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Diurnal variation in thermal environment experienced by salmonids in the North Pacific as indicated by data storage tags

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Abstract:

Eight temperature-recording data storage tags were recovered from three salmonids in Alaska (pink and coho salmon and steelhead trout) and five chum salmon in Japan after 21–117 days, containing the first long-term records of ambient temperature from Pacific salmonids migrating at sea. Temperature data imply diel patterns of descents to deeper, cooler water and ascents to the surface. Fish were found at higher average temperatures at night, with narrower temperature ranges and fewer descents than during the day. Fish tagged in the Gulf of Alaska were at higher temperatures on average (10–12°C) than chum salmon tagged in the Bering Sea (8–10°C). Chum salmon were also found at a wider range of temperatures (-1–22°C vs 5–15°C). This is probably related both to the different oceanographic regions through which the fish migrated, as well as species differences in thermal range and vertical movements. Proportions of time that individual fish spent at different temperatures seemed to vary among oceanographic regions. Steelhead trout may descend to moderate depths (50 m) and not be limited to the top few metres, as had been believed. Japanese chum salmon may seek deep, cold waters as they encounter warm surface temperatures on their homeward migrations. Temperature data from all fish showed an initial period (4–21 days) of day and night temperatures near those of sea surface temperatures, suggesting a period of recuperation from tagging trauma. A period of tagging recuperation suggests that vertical movement data from short-term ultrasonic telemetry studies may not represent normal behaviour of fish. The considerable diurnal and shorter-term variation in ambient temperatures suggests that offshore ocean distribution may be linked more to prey distribution and foraging than to sea surface temperatures.

Keywords: Bering Sea; North Pacific; Pacific salmon; data storage tags; steelhead trout; tagging effects; thermal habitat

Document Type: Research Article

Affiliations: 1: University of Washington, School of Fisheries, Fisheries Research Institute, Box 355020, Seattle, WA 98195–5020, USA 2: UMass/NOAA CMER Program, University of Massachusetts, Amherst, MA 01003–0040, USA 3: National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratory, Juneau, AK 99801–8626, USA 4: National Marine Fisheries Service, Southwest Fisheries Science Center, Pacific Fisheries Environmental Laboratory, Pacific Grove, CA 93950–2097, USA 5: Fisheries Agency of Japan, National Salmon Resources Center, Sapporo 062–0922, Japan 6: Current address: Fisheries Agency of Japan, Tohoku National Fisheries Research Institute, Hachinohe Branch, Hachinohe 031–0841, Japan 7: Hokkaido University, Faculty of Fisheries, Hakodate, Hokkaido 041–8611, Japan

Publication date: 2000-06-01

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