Estuaries & Salmon
Estuaries are productive ecosystems providing important habitat for a diversity of species, including juvenile salmon, yet they also experience intense levels of anthropogenic development that could harm salmon in many ways.
The SMOLT film below shares imagery and science of the outmigration of young salmon from freshwaters to estuaries and beyond. In support of the SMOLT film, below the video we expand on some of the science of salmon outmigration and estuary ecology, with particular focus on the collaborative research from the Salmon Watersheds Lab.
Supplementary science for the SMOLT film
Biodiversity of migration. Different populations of salmon have different patterns of migration. Using genetic stock identification of sockeye salmon smolts in the Skeena estuary, we discovered that different populations of sockeye migrate through the estuary at different times, with peak migration varying by more than 5 weeks (Carr-Harris et al. 2018).
Estuaries as nursery habitats. Juvenile salmon use estuaries to feed and grow. This reliance on estuaries appears to vary across species and life-histories. We used stable isotopes and extensive sampling of juvenile salmon in the Skeena estuary to estimate how long individual salmon had been residing and growing in the estuary (Moore et al. 2016). We discovered that residency ranged from days to weeks, depending on the species. This work, and the work of others, also found that growth rates of young salmon in estuaries can be quite high, generally higher than that in freshwater.
Estuary food webs. The estuary food webs that support young salmon are complex. Arbeider et al. (2019) examined what young salmon and other fishes, like herring, are eating in the Skeena estuary. We discovered that different species had different diets. For example, young coho salmon mostly ate larval fish and terrestrial insects, while sockeye salmon mostly ate harpacticoid copepods, a type of invertebrate that seems to be dependent on eelgrass habitats.
Critical habitats within estuaries. Certain habitats in estuaries appear to be particularly important for salmon. For example, in the Skeen River estuary, sockeye, Chinook, and coho salmon abundances were particularly abundant in the Flora Bank region (Carr-Harris et al. 2015; Sharpe et al. 2019). Learn more about our work to protect Flora Bank.
Estuaries as integrators of upstream salmon biodiversity. Because estuaries at the base of large rivers integrate the upstream salmon biodiversity, they can support scores of populations. For example, collaborative research and genetic stock identification discovered that the Flora Bank region of the Skeena supported more than 50 different populations of salmon (Moore et al. 2015). Coauthor Allen Gottesfeld called it ‘Grand Central Station’ for young salmon.
Influence on salmon survival. The size and timing of migration can control whether salmon live or die. Collaborative research by Wilson et al. (2021) on juvenile steelhead discovered that larger smolts had a higher chance of survival than smaller individuals. In addition, timing of migration influenced survival. Studies by other research groups have also found evidence that size and timing of outmigration can control marine survival among young salmon. These findings mean that growth in the estuary, as well as freshwater habitat conditions, will have carryover impacts on marine survival.
Estuary development and salmon. We performed a systematic review of studies that have examined how different estuary stressors impact salmon (Hodgson et al. 2020). We reviewed 167 studies that consisted of 1,369 comparative tests examining the impacts from 24 different activities and 14 stressors! We discovered that the weight-of-evidence was that many different stressors, ranging from pollution to connectivity loss, cause negative impacts on salmon. Further, there were substantial knowledge gaps around many activities and stressors. Previous work by others have found that industrialization of estuaries is associated with decreased survival of salmon (Magnusson and Hilborn 2003), indicating that protecting and restoring estuaries will have population-level benefits for salmon. Learn more about our work with Nature Trust BC to restore BC estuaries.
We collaborate with various groups that help translate our scientific research into conservation and management outcomes. First, there is a need for science-based environmental decision making of proposed development of salmon estuaries. Research can help clarify potential risks of development and identify critical habitats. Second, restoration activities can improve the current state and future resilience of estuaries.