Seasonal estuarine movements of green crabs revealed by acoustic telemetry.
Green crabs Carcinus maenas are considered among the most influential invasive species in temperate estuaries worldwide. Yet management can be hindered by the lack of high-resolution data on green crab movement ecology. We addressed this knowledge gap by coupling passive acoustic telemetry and water quality monitoring to examine daily and seasonal movements of individual green crabs in the Webhannet River Estuary (Maine, USA). We tracked 22 adult green crabs (mean [±SD] carapace width = 63.8 ± 6.5 mm) between 2 successive tagging deployments from July 2018-January 2019, with one receiver maintained until mid-April 2019. Overall, our study demonstrated the viability of using acoustic telemetry to assess seasonal movements of green crabs, with an average (±SE) individual detection rate of 27.9 ± 2.8 detections h-1 from July-January. Most crabs remained localized to very specific regions of the estuary, with each region representing a 300-600 m linear distance. Logistic regression models indicated that movements by green crabs to the downstream area were associated with a shift in temperature below 10°C, regardless of sex. From January-April 2019, 9 crabs were found to overwinter in the downstream area, potentially taking refuge in deeper waters. Movement patterns identified in this study further contribute to our understanding of the distances traveled and the areas used by green crabs, as well as further resolve overwintering behavior with consequences for mortality risk due to low temperatures. This additional knowledge of adult green crab movement and dispersal dynamics is valuable to resource managers considering intervention strategies.