Miller Emily A, Singer Gabriel P, Peterson Matthew L, Webb Molly, Klimley A Peter
Graduate Group in Ecology, University of California, Davis, California, USA.
Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, California, USA.
J Fish Biol. 2024 Jan;104(1):240-251. doi: 10.1111/jfb.15579. Epub 2023 Oct 30.
Green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) are closely related, sympatric species that inhabit the San Francisco estuary. Green sturgeon have a more marine life history but both species spawn in the Sacramento River and reside for some duration in San Francisco Bay. These sturgeons are of conservation concern, yet little is known about their dietary competition when they overlap in space and time. To examine evidence of dietary differentiation, we collected whole blood and blood plasma from 26 green sturgeon and 35 white sturgeon in San Francisco Bay. Using carbon and nitrogen stable isotope analyses, we compared their relative trophic levels and foraging locations along the freshwater to marine gradient. Sampling blood plasma and whole blood allowed comparison of dietary integration over shorter and longer time scales, respectively. Plasma and whole blood δ C values confirmed green sturgeon had more marine dietary sources than white sturgeon. Plasma δ N values revealed white sturgeon fed at lower trophic levels than green sturgeon recently, however, whole blood δ N values demonstrated the two species fed at the same trophic level over longer time scales. Larger individuals of both species had higher δ C values than smaller individuals, reflecting more marine food sources in adulthood. Length did not affect δ N values of either species. Isotope analyses supported the more marine life history of green than white sturgeon and potentially highlight a temporary trophic differentiation of diet between species during and preceding the overlapping life stage in San Francisco Bay.
绿鲟（Acipenser medirostris）和白鲟（A. transmontanus）是关系密切的同域物种，栖息于旧金山河口。绿鲟具有更多的海洋生活史，但这两个物种都在萨克拉门托河产卵，并在旧金山湾停留一段时间。这些鲟鱼受到保护关注，但对于它们在时空上重叠时的饮食竞争却知之甚少。为了研究饮食分化的证据，我们从旧金山湾的26条绿鲟和35条白鲟身上采集了全血和血浆。通过碳和氮稳定同位素分析，我们比较了它们在淡水到海洋梯度上的相对营养级和觅食位置。分别采集血浆和全血可以比较短时间和长时间尺度上的饮食整合情况。血浆和全血的δC值证实绿鲟的海洋饮食来源比白鲟更多。血浆δN值显示，白鲟最近的觅食营养级低于绿鲟，然而，全血δN值表明这两个物种在较长时间尺度上处于相同的营养级。两个物种中较大的个体比较小的个体具有更高的δC值，这反映了成年后更多的海洋食物来源。体长对两个物种的δN值均无影响。同位素分析支持绿鲟比白鲟具有更多海洋生活史的观点，并可能突出了在旧金山湾重叠生活阶段期间及之前物种间饮食的暂时营养分化。
