July 6, 2021 — The following was released by the Science Center for Marine Fisheries:
A newly released study finds that, for many predator species, extra-precautionary management of forage fish is unlikely to bring additional benefits. How to manage forage fish sustainably, both by themselves and for the rest of the ecosystem, has become a much-discussed topic in fisheries management, with regulators of several forage fisheries beginning to adopt precautionary strategies on the premise that they will better provide for the needs of predator species including seabirds, marine mammals, and fish.
The study, from Drs. Chris Free of the University of California-Santa Barbara, Olaf Jensen of the University of Wisconsin-Madison, and Ray Hilborn of the University of Washington, examines decades of historical abundance data of both forage species and their predators, and uses mathematical models to determine to what extent predator populations benefited from increasing abundance of their forage fish prey. Of the 45 predator populations examined, only 6, or 13 percent, were positively influenced by extra forage.
“Our work suggests that the sustainable limits that we already employ are sufficient for maintaining forage fish abundance above the thresholds that are necessary for their predators,” said Dr. Free. “Predators are highly mobile, they have high diet flexibility, and they can go and look for forage fish in places where they’re doing well, switch species for species that are doing well, and have often evolved to breed in places where there’s high and stable forage fish abundance.”
The results have important implications for how strictly to manage forage fisheries. The study finds that, at least in forage fisheries that are already being well managed and are closely monitored, adopting additional precautionary measures will “rarely” provide any additional benefits to predator population growth. However, fishery managers who deal with less well-monitored fisheries may consider more precautionary strategies.
“In places of the world where we already have really strong, very effective fisheries management, additional limitations on forage fish catch are not likely to benefit their predators,” said Dr. Free.
“Management of forage fish populations should be based on data that are specific to that forage fish, and to their predators,” said Dr. Jensen. “When there aren’t sufficient data to conduct a population-specific analysis, it’s reasonable to manage forage fish populations for maximum sustainable yield, as we would other fish populations under the Magnuson-Stevens Act.”
According to the models used in the study, other environmental factors, such as water temperature, are more likely to influence predator populations. These results are consistent with previous efforts to examine the relationship between predator and prey populations.
“What we’ve done here that’s different from previous analyses is try to control for some of the other factors that influence predator population dynamics,” said Dr. Jensen. “In this case, we included in the models a covariate representing ocean temperature.”
SCEMFIS produced a video of the authors and independent experts discussing the results of the paper. Watch it here.