villegas-ríos at the 2nd icft south africa

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Seasonal patterns of behaviour of a temperate coastal fish: drivers and implications for vulnerability

David Villegas-Ríos, J. Alós, M. Palmer, R. Bañón, S. Barbieri, A. Alonso-Fernández, F. Saborido-Rey

Grahamstown, 15th July 2013

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If catches represent fish abundance is an old question1,2

CPUE=q·N Catchability:

Probability of a single fish to be caught by a defined unit of fishing effort

Often considered constant in stock assessment

Affected by a number of variables , e.g. fish behaviour: Migrations Spawning aggregations Fish personality (boldness,

activity) …

Background

1 Cooke JG, Beddington JR (1984). Math Med Biol 1:391-4052 Pauly D, Hilborn R, Branch TA (2013) Nature 494:303-306

INTRODUCTION

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Relationship between environment (T) and catchability (e.g. lobster3)

Relationship between environment and activity

Relationship between activity and catchability with telemetry (e.g.: cod4)

The probability of catching a fish with passive gears depends on (1) the probability of the fish encountering the gear and the (2) probability of being trapped in it5

In passive gears, fish behaviour is important

Background

Catchability of lobster in Tasmania (Ziegler et al., 2004)

3 Ziegler et al. (2004). Marine Biology, 145: 175-1904 Olsen et al. (2012). Ecology and Evolution, 2(7): 1549-15625 Rudstam (1984). CJFAS, 41(8): 1252-1255

INTRODUCTION

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Many harvested nearshore fish species are sedentary and move within a small home range

Many of them are fished in coastal areas with passive gears (hook and line, gillnets, traps…)

In temperate environments, those fish are subject to seasonal environmental cues that may determine seasonal patterns in the physiological state (feeding, reproduction)

More evident in capital breeders with determinate fecundity

Background

Serranus cabrilla

Serranus scriba

Diplodus sargus

INTRODUCTION

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Labrus bergylta NE Atlantic, Mediterranean Commercial and recreational

interest Fished with gillnets (95%)6

Sedentary species, small home range (~0.1 km2)7

High residency and site fidelity 7

Diel behaviour, more active during daytime 7

Capital breeder, determinate fecundity 6

Feeding in summer, reproduction in winter 6

6 Villegas-Ríos et al. (2013). PhD Thesis7 Villegas-Ríos et al. (2013). Journal of Sea Research, 80:61-71

INTRODUCTION

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Relate environmental cues, physiological state, fish behaviour and catchability in a marine costal fish (Labrus bergylta)

HypothesesH1: The existence of a seasonality in the environmental

cues determines physiological variations over the year which in turn influence the behavioural pattern

H2: The existence of a seasonal pattern of behaviour should determine a pattern of fish catchability with passive gears

Objective

INTRODUCTION

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Receiver array Twelve receivers (VR2W) Complete overlap in the study area Fixed in sandy bottom with auger anchors September 2011- September 2012

360º

MATERIAL AND METHODS

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V13

V9

Fish tagging Hook and line and night diving 25 individuals Surgery Residence index (DD/TP) in the

study area during the duration of the experiment=0.99

Ø= 13 mm6 g Ø= 9 mm2.9 g


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Behavioural variables Centers of activity (COAS) at 30 min time bins Home range based on Kernel utilization distributions Distance travelled: distance between consecutive centers of

activity Estimated for 10d periods to reduce the inherent variability of

the data


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Additional sampling Sea surface temperature (2 yr):

oceanographic buoy

Biological sampling (2 yr) Reproductive activity: gonads

from 1529 individuals collected in the local fish markets. Reproductive state (spawning vs. Non-spawning) based on GSI and maturity ogive

Feeding activity: gut weight from 570 individuals. F=stomach weight/gutted weight

Catchability (10 yr): artisanal fishing data from a monitoring program (>800 hauls) by scientists. Abundance index from UVC


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Simple approach! Variables

Drivers: temperature, reproductive activity and feeding activity

Behaviour: home range size and distance travelled (activity)

Catchability Difficult to assess cause-effect relationships from observational

data Our strategy: to estimate and compare the phase (φ) of each

variable individually fitted to a sinusoidal function (julian day) Assumed sinusoidal cycle if β1 or β2 ≠ 0

Model


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ModelTemperature

Temporal autocorrelation term

Home range size and distance travelled Temporal autocorrelation term Fish as random factor (mixed-model) Fish size as a continuous variable (β3)

Catchability Offset: panel lenght and haul time


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Results Significant sinusoidal

cycle in all cases except the home range size

Distance travelled influenced by fish size

RESULTS AND DISCUSSION

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Results216.5

232.4

214.0

Significant sinusoidal cycle in all cases except the home range size


Clear relationship between sea surface temperature and physiological state

temperature

feeding


reproduction

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Results216.5

232.4

214.0

176.0




Relationship between physiological state and activity activity

temperature

feeding


reproduction

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Results216.5

232.4

214.0

176.0

173.8




Relationship between physiological state and activity

Clear relationship between activity and catchability

catchability

activity

temperature

reproduction

feeding


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Conclusions We used a simplistic approach that facilitated the

interpretation of the results

Forced the variables to a lag of 6 months between maximum and minimum

There is an alternation between: a predominantly reproductive state with low activity

in winter and a predominantly feeding state of high activity when

catchability is higher in summer


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Conclusions The pattern of behaviour determines the pattern of

catchability and thus vulnerability, in agreement with other theoretical (Alós et al., 2012) or experimental results (Biro and Post, 2008)

Implications for stock assessment since catchability decouples catches and abundance (temporal variation) and should be considered in stock assessment models

Highlights the need to study fish behaviour in coastal sedentary fish, not only in migratory or highly-mobile species.


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Thanks!

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villegas-ríos at the 2nd icft south africa

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