Katharine Gammon, THE GUARDIAN
New study shows marine heat wave was causing marine life to cluster in an area that made feeding dangerous
When humpback whales began to appear in large numbers off the California coast in 2015 and 2016, people celebrated the comeback of the whales after a near-miss with extinction.
However, the excitement was quickly met with new worries – the whales increasingly got caught up in fishermen’s crab ropes. By 2016, there were more than 50 recorded entanglements that left whales injured or killed. Whales got ropes tangled around their mouths, making it difficult for them to eat. Crab lines cut through tissue and caused infections.
Although whales and fishing had coexisted for decades, this was a new problem. So what was driving it?
A new study published in the journal Nature Communications points at climate breakdown as a factor in the mass entanglements.
When the situation was unfolding in 2015 and 2016, it surprised most people, but not Jarrod Santora, an ecologist at the University of California, Santa Cruz and the lead author of the paper.
Santora was studying the ecosystem effects of the marine heat wave, known as “the blob”, that was happening off the coast of California at the time. Heat waves alter the ocean’s upwelling – the process in which deep, cold, nutrient-rich water rises to the surface. The upwelling in 2015 and 2016 shrunk to just a narrow band along the coast, causing organisms to cluster there. Due to a heatwave-related decline in krill, whales switched to feeding on anchovies in shallower and shallower waters. In addition, the crab fishing season – an $88m industry on the US west coast – had been delayed from November to April, and came to coincide with the whales’ presence.
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