Rising Water Temperatures in Long Island Sound Brings a Change in Fish

Water temperatures are rising in the Long Island Sound, and bringing a change in the fish population, a new report finds.

The findings were published last week by the Connecticut Department of Energy and Environmental Protection, which has tracked shifts in fish stocks in the Sound due to changes in water temperature for nearly a quarter century. 

Penny Howell, a fisheries biologist with the department and one of the authors of the study, said average temperatures have increased one degree centigrade over the last decade. The change has had a big impact on the fish, who require certain temperatures in order to live and spawn. In addition, those warmer temperatures are lasting longer.

"When the temperature goes up," she said, the fish "have certain thresholds where they go into thermal stress, and those thresholds are being exceeded many continuous days for a longer period of time."

She says climate warming, seasonal rainfall and salinity levels are contributing factors to the increase in temperature.

As the temperature has increased, cold-water species, like winter flounder and the American lobster, have moved farther north, while warmer-water fish have come in in increasing numbers. One of those moving in, Howell says, is the moonfish.

"It actually looks like a huge silver dollar. It's very silvery, very bright, and small and flattened,” she said. “They used to be a novelty and now they're among the thirty most common species that we have in the sound."

Howell says that diversity of species remains high and may be actually increasing, but the rapid rate of the change concerns biologists.

If you have ever wondered how, exactly, scientist count fish, there is a slide show available on the department's website.