GULF OF MAINE COD: REBUILT BY 2033?

 

Gulf of Maine cod have been in trouble for a long time.

The most recent management-track stock assessment, completed in 2021, found the stock to be badly overfished, with biomass at a mere 5% of the target level, which is the biomass needed to achieve maximum sustainable yield.  Depending upon the assumed level of natural mortality, it may or may not be experiencing overfishing.

Compared to a management-track assessment completed two years earlier, the 2021 assessment modestly reduced the target biomass which, again depending on the assumed level of natural mortality, was either lowered from 42,692 metric tons to 39,912 mt, or from 63,867 mt to 60,010 mt; the latest assessment also reduced the corresponding estimates of maximum sustainable yield from either 7,580 mt to 7,171 mt, or from 11,420 mt to 10,873 mt.  In what seems like somewhat better news, the mean number of fish recruited into the population each year increased from either 4,377,000 to 4,677,000 recruits or from 8,464,000 to 9,249,000 recruits, with natural mortality again determining which one is closer to the truth.  

Yet, while the estimates of biomass, MSY, and recruitment vary depending on whether biologists assume a constant M=0.20 or a rate that ramps from M=0.20 to M=0.40, the fishing mortality threshold remains relatively constant, at F=0.173 for the former natural mortality rate, and F=0.175 for the latter.  

Still, despite slightly improved recruitment, any fish stock that can increase tenfold and still be perched right on the biomass threshold that defines an overfished stock is in a very bad place.

Thus, the New England Fishery Management Council’s announcement that it had approved new fishery management measures that had a 70% probability of rebuilding the stock within ten years came as a very big surprise.

Rebuilding the stock to its target level by 2033 will require the stock to increase to twenty times its current size within just ten years.  The New England Council proposes to do that by reducing the fishing mortality rate to 0.104, about 60% of the fishing mortality threshold rate, and keep it there for a decade, at which point the stock will hopefully be rebuilt.

The rebuilding plan was included in Framework Adjustment 65 to the Northeast Multispecies Fishery Management Plan, which was adopted by the New England Council at its December 2022 meeting, and is now awaiting final approval by the National Marine Fisheries Service.  Materials from the December meeting explain,

“The rebuilding plan for Gulf of Maine (GOM) cod developed under Amendment 13 was revised in Framework Adjustment 61 due to inadequate progress.  In an August 13, 2021, [sic] letter from [NMFS’ Greater Atlantic Region Fisheries Office] to [the New England Fishery Management Council], GOM cod was identified as making inadequate progress toward rebuilding following the 2019 stock assessment.  The letter explains that the Council must implement a new rebuilding plan withing two years of the date of notice (i.e., by August 13, 2023), as required by Section 304(e)(3) of [the Magnuson-Stevens Fishery Conservation and Management Act].  Furthermore, the cod rebuilding plan may need to be modified after the 2023 research track [stock assessment] for Atlantic cod is completed…”

The meeting materials state that, if fishing mortality could somehow be reduced to zero, there was a 67% probability that the stock could be rebuilt within seven years; unfortunately, eliminating all fishing mortality is a practical impossibility, as some level of bycatch will always occur, even setting aside the likelihood of some illegal landings by both commercial and recreational fishermen.  But even if fishing mortality was cut by a lesser amount, the stock might still be rebuilt; if the fishing mortality rate could be reduced to just half of the fishing mortality threshold, there is a 52% chance of rebuilding the stock within eight years, while a fishing mortality rate equal to 75% of such threshold has a 58% chance of rebuilding the stock within a decade.

However, such rosy projections require us to ignore that troublesome devil that is inevitably found carousing among the details.  

Earlier, I noted that both the 2019 and the more recent 2021 management-track stock assessments produced two different estimates of target biomass, maximum sustainable yield, and recruitment, which differed substantially depending on whether the assessors assumed a consistent, and relatively low, natural mortality rate of 0.20, or whether they assumed that natural mortality ramped between 0.20 and 0.40.

Framework 65 only has a 70% chance of rebuilding the stock within 10 years if the lower, M=0.20 assumption holds true.  Otherwise, the meeting materials advise,

“Projections examined under the M-ramp, M=0.4 model, which assumes natural mortality remains high, indicates the stock cannot rebuild even when F=0.”

Right now, managers aren’t sure which natural mortality model best reflects reality, so the best that it can do is hope that it is M=0.20, and that rebuilding can be achieved.

At the same time, the meeting materials reveal that uncertainty regarding the natural mortality rate isn’t the only concern.  It also notes that

“this stock has exhibited below average recruitment in recent years, and recruitment may not increase as is assumed in the rebuilding projections,”

and

“Based on experience with many groundfish projections, concerns remain that long term projections tend to be overly optimistic such that future levels of biomass are overestimated, and fishing mortality is underestimated.”

So while, in the largely distant past, I did a fair amount of cod fishing on boats departing various ports in New York and New England, and would love to see the stock rebuild in time for me to put a few more fish on ice before I end up dropping dead, I’m not getting my hopes up.  When I first heard that there was a 70% chance of rebuilding Gulf of Maine cod by 2033, it sounded too good to be true.  Now that I’ve researched the issue a bit, it’s clear that such 70% probability reflects the sort of best-case scenario that usually just paves the road to disappointment.

I also can’t help thinking about Newfoundland’s northern cod stock.

Like the Gulf of Maine cod, the fish off Newfoundland were once incredibly abundant, and supported a very large, thriving fishing industry.  Like the Gulf of Maine cod, the fish off Newfoundland attracted too much attention, from both local vessels, which became more and more sophisticated as time went on, and also from foreign fleets, until such fleets were pushed farther offshore.  And like the Gulf of Maine cod, the Newfoundland cod stock collapsed.

The biomass of Newfoundland cod fell so far that, in 1992, Canada shut down the fishery and put 30,000 fishermen out of work.  It has since allowed what it calls a “stewardship” fishery that has been permitted to land between 9,500 and 13,000 metric tons of cod each year, but such landings are tiny compared to the hundreds of thousands of tons landed in years before the collapse.  Yet, 30 years later, the Newfoundland cod stock has neither been rebuilt nor even achieved substantial growth, and some conservation advocates are saying that landings must be capped at 5,000 metric tons if the stock is to have a realistic chance at recovery.

Conditions affecting the Newfoundland fishery are not the same as those impacting the Gulf of Maine, although both stocks of cod are victims of severe overfishing, and both now face the prospect of significant ocean warming, and its impacts on the ecosystems in which the fish must survive.  Even so, it’s hard to ignore the voice in the back of my head that keeps saying that Gulf of Maine cod are more apt to follow the Newfoundland fish’s fate, rather than to enjoy a speedy recovery.

Yet, there is nothing lost by putting the proposed rebuilding plan in place, and seeing how the Gulf of Maine cod respond.

Maybe they’ll beat the odds, and conform to the best-case scenario.  Even if that doubtless unlikely outcome does not occur, reducing the fishing mortality rate could spur a modest recovery, if not a full rebuilding.  While a fully rebuilt stock is the ideal, and certainly a worthwhile goal, if the Gulf of Maine stock only manages to double or triple its numbers by 2033, and not achieve the 20-fold increase needed to fully rebuild, it will be in a better place than it is in today.

And while that’s not good enough in the long term, it’s far from the worst of all the possible outcomes.