Washington Sea Grant Trap Survey Report: Update on the Status of Green Crabs using Trap Survey Data from 2025 and 2026

Abstract

European green crabs (EGC; Carcinus maenas) are a destructive invasive species that has been present in Washington since 1998, preying on native crabs and destroying vital eelgrass habitat. Washington Sea Grant Crab Team has created a survey program using minnow traps to monitor the spread of EGC throughout Washington shorelines. In July 2025, EGCs were observed at False Bay on San Juan Island for the first time since 2019 (WDFW). This paper examines differences in species abundance and richness between a trap survey of Argyle Beach in 2025 (before the last EGCs were observed) and surveys of Argyle and False Bay from 2026, using the WSG protocol. There was a significant increase in overall abundance and a slight decline in species richness in the 2026 Argyle survey compared to 2025. EGCs were not observed in either year, nor were multiple crab species of interest that were observed in visual surveys of Argyle Beach weeks before the 2026 trapping. These holes in the data may indicate flaws in the trap survey methods, whether it be trap type, location, or sample size. The surveys indicate that EGCs have not established a population on San Juan Island yet and can be referenced in the future if EGCs establish a population.