Mapping the fish highways we should protect

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Large Pacific fish return to their own hatching sites when they produce offspring. A new map of their migration routes could mean better protection for them.

Invisible highways crisscross the Pacific: the migration routes of tuna, marlin and other big fish. So far, science has not been able to map these “blue corridors”, but new to research could have mapped them, creating better marine sanctuaries.

Understanding the migration cycles of large Pacific fish is important for commercial and artisanal fisheries, indigenous cultures and marine conservation. Traditionally, scientists have used tagging, satellite tracking and examining genetic links between populations to map migration routes, but this has produced an incomplete understanding of where fish go.

Large Pacific species tend to return to the places where they were born (their natal sites) when producing offspring. Researchers in a recent study therefore took a deductive leap: fish migrations must involve a loop that completes an annual cycle.

Focusing on 11 species with high capture ratessuch as skipjack tuna and striped marlin, researchers have proposed migration routes based on traditional research results and the tendency of Pacific fish to return to their natal sites.

The researchers’ intuition was correct: when they compared their proposed routes with a map showing reconstructed catch data from 1950 to 2016, similarities emerged. The catch data showed where the fish were caught, which matches the researchers’ inference of where the fish would be based on previous research findings and the idea that the fish would return to their natal sites.

The new map below shows the areas of the Pacific used as habitat by the 11 species and highlights areas of high and very high priority for conservation based on the number of species present.

“Very high priority” areas are home to at least nine of the species studied.

In the blue corridors, industrial fishing of large species would ideally be prohibited or reduced, rebuilding stocks and boosting fishing. The recommended blue corridors would cover at least the “very high priority areas” for conservation (in red on the map) and even better the “high priority areas” (in orange on the map) as well.

The best case scenario consists of two large bands in the North Pacific and the South Pacific. In the North Pacific, a protected Blue Corridor would run from Baja California to the Federated States of Micronesia all the way down and along the equator. The South Pacific, a blue corridor, would run roughly from the Pitcairn Islands east of Australia, then to and along the equator.

Blue corridors may change over time in response to climate change, but they could be managed with the same principles drive the most effective marine protected areas.

International Cooperation and development efforts have done much to protect marine resources. But national and commercial interests (shipping routes, fishing and military operations, deep-sea mining plans, etc.) create complex challenges for ocean management.

Polynesians and other Pacific Islanders have a long history of resilience to environmental variations and unpredictability because of their traditional fishing methods and the management of their environment. Commercial activities and climate change are now threatening this resilience, leaving Pacific communities vulnerable to food insecurity.

Agreements within blue corridors may include stricter regulations or partial bans on industrial fishing, while artisanal and subsistence fishing could be encouraged in the 12 nautical mile territorial seas around the islands. Many remote areas of the Pacific are not well studied, so marine resource management will benefit from more research into historically and culturally grounded conservation efforts.

The migration routes proposed by the researchers suggest possible areas for effective conservation of large Pacific fish. Their findings are a way to start a conversation about large-scale conservation of marine ecosystems – and in the future, the conversation would ideally also be a platform for Pacific peoples to share their local and traditional knowledge. Strengthened governance and cooperation will support the recovery of tuna, marlin and other large Pacific species – all essential to the underwater world and the vital resources on which so many people depend.

The author received funding from PEW Charitable Trusts.

This article has been republished to align with Australia’s State of the Environment Report. It was first published on June 6, 2022.

Originally published under Creative Commons by 360info™.

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