Female Spawning Stock of Atlantic Stripers in Trouble
May 25, 2020
Atlantic striped bass, commonly called stripers, are among the most prominent and heavily targeted recreational species in the United States, according to NOAA Fisheries. The highly migratory fish can live for up to 30 years, grow up to 5 feet long, and weigh more than 75 pounds. They are caught from the Gulf of Maine to Albemarle Sound in North Carolina.
In 2017, nearly 18 million angler fishing trips targeted or caught striped bass, representing 9 percent of such U.S. trips, according to NOAA Fisheries. Striped bass harvest, by weight, was the largest of all recreationally targeted species in the nation that year.
However, a 2019 benchmark assessment found the stock to be overfished and experiencing overfishing.
“Anglers place a relatively high value on catching trophy-sized stripers — fish that are about 34 inches or longer in total length,” said Andrew Carr-Harris, an economist at NOAA’s Northeast Fisheries Science Center in Woods Hole, Mass., and co-author of a January study with colleague Scott Steinback. “But trophy-sized stripers are almost exclusively part of the female spawning stock, and if too many are removed from the fishery the stock has trouble rebuilding.”
High levels of removals were found to have contributed to a steady decline in the numbers of female spawners during the past decade. A mandated harvest reduction in 2015 from two fish to one fish, 28 inches or longer, to achieve the desired mortality rate did little to increase the female spawning stock. In 2017 the stock was estimated at a roughly 25-year low.
Given heavy fishing pressure on the species, fishery managers must make trade-offs between achieving conservation objectives and satisfying angler demands when designing policy, according to the study’s authors.
The researchers wanted to better understand what policies might work to rebuild the fishery while minimizing adverse impacts to anglers. Carr-Harris and Steinback evaluated the immediate economic and biological impacts of different types of recreational striped bass fishing policies.
The first step was understanding the drivers of individual angler behavior. They used data from a survey of 469 recreational anglers that fish in coastal waters from Maine to Virginia. Those survey results were then integrated into a model. The model simulated the aggregated effects of policy-induced changes in trip expectations on: angler welfare, the value that anglers obtain from striped bass fishing; participation; fishing mortality; and female spawning stock biomass, the combined weight of females that have reached sexual maturity and are capable of reproducing.
This approach allowed the researchers to examine the immediate economic and biological consequences of full or partial harvest restrictions on trophy-sized striped bass. To date, these restrictions haven’t been considered jointly in policymaking, according to NOAA Fisheries.
“We found that there are many economically efficient management policies available if the primary objective is to control fishing mortality, but few policies if the primary objective is to protect female spawning stock biomass,” Steinback said. “Of the 36 possible policies we evaluated, only one achieved the intended reduction in fishing mortality while at the same time mitigating removals of the mature females.”
That policy was taking one fish per trip in the “harvest slot” of 28-36 inches. Harvest-slot policies specify both a minimum and maximum size limit. Carr-Harris and Steinback found that implementing that policy achieved a significant reduction in both total and female spawning stock removals. These changes were relative to the 2015 policy of allowing one fish, 28 inches or longer per trip. This policy produced only a slight reduction in angler welfare, due to the relatively low rate at which trophy striped bass larger than 36 inches are encountered. The researchers concluded that additional consideration for this or similar striped bass slot limits is warranted.
“Our findings provide empirical evidence supporting the recent decision made by the Atlantic States Marine Fisheries Commission to direct Atlantic coastal states to eliminate minimum size restrictions for striped bass in 2020 and instead impose a slot limit of 28 to 35 inches to reduce spawning stock mortality,” Carr-Harris said.
The commission has primary management responsibility for the East Coast striped bass fishery.
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