Fishermen on a beach

Extreme marine heat events will devastate global fisheries in the coming decades

Extreme marine high temperature events, such as the one that killed more than a billion shellfish off the West Coast last June, will devastate global fisheries over the decades to come, a new UBC study suggests.

William Cheung, Director and Professor Institute for the Oceans and Fisheries – Courtesy UBC

There have been 13 to 14 extreme weather events, lasting for days or months,  since 1981 and the frequency has doubled.   

“The aim of this study is to look at extreme temperature events and how they affect  fish, including shellfish and invertebrates, fisheries and the people who are dependent on them,” said Dr. William Cheung, director of UBC’s Institute for the Oceans and Fisheries and lead author of the paper published in Science Advances on October 1st.

The institute used computer simulations to model climate change and what will probably happen to fisheries if humanity continues to neglect addressing its emissions.  

Millions of fishermen may lose their livelihood in countries like Peru, Indonesia and Bangladesh.

British Columbia’s annual sockeye salmon harvest could decrease more than 50% if a high temperature event occurs in the 2050s. 

Cheung said there definitely will be more marine heat events coming, but scientists cannot be certain when or where they will strike next.

Dr Chris Harley initially estimated that there were a billion die-offs along the West Coast during the heat dome at the end of June. That estimate was based on a calculation of the fatalities among mussels. Harley subsequently emailed Cortes Currents that his figure was too low.

It also does not include remote areas like Cortes Island, where there were high numbers of shellfish fatalities. There were losses among the clams and oysters grown on beaches. Cortes Currents found a large number of dead mussels on the rocks at Smelt Bay. 

Local biologist Deb Cowper suggested up to 85% of the sand dollars in Mansons Lagoon may have perished. 

That number may be higher amidst the more exposed waters at Smelt Bay. There do not appear to be any survivors in a series of 20 photos taken by Cortes Currents. 

Picture 6/20 of the sand dollar losses at Smelt Bay (July 14, 2021). Dr Harley suggested the green ones probably died before the heat dome. The black flecks are fragments of mussel shells from the nearby rocks – Photo by Roy L Hales

(Harley suggested that a metre stick be placed in each photo, to indicate the scale. He also pointed out that the greenish sand dollars probably died sometime prior to the heat wave, as they had been dead long enough to acquire some algal growth.)

Cheung’s study focused on edible fish stocks. 

He stressed the need to start taking actions now. 

While changes could take place relatively quickly in the atmosphere, they would be slow to reach the depths of the ocean.

Cheung added, “For the surface part of the oceans, where lots of the marine life people are depending on are found, the changes can be very quick.  In a decade, it would be fairly responsive to climate actions.” 

He said that there was not that much difference in the high and low emissions models within a decade, they grow more noticeable after that.

 The potential impacts to salmon, for example, could be 15-20% less severe by 2050 in a low emissions scenario. 

Cheung compared addressing humanity’s emissions to stopping a train. You do not wait to reach the station before putting on the brakes. 

Top image credit: Fishermen on a beach Photo by Credit: Cassiano Psomas/Unsplash

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