Trade‐offs between supportive and provisioning ecosystem services of forage species in marine food webs

Abstract

Ecosystem‐based management of natural resources involves an explicit consideration of trade‐offs among ecosystem services. In marine fisheries, there is the potential for a trade‐off between the supporting role of small pelagic fish and cephalopods in food webs, and the provisioning service they play as a major target of fisheries. Because these species play central roles in food webs by providing a conduit of energy from small prey to upper trophic level predators, we hypothesized that trade‐offs between these two ecosystem services could be predicted based on energetic properties of predator–prey linkages and food‐web structure. We compiled information from 27 marine food‐web models (all within the Ecopath framework) that included either small pelagic fish or cephalopods, described predator–prey linkages involving these species, and developed a novel analytical framework to estimate how changes in yields of forage species would propagate through food webs and other fisheries. Consistent with expectations, diet overlap between predators and prey was generally low, and predator–prey linkages tended to be asymmetric; contribution of these species to predator diets was, on average, larger than the contribution of individual predator stocks to prey mortality. The estimated trade‐offs between yields of forage fish and predator species were highly variable when we assumed joint bottom‐up and top‐down control on predation. Roughly one‐third of this variance was related to an interactive effect of fishing and predation intensity; strong trade‐offs were predicted when fishing intensity on forage species is high and when predators account for a high proportion of total forage mortality. When trophic connections were presumed to be driven by bottom‐up processes, trade‐offs were more predictable, but generally very small. Contrary to our expectations, trade‐offs were not easily predicted from energetic properties, largely because predators of forage species exhibited a high degree of intra‐guild predation, and also consumed many of the same prey as forage species. Given the limited ability to a priori predict the food‐web implications of forage fisheries, we suggest that a precautionary risk‐based approach be applied to decisions about acceptable biological removals of forage fish and biological targets used for their management.

Fishing amplifies forage fish population collapses

“…Some predators, particularly piscivorous fishes, are generalist consumers that can adapt to changing prey abundances by shifting foraging strategies (23). Finally, not all forage fish are critically important for food webs (24,25), and therefore, some stock collapses may not have widespread ecological effects. These considerations are important, but it is equally important to identify ways that our assessment might underestimate ecological consequences.…”

Feeding Interactions between Fishes in a Coastal Ecosystem in the Southern Gulf of St. Lawrence, Atlantic Canada

“…; Bundy et al. ; Essington and Munch ). Atlantic Herring, Atlantic Mackerel, and sand lances are common to both water masses in the sGSL.…”

“…; Link ; Bundy et al. ; Essington and Munch ). Where such information exists, complex (mainly mass‐balance) multispecies models have been developed for large marine ecosystems in the Northwest Atlantic (e.g., Zhang and Chen ; Bundy et al.…”

Evolutionary social and biogeophysical changes in the Amazon, Ganges–Brahmaputra–Meghna and Mekong deltas

“…When linked to wellbeing indicators (Table 1) these variables give valuable information on how the trajectories in food production translate into the actual availability of food to the populations living in the delta. Furthermore, we can hypothesize how increases or decreases in production feed back into important regulating services and human wellbeing indicators (Essington and Munch 2015;Macadam and Stockan 2015;Albert et al 2016;Wood et al 2016). …”