HAVE WE BEEN MANAGING ATLANTIC COD WRONG--FOR DECADES?

The collapse of New England cod stocks, and their stubborn refusal to rebuild, has caused decades of frustration for northeastern fisheries managers.

The reason for the collapse was clear enough.  People were killing too many cod, and the New England Fishery Management Council spent far too much time trying to look like it was seeking solutions, at the same time that it chronically refused to implement annual quotas or any other measure that would meaningfully restrict fishermen’s landings.

Eventually—meaning after Congress passed the Magnuson-Stevens Fishery Conservation and Management Reauthorization Act of2006, which finally forced the New England Council to adopt annual catch limits—real restrictions were placed on cod landings, although there is some speculationthat a lot of cod are still being caught and dumped at sea, so that fishermen stillappear to have available quota, which allows them to continue to fish forother, more abundant species such as haddock and pollock under the terms of the catch share management system that is currently in place.

Despite a decade of quota-based management, neither the Gulf of Maine nor the Georges Bank stock of Atlantic cod has shown significant signs of rebuilding.  An operational stock assessment released early this year determined that, as of the end of 2018,

“the stock status for the Gulf of Maine Atlantic cod (Gadus morhua) stock is overfished and overfishing is occurring…Spawning stock biomass (SSB) in 2018 was estimated to be 3,752 (mt) under the M=0.2 model and 3,838 (mt) under the M-ramp model scenario [describing the models isn’t necessary for the purposes of this essay; readers only need to note that biologists aren’t in agreement on which best reflects the population dynamics of the stock] which is 9% and 6% (respectively) of the biomass target…The 2018 fully selected fishing mortality was estimated to be 0.188 to 0.198 which is 109% and 113% of [the fishing mortality rate that would produce maximum sustainable yield].

To put those figures in context, the spawning stock biomass at the end of 2018 was well below the 6,723 metric ton [M=0.2 model] or 8,009 metric ton [M-ramp model] spawning stock biomass that existed at the end of 2011, but is well above the 1,263/1,809 metric ton SSB that occurred when the stock bottomed out in 2014.  On the plus side, the fishing mortality rate, although still too high, has steadily fallen from 1.504/1.308 in 2011 to something that is finally approaching sustainable levels, while the recruitment of new fish into the population is, depending on the model, at or near an 8-year high.

So all of the news coming out of the Gulf of Maine isn’t dismal, although there is little or nothing that might be considered good.

The status of the Georges Bank stock isn’t so clear, with the operational assessment noting that

“the Georges Bank Atlantic Cod (Gadus morhua) stock status cannot be quantitatively determined due to a lack of biological reference points associated with the PlanBsmooth approach but is recommended to be overfished due to poor stock condition, while recommended overfishing status is unknown…”

By the end of 2018, the biomass appears to have grown slightly larger than it was in 2011, after bottoming out in 2014, while the exploitation rate has generally fallen significantly over the same period.  However, substantial uncertainty still surrounds the assessment.

Now, a new study suggests that such uncertainty, as well as the cod’s frustratingly slow recovery, may result from the fact that fishery managers got the cod’s stock structure all wrong.  

Instead of there being only two cod stocks that need to be managed as distinct units, there may be five separate stocks, all with their own, somewhat different, life histories.  By trying to cram those five distinct stocks into just two management buckets, fishery managers could have seriously prejudiced the health and recovery of cod in the northeast.

The study, titled “An Interdisciplinary Review of Atlantic Cod (Gadus morhua) Stock Structure in the Western North Atlantic Ocean,” was edited by Richard S. McBride of the National Marine Fisheries Service and R. Kent Smedbol of Fisheries and Oceans Canada.  It reflects the work of the Atlantic Cod Stock Structure Working Group, which reviewed existing information relating to Atlantic cod stock structure in the northeast.  In their introduction to the study, those editors note that

“Defining the number of stocks of an exploited species, including stock boundaries and other components of its spatial complexity, is fundamental for efficient monitoring, predictive assessment, and successful management.  For example, estimates of abundance and vital rates assume samples come from a unit stock; a well-mixed, reproductively isolated population without significant immigration or emigration…

“Cod in US waters are overfished and subject to overfishing, and among plausible mechanisms impeding its recovery are concerns that cod’s biological population structure is not properly aligned with the current assessment and management units.”

The study looked at a number of factors that could be used to define stock structure.  

The first was the early life history of the fish:  Where are cod spawned, and where do those spawned cod end up?  It turns out that cod populations in the Gulf of Maine and on Georges Bank depend on local spawning.  However, cod spawned in the Gulf of Maine also make significant contributions to cod populations off Cape Cod and in southern New England, even though those regions are, for the most part, managed as part of the Georges Bank stock; the study suggested that managing those two southern regions as part of the Gulf of Maine stock would better match the spawning and settlement patterns.

Genetic markers were also considered.  There have been a number of genetic studies of cod, intended to define spawning stock structure.  Most were spatially limited, but when the results of multiple genetic studies were analyzed as a whole, patterns began to emerge.  The Working Group study found that, when taken collectively, the genetic studies provided evidence that

“the Gulf of Maine stock is comprised of at least two discrete populations that spawn, sometimes in the same inshore locations in the [western Gulf of Maine], in different seasons (winter and spring); there is some degree of connectivity between the western Gulf of Maine and cod that spawn offshore of Cape Cod and in southern New England; the cod that spawn in Georges Bank are distinct from the remainder of the cod considered in that stock (those that spawn in the waters of the Cape Cod area and southern New England); finer scale differences may also occur among geographically separate populations, e.g., southern New England vs. Gulf of Maine; [and] non-neutral markers drive the patterns of genetic differentiation, suggesting the population structure reflects differential adaptation of populations to local environmental conditions.”

One very comprehensive genetic survey concluded that there were probably four or five genetically distinct stocks, including

“1) spring-spawning western [Gulf of Maine]; 2) winter-spawning cod in western [Gulf of Maine] and fall and winter-spawning cod in the Cape Cod and Nantucket Shoals area, including the western part of the Great South Channel; 3) cod spawning on western and eastern Georges Bank; 4) southern New England waters (coastal areas south of the Cape Cod/Great South Channel area); and 5) potentially the eastern [Gulf of Maine], with the caveat that conclusions could not be reached in the absence of data from spawning cod in this area.”

Once again, the current two-stock model, which links Georges Bank with the other southern regions, is not in accord with scientists’ findings.  The Working Group study observed that

“The five-population genetic groupings put forth in the synthesis model are consistent with aspects of prior hypothesized stock structures and with data from other disciplines, including tagging, natural markers, early life history stages, and what is known about oceanographic currents.”

The study included sections addressing such other disciplines, along with a section that reflected fishermen’s on-the-water experience; in the interests of length, I won’t go into them here, except to note that they tended to confirm the findings described at length above.

The question is, now that such information has been gathered, what should managers do?

The Conservation Law Foundation, an organization that has long advocated for more effective management of northeastern groundfish, and has already petitioned the Secretary of Commerce, asking him to impose much stricter management measures on the cod fishery, has responded to the Working Group’s report by asking the New England Fishery Management Council to request that the Secretary take emergency action

“to protect all known spawning areas of Atlantic cod in the Western Gulf of Maine during the entirety of the spawning seasons.”

In its letter, the Conservation Law Foundation noted that

“The law requires the Council to take all necessary actions to end overfishing and rebuild Atlantic cod using the best scientific information available.  Appropriate consideration of stock structure is one of those actions.  As Dean et. al. (2019) stated when referring to assessment models and the importance of accounting for sub-populations, misrepresenting ‘the aggregate dynamics of the population will yield inaccurate catch advice and lead to misguided management, perpetuating, and amplifying the problem.  In short:  it matters where, when, and which cod are harvested from the population…”

The New England Council is expected to address the Conservation Law Foundation’s letter today.

As someone who first fished for cod in the early 1960s, and was active in the fishery until a collapsing population no longer made it worthwhile, I hope that they act on the request.

But as someone who has watched the New England Council fritter away the cod’s future for decades, I’m also not holding my breath.