Using Acoustic Telemetry to Track Green Crab Movements

Background

Numerous studies have examined green crab impacts on estuarine and salt marsh systems, but knowledge of their movements is limited. Characterizing movements of individual green crabs within systems vulnerable to invasion, such as estuaries, is needed as a tool for decision-makers considering intervention efforts against this invasive species.

Objective

Use acoustic telemetry in a model estuarine system (Webhannet River estuary) to track movements of green crabs over several months with these goals:

1. Identify behavioral patterns across daily and seasonal scales
2. Relate movements to environmental conditions
3. Assess the relationship between sex and behavior

Project Period

2018-2019

Results

Male and female green crabs equipped with acoustic tags behaved differently. Males moved up the estuary into generally warmer and shallower water, while females tended to move down estuary where water was colder.

Publication

Zarrella-Smith KA, Woodall JN, Ryan A, Furey NB, Goldstein JS. 2022. Seasonal estuarine movements of green crabs revealed by acoustic telemetry. Marine Ecology Progress Series 681:129-143. https://doi.org/10.3354/meps13927

Abstract—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.

Funding

• Maine Sea Grant
• George and Eleanor Ford Research Fund at Laudholm Trust
• University of New Hampshire