Trade-offs between forage fish fisheries and their predators in the California Current

Abstract

Forage fish generate economic benefits through directed fisheries, but also generate benefits through their role as prey to other valued species (large piscivorous fish, seabirds, and marine mammals). Previous evaluations of the ecosystem consequences of forage fish fisheries used models with coarse taxonomic resolution of forage fish and their predators. Here, we quantify trade-offs between forage fish fisheries and predator fisheries, and between forage fish fisheries and species of conservation interest in the California Current, using a taxonomically detailed foodweb model and a generalized equilibrium model. We propagated uncertainty in trade-offs to forage fish fishing based on uncertainty in foodweb model parameterization and uncertainty in predator–prey functional relationships in the generalized equilibrium model. The model predicted loss in catch of some higher trophic level fisheries [mainly salmon (Oncorhynchus sp.) and halibut (Paralichthys californicus)] from fishing sardine (Sardinops sagax), anchovy (Engraulis mordax), herring (Clupea pallasii), or aggregated forage fish, but the lost economic revenue from predators never exceeded the economic benefit from additional forage fish catch. Predicted reductions in biomass of seabirds and marine mammals were sufficiently large that, depending on the value of these nonmarket species, consideration of nonmarket predators could tip the balance of trade-offs toward conservation of forage fish and away from harvest. This work highlights specific predators [brown pelicans (Pelecanus occidentalis), marbled murrelets (Brachyramphus marmoratus), multiple other seabirds, sea lions (Zalophus californianus and Eumetopias jubatus), baleen whales (Mysticeti)] that are potentially sensitive to specific forage fish fisheries in the California Current.

Assessing trade-offs in large marine protected areas

“…We categorised four types of causal mechanisms that can lead to trade-offs ( Table 3 ): 1) deliberate a priori management decisions to prioritize some outcomes over others (32), or the allocation of finite resources to some activities over others (33); 2) everyday resource use decisions by resource users that influence well-being and resource conditions [ 39 , 40 ]; 3) unintended consequences of resource use where the exploitation of one resource has a direct impact on others (e.g., by-catch) [ 41 ]; 4) indirect consequences that occur when two or more resources are connected via biophysical relationships or ecosystem processes (e.g., food webs) [ 42 ]. This last type of trade-off mechanism is less visible than others and can take longer to manifest.…”

Extreme mortality and reproductive failure of common murres resulting from the northeast Pacific marine heatwave of 2014-2016

“…If the GOA marine ecosystem was operating at "relative equilibrium" [139,140] prior to the heatwave, then we hypothesize that this massive increase in foraging rate would have eventually led to prey deficits [69,136] for the groundfish themselves (creating intra-specific competition) and for other competitors such as seabirds and marine mammals (creating inter-specific competition) [136,141]. In this scenario, murres would be more sensitive to reductions in key forage fish species than competing groundfish, which typically have much broader diets and less sensitivity to fluctuations in any one prey type [136,142]. Also, it would presumably require a passage of some time for elevated grazing to deplete prey stocks below critical levels needed by murres.…”

The role of sand lances (Ammodytes sp.) in the Northwest Atlantic Ecosystem: A synthesis of current knowledge with implications for conservation and management

“…Their indirect value may outweigh any commodity services arising from direct harvest and sale of NWA Ammodytes if a large‐scale commercial fishery was ever pursued in the region. A formal valuation analysis of existing supporting and projected commodity services (e.g., based on harvest targets), derived from NWA Ammodytes , would be an important preliminary step to assess potential trade‐offs, stakeholder conflicts and competing demands within the NWA region (Hunsicker et al, 2010; Koehn et al, 2017).…”