Bradford, M. J. | bioRxiv Science

bioRxiv2020

Can the creation of new freshwater habitat demographically offset losses of Pacific salmon from chronic anthropogenic mortality?

Over 1 billion USD are devoted annually to rehabilitating freshwater habitats to improve survival for the recovery of endangered salmon populations. Mitigation often requires the creation of new habitat (e.g. habitat compensation) to offset population losses from human activities, however compensation schemes are rarely evaluated. Anadromous Pacific salmon are ecologically, culturally, and economically important in the US and Canada, and face numerous threats from climate change, over-harvesting, and degradation of freshwater habitats. Here we used a matrix population model of coho salmon (Oncorhynchus kisutch) to determine the amount of habitat compensation needed to offset mortality (2-20% per year) caused by a range of development activities. We simulated chronic mortality to three different life stages (egg, parr, smolt/adult), individually and in combination, to mimic impacts from development, and evaluated if the number of smolts produced from constructed side-channels demographically offset losses. We show that under ideal conditions, the typical size of a constructed side-channel in the Pacific Northwest (PNW) (3405 m2) is sufficient to compensate for only relatively low levels of chronic mortality to either the parr or smolt/adult stages (2-7% per year), but populations do not recover if mortality is >10% per year. When we assumed lower productivity (e.g.; 25th percentile), or imposed mortality at multiple life stages, we found that constructed channels would need to be larger (0.2-4.5 times) than if we assumed mean productivity or as compared to the typical size built in the PNW, respectively, to maintain population sizes.. We conclude that habitat compensation has the potential to mitigate chronic mortality to early life stages, but that current practices are likely not sufficient when we incorporate more realistic assumptions about productivity of constructed side-channels and cumulative effects of anthropogenic disturbances on multiple life stages.

ecology↗

bioRxiv2020

Prioritizing conservation actions for Pacific salmon in Canada

O_LICurrent investment in conservation is insufficient to adequately protect and recover all ecosystems and species. The challenge of allocating limited funds is acute for Pacific salmon (Oncorhynchus spp.) in Canada, which lack a strategic approach to ensure that resources are spent on actions that would cost-effectively recover diminished populations. C_LIO_LIWe applied the Priority Threat Management framework to prioritize strategies that are most likely to maximize the number of thriving Pacific salmon populations on the Central Coast of British Columbia, Canada. These included 79 genetically, ecologically and spatially distinct population groups called Conservation Units (CUs) for five salmon species. This region has high salmon biodiversity and spans the territories of four First Nations: the Heiltsuk, Nuxalk, Kitasoo/Xaixais and Wuikinuxv. C_LIO_LIUsing structured expert elicitation of Indigenous and other experts, we quantified the estimated benefits, costs and feasibility of implementing 10 strategies. Under a business-as-usual scenario (i.e., no additional investments in salmon conservation or management), experts predicted that only one in four CUs would have >50% chance of achieving a thriving status within 20 years. Limiting future industrial development, which was predicted to safeguard CUs from future declines, was identified as the most cost-effective strategy. Investment in three strategies: 1) removal of artificial barriers to fish migration, 2) watershed protection, and 3) stream restoration - at 11.3M CAD per year - was predicted to result in nearly half (34 of 79) of the CUs having a >60% chance of meeting the conservation objective. C_LIO_LIIf all conservation strategies were implemented, experts estimated a >50% probability of achieving a thriving status for 78 of 79 CUs, at an annual cost of 17.3M CAD. However, even with the implementation of all strategies, most sockeye salmon CUs were unlikely to achieve higher probability targets of reaching the objective. C_LIO_LIPolicy implications: We illustrate how Priority Threat Management can incorporate the perspectives and expertise of Indigenous peoples and other experts to evaluate and prioritize conservation strategies based on their cost, benefit and feasibility. Timely investment in the strategies outlined in this assessment could help safeguard and recover Pacific salmon in this region of Canada. C_LI

ecology↗