A Klamath River salmon.
A Klamath River salmon.

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Efforts to restore salmon habitat and rebuild healthy, wild salmon populations in much of the Pacific Northwest have perhaps never been stronger. Dams are coming down, government agencies are reducing stocking efforts and their damaging effects on wild fish populations and researchers are learning more each day about what steps are required to bring back the once vibrant salmon populations of Pacific northwest states like California, Oregon and Washington. Unfortunately, the results of a recent study published in the journal Progress in Oceanography suggest that these efforts may be fighting a losing battle, thanks to the effects of climate change. The results of the study identify waters off the coasts of states like California and Oregon as likely hot spots for local extinctions, as populations of sensitive coldwater fish species -- including steelhead and all five Pacific salmon species -- flee northward to avoid warming ocean waters.

According to the study, anthropogenic climate change is causing changes in ocean conditions that are much more rapid than previously known natural changes. These include physical changes such as those to water temperatures and ocean currents, as well as chemical changes in acidity and oxygen content. These have led to changes in spatial distribution of many marine species and to a lesser degree biological changes such as effects on physiologies and phenologies.

Shifts of species northward have been one of the most commonly observed changes, notes the study, "given that the physiology, reproduction, and dispersal of marine species are strongly responsive to temperature and ocean current patterns." The study predicts changes in species distribution by 2050, when it projects that many species now distributed over more southerly ranges will have concentrated in northern waters such as the Bering Sea and the Gulf of Alaska. According to the study's results, distribution of the species included in the study are projected to shift by an average of 30 km per decade.

Marine Species Redistribution Due to Climate Change by 2050
Predicted changes in species assemblages in each 30′ × 30′ cell by 2050 relative to 2005 represented by (a) rate of species invasion and (b) rate of local extinction.

For salmon and steelhead, coldwater species that are more sensitive to temperature changes than their warmwater brethren, this could mean changes of range of upwards of 100 km. When combined with changes in ranges of species that salmon and steelhead prey upon, invasions by warmwater species and the tendency of coldwater species to avoid living at the edges of their preferred temperatures ranges -- these alterations have the potential to translate into the absence of these native fish in areas like Oregon and California sometime during this century.

The report notes that ocean temperature changes of almost a half a degree celsius have been observed in parts of the study region since 1980 and are expected to increase another 1.0–1.5 °C by 2050 (relative to 2000). These changes are expected to have what the study calls "large impacts" on species distribution. The results note clearly that, due to the complex nature of climate and ocean modeling and the number of biological factors at play, the exact effects are "poorly understood," but stresses that the general picture of things to come is clear.

The results also noted that "the projected changes in species assemblages may have large ecological and socio-economic implications through mismatches of co-evolved species, unexpected trophic effects, and shifts of fishing grounds."

Comments

Kudos to Hatch Magazine, and Ben Kryzinski, for such a timely and important story. If you love to fish for salmon and steelhead - or for trout - then you need to understand that climate change is the single biggest threat to our fly fishing.

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