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California salmon with rare, late-migration strategy able to survive drier, hotter years

Experts say these late bloomers and their unique migration timing have helped them survive years plagued by drought and warmer ocean temperatures as a result of climate change and could be the key to population diversity moving forward.

(CN) — A new study reveals that some California salmon with an unusual tendency to migrate late in the season have a better shot at surviving drought conditions than their on-time brethren.

As the effects of climate change continue to put the pressure on threatened wildlife and their habitats, experts from across the world have been scrambling to understand which species are best suited to surviving the landscapes of a warmer, drier planet.  

One such group that has earned notable attention from scientists and conservationists alike has been wild salmon, a fish variety that spans across myriad unique species. This is in part because many salmon species undergo an exhaustive migration journey as part of their reproduction cycle, one that takes them across multiple environments in their quest to travel between freshwater and salt water.

This need to journey across climates puts many salmon in a uniquely vulnerable position while Earth continues to grapple with climate change, given that even the smallest changes to water temperatures and habitat availability have the ability to drastically hinder many salmons’ pilgrimage to new waters.

Now, new research in the journal Nature Climate Change shows that some salmon possess a rare interest in putting off their migration until well after their fellow fish have made their journeys — and it looks like it might help them stay alive in an uncertain future.

According to the study published Thursday, Californian Chinook salmon — which were first federally recognized as a threatened species in the late 90s — have a unique migration approach that causes them to depart much later than typical salmon. While many salmon groups tend to migrate around the spring or first winter, Californian Chinook will stay in the freshwater streams they were born in all the way up to the end of summer before making the trek.

But researchers found that this delay actually results in a win for many Californian Chinook.

After using strontium isotopes deposited in the ear bones of spring-run Chinook salmon to help establish a geographic record on the lives of 123 different salmon that made their migration between 2007 and 2018, experts determined that the late-breakers can survive better in hotter- drought-threatened years when compared to the salmon that migrated on time.

Experts say this ability is due to a phenomenon known as phenotypic diversity, an ability that allows some creatures to respond to changes in the environment and adapt in such a way that it allows them to thrive amid new conditions.

Researchers believe that this phenotypic diversity has allowed Californian Chinook salmon to thrive even as their habitats shrink dangerously around them.

“The phenotypic diversity expressed by California Central Valley spring-run Chinook salmon has thus far enabled these populations to persist despite habitat loss and degradation along their migratory corridor, warming temperatures and an increasingly volatile Mediterranean climate,” Thursday’s study states.

These findings also help to illustrate a need for these salmon that humans should be prepared to address. This migration strategy relies on access to cooler rivers, and as climate change continues shrink habitats and man-made dams cut off certain travel routes, ensuring that Chinook salmon have access to the waters they need is going to have to be a priority.

“This study shows how important it will be for the future of this threatened species to reconnect the mosaic of habitats that were once found in the Central Valley and support their various life history strategies, and especially to improve access to cold water refugia,” Flora Cordoleani, Associate Project Scientist at the Southwest Fisheries Science Center, said in an email.

Cordoleani also notes that these goals will need to be addressed even as many Californian areas continue to contend with harsh water shortages. This means that policymakers are going to be given the challenging task of balancing human water needs with that of protecting these threatened salmon species.

“I would like to add that there is growing water insecurity in California in this period of warming, which means that there is also growing human demand for dams and other water projects that could lead to further shrinking of those thermal refugia and increased passage impediments,” Cordoleani said. “So stakeholders will have the difficult task to address this growing human water demand while preventing emblematic Chinook salmon populations from going extinct.”

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