Improving Inferences from Fisheries Capture‐Recapture Studies through Remote Detection of PIT Tags

Abstract

Models for capture‐recapture data are commonly used in analyses of the dynamics of fish and wildlife populations, especially for estimating vital parameters such as survival. Capture‐recapture methods provide more reliable inferences than other methods commonly used in fisheries studies. However, for rare or elusive fish species, parameter estimation is often hampered by small probabilities of re‐encountering tagged fish when encounters are obtained through traditional sampling methods. We present a case study that demonstrates how remote antennas for passive integrated transponder (PIT) tags can increase encounter probabilities and the precision of survival estimates from capture‐recapture models. Between 1999 and 2007, trammel nets were used to capture and tag over 8,400 endangered adult Lost River suckers (Deltistes luxatus) during the spawning season in Upper Klamath Lake, Oregon. Despite intensive sampling at relatively discrete spawning areas, encounter probabilities from Cormack‐Jolly‐Seber models were consistently low (< 0.2) and the precision of apparent annual survival estimates was poor. Beginning in 2005, remote PIT tag antennas were deployed at known spawning locations to increase the probability of re‐encountering tagged fish. We compare results based only on physical recaptures with results based on both physical recaptures and remote detections to demonstrate the substantial improvement in estimates of encounter probabilities (approaching 100%) and apparent annual survival provided by the remote detections. The richer encounter histories provided robust inferences about the dynamics of annual survival and have made it possible to explore more realistic models and hypotheses about factors affecting the conservation and recovery of this endangered species. Recent advances in technology related to PIT tags have paved the way for creative implementation of large‐scale tagging studies in systems where they were previously considered impracticable.

Incorporating Spatial Structure in Stock Assessment: Movement Modeling in Marine Fish Population Dynamics

“…The rapid development of tag-integrated stock assessment models that incorporate tagging data and movement reflects the increasing application of mark-recapture and tag-recovery models for estimating abundance or mortality of fishery resources (e.g., Pine et al, 2003;Coggins et al, 2006;Hewitt et al, 2010). However, both developments illustrate the need for carefully designed tagging studies that support the analytical design and estimation of parameters.…”

Effects of Lake Surface Elevation on Shoreline‐Spawning Lost River Suckers

“…Model selection statistics from previous analyses have consistently supported CJS models for shoreline spawning Lost River Suckers that include separate estimates of reencounter probability for each sex in each year (Hewitt et al 2010(Hewitt et al , 2012. Excluding the estimates for 2010, estimated reencounter probabilities between 2006 and 2012 always exceeded 0.97 for females (average D 0.973) and 0.98 for males (average D 0.984) ( Figure 5).…”

“…Suckers were redetected on remote underwater detection systems beginning in 2006 ( Figure 2). Methods for this ongoing population dynamics research project are described in detail in Hewitt et al (2010). Briefly, adult suckers were captured in 30.5-m trammel nets set in a semicircle around areas of concentrated spawning at shoreline spawning areas from February to May each year.…”

“…Methods for developing encounter histories and analysis models are given in detail in Hewitt et al (2010Hewitt et al ( , 2012. Because CJS models simultaneously estimate annual survival and reencounter probabilities, the reencounter probabilities provide direct information about the live proportion of the subpopulation that joined the spawning aggregations in each season.…”

Comparison and cost-benefit analysis of PIT tag antennae resighting and seine-net recapture techniques for survival analysis of an estuarine-dependent fish

“…Each antenna operated continuously with power from two 6 V batteries connected in series and charged by a 130 W solar panel. This antenna design permitted substantially greater coverage of creek width than the flat plate antenna of Hewitt et al (2010), but required a moderate degree of self-fabrication.…”