WILL "STEEPNESS" STYMIE OPPONENTS OF FLUKE REGULATIONS

If there is one constant in mid-Atlantic fisheries management, it is that restrictions on the recreational summer flounder harvest will always be controversial.

That is particularly true in 2017, after six years of below-average recruitment—the number of young fish entering the population—has caused the population to decline to just 58% of the target level, forcing the National Marine Fisheries Service (NMFS) to reduce the annual catch limit by 30%.

As is typically the case, those who oppose NMFS’ action are attacking the science that underlies the agency’s decision to reduce recreational landings. The American Sportfishing Association (ASA), which represents the fishing tackle industry, claims that “the decision is being based on an outdated benchmark stock assessment,” while an article in The Fisherman magazine railed against “‘fatally flawed’ MRIP data, [and] the inherent issues with NOAA’s trawl survey methodologies,” even though a recent National Academy of Sciences report gave the Marine Recreational Information Program a very favorable review.

This year the opponents of fluke regulation are claiming that a new study, prepared by biologists hired by a group calling itself the Save the Summer Flounder Fishery Fund (SSFFF), justifies their criticism of the current stock assessment. Such study found that “female summer flounder dominate the recreational catch; however…this does not hold below the legal size limit. On average, across all ports, dates, and depths, the sex ratio approximates 50:50 at 39 cm [15.6 inches], with males dominant in the size classes less than 39 cm and females dominant above 39 cm.”

They use the study to support the notion, expressed in another Fisherman article written by Nick Cicero, one of the founders of SSFFF, that “blame must be assigned to any management strategy that forces us to target spawning class females exclusively. It’s crazy, we’re talking biological suicide!” To avoid catching so many large females, opponents of the current regulatory approach suggest that “management strategies in the recreational fishery in the future should include the potential for a slot limit fishery” that established both a minimum and maximum size for fish that may be retained by anglers.

Proponents of such a “slot limit” argue that a slot that allowed anglers to keep smaller fish, and assure that males made up a significant portion of the recreational harvest, would better assure that enough large females survived to maintain the population at a sustainable level.

However, such argument runs afoul of two fisheries management principles: The need for a closed season to control harvest, and a measure of stock productivity known as “steepness.”

Season length comes into play because there are only three ways that fishery managers can limit anglers’ landings: size limits, bag limits, closed seasons or some combination thereof. As a rule, both anglers and the businesses they support consider a reasonably long season the most important management measure because it provides anglers more time to fish, which in turn results in more money flowing to angling-related businesses. There is no biological reason for recreational size limits to be as high as they are today; anglers could enjoy the same 14-inch minimum size that governs the commercial fishery, if they were willing to accept a much shorter season in exchange.

Proponents of a slot limit seem to forget that if anglers were allowed to retain smaller “slot” summer flounder (so far, no slot size has been proposed, but it’s reasonable to assume that any slot would bracket the point where males and females are equally represented in anglers’ catch), the season would have to be shortened to compensate for the greater number of legal-sized fish that would be caught.

And that’s where “steepness” comes in.

Like fishing mortality and spawning stock biomass, steepness is a parameter that fisheries managers must consider when setting annual catch limits. NMFS defines it as “the ratio of two recruitment levels; the recruitment obtained when the spawning stock is at 20% of its virgin level, and the recruitment at the virgin population level.” It is expressed as a number between 0 and 1; the lower the number, the more recruitment—the number of young fish entering the population—is dependent on stock size. A high steepness number, on the other hand, suggests that good recruitment can occur even when the spawning stock is relatively small.

Thus, proponents of a slot limit for summer flounder, who use the SSFFF study to justify their position, are actually contradicting themselves.

If the summer flounder population must include a large number of large females to guarantee good recruitment—that is, if summer flounder steepness is low—fishing mortality needs to be tightly constrained in order to maintain the large spawning stock necessary to maintain a healthy population. A slot limit, without a significantly shortened season, would allow anglers to kill too many fish.

On the other hand, if steepness is high enough to justify the higher fishing mortality that would result from a slot limit combined with the current season, then there is no need to assure that a large number of older females remain in the population, as good recruitment can result from a small spawning stock.

Whichever scenario turns out to be the right one, neither justifies a claim that the SSFFF study somehow negates the need to reduce fishing mortality today.

In fact, current science supports high steepness for summer flounder.

A stock assessment update performed in 2006 notes that steepness was calculated at 0.984, a very high figure. 

The last benchmark stock assessment determined that calculations based on such a high steepness number were “suspect,” and did not consider such figure in setting the permissible (threshold) fishing mortality rate. But even if the actual steepness figure for summer flounder is somewhat lower, that figure will still be high enough to assure fisheries managers that there is no need to increase the number of females present in the spawning stock.

Although, according to the benchmark assessment, the stock could actually tolerate a higher fishing mortality rate and smaller target biomass. Managers determined that “little gain…(<5%) was realized at fishing mortality rates higher than [the current threshold of] F35%=0.310," while the current target biomass and threshold fishing mortality rate provided a "buffer against short-term declines in recruitment," which is exactly the situation which faces the stock right now.

Thus, arguments that the SSFFF study has rendered to benchmark assessment obsolete, and that a new benchmark assessmentmust be performed before additional harvest restrictions are imposed, are not supported by science. The current assessment passed peer review by a panel of internationally-recognized fisheries scientists, and has been accepted by the eighteen PhD-level biologists that make up the Mid-Atlantic Fishery Management Council’s Science and Statistics Committee. That should be a good enough endorsement for anyone.

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This post first appeared in "From the Waterfront," the blog of the Marine Fish Conservation Network.  "From the Waterfront" may be found at http://conservefish.org/blog/