Abstract
Euphausia pacifica and Thysanoessa spinifera comprise a substantial proportion of the diet of Cassin's auklet Ptychoramphus aleuticus in the Gulf of the Farallones, California. Ocean climate variability has been linked to fluctuations in euphausiid abundance and life-history parame- ters. We tested the hypothesis that seasonal patterns of prey use by auklets correspond to within- season variation in upwelling and sea surface temperature (SST), by comparing the proportion (by number) of E. pacifica and T. spinifera in auklet diet samples obtained during the chick-rearing period to SST and an upwelling index (UI) over 11 years. We found that the proportion of E. pacifica adults in auklet diet decreased over the chick-rearing period, and increased with increasing UI and decreasing SST. We detected curvature in the relationship between adult E. pacifica and UI, with E. pacifica increasing to a point and decreasing thereafter. T. spinifera in auklet diet showed an increase over the chick-rearing period, but no relationships were detected with UI or SST. Mass of individual adult E. pacifica increased with increasing UI and decreasing SST. We detected moderate curvature in the relationship between mass of individual adult T. spinifera and SST. The proportion of E. paci- fica juveniles in auklet diet did not change seasonally and was not related to UI or SST, while the pro- portion of T. spinifera juveniles in auklet diet increased seasonally and with increases in UI. Seasonal changes in the ingestion of euphausiids by auklets appeared to be affected by ocean climate variabil- ity; however, prey-selection via a shift in foraging location or competition with other marine preda- tors are alternative valid explanations. This study highlighted the utility of using top marine preda- tors to sample prey availability, thereby complementing traditional net sampling procedures for determining the distribution and abundance of euphausiids in marine systems.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
