Title Relationship among primary production, marine environment and fisheries production of bivalves in the Seto Inland Sea
Authers Masami Hamaguchi
Keywords manila clam, marine environmental condition, Suo-Nada
Citation Bull. Fish. Res. Agen. No.34, 33-47, 2011
Abstract
The manila clam, Ruditapes philippinarum, is widely distributed all over Japan and the most common and commercially important shellfish in the country. The Fisheries production of Manila clam in Suo-Nada, which amounts to more than 90% of the total clam production in the Seto Inland Sea in mid-1980s. Maximum fisheries production of the clam in Suo-Nada was 41883 metric ton in 1986. However, the census shows a rapid decrease in fisheries production of the clam since 1990 and its was less than 100 metric ton in recent years.
 During the course of the research on the possible reasons for the deterioration of production, we noticed lots of reasons as follows; 1) the marine environmental conditions have gradually changed since mid-1980s with global climate changes. 2) Nutrient level of the Seto Inland Sea has gradually decreased by tighter regulation of total emission of nutrient salts. 3) Overexploitation of the natural resources of the clam has rose in demand by crash of other local population.
 In this review, I summarized and reanalyzed the relationship among the primary production, marine environment and fisheries production of the clam in the Seto Inland Sea. In the results, water temperature in winter was gradually increased since mid 1980s, and the fisheries production of the clam was inversely related to water temperature in winter. Similarly, nitrogen levels was gradually decreased since mid 1980s, and the fisheries production of the clam was related to concentration of the inorganic nitrogen in summer.
 The fact shows that one of the possible reasons for the deterioration of the clam production would cause by changes in marine environmental conditions.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull34/33-47.pdf