Is Climate Change Driving Fish Stocks to Deeper Cooler Waters?

Climate change is driving marine species to migrate towards cooler waters or deeper depths, making it increasingly challenging to manage fisheries that rely on species found in both exclusive economic zones (EEZs) and the high seas.

These shared species, known as straddling stocks, are becoming harder to monitor and regulate as their habitats shift.

What are straddling stocks?

Straddling stocks are fish populations that move between or are distributed across the EEZs of two or more countries and adjacent international waters. As the ocean warms, these migrations are expected to accelerate, complicating how nations share and manage these vital resources.

Fish stocks are generally more prone to overexploitation when they move between jurisdictions, compared to those that remain within a single EEZ.

A study titled “Climate change drives shifts in straddling fish stocks in the world’s ocean,” published in Science Advances on 30 July 2025, found that over 50% of the world’s straddling stocks will move across maritime boundaries between EEZs and the high seas by 2050. Most of these shifts will occur in areas with weaker fisheries management, increasing the risk of overfishing.

These shifting populations include valuable migratory species such as skipjack, yellowfin, and bluefin tuna, as well as non-migratory species such as Japanese flying squid and chub mackerel.

Researchers identified 347 straddling stocks across 67 species and projected that by 2030, at least 37% of these stocks will cross EEZ boundaries, rising to 54% by 2050.

Many of these species are expected to drift into the high seas, where management by multiple Regional Fisheries Management Organisations (RFMOs) will become increasingly complex.

Gainers and losers in the shifting seas

According to the study, 11 of 12 global regions are likely to see fish stocks migrate toward the high seas by 2030, while 10 areas could see new stocks enter their EEZs.

The central Indo-Pacific region, which includes Palau, the Philippines, and the Solomon Islands, is projected to face the most significant losses, with 58% of its straddling stocks expected to move into the high seas.

Similarly, the tropical eastern Pacific, home to Ecuador, Colombia, and Costa Rica, is likely to experience significant declines, albeit on a smaller scale.

Conversely, Arctic and Southern Ocean EEZs, including those of Greenland, Canada, Iceland, and New Zealand, are predicted to gain fish stocks from the high seas. Despite these regional gains, tropical EEZs overall are expected to face a net loss, meaning more fish will migrate away than arrive.

Global implications and the need for cooperation

These shifting distributions will create significant challenges for sustainable fisheries management, increasing the likelihood of international conflicts over access and exploitation rights.

For coastal and island nations that rely heavily on fisheries for food, employment, and national income, the consequences could be severe.

As straddling stocks move into the high seas, small island and developing coastal nations could lose valuable revenue from fishing agreements with foreign countries. This not only threatens economic stability but also heightens the risks of food and nutrition insecurity.

To address these changes, the study’s authors urge coastal states and RFMOs to update their governance frameworks.

This includes assessing the domestic capacity to manage shifting fish stocks and evaluating the economic importance of fisheries across EEZs.

Such assessments are crucial to developing fair, adaptable, and collaborative management strategies that ensure long-term sustainability in a rapidly changing ocean.