The distribution of Northern Shelf haddock. Introduction

Transcription

1 Evaluating the bio-economic performance of the Northern Shelf haddock (Melanogrammus aeglefinus) fishery using age-structured harvesting strategies and variable growth trajectories Adam Delargy, University of Aberdeen (now Bangor University) Coby Needle, Marine Laboratory, Marine Scotland Science Tara Marshall, University of Aberdeen Correspondence

2 Introduction The distribution of Northern Shelf haddock Bio-economic assessments can overlook size-dependent fecundity (SDF) and sizedependent market pricing (SDP) SDF is where fish of different sizes produce different number of eggs SDP is where fish of different sizes are sold at different prices Another consideration is that individual growth trajectories change over time These changes in individual body size will have biological and economic effects through SDF and SDP

3 Decrease in L Estimated L for the cohorts L is a parameter from the von Bertalanffy individual growth model which indicates maximum size of fish A decrease in L has been observed for North Sea haddock cohorts from the years Maximum adult sizes in North Sea haddock have shrunk by ~28%, possibly due to warming temperatures (Baudron et al 2014) Data from: Baudron et al 2011

4 Aims and Objectives Define a harvesting policy, termed the Adaptive Harvesting Policy (AHP), which targets age-classes for harvest if and only if the current market value > reproductive value over the cohort s lifespan 1. Evaluate the AHP s bio-economic performance against a series of age-at-first-capture selectivity policies - Economic performance of AHP and different ageat-first-capture policies were compared using Net Present Value (NPV), incorporating discounting 2. Compare the NPV of all selectivity policies when using a growth trajectory associated with large adults and one associated with small adults 3. Estimate the NPV of the fishery using a series of historical individual growth trajectories (cohorts from )

5 Methods Assigning a reproductive value to age-classes Caddy & Seijo (2002) developed a methodology to valuate different ageclasses of European hake (Merluccius merluccius), taking into account SDF and SDP Reproductive value accounts for both current and future egg contribution. Future egg contribution was estimated by predicting the number of fish to reach future age-classes using survival probability estimates Reproductive values (expressed in units as price/kg) allow for defining a harvesting policy where age-class were targeted if and only if current SDP (price/kg) market value > reproductive value

6 Selectivity Policies Selectivity Policy Age-classes Targeted 1 (age-at-first capture 0) 0,1,2,3,4,5,6,7,8+ 2 (age-at-first capture 1) 1,2,3,4,5,6,7,8+ 3 (age-at-first capture 2) 2,3,4,5,6,7,8+ 4 (age-at-first capture 3) 3,4,5,6,7,8+ 5 (age-at-first capture 4) 4,5,6,7,8+ 6 (age-at-first capture 5) 5,6,7,8+ 7 (age-at-first capture 6) 6,7,8+ 8 (age-at-first capture 7) 7,8+ 9 (age-at-first capture 8) 8+ AHP Age-classes were targeted if and only if market value > reproductive value

7 Growth trajectories used in simulations The solid black trajectory was based on 2014 survey data and represented a population with small adults. The dashed trajectory was the theoretical growth curve and represented a population with large adults The remaining trajectories were the historical cohorts corresponding to the years

8 Model Structure 39 times START GROWTH TRAJECTORY 10 times SELECTIVITY POLICY 500 times REPETITIONS 50 YEARS For historical growth trajectories only use AHP Three coupled components: biological, harvest and economic The core of the model simulates the stock, harvesting and profits, estimating the NPV for each 50 year simulation period. 95% confidence intervals were calculated for the 500 repetitions of NPV FINISH

9 Model Core The biological component of the model simulated the annual abundance in each age-class based on SDF, recruitment, natural mortality and growth. The harvest component simulated the abundance of fish that were harvested from each age-class. The selectivity policies determined which age-classes were available for harvest The economic component then simulated the annual profits based on the harvest using SDP and costs of fishing The annual profits were added to the total profits, to estimate the NPV

10 Input parameters and data Data Units Years used Source Abundance Thousands of fish 2015 (prediction) ICES (ICES, 2015b) Recruitment Thousands of fish ICES (ICES, 2015b) TEP Thousands of eggs Peter Wright (unpublished data) Mean length (Spawning stock) Relative TEP cm Peter Wright (unpublished data) TEP/SSB (Spawning Stock Biomass) (eggs per gram) Peter Wright (unpublished data) Age-length data Years and mm 2014 (all quarters) ICES North Sea International Bottom Trawl Survey (NS- IBTS) North Sea haddock Mm, rate and age Baudron et al (2011) VB growth (years) parameters Weight-at-age kg ICES (ICES, 2015a)

11 Input parameters and data continued Sex ratio data Count, M or F 2014 (all quarters) ICES NS-IBTS obtained from DATRAS Instantaneous Instantaneous rates ICES (ICES, 2015a) fishing mortality rates Instantaneous Instantaneous rates ICES (ICES, 2015a) natural mortality rates Global effort Kw-days STECF ( Catch data Tonnes ICES ( NSH harvest Tonnes ICES (ICES, 2015a) NSH biomass Tonnes ICES (ICES, 2015a) Haddock market price data per kg 01/01/ /04/2015 Shetland Seafood Auctions ( NSH catch Thousands of fish ICES (ICES, 2015a) NSH discards Thousands of fish ICES (ICES, 2015a) Income data s Seafish ( Cost data s Seafish (

12 Results The NPV estimated for the AHP was the maximum, or not significantly different from the maximum, for all policies under each growth type The highest NPV for each growth trajectory is generated by an optimal age-at-first-capture in the mid-range of ages The NPVs estimated for the large adult growth curve are approximately double the NPVs estimated for the small adult growth trajectory

13 Results After a peak in 1987 there is a decreasing trend in mean NPV The mean NPV of the cohorts from are ~22% less than the mean NPV of the cohorts from This decrease could be caused be rising sea temperature, density-dependent effects or fishing pressure

14 Conclusions The AHP generated maximum, or near maximum, mean NPVs in comparison to the age-at-first-capture policies The AHP was also a consistently high performer for both growth trajectories The AHP is not feasible as a real-world policy as too difficult to annually reassess the stock and adapt the fishery. However the AHP can be used as a reference point for the performance of real-world options The UK NS haddock fishery has experienced a loss in economic performance due to the changes that have occurred in growth trajectories. Linking the decrease in NPV shown post-1989 from the historical cohort analysis with the shrinking of haddock shown in previous studies Future research avenues could include incorporating alternative recruitment models, management strategies and effort regimes into the bio-economic model and investigating the effects of density-dependence within the NS haddock stock

15 Acknowledgements Florian Diekert (University of Oslo) Martin Leyland (The Shetland Seafood Auctions) Funded by the Marine Collaboration Research Forum (MarCRF) - a collaborative project between the University of Aberdeen and Marine Scotland Science

16 References Baudron, A. R., Needle, C. L., & Marshall, C. T. (2011). Implications of a warming North Sea for the growth of haddock Melanogrammus aeglefinus. Journal of Fish Biology, 78(7), Baudron, A. R., Needle, C. L., Rijnsdorp, A. D., & Tara Marshall, C. (2014). Warming temperatures and smaller body sizes: synchronous changes in growth of North Sea fishes. Global change biology, 20(4), Caddy, J. F., & Seijo, J. C. (2002). Reproductive contributions foregone with harvesting: a conceptual framework. Fisheries Research, 59(1), Diekert, F. K. (2013). The growing value of age: exploring economic gains from age-specific harvesting in the Northeast Arctic cod fishery. Canadian Journal of Fisheries and Aquatic Sciences, 70(9),

17 Supplementary material The percentage of times an age-class was targeted for harvest under the AHP Ageclass %

18 Supplementary Material

19 Supplementary Material