Using predator distributions, diet, and condition to evaluate seasonal foraging sites: sea ducks and herring spawn
نویسندگان
چکیده
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.
منابع مشابه
Contrasts in Energy Status and Marine Foraging Strategies of White-Winged Scoters (Melanitta fusca) and Surf Scoters (M. Perspicillata)
—White-winged Scoters (Melanitta fusca) and Surf Scoters (M. perspicillata) are often assumed to rely on similar marine resources. To evaluate the accuracy of this assumption, we contrast seasonal distributions, foraging effort, and indicators of energy status (body mass and composition, plasma metabolites) in three major foraging sites in Puget Sound, Washington, for these rapidly declining se...
متن کاملSeasonal plankton-fish interactions: light regime, prey phenology, and herring foraging.
When prey and predator are seasonal migrants, encounters depend on migration phenologies and environmental constraints on predation. Here we investigate the relative contribution of seasonality in irradiance and prey abundance in shaping the rapid seasonal body condition increase of a migrating predator searching visually for its prey: the Norwegian spring-spawning herring, Clupea harengus, fee...
متن کاملSeasonal Variation of Harbor Seal's Diet from the Wadden Sea in Relation to Prey Availability.
The Wadden Sea has an important role for marine mammals in terms of resting, nursing and foraging. Harbor seal is the most abundant marine mammal species in this area. The use of the food resources of the Wadden Sea by seals is not clear, and previous studies showed that this species can travel kilometers away from their haul-outs to forage in the North Sea. In this study, we analyzed the stabl...
متن کاملFeeding in a heterogeneous environment: spatial dynamics in summer foraging Barents Sea cod
Cod Gadus morhua are important predators in many ecosystems in the North Atlantic, but their ecological importance has diminished in many areas due to stock size reductions. In contrast, the Barents Sea cod stock is currently the world’s largest and at a high level. The goal of our study was to elucidate spatial aspects of cod−prey interactions in the Barents Sea during recent warm years (2004 ...
متن کاملMarine ecosystem connectivity mediated by migrant–resident interactions and the concomitant cross‐system flux of lipids
Accumulating research argues that migrants influence the functioning and productivity of local habitats and ecosystems along migration routes and potentially drive cross-system energy fluxes of considerable magnitude, yet empirical documentation of local ecological effects and descriptions of the underlying mechanisms are surprisingly rare. In this study, we discovered migrant-resident interact...
متن کامل