Poster Abstract
24. A SIMULATION MODEL TO EVALUATE FISHERY STOCK ENHANCEMENT AND MANAGEMENT STRATEGY: A CASE STUDY OF JAPANESE SPANISH MACKEREL IN THE EASTERN SETO INLAND SEA
Yasuhiro Obata, Katsuyuki Hamasaki, Kaori Nakajima and Shuichi Kitada
National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan
yobata@fra.affrc.go.jp
Japanese Spanish mackerel (JSM), Scomberomorus niphonius, is a large migratory fish that feeds on small fish and is mainly distributed off the western coast of Japan. The species is an important fishery resource, especially in the Seto Inland Sea (SIS), with the fishery targeting adult fish migrating into the spawning grounds from the Kii Channel from April to June, and immature fish from September to November. The annual catch has decreased since 1986, when the highest catch of 6,255 tons was recorded. In 1998, the catch reached a historical minimum of 196 tons. To increase the commercial catch of this species, the National Center for Stock Enhancement has initiated a stocking program, and since 1998, fishers have been prohibited from targeting young JSM in autumn. In 2002, the Fisheries Agency of Japan commenced implementing the nationwide stock recovery plan for depleted populations including JSM in the SIS.
To predict the effects of various scenarios of hatchery releases and fishing regulations on target populations, we developed a simple population dynamics model that accounts for variation in natural recruitment. We applied this model to the stock recovery plan for JSM in the eastern SIS and predicted probabilities to achieve the goal of the stock recovery plan, i.e., to recover the 2000 stock biomass by 1.2 times in 2006. Under the present management strategy of 10% effort reduction for immature fish with 100,000 juveniles released, the success probability for achieving the goal was evaluated at 97.2% and the expected catch was 708 tons. On the other hand, the actual catch in 2006 was 580 tons and decreased thereafter (Fig. 1).
In this model, we assumed that released fish augment the fishery production without replacement of wild by hatchery fish. Similar growth rates were also assumed for hatchery and wild fish. The gap between actual and predicted catches is discussed in terms of replacement of wild by hatchery fish and the carrying capacity, with the results given in the companion paper by Nakajima et al., which will be presented in the poster session.
Fig. 1. Actual and predicted catch of JSM in the eastern SIS under the present management strategy of 10% effort reduction with 100,000 juveniles released.
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