Gregg E. Horton

Electroshocking and PIT tagging of juvenile Atlantic salmon: Are there interactive effects on growth and survival?

Abstract Electroshocking and tagging of fish with passive integrated transponder (PIT) tags are two commonly used methods for conducting mark–recapture studies in freshwater environments and are frequently used in combination. We conducted an experiment to test for the effects of electroshocking, tagging, and a combination of electroshocking plus tagging on the growth and survival of Atlantic salmon Salmo salar parr. We used five treatments that included the presence or absence of PIT tags and electroshocking at 300 or 500 V plus a control group. Fish were measured, weighed, and electroshocked on four occasions separated by approximately 2-month intervals. The average (±1 SD) fork length was 62.1 ± 1.9 mm and the average weight was 2.5 ± 0.3 g at the start of the experiment; at the end of the experiment, length averaged 120.5 ± 11.6 mm and weight averaged 20.9 ± 6.1 g. We did not detect any significant effects of electroshocking on growth or survival over the course of the experiment. However, there was e...

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 pai...

Juvenile Steelhead Locate Coldwater Refugia in an Intermittently Closed Estuary

AbstractMany coastal estuaries in Mediterranean climates are susceptible to inlet closures resulting from barrier beach formation. These closures are ecologically important because they eliminate tidal exchange and connectivity of nekton movement to the coastal ocean and, depending on closure duration, can convert a dynamic estuary into a quiescent lagoon. Although closures can create lethal or stressful conditions for nekton and benthic communities, especially obligate diadromous species, under some conditions they can enhance survival of juvenile steelhead Oncorhynchus mykiss. However, the mechanisms explaining how closed conditions enhance the growth of juvenile steelhead and how inhabitants avoid physiologically stressful conditions remain unknown. In the present study, recent technological advances in sensor-encoded acoustic telemetry provided the ability to simultaneously locate and determine the temperature of juvenile steelhead as small as 93 mm FL by using mobile and stationary tracking. In the R...