Incorporating antenna detections into abundance estimates of fish

Autonomous passive integrated transponder (PIT) tag antennas are commonly used to detect fish marked with PIT tags but cannot detect unmarked fish, creating challenges for abundance estimation. Here we describe an approach to estimate abundance from paired physical capture and antenna detection data in closed and open mark-recapture models. Additionally, for open models, we develop an approach that incorporates uncertainty in fish size, because fish size changes through time (as fish grow bigger) but is unknown if fish are not physically captured (e.g., only detected on antennas). Incorporation of size uncertainty allows for estimation of size-specific abundances and demonstrates a generally useful method for obtaining state-specific abundances estimates under state uncertainty. Simulation studies comparing models with and without antenna detections illustrate that the benefit of our approach increases as a larger proportion of the population is marked. When applied to two field data sets, our approach to incorporating antenna detections reduced uncertainty in abundance substantially. We conclude that PIT antennas hold great potential for improving abundance estimation, despite the challenges they present.

Adult males in maternity colonies of Daubenton’s bat, Myotis daubentonii: what are they?

During summer, females of temperate zone bats form maternity colonies consisting almost exclusively of mothers and their offspring. However, in some species the proportion of males in nurseries is relatively high. We explored the presence of these males in Daubenton’s bat, with respect to their age and relatedness to the local maternity colony. Using automatic PIT-tag readers, we recorded individual swarming activity at roosts used for day roosting and discovered that most of the males were yearlings that returned to their nursery roost after hibernation. The elevated occurrence of yearling males in spring could be explained by late mating attempts or toleration in the territory of adults.

Fishways as Downstream Routes in Small Hydropower Plants: Experiences with a Potamodromous Cyprinid

Fish need to move upstream and downstream through rivers to complete their life cycles. Despite the fact that fishways are the most commonly applied solution to recover longitudinal connectivity, they are not considered viable for downstream migration. Therefore, alternative facilities are recommended to facilitate downstream migration. However, a few recent studies have disagreed with this general assumption, showing the potential for bidirectional movements. This study advances our understanding of the potential of fishways for downstream migration by studying their efficiency in a run-of-the-river hydropower plant in the Duero River (Spain). To achieve this, downstream movements of the Iberian barbel (n = 299) were monitored in a stepped fishway for two years with passive integrated transponder (PIT)-tag technology, considering the effect of fish origin and release zone. The results showed that 24.9% of barbels descended through the fishway, with the origin and release zone affecting the fishway location. In addition, downstream movements were observed throughout the whole year, except in winter. The study concludes that, under specific scenarios, fishways could act as safe alternative routes for downstream migration.

Effects of experimental flow manipulations on water quality, hypoxia and growth of Threatened Salish sucker (Catostomus sp. cf. catostomus) and juvenile Coho salmon (Oncorhynchus kisutch)

The Salish sucker (Catostomus sp. cf. catostomus) is a federally Threatened species in Canada, inhabiting small lowland streams along with juvenile Coho salmon (Oncorhynchus kisutch) in southwestern British Columbia and adjacent Washington State. Experiments were conducted in two ponds to determine the effects of reduced flow on dissolved oxygen (DO), growth of Salish sucker and juvenile Coho salmon, and fish movement using Passive Integrated Transponder (PIT) tags. Sequential flow reduction in the first experiment resulted in a significant decrease in DO (9.1 to 3.1 mg·l-1) and Salish sucker growth (23% decline), although lower DO and growth were confounded with decreased temperature. Flow reduction in a second split-pond experiment including Coho salmon resulted in significantly lower DO (6.9 to 2.9 mg·l-1), a 51% reduction in growth of Coho salmon, but no detectable change in Salish sucker growth. PIT tag detections demonstrated increased use by both species of a well-oxygenated refuge in the flow reduction treatment, indicating sublethal effects of hypoxia on fish behaviour and habitat use. These experiments demonstrate the induction of severe hypoxia by reduced flows under eutrophy, with the potential for negative impacts on Salish sucker and juvenile Coho salmon growth and habitat use.

Partial migration and spawning movements of humpback chub in the Little Colorado River are better understood using data from autonomous PIT tag antennas

Choosing whether or not to migrate is an important life history decision for many fishes. Here we combine data from physical captures and detections on autonomous passive integrated transponder (PIT) tag antennas to study migration in an endangered fish, the humpback chub (Gila cypha). We develop hidden Markov mark-recapture models with and without antenna detections and find that the model fit without antenna detections misses a large proportion of fish and underestimates migration and survival probabilities. We then assess survival and growth differences associated with life history strategy and migration for different demographic groups (small male, small female, large male, large female). We find large differences in survival according to life history strategy, where residents had much lower over-winter survival than migrants. However, within the migratory life history strategy, survival and growth were similar for active migrants and skipped migrants for all demographic groups. We discuss some common challenges to incorporating detections from autonomous antennas into population models and demonstrate how these data can provide insight about fish movement and life history strategies.