Relationship between salmon egg subsidy and the distribution of an avian predator

Abstract

As a spatial subsidy, which is the phenomenon of transferring resources from a donor system to a recipient system, anadromous salmonids contribute to the supply of marine‐derived nutrients to freshwater and terrestrial systems. Live salmon and salmon carcasses and eggs are utilized by various organisms and affect their abundance and distribution. However, the evaluation of the effect of salmon subsidies on the abundance and distribution of terrestrial animals is biased toward predators or scavengers that utilize spawning adults and carcasses, and few studies have focused on the effect of salmon eggs as a subsidy. To avoid underestimating the function of salmon subsidies, the response to the availability of salmon eggs in various systems should be investigated. Here, we investigated the abundance and feeding behavior of the brown dipper Cinclus pallasii, as a consumer of salmon eggs, based on the hypothesis that the availability of salmon eggs affects the diet composition and stream distribution of this small predator. In addition, to test whether changes in the abundance of brown dippers are determined by salmon spawning, their abundance was compared upstream and downstream of the check dams in three streams during the peak spawning period. Brown dippers used salmon eggs during the spawning season (53.7% of diet composition), and their abundance increased as the number of spawning redds increased. In contrast, this pattern was not observed upstream of the check dam. These results suggested that the abundance and stream distribution of brown dippers vary according to the variation in the spatiotemporal availability of salmon eggs.

Watershed hydrogeomorphology drives freshwater productivity of anadromous salmonids: Implications for habitat conservation and restoration

“…Specifically, we predicted that watershed slope and stream power would negatively affect the productivity of pink salmon. Pink salmon are the most abundant and widely distributed salmonid species in the Northern Pacific region (Heard, 1991;Quinn, 2018) and function ecologically as a spatial subsidy transporting marine-derived nutrients (Koshino et al, 2013;Yamada, Katahira, et al, 2022). Our research findings can contribute to selecting streams and rivers where conservation and restoration efforts for pink salmon should be prioritized.…”

“…Anadromous salmonids contribute significantly to biodiversity maintenance in freshwater and surrounding ecosystems. They affect the abundance and distribution of other organisms and the structure of biological communities by transporting marine-derived nutrients to freshwater and terrestrial ecosystems as a resource subsidy (Field & Reynolds, 2011;Hocking & Reynolds, 2011;Yamada, Katahira, et al, 2022); therefore, they are often regarded as keystone species (Willson & Halupka, 1995). In addition, they are also important organisms providing ecosystem services (Holmlund & Hammer, 1999;Watz et al, 2022) as valuable fishery and recreational resources (Quinn, 2018).…”

Pink salmon productivity is driven by catchment hydrogeomorphology and can decline under a changing climate

“…Pink salmon are the most abundant and widely distributed salmonid species in the northern Pacific region (Heard, 1991;Quinn, 2018) and have a crucial ecological function as a spatial subsidy in transporting marine-derived nutrients to freshwater and terrestrial ecosystems (Koshino et al, 2013;Yamada, Katahira, et al, 2022). Our research findings can contribute to identifying streams and rivers where conservation efforts for pink salmon should be prioritised.…”

“…Specifically, we predicted that high catchment slope and stream power would adversely affect the productivity of pink salmon and that future productivity would be lower than current productivity as a result of increased flood disturbance caused by climate change. Pink salmon are the most abundant and widely distributed salmonid species in the northern Pacific region (Heard, 1991; Quinn, 2018) and have a crucial ecological function as a spatial subsidy in transporting marine‐derived nutrients to freshwater and terrestrial ecosystems (Koshino et al., 2013; Yamada, Katahira, et al., 2022). Our research findings can contribute to identifying streams and rivers where conservation efforts for pink salmon should be prioritised.…”

Invasion status of hatchery‐origin pink salmon in an unstocked river at the Shiretoko World Natural Heritage Site in northern Japan

“…The central part of the Shiretoko Peninsula has been inscribed as a World Natural Heritage Site, in part because of the close linkages between the terrestrial and marine ecosystems supported by pink and chum salmon ( Oncorhynchus keta ) (IUCN, 2005). For example, these two species are utilized by aquatic invertebrates, stream fishes, and terrestrial animals (Koshino et al, 2013; Shirane et al, 2021; Yamada et al, 2022). Although Hokkaido is one of the most active regions in salmon hatchery programmes (Morita et al, 2006), a decline in pink salmon returns has been observed in recent years (Saito, 2021).…”