SHEDDING LIGHT ON BLACK SEA BASS

Depending on who you speak with, black sea bass management in New England and the Mid-Atlantic is either a blazing success or a horrible failure, and some folks might even tell you that it’s a little of both.

Here on Long Island, and up into New England, black sea bass seem to be extremely abundant, with fish showing up in places where they’ve seldom, if ever, been seen before.  

At the same time, because they’re a data-poor species, and because the last stock assessment failed to pass peer review five years ago, black sea bass have been subject to a very precautionary management scheme that has seen regulations tighten at the same time that the population has appeared to grow.

It has been a frustrating situation for fishermen and fisheries managers alike.

However, a new stock assessment, which has not yet been finalized, could usher in a new era of black seas bass management.

I should caution readers right now that the information is preliminary.  The cover sheet of the assessment bears a blurb that proclaims

“This information is distributed solely for the purpose of pre-dissemination peer review.  It has not been formally disseminated by NOAA.  It does not represent any final determination or policy.”

The peer review is still underway.  The Stock Assessment Review Committee—the peer review panel—concluded its meeting on December 2, and its report on the assessment is being prepared.  Until that report is released, we won’t know whether the assessment will be deemed “suitable for management use” or whether it will fail to get through the peer review process, just as its predecessor failed five years ago.

However, if the assessment holds up, it will provide us with a lot of new and interesting information.

It confirms one thing that we already know—there are a lot of black sea bass out there.  Total biomass at the close of 2015 is estimated to have been 24,148 metric tons, 40% above the 17,256 metric tons that the assessors believe necessary to produce maximum sustainable yield.  If retrospective patterns in the stock assessment, which measure changes in the estimates as more years of data are added to the model, are taken into account, things look even better; the 32,061 metric ton estimate that results is fully 86% above B_msy.

Because of extremely good recruitment a few years ago, which lead to an abundance of mature fish in the current population, spawning stock biomass looks even better.  2015 spawning stock biomass is estimated to have been 16,547 metric tons, 86% above the 9,667 metric tons estimate for SSB_msy.  Once again, accounting for retrospective patterns increases the estimate, in this case to 22,199 metric tons, 129% of SSB_msy.

Fishing mortality is also being kept under control.  For species such as black sea bass, the population is thought to be healthy if abundance is equal to about 40% of the abundance of an unfished stock, and for black sea bass specifically, a fishing mortality rate of 0.36 is believed to produce maximum sustainable yield.  2015 fishing mortality, at 0.24, was 35% below F_msy; if adjusted for retrospective patterns, it climbed a bit higher, to F=0.27, 25% below F_msy.

However, the fish were not evenly distributed.

A tagging study described in 2009 determined that the black sea bass population in the New England/Mid-Atlantic region is composed of three distinct stocks that remain separate during the warmer months, but mix on their wintering grounds.

There is a northernmost stock, which spends the summer from New England south to, approximately, Moriches Inlet, New York, and winters anywhere from the canyons off New York and New Jersey south to Virginia, a central stock that summers between Moriches Inlet and northern Virginia and makes shorter winter migrations in a generally southeastern direction, and a southern stock off southern Virginia and North Carolina, which makes remains local, migrating between inshore and offshore waters as the seasons change.

The stock assessment didn’t try to model such a complicated stock structure, but did break the New England/Mid-Atlantic region into a northern and southern area, with Hudson Canyon the dividing line.

The northern area appears to hold significantly more fish.  In 2015, the total northern area biomass was estimated to be 17,310 metric tons, while spawning stock biomass was 11,713 metric tons.  In the southern area, total 2015 biomass was far smaller, just 6,838 metric tons, while spawning stock biomass was estimated at 4,834 metric tons. 

Yet if there are more fish in the northern area, the fish in the southern area are subject to a higher level of fishing mortality.  F=0.39 in the southern area, but just 0.14 in the north.

Although the black sea bass stock should remain healthy well into the future, the current abundance of fish is not expected to last. 

Recruitment into the population appears to depend not on the size of the spawn itself, but on oceanographic conditions at the edge of the continental shelf during the age 0 fish’s first winter, with warm, salty water tending to favor higher recruitment levels.  Thus, the size of each incoming year class is based on recruitment of age 1 fish. 

For the years 1989-2015, recruitment has averaged about 24.319 million age 1 fish per year.  Highs occurred in 1991 (29.149 million), 1994 (27.188 million) and 2000 (37.256 million).  However, all of those years pale when compared to the 2011 year class which, in 2012, saw 68.943 million age 1 black sea bass recruited into the population. 

It is that 2011 year class which is driving the abundance that anglers have enjoyed over the past few years, but a significant portion of that year class has already been removed from the population.   Both total biomass and spawning stock biomass peaked in 2014, and has now begun to decline.  Thus, harvests will also decline in the future.

If fishing mortality is equal to F_msy, 2017 landings could be as high as 5,490 metric tons, but that would decline to 3,918 metric tons by 2019.  If fishing mortality for 2017 through 2019 was no different than it was in 2015, 2017 landings would equal 3,034 metric tons in 2017 and decline to 2,781 metric tons by 2019.

The good news is that, despite a reduction in total biomass, the stock should be able to easily replenish itself so long as overfishing does not take place.  The fact that black sea bass are protogynous hermaphrodites, which generally begin life as females and then, at some point, transform into males, had raised concerns about the number of large males that could be removed without disrupting the reproductive capacity of the stock.  However, biologists have determined that

“the presence of mature secondary males (males without bright coloration or nuccal humps, sometimes called sneaker males during spawning) increases the resilience of a population to exploitation.  If the large dominant male is removed and smaller mature males are available to spawn, the population is more robust than a population totally dependent on the large males or requiring mature females to change sex to replace the male.  The black sea bass simulation study concluded that the northern stock of black sea bass was not a typical protogynous hermaphrodite and was more resilient to exploitation.  The resilience is a result of a sex ratio which is not completely male at larger sizes and contributions by the secondary males which in combination bring black sea bass life history more in line with gonochoristic species.”

The bottom line is that, should the new assessment pass peer review, black sea bass anglers should enjoy more liberal regulations in upcoming seasons, without putting the health of the stock at risk.

Of course, if the assessment does not pass peer review, things will remain largely unchanged, and regulations will probably tighten a bit more next year.

Right now, it’s impossible to say what will happen.  Some state managers are optimistic that the new assessment will sail through peer review with flying colors.  On the other hand, anyone familiar with the 2011 peer review report knows that the Stock Assessment Review Committee set the bar for a new assessment fairly high, and that there are a number of ways that the 2016 assessment can stumble.

Still, there is reason to hope that the ambitious new assessment will be found adequate for management.  In any event, we shouldn’t have to wait too long to find out what happens, as the report of the peer reviewers should be released in the next few weeks.