Can smartphones kill Trout? Mortality of memorable-sized Bull Trout (Salvelinus confluentus) after photo-releases

Abstract

Mortality associated with catch-and-release (C&R) fisheries is typically estimated as a single value associated with fish that are immediately released after capture. However, with the widespread use of smartphones by anglers, memorable or rare fish may be subjected to prolonged handling time for photographs and measurements, resulting in increased air exposure and subsequent increased potential for post-release mortality. In situations of overfishing, large fish become rarer and their memorable status may increase. This may create a depensatory cycle of additional handling and mortality. The combination of mortality from prolonged handling, immediate release, and illegal harvest is a cumulative C&R-related cryptic mortality that may have population-level effects in high-effort sport fisheries. We investigated the potential post-release mortality of memorable-sized (average length of 60 cm) bull trout after simulating prolonged handling (involving photographing and measuring) and immediate release in a controlled angling study at a remote Albertan lake during summer. We found that handling time and air exposure of large bull trout subjected to photography and measurement was long (112 s) and associated post-release mortality was high (10 dead / 30 fish; 33 % after 24 h observation). Immediate release mortality was also high (3 dead / 20 fish; 15 %). These levels of mortality, combined with high angler effort, can potentially lead to population-scale declines at C&R fisheries. The complexity and difficulty of population-scale and field-level measurements of cryptic mortality suggest that adaptive management experiments in reductions in angling effort and improved fish handling may be effective in increasing understanding of sustainable angling.