In recent weeks, we learned more sobering news for New England’s cod population. A paper published in Science detailed how rapidly increasing ocean temperatures are reducing cod’s productivity and impacting – negatively – the long-term rebuilding potential of New England’s iconic groundfish. The paper confirmed both the theoretical predictions associated with climate change and the recent scientific federal, state, and Canadian trawl surveys that reported a record-low number of cod caught in recent months.
To be clear, the Science authors do not conclude that ocean temperature changes associated with climate change have caused the collapse of cod. We have management-approved overfishing of cod to thank for that.
What rising ocean temperatures do seem to be doing, according to the Science paper, is dramatically changing the productivity of the remaining cod stocks. This makes it more difficult for cod to recover from overfishing today than at any other time in history, and perhaps reduces the ultimate recovery potential even if all fishing were halted. Stock assessments conducted without taking these productivity reductions into full account will dramatically overestimate cod populations and, in turn, fishing quotas.
The Science paper is potentially very important, with major implications for fishing limits on cod for decades to come, But stock assessment scientists have warned for years that their recent models were likely overestimating the amount of cod actually in the water – and the corresponding fishing pressure the stock could withstand. Unfortunately, those warnings have fallen on deaf ears at the New England Fishery Management Council.
In fact, the managers at the Council, dominated by fishermen and state fisheries directors with short-term economic agendas, could hardly have done more than they already have to jeopardize Atlantic cod’s future—climate change or not.
Overfishing, a Weakened Gene Pool, and the Loss of Productive Female Fish
As a result of chronic overfishing, New England’s cod population is likely facing what geneticists call a “population bottleneck,” meaning that the diversity of the remaining cod gene pool is now so greatly reduced that the fish that are left are less resilient to environmental stresses like increasing sea temperatures.
Overfishing has also caused the collapse of the age structure of the cod populations by removing almost all of the larger, more reproductive females (also known as the Big, Old, Fat, Fecund Females, or BOFFFS). Scientists have previously warned that losing these old spawners is a problem for cod productivity, but this new research suggests that the potential damage from their elimination may be significantly greater than imagined as a result of poor, climate change–related ecological conditions.
The Science paper hypothesizes that an underlying factor in the productivity decline of cod this past decade was the correlation between extremely warm spikes in ocean temperatures and the drop in zooplankton species that are critical to the survival of larval cod. With fewer zooplankton, fewer cod larvae make it to their first birthday.
The impacts of this zooplankton decline on cod productivity, however, could be exacerbated by the loss of the BOFFFs. Here’s why:
Cod start to spawn at three to four years old, but young females produce significantly fewer and weaker eggs and cod larvae than their older counterparts. Those elder female fish, on the other hand, produce larger, more viable eggs – sometimes exponentially more healthy eggs – over longer periods of time. If the older female cod population had still been plentiful, they might have produced larvae more capable of surviving variations in zooplankton abundance.
Perhaps the continued presence of larger, older, spawning females to the south of New England (where there is no commercial cod fishery) is one of the reasons that the cod fishery in the nearby warm waters off New Jersey is healthier now than it has been in recent history.
The Cod Aren’t Completely Cooked Yet: Four Potential Solutions
Cod have been in trouble since the 1990s, and now climate change is magnifying these troubles. This new reality, however, is not cause for us to throw in the towel. There are actions that our fishery managers can take now that will make a difference.
First, large cod habitat areas have to be closed to fishing – permanently. This is the only way to protect the large females and increase their number. Designating cod refuges such as the Cashes Ledge Closed Area as a marine national monument will remove the temptation for fishery councils – always under pressure to provide access to fish – to reopen them in the future.
Such monuments would also sustain a critical marine laboratory where more of these complex interactions between cod and our changing ocean environment can be studied and understood.
Second, managers need to gain a better understanding of the cod populations south of Cape Cod. While it is well and good to land “monster” female cod on recreational boat trips, those fish may be the key to re-populating Georges Bank. Caution, rather than a free-for-all, is the best course of action until the patterns of movement of those cod populations, as related to ocean temperature increases, are better understood.
Third, as observed in the Science paper, stock assessment models as well as guidance from the Council’s Science and Statistical Committee must start incorporating more ecosystem variables and reflecting a more appropriate level of scientific precaution in the face of the reality of climate change shifts. Enough talk about scientific uncertainty and ecosystem-based fisheries management; action is needed, and science should have the lead in guiding that action.
Finally, the importance of funding data collection and fishery science is evident from this important Science paper, which was supported by private, philanthropic dollars. NOAA should be undertaking this sort of work – but it is not in a position to even provide adequate and timely stock assessments, because limited funding forces the agency to use the existing outdated models.
NOAA’s funding limitations are constraining both collection of the essential field data needed to understand our changing world as well as the analysis of that data into meaningful and appropriate management advice. If Congress can find $33 million to give fishermen for the most recent “groundfish disaster,” it ought to be able to find money to prevent such avoidable disasters in the future.
Ultimately, the Science paper shines some much needed light on our climate change–related fishery issues in New England, but we can’t let it overshadow decades of mismanagement or justify a fatalistic attitude toward cod rebuilding. Steps can and must be taken, and fishery managers are still on the hook for the success or failure of our current and future cod stocks.