Review of Marking Methods and Release-Recapture Designs for Estimating the Survival of Very Small Fish: Examples from the Assessment of Salmonid Fry Survival

The survival of very small fish can have a major impact on the dynamics of fisheries stocks. Numerous marking techniques have been developed or adapted to small fish in order to investigate either early life histories or small-sized species. Some techniques provide batch marks, while others provide individually unique identification with or without the need for destructive sampling. We review 20 marking techniques in the context of conducting survival studies for small fish, with examples focused on salmonid fry survival. Sixteen alternative release-recapture designs for conducting survival investigations are also examined. Eleven approaches are found capable of estimating survival parameters, while five are not. Of those methods capable of estimating fish survival, five require unique marks, and six permit batch-specific marks. No approach based on a single release of batch-marked fish is capable of statistically estimating survival. Investigators are encouraged to carefully coordinate their choice of marking technique with the design and analysis of the release-recapture model used.