Study finds fish surprisingly resistant to marine heatwaves

Subject: Geography

Section: Physical geography

Context:

A new study has found that fish are surprisingly resistant to heatwaves in the ocean.

About the study:

Researchers in Canada, Europe and the United States collaborated on the study, titled Marine heatwaves are not a dominant driver of change in demersal fishes.
The study relied on data from long-term scientific trawl surveys of continental shelf ecosystems in North America and Europe conducted between 1993 and 2019.
- Trawl surveys are conducted by towing a net above the seafloor to assess the abundance of species at the ocean’s bottom.
During the survey period, 248 marine heatwaves with extreme sea bottom temperatures were included in the analysis.

Blob:

The Blob was a large mass of relatively warm water in the Pacific Ocean off the coast of North America.
The Blob is caused by a combination of warmer air temperatures (that warms the ocean’s surface), changes in the patterns of wind speed, direction and duration (wind helps mix the ocean and by bringing cool water from depth) and the persistent mass of warmer water along the equator known as ENSO.
- This very warm mass of water is unusual, an anomaly.
- Nothing like it has been seen in the climate record since climatologists have been recording data in this region.
- It is unprecedented in its magnitude (how warm and widespread) and its duration (to last multiple years).

Impact of blob on marine ecosystem:

The scientists looked at the infamous “Blob” that hit the British Columbia coast from 2014 to 2016.
The researchers studied how it affected populations of demersal fish or groundfish, which include some of the world’s largest fisheries like Alaskan pollock and Atlantic cod.
They found no evidence that marine heatwaves have a significant impact on regional fish communities.
While the Blob resulted in a 22 per cent loss of groundfish biomass in the Gulf of Alaska, a 2012 marine heatwave resulted in a 70 per cent biomass gain in the Northwest Atlantic.
The scientists also considered whether marine heatwaves were causing changes in the composition of fish communities, looking for losses of species associated with cold water and an increase in species associated with warm water (known as “tropicalisation”).
They found no consistent signature for such losses caused by marine heatwaves.

Marine heatwaves can lead to: