The Diet of Adult Chinook and Coho Salmon
Driven by Citizen Science
Keystone Species
Chinook and coho are two of five Pacific salmon species identified as keystone species in the Pacific Northwest¹. In particular, Chinook and coho salmon play a key role being a source of nutrients for a variety of species including other fish, orcas, birds of prey, seals, and trees on the banks of spawning rivers. As such, the health of salmon populations are key to the overall ecological health of the Salish Sea.
Juvenile Chinook salmon (photo by Eiko Jones)
Billie Johnson, top and Alex Chartrand Jr. show off some big salmon from Wuikinuxv on the Central Coast (photo by Gloria Walkus Brotichie)
Salmon are also vital to many indigenous communities². The Coast Salish people have deep-rooted cultural ties with salmon, often presenting them in works of art and utilizing them as a key source of nutrients in their diet. Consequently, as salmon populations decline, there will be significant impacts to indigenous communities whose traditional knowledge has taught co-existence with salmon for centuries. The conservation of salmon is therefore a top priority for the protection of both the people and the ecosystems of the Pacific Ocean.
While juvenile salmon diets have been the subject of extensive research, recent data on adult salmon diets in B.C. are sparse. A key component in the conservation of Chinook and coho salmon is understanding their place in the contemporary marine food web. By understanding the regional and seasonal changes in adult salmon diet year by year, we can begin to understand factors limiting growth and survival of these keystone species. In addition, monitoring of salmon diets provides a novel method of monitoring ecosystem scale changes.
Short Term Goals of the Adult Salmon Diet Program
- Characterize current adult Chinook and Coho diets.
- Discern regional and seasonal differences in diets within the Salish Sea.
- Obtain samples and data on forage fish to facilitate cooperative research with other programs and institutions.
Long Term Goals of the Adult Salmon Diet Program
- Develop ecosystem monitoring tools/programs through representative (widespread) sampling of adult Chinook and coho diets.
- Publicly share the collected data through the Strait of Georgia Data Centre , a public archive of marine data in and around the Strait of Georgia.
- Develop and maintain a citizen science program with a focus on an improved working relationship and two-way exchange of information between fishery scientists and fishers. Ultimately, leading to increased engagement in public ecosystem monitoring.
The Citizen Science Initiative
To obtain stomach samples for study, the Adult Salmon Diet Program relies on recreational anglers. When recreational anglers land a Chinook or coho salmon they remove the stomach, esophagus, and intestine. These parts are traditionally composted, or used as bait. However, instead, participating anglers can submit these parts for the Adult Salmon Diet Program to analyze.
More information on getting involved will be provided at the bottom of the story map.
Steps for stomach sampling
Catch an adult Chinook or coho salmon
Step 1
Record the species, date, location, length, and more
Step 2
Remove the stomach, esophagus, and intestine
Step 3
Drop off the samples at a local depot or contact the program to arrange pickup
Step 4
Identification of stomach contents by the lab
Step 5
"We're collecting a really unique dataset on what salmon are eating in B.C. and trying to understand the dynamics of the forage fish they depend on" - Will Duguid, University of Victoria, 2020
Primary Components of Adult Chinook and Coho Diet
Analysis by the Adult Salmon Diet Program has revealed that Chinook and coho salmon consume a large variety of prey. Below are three of the most prevalent forage fish in the diet of Chinook and coho salmon.
Pacific Herring
- Most important prey item for Chinook and coho salmon.
- Rely on eelgrass as critical spawning habitat³.
- Most abundant fish in B.C. coastal waters but are under stress from changing ocean conditions.
- Herring roe have been an important food source for First Nations for thousands of years.
Northern Anchovy
- B.C. is the northern end of a distribution that extends south to California.
- Spawning is more successful in warmer waters. Continued warming of the Salish Sea may lead to an increase in abundance, resulting in a shift in the food web⁴.
- Important food source for Chinook salmon in Howe Sound.
Pacific Sand Lance
- Spawn and burrow in intertidal sand beaches.
- Foreshore development can damage sand lance spawning habitat⁵.
- Important food source for Chinook salmon in the Southern Gulf Islands.
For more detailed information on forage fish see our previous story map here:
Summer Diets of Adult Chinook - Regional Differences in Primary Prey and Stomach Fullness
Prey distributions vary greatly across the Salish Sea. As a result, the Chinook stomachs sampled from the Salish Sea have been found to be divided into unique regions of primary prey.
Below is a map that will guide you through the primary prey and the 'stomach fullness' of Chinook stomachs sampled in each region. Samples for this study were from the summers of 2017 to 2019.
01 / 04
1
Strait of Georgia
• The summer diet of Chinook in this region is dominated by herring (83%)
• The stomachs sampled in this region are found to be the most full (Rank 1)
2
Howe Sound
• The summer diet of Chinook in this region is dominated by herring (55%) and northern anchovy (25%)
• The stomachs sampled in this region are found to be the second most full but close to Haro Strait/Southern Gulf Islands (Rank 2)
3
Haro Strait | Southern Gulf Islands
• The summer diet of Chinook in this region is dominated by herring (45%) and sand lance (40%)
• The stomachs sampled in this region are found to be the third most full, just behind Howe Sound (Rank 3)
4
Juan de Fuca
• The summer diet of Chinook in this region is dominated by herring (69%)
• The stomachs sampled in this region are found to be the least full (Rank 4)
Summer Diets of Adult Coho
Samples from coho salmon were not spatially distributed enough to warrant a regional analysis. However, from the samples obtained, analyses reveals a greater importance of invertebrates in coho diets. Compared to Chinooks, coho consume a wide variety of smaller crustaceans as their primary invertebrate prey source. However, similar to Chinook, herring was the most important prey for coho. Coho also consume prey fish that were not as prevalent in Chinook stomachs, such as rockfish and sablefish off Haida Gwaii, and pink and chum salmon in the Juan de Fuca Strait.
Coho salmon (photo by Eiko Jones)
Importance of Herring Size and Life History Stage to Salmon
The size-frequency distribution of herring found in Chinook and coho salmon stomachs suggests that juvenile (Age-0/1) herring are important throughout the year. Larger (Age-2+) herring dominate the diets of Salish Sea salmon in the spring and summer.
Herring in a frozen salmon stomach sample. The red dotted structures are roe (photo by the UVic Adult Salmon Diet Program).
The majority of the primary spawning biomass of herring from the Strait of Georgia is thought to rear outside the strait after their first summer. They return in the winter prior to spawning in the early spring and leave again shortly afterwards⁶.
The herring that do not follow this migratory pattern and reside in the Salish Sea after their first marine summer are crucial to the diets of Salish Sea Chinook and coho salmon.
Winter Diet in Chinook Salmon
- Little is known about the diet of Chinook and coho salmon in the winter time.
- The Adult Salmon Diet Program is currently using Chinook salmon diets to characterize the spatial structure of Salish Sea forage assemblages during the winter. Interesting changes in Chinook diets in the winter are highlighted in the section below (results from ongoing analyses will be added to this story map when available).
01 / 05
1
Increased Myctophid Consumption (16.3%)
Also known as lanternfish, they are named for their use of bioluminescence.
2
Increased Euphausiid Consumption (12.7%)
Also known as krill, they are an important trophic level link between phytoplankton and salmon.
3
Increased Surfperch Consumption (9.1% to 15.0%)
Surfperch are commonly found in shallower bays and estuaries. Their consumption by Chinook salmon increases in the eastern Strait of Georgia during the wintertime.
4
Increased Mysid Consumption (17.5%)
Also known as opossum shrimp, they are named for their characteristic 'brood pouch' where they raise their larvae.
5
Increased Herring Consumption
Winter adult Chinook stomach samples from this area highlight a decrease in sand lance consumption and an increase in herring consumption.
The Power of Citizen Science
Secchi sampling by a citizen scientist in the Salish Sea
Typical scientific oceanographic cruises are expensive to manage and operate. Initial results are already showing that with the assistance of citizen scientists, we can learn about our oceans in a cost effective, collaborative manner.
The samples obtained from the Adult Salmon Diet Program also provide data for a multitude of other research programs. For example:
- Utilizing the otoliths of herring in the Strait of Georgia to understand their migration patterns (Jessica Qualley, UVic)
- Genetic stock identification of salmon using stomach tissue samples (DFO)
- Microplastic consumption by Pacific sand lance (DFO, ECCC, SFU)
These data will ultimately be publicly available on the Pacific Salmon Foundation's Strait of Georgia Data Centre (https://sogdatacentre.ca/).
Optimistically, continued collaboration with First Nations, government, stakeholders, and local communities will proactively determine evidence based conservation strategies. Thanks to citizen scientists, the Adult Salmon Diet Program is able to be a part of that science based decision making to help protect salmon for many generations to come.
Interested in getting involved?
As an incentive for anglers to submit samples, each Chinook or coho salmon stomach submitted will qualify as one entry for a variety of prizes donated by Islander Reels and AP Tackleworks. In addition, anglers who submit more than ten samples in 2021 will receive an additional gift from the program
Email contact: juaneslabmanager@gmail.com
Acknowledgements
We would like to thank Will Duguid and Wesley Greentree of the UVic Adult Salmon Diet Program. Their expertise and guidance was key in publishing this storymap.
