Divergent use of spawning habitat by male capelin (Mallotus villosus) in a warm and cold year

In a patchy environment, animals must make habitat choices, presumably based on environmental cues that provide reliable fitness-related information. Capelin Mallotus villosus is a small (<200 mm), short-lived (3-6 years) forage fish that spawns adhesive eggs in 2 habitats with divergent temperature regimes: beach (warm, variable) and deep water (demersal; cool, stable). In 2009 and 2010, I investigated the influence of temperature on spawning habitat selection in coastal Newfoundland by quantifying habitat-specific temperature, population-level habitat use, and individual-level movements of male capelin via acoustic telemetry. Drastically, different temperature in both years was associated with divergent habitat use. Capelin spawned only at beaches in 2009, when temperatures were significantly colder and frequently fell below suitable ranges at demersal sites (2-12 degrees C), whereas demersal sites were predominantly used under opposing conditions in 2010. Most male capelin (76%, n = 22) were detected in one habitat only per year (beach: 10%, n = 3; demersal: 66%, n = 19). Males detected in both habitats (17%, n = 5) primarily dispersed from the initial habitat when temperatures routinely fell outside of suitable ranges. This movement often involved traveling long distances (11.0-32.7 km) against currents, suggesting energetic costs. Other males (7%, n = 2) were only detected at unused sites in 2009, implying these fish did not spawn despite having developed secondary sexual characteristics. Overall, temperature appeared to be an important environmental cue for habitat selection by capelin. The flexible use of spawning habitats under divergent temperature conditions suggests that capelin have a high capacity to respond to and possibly tolerate predicted ocean-climate change.