Trapping Methods for the Invasive European Green Crab in Canada

European Green Crab (EGC; Carcinus maenas) is a voracious aquatic invasive species (AIS) that threatens Canada’s Atlantic and Pacific marine and estuarine ecosystems. It preys on and competes with commercial and recreational shellfish, negatively impacts commercial fisheries, and destroys ecologically- and biologically-significant habitat for native species. Fisheries and Oceans Canada (DFO) has developed substantial knowledge of EGC, particularly regarding trapping for early detection, monitoring, research, and physical removal for control. Information on trapping method considerations (deployment, environment, behaviour, catch) and goal focussed protocols for different objectives including control measures and mitigation strategies has been compiled to provide advice on detection and control of EGC. Trapping EGC is critical for early detection, determining impacts on native species and habitat, and rapid response and control efforts to prevent ecosystem degradation and commercial fishery loss. A review of 69 peer reviewed studies and unpublished projects on EGC trapping were reviewed to examine trap types used in Canada (46 studies) and elsewhere (23 studies). Fifteen traps were categorized by type and usage in Canada and 13 additional traps that were used in North America and other parts of the world. The Fukui collapsible crab trap was the most utilized trap in Canada based on the review. Other traps have proven effective and direct trap type comparisons have been conducted in several regions. Trap selection must consider the trapping objective, in particular, the targeted portion of the EGC population, as some trap types can disproportionately catch large adult EGC due to trap design and intraspecific EGC behaviours. Several factors are key in selecting an appropriate trap type based on trapping objectives, which can include habitat type, depth and site location, deployment method, life stage of targeted population, bycatch considerations and available resources. Trapping is an effective methodology for monitoring relative changes in EGC abundances and population dynamics, including changes in co-occurring native species (e.g., rock crab, lobster, and some fish depending on the trap type) that may be impacted by the invasion. Trapping for rapid response and control can effectively reduce EGC numbers and alter population dynamics. Outcomes could include reduction of EGC mean body size and recovery of impacted native species and habitat, but trapping efforts may need to be sustained to maintain low impacts of EGC on ecosystem components. Knowledge gaps identified include a lack of information on trapping juvenile EGC and determining effective threshold levels or numbers for control to prevent environmental and fishery impacts. This EGC trapping advice could be incorporated by managers into a decision making tool for guiding action related to early detection, rapid response, and control management activities.

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