Facilitation of fisheries by natural predators depends on life history of shared prey

Abstract

Predators commonly share prey with human exploiters, intuitively suggesting that there is an inherent human-predator conflict through competition for prey. Here we studied the effects of fishing and predation mortality on biomass distributions and yields of shared prey using a size-structured model of competing populations, describing the life histories of Baltic Sea sprat and herring. Whereas both species responded in a similar fashion to increased fishing mortality, with decreasing juvenile and adult biomasses, we found that responses to predation mortality differed between species. Sprat only display weak compensatory responses with increasing predation mortality, while over a substantial range of mortalities there was a strong increase in adult (and total) herring biomass, i.e. overcompensation. The observed biomass overcompensation results from relaxed intraspecific competition as predation mortality increased, allowing for faster individual growth rates that in turn lead to a change in population composition (juvenile:adult biomass ratio). Our results suggest that the potential for biomass overcompensation is higher for species exhibiting substantial growth after maturation. Differences in size-selectivity of predators and fishing mortality resulted in a positive effect of predation mortality on fisheries yields, which can be explained by an overcompensatory response in adult herring biomass. Thus, somewhat counter intuitive, our results suggest that fishermen, depending on prey life history, may actually benefit from allowing for a higher abundance of predators, despite competing for shared prey.

Linking consumer physiological status to food-web structure and prey food value in the Baltic Sea

“…The importance of benthic invertebrates for pelagic top consumers is often neglected in multi-species models (but see e.g. Niiranen et al 2012;Huss et al 2014) and in the management of commercially important fish species (ICES 2016). Benthic population stocks may decrease in the future due to continuously decreasing oxygen conditions in the deep water of the Baltic Proper related to eutrophication and climate change, and attributed to climate-related brownification in the Bothnian Bay (Andersson et al 2015).…”

Incidence and phenotypic variation in alewife alter the ontogenetic trajectory of young‐of‐the‐year largemouth bass

“…trophic interactions and ecosystem function (Treseder and Vitousek 2001, Proffitt et al 2005, Wimp et al 2005, Walsh and Post 2011. In our study lakes, the presence-and phenotypic variation of alewife structure the zooplankton community , Howeth et al 2014, drives evolutionary divergences in Daphnia, an important prey for YOY fishes (Walsh and Post 2011), and alters foraging morphology and behavior in competitors (Huss et al 2014) and top-predatory chain pickerel (Brodersen et al 2015). Here we have shown that the strong effect of the presence of and phenotypic variation in alewife on zooplankton community also alters the ontogenetic trajectory of YOY largemouth bass.…”

“…Recently studies have started to address the ecological consequences of phenotypic variation within species (Treseder and Vitousek 2001, Proffitt et al 2005, Wimp et al 2005, Walsh et al 2012, Des Roches et al 2018). Variation within a species (phenotypic variation) can have strong direct effects upon prey communities and prey evolution and predators , Palkovacs and Post 2009, Walsh and Post 2011, Howeth et al 2014, Brodersen et al 2015, and strong indirect effects that propagate through the food web to alter the strength of trophic cascades and the phenotype and foraging of competitors , Walsh et al 2012, Huss et al 2014. These direct and indirect effects of phenotypic variation can create seasonal variation in prey availability , that may have important consequences for the diet, growth and, ultimately, survival of coexisting species, particularly those that undergo pronounced seasonal ontogenetic niche shifts.…”

“…Across the eastern North America, there are two forms of alewife that differ with respect to life history. This phenotypic variation has effects that propagate through food webs and affects coexisting species and ecosystem functions , Walsh and Post 2011, Walsh et al 2012, Huss et al 2014, Brodersen et al 2015. Anadromous alewife spawn in and spend their first summer of life in freshwater, but then migrate to the ocean where they do most of their feeding and growth before returning to freshwater each year to spawn at around 3-4 years of age.…”

Competition between marine mammals and fisheries in contemporary harvested marine ecosystems

“…As examples, we can take the case of grey and harbour seal trophic overlap in the North Sea (ICES WGMME 2015), as well as the potential of resource competition between marine mammals, fisheries, and other marine megafauna, such as sharks, marine birds, as well as predatory fish (e.g. Huss et al 2014). For instance, the resource competition between cod, harp seals and minke whales in the Barents Sea was explored given the availability of shared prey and historic environmental conditions in an attempt to reveal possible mechanisms of the competition (Bogstad et al 2015).…”