Temporal change in the benthic biota and the demersal fish composition in the heavily exploited fishing ground on the continental slope off the Pacific coast of northern Japan, between the 1950's and recent years

International Symposium on Long-term variations in the coastal environments and ecosystems （国際シンポジウム「世界の沿岸海域における環境と生態系の長期変動」）. 27-28 September 2004. Matsuyama, Japan.

We examined the physical oceanographic condition, the macro-benthos composition, and the demersal fish composition in the continental slope (300-800m in depth) off the Pacific coast of northern Japan in summer of 2002 and 2003, and compared with the data collected and published in the 1950's. Macro-benthos was collected by the Niino's dredge and the Smith-McIntyre bottom sampler, and fish was caught by the bottom trawl. No clear difference in the physical condition was observed between the 1950's and recent years. In 1955, Annelida (mainly Polychaeta) and Mollusca (mainly Bivalvia) frequently appeared in the macro-benthos composition. In 2002, however, only Annelida was much and appearance frequency of Mollusca became low. Demersal fish composition was remarkably different between the 1950's and recent years. Fishing target species, namely, Scorpaenidae (Sebastes and Sebastolobus) and Pleuronectidae (mainly Clidoderma) frequently appeared in the 1950's. But, in recent years, fishing target species decreased, and Zoarcidae (mainly Bothrocara and Zestichthys), Macrouridae (mainly Albatrossia and Coryphaenoides) and Synaphobranchus increased alternately. This difference in the demersal fish composition must result from high fishing intensity in 50 years. And, change in the fish composition might influence the benthic fauna through their feeding habits. Our results suggest that direct and/or indirect impact of fishing should be taken into consideration for conservation of the marine environment and ecosystem.