru-Chile Trench 47? 10' S 76? 30' W C Equatorial Pacific 6 S 1580 W D So. of Pta. Eugenia, Baja Calif., Mex. 260 39' N 114? 21'W E No. of Pta. Eugenia, Baja Calif., Mex. 300 50'N 120? 40'W F California Current, Calif. 32? 02' N 123? 20'W G Base of Continental Slope, Calif. 32? 40' N 120' 35' W H Continental Slope, Calif. 320 23' N 120' 17' W I West Cortez Basin, so. Calif. 32? 16' N 119? 17'W J San Nicholas Basin, so. Calif. 33? 02'N 119? 04'W K San Clemente Basin, so. Calif. 32? 42'N 118? 17'W L Santa Catalina Basin, so. Calif. 330 20'N 118? 42'W M San Diego Trough, so. Calif. 32? 44' N 117? 33'W N Santa Cruz Basin, so. Calif. 33? 45' N 119 39'W O Hueneme Canyon, so. Calif. 33? 58'N 119' 12'W P Santa Barbara Basin, so. Calif. 340 15'N 119' 58'W Q Continental Shelf off San Francisco, Calif. 38 12' N 124? 07' W R Continental Shelf off Oregon 43? 40'N 125? 01'W S Continental Shelf off Brit. Col. 51' 15'N 130? 48'W

This paper summarizes the kinds of food recovered from the stomachs of 1087 specimens of 42 species of midwater fishes from the eastern Pacific, and includes data on the forage of species collected in the deepwater basins off southern California that were also sampled by Paxton (1967b) and Anderson (1967). While these data indicate the extent to which the more abundant lanternfishes exhibit preferential feeding, the collecting program used was not designed to sample fishes at specific depths or at particular times of the day, thus precluding useful discussion of where (in the water column) and when these diel vertically migratory fishes feed.

METHODS

Fishes were caught with a six- or ten-ft Isaacs-Kidd midwater trawl (Isaacs and Kidd, 1953) during the period 1963-66 and were either examined on shipboard, frozen, or pre- served in formalin for later examination

(Table 1). During parasitological examination, stomachs were cut open longitudinally, and their contents examined with a binocular dissecting microscope. The contents of each stomach were then placed into one of ten categories as follows (prey organisms were not identified to species): (1) stomach empty; (2) debris-major constituents of stomach contents unrecognizable and/or in advanced

stages of digestion, and not falling into any of the other nine categories; (3) crustacea- stomach contained a mixture of various crustaceans or crustacean remains with no one type being predominant. Mixtures contained combinations of copepods, euphausiids, sergestid shrimps (often Sergestes similis), small ostracods, hyperiid amphipods, glass shrimps (usually Pasiphaea emarginata or P. pacifica), zoea of Emerita analoga and, rarely, small mysids. Other invertebrates (e.g. chaetognaths, cephalopods) were never found in these mixtures; (4) fish-stomach contained fish in any quantity, regardless of condition or of other components; (5) molluscs-stomach contained molluscs in any quantity regardless of other components; (6) copepods- the stomach contained only copepods (these were not all identified, but were mostly small calanoids; Gausia princeps was one of the more commonly encountered species off southern California); (7) euphausiids-the stomach contained only euphausiids (mostly Euphausia pacifica, E. hemigibba or Nema- toscelis difficilis off California); (8) euphausiids and copepods-the stomach contained only these two kinds of crustaceans, with no record of their abundance relative to one another; (9) amphipods-the stomach contained only amphipods (mainly small hyperi- ids); (10) other-this category accounted for

349



TABLE 2. SUMMARY OF STOMACH CONTENTS BY FOOD CATEGORY AND FISH SPECIES. Percentages are based upon the total number of fishes having identifiable stomach contents. For explanation of food categories, see "Methods" section of the text. Areas of collection indicated in parentheses (Table 1). Species with no identifiable stomach contents (number examined and location of capture in parentheses) are: Cyclothone pallida (G-15); Cyclothone signata (L, N, P-15); Danaphos oculatus (L-1); Melamphaes acanthomus (L-1); Poromitra crassiceps (L-2); Myctophum brachygnathos ? (C-2); Protomyctophum crockeri (P-1); Avocettina bowersi (E-1); Nemichthys scolopaceus (N-1);

Macroparalepis sp. (L, N-3); Argyropelecus pacificus (L, D-12); Argyropelecus sp. (0-1); Stomiatidae sp. (C-1); Melanostigma pammelas (L-2).

Food Category

With Identifi- Euphausi- Exam- able Stomach Crus- Mol- Euphau- acea and Amphip-

ined Contents tacea Fish lusca Copepoda siacea Copepoda oda

Species (Area) n n % n % n % n % n % n % n %

Evermannellidae Evermannella sp. L

Gonostomatidae Cyclothone acclinidens L, N

Idiacanthidae Idiacanthus antrostomus N

Melamphaidae Melamphaes lugubris G Scopelogadus mizolepis bispinosus L, N

Myctophidae Ceratoscopelus townsendi C, E Diaphus coeruleus C Diaphus elucens C Diaphus spp. C Diaphus theta G, L, N, P Diogenichthys laternatus L Lampanyctus australis B Lampanyctus macropterus C Lampanyctus regalis J Lampanyctus ritteri I, L, N, P, R Myctophum aurolaternatum ? C Myctophum spinosum C Parvilux ingens E, G, K, L, N Protomyctophum anderssoni A Stenobrachius leucopsarus L, N, P, R, S Symbolophorus californiensis H Tarletonbeania crenularis F, G, L, N, Q, R Triphoturus mexicanus L, N, P

Scyliorhinidae Parmaturus xaniurus L, P

Serrivomeridae Serrivomer sector D, H, L, N

Sternoptychidae Argyropelecus lychnus L Sternoptyx diaphana E, L

Stomiatidae Stomias atriventer E, L, M, N

Totals: Rank:

No. of Species:

1 1 100

21 2 10

1 1 100

1 1 100 10 1 10

39 2 7 3

60 1

35 3 5

53 1 6

21 29

486 35 35

120

5 1 1 1

39 1

20 1 4

38 1 5

11 3

207 35 14 56

13 50 14 33 66

100 57 33 80 72

100 83 52 10 42

100 90 46

1 100

1 50

1 100

5 100

1 100

15

13

22

1 4 2

52 29 11 19

39

65

58

20 36 66 25 83 79 34

10 2 20

7 1 14

5 4 80 2 50 17 6 35 4 66

15 3 1029 465

28 28

21 43 181

14

39 1

1 5

3

1

8

20

7 18 1 100 2 40

7 3

1 2

1 50 1 50

20 52 2 1

3 15 2 1 4

1 3 4

6 100

10 100 100

11

4 36 3 27

70 2 2

22

34 6

14 39

62 2 1

10

30 6 7

18

1 5

1 50

n 0

1 100 >

1 100 3 ,- 1 3 '

1 3 1 3 r,~

1 20

8 2

4

4 6

7

1 33 8 4

1 100

2 50 2 33

3 22

11

100 5 4

11

4

2 127 7

10

27 2

93

12

20 3

16

5

3 5

15

8

3 6

CT 0




100

90 -70

so

I 50

540

I 30

50

O

o

_ _-q - E ~ u -' _ I- h F 7N

_ RX _'

DEC-FEB MAR-MAY JUN-AUG (37) [33) (49)

SEASONS

SEP- NOV (40O

Fig. 1. Seasonal distribution of food categories of Stenobrachius leucopsarus from the Santa Bar- bara and Santa Cruz basins. Percentages are based upon the number of specimens (in parentheses) collected in each season with identifiable stomach contents. Total number of specimens examined during 1964-65: Dec.-Feb. 102; Mar.-May 100; June-Aug. 103; Sep.-Nov. 95. Solid bars represent Crustacea; clear bars represent Copepoda only; stippled bars represent Euphausiacea only; slashed bars represent all other categories (see text).

the presence of any kind of organism not covered by the other nine categories. Crus- taceans such as sergestid and pasiphaeid shrimps were always found as constituents of mixtures of crustacea, and were accord- ingly placed in category (3). Cephalopods, chaetognaths, salps, siphonophorae, etc. were never found, and this category is omitted from Table 2.

OBSERVATIONS

Stomachs of 465 (45%) of the 1087 fishes examined contained identifiable, probably recently ingested food. Of the remaining 622 specimens, 363 (32%) had completely empty stomachs, and 252 fishes (23%) had stomachs containing food unidentifiable be-

cause of its partial or complete digestion. Of the 42 species of fishes that were examined, 38 were represented by less than 50 individuals. Stomach contents of these forms are presented without interpretation for comparative purposes, and because of the general paucity of previous records (Table 2). Generally these fishes were found to have varied diets consisting principally of crustaceans. A total of 197 specimens (42%) had stomachs containing more than one kind of crustacean; 127 fish (27%) had stomachs containing only copepods; 93 (20%) of the fish were found to have eaten only euphausiids, and 15 (3%) of the fish had stomachs containing only amphipods. The large number of specimens whose stomachs contained only

TABLE 3. NUMBER OF SPECIMENS OF Stenobrachius leucopsarus IN EACH OF 10 FOOD CATEGORIES, IN EACH OF FOUR SAMPLING SEASONS FROM THE SANTA BARBARA, SANTA CRUZ, AND SANTA CATALINA BASINS

OFF SOUTHERN CALIFORNIA. Roman numerals represent four three-month sampling periods during 1964-65: I, December-February ("Winter"); II, March-May ("Spring"); III, June-August ("Sum-

mer"); IV, September-November ("Fall").

Santa Barbara Santa Cruz Catalina

Grand Category I II III IV Total I II III IV Total I Total

Empty or unidentifiable 31 37 22 24 114 34 30 33 31 128 19 260 Crustacea 3 1 8 9 21 4 2 4 4 14 11 46 Fish 0 0 0 2 2 0 1 0 0 1 4 7 Mollusca 0 0 0 0 0 0 0 0 0 0 0 0

Copepoda 9 6 2 14 31 6 12 1 1 20 10 51 Euphausiacea 7 5 19 3 34 5 3 11 5 24 3 61

Euphausiacea and Copepoda 0 2 0 0 2 0 1 1 1 3 2 7

Amphipoda 1 0 1 1 3 2 0 1 0 3 1 7

Totals: 51 51 52 53 207 51 49 51 42 193 50

Grand Totals: 207 193 50 450

351



COPEIA, 1970, NO. 2

I-

W U

100

80 BO

40

0

100

so

40

BO

0

50

EUPHAUSI ACEA

FkfflTh 125

0

B 100 _ 50 m 1 Z

25

20

0 0

100 - 50

80so COPEPOaA

so 25

40

0 0 15 25 35 45 55 65 75 B5

LENGTH (MMSL)

Fig. 2. Percent of Stenobrachius leucopsarus in four main food categories by standard length groups. Specimens were collected in the Santa Barbara, Santa Cruz, and Santa Catalina basins off southern California. Number of specimens in each length category indicated by solid lines.

copepods or only euphausiids cannot be at- tributed to preferential feeding, since these categories include many species, and the stomach of a given fish was often observed to contain more than one kind of copepod or

euphausiid. Collectively the crustacean categories accounted for 95% of the food records, similar to the findings of Paxton (1967b) and of Anderson (1967).

Three species, Triphoturus mexicanus, Diaphus theta, and Lampanyctus ritteri were represented by moderate numbers of individuals (120, 60, and 53, respectively). These lanternfishes are abundant and sympatric in the areas from which they were collected (Table 1). The diets of all three species are varied, but individual differences in forage are clearly evident (Table 2) and perhaps an indication of niche diversification.

The most abundantly sampled species, Stenobrachius leucopsarus, forages mainly on crustaceans, predominantly on euphausiids and copepods (Table 2). Approximately equal sample sizes of this species were ob- tained from the Santa Barbara (207 specimens) and Santa Cruz basins (193 specimens) during each of four consecutive three-month periods from December 1964 to November 1965. An additional 50 specimens were collected in the Santa Catalina Basin during the December-February ("winter") period for comparison with the other two basins. Quali- tative comparisons between the diets of these fishes from the three basins and at different times of the year are presented in Table 3 and Fig. 1.

Variability in the frequency of occurrence of the euphausiid, copepod, and crustacea food categories is apparent with respect to both the season (e.g. between II and IV for crustacea, between II and III for copepods and euphausiids) and area (e.g. in crustacea,

TABLE 4. STANDARD LENGTHS (MM) OF Stenobrachius leucopsarus IN EACH FOOD CATEGORY. Data are based on specimens collected in the Santa Barbara, Santa Cruz, and Santa Catalina basins off south-

ern California.

Length Food

Category 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 Total

Empty or unidentifiable 5 23 18 49 39 69 47 3 254

Crustacea 0 44 33 10 55 16 77 1 446 Fish 0 0 0 1 0 5 1 0 7 Mollusca 0 0 0 0 0 0 0 0 0 Copepoda 1 3 4 7 11 25 10 0 61

Euphausiacea 0 0 7 15 16 23 6 0 67 Euphausiacea

and Copepoda 0 0 0 2 1 1 4 0 8 Amphipoda 0 0 0 2 0 2 2 1 7

Total: 6 30 32 86 72 141 77 5 450

352




copepods, and euphausiids) of sampling (Table 3). Because of population age-struc- ture, depth- and time-of-capture (day-night) sampling variability, it is unrealistic further to quantify or speculate upon the significance of these observed differences in forage.

A combined seasonal frequency distribution of the major food categories of S. leucopsarus collected in the Santa Barbara and Santa Cruz basins (Fig. 1) indicated that the greatest variation in forage occurs during the spring and summer periods. The frequency of copepods varied from 55% in spring to 6% in summer, while the opposite trend occurred in the frequency of euphausiids which varied from 24% in spring to 61% in the summer. During fall and winter months S. leucopsarus apparently fed upon a wider variety of organisms as evidenced by the generally high frequency of the "crustacea" and "other" categories, and the more uni- form (baseline) frequency of euphausiids and copepods.

Examination of S. leucopsarus stomach contents with respect to standard lengths re- vealed little relationship between food categories and fish size. Larger fishes added components to their diets but did not ex- clude types eaten by smaller specimens (Table 4, Fig. 2).

DISCUSSION

Contamination of stomach contents by the feeding of specimens in the net after capture was found by Anderson (1967) to depend upon the particular species that was sampled. He found that such contamination (as evidenced by the presence of large scales and other non-food items) was negligible for the lanternfish, T. mexicanus, but extensive for the deepsea smelt, Bathylagus stilbius. The large number of specimens (55%) whose stomachs were empty or contained only food in advanced stages of digestion is presump- tive evidence that, at least with the sampling gear used in this study, net feeding is probably not an important source of contamination. It is not known to what extent midwater fishes traumatized by capture eject food from their stomachs, however, and this should be considered as a possible source of bias. It is likely that both net feeding and ejection of food occur to a limited extent after capture.

The accuracy of observations on the dietary diversity of a species depends upon the

size of the sample examined, the size of the individuals examined, and the time and location of capture. Thus, species represented by only a few specimens (Lampanyctus regalis) may appear to be highly preferential in their choice of prey, while species represented by larger numbers of individuals (T. mexicanus) appear to be nonpreferential in their selection of prey. It is thus unreason- able to make unqualified statements about the diet of any species represented by only a few specimens, a single age group, a single small geographic area, or at an instant in time.

Paxton (1967b, Table 1), on the basis of 300 adult fishes selected for stomach content examination because they had visibly distended abdomens, concluded that S. leucopsarus, T. mexicanus, Symbolophorus californiensis, Diaphus theta, and Lampanyctus ritteri were highly specific feeders. Of 95 S. leucopsarus with identifiable stomach contents, he found that 69 had fed on euphausiids, ten on copepods, eight on sergestids, four on unidentifiable fishes, three on Leu- roglossus (= Bathylagus) stilbius, and one on S. leucopsarus. To me Paxton's data sug- gest that S. leucopsarus, at least, is not a

highly specific feeder, but is opportunistic in its selection of prey. It is well-known that

many zooplankton species are found in spa- tially separated aggregations, or "patches" (Cassie, 1963) and it is likely that a randomly feeding midwater fish feeds more efficiently when in or near such a concentration of a

potential prey species (Aughtry's, 1953 re- covery of nine Tarletonbeania crenularis whose stomachs contained only euphausiids). In other words, it is likely that a given fish, collected at a given instant in time, and selected for examination because of a "vis-

ibly distended abdomen" would have eaten a limited number of different kinds of prey.

Because of sampling bias and the lack of knowledge about stomach clearing rates in

mesopelagic fishes, Paxton's (1967b) findings, that approximately equal numbers of specimens with identifiable stomach contents were

caught diurnally and nocturnally, do not pro- vide conclusive evidence that lanternfishes feed with equal intensity throughout the day or in all parts of their depth range. Likewise, Anderson's (1967) antithetic conclusions about the feeding chronology of T. mexicanus are, as he pointed out, also provisional. On the basis of present information then, it

353



COPEIA, 1970, NO. 2

must be concluded that where and when the lanternfishes off southern California feed remains largely unknown.

Mesopelagic fishes living in the continental borderland off southern California are

non-specific feeders. Apparent preferential feeding may be because of enforced selection of prey in an optimum size range, small

sample sizes, or the predominance of certain

species in the area(s) of maximum feeding. Forage of S. leucopsarus is largely indepen- dent of fish length (one measure of age), except that older fishes may add food items to their diets that younger fishes are too small to ingest. Seasonal differences in the diet of S. leucopsarus are apparent, possibly because of seasonal variation in zooplankton abundance or availability, or to seasonal differences in foraging activity. Geographical differences in the diets of S. leucopsarus lend

support to the conclusion that they are not, per se, preferential feeders, but are instead

opportunistic in their food-getting. Net

feeding, with the equipment used, is probably not an important source of contamination.

ACKNOWLEDGMENTS

I am indebted to the following individuals and their respective institutions for

providing specimens for study: Drs. Carl Hubbs, Richard Rosenblatt, Bert Kobayashi, Basil Nafpaktitis, Robert Lavenberg, John Paxton, Rohlf Bolin, William Follett, Mrs. Lillian Dempster, Drs. William Pearcy, John Marr, Lucian Sprague and William Aron.

Special thanks go to Drs. Alfred Ebeling and Elmer Noble of the University of California, Santa Barbara for providing specimens, ship, and laboratory facilities. Much of the work was accomplished at the University of Cali- fornia, Santa Barbara and supported by USPHS-NIH Predoctoral Fellowship TIGM 990-02; ship time was supported by NSF Grant GB2867. Later phases of the study were supported by NSF Postdoctoral Fellow- ship 48060 at Harvard University and the Woods Hole Oceanographic Institution. I

thank Drs. Richard Backus, James Craddock, Giles Mead and Mrs. Penny Collard for critically reading the manuscript and offering suggestions of value. Drs. Bruce Collette and Richard Haedrich made valuable suggestions on an earlier version of the manuscript. My thanks to Mrs. Barbara Hart for typing the

manuscript.

LITERATURE CITED

ANDERSON, R. 1967. Feeding chronology in two deep-sea fishes off California. M.S. thesis, Univ. So. Calif., Los Angeles, Calif.

AUGHTRY, R. H. 1953. A note on mass mor- tality of the myctophid fish Tarletonbeania crenularis. Copeia 1953(3):190-192.

CASSIE, R. M. 1963. Microdistribution of plankton. In: Oceanogr. Mar. Biol. Ann. Rev. H. Barnes, ed., 1:223-252. G. Allen and Unwin, London.

COLLARD, S. B. 1968. A study of parasitism in mesopelagic fishes. Ph.D. diss., Univ. Calif., Santa Barbara, Calif.

HAEDRICH, R. L. AND J. G. NIELSEN. 1966. Fishes eaten by Alepisaurus (Pisces: Iniomi) in the southeastern Pacific Ocean. Deep-sea Res. 13:909-919.

ISAACS, J. D. AND L. W. KIDD. 1953. Isaacs-Kidd midwater trawl. Scripps Instit. Oceanogr. Ref. 53-3:1-21.

LAVENBERG, R. J. 1964. An ecologic analysis of midwater fishes of the San Pedro Basin. M.S. thesis. Univ. So. Calif., Los Angeles, Calif.

MAUL, G. E. 1959. On a specimen of Bathylaco nigricans Good and Bean taken from the stomach of Aphanopus carbo. Bogagiana, Mus. Municipal Funchal, Madeira Dec. 1959(4):1-8.

MEAD, G. W. AND F. H. C. TAYLOR. 1953. A collection of oceanic fishes from off northeast- ern Japan. J. Fish. Res. Bd. Canada 10(8):560- 582.

PAXTON, J. R. 1967a. A distributional analysis for the lanternfishes (family Myctophidae) of the San Pedro Basin, California. Copeia 1967 (2): 422-440.

. 1967b. Biological notes on southern California lanternfishes (family Myctophidae). Calif. Fish Game 37(2):111-120.

ROFEN, R. R. 1966. Family Paralepididae. In: Fishes of the western North Atlantic. G. W. Mead, ed. Mem. Sears Found. Mar. Res. 5(1): 205-461.

WOODS HOLE OCEANOGRAPHIC INSTITUTION, WOODS HOLE, MASSACHUSETTS 02543.

354



forage of some eastern pacific midwater fishes

Documents