Efforts to reduce fishing effort on species like herring and menhaden in the name of “extra precautionary management” in most cases, new study finds unlikely to deliver additional benefits for the stocks of predatory species that eat them.
“Our results indicate that predator productivity was rarely influenced by the abundance of their forage fish prey,” wrote authors Christopher Free of the University of California-Santa Barbara, Olaf Jensen of the University of Wisconsin-Madison , Ray Hilborn of the University of Washington. . “Only 6 predator populations (13 percent of the total) were positively influenced by the increase in prey abundance and the model showed high power to detect prey influences when they existed,” according to their article entitled “Evaluate the impacts of the abundance of forage fish on marine predators”, originally published in the journal Conservation biology.
“These results suggest that further limiting the harvest of forage fish to levels well below sustainable yields would rarely lead to detectable increases in marine predator populations.”
The results were released on July 6 through the Science Center for Marine Fisheries, a cooperative effort to improve the sustainability of fisheries and reduce uncertainty in biomass estimates through the work of academic partners with University of Mississippi Institute of Marine Sciences in Virginia, College of William and Mary, as academic sites.
“Our work suggests that the sustainable limits we are already using are sufficient to keep forage fish abundance above the levels needed by their predators,” Free of UC Santa Barbara said in a statement describing the results. “Predators are very mobile, they have great flexibility in their diet and they can go and find forage fish in places where they are doing well, change species to species that are doing well and have often evolved to breed in places where there are strong and stable abundances of forage fish.
The researchers used models incorporating data on 45 species of predators, including fish, seabirds and marine mammals, and adding environmental factors. According to the models, these other 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. “
Data sets dating back to the 1950s and 1960s on predator populations have been exploited in five regions of the world along with records of forage fisheries, Free said in a report. video presentation on the results.
“We were able to relate these two sets of data to ask the question: How has the abundance of prey influenced the growth of the population of these predators around the world? ” he said.
“What we’ve done here that differs from previous analyzes is try to control some of the other factors that influence predator population dynamics,” said Jensen of the University of Wisconsin. “In this case, we included in the models a covariate representing the temperature of the ocean.”
The paper contributes to ongoing debates in fisheries management in the United States over how to tightly regulate fish at the lower end of the trophic scale that feed larger, more commercially valuable, and recreationally sought-after fish. , and protected species, including whales and other marine mammals.
“The study reveals that, at least in forage fisheries which are already well managed and closely monitored, the adoption of additional precautionary measures will ‘rarely’ provide additional benefits to the growth of the predator population,” according to the evaluation of the Science Center for Marine Fisheries. “However, fisheries managers dealing with less well-monitored fisheries may consider more cautious strategies.”
“In places in the world where we already have very strong and efficient fisheries management, additional limitations on catches of forage fish are unlikely to benefit their predators,” Free said.
“Management of forage fish populations should be based on data specific to these forage fish and their predators,” Jensen said. “When there is not enough data to perform a population-specific analysis, it is reasonable to manage forage fish populations for maximum sustainable yield, as we would for other fish populations under of the Magnuson-Stevens Act. “
“No one has seriously suggested that overfishing for forage species is a good idea,” Jensen said. However, the study suggests that in countries with good management systems, these stocks could be fished closer to their maximum sustainable yield without negatively affecting predatory species, he said.
There are still caveats to these findings, said scientist Eva Plaganyi of Australian government agency CSIRO Oceans and Atmosphere, in a video commentary on the document.
For example, “if you fish near the breeding colony” of a predatory species dependent on forage fish, forcing these animals to travel father and expend more energy in foraging could impact their success, Plaganyi said: “I think it’s very specific to the case.