September 10, 2023 — It’s been a hot summer. The ocean has been hot too. Marine heat waves, or patches of warmer-than-normal sea surface temperatures, are making headlines because we’ve never seen anything quite like what’s going on in the ocean right now.
These heat waves will cause marine species to disappear in some areas and appear in others. Previous scientific research found that mobile marine species — including tuna, penguins and sharks — will shift toward the poles during heat wave events. But a new study published this week shows a much more complicated story of how mobile animals respond to marine heat waves and the costs and responsibilities this movement will carry for countries receiving these species.
An influx of leatherback turtles into a country’s waters may require shutting down or relocating fisheries to avoid entanglement in fishing gear; an influx of blue whales could necessitate speed reductions for cargo vessels to avoid ships striking the animals. When valuable species such as tunas cross borders, the influx nation may need to increase processing plant capacity, while the outflow nation may need to compensate their fishermen for lost revenue.
Waters around the world are seeing these elevated temperatures. A record-breaking marine heat wave is occurring in the North Atlantic, producing the warmest waters seen in the last 170 years. In the Gulf of Mexico, water temperatures off the coast of Florida have surpassed 100 degrees; off Baja California, an unprecedentedly warm ocean generated the first tropical storm to hit Los Angeles in 84 years. Normally, around 10% of the ocean surface is expected to be in a marine heat wave state, but the latest forecast predicts that up to 50% of the ocean surface will experience marine heat wave conditions by this fall.
For the report, my colleagues and I studied the effect of four major marine heat waves from recent years on 14 mobile marine species in the Northeast Pacific (bounded by Alaska, Hawaii and the West Coast of North America). We found evidence of species shifting their habitats in all four cardinal directions.