Size-selective competition between cod and pelagic fisheries for prey

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.

Automated summary

Predators and fisheries may compete for the same prey, with immediate effects when sizes overlap; Predators consuming smaller sizes may lead to a potential loss of future fishing opportunities; Size-selective cod predation on sprat and herring in the Baltic Sea influences the fishing opportunities through immediate and delayed effects.