A Landscape Risk Assessment Framework for Salmon: A generalized approach and annotated bibliography to assess ecological risk to wild salmon associated with resource and urban development in Alaska

Ecological risk assessment (ERA) has become an essential tool for evaluating impacts to biological systems associated with wide range of human activities. Several applications of ERA methodology have been developed to analyze potential risks to wild salmon systems in Alaska, including risks associated with potential large-scale mining in Bristol Bay, as well as risk associated with large-scale hydropower on glacial rivers in Alaska. The purpose of this type of analysis is to improve understanding of the likelihood, magnitude and geographic scope of potential stressors associated with development. In the case of salmon, the framework considers key ecological functions that support all freshwater life-stages of salmon, including in-migration, spawning, incubation, rearing and out-migration. A generalized list of potential stressors included loss or alteration of freshwater habitat, changes in water quality, sedimentation, acid mine drainage, as well as smalland large-scale pollution events. While it is not possible to predict future conditions with certainty, this conceptual framework provides a systematic approach to evaluate the potential scope and severity of a range of risk factors, as well as potential effects on ecological systems that support salmon, to inform decision-making and risk management. The purpose of this review is to provide a brief synopsis of this approach as it has been applied in Alaska related to large-scale mining and hydropower development, and a brief bibliogrpahy of literature on potential future applications in the context of community residential, urban and industrial development. Summary of Risk Assessment Approach: The methodology of ecological risk assessment is flexible, compatible with a wide range of approaches to conservation planning, and is well suited to a range of applications in Alaska. Typical steps includes: (1) problem formulation; (2) analysis; (3) risk characterization; and (4) risk management, with analyses designed to characterize both the exposure to ecological stressors and the effects of those stressors on target species and systems (Fig. 1; Suter 2006). Problem Formulation: A conceptual framework of potential physical and chemical stressors and identification of biological and other resource potentially at risk. Characterization of Exposure: Estimation of the likelihood, spatial distribution, timing and magnitude of potential changes in ecological attributes that support salmon such as stream flow, ground water, stream temperature, water chemistry, etc. In a predictive risk assessment, this step 7/30/15 The Nature Conservancy develops estimates based on analogous examples in the scientific literature and on physical, chemical and hydrologic models of site-specific conditions. Characterization of Ecological Effects: A systematic review of ecological requirements and effects of potential stressors on target species and systems (e.g., toxicity thresholds), as well as site-specific factors that mediate biological response. Risk Characterization: A quantitative characterization of risk would involve a spatial overlay of predicted exposures to ecological stressors with estimated thresholds of effect on target species and systems over a range of reasonably foreseeable scenarios. These comparisons provide the basis for evaluation of the likelihood and degree of risk for scenarios under consideration. A range of methods have been developed for such assessment, including qualitative Relative Risk Method (Landis 2003) and more quantitative stressor-based risk analyses (e.g., spatial analysis of copper concentration vs. toxicity thresholds). Salmon Life History and Implications of Conservation Planning: A systematic framework for conservation of wild salmon ecosystems must account for all phases of the salmon life cycle. Each phase is a necessary link in the chain that maintains healthy populations over time. While the salmon reliance on freshwater habitats for spawning and rearing has contributed to their success, it also makes them vulnerable to disturbance by people. By understanding the ecological requirements of each life phase, we can better manage human activities to ensure the continued diversity and productivity of salmon systems. The basic aspects of a salmon life cycle have been widely documented (e.g., Quinn 2005), but a basic summary here will suffice. The mature adults return to spawn in the rivers and streams they were born, which involves laying their eggs in a nest of gravel and then they die. The eggs require clean gravel, without too much fine sediment, to allow adequate flow of water through the redd. This continuous supply of water, both from surface flow and ground water, is critical to provide dissolved oxygen and to prevent the redd from drying or freezing during the winter. After a few months, the eggs hatch, and an intermediate life stage called an “alevin” emerges, and seeks shelter deeper in the gravel often moving in the direction of their supply of dissolved oxygen. Remember, this is happening during the winter when rivers in Alaska are typically frozen over, so sufficient ground water remains critical for survival at this time. The free-swimming juvenile salmon that emerge from the gravel are called “fry”. Juvenile salmon may spend several years in freshwater, so sufficient food, protective cover, adequate stream flow, habitat to survive the winter, and connectivity throughout the watershed all are important during this time. The goal of this phase is for juvenile salmon to grow large enough that they’ll have a better chance to survive once they leave the freshwater and enter the marine environment. Salmon behavior during this period varies widely by species as well as within species and even populations. Typically pink and chum salmon emigrate directly to the salt water in their first summer, sockeye salmon will rear in lakes, king salmon in larger streams and coho 7/30/15 The Nature Conservancy are widely distributed throughout the watershed. These are the typical life history strategies, but a high degree of variability within each species and within populations is a key to the resilience of salmon in a changeable environment. Ultimately, juvenile salmon will leave their home rivers and enter a period of transition as “smolt”. This involves a complex physiological transformation from a freshwater to a saltwater dwelling creature. They’ll often use the mixed fresh and saline waters and higher productivity of the estuary to prepare for a life at sea. Adult salmon will spend a number of years at sea, depending on the species, where growth is very rapid and they travel vast distances around the north Pacific. The life cycle completes itself when the maturing adults return to their natal streams to breed and die. The particular fact that salmon die after spawning is a key aspect of their ecology. All their life’s energy is invested in a single clutch of large, well-developed eggs. Their bodies fertilize the streams where their young will emerge and grow, thereby improving the fitness of their own offspring. In this way, salmon represent a self-sustaining, positive-feedback delivery system of nutrients from the ocean to the relatively nutrient-poor streams and lakes of Alaska. The abundance of salmon we see in Alaska’s rivers today, and that used to occur in rivers throughout the Pacific Northwest, is the result of this positive feedback over millennia. Without that abundance, as in cases where salmon have declined to very low levels, the entire ecosystem, including the food and economic opportunities for its people, is changed. Last, the strong homing ability of salmon that brings them back to their natal streams means that breeding populations become finely adapted to local conditions, including seasonal temperature, flooding and freezing, and availability of various habitats. This localized diversity within larger populations is an important element of their long-term success and productivity, and provides stability in salmon fisheries over time. This concept of an “ecological portfolio” has important implications for how we think about salmon conservation in Bristol Bay: This is the portfolio that provides high sustained salmon production over time. It functions similar to a financial portfolio, in that the breeding populations within any stream will be more variable, but the sum-total of returns averaged across many streams will be more stable. It is diversified, in that populations in different parts of the watershed are adapted to a diversity of local environments, which makes the larger salmon system more resilient to large-scale disturbance such as climate change. This level of diversity in Bristol Bay, particularly within sockeye populations, is unique in the world, and can be considered a form of “natural capital” that contributes to the overall value of the portfolio. Another aspect of this “natural capital” is the unique hydrologic system within these watersheds: wetlands, groundwater, river habitats, large lakes and overall productivity. 7/30/15 The Nature Conservancy 7/30/15 The Nature Conservancy Key Ecological Attributes Key ecological attributes are the conditions necessary for each phase of the salmon life cycle to be successful. While specific attributes and critical values necessary to support survival and reproduction will vary according to species, a general set of attributes can be described related to water quality, water quantity, connectivity and habitat structure. This framework provides a template to evaluate potential risks to salmon across a wide range of potential topics, including large-scale mining (E&E 2010, EPA 2014), hydropower development (Anchor QEA 2014), forestry and urban development. Figure 2. A generalized framework of key ecological attributes associated with specific phases of salmon life history (From: Anchor QEA 2014). Characterization of Exposure and Sources of Stress: The example below illustra