A Multistate Capture–Recapture Modeling Strategy to Separate True Survival from Permanent Emigration for a Passive Integrated Transponder Tagged Population of Stream Fish

Abstract

Robust estimates of survival and movement are important for informing the recovery of fish populations as well as for the study of life history, behavior, and population ecology. We present a multistate capture–recapture model that allows separate and simultaneous estimation of true survival and fidelity to the study reach in the presence of imperfect recapture and detection probabilities. The key study design element that permitted this separation was the use of a multiple-antenna array to detect passive integrated transponder (PIT) tagged individuals as they emigrated from the study area. The modeling approach incorporated live recapture data during discrete sampling occasions with observational data on antenna detections of tagged individuals as they exited the study area between sampling occasions. The multistate emigration model was applied to empirical data from a stream-dwelling, PIT-tagged cohort of Atlantic salmon Salmo salar for which emigration was continuously monitored by using a pair of stationary PIT tag antennas. The study design we outline presents a way to inform key management, recovery, and ecological questions. Our analysis showed how estimates of the joint probability of surviving and remaining faithful to the study reach (apparent survival) that were based solely on live recapture data (e.g., from the Cormack–Jolly–Seber model) masked the patterns that were revealed when true survival and emigration were separately estimated with the multistate emigration model. Use of the multistate model also allowed us to consider size dependence in survival and emigration in a straightforward way; the estimated size-dependent functions support hypotheses regarding the mechanisms leading to survival or emigration responses of Atlantic salmon and other stream-dwelling salmonids.

Received August 18, 2010; accepted December 25, 2010

ACKNOWLEDGMENTS

We thank the West Brook sampling crew for assistance in collecting field data, and we are grateful to Bob Duda for allowing access to operate and maintain the PIT tag antenna array. We also thank the three anonymous reviewers, who helped strengthen the paper. Funding was provided by a grant through the Northeast Fisheries Science Center (National Oceanic and Atmospheric Administration, National Marine Fisheries Service) and the U.S. Forest Service Northern Experimental Research Station.