National Fisherman’s Melissa Woods has a straightforward, on-the-ground (or rather, on-the-sea) perspective on the complex interactions between overfishing and ocean acidification caused by the ocean absorbing increasing amounts of carbon dioxide:
Greater amounts of CO2 have created an imbalance in the ocean: more acid and less limestone, which is a critical building block for coral reefs and shellfish.
How bad is more acid? If the trend continues, increased acid in the oceans could cause flatlining of shellfish species in some areas, especially in colder waters like those in the Gulf of Maine and Alaska. The acid levels could also critically damage reefs and petite pteropods —part of the foundation of the ocean food chain. These events could happen in our lifetime.
Right now, Maine has its own imbalance problem. In 2010, Maine enjoyed a record-breaking lobster harvest, and currently shellfish account for 90 percent of Maine’s wild harvested species.
That’s not exactly bad news, but acidic waters are bad for shellfish. They need limestone for their shells (the amount a lobster has is the difference between a shedder and a hardshell lobster). As scary as this is to think about, Steneck also said the lobster’s hyper-abundance combined with acidification may be putting them at a greater risk for a shell disease similar to the one that hit Long Island Sound’s lobsters in 1998.
Just one quick point to add here: how ocean acidification will impact lobster shell growth, specifically, is still a bit of a grey area. But acidification isn’t the only possible climate-change-related culprit in the dire condition of lobsters in Long Island Sound, and more generally, south of Cape Cod. Water temperatures have risen 2-4ºF in the past fifty years, putting lobsters in the region at the edge of their comfort zone and impeding the recovery of historically overfished populations. Water temperatures in the Gulf of Maine haven’t reached this critical point yet, and some scientists say that could explain why lobsters there have rebounded since stricter harvest limits went into effect. But back to Woods’ story:
Part of the reason lobsters may be doing so well is that many of their predators, such as cod, are scarce. Steneck said groundfish are not as directly impacted by acidification. His point? Getting their stock back up to healthy levels may ultimately prove to be a lifesaver for Maine’s fishing industry.
Overfishing and climate change are distinct problems, but together they deliver a potentially deadly one-two punch for commercially exploited fish (and lobster) populations. They also present similar challenges for fishermen, namely fewer and smaller fish. And while measures aimed at curbing overfishing can’t directly reduce the impacts of climate change, they can help put both fish and fishermen in better positions to weather the challenges ahead.
Heather Goldstone, Climatide, 13 April 2011. Article.
Ries et al. (2009) showed that growing lobsters add shell at ever increasing rates in waters equilibrated with 400, 600, 900, and even up and including 2,850 ppm CO2, in a two month long experiment. Aragonite saturation, of course, was substantially lessened as CO2 increased. Water temperature was about 25 degrees C. It is hard to see how increasing CO2 will harm lobsters by decreasing pH levels.
The authors are certainly correct that overfishing has dramatically reduced many fish species in New England and Canada, most notably cod. Fishing was banned on the Grand Banks off Nova Scotia in 1991, when cod were finally fished out (with fishermen denying there was any trouble, against the advice of fisheries scientists, until it was too late). 20 years later, in 2011, they haven’t come back. That is pretty catastrophic. It took about 500 years of cod fishing off the NE coasts of the US and Canada to get to this point, but it doesn’t look like we will recover, at least for cod.
These two paragraphs suggest to me that overfishing is the most catastrophic issue currently before us. There is far more to say, but I won’t write an essay here, just leave this comparison. Yes, it is far more complex, but to address the complexities would require that essay….