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280 Mar Ecol Prog Ser 459: 275–292, 2012 ulated systems, the low productivity of the elasmobranch species (skates and dogfish) with their characteristically delayed maturation, low fecundity, and relatively slow growth rates leads to a low F MSY around 0.1 (Table 1). Similarly, both Georges Bank redfish and Gulf of Alaska Pacific ocean perch (POP) (both long-lived, slow growing Scorpaenids) have generally low F MSY and resilience to exploitation. Conversely, cod and herring had the highest production rates in both systems, along with haddock in Georges Bank and walleye pollock in the Gulf of Alaska, resulting in relatively high F MSY at 0.3 or above. However, production of flatfish differed be - tween systems; Georges Bank species (yellowtail, winter, and windowpane flounder) had productivity similar to cod and herring, while Gulf of Alaska species (arrowtooth flounder, halibut, and flathead sole) had productivity more similar to elasmobranchs and scorpaenids. The relatively low production to biomass ratios for both Georges Bank Atlantic mackerel and Gulf of Alaska sablefish result in low to intermediate F MSY . With these contrasts as a basis, we next compare aggregate properties of the simulated systems. Our simulated systems are ‘cartoons’ of the actual systems, but parameters were based on data from each ecosystem such that broad productivity comparisons are possible. Overall, the simulated Georges Bank system has higher MSYs than the simulated Gulf of Alaska system on a per unit area basis, with a full system MSY of 3.40 t km −2 compared with 1.96 t km −2 , respectively (Table 1). Results from both systems support previous findings that the sum of single species yield exceeds total system yield (with single species sums of 4.174 and 2.586 t km −2 , respectively). Table 1. ‘True’ F MSY (F, fishing mortality rate; MSY, maximum sustainable yield) and MSY with species interactions, for each species and aggregation of the various 10-species simulation models. fl.: flounder; zoopivore: consumes shrimp and other small crustacean prey; P.: Pacific Aggregation Species F MSY MSY ID no(s). (t km –2 ) Georges Bank Species grouping Cod 1 0.325 1.069 Haddock 2 0.25 0.877 Yellowtail fl. 3 0.35 0.306 Winter fl. 4 0.375 0.129 Windowpane fl. 5 0.3 0.036 Redfish 6 0.1 0.129 Herring 7 0.325 0.973 Mackerel 8 0.15 0.124 Skates 9 0.1 0.487 Dogfish 10 0.1 0.044 Full system 1–10 0.275 3.398 Taxonomic affinity Groundfish 1, 2, 6 0.275 1.924 Flatfish 3–5 0.35 0.470 Forage a 7, 8 0.275 1.015 Elasmobranchs 9, 10 0.1 0.532 Habitat Pelagics a 7, 8 0.275 1.015 Demersals 1–6, 9, 10 0.275 2.383 Feeding functional group Piscivores 1 0.325 1.069 Benthivores 2–5, 9 0.15 1.395 Zoopivores 6, 10 0.1 0.174 Planktivores 7, 8 0.275 1.015 Average adult body length Large 1, 2, 9, 10 0.275 1.925 Medium 3–5 0.35 0.470 Small 6–8 0.25 1.028 Aggregation Species F MSY MSY ID no(s). (t km –2 ) Gulf of Alaska Species grouping P. cod 11 0.3 0.234 Sablefish 12 0.1 0.085 Arrowtooth fl. 13 0.125 0.633 P. halibut 14 0.075 0.019 Flathead sole 15 0.15 0.059 P. ocean perch 16 0.05 0.052 Herring 17 0.35 0.565 Walleye pollock 18 0.325 0.879 Skates 19 0.1 0.045 Dogfish 20 0.05 0.015 Full system 11–20 0.2 1.955 Taxonomic affinity Groundfish 11, 12, 16 0.15 0.254 Flatfish 13–15 0.125 0.705 Forage a 17, 18 0.325 1.440 Elasmobranchs 19, 20 0.075 0.056 Habitat Pelagics a 17, 18 0.325 1.440 Demersals 11–16, 19, 20 0.125 1.006 Feeding functional group Piscivores 11, 13, 14 0.15 0.809 Benthivores 15, 19 0.125 0.101 Zoopivores 12, 20 0.1 0.093 Planktivores 16–18 0.325 1.440 Average adult body length Large 11, 12, 14, 19, 20 0.125 0.291 Medium 13, 15, 16, 18 0.175 1.299 Small 17 0.35 0.565 a These categories (Forage and Pelagics) contained the same species aggregations for their respective locations
Gaichas et al.: Simulating aggregate species production 281 Yield (t km –2 ) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 2.0 1.5 1.0 0.5 0.0 a b Yield Proportion not collapsed 0.0 0.2 0.4 0.6 0.8 1.0 Fishing mortality rate Fig. 2. Full 10-species system aggregate yield and collapse curves (where collapse is defined as biomass
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