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

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.

First record of the at-sea swimming speed of a Pacific salmon during its oceanic migration

“…The present results are generally in accord with the values estimated from tagging, although we calculated speed through the water, not ground speed. The reduction in swimming speed during the initial week may have been a response to tagging trauma (Walker et al 2000). If we adopted the average swimming speed excluding data from the initial 10 d (42.3 km d -1 ), the total cumulative horizontal swimming distance would be 2580 km.…”

“…In the central Bering Sea, chum salmon consume fish, pteropods, and gelatinous zooplankton during the daytime (Davis et al 2000). The peak biomass of micronekton and gelatinous plankton is in the upper 20 m during the night, and these organisms move deeper in the water column during the day (Nishikawa et al 2001).…”

Movement and Mortality of Adult Brown Trout in the Motupiko River, New Zealand: Effects of Water Temperature, Flow, and Flooding

“…It is possible that the trout exhibited unnatural behavior for a short period after tagging (e.g., Walker et al 2000), but this would presumably only affect results from the first tracking occasion, which occurred 12 d after the last fish was tagged. The tags transmitted signals with frequencies of 160.121 to 161.102 MHz, in approximately 20 KHz steps, so each fish could be identified by its specific frequency.…”

Anglerfish (Lophius spp) in Nordic waters

“…The recent development of Data Storage Tags (DSTs), where data on external parameters can be logged (depth, temperature and now also light intensity) has resulted in the value of tagging studies becoming more pronounced. Tagging studies using DSTs have been successful on species such as cod (Godø & Michalsen, 2000;Stensholt, 2001;Turner et al, 2002), plaice (Solmundsson et al, 2003), tunas (Block et al, 2001;Schaefer & Fuller, 2002) and salmonids (Walker et al, 2000) and have yielded important information relating to, for example, migration and spawning behaviour and behavioural differences between stocks. Aspects of the information obtained can be directly related to both stock assessment and fisheries management.…”