Mapping the Pacific’s Busiest ‘Blue Corridors’ Could Help Us Save Fish Populations

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Big fish on the high seas have declined at least 90% over the past century due to overexploitation.

To pull fish like tuna, swordfish and marlin from the brink, scientists say we need to protect their migration highways known as ‘blue corridors’.

A recent study of the Pacific Ocean mapped the busiest underwater traffic lanes using a fish’s tendency to return to its birthplace.

This behavior is known as philopatryor natal homing, and it’s not just an impulse for salmon.

Other species of fish also return to their birthplace to breed, and experts want to use this information to reveal where we need to limit or ban fishing.

Tracking large fish as they swim across vast expanses of ocean is incredibly difficult, meaning scientists don’t know much about deep-sea migration routes.

If some fish are expected to return to their spawning grounds, their movements should create an annual loop through certain parts of the ocean.

By comparing data on where fish are most caught and where fish spawn, researchers at the University of British Columbia have inferred the migration loops of 11 fish species in the Pacific Ocean.

The 11 species considered were skipjack tuna, yellowfin tuna, bigeye tuna, albacore tuna, Pacific bluefin tuna, swordfish, dolphin fish, striped marlin, black marlin, wahoo and Indo sailfish. -Peaceful.

The results are only tentative and rely on several assumptions, but they provide important clues about where fish might be swimming at certain times of the year.

When all the flyways are overlaid on a map, the overlap reveals several “high priority” and “very high priority” conservation areas.

Below is the final map, showing which areas of the Pacific should be protected first. The red and orange spots represent ocean regions traversed by all or nearly all of the fish species considered in the study.

(Relano and Pauly, Sustainability, 2022)

Above: Habitat use maps of large pelagics in the Pacific, generated by overlaying habitat use maps of the different stocks.

In the busiest blue corridors, the authors recommend banning or reducing industrial fishing for large pelagic species, such as skipjack, yellowfin, striped marlin and swordfish.

“These high-traffic areas, two of which are in the northeast and central sections of the Pacific Ocean and two in the southwest and central sections, should be part of the blue corridors, which are routes where strict measures fisheries management or partial bans on industrial fishing should be applied to allow for increased connectivity of habitats and thus allow populations of marine species to sustain themselves”, said Daniel Pauly, senior researcher at UBC’s research institute, The Sea Around Us.

Today very few marine reserves exist on the high seas. whale migration routes remain relatively calm.

For large pelagic species that roam far away, blue corridors are particularly important. And the bigger, the better.

“[T]”best-case scenario for stock conservation and recovery”, the authors write“would be an even larger, continuous blue corridor extending from 30° N to 40° S and 160° E to 110° W of the Pacific.”

A blue belt of this size could help rebuild fish stocks and boost fishing across the Pacific.

The study was published in Sustainability.

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