Temperature and Salish Sucker System Capacity

Three data sources of information were considered for deriving the final curve i.e., Pearson (2004), Rosenfeld et al. (2021) and Edwards (1983). In addition, we considered the expert opinion provided at the workshop conducted in November 2024. Maximum system capacity was defined by standardizing data to the highest value for CPUE (fish trap-1). It should be noted that Salish sucker are thought to be somewhat more warm-adapted than Longnose sucker, which are much more widely distributed and considered to be a cool-water species; temperature data for Salish sucker appears to support this inference, since the temperature curve foe Salish sucker appears right-shifted to higher temperatures relative to Longnose sucker. The final curve was derived by fitting a Generalized Additive Model (GAM) to original CPUE data from Rosenfeld et al. (2021). The fitted GAM curve was marginally significant (p<0.1) with wide confidence intervals at the high and low temperature extremes, which is likely due to fewer data points at very low and high temperatures. However, we can be fairly confident that the confidence intervals are in fact likely low at very high and low temperatures, despite the wide intervals implied by the GAM. This is apparent in the narrower confidence intervals in the CPUE-temperature function fit to temperature classes in Rosenfeld et al. (2021; see Fig. 2 below). The lower and upper x-intercepts in the final function (temperature at which system capacity is 0, i.e., 6oC and 23oC respectively) were determined based on the upper and lower temperatures where fish were caught in traps (see supporting SR function Excel file, cells AK157 and AK 171). The habitat suitability index model for Longnose Sucker (Edwards 1983) provided additional supportive evidence for the shape of the function, as did superimposition of Pearson (2004) data on top of the CPUE-temperature SR function. The function was further modified based on input received at the expert workshop i.e. the response to temperature should be a step faction and therefore, the maximum system capacity (100%) should be a plateau rather than a peak. The temperature range of the plateau was chosen as 14 to 18°C (Sierra Sullivan and Mike Pearson, Pers. Comm., 2024).