Evaluation for the Effect of Filling a Sea Caldron on Habitat of Branchiostoma japonicum

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  • 海釜底上げによるヒガシナメクジウオ生息場への影響評価
  • カイガマ ソコアゲ ニ ヨル ヒガシナメクジウオ セイソクジョウ エ ノ エイキョウ ヒョウカ

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Abstract

There are some sea caldrons in Seto Inland Sea, Japan, whose bottom is formed by muddy sediment and thus which has low productivity of fisheries. A construction of fishing ground by filling the caldrons is proposed as one of the countermeasures. It is necessary to estimate the effect of the construction on aquatic species around new fishing ground. Thus an environmental assessment is conducted by using numerical hydrodynamic model and Habitat Evaluation Procedure (HEP) in order to evaluate the effect on habitats for Branchiostoma japonicum, which is living around the new fishing ground and is also academically valuable. Using a multi-level density flow model, tidal currents before and after filling the caldron are firstly simulated. Then, using resultant flow field, the distribution of maximum resuspended particle sizes on the sea bottom is estimated based on the threshold of sediment movement. Habitat Suitability Index (HSI) is developed for the evaluation of habitat environment for Branchiostoma japonicum. Based on earlier studies and field observations, the median particle diameter and mud content of the sea bed are employed for calculating values of SI, and then HSI is calculated as a geometric mean of SIs. The results show that the values of HSI in the habitats after the construction are equal or larger than those before the construction.

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