Mapping the Pacific’s busiest blue corridors could help us save fish populations

(ORDO NEWS) — Large fish stocks on the high seas have declined by at least 90 percent over the past century due to overexploitation.

To bring fish like tuna, swordfish and marlin back from the brink, scientists say we need to protect their migratory superhighways, known as “blue corridors”.

A recent study in the Pacific Ocean mapped the busiest of these underwater transportation routes using the propensity of fish to return to their birthplace.

This behavior is known as philopatrism, or generic homing, and is not unique to salmon.

Other fish species also return to their birthplace to breed, and experts want to use this information to identify areas where fishing should be restricted or banned.

Tracking large fish swimming across vast expanses of the ocean is incredibly difficult, so scientists know little about migration routes on the high seas.

However, if some fish are supposed to return to spawn, then their travels should create an annual loop through certain parts of the ocean.

By comparing data on where most fish are caught and where they spawn, researchers from the University of British Columbia have identified migratory loops for 11 species of fish in the Pacific Ocean.

The 11 species included skipjack, yellowfin tuna, bigeye tuna, albacore, Pacific bluefin tuna, swordfish, common dolphin, striped marlin, black marlin, wahoo and Indo-Pacific sailfish.

The results are only preliminary and based on a few assumptions, but they provide important clues as to where the fish might be swimming at certain times of the year.

When all migration paths are overlaid on the map, the overlay reveals several “high priority” and “very high priority” areas for preservation.

Below is the final map showing which areas of the Pacific should be protected first. The red and orange patches represent regions of the ocean through which all or nearly all of the fish species examined in the study pass.

Mapping the Pacifics busiest blue corridors could help us save fish populations 2

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

“These high-traffic areas, two of which are in the Pacific Northeast and Central and two in the Southwest and Central, should be part of the Blue Corridors – routes where strict fisheries management measures or a partial ban should be applied.

Commercial fishing to increase habitat connectivity and thus allow marine species populations to sustain themselves,” said Daniel Pauley, principal investigator at UBC’s Sea Around Us Research Institute.

Today, there are very few marine reserves in the open ocean. Blue corridors could help extend the protection afforded to coasts right out to the open sea, ensuring that the migration routes of large fish and whales remain relatively undisturbed.

For large pelagic species that roam far and wide, blue corridors are especially important. And the more the better.

“The best scenario for stock conservation and recovery,” the authors write, “would be an even wider and continuous blue corridor extending from 30°N to 40°S and from 160°E to 110°W of the Pacific Ocean.”

A Blue Belt of this size could help restore fish stocks and stimulate fisheries throughout the Pacific.

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