An aerial view of the Fraser River.

The Lower Fraser River offers a range of diverse freshwater habitats to a large volume and variety of salmon populations, making it vital to the survival of B.C.’s native salmon, and so in turn to the Southern Resident killer whales. However, new research released in 2021, revealed that pervasive human impacts to these unique habitats have helped drive down once plentiful and robust salmon populations.

Researchers examined the impacts of “intense development and environmental degradation” on habitats essential to 14 populations of Pacific salmon, including Chinook, in the Lower Fraser ecosystem. They found that only 15% of historic floodplain habitat remains, while over 64% of stream habitat has been rendered inaccessible due to man-made barriers such as dams, floodgates and road culverts.

To reach these staggering conclusions, the researchers studied historical field manuals, together with surveyor maps, vegetation descriptions and other historical records to compare today’s Lower Fraser River landscape with that of the 1850s, and early 1900s. This may be the first ever attempt to accurately assess the extent of salmon habitat lost—or simply made inaccessible—due to human development.

Their assessment led the researchers to conclude that—due to the unique lifecycle of salmon, who must return to their natal rivers to spawn—“loss and alienation of habitat is a major driver of observed salmon declines for some populations.” In fact, loss of floodplain habitat may disproportionately impact Coho and Chinook who rely on this habitat for spawning, and growth in early life.

These researchers concluded that, “Fraser salmon are being impacted by multiple threats in both their freshwater and marine habitats,” and yet, as they noted, fisheries managers have chosen to focus on marine impacts as the primary driver behind salmon decline. As senior study author Dr. Tara Martin concluded, “if salmon are not given sufficient habitat to breed and complete their life cycle, then none of the other conservation management actions we take will matter.”  In other words, the Fraser River salmon won’t just fail to thrive, they will fail to spawn.

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Chinook returning to spawn in the Fraser are a large part of the spring and summer diet of the Southern Residents. Given the significance and breadth of the salmon habitat loss reflected in this research, it is hardly surprising that the whales are increasingly more absent from the Salish Sea as Fraser River spring Chinook declines. Such change is unprecedented, and of great concern is that all west coast rivers have degraded habitat, with coinciding Chinook population declines.

Yet, as these same researchers concluded: “large-scale habitat protection and restoration can no longer be ignored as a key factor in wild salmon recovery efforts.” Fortunately, their research demonstrates how small changes can have large-scale impacts. By assessing habitat through a salmon lens, they are confident that areas of high priority can be identified, where removal of relatively few barriers could restore large portions of Fraser River habitat with the “greatest benefits to salmon recovery”. In other words, the path of least resistance could produce maximum gains for both Chinook and the Southern Resident killer whales, and that’s some good news.