Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

The Marine Nutrient Shadow: A Global Comparison of Anadromous Salmon Fishery and Guano Occurence

Takeshi Murota


Abstract.—While the ecology of seed dispersal has been widely studied, the ecology of nutrient dispersal has not. Growing concerns about loss of biodiversity has resulted in an increasing number of studies on anadromous fishes as vectors for uploading and dispersing marine nutrients into freshwater and terrestrial ecosystems through various pathways. As an outgrowth of the idea of Lindebroom (1984), who analyzed the penguin-derived “ammonia shadow” over a vigorous plant growth on an Antarctic island, this paper develops the concept of the “nutrient shadow” as the geographical space on terrestrial land that is covered by marine nutrients, due primarily to anadromous fishes, especially Pacific salmon Oncorhynchus spp., and secondarily to other animals that have fed upon them. Here, I present a quantitative estimate of the relative position of anadromous salmon as vectors of marine nutrient uploading onto lands compared with those of marine fishery by human hands and of guano (sea birds’ feces) occurrences as a final product of upwelling ecosystems. Then, I assess the extent of the nutrient shadow cast by spawning runs of salmon in view of the dynamics of nutrient condensation and dispersal (thinning) and conclude with some speculation about the vastness, albeit thin, of salmon-derived nutrient shadows over wild environments and the effects of anadromous salmon on fertilizing terrestrial ecosystems that may even be larger than those of marine fishery and guano occurrence, if we interpret such fertilization as the material basis for increasing biodiversity.