Photo – RICK HACKINEN, BRIGHTFISH CHARTERS
UVic research shows Chinook salmon in the Salish Sea are changing diets as prey shifts with climate change, revealing new ecosystem patterns.
Salish Sea Salmon Diets Are Changing
Chinook salmon in the Salish Sea are not eating the same way they used to. Moreover, new research from the University of Victoria shows their diets are shifting with ocean changes. However, herring still remains their top food.
In addition, salmon now eat anchovy, lantern fish, and small crustaceans. For example, what they eat often depends on where they swim and what is available. Therefore, their diet is more flexible than many thought. Meanwhile, scientists are seeing clear regional differences across the Salish Sea.
Anglers Help Scientists Collect Data
Recreational anglers play a big role in this research. Moreover, they bring salmon stomach samples to researchers through a long-running program. In addition, more than 250 anglers have joined since 2017.
As a result, scientists have studied over 7,000 salmon stomachs. However, this work is not simple. Instead, it involves careful sorting of fish remains to identify prey. For example, anglers drop samples at freezer depots across Vancouver Island. Therefore, the public directly supports the science behind salmon survival.
Seasonal Food Shifts Tell a Bigger Story
Salmon diets change with the seasons. Moreover, winter diets show more variety than summer diets. In addition, shrimp and krill become important in colder months.
For example, salmon near Sooke eat more crustaceans in winter. Meanwhile, lantern fish appear more often in salmon from Campbell River and Victoria. However, in summer, herring dominates most diets. Therefore, salmon adjust quickly to seasonal food changes.
Ocean Features Shape What Salmon Eat
Different parts of the Salish Sea shape what salmon eat. Moreover, ocean currents and river flows influence prey movement. For example, anchovy now appear year-round near Howe Sound.
In addition, sand lance show up more often near Victoria and Sidney. Meanwhile, Strait of Georgia salmon often have the fullest stomachs. However, salmon in the Strait of Juan de Fuca tend to eat less overall. Therefore, geography plays a major role in diet patterns.
Also, ocean features act like natural boundaries. Moreover, these boundaries match changes in fish communities. As a result, scientists can link food webs to water movement and temperature shifts.
Tagging Program Tracks Salmon Journeys
Researchers also track salmon movement using tiny PIT tags. Moreover, these tags help identify fish across long distances. In addition, they work like microchips that store identity data.
For example, a tagged salmon released near Quadra Island can later appear in the Cowichan River. Meanwhile, detectors in rivers pick up the tag automatically. Therefore, scientists can follow survival and migration paths more clearly.
Also, more than 450,000 salmon have been tagged since 2020. Moreover, this work covers 11 watersheds on Vancouver Island. As a result, researchers now understand salmon movement better than ever.
What This Means for the Future
This research helps show how climate change may affect ocean food webs. Moreover, salmon diets act like a signal of ecosystem health. In addition, older studies from the 1920s to 1960s give useful comparisons.
For example, sardines once played a major role in salmon diets but are now rare in B.C. waters. Meanwhile, anchovy and other species are becoming more common. Therefore, the food chain is clearly shifting.
However, scientists continue building long-term records to track these changes. Moreover, this work helps guide conservation decisions in the future. As a result, researchers hope to protect both salmon and the ecosystems they depend on.
