ABSTRACT: Stable isotope analyses of archival specimens have revealed trophic declines over the past 150 yr in a growing number of predatory pelagic seabirds that breed in the Hawaiian Islands. However, they have not examined whether isotopic shifts occurred primarily during a specific phase of the annual cycle, which could allow us to better identify the causes of trophic declines and potential consequences for affected populations. We evaluated seasonal (breeding versus nonbreeding season) foraging habits of 2 ecologically distinct species, Newell’s shearwater Puffinus newelli and Laysan albatross Phoebastria immutabilis, and extended this analysis back 50 and 100 yr, respectively. Our assessment relied on amino acid δ¹⁵N proxies for nutrient regime use (δ¹⁵N_Phe) and trophic position (Δδ¹⁵N_Glu-Phe) from 2 tissues (feather and bone collagen) reflecting different time scales. Both study species exhibited season-specific isotopic shifts resulting in more pronounced seasonality in modern populations. We also identified inter-species differences in nutrient regime use, regardless of season. Laysan albatross experienced a trophic decline exclusive to the breeding season, while their nonbreeding season foraging ecology has remained constant over the past century. In contrast, the nutrient regime at the base of the food chain for Newell’s shearwaters during the nonbreeding season underwent a shift within the last 50 yr, and the trophic decline they experienced was heavily weighted toward the nonbreeding season. Efforts to mitigate potential fitness consequences of future trophic declines might benefit from focusing on fisheries management near the Hawaiian Islands, where susceptible seabirds forage during winter/spring, rather than the entire North Pacific.

中文翻译：

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Laysan信天翁和Newell的切水上的年代际尺度的营养下降和养分变化的季节性

摘要：对档案标本的稳定同位素分析显示，过去150年中，在夏威夷群岛繁殖的掠食性中上层海鸟的营养下降。但是，他们尚未检查同位素变化是否主要发生在年度周期的特定阶段，这可以使我们更好地确定营养下降的原因和对受影响人群的潜在后果。我们评估了两种生态学上不同的物种的季节性（繁殖期与非繁殖期）的觅食习性，即纽厄尔的剪毛水牛Puffinus newelli和Laysan albatross Phoebastria immutabilis，并将这一分析分别延长至50和100年。我们的评估依赖于氨基酸δ ^15个为养分制度使用N-代理（δ¹⁵ Ñ_苯丙氨酸）和营养位置（Δδ ¹⁵ Ñ_的Glu-PHE）来自反映不同时间尺度的2个组织（羽毛和骨骼胶原蛋白）。两种研究物种均表现出特定季节的同位素变化，从而导致现代种群中更为明显的季节性变化。我们还确定了不同季节之间养分使用方式的种间差异。来山信天翁经历了仅在繁殖季节出现的营养下降，而其非繁殖季节的觅食生态在过去一个世纪中一直保持不变。相反，在过去的50年中，纽厄尔的剪力水食物链基础上的营养状况在过去的50年中发生了变化，他们经历的营养下降在非繁殖季节的影响很大。