Warmer water, less oxygen hinder Gulf shrimp

Northern shrimp stocks shrinking because of unfavourable environmental conditions

Northern shrimp are a demersal species — living on or near the cold ocean floor — but they are not being spared from warming seas.

The federal Department of Fisheries and Oceans (DFO) held a technical briefing for media recently to describe the latest effects the changing oceans are having on northern shrimp found in the Gulf of St. Lawrence, the southern limit of the species.

The waters of the Gulf of St. Lawrence and the St. Lawrence River estuary form a well-stratified system that has three distinct layers.

Between 2009 and 2022, average water temperatures in the Gulf have risen from 5.2 C to 7.0 C, and that 1.8 C difference is affecting the deepest layer, DFO says.

In addition, those deep waters are seeing decreased concentrations of the oxygen needed for marine life to survive. In some of the deepest reaches of the Gulf, which are 300 to 400 metres deep, the oxygen levels have reached lethal thresholds.

SHRIMP DISPLACED

While the warming ocean has increased lobster habitat, this and the other factors listed have led to northern shrimp being displaced to the more shallow parts of the deepest water layer, DFO says.

It has also delayed maturation and the timing of spawning, resulting in fewer shrimp in the ecosystem.

“Essentially, there has been a contraction,” said Mariejulie Roux, a DFO research scientist. “Northern shrimp distribution used to be quite widespread in the Gulf. … Now, they are increasingly concentrated in smaller areas.”

Predation and concentrated harvesting are also having an impact on northern shrimp. Roux said harvesters did not land their quota of shrimp last year.

UNSURE WHAT 2024 WILL BRING

While there has been a warming trend in recent years, DFO oceanographers have indicated that, in 2023, the temperature did not increase for the first time in several years, Roux said.

“Oceanographers said there had been a slight change in water masses coming into the Gulf,” she explained.

“So, there was some stabilization in 2023, but it was a stable high. So, still not necessarily good news and we will see what 2024 will bring.”

Roux said the outlook for northern shrimp stocks in the estuary and Gulf of St-lawrence will depend on their sensitivity to ongoing environmental changes, predation pressure and fishing pressure.

“Clearly, the environment is increasingly unfavourable for these stocks,” she said.