Using predator distributions, diet, and condition to evaluate seasonal foraging sites: sea ducks and herring spawn

Marine Ecology Progress Series

W. Sean Boyd¹  James R. Lovvorn¹  Daniel Esler¹  Eric M. Anderson¹  Kurt C. Stick¹ 

关键词: Clupea pallasii;    Herring spawn;    Melanitta fusca;    Melanitta perspicillata;    Spring migration;    Surf scoter;    White-winged scoter;   

DOI  :  10.3354/meps08048

学科分类：海洋学与技术

来源: Inter-Research

【 摘 要 】

ABSTRACT: Identifying important foraging sites for highly mobile marine predators has relied mainly on relating their distributions to broadly defined habitat data. However, understanding functional dependencies on foraging sites also requires knowledge of the relative contributions of foods to predator condition. We coupled predator distributions with measures of their diet and condition to assess the importance of Pacific herring Clupea pallasii spawning events to 2 closely related and declining sea duck species. In Puget Sound, Washington, the numerical response of scoters to spawn increased with increasing biomass of spawning herring; this response was 4-fold greater for surf scoters Melanitta perspicillata than for white-winged scoters M. fusca after accounting for local differences in their abundances. In the Strait of Georgia, British Columbia, diets estimated from fatty acids and stable isotopes indicated that both scoter species gained mass by consuming spawn during late March to early April. At a site without spawn during this period, only male white-winged scoters gained mass. In contrast, body mass of male surf scoters declined appreciably before spawn became available in one study year, suggesting greater dependence on spawn for restoring depleted reserves. From winter to spring, surf scoters attained greatest body mass during late April to mid-May while migrating through southeast Alaska; during this period, plasma triglycerides suggested that fattening was not related solely to spawn consumption, yet surf scoters aggregated to consume spawn whenever it was available. Although it is not clear whether herring are essential to their population processes, surf scoters and a range of other predators for which spawning areas are clearly preferred foraging sites would likely benefit from efforts that preserve declining herring stocks.

【 授权许可】

Unknown