Recent change in water temperature and its effect on fisheries catch of bottom gillnets in a coastal region of the Tsushima Warm Current

Effect of water temperature change in the recent decade on coastal fisheries in the Tsushima Warm Current region is discussed using monitoring data on the water temperature and fisheries catch of bottom gillnets from 1995-2005 near the Awashima Island, Niigata. Interannual change in water temperature at Awashima showed significant negative correlation with the Pacific Decadal Oscillation (PDO) index, indicating that even coastal water temperature is under the strong influence of climate events. The dominant species in the catch of bottom gillnets has changed in response to water temperature. Turban shell (Turbo cornutus) was most dominant in 1995-1998 and then rapidly declined responding to temperature increase, while yellowtail (Seriola quinqueradiata) dominated in warm years (1998-2001), followed by cod (Gadidae spp.) in 2001-2005. Further, flounder (Paralichthys olivaceus) preferred colder years as opposite to the yellowtail. It should be noted that a regime shift accompanied with ENSO in 1997/1998 could have large effect on the catch composition. The recent decline of the turban shell is closely connected with decrease of larger-sized individuals in the regional population. Reduced food availability and intensified wave due to increased winter wind could be the critical causes for this decline.