Euphausiids in the diet of a North Pacific seabird: annual and seasonal variation and the role of ocean climate

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 390:277-289 (2009) - DOI: https://doi.org/10.3354/meps08209 Euphausiids in the diet of a North Pacific seabird: annual and seasonal variation and the role of ocean climate J. Mark Hipfner* Centre for Wildlife Ecology, Simon Fraser University and the Canadian Wildlife Service, RR#1 5421 Robertson Road, Delta, British Columbia V4K 3N2, Canada *Email: mark.hipfner@ec.gc.ca ABSTRACT: Across the California Current System (CCS), euphausiid crustaceans are important prey for many vertebrate predators, including the seabird Cassin's auklet Ptychoramphus aleuticus. However, the effects of ocean climate on euphausiid biology, and their consequences for predators, remain poorly understood. Over a 13 yr period (1996 to 2008), Euphausia pacifica, Thysanoessa spinifera and T. inspinata cumulatively averaged about 35% of the annual biomass in the nestling diets of auklets at Triangle Island, but there was marked inter-annual variation. Whereas ocean climate had little influence on the amounts of E. pacifica or T. inspinata delivered, diets included more T. spinifera if spring sea-surface temperatures in the previous year had been lower. Cold conditions might facilitate the production of a strong annual cohort, thus increasing adult biomass in the following year. Within seasons, the amount of E. pacifica in diets declined with date, and the decline was consistent across both warm- and cold-water years. In contrast, diets were especially rich in both Thysanoessa spp. late in the provisioning period in warm-water years, when the harvest of Neocalanus cristatus declined dramatically due to a temporal mismatch between the auklet predator and this copepod prey. Both the annual nestling survival rate and the mean fledging masses of Cassin's auklets were tightly correlated to the amount of N. cristatus in their diets, and for fledging mass there was a further small, additive effect of increased amounts of T. inspinata. Results of the present study add new insight into effects of ocean climate on euphausiid biology in the northern CCS, and their potential consequences for population processes of an important euphausiid predator. KEY WORDS: Auklet · Diet · Euphausiids · Ocean climate · Prey-switching Full text in pdf format PreviousCite this article as: Hipfner JM (2009) Euphausiids in the diet of a North Pacific seabird: annual and seasonal variation and the role of ocean climate. Mar Ecol Prog Ser 390:277-289. https://doi.org/10.3354/meps08209 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 390. Online publication date: September 18, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.