No comment on the conspiracy theory (Warmer waters ...):
In the vast gulf that arcs from Massachusetts’s shores to Canada’s Bay of Fundy, cod was once king. It paid for fishermen’s boats, fed their families and put their children through college. In one halcyon year in the mid-1980s, the codfish catch reached 25,000 tons.
Today, the cod population has collapsed. Last month, regulators effectively banned fishing for six months while they pondered what to do, and next year, fishermen will be allowed to catch just a quarter of what they could before the ban.
But a fix may not be easy. The Gulf of Maine’s waters are warming — faster than almost any ocean waters on earth, scientists say — and fish are voting with their fins for cooler places to live. That is upending an ecosystem and the fishing industry that depends on it. ...
Regulators this month canceled the Maine shrimp catch for the second straight year, in no small part because shrimp are fleeing for colder climes. Maine lobsters are booming, but even so, the most productive lobster fishery has shifted as much as 50 miles up the coast in the last 40 years. Black sea bass, southerly fish seldom seen here before, have become so common that this year, Maine officials moved to regulate their catch. Blue crab, a signature species in Maryland’s Chesapeake Bay, are turning up off Portland.
In decades past, the gulf had warmed on average by about one degree every 21 years. In the last decade, the average has been one degree every two years. ...
A warmer ocean is not merely a matter of comfort or discomfort for creatures that dwell there. Scientists suspect that some species struggle to spawn when the temperature fluctuates. Others may spawn at the wrong time when food is scarce. Freshwater from melting arctic glaciers may be altering levels of minerals crucial to plankton, the base of the gulf’s food chain.
There is a human toll as well. Cod-fishing restrictions have ravaged, at least temporarily, the community of day boats — the ones owned by small-business fishermen, with smaller boats and incomes than corporate trawler fleets — that defined New England for centuries. ...
But many other fishermen do not blame climate change. They blame the regulators, calling the moratorium cruel and needless, because they say their latest cod catches are actually better than in recent years. More than a few talk of a conspiracy between scientists and environmentalists to manufacture a fishing crisis that will justify their jobs.
Scientists say the truth is more prosaic: Although the gulf is generally warming — 2012 was the hottest year on record — the last year was cooler, and kinder to cod. Moreover, the gulf’s remaining cod have congregated in deeper, colder waters in southern Maine and Massachusetts, where their abundance masks their scarcity elsewhere. ...
That said, much about warming’s effect on the gulf remains unclear. Years of overfishing have winnowed some fish populations, muddling efforts to measure climate change’s impact. Fishermen, scientists and regulators often disagree over whether the current changes are temporary or the new normal.
And in fact, the latest warming is not unprecedented. Weather records document a steady, if slow warming of the region’s waters since the 1850s, and a 50- to-70-year climatic cycle set off unusual ocean warming in the 1950s. A similar cycle is believed to be heating up the northwest Atlantic today.
But scientists say those cyclical effects are now being turbocharged by human-caused climate change. The gulf has been at least two degrees warmer than its historical 50-degree average in each of the last five years. In 2012, it measured four degrees higher, according to the National Oceanic and Atmospheric Administration. If that is a clear win for sea bass, and a loss for cod, the consequences for some species are not so easily tallied.
I've worked on two climate change and (recreational) fishing studies. One focused on sea level rise and shore fishing and, the most recent, temperature and precipitation on fishing days. Neither have considered changes in stock ranges due to water temperature changes. I'm not quite sure how this would be done in a simple-minded model (i.e., one that isn't funded at the interdisciplinary level).