Salmon require immense amounts of energy to move up glacial streams to their home rivers for reproduction, but in hotter waters, they could run out and perish before ever getting there.
Glacial discharge moderates streamflow and turbidity provides nutrients and organic carbon to support the biodiversity of freshwater invertebrates and supports aquatic diversity. Yet other factors impact fish community structures at these sites.
How Glaciers Create New Salmon Habitat
Pacific salmon are constantly on the move, traveling between inland streams and ocean water where they live and breeding in freshwater rivers for their adult lives before returning to freshwater streams to spawn again. But climate change has caused irreparable harm to salmon habitat by overheating spawning streams and flooding their eggs with water that washes away eggs and young fish – but new research published in Nature Communications provides hope by showing glacier retreat may offer Pacific salmon some respite from these harsh realities.
Researchers led by Kara Pitman and Jon Moore from Simon Fraser University employed a computer model to digitally “peel back the ice” of 46,000 glaciers across southern British Columbia and south-central Alaska, and study their terrain beneath to identify any future rivers with suitable gradients for salmon to swim upstream. 315 retreating glaciers may provide material for future streams with suitable slopes and flows;
Glacier-fed streams often begin as inhospitable environments for salmon, with cold, murky water and plenty of sediment deposited by glaciers; but over time as their ecosystem adapts and balances itself out, salmon populations may eventually move in to inhabit these new river systems. At Stonefly Creek in Glacier Bay, for instance, pink salmon have colonized an otherwise glacier-less stream since as early as the 1970s!
Pitman and colleagues used different climate change scenarios to simulate glacier retreat, then calculated how many new salmon-accessible streams would emerge by 2100. They divided this figure by the total current-day stream kilometers below 10% or 15% gradient thresholds (which corresponds with stream orders One through Four in this instance) in order to determine their relative increase of new salmon-accessible stream kilometers.
Results revealed that in areas where glaciers are expected to melt, salmon-accessible streams are projected to double, while those where most glaciers remain intact only see slight increases. This information is essential for salmon conservation efforts because salmon use specific spawning streams as part of their habitat, so this research can guide management decisions in landscapes where salmon populations may be at risk due to climate change effects.
How Salmon Move Into New Streams
As glaciers retreat, rivers may become accessible for salmon. According to a modeling study in Nature Communications, however, how productive this habitat will be will vary based on river type and topography; salmon in the Pacific Northwest, for instance, can thrive across a wide range of stream gradients; however, if it slope is too steep then it won’t be suitable for breeding and rearing purposes.
Salmon are fish species known for migrating between rivers and the sea as juveniles, where they feed and develop into adulthood before returning home for reproduction. Although they travel vast distances at sea, salmon have an impressive ability to find their birth rivers with uncanny accuracy using environmental cues; such as scent memories they encounter as they migrate towards adulthood as smolts are stored away in memory banks to help locate where their home stream drains to.
Once reaching their natal streams, salmon use various cues to identify where they want to lay their eggs. A key indicator is sunlight’s position and polarization which affects how it hits their olfactory receptors; when they detect their own stream’s light they stop feeding and begin making preparations for spawning: females dig shallow pits in gravel beds called redds where hundreds or even thousands of eggs will be laid; then waiting for males to fertilize the eggs using tail sweeps before fertilization by males who fertilizes them before fertilizing them by males using tail sweeps using powerful tail sweeps to deposit hundreds or thousands of eggs that await fertilization by males to fertilization by males who sperm or by pollinators wings if needed.
As climate change progresses, new streams will emerge to provide salmon with new homes; however, climate change could create challenges for both salmon and people who rely on these waters. For instance, once glacier-fed streams with high-quality waters could now be mined for minerals. To address such impacts more efficiently and minimize negative consequences caused by climate change on salmon populations, researchers suggest predictive modeling, more responsive escapement targets, and prioritizing process-based river restoration such as floodplain reconnection or channel repair as means for restoration over infrastructure approaches; such measures could help mitigate negative consequences caused by climate change on salmon populations.
How Glaciers Change Salmon Habitat
As glaciers retreat, they carve out valleys that salmon migrate upstream into. This creates new stream habitat that may initially be uninhabitable for fish due to low temperatures and lots of boulders; but over time this stream stabilization happens, water temperatures rise, sediment loads decline, and vegetation forms food webs for salmon to move in and thrive in their new homes.
Simon Fraser University researchers led by Kara Pitman employed a computer model to simulate glacier retreat under moderate climate change scenarios, using 46,000 glaciers in southern British Columbia and south-central Alaska as test cases to “peel back the ice.” They determined how much new salmon habitat may be exposed when bedrock is revealed and new streams flow, discovering that Pacific salmon could gain access to over 6,146 kilometers of new stream habitat by 2100 — almost reaching across the length of the Mississippi River!
Although glacial retreat provides salmon with a new habitat, this study does not negate that climate change still poses threats to their home habitat. Ocean heat waves, low summer stream flows and excessively warm waters have already contributed to population decreases around the globe.
Researchers from UM caution that any new salmon habitat created by glacier retreat may only last temporarily as global warming trends advance since any of these new, pristine habitats that salmon colonize could eventually overheat and disappear as many of their existing homes have.
Jonathan Moore, co-author of a recent study and professor of biological sciences at Simon Fraser University in Vancouver, British Columbia suggests prioritizing predictive modeling and more responsive escapement and fishing targets as part of river restoration strategies; as well as process-based approaches (like floodplain reconnection or natural flow patterns restoration) over infrastructure approaches that may degrade stream habitat in future. Furthermore, Moore urges investments in researching interactions between salmon populations and their ecosystems – an area underfunded by government funding in recent years.
How Glaciers Impact Salmon Populations
Glacier retreat leaves behind a vast network of potential salmon habitat. However, these streams don’t always provide safe havens; their water temperatures could be too cold or the sediment loads too high; but provided ecosystems can remain stable, salmon will quickly colonize these new landscapes.
Researchers studied the potential impact of retreating glaciers on Pacific salmon by modeling their watersheds. They “peeled back” 46,000 glaciers in southern British Columbia and Alaska to observe their bedrock topography; 315 glaciers provided desirable stream habitat (low gradient slope, less than 10% inclines, connected directly to ocean waters with retreating glaciers at their headwaters).
By 2050, they predict, the area accessible to salmon could expand by 27%. The greatest gains will occur in the Gulf of Alaska region where large coastal glaciers still exist, but this won’t just benefit salmon; new mining operations could target this newly exposed terrain too!
Glaciers play a pivotal role in the Pacific salmon life cycle. They provide sustenance by depositing gravel and sand, controlling river channels’ size, altering landscapes they travel through, as well as shaping climate patterns by altering air temperatures, surface runoff rates, and precipitation patterns.
Climate change is leading to glacier melt faster than ever, along with other stressors such as habitat loss and hatchery practices, that threaten Pacific salmon populations’ long-term viability.
The NCGCP study examined how glacier runoff impacts conditions essential to salmon, such as stream temperature, turbidity, and sediment load. To investigate this further, the team compared two segments of Nooksack River in northwest Washington – one heavily glaciated and another unglaciated– in order to gauge how glacier-fed water contributed to heat stress responses during 24 heatwaves over 10 years.
Research indicates that salmon will likely take advantage of the opportunities created by melting glaciers; however, other threats remain. Alongside climate change, habitat is being degraded due to human activities like damming rivers or clearing land for agriculture – which only further puts these endangered creatures in jeopardy.
