Earth’s oceans may seem like an expanse of the same water to us, but try telling that to a sea turtle or a whale shark.
To trace the invisible routes that more than 100 migratory marine species regularly take across international lines, scientists in Australia and the US have now created an interactive map that reveals the narrow paths connecting ocean habitats.
Many marine species rely on specific routes to traverse their watery domain. These roads offer seafaring travelers the right conditions, at the right time of year, to guide them through otherwise hostile landscapes.
But we humans have drawn our own lines across these paths, based on our fisheries, shipping routes, and national borders. It’s more obvious to us when nature is fragmented on land; the passageways connecting marine ecosystems are often intangible to us landlubbers.
The new map, named the Migratory Connectivity in the Ocean (MiCO) database, makes it easier for scientists, policymakers, and regular people to see where migratory marine species may be falling through the cracks.
From birds and marine mammals to fish and turtles, the database includes information on 109 species, based on around 30 years of data, and reveals where in the world they’re going to and from – including which species cross into whose national waters.
“The tool connects almost 2,000 crucial habitats and spotlights the importance of cross-boundary cooperation,” says movement ecologist Lily Bentley, from the University of Queensland (UQ) in Australia, who led the development of the database’s models.
All of the species recorded in MiCO have less protection at some point in their life history due to differences in jurisdictions. That means no country is able to fully protect migratory species without help from others.
“A classic example are green turtles that nest in Costa Rica and migrate north through Nicaragua and out to islands in the Caribbean,” marine conservation scientist Daniel Dunn, also from UQ, told ScienceAlert.
“While largely protected in Costa Rica (and nesting in a protected area), it is legal to fish for turtles in Nicaragua and huge numbers are lost off the coast there every year.”
In 2023, a UN report found climate change is having catastrophic effects on migratory species, because temperature changes affect the timing, abundance, range, and survival of key food sources, like krill, which are the foundation species of many marine food webs.
Climate change is also constricting the ranges of many species towards the poles, messing with ocean currents, and overcrowding key breeding and feeding sites.
While the migration paths in MiCO are snapshots in time, the team hopes that eventually, information from different time periods may be used to identify changes in connectivity.
“This is really critical because we know those changes are happening – for instance, the opening of the Northern Passage absolutely changes the permeability of the Arctic to a variety of species (and ships),” Dunn said.
MiCO also reveals gaps in migratory species research. There’s insufficient data on more than two-thirds of marine migratory species, and the team hopes that over the years MiCO will incorporate data on more of these underrepresented species.
“The extensive migratory information revealed within the MiCO system only scratches the surface of the true connectivity of the global oceans,” the team writes.
The process of mapping out existing data also revealed sampling biases that researchers can now address. For instance, seabird data are biased towards polar regions and lack representation in the tropics, despite those regions being among the most species-rich and human-impacted areas.
The map also shows obvious geographic biases reflecting the wealth and distribution of university researchers.
This research is published in Nature Communications, and anyone may explore the MiCO database here.
