Pershing et al. (2015) analyzed a lot data from 1982-2013 about the Gulf of Maine temperatures, cod population metrics, and global warming indices. Global warming has hit the Gulf of Maine harder than anywhere else on the planet, with temperatures rising much faster than the rest of the global ocean during the last decade (about 0.23 Cº per YEAR). As a direct consequence, the cod population has declined very rapidly in the last two decades: “The most recent assessment found that the spawning biomass in this stock is now less than 3,000 mt, only 4% of the spawning stock biomass that gives the maximum sustainable yield” (p. 2)., which means, to my non-marine biologist understanding, that 96% of the little fishes required to make a sustainable pool for fishing are dead.
The authors go further and analyze predator behavior, zooplankton availability (which has declined due to… you are correct, that pesky global warming again) coupled with the recent heat waves and they say that, despite the horribly rapid decline in the population, the cod would have bounced back if it wasn’t for overfishing. That’s right, folks! Is not enough that global warming (which is also man-made, the nay-sayers are deluded, period) has jeopardized this species, but we made sure is on the brink of extinction by overfishing it. The quotas set for the fishing industry failed to take into the account the global warming effect of the population, setting fishing quotas for a steady-state system, which obviously the Gulf of Maine is not.
You may say, “All righty, then. Let’s fish some less cod until it bounces back. Some major fisheries will go bankrupt, but, hey, we’re saving the fishes so we can eat them later. Easy-peasy”. Not so fast. The gravity of the situation is further accentuated by the very doom and gloom predictions of a basic population dynamics model that the authors publish in the form of Fig. 3 of the paper. The cod population may bounce back, if we stop the fishing now COMPLETELY. Not a little bit, not a few here and there, not the slow and the weak, but ALL fishing needs to stop now if we want to rebuild the cod stock population. And you don’t get to say “damn the cod, I don’t eat it anyway’, because you don’t know what else might be driven to extinction by the disappearance of the cod.
I am not exaggerating here with metaphors. Read the paper and take a look at the scientists’ simulations and predictions yourselves.
Reference: Pershing AJ, Alexander MA, Hernandez CM, Kerr LA, Le Bris A, Mills KE, Nye JA, Record NR, Scannell HA, Scott JD, Sherwood GD, & Thomas AC (Epub 29 October 2015). Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery. Science, DOI: 10.1126/science.aac9819. Article | FREE FULLTEXT PDF
By Neuronicus, 30 October 2015