Local Variability Mediates Vulnerability of Trout Populations to Land Use and Climate Change

Abstract

Land use and climate change occur simultaneously around the globe. Fully understanding their separate and combined effects requires a mechanistic understanding at the local scale where their effects are ultimately realized. Here we applied an individual-based model of fish population dynamics to evaluate the role of local stream variability in modifying responses of Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) to scenarios simulating identical changes in temperature and stream flows linked to forest harvest, climate change, and their combined effects over six decades. We parameterized the model for four neighboring streams located in a forested headwater catchment in northwestern Oregon, USA with multi-year, daily measurements of stream temperature, flow, and turbidity (2007–2011), and field measurements of both instream habitat structure and three years of annual trout population estimates. Model simulations revealed that variability in habitat conditions among streams (depth, available habitat) mediated the effects of forest harvest and climate change. Net effects for most simulated trout responses were different from or less than the sum of their separate scenarios. In some cases, forest harvest countered the effects of climate change through increased summer flow. Climate change most strongly influenced trout (earlier fry emergence, reductions in biomass of older trout, increased biomass of young-of-year), but these changes did not consistently translate into reductions in biomass over time. Forest harvest, in contrast, produced fewer and less consistent responses in trout. Earlier fry emergence driven by climate change was the most consistent simulated response, whereas survival, growth, and biomass were inconsistent. Overall our findings indicate a host of local processes can strongly influence how populations respond to broad scale effects of land use and climate change.

Simulated juvenile salmon growth and phenology respond to altered thermal regimes and stream network shape

“…Penaluna et al. () found that variability in habitat conditions mediated the response of Cutthroat Trout ( Oncorhynchus clarkii ) to climate change in northwestern Oregon. Boughton et al.…”

“…, Railsback and Harvey , Piou and Prévost , Penaluna et al. ). The role of stream network topology was investigated by Leibowitz and White () in a life cycle model to better understand Coho Salmon ( Oncorhynchus kisutch ) population dynamics, but they did not consider effects of decisions made by individual fish.…”

Aquatic biodiversity in forests: a weak link in ecosystem services resilience

“…Aquatic-obligate cold-and cool-water species may be particularly vulnerable to the effects of climate change because they require cold, connected, and high-quality habitats. Under contemporary climate change, fish and amphibians are shifting, including range contractions (e.g., Araújo et al 2006;Wenger et al 2010), fluctuations in phenology (Parmesan and Yohe 2003), and reductions in body size (Penaluna et al 2015b). As climate change continues into the future, extinctions of life-history forms and species can be anticipated, especially because high endemism is characteristic of aquatic organisms.…”

Full Issue PDF, Volume 41, Issue 6

“…Interactions among threats have become increasingly apparent in recent years; hence, it is critical to recognize cumulative effects when considering the status and persistence of Pacific trout (Bisson et al 1992;Schindler 2001;Penaluna et al 2015).…”

“…For some streams, there is increasing evidence for elevated stream temperatures Arismendi et al 2012) and reductions in flows (Luce and Holden 2009;Safeeq et al 2013) across western North America. Combined with other threats, these climateinduced changes will continue to have noticeable effects on Pacific trout distribution (Rahel et al 1996;Wenger et al 2011;Roberts et al 2013), demography (Al-Chokhachy et al 2013;Quiñones et al 2014;except Penaluna et al 2015), phenology (Kovach et al 2013;Penaluna et al 2015), and genetic diversity . Pacific trout are especially vulnerable to the effects of climate change in freshwater habitats because they require cold, interconnected, and high-quality habitats, which have already been fragmented and degraded by other anthropogenic activities in many areas.…”