Climate change and fish

News from Alaska (and sorry the extract is long, but it's important to understand it is not an overfishing problem per se):

In an unprecedented response to historically low numbers of Pacific cod, the federal cod fishery in the Gulf of Alaska is closing for the 2020 season.

The decision, announced Friday, came as little surprise, but it's the first time the fishery has closed due to concerns over low stock.

"We're on the knife's edge of this over-fished status," North Pacific Fishery Management Council member Nicole Kimball said during talks in Anchorage.

It's not over-fishing to blame for the die-off, but rather, climate change.

Warming ocean temperatures linked to climate change have wreaked havoc on a number of Alaska's fisheries in recent years, decimating stocks and jeopardizing the livelihoods of fishermen and locals alike who rely on the industry.

A stock assessment this fall put Gulf cod populations at a historic low, with "next to no" new eggs, according to Steven Barbeaux, a research biologist with the National Oceanic and Atmospheric Administration, who authored the report. At their current numbers, cod are below the federal threshold that protects them as a food source for endangered steller sea lions. Once below that line, the total allowable catch goes to zero. In other words, the fishery shuts down.

Up until the emergence of a marine heatwave known as "the blob" in 2014, the stock of cod in the Gulf of Alaska was doing well. But the heat wave caused ocean temperatures to rise 4-5 degrees. Young cod started dying off, scientists said.

"A lot of the impact on the population was due to that first heat wave that we haven't recovered from," Barbeaux said during an interview last month. Following the first heat wave, cod numbers crashed by more than half, from 113,830 metric tons in 2014 to 46,080 metric tons in 2017.
The decline was steady from there.