Abstract
Abstract Predators often predate on a limited size range of prey, which may or may not overlap with size ranges of same prey targeted by fisheries. When they do overlap, the effect of competition over that prey is immediate, as the predator removes prey, which are at the same time suitable for the fishery. However, if the predator consumes the same prey species as the fishery, but targets smaller prey sizes, this predation on smaller sizes may result in a potential loss of future, rather than current, fishing opportunities. Comparative analyses of predator size preference and fisheries selectivity are scarce, despite their relevance in the context of integrated management of fish populations. We evaluated how size-selective cod predation influences the dynamics of sprat and herring in the Baltic Sea, as well as the competition with pelagic fisheries through immediate and delayed effects. We found a large overlap (30–60%) between prey lengths targeted by cod and fisheries, which was largest in the 1970s–1980s, when cod had higher abundance and was larger in size. Cod generally consumes herring and sprat, which are smaller than those caught by the fisheries, causing both immediate and delayed effects on prey biomass available for the fisheries.
Highlights
Targeting the same prey makes competition between humans and predators unavoidable
We aimed to evaluate how size-selective cod predation influences the dynamics of sprat and herring as well as competition with pelagic fisheries through immediate and delayed effects during three contrasting historical periods differing in the ecosystem state: a cod-dominated state (1974–1988), a sprat-dominated state (1989– 2006), and the more recent period of high cod density with decreased cod size (2007–2013)
We found a large overlap (30–60%) between prey lengths targeted by cod and fisheries
Summary
Targeting the same prey makes competition between humans and predators unavoidable. Competition between fisheries and marine mammals (reviewed in Plagányi and Butterworth, 2009) and sea birds (reviewed in Sydeman et al, 2017) has been widely described. The effect of competition on that prey is immediate, as consumption by the predator affects the availability of fish to a fishery that is conducted simultaneously This effect has been most often described in previous comparisons (Hjermann et al, 2004; Plagányi and Butterworth, 2009; Sydeman et al, 2017). Another example of a delayed effect of competition is when one of two competitors targets larger
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