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Providing evidence to improve practice

Individual study: A systematic review of the effects of salmonid stocking in lakes on native fish populations and other fauna

Published source details

Stewart G.B., Bayliss H.R., Showler D.A., Sutherland W.J. & Pullin A.S. (2007) What are the effects of salmonid stocking in lakes on native fish populations and other fauna and flora? Part A: Effects on native biota. Systematic Review No.13. Centre for Evidence-Based Conservation


In Europe and North America, lakes are often stocked with salmonid fish, primarily to provide game fisheries. Concerns have long been raised about the ecological consequences of this practice. As well as predation of other organisms with concurrent effects through the food chain, interbreeding between stocked and native fish may affect population viability, with taxa potentially lost through hybridization, competition or inadvertently introduced diseases.

A systematic review drawing together empirical evidence regarding the impact of salmonid stocking in lakes was therefore considered pertinent by policy-makers and practitioners to inform decision-making regarding stocking policy and conservation management.

A systematic review (see: for methodology) was undertaken to assess the impact of salmonid stocking on the abundance and species richness of non-stocked native fish species in lakes, and also changes in the abundance or species richness of other fauna including amphibians, invertebrates and plankton.

Despite the large salmonid-stocking literature base, insufficient information was available regarding stocking impacts in lakes on non-stocked native fish for management to be based on empirical evidence. Of 316 potentially relevant studies identified, only six present sufficient standardized empirical measures for data synthesis.

Available evidence indicates that Urodela (newts and salamanders) are less likely to be found in water bodies stocked with salmonids than those with no stocking. There was overall no significant difference in anuran (frog and toad) occupancy between stocked and unstocked water bodies, but this was again based on a small sample size. Some species e.g. cascades frog Rana cascadae (western USA) and mountain yellow-legged frog Rana muscosa (a species of conservation concern endemic to southwest USA) are significantly less likely to be present in water bodies stocked with salmonids, whilst the converse is true for Western toad Bufo boreas (a widespread species in western North America). Results for other biota are not presented in sufficient numbers or in consistent formats across studies, making it impossible to draw robust conclusions regarding any other impact of stocked salmonids on lake ecosystems from the data currently available.

Monitoring the impacts of stocking programmes, both before and after stocking events, is necessary in order to develop an evidence base.

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