Juvenile Chinook salmon (Oncorhynchus tshawytscha) residency and early growth in the lower Fraser River estuary

The Fraser River has historically supported the most abundant salmon runs in North America, which have been declining for decades. Despite its importance and ongoing threats of climate change and habitat degradation, the Fraser River estuary is particularly understudied, with the latest comprehensive fish survey occurring in the early 1980s. We were particularly interested in the role of estuarine habitat in supporting juvenile salmon during the critical outmigration period. As part of a two-year study, which surveyed 20 sites in the lower estuary across three habitat types, we sampled over 3,000 juvenile Chinook salmon. We caught the majority of all salmon in the marsh habitat in both 2016 and 2017, despite large differences in seasonal flows, temperatures and previous escapement. In 2016 we retained a subsample of 264 Chinook salmon for genetic and growth analyses. The vast majority of these (237) were identified by the Pacific Biological Station as lower Fraser Chinook (Harrison or Chilliwack stock), which produce the highest proportion of fall-run, ocean type Chinook in the Salish Sea. Using a combination of visual and chemical analyses of the otoliths using LA-ICPMS, we can assess the precise entry timing of these fish into the estuary, and measure their estuarine growth. In our preliminary results, we have found diverse entry and residency times among these fish of presumed similar life history strategy. Importantly, we can detect an elemental signature for marine entry in fish that have been in the estuary for a short time, which indicates that studies focusing on Chinook at later time points may be attributing estuarine growth to marine growth. Our results will help us determine the importance of the lower estuary in the marine survival of these Chinook populations, and provide some insight into life history trade-offs for ocean type juveniles

Prioritizing management actions for the Fraser River estuary

Conservation research has predominantly focused on identifying where and why species or habitats are under threat. While this is a crucial first step, it does not tell us how to optimize the allocation of resources in order to conserve threatened biodiversity. The time is ripe to focus on identifying the key management actions needed to respond to multiple threats and emerging risks. Using state-of-the-art techniques in conservation decision science, priority threat management assessment, and expert elicitation, we seek to identify the most ecologically effective and at the same time, least costly management actions needed to ensure the long-term persistence of at risk biodiversity of the Fraser River Estuary. This estuary is the mouth of the largest salmon bearing river in the world and a stopover point for more than one million migratory birds. Many species on the estuary are at risk due to water pollution and loss of habitat resulting from industrial and urban development, exploitation of fish stocks, and climate change. This study region serves as a prime example of a complex system under siege from multiple threats but with limited scientific data. We show that such systems can be analyzed to generate management actions ranked according to estimated cost, ecological benefits, the probability of success. Importantly, this analysis can clarify what can and cannot be achieved for different levels of conservation investment, and can be used to leverage increased investment in conservation management

Blue Carbon Storage Capacity of Temperate Eelgrass (Zostera marina) Meadows

Despite the importance of coastal ecosystems for the global carbon budgets, knowledge of their carbon storage capacity and the factors driving variability in storage capacity is still limited. Here we provide an estimate on the magnitude and variability of carbon stocks within a widely distributed marine foundation species throughout its distribution area in temperate Northern Hemisphere. We sampled 54 eelgrass (Zostera marina) meadows, spread across eight ocean margins and 36° of latitude, to determine abiotic and biotic factors influencing organic carbon (Corg) stocks in Zostera marina sediments. The Corg stocks (integrated over 25‐cm depth) showed a large variability and ranged from 318 to 26,523 g C/m2 with an average of 2,721 g C/m2. The projected Corg stocks obtained by extrapolating over the top 1 m of sediment ranged between 23.1 and 351.7 Mg C/ha, which is in line with estimates for other seagrasses and other blue carbon ecosystems. Most of the variation in Corg stocks was explained by five environmental variables (sediment mud content, dry density and degree of sorting, and salinity and water depth), while plant attributes such as biomass and shoot density were less important to Corg stocks. Carbon isotopic signatures indicated that at most sites <50% of the sediment carbon is derived from seagrass, which is lower than reported previously for seagrass meadows. The high spatial carbon storage variability urges caution in extrapolating carbon storage capacity between geographical areas as well as within and between seagrass species

Using systematic conservation planning to inform restoration of freshwater habitat and connectivity for salmon

Abstract Instream barriers remain ubiquitous threats to freshwater species and their habitats. Decisions regarding barrier removal are often aimed at maximizing habitat area and connectivity for freshwater fish; yet can be challenging due to the sheer number of barriers, uncertainty in species presence, abundance, and habitat quality, as well as limited budgets alongside high costs of restoration. Here, we apply systematic conservation planning to prioritize in‐stream barrier removal aimed at restoring habitat connectivity for 14 populations of wild Pacific salmon in the lower Fraser River, Canada's most productive salmon‐bearing river. To understand how priorities change when stream quality is considered, we contrast scenarios that maximize habitat extent with scenarios that include four indicators of habitat quality. Region‐wide, approximately 64% of naturally accessible stream length is currently blocked by barriers. We estimate approximately 75% of this alienated habitat (over 1600 km of stream), could have full access restored with an investment of $200 million CAD, whereas 60% could be restored for half this amount. When stream quality was considered within the optimization, priorities for barriers removal shifted away from urbanized floodplain valleys towards less developed areas. The spatial shift in priorities meant that species like chum salmon (Oncorhynchus keta) would see less restored habitat. To inform barrier removal strategies using these model scenarios, an iterative and adaptive approach will be required that includes the values and priorities of rights and titleholders. Continuous improvement in data quality, accuracy, and feedback from monitoring as barriers are restored is also crucial

Chinook salmon exhibit long-term rearing and early marine growth in the Fraser River, B.C., a large urban estuary

Estuaries represent a transition zone for salmon migrating from freshwater to marine waters, yet their contribution to juvenile growth is poorly quantified. Here, we use genetic stock identification and otolith analyses to quantify estuarine habitat use by Chinook salmon (Oncorhynchus tshawytscha) – the Pacific salmon species considered most reliant on this habitat – in Canada’s most productive salmon river, the Fraser. Two years of sampling revealed subyearling migrant (“ocean-type”) Chinook from the Harrison River to be the estuary’s dominant salmon population throughout the emigration period. These Chinook salmon were caught predominantly in the estuary’s brackish marshes but shifted to more saline habitats as they grew. Otolith analyses indicated that these Chinook salmon have wide-ranging entry timing (from February to May), and longer estuarine residency (weeks to months, mean 41.8 days) than estimated by prior studies, but similar daily growth rates (mean 0.57 mm +/- 0.13 SD) across entry dates and residency periods, implying sufficient foraging opportunities throughout the emigration period and habitats. Together, these results suggest that estuarine habitat is more important for early marine growth of subyearling migrant Chinook salmon than previously recognized.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Natural killer cell cytokine response to M. bovis BCG is associated with inhibited proliferation, increased apoptosis and ultimate depletion of NKp44(+)CD56(bright) cells

Mycobacterium bovis BCG, a live attenuated strain of M. bovis initially developed as a vaccine against tuberculosis, is also used as an adjuvant for immunotherapy of cancers and for treatment of parasitic infections. The underlying mechanisms are thought to rely on its immunomodulatory properties including the recruitment of natural killer (NK) cells. In that context, we aimed to study the impact of M. bovis BCG on NK cell functions. We looked at cytotoxicity, cytokine production, proliferation and cell survival of purified human NK cells following exposure to single live particles of mycobacteria. We found that M. bovis BCG mediates apoptosis of NK cells only in the context of IL-2 stimulation during which CD56(bright) NK cells are releasing IFN-γ in response to mycobacteria. We found that the presence of mycobacteria prevented the IL-2 induced proliferation and surface expression of NKp44 receptor by the CD56(bright) population. In summary, we observed that M. bovis BCG is modulating the functions of CD56(bright) NK cells to drive this subset to produce IFN-γ before subsequent programmed cell death. Therefore, IFN-γ production by CD56(bright) cells constitutes the main effector mechanism of NK cells that would contribute to the benefits observed for M. bovis BCG as an immunotherapeutic agent