Investigation of the implications of different reef fish life history strategies on fisheries management Final Technical Report 10 50 8 6 40 4 30 Frequency 2 20 Fork Length (cm) 0 10 25 27 29 31 33 35 37 39 41 43 45 Total Length (cm) 0 0 2 4 6 8 10 12 14 16 Age (yrs) Back-calculated Individual length at age Observed data Assessment Management Advice Biological Fishery Fishery Management Sampling Sampling Regulations Catch Growth Natural Recruitment Mortality Operating model August 2004 Front cover: Length-based and age-based assessment methods for Lethrinus mahsena (left) and Siganus sutor (right). Images available from Fishbase: www.fishbase.org (Froese and Pauly, 2000) Document to be cited as: Wakeford, R.C., Pilling, G.M., O’Neill, C.J. and A. Hine. (2004). Investigation of the implications of different reef fish life history strategies on fisheries management. FMSP Final Tech. Rep. MRAG, London. 139pp. Final Report – Administrative Details DATE COMPLETED: 31/03/2004 TITLE OF PROJECT R7835: Investigation of the implications of different reef fish life history strategies on fisheries management PROGRAMME MANAGER / Professor John Beddington INSTITUTION MRAG Ltd 47 Prince’s Gate London SW7 2QA FROM TO REPORTING PERIOD 01/04/2001 31/03/2004 AUTHORS OF THIS REPORT Dr Robert Wakeford, Dr Graham Pilling, Mrs Catherine O’Neill, Mr Adrian Hine R7835 Effects of fish life history strategies on management Page i Page ii R7835 Effects of fish life history strategies on management Acknowledgments Thanks go to Dr Geoff Kirkwood and Dr Chris Mees for their helpful consultations during the project and Dr Ashley Halls for his assistance in part of the analyses. Many thanks also go to Ed Grandcourt and Jan Robinson for their helpful comments on the biology of the shoemaker spinefoot rabbitfish (Siganus sutor). The project was funded through the UK Department for International Development (DFID) Fisheries Management Science Programme (FMSP), which is managed by MRAG Ltd. This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID. R7835 Effects of fish life history strategies on management Page iii Page iv R7835 Effects of fish life history strategies on management Contents Final Report – Administrative Details .................................................................................. i Acknowledgments ............................................................................................................... iii Contents ................................................................................................................................ v List of Tables....................................................................................................................... vii List of Figures ...................................................................................................................... ix Final Technical Report ......................................................................................................... 1 1 Introduction ...................................................................................................................11 1.1 Project aims.......................................................................................................... 11 1.2 Report Structure ................................................................................................... 11 2 The use of analytical methods of stock assessment in fisheries ............................ 13 2.1 Introduction........................................................................................................... 13 2.2 Methods................................................................................................................ 14 2.2.1 Introduction ............................................................................................. 14 2.2.2 Methodology ........................................................................................... 14 2.2.3 Results.................................................................................................... 14 2.3 Review of assessment tools ................................................................................. 16 2.3.1 Exploitation rate ...................................................................................... 16 2.3.2 Yield per recruit....................................................................................... 17 2.3.3 Virtual population/cohort analysis ........................................................... 19 2.4 Performance of assessment methods .................................................................. 21 2.4.1 Exploitation rate ...................................................................................... 21 2.4.2 Yield per recruit....................................................................................... 23 2.4.3 VPA......................................................................................................... 24 2.5 Analysis of assessment methods ......................................................................... 26 2.5.1 Methods .................................................................................................. 26 2.5.2 Results.................................................................................................... 28 2.5.3 Discussion .............................................................................................. 32 3 Biological characteristics of a moderately fast (Siganus sutor) and slow (Lethrinus mahsena) growing species .......................................................................................... 33 3.1 Introduction........................................................................................................... 33 3.2 A moderately fast growing species: Siganus sutor............................................... 33 3.2.1 Growth .................................................................................................... 33 3.2.2 Length-weight ......................................................................................... 35 3.2.3 Natural mortality...................................................................................... 36 3.2.4 Reproduction .......................................................................................... 37 3.2.5 Stock-recruitment.................................................................................... 37 3.2.6 Annual variation in recruitment ............................................................... 37 3.2.7 Seasons.................................................................................................. 38 3.2.8 Age/length-at-capture ............................................................................. 39 R7835 Effects of fish life history strategies on management Page v 3.3 A slow growing species: Lethrinus mahsena........................................................ 39 3.3.1 Growth .................................................................................................... 39 3.3.2 Covariance matrix of growth parameters................................................ 39 3.3.3 Length-weight ......................................................................................... 40 3.3.4 Estimation of natural mortality ................................................................ 40 3.3.5 Reproduction .......................................................................................... 41 3.3.6 Stock-recruitment.................................................................................... 41 3.3.7 Annual variation in recruitment ............................................................... 41 3.3.8 Seasons.................................................................................................. 42 3.3.9 Age/length-at-capture ............................................................................. 42 3.4 Summary .............................................................................................................. 43 4 Management strategy simulation ................................................................................ 45 4.1 Introduction........................................................................................................... 45 4.2 Historical overview of management simulations................................................... 46 4.2.1 Initial setup and parameter estimation.................................................... 46 4.2.2 Management Simulations ....................................................................... 49 4.3 Estimation of fishing mortality............................................................................... 53 4.3.1 Bias in existing length-based equilibrium methods................................. 53 4.3.2 Tuning..................................................................................................... 54 4.3.3 A non-equilibrium length-based method for estimating fishing mortality 55 4.3.4 A non-equilibrium age-based method for estimating fishing mortality .... 56 4.4 Simulation of management................................................................................... 57 4.5 Management performance measures................................................................... 58 5 The suitability of length-based and age-based methods for informing management based on species with different life histories ...........................................................