Fishing is a profession often passed down from one generation to the next. Many lobstermen in Maine fish the same bottom their fathers and grandfathers fished, and the same holds true of fishermen father offshore as well. Yet increasingly, anecdotal evidence has suggested that the old faithful fishing spots are no longer quite so reliable.
In northern regions these shifts could lead to conflicts over fishing rights and access to traditional fishing grounds. In the tropics, the problem could be more dire. As our oceans warm, species may not be able to adapt at all, leaving tropical oceans with severely depleted fish stocks and some of the most vulnerable human populations with a distinct shortage of a vital protein source.
Much of this scarcity of native species can be attributed to overfishing, a practice now largely halted in U.S. waters thanks to strict new science-based management tactics implemented as a result of a 2006 reauthorization of the law that governs our fisheries. But increasingly, both scientists and fishermen have been eying climate change as a reason some fish are showing up in new places and the catch fishermen are accustomed to finding have been surprisingly slow to rebuild.
A new study published this week in the journal Nature puts some peer-reviewed punch behind what up until now was a common-sense theory. Most fish have a preference for a certain water temperature range, and because they are mobile creatures, as water warms due to climate change, fish populations are on the move toward the poles. The study found:
Except in the tropics, catch composition in most ecosystems slowly changed to include more warm-water species and fewer cool-water species. In the tropics, the catch followed a similar pattern from 1970 to 1980 and then stabilized, likely because there are no species with high enough temperature preferences to replace those that declined. Statistical models showed that the increase in warm-water species was significantly related to increasing ocean temperatures.
This latest research builds on the authors’ 2009 study that stated:
…climate change may lead to large-scale redistribution of global catch potential, with an average of 30–70% increase in high-latitude regions and a drop of up to 40% in the tropics.
This trend could have dire implications for both fishermen and fish.
As U.S. fishermen are increasingly operating under management systems that set the total amount of fish they can catch based on their historic landings, this kind of habitat shift can lead to complex management conundrums. If a fisherman from Massachusetts is suddenly catching more summer flounder (which prefer warmer water) and less winter flounder (which prefer colder water) but his catch allocation was set based on his history of catching winter flounder, his business will not last.
Meanwhile the New Jersey fisherman’s boat may not be equipped to catch the species that will replace summer flounder in his waters so he will either have to move with the fish into an area where he may not be permitted to fish, or invest in new gear and face the possibility of learning a new fishing method entirely. Neither is an attractive option.
In tropical regions, particularly in less-developed countries, the results could be much worse. Fish is the primary source of protein for more than three billion people on the planet, many of them in less-developed tropical countries. But in their case, the fish that migrate out of their waters won’t be replaced by anything. This is not a question of parsing out a different mix of fish. It will result in a complete loss of a major food source.
And if it’s bad for the people who depend on the fish for protein, it’s worse for the fish themselves. As Daniel Pauly, one of the new study’s authors put it in an interview with NPR on Wednesday, “imagine a reef fish that is driven by temperature into North Carolina or the Delaware coast. That reef fish will not find reefs. It’s like you having to move, but you cannot take your furniture with you, or your house.”
The challenge of rebuilding today’s depleted fish populations is already a herculean one for fishery managers to address. Unfortunately, it now appears they’re going to have add the complexity of tomorrow’s warming and acidifying oceans to the equation.
Michael Conathan, Director of Ocean Policy at the Center for American Progress