Seasonal aggregations of sharks near coastal power plants in Israel: an emerging phenomenon

摘要

Sharks in the Mediterranean Sea are at extremely high risk, and their populations are rapidly declining. In the Eastern Mediterranean along the Israeli coastline, anecdotal observations have suggested that sharks aggregate at warm water outflows from coastal power plants. Using interviews, we examined fishermen's perceptions in order to (1) verify the presence of shark aggregations at power plant outflows; (2) examine whether there are differences in sighting frequencies among seasons; and (3) examine whether there is a trend of increased sightings of sharks during the past 2 decades (1993-2013) compared to the previous 20 yr period (1973-1993). A total of 128 fishermen were interviewed at 4 power plants and 4 nearby marinas along the shore: Hadera, Tel Aviv, Ashdod and Ashkelon. Results indicate that (1) sharks are observed much more frequently near power plants where there is a continuous warm water outflow (all except Tel Aviv); (2) shark sightings at the outflows peak during the cold season and are negatively correlated with water temperatures; and (3) there has been a general increase in shark sightings between 1993 and 2013 compared to the previous 2 decades. Shark aggregations occur at power plant outflows most likely due to elevated water temperatures. Further research is needed to understand the process underlying the recent increase in shark abundance at power plants, and its ecological implications on these endangered species and the structure of local communities.