Research Document 2020/029

Influence of water temperature on mortality of Atlantic Salmon after catch and release angling

By Van Leeuwen, T.E., Dempson, J.B., Burke, C.M., Kelly, N.I., Robertson, M.J., Lennox, R.J., Havn, T.B., Svenning, M-A., Hinks, R., Guzzo, M.M., Thorstad, E.B., Purchase, C.F., and Bates, A.E.

Abstract

Average global air temperature has increased in recent decades resulting in accompanying changes in river temperatures. Poikilotherms, like Atlantic Salmon (Salmo salar L.), are vulnerable to temperature fluctuations. At the same time, many Atlantic Salmon populations are subject to catch and release angling. Catch and release mortality is influenced by angler practices and water temperature. Because Atlantic Salmon are commonly caught by anglers during the warmest months, angled fish can be exposed to physiologically stressful and potentially lethal water temperatures. Here we test interactions between river warming and mortality in recreational Atlantic Salmon fisheries. We first quantify the range of mortality rates observed at a given water temperature for caught and released Atlantic Salmon by compiling and analyzing published and unpublished data on catch and release mortality. We then focus on the region of Newfoundland and Labrador, Canada, and provide mortality estimates for caught and released Atlantic Salmon on an individual river basis by combining estimates for number of caught and released salmon from angler survey data with river temperature data. Lastly we update and compare regional and temporal trends (~1978 to 2018) for river temperatures and river closures due to high water temperatures and/or low water levels. Catch and release mortality for Atlantic Salmon was variable across studies with the majority of published data (~75%) having mortalities of <0.10. Mean mortality among control fish was 0.004. Probability of mortality increased with water temperature and depended on life history and gear type. At mean water temperatures between 0 and 12°C, catch and release mortalities (±95% confidence interval [CI]) ranged from 0.01 to 0.05 and at temperatures between 12 and 18°C from 0.04 to 0.14. Furthermore, at mean water temperatures between 18 and 20°C, mortalities ranged from 0.07 to 0.33 and at 20 to 25°C from 0.14 to 0.65. Average monthly river temperatures in July and August for Newfoundland showed a significant increase over time with a simultaneous increase in percent of days closed to angling due to high water temperatures and/or low water levels in more recent years. River temperatures for Labrador in August showed a slight increase over time and had only one documented river closure due to high water temperatures and/or low water levels. On a local scale, monitored rivers on the East and Southeast Coasts of Newfoundland increased in river temperatures in both July and August, whereas rivers on the South, West and North Coasts did not change through time, or cooled. Results of this study highlight the need for adaptive management considerations in recreational catch and release Atlantic Salmon fisheries in response to climate change.

Research Document 2020/029 (PDF, 3,326 KB)

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