588 



Fishery Bulletin 104(4) 



Materials and methods 



Data modification 



Stock assessment model 



The simulations to determine impacts of a lack of 

 fishery-dependent data involved the use of a recent 

 stock assessment model for red porgy, a forward-pro- 

 jecting age-structured model developed during the 

 Southeast Data, Assessment, and Review (SEDAR) 

 stock assessment workshop. The model was an expan- 

 sion of the Methot (1989) stock-synthesis model and 

 is similar in structure to models used in assessment 

 of cobia (Williams, 2001). With the red porgy model, 

 we simulated a population through time, applying 

 annual fishing mortality, natural mortality, recruit- 

 ment, and growth (SAFMC'^) while attempting to 

 statistically match the simulated population with 

 observed data sources. The stock assessment model 

 incorporated data from 1972 through 2001. These data 

 included information from fishery-dependent sources 

 (commercial hook-and-line, trawl, and trap fisheries, 

 and recreational headboats, charter boats, and pri- 

 vate boats) and the fishery-independent MARMAP 

 survey. Data included annual values for total land- 

 ings by fishery, length an(i age frequencies by gear, 

 and indices of abundance for the headboat fishery 

 and MARMAP survey. Additional parameters incor- 

 porated in the model included natural mortality rate 

 (assumed to be constant over time), gear selectivity 

 for both MARMAP and fishery data, growth (based 

 on the von Bertalanffy growth equation), recruitment 

 (based on a Beverton-Holt recruitment model), and 

 fishing mortality (SAFMC''). This model was speci- 

 fied and programed by SEDAR workshop participants 

 using AD Model Builder software (vers. 6.0.3, Otter 

 Research, Sidney, B.C., Canada). 



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2009 2013 201 i' 

 Year 



2021 



To simulate the lack of fishery-dependent information 

 resulting from a moratorium, we omitted length- and 

 age-frequency data used as input for the stock assess- 

 ment model from commercial and headboat fisheries for 

 the most recent 0, 1, 2, 3, 4, 5, or 6 years (Table 2). Land- 

 ings, catch per unit of effort, life history parameters, 

 and the model code were not altered. We did not remove 

 landings from the stock assessment model because omit- 

 ting landings would have changed the estimates of both 

 fishing mortality and biomass, making comparisons 

 of results among models impossible. Therefore, these 

 simulations represent how the lack of fishery-dependent 

 length and age information due to a moratorium would 

 affect assessment results, rather than show the direct 

 effects of reduced fishing mortality on the population. 

 To incorporate stochasticity, we randomly sampled (with 

 replacement) MARMAP length and age frequencies 

 from observed frequencies. For each duration of mora- 

 torium (0, 1, 2, 3, 4, 5, and 6 years), we conducted 50 

 model runs. Results from the stock assessment models, 

 including the status indicators relative biomass (BIB 



MS\ 



Figure 3 



SEDAR population projections for red porgy (Pagrus pagrus) under 

 four potential management scenarios. For a management option to 

 be recommended, there must be at least a 50% likelihood (horizontal 

 line) of the population biomass being greater than B^j^y before the 

 year 2016 (vertical line). 



and relative fishing mortality (F/F,^gy), were compared 

 among simulations. In order to identify differences in 

 variability, we calculated the standard deviation of 

 status indicators among the 50 simulations for each 

 simulated moratorium duration. 



Population projections 



Output from each of the stock assessment model runs 

 was used as input for population projections to evaluate 

 potential management options according to the method 

 developed during the SEDAR process (SAFMC-^). Start- 

 ing with the biomass estimate from the most recent year 

 (as estimated by each stock assessment model), stock 

 projections were run under four potential 

 management scenarios: 1) no fishing mor- 

 tality or bycatch mortality, as if all fish- 

 eries in the region were closed (F=0); 2) 

 fishing mortality under a red porgy mora- 

 torium (i.e. where there is only bycatch 

 mortality [F=0.054]); 3) fishing mortality 

 representative of Amendment 9 (F=0.173); 

 and 4) fishing mortality representative of 

 Amendment 12 (F=0.107; Table 1). SEDAR 

 workshop attendees determined fishing 

 mortality rate (F) for each option, and 

 SEDAR projection results are shown in 

 Figure 3 (SAFMC''). 



The 25 -year projections were based on a 

 simulated age-structured population with 

 stochastic stock-recruit relationship and 

 fishing mortality. Initial (2001) stock size- 

 at-age, weight-at-age, annual biomass and 



2025 



recruitment, B^/gy, and steepness estimat- 

 ed by the stock assessment model for each 

 model run were used as input for popula- 

 tion projections. Other projection input 



