Patti Wohner | USGS Science

USGS2024

Evaluating streamflow and temperature effects on Bull Trout migration and survival with linear spatial capture-recapture models

Objective In the U.S. Pacific Northwest, climate change is increasing air temperatures, decreasing warm season (April–September) streamflow, and increasing cool season (October–March) streamflow. Warmer water temperatures may alter conditions for migratory coldwater fishes like the Bull Trout Salvelinus confluentus . Consequently, an understanding of Bull Trout migration and survival is critical for species conservation and restoration. In the Salmon River basin, Idaho, 1992 and 1993 transpired to be two of the most opposing extreme years among the past three decades for warm season water temperature and streamflow. These extremes provided a unique opportunity to retrospectively compare Bull Trout survival and migration under potential climate change scenarios. Methods We evaluated prespawning and postspawning migrations and survival of fluvial Bull Trout that were radio-tagged and tracked from 1992 to 1994. We used a Cormack–Jolly–Seber linear spatial capture–recapture model to simultaneously model the migration and survival of radio-tagged prespawn ( n = 58) and postspawn ( n = 23) Bull Trout among weeks and river reaches with streamflow, water temperature, and habitat covariates. Result Most individual prespawning migrations were similar among tagged fish, whereas postspawn fish adopted multiple migration and overwintering strategies. Movements of prespawn Bull Trout were larger when (1) weekly average daily maximum streamflow increased and (2) weekly average daily maximum water temperature increased. The model estimated that at least 52% of spawners survived to spawning, and mean weekly prespawning apparent survival was higher in the low-streamflow year (1992) than in the year with higher and more variable streamflow (1993). Survival of 1992–1994 fish during the 38-week postspawning period was intermediate to that in the prespawning period. Detections of prespawn Bull Trout were generally higher at sites with more complex habitats, less large woody debris, and fewer undercut banks. Conclusion We found that the prespawn life stage can represent a shorter time frame (14–18 weeks) with increased mortality compared to the longer postspawning period (38 weeks). Bull Trout apparent survival increased with lower streamflow variability, indicating that expected future changes in climate may adversely affect Bull Trout.

Idaho↗

USGS2024

Prototyping structured decision making for water resource management in the San Francisco Bay-Delta

A structured decision making (SDM) approach can help evaluate tradeoffs between conservation and human-benefit objectives by fostering communication and knowledge transfer among stakeholders, decision makers, and the public. However, the process is iterative and completing the full process may take years. It can be difficult to initiate an SDM effort when problems seem insurmountable. Occasionally, SDM may not even be the best or correct approach for addressing the conservation problem at hand. We describe the implementation of an SDM process to help inform difficult decisions related to competing objectives. We convened a diverse stakeholder group from the largest estuary in the western United States; the San Francisco Bay and Sacramento-San Joaquin Delta (Bay-Delta). The stakeholder group consisted of representatives from local, state, and federal agencies, non-profit organizations, and recreational fishers. The stakeholder group agreed on a problem statement and identified four priority objectives related to Chinook salmon, delta smelt, water availability and reliability, and agricultural water use. Furthermore, they proposed 14 candidate management actions to achieve their objectives. The group then used existing quantitative models and data to evaluate trade-offs in proposed management actions to identify areas of agreement of proposed candidate actions. The clear communication of the problem statement and objectives among the stakeholder group, along with evaluation of tradeoffs and uncertainty via decision-support models suggest that a full SDM approach may work in the Bay-Delta. We further communicate lessons learned during our implementation of SDM to help guide future SDM efforts in the region and elsewhere.

California↗