Melting ice caps is just one consequence of global warming and has the potential to affect ecosystems all over the world. Habitat loss, sea level rise, and Arctic amplification are just some of the hazardous results of polar melting.

However, glacial retreat may also give way to some opportunities.

Salmon are a type of ray-finned fish of the Salmonidae family. Pacific salmon (Oncorhynchus) can be found in coastal waters all along the west coast of America and as such, support lucrative fisheries which pull in billions of dollars every year.

Salmon are anadromous species; upon birth they migrate to ocean waters and return to fresh water to reproduce. Thus, rivers are an integral component of the salmon life cycle and as is to be expected, changes to river functioning can greatly affect salmon populations.

Close up of a large group of Sockeye salmon (Oncorhynchus nerka) returning to spawn in the lower Adams River, British Columbia, Canada. Picture by Andrew S. Wright / WWF-Canada

Pacific salmon is greatly impacted by climatic variability; abundance fluctuations have been recorded consistently over several decades. Ocean heat waves, low summer water flows, and water temperature increases are all placing severe stress on wild salmon population.

In conjunction with these impacts, warming Arctic and subarctic freshwaters and the associated glacial retreat, may produce thousands of kilometres of habitable space for Pacific salmon and other anadromous species.

In fact, salmon colonisation has already been recorded. A 2011 study, revealed that recent glacial retreat in Glacier Bay, Alaska, has resulted in new streams which have been occupied by pink salmon. Pink salmon abundance grew dramatically in the newly formed habitat; over 5000 adult spawners have matured in the course of 15 years.

Being the economically important species that it is, increases in salmon habitat and populations holds the potential for the creation of new ecosystems and fisheries that have yet been unaffected by man.

However, the true extent of salmon colonisation is difficult to predict. The opening of new streams and rivers not only presents opportunities to aquatic life, but also to mankind. Large-scale resource extraction industries such as mining will doubtless exploit the newly accessible environment. This holds the potential to degrade the newly formed salmon habitat and put a stop to a valuable fishery before it has even begun.

An international team, comprised of researchers from the Simon Fraser University (Canada) and the University of Birmingham, have tasked themselves with uncovering just how much Pacific salmon habitat will be created in response to glacial retreat.

Using several climate change scenarios with varying degrees of glacial retreat, the team explored 46,000 glaciers in the Pacific Mountain ranges of North America in the search for new salmon habitats.

Coast Mountains, north-western British Colombia, Canada. Sourced from Britannica

The criteria for a salmon habitat included relatively low gradient streams (less than 10% incline), ocean connectivity, and the presence of retreating glaciers at the headwaters. The search revealed that 315 glaciers of those assessed met the above criteria.

The team predicts that by 2100, over 6000 kilometres of new streams will be open for Pacific salmon colonisation. Of this, nearly 2000 kilometres are potential nursery habitats, in which spawning and juvenile rearing can take place.

Lead author and spatial analyst Dr Kara Pitman comments:

“We predict that most of the emerging salmon habitat will occur in Alaska and the transboundary region, at the British Columbia‒Alaska border, where large coastal glaciers still exist. The Gulf of Alaska sub-region is predicted to see the most gains—a 27% increase in salmon-accessible habitat by 2100.

“Once conditions stabilise in the newly formed streams, salmon can colonise these areas quite quickly. It’s a common misconception that all salmon return home to the streams they were born in. Most do, but some individuals will stray—migrating into new streams to spawn and, if conditions are favourable, the population can increase rapidly.”

This study is a rare glimpse of positivity in the current climate crisis. However, Dr Pitman remains cautious.

“On one hand, this amount of new salmon habitat will provide local opportunities for some salmon populations. On the other hand, climate change and other human impacts continue to threaten salmon survival—via warming rivers, changes in stream flows, and poor ocean conditions.

“Climate change means we increasingly need to look to the future. We can’t just protect current-day habitat for species but need to consider what habitats they might rely on in the future.”

Written by Lucas King