Quantifying regional patterns of collapse in British Columbia Central Coast chum salmon (<i>Oncorhynchus keta</i>) populations since 1960

In recent decades, chum salmon ( Oncorhynchus keta) on the Central and North Coasts of British Columbia have experienced increasing variability and declining abundance. Chum are targeted by mixed-stock commercial fisheries despite declining trends and limited stock assessment to clarify conservation and fishery tradeoffs. We analyzed trends in chum salmon run sizes to 25 watersheds in the Central Coast region, to support co-governance of fisheries under newly ratified Fisheries Resources Reconciliation Agreement. Central Coast chum have declined by ∼90% since 1960, and only three populations did not undergo an evident decline. Bella Coola enhanced chum had an increasing trend but have experienced 29-fold variation in run sizes since 2005. Recently, Bella Coola enhanced chum comprised over 50% of Central Coast chum abundance and the contribution of this stock to overall abundance has more than tripled (from 13.8%) since enhancement began. Given concerns about the long-term health of chum salmon stocks and the social–ecological systems they support, commercial fisheries were closed on the Central Coast in 2021. If current trends continue, fishery opportunities may remain limited. </jats:p

Correlates and consequences of injury in a large, predatory stream salamander (Dicamptodon tenebrosus)

Conspecific aggression is an important factor structuring population dynamics through intra- and interspecific interactions, but is rarely studied in un-manipulated populations. In this study, we evaluated rates of injury as a proxy for conspecific aggression using a depletion survey of predatory coastal giant salamanders (Dicamptodon tenebrosus) in a tributary of the South Fork Eel River, California. We tested a range of hypotheses including a suite of environmental and biotic factors for the rate of injury in a population by using an AIC model-selection approach that examined the weight of evidence for individual models. We examined both the probability of a given individual being injured, and the proportion of individuals within a given study pool being injured. We found strong support for models including salamander size, density of young-of-the-year steelhead, and density of the largest size-class of salamander as factors positively influencing the rate of injury at both the individual and habitat levels. We also found that density of older steelhead (1+ steelhead) had a strong, but highly variable positive impact on frequency of injury. This study shows that both conspecific and heterospecific factors influence intraspecific aggression for the dominant salamander throughout coastal Pacific Northwest streams. Our methodology demonstrates a non-manipulative approach to identifying correlates of natural injury in a cryptic species of amphibian. More work is needed to determine how these factors directly and indirectly influence the spatial distribution, individual fitness, and dynamics of salamander populations within streams.</jats:p