Application and Verification of Model for Annual Life Cycle of Sand Lance in the Ise Bay

Abstract

In Ise Bay, the catch of sand lance has decreased, and fishing has been prohibited since 2016. The main factor behind the decline in sand lance in Ise Bay is thought to be a decline in their water temperature tolerance, which is accompanied by a decrease in condition factor due to food scarcity in the center and mouth of the Ise Bay, from the period of feeding migration to the onset of aggregation around the aestivation ground. In this study, we expressed productive structure of sand lance in Ise Bay using the life cycle model, a Lagrangian model coupled with Eulerian hydrodynamic and lower-trophic ecosystem models, developed in our previous study on the sand lance (Ammodytes japonicus) in the eastern Seto Inland Sea. The model was validated with numerical experiment over the 2-year period from 2014 to 2015. As a result, the growth dynamics of sand lance from hatching through aestivation to spawning and hatching in the following year, as well as ecological features of the lower trophic ecosystem including plankton abundance and nutrient stocks, were reproduced fairly showing a good agreement with the observational data. The model turned out to provide a quantitative evaluation on the interaction between sand lance—the higher trophic organism—, plankton and nutrients—the lower trophic constituents—. In addition, compared to the eastern Seto Inland Sea, Ise Bay showed greater changes in sand lance production due to changes in nutrients and the production of the lower trophic level ecosystem.