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Inaugural post: issues facing Puget Sound Chinook salmon

cat(‘Hello, world!\n’)

I’m Iris, and I used to blog over at From Alevin to Adult. An alevin is a newly-hatched salmon and, as you might guess, my current research is fairly salmon-centric. I’m studying factors that influence estuarine and early marine growth of salmon, and how growth links to overall survival.

Salmon are anadromous, meaning that they move between freshwater and saltwater at different stages of their lifecycle and, as such, they depend on a variety of habitats. Furthermore, salmon are often subject to intense size-selective mortality – meaning that a fish’s growth can determine whether or not it survives. Several studies have shown that the time spent and size gained in estuarine and early marine environments affect overall survival for salmon. Growth is largely determined by feeding success, and faster early marine growth has been associated with higher marine survival for salmon.

So, what could influence salmon feeding in these early life stages? Surely what they’re eating might play a role – where is their food, and how much food is there?

crab zoea

Most juvenile salmon eat primarily zooplankton in these early life stages and switch to a fish-based diet as they grow.

Environmental stressors may affect feeding. High temperature and low-oxygen waters can be inhospitable to salmon. This can physiologically affect the fish so that it does not get as much net energy from its prey, or it can prevent the fish from reaching its prey altogether.

Finally, interactions with other fish may have a large effect on feeding. Juvenile salmon are tasty. They are often targeted by larger fish and, to avoid this, they may have to adjust their feeding behavior. Additionally, juvenile salmon aren’t the only small fish out there. Other planktivores (fish that eat zooplankton) might compete with salmon for food resources. Competition among salmon species and other forage fishes has been linked to reduced growth, likely because it limits food availability.

juvenile salmon & Pacific herring

Pacific herring eat many of the same prey types as juvenile salmon.

In Puget Sound, where I work, juvenile Chinook salmon spend a period of months feeding in the estuary before they head out to the ocean. Fish that are bigger after this period are more likely to survive to adulthood. The variability in growth is affected by diet, especially for some key prey taxa, like crab larvae and insects. Feeding rate (a surrogate for food availability) is highly variable, which suggests some amount of food limitation. What my work explores is whether there is potential for competition between salmon species and Pacific herring in offshore environments of Puget Sound. In order for competition to occur, the fish need to be in the same place, at the same time, using the same resources (for example, prey) – and at least one resource must be limiting. I use midwater trawl data and hydroacoustic surveys to determine where the fish are during the summer, I do lots of gut analysis to find out what they are eating, and I use bioenergetics models to quantify feeding rate and consumption demand for each species.

Interesting, right? But why Puget Sound? Why Chinook salmon?

Puget Sound

Puget Sound is the second-largest estuary in the U.S. and plays an important economic, recreational, and ecological role in the Pacific Northwest.

Puget Sound Chinook salmon have shown a pattern of declines in survival since the 1980s. At least half of Puget Sound Chinook populations are influenced by hatcheries, and hatchery Chinook smolt-to-adult survival has been around 1% in recent years. That means that for every 100 young salmon that leave the river, only 1 returns to spawn.

marine survival graph

Figure from Duffy & Beauchamp 2011. Average marine survival of Puget Sound hatchery Chinook salmon. Survival data are from the Regional Mark Information System database (available via rmpc.org) and expressed as percentage survival. The number of groups included in each year is listed at top, and error bars represent +/- 1 standard error.

Puget Sound Chinook salmon are currently listed as threatened under the Endangered Species Act. Chinook salmon are the most dependent of all salmon species on estuarine environments and have a history of extensive use of nearshore and offshore habitats in Puget Sound. The continued poor performance of Chinook populations may reflect estuarine issues in Puget Sound – for example, degraded rearing conditions due to habitat loss, reduced prey abundance, reduced prey quality, pollutant levels, etc. Reducing early marine mortality could be an effective way to stabilize shrinking populations: therefore, assessing factors that affect growth and survival is much needed.

Of course, though my graduate work contributes towards defining and addressing the issues facing Puget Sound Chinook salmon, it is only one piece of the puzzle. When I’m not at school, I am a research assistant for the Salish Sea Marine Survival research initiative. The project is a collaboration between a fairly comprehensive group of US and Canadian scientists, and asks, on a very broad level, what is driving ecosystem-wide salmon declines in Puget Sound and the Strait of Georgia? I love this work because it encourages collaboration and a broad perspective on the issue: our collective research areas range from physical oceanography to marine mammal tracking. I strongly believe that a comprehensive view of the Puget Sound ecosystem is necessary to address the ecological issues it faces, and that a single-species approach is not effective.

So. That’s me. I admit that I have fallen into something of a love affair with salmon, but my overarching research interest is in species interactions – for example, predator-prey dynamics and competition. I’m fascinated by the linkages between groups in an ecosystem, and particularly in how these linkages operate in the context of the entire ecosystem. Most recently, I’ve been ruminating about ecosystem-based management needs and implications, and the role of science and scientific advocacy in the public discourse. I very much look forward to discussing these and other topics with you.


Gratuitious fluff: my cat also has scientific aspirations. Happy early Caturday!




Please also check out my (not very short) reply to denstormer’s excellent comment. And here are a couple more graphs:

From Beamish 2011. Survival trends for Puget Sound and Strait of Georgia Chinook salmon.

From Beamish 2011. Survival trends for Puget Sound and Strait of Georgia Chinook salmon.

Average marine survival for Puget Sound hatchery Chinook stocks. These data are available from the RMIS database (rmpc.org). Note that yearling Chinook are released after a longer hold time and at a larger size.

Average marine survival for Puget Sound hatchery Chinook stocks. These data are available from the RMIS database (rmpc.org). Note that yearling Chinook are released after a longer hold time and at a larger size.

From Mahnken et al. 1998. These illustrate the different survival responses among areas.

From Mahnken et al. 1998. These panels illustrate different survival responses among areas.