The Fraser River estuary supports a multitude of fish species, and is a crucial habitat for juvenile salmon from throughout the Fraser watershed. Currently however, more than 70% of the rearing habitat historically accessible to these salmon has been lost or disconnected. Estuaries are also comprised of different types of habitats, including eelgrasses, marshes and sand flats. Researchers from the Raincoast Conservation Foundation and the University of Victoria studied how different fish use these distinct but connected habitats within the Fraser River estuary to understand their relative importance for different fish species. Over two years they caught more than 55,000 fish from 40+ different species, including almost 9,000 juvenile salmon.
Their study, published today in the journal Marine Ecology Progress Series, demonstrates that each habitat is required if the overall fish biodiversity of the estuary is to be conserved.
“We quantified fish biodiversity, community distinctness and catches (of Chinook and chum salmon, other migratory fish and resident fish), in the Fraser River estuary, the terminus of what was once the world’s most productive salmon basin,” said Lia Chalifour, the study’s lead author and a PhD candidate at the University of Victoria.
The study indicates that from spring to fall, eelgrass supports three quarters of the estuary’s fish catch and 80% of the fish diversity. Two thirds of the Fraser River salmon, however, were caught in marsh habitat, and the Chinook that rear in the estuary particularly favoured the marsh. “Importantly, no one habitat supported the full estuarine fish community. All habitats are important, and their connectivity is crucial for the functioning of the Fraser estuary’s ecosystem,” said Misty MacDuffee, co-author and Wild Salmon Program Director at the Raincoast Conservation Foundation.
The new study underscores the importance of habitat connectivity to fish biodiversity and estuarine productivity at a time of increased development pressures in the Fraser River Estuary.
Focusing conservation or management efforts on a single habitat risks underestimating the value brought to the system by each component – in the case of the Fraser, focusing solely on habitat remediation for eelgrass and ignoring the ongoing loss of marsh could lead to further declines in salmon populations. Even though eelgrass habitat supported the greatest fish species richness (37 species) and catches (37,402 fish), exceeding that of either the marsh (19 species, 7,154 fish) or sand flat (22 species, 6,697 fish), the majority of salmon were caught in the marsh (61%). Each of the three habitats supported at least one unique species (not caught in the other habitats during the study) and contributed to the overall ‘seascape’ for the estuarine fish community.
“The differences we saw between habitats underscore the importance of connected seascapes for fish conservation in estuaries,” added co-author and Raincoast salmon biologist, David Scott. “Much of the marsh habitat in the Fraser estuary has been alienated by flood control structures or lost to infilling for urban and agricultural development. The ongoing loss of this habitat is especially concerning given the state of many Fraser River Chinook and other salmon populations.”
Additional facts on the Fraser River estuary
- Largest contributor of freshwater to the Salish Sea
- Supports majority of BCs human population
- Fraser Valley Regional District produces 39.4% of BC’s agricultural revenue on 2.3% of the land base (Ministry of Agriculture 2017)
- Fraser estuary hosts Canada’s most active port
- Fraser Estuary supports more than 100 species that are recognized as “at-risk” (threatened, endangered or of concern) either provincially or federally
- Fraser Estuary is rearing habitat for 21 salmonid populations in 4 different species that are listed as threatened or endangered by COSEWIC (Committee on the Status of Endangered Wildlife in Canada)
Research funding and support
This research was supported by the Pacific Institute for Climate Solutions, the Marine Environmental Observation Prediction and Response Network, Pacific Salmon Foundation and the Natural Sciences and Engineering Research Council of Canada. The work was conducted with support and assistance from the Tsawwassen First Nation.
Raincoast Conservation Foundation
As part of our efforts to understand, mitigate, and reduce habitat impacts from industrial proposals, Raincoast is working with its partners -including UVic’s Baum Lab– to characterize the use of the estuary by different species of juvenile wild salmon at different times and places. Since 2016, we’ve been surveying out-migrating juvenile salmon across the Fraser River delta that arrive from lower and upper parts of the Fraser watershed. We monitor more than 20 sites in marsh, eelgrass and sandflat habitats on Roberts and Sturgeon Banks. Our research is advancing the understanding of juvenile salmon use (or not) in different habitats in the estuary, including the population origin, the size and growth rate of Chinook fry and smolts, the arrival and residency times, and migration patterns.