Environmental monitoring using small fishing boats in Ise Bay for fishery management

Abstract

It is important to understand and predict fish behavior to assess the impacts of coastal development on ecosystems and to conduct appropriate fishery management. Fish dynamics models have been developed to consider the migration, growth, and population change for conger eel, etc. These models calculate fish behavior based on environmental factors (e.g., water temperature and dissolved oxygen). Meanwhile, since the responses to environmental factors are mainly determined by qualitative information or laboratory experiments, a more detailed investigation is required on the fish behavior in the actual sea. In the present study, in order to collect information for behavioral modeling of fish, we measured the environmental factors and the distribution of fish simultaneously by using fishing boats. The sensors were attached to the fishing gear of the small trawling boats in Ise Bay, Japan, through which the water temperature, and dissolved oxygen were measured along with positional information by using a global positioning system. At the same time, the fish catch of each haul by trawling was recorded, to grasp the fish distribution. The obtained data provided more information for temporal and spatial distribution of water qualities than conventional monitoring. The relationship between the fish density, indicated by Catch Per Unit Effort (CPUE), and environmental factors also were analyzed. The CPUE of the conger eel increased at water temperatures of 18–20 °C and dissolved oxygen values around 2 mg L−1. These results explained the location of fishing grounds based on the fishermen's experiences that the conger eel tends to gather in marginal areas of hypoxia in the summer. These results will be useful to determine the parameters for the fish behavior model.