is angling a stochastic process for life-history traits? an empirical assessment for marine coastal...
DESCRIPTION
Larger and older fish individuals within a population tend to experience a larger mortality probability than smaller and younger individuals. This implies that fishing selects against life-history traits correlating with body size, such as growth capacity, reproductive investment and timing of maturation. It is currently unkown whether individuals vulnerable to fishing gear differ systematically from the average individual in terms of growth capacity and reproductive investment. Here, we present results that supports that angling does not constitute a stochastic process for targeting life-history traits in a marine sedentary fish populations. Individuals from a wild population of Serranus scriba were sampled using two different gears to obtain a random sample regarding life-history traits (beam trawl) and a hook-and-line-sample (angling). We fitted individual back-calculated size-at-age data to life-history models to obtain the parameters maximum size (Lmax) and reproduction investment (g). In line with expectations we found that individuals vulnerable to angling exhibited larger maximum sizes and lower values for reproductive investments, collectively indicating faster growing individuals in terms of somatic growth. Thus, our study suggests that systematic removal of vulnerable fish will exert selection pressures for increasing reproductive investment and smaller maximum sizes, which will penalize the average growth rate of individuals in the population.TRANSCRIPT
Is angling a stochastic process for life‐history traits? An empirical assessment for marine
coastal fisheries
Josep Alós1, Robert Arlinghaus2,3, Miquel Palmer1, Lucie Buttay1and Alexandre Alonso‐Fernández4
1IMEDEA (CSIC‐UIB), Spain2Leibniz‐Institute of Freshwater Ecology and Inland Fisheries , Berlin, Germany
3Inland Fisheries Management Laboratory, Humboldt‐University at Berlin, Germany4IIM (CSIC), Spain
Overview
1. Fishing is almost never random. Typically, gear is designed to remove some kinds of individuals, usually individuals that are larger and, indirectly, older (e.g. mesh size of nets)
2. Fishing mortality is therefore size‐selective with respect both to species and to phenotypic variation within species (Stokes et al 1993; Jennings et al 1998)
Overview
3. Similarly, in recreational fisheries, vulnerability to capture can be size‐related, but also depends on a fish’s decision to attack and (or) ingest baited hooks (e.g. Cooke et al 2007).
4. In this context, individuals with lower cognitive abilities and those with higher metabolism and growth capacity often take more risks, rendering these fish more vulnerable to capture (Reviewed in Uusi‐Heikkilä et al. 2008)
Overview
5. If some part of the phenotypic variation within species is due to genetic differences between individuals, then fishing might causes evolutionary change
6. Thus, behaviour‐driven vulnerability to fishing might constitute an underappreciated mechanism for selection on growth rate and (or) other life‐history traits (Uusi‐Heikkilä et al. 2008)
Overview
7. The potential for evolution of behavioural and physiological traits and its consequences for life history, yet largely overlooked research area within the emerging context of Fisheries‐induced evolution of FIE (Uusi‐Heikkilä et al. 2008)
8. Moreover, most of work are focused in freshwater recreational fisheries and empirical evidences in marine wild populations is still scarce
Objectives
The main objective of this study is to provide an empirical prove to know if angling is a selection process rather than a random
process for life‐history traits in marine coastal fisheries
With the main task:
Estimating individual life‐history traits (reproduction investment, infinite size, immature growth and maturation age/size) from
individuals randomly and angling sampled from a wild population
The case study: marine coastal sedentary fish
Case study: Painted comber, Serranus scriba (Serranidae)
1. Simultaneous hermaphrodite (indeterminate spawners)2. Maximum size (25 cm), short life‐span (maximum age 11 years), fast
growth and early age of maturation (~1st 2nd year)3. Limited home range ( ~1 km2)
4. Low interest for commercial fisheries, but…One of the most important targeted species for the recreational fishery
from Balearic Islands (Morales‐Nin et al 2005)
Materials and methods
Experimental site (EA):
1. 1 experimental area at Palma Bay (wild population)
2. Area of 1 km2 (~ mean of home range of S. scriba)
Materials and methods
Sampling methods (Experiment):
1. Random‐sample: based in beam trawl fishing (non‐selective for life‐history traits a priori)
2. Angling‐sample: based in experiment angling session using conventional recreational gears (Static fishing with natural baits) ↔ High vulnerable fish
Vs.
Materials and methods
Biological sampling:
For each fish: Otolith extraction, total length (mm), age (years), weight (g) and gonad extraction (batch fecundity and dry weight)
y = 8E-06x3.0843
R2 = 0.9915
0
20
40
60
80
100
120
50 75 100 125 150 175 200
Total length (mm)
Wei
gth
(g)
N=338
Materials and methods
Estimating life‐history traits (individual growth and reproduction investment):
1. Estimating life‐history traits is almost never easy at individual level (we need to track the individual over time)
2. Ideally direct measures of the trait should be obtained throughout their lifespan and only captivity and mark‐and‐recapture programs (e.g. Smith et al 1997 or Zhang et al 2009) allow it
3. However, the representativeness of captivity studies, and the difficulties for mark‐and‐recapture programs (time scale and effort, e.g. Palmer et al 2011) present different sources of bias(altering biological traits)
y = 57.7x - 20.872r 2 = 0.8369
0
50
100
150
200
250
300
1.5 2 2.5 3 3.5 4 4.5
Otolith radius (mm)
Tota
l len
gth
(mm
)Materials and methods
020406080
100120140160180200
0 2 4 6 8 10
Age (years)To
tal l
engt
h (m
m)
However, the back‐calculation of length‐at‐age using growth marks in the otoliths, can offer reliable methods to obtain information on individual level over its life‐span (Pilling et al 2008_CJFAS)
Materials and methods
Estimating life‐history traits (Lester et al. 2004) fitting back‐calculated data (4 main considerations)
1. The life time growth pattern (individual growth trajectory) is biphasiccharacterized by a lineal growth in immature ages (all the energy is invested in somatic growth)
2. Adult somatic growth is represented by a Von Bertalanffy (VB) growth equation (the characteristic asymptotic shape arising primarily from the allocation of energy to reproduction
0 5 10 150
12
34
5
Age (years)
Fis
h si
ze in
oto
lith
scal
e (m
m)3. Lester et al. 2004 model offered a
biological interpretation of the VB growth parameters (L∞, k and T0).
We can estimate the biological traits: maximum immature growth (h), reproduction investment (g), infinite size (L∞) and size‐age of maturation (T) at individual level
010203040
1 2 3 4 5 6 7 8 9 10
Age (years)
Num
ber o
f fish (%
)Materials and methods
4) Problem: species with short life‐span
‐10
40
90
140
190
240
290
0 3 6 9 12 15 18Age (years)
TL (m
m)
Solution
Fitting the longitudinal data in a Bayesian context to include two kinds of a priori information:
The estimation of the parameters depends on the:1) Populations mean, 2) Previous data published and 3) Individual data
Bayesian credibility intervals of the posteriors distributions was used to assess with the differences among groups (Low and high “angling” vulnerable fish)
Materials and methods
Frequentist statistics: GLMM
In all cases data were non‐independent and hierarchically structured in fishing trips which were considered as random factor
Direct measures of reproduction investment:
1.Batch fecundity ~ “Quantity”
2.Mean dry weights of eggs ~ “Quality”
Results
1. Sample size (fish size and age):
Fish size (mm) and age (years) frequency distributions was not different among group‐samples (GLMM, p = 0.490 and GLMM, p = 0.695 respectively)
-0.6 1.2
-1.0
1.0
Fish size
Age
Immature growth
Reproduction investment (g)
Infinite size
Maturation size
PCA Axis 1 (46.5%)
PC
A A
xis
2 (7
0.5%
)
N=337
2. PCA
• Independence of age and size
• Infinite size (L∞) and reproduc on investment (g) negatively correlated
• High pre‐maturation somatic growth (h) associated with higher maturation size
Results
High growth ability in high vulnerable individuals
(angling sample)
3. Maximum fish size (Lmax):
The maximum size that the individual raise up to age ∞ (Lmax) was different between vulnerability groups
Low High
140
160
180
200
220
240
L max
Results
Low reproduction investment in high
vulnerable individuals (angling sample)
Low High
0.6
0.7
0.8
0.9
Rep
rodu
ctio
n in
vest
emen
t (g)
4. Reproduction investment (g):
Strong evidence for the hypothesis that the indirect measure of individual reproduction investment (g) differs between groups
Results
5. Age of maturation (T) and immature growth rate (h):
Posterior distributions reveals no differences between vulnerability groups for the age of maturation (T) and the immature growth (h)
Low High
1.1
1.2
1.3
1.4
1.5
1.6
1.7
T
Low High
2530
3540
4550
h
Results
6. Summary: “averaged” individual trajectory per group
Angling are doing an artificial selection against grow faster individuals with high grow capacity and less investment to reproduction
0 5 10 15 20
01
23
4
Age (years)
Fis
h si
ze in
oto
lith
scal
e (m
m)
LowHigh
Fishing selection
Results
7. Direct measures of reproduction investment (batch fecundity and dry weight of eggs):
Low High 0.
005
0.01
00.
015
0.02
0E
gg W
eigh
t (m
g)50 100 150 200 250
34
56
78
910
Fish Length(mm)
log
( bat
ch fe
cund
ity )
LowConf.Int. 95%HighConf.Int. 95%
P < 0.01 P < 0.05
Beam trawlAngling
Results
8. Relationship between Indirect measures and direct measures of reproduction investment
There was a significant relationship among batch fecundity and dry weights of eggs and the reproduction investment obtained from the otoliths
0.6 0.7 0.8 0.9 1.0
0.00
00.
005
0.01
00.
015
0.02
0
g
Egg
Wei
ght (
mg)
0.6 0.7 0.8 0.9 1.0
2.0
2.5
3.0
3.5
4.0
4.5
g
log
( Bat
ch F
ecun
dity
)
P < 0.01 P < 0.05
Discussion: general
Is angling a stochastic (random) process for life‐history traits in marine wild populations?
Vulnerable fishNon‐vulnerable fish
The answer is noSome individuals have
higher probability to be caught
Discussion: methods
1. General results showed good performance of the Bayesian framework to estimate individual life‐history traits Lmax , g, hand T (Credibility intervals are relatively small and unbiased for all the parameters)
2. Life‐history parameters were successfully estimated at individual level
3. Estimations were independent of fish size and age
0 5 10 15
01
23
45
Age (years)
Fis
h si
ze in
oto
lith
scal
e (m
m)
Discussion: growth
Our empirical approach demonstrated how angling exercises an artificial selection against faster grow individuals
This result is well known (e.g. Biro and Post 2008_PNAS), but our case‐study is one of the first studies in marine wild populations
0 5 10 15 20
01
23
4
Age (years)
Fis
h si
ze in
oto
lith
scal
e (m
m)
LowHigh
Fishing selection
Biro & Post PNAS 2008
Discussion: growth
This fast grower individuals have higher grow ability with larger maximum sizes
In terms of fish size (length‐at‐age) “be smaller” should be the optimal strategy to increase survival in an mortality‐environment dominated by angling
Low High
140
160
180
200
220
240
L max
Discussion: reproduction investment (indirect measures)
In this scenario, increase investment of energy to reproduction rather than somatic growth should be the “optimal life‐history strategy” in exploited populations
Lester et al 2004 PRSLB 2008
Fish sampled by angling have lower values of reproduction investment
Angling exercises an artificial selection against the individuals that invest less energy to reproduction (and invest more energy to somatic growth)
Discussion: reproduction investment (direct measures)
Direct measures of reproduction investment (Quantity ~ batch fecundity and Quality ~ dry weigth of eggs) agreed with indirect estimations (g)
Direct and indirect measures are correlated <‐> good to get a “averaged” measure of reproduction investment in indirect spawners ( batch fecundity is too variable at individual level)
Shuter et al 2005 CJFAS
Discussion: age of maturation (T)
It is expected that the age of maturation and fishing mortality are negatively correlated, and exploited population tended to mature earlier
Thus fishing should drive selection against later maturation individuals
There were no differences (but a tendency) among the age of maturation among the two kind of sampling
Two reasons explain that result:
1) Early maturation per se (short life span) <‐> mature at 1+ years
2) In early maturations species, relationship among T and M is not so clear Lester et al 2004 PRSLB 2008
Low High
1.1
1.2
1.3
1.4
1.5
1.6
1.7
T
Discussion: immature growth (h)
Values of growth prior maturation h, (mm year‐1) were highly variable and posterior distribution were highly overlapped
Here, we can not sure if the negative results is consequence of the method (early maturation of Serranus results in poor information in early stages) or the true lack of differences
Low High
2530
3540
4550
h
0 5 10 15 20
01
23
4
Age (years)
Fis
h si
ze in
oto
lith
scal
e (m
m)
LowHigh
Conclusions and implications
Given the high heritability of this life‐history traits and the intensity of size‐selective fish harvest of this species, evolutionary responses in this sedentary fish population could modify optimal strategies (driven evolutionary responses to “be smaller”)
Physiology
Vulnerability
Fisheries‐induced evolution
Phenotype
Selection
Life‐history
BehaviorGenotype
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