Infamous Northern Cod makes a Comeback while Gulf of Maine Cod Suffers

Two stories on cod in North American have appeared this week. In an article entitled Northern Cod Comeback, George Rose describes the changes in the  abundance of this stock in the last 30+ years. The collapse of the northern cod fishery in Canada and the subsequent moratorium was the poster child for fisheries failure in the 1990s, and the failure to rebuild for almost 20 years a source of much mystery. The collapse was ascribed to a perfect storm of overfishing combined with unfavorable, colder temperatures and the collapse of the main prey species, capelin. But what was once one of the largest fish stocks in the world is coming back, with large spawning aggregations and large old fish reappearing. Water temperatures have warmed and the capelin stock has rebuilt.

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Note that cod and capelin biomass are on a logarithmic scale.

Another paper appeared this week on cod in the Gulf of Maine with quite a different story. This stock is in terrible shape, again due to a combination of overfishing and temperature. However, in this case it is still too warm for the cod. Gulf of Maine cod are at the southern end of cod’s range in the U.S. and Northern cod at the northern end, so warmer years are good for Northern cod, but bad for Gulf of Maine cod.

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The lesson from both of these papers is that rebuilding the stocks to historical levels depends both on fisheries management reducing harvest to sustainable levels and on the return of favorable environmental conditions.

Comment by Steve Cadrin, University of Massachusetts Dartmouth

The signals of northern cod rebuilding are both encouraging and informative.  I think the first lesson is that cod and most other fishes have a great capacity for recovery, and eventually can rebuild from depleted conditions.  The permanent damage from the collapse of northern cod was a socioeconomic collapse of fishing communities, but not an irreversible condition for the resource.  The second lesson is that fishing was not the primary factor of cod productivity.  Ten years after closing the fishery, the stock still had not shown any signs of rebuilding. Recovery didn’t begin until environmental conditions were favorable for cod production.
These lessons are relevant for assessment and management of the Gulf of Maine cod fishery.  Emergency management actions are permanently changing fishing communities to end overfishing as quickly as possible.  The cod resource is not endangered, but the fishing community is. The primary reason for slow recovery and continued overfishing of Gulf of Maine cod has been scientific uncertainty and abrupt changes in our perception of the resource. Fishery managers have followed the scientific recommendations, but in retrospect, those recommendations were misleading. The relative influence of fishing and the environment on northern cod should be considered for the Gulf of Maine cod. Stock assessment models are simplifications of a much more complex reality. Stock assessments typically assume that components of productivity (survival from natural mortality, reproductive rates, growth) are relatively constant. These assumptions may be reasonable for relatively stable ecosystems.  However, considering the extreme climate change experienced in the Gulf of Maine, such assumptions need to be re-considered.  Alternative approaches to science and management are needed to help preserve the fishing communities that rely on Gulf of Maine cod.
Steve Cadrin is a Professor in the Department of Fisheries Oceanography and School for Marine Science & Technology at the University of Massachusetts Dartmouth
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