Effects of interdecadal climate variability on marine trophic interactions: rhinoceros auklets and their fish prey

This paper presents time-series information on the diet composition and breeding performance of rhinoceros auklet Cerorhinca monocerata at Triangle Island, British Columbia, Canada, during 15 breeding seasons between 1976 and 2001. Three shifts in ocean climate occurred within British Columbia during this period (1976–77, 1989–90, 1998–99), allowing us to evaluate associations between marine environmental conditions and the reproduction of this piscivorous seabird. Lipid-rich Pacific sand lance Ammodytes hexapterus was the single most important prey delivered to chicks across years (15 yr avg. 38%; annual range 4 to 86%). Interannual variability was high, but in general breeding performance was strongest when 0+ sand lance predominated chick diets. Other annually important prey taxa included Pacific saury Cololabis saira, juvenile rockfishes Sebastes spp., Pacific herring Clupea pallasi and juvenile salmonid Oncorhynchus spp. The dietary importance of these prey also varied seasonally. Marine environmental conditions (evaluated using sea surface temperatures, SSTs) were clearly associated with reproduction of rhinoceros auklet, as both occurrence of sand lance in the diet and the growth rates of chicks diminished as spring SSTs increased (r = –0.680, p < 0.01, and r = –0.697, p < 0.01, respectively). We hypothesized that recruitment to local sand lance populations was temperature dependent. The strong negative relationship between dietary occurrence of 0+ sand lance and spring SST (r = –0.560, p < 0.05), coupled with the lack of a similar relationship for 1+ sand lance (p > 0.20), was consistent with the temperature-dependent recruitment hypothesis. Our data suggest that SSTs could interact with population age structure to affect the recruitment dynamics of Pacific sand lance. We estimated the annual dietary importance of 0+ sand lance to rhinoceros auklets using spring SST and the importance of 0+ sand lance in the diet the previous year.