A new study on the Pacific Ocean has spotted four busiest areas that should be regarded as high priority areas if conservation measures focused on large pelagic fishes such as tuna, blue marlin and swordfish are to be successful.

According to United Nations Conference on Trade and Development(UNCTAD), nearly 90% of the world’s marine fish population is now overexploited or depleted. Excessive Fishing is one of the main drivers of declines in marine fish populations. Fishing is not that bad for the ocean, but catching fish faster than the stocks can replenish is very bad, this is called overfishing.



Scientists strongly suggest that we must protect the migration superhighways of fish such as swordfish, tuna, and marlin known as “Blue Corridors’ to pull fish back from the verge of extinction.

Recent research on the Pacific Ocean has pinpointed the high-traffic areas using a fish’s tendency to return to its birthplace. The tendency of an organism to stay in or habitually return to a particular area to breed is called Philopatry or Natal Philopatry.


Not only salmon have this notion. But other fish species also tend to return to their birth location to reproduce, and researchers want to use that information to decide where we need to limit overfishing and where we need to stop fishing.

“We applied the concept of philopatry to the movements extracted from tagging studies of species such as the near-threatened Pacific bluefin tuna and the heavily-fished yellowfin tuna, and we also combined this information with the links between populations inferred from genetic studies. This allowed us to identify tentative annual migration cycles,” said Veronica Relano, a doctoral candidate with the Sea Around Us and lead author of the study.

Fish Blue Corridors
A school of Jack fish in the waters off the coast of Vanua Levu, Fiji.

“The interesting thing is that when we compared our proposed migration routes and the mapped catch data from 1950 to 2016 available on the Sea Around Us website, we found many coincidences. Clearly, the accuracy of these routes is reinforced by considering philopatry, although they are still tentative,” she said.

Scientists don’t know much about the migratory routes on the high seas. Because tracking large fish as they swim through the ocean and mapping their migratory routes is very difficult. If some fish are assumed to return to their home, then their travels should create an annual loop through certain parts of the ocean, according to Science Alert.


Scientists at the University of British Columbia have theorized and inferred the migration loops of 11 fish species in the Pacific Ocean by analyzing and comparing data on where fish are caught most and where fish spawn.

These 11 species are skipjack, yellowfin, bigeye tuna, albacore, pacific bluefin tuna, swordfish, common dolphinfish, striped marlin, black marlin, wahoo, and Indo-Pacific sailfish.


Even though the results and conclusion are not certain and are based on several assumptions and calculations, they gave valuable clues about where those 11 fish species might be swimming at certain times of the year.

All the migration pathways are superimposed on a map, the migration pathways reveal several “high priority” and “very high priority” areas for conservation.

The final map is shown below, the map shows which areas of the Pacific should receive protection first. The red and orange spots represent ocean regions traversed by all or nearly all of the fish species considered in the study.

Above: Habitat use maps for large pelagic species in the Pacific, generated by superposing the habitat use maps of the different stocks.

In the high-traffic blue corridors, researchers recommend banning or limiting industrial fishing of large pelagic species, like skipjack tuna, yellowfin, striped marlin, and swordfish.

The principal investigator at the UBC’s research institute, the Sea Around Us, Daniel Pauly says: “Those high-traffic areas, two of which are in northeastern and central sections of the Pacific Ocean and two in the southwestern and central sections, should become parts of blue corridors, which are routes where strict fisheries management measures or partial bans of industrial fishing

ought to be enforced to allow for increased connectivity of habitats and thus allow populations of marine species to maintain themselves.”

“But before setting up any protected area to support the rebuilding of diminished fish populations, it is important to consider the entire body of knowledge available on the migrations and movements of different species. This is what we set out to do with this study. Our findings suggest in which areas such efforts would be more effective, but as stated in our title, the closed migration cycles we propose are tentative, and thus it would be nice if other researchers set out to test their validity,” he said.

Today, there are only a few marine reserves in the open ocean. Blue corridors will definitely help extend the protection bestowed on coasts right out into the high seas, guaranteeing both large fish and whale migration routes remain undisturbed.

“The best-case scenario for conserving and rebuilding stocks,” according to the authors, “would be an even larger and continuous blue corridor extending from 30° N to 40° S and from 160° E to 110° W of the Pacific.”

A blue belt of that size could help rebuild the fish population and boost fisheries throughout the Pacific.


Source: Science Alert


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