CURRENT REGULATIONS SHOULD REBUILD STRIPED BASS STOCK

 

This morning, the Atlantic States Marine Fisheries Commission’s Atlantic Striped Bass Technical Committee met to discuss the pending stock assessment update, which will be presented to the Atlantic Striped Bass Management Board in early November.

Anglers all along the striper coast have been eagerly awaiting the update’s findings, particularly because Amendment 7 to the Interstate Fishery Management Plan for Atlantic Striped Bass included the provision

“If the 2002 stock assessment results indicate the Amendment 7 measures have less than a 50% probability of rebuilding the stock by 2029 (as calculated using the low recruitment assumption) and if the stock assessment indicates that at least a 5% reduction in removals is needed to achieve F rebuild, the Board may adjust management measures to achieve F rebuild via Board action (change management measures by voting to pass a motion at a Board meeting).”

Most people familiar with the striped bass resource probably believed that a rebuilding plan would emerge later this year.  I know that I certainly did.  After the Technical Committee met a little over a month ago, it appeared that the most likely outcome would be a fishing mortality reduction in the 25% range.  

However, the final numbers on the stock assessment were yet to be crunched; scientists were still uncertain about a number of points, including how to address retroactive patterns in the data, and whether the regulations that became effective in 2020 impacted the selectivity of fishery-dependent samples.  Depending on how such issues were resolved, the actual reduction needed to rebuild by 2029 seemed likely to fall somewhere between 9 and 27%.

Anyone who listened to the proceedings of the August 2 Management Board meeting, where the various options that might be included in any rebuilding plan were discussed in detail, almost certainly got the impression that most of the Management Board, and certainly most, if not all, of the professional fishery managers, were expecting some sort of rebuilding plan to be needed.

Thus, it certainly came as a surprise to me, and I suspect to many other people as well, when Dr. Katie Drew, until recently the Chair of the Technical Committee, announced that while the striped bass stock is still overfished, overfishing is not occurring, and there is a 78.6% chance that the female spawning stock biomass could be rebuilt to its target level under current regulations.

There will be no fast-tracked rebuilding plan, and there is virtually no chance that the Management Board will decide to adopt a precautionary harvest reduction at this point in time.

While I was caught by surprise, after listening to the Technical Committee meeting, having an opportunity to question the Technical Committee about some of the data, and having thus gained an understanding of the rationales that undelie the Technical Committee’s findings, it’s clear that the rebuilding projection was based on the best scientific information available. 

Some of the facts are a little confusing, so the easiest way to begin is probably by addressing the sources of the initial uncertainty, beginning with selectivity.

It’s a relatively simple concept to explain.  Striped bass stock assessments are based on a wide array of fishery-independent and fishery-dependent surveys.  Fishery-independent surveys are generally surveys conducted by the state, or another fisheries management body.  They may involve trawls, gill nets, or other gear, and they may seek to survey fish at any stage of their lives, from young-of-the year to the oldest and largest spawning females.  Such surveys are designed, to the extent possible, to provide objective, statistically-valid samples of the striped bass resource.

Fishery-independent surveys are a little different, as they survey fish that have been captured by commercial and recreational fishermen.  Thus, such surveys always have some sort of inherent bias, because fishermen’s landings are often disproportionately composed of a few ages and sizes of fish, because such fish are particularly vulnerable to the gear used (e.g., gill nets with a particular mesh size) and/or because regulations place restrictions on the size of the fish that may be retained.

Addendum VI to Amendment 6 to the Atlantic Striped Bass Interstate Fishery Management Plan abandoned the previous 28-inch minimum size for coastal recreational anglers with a 28- to 35-inch slot limit, beginning with the 2020 fishing season.  It also resulted in changes to the regulations affecting anglers in the Chesapeake Bay, and led to some states changing the size limits in their commercial fisheries.  Such altered selectivity would be reflected in fishery-dependent surveys.  Some year classes of fish might appear more abundant than they actually were, simply because new regulations made them more likely to be retained; at the same time, other year classes, which the new rules required fishermen to release, might be underrepresented in the new surveys, compared to their true abundance in the sea.

Thus, the Technical Committee decided to adopt new selectivity curves for the years 2020 and 2021, for both the ocean and for the Chesapeake Bay. 

Had the Technical Committee not adopted the new selectivity curves, and instead based its 2020 and 2021 calculations on the same selectivity assumed for the period 1996-2019, an action that no one on the Technical Committee supported, the outcome would have been very different.  

Under such selectivity assumption, current regulations would only have had a 20% chance of achieving the spawning stock biomass target by the 2029 deadline; an 8.6% fishing mortality reduction would have been needed to achieve a mere 50% probability of rebuilding success.

While such reduction might appeal to those seeking more conservative striped bass management, it would ignore the effects of Addendum VI, and thus not be based on the best science.  The decision not to make a retrospective adjustment also appears to have been the right one.

To understand the retrospective adjustment issue, one must first understand that estimates of spawning stock biomass and fishing mortality are just that—estimates.  They are based on the best available data.  In the case of striped bass, such data is abundant, but they nonetheless always include some level of uncertainty.  More data makes for better estimates, so the estimates for the terminal year of any stock assessment always incorporate the greatest amount of uncertainty; as additional years of data are added, each year’s estimate grows more precise. 

Even so, every “point estimate” contained in a stock assessment includes a “confidence interval” (CI) that reflects the acknowledged uncertainty.  Thus, in the last striped bass benchmark assessment, we see the statement

“Female [spawning stock biomass]…was estimated at 68.5 metric tons (95% CI 53,520-83,431 mt),”

which tells us that the point estimate used to determine the status of the stock was 68.5 metric tons wasn’t the precise measure of the SSB; instead, there was a 95% probability (“95% CI”) that the SSB fell somewhere between 53,250 and 83,431 metric tons.

When the stock assessment update added four additional years of data to the data used in the benchmark assessment, it revealed that the spawning stock biomass in 2017, the terminal year of the benchmark assessment, was actually somewhat less than the benchmark assessment revealed, and that the fishing mortality rate was higher.

The stock assessment update estimated spawning stock biomass at the end of 2021 to have been 64,805 metric tons, and fishing mortality at the time to have been 0.14; the former is well below the biomass threshold, although showing an increasing trend, while the latter is below the biomass target. 

Based on those numbers (and the new selectivity curves), current regulations will rebuild the stock by 2029.

But those terminal year estimates are subject to some level of uncertainty, and the model used to assess the striped bass stock has a retrospective pattern of overestimating the size of the spawning stock biomass, while underestimating fishing mortality.  If a retrospective adjustment was made, the spawning stock biomass value would have been less than 64.8 million metric tons, and the fishing mortality rate would have exceeded 0.14.  Based on such adjusted figures, a rebuilding plan, and fishing mortality reductions, would have been needed to fully rebuild the stock by 2029.

So why are we likely to see regulations remain unchanged?

Again, uncertainty and the confidence interval come into play.

The Northeast Fisheries Science Center has advised that a retrospective adjustment shouldn’t be made if the adjusted value would fall within a 90% confidence interval from the point estimate (although it might, at first, seem counterintuitive, a 90% confidence interval includes a narrower range of values than a 95% CI, so is a fairly restrictive standard).  The retrospective adjustment to the assessment update’s estimates would have fallen well within the 90% CI for such estimates.

Thus, in conformity with accepted fisheries management standards, no retrospective adjustment was made, and no rebuilding plan is required.

The third contributor to the conclusion that no mortality reduction is needed is also based on retrospective patterns.

The spawning stock biomass threshold is equal to the estimated female spawning stock biomass in 1995; the SSB target is 125% of the threshold; the 1995 estimate is not a fixed value but, like all other estimates of SSB, varies as new data is developed.  

Amendment 6 to the Interstate Fishery Management Plan for Striped Bass, adopted in 2003, set the value at 14,000 metric tons.  Additional data caused that estimate to be revised sharply upward, to 36,881 metric tons, by the time that a stock assessment update was released in 2011.  The SSB threshold was revised upward again, to 57,904 metric tons in the 2013 benchmark stock assessment; five years later, the 2018 benchmark assessment nearly doubled the SSB threshold to 202 million pounds, or about 91,625 metric tons.

The 2022 stock assessment update has finally reversed the two decade long history of increasing SSB thresholds; when data for the years 2018-2021 were added to the model, the SSB threshold dropped slightly, to 85,457, making the tasks of ending overfishing and rebuilding the stock just a little easier to achieve.  (It should be noted that the 2022 stock assessment update slightly reduced the fishing mortality refence points as well; the fishing mortality threshold dropped from 0.22 to 0.20, while the target fell from 0.18 to 0.17.)

Still, the fact that the Technical Committee determined that the current striped bass regulations have a 78.6% probability of rebuilding the stock by 2029 doesn’t mean that successful rebuilding is a foregone conclusion. 

For a start, the 78.6% probability of achieving that goal is based on maintaining the current fishing mortality rate of 0.14.  While that could occur, an influx of fish from the 2015 year class into the 28- to 35-inch slot might well cause coastal recreational harvest to spike.  An abundance of fish from the large 2011, 2014, and 2015 year classes could also attract more anglers into the fishery, and push fishing mortality higher.

In addition, the proposed Draft Addendum 1 to Amendment 7 to the Interstate Fishery Management Plan for Atlantic Striped Bass, if approved, would allow coastal states to transfer uncaught quota to states elsewhere on the coast that were likely to exceed their annual allocations.  Such transfers would have the effect of increasing overall commercial landings, and so overall fishing mortality.

Estimates of spawning stock biomass might be far too high high, and estimates of fishing mortality might be far too low.  The stock may just not respond to management in the way the people expect.

That’s why Maryland biologist Alexi Sharov warned that the stock assessment update should not strike too optimistic a tone; there are always far too many uncertainties in any rebuilding effort to guarantee success, even if managers do their best to make such rebuilding happen.

So what are we to make of the stock assessment update’s advice, assuming such advice remains substantially unchanged from this morning’s meeting?

We should recognize that we have a good chance of rebuilding the stock, but we shouldn’t be too surprised if completing the rebuilding process takes more than seven years.  Although the decision not to make a retrospective adjustment conforms to accepted scientific norms, it still could have the real-world effect of making rebuilding a little more difficult.  

I suspect that quite a few striped bass anglers, who have dedicated substantial time and effort in calling for more conservative management, will not be pleased with the Technical Committee's advice.  I suspect that they will argue that the assessment update's findings do not coincide with what they’re seeing on the water.  I know that may of them believe that the stock is in serious trouble, that is is still declining, and that a collapse is already in view.

Such folks ought to take a deep breath, and take some time to really think about what is happening now.

Throughout the striped bass management process, and the process of managing other species as well, we’ve complained about people who deny the science, and argue that the datga is wrong, because the biologists don’t know what’s happening out on the water, that the scientists are underestimating the size of fish population, that managers are looking for fish in the wrong places, etc.

We’ve repeatedly argued that management measures shouldn’t be based on anecdotal information, or people’s beliefs, but on the best scientific information available, applied by competent and disinterested biologists who are just trying to get fisheries management right.

The stock assessment update is giving us just what we have long asked for.

And if we hoot and holler and complain that it overestimated the size of the SSB, or underestimated the fishing mortality, or that the bass are going to disappear because the scientists didn’t consider the lack of fish off some of our favorite beaches or in some of our favorite rips, we become nothing more than a mirror image of the people we’ve always complained about, who challenge the science not with fact, but with mere anecdote and opinion.  

The only difference would be that the other guys claim that there are more fish in the ocean than the assessments reveal, while we would be claiming that there are less.

The technical folks deserve more respect than that.  And we know better than to make bogus claims.

Thus, I’ll close with something that I wrote just one month ago.

“The Technical Committee is composed of capable and experienced fishery scientists, who have always demonstrated both competence and integrity, along with a desire to produce the best scientific advice possible.  I have confidence that their final recommendation will, in their professional judgment, reflect the current state of the striped bass stock and provide good advice on how to move forward.”

I stand by that statement today.