Differences in water temperatures experienced by embryo and larval Coho Salmon (Oncorhynchus kisutch) across their geographic range in British Columbia

Abstract

For species of fish that spawn over a large geographic range, it is expected that populations will experience different water temperatures during early development. To gain a better understanding of water temperature regimes experienced by embryo and larvae among populations, we surveyed surface and intragravel temperatures at 10 locations where Coho Salmon (Oncorhynchus kisutch) spawn across British Columbia from mid-November to May. We chose coastal systems and interior systems at southern and northern latitudes to represent the range of potential conditions where fish spawn. Intragravel water temperatures varied significantly across study sites and were also significantly warmer than surface water temperatures – particularly during the coldest winter months. Northern interior populations experienced temperatures below 1 °C early in embryo development; less than a month after spawning and with fewer than 50 accumulated thermal units in some locations. Throughout the experimental period, temperature variability was less in intragravel water than surface water, but differences also existed among locations. Daily fluctuations in temperature were greatest for the southern-most coastal locations. Our results represent important findings when attempting to extrapolate incubation temperature from surface water temperature since even small differences in temperature have a cumulative effect in embryo and larval development.