Sampling methods and approaches to inform standardized detection of marine alien fouling species on recreational vessels

Recreational vessels are important contributors to the spread of marine alien species, particularly in relation to secondary spread within novel regions. As such, these vessels should be considered a monitoring priority. The aim of this study was to identify a preferred method for monitoring recreational vessels for alien species, while simultaneously developing a framework that enables managers to objectively choose the most effective sampling approach given their financial constraints. Divers and a remotely operated vehicle (ROV) were considered in relation to four sampling approaches i.e. meanders, transects, inspection of niche areas and the collection of quadrats. Each was applied to the same 53 vessels which represented a spectrum of hull fouling cover. The most effective methods were diver scrape quadrats (Range of alien species numbers per quadrat: 0–9, Total alien species: 20) and inspections of niche areas (Range of alien species numbers: 0–5, Total alien species: 9). All methods employed using an ROV had low efficacy and incurred high costs. While scrape samples were one of the most expensive methods, this was offset by the lowest cost per species detected. Thus, it is recommended that monitoring programmes utilize scrape samples and niche area inspections, but when faced with financial constraints, diver meanders and niche inspections offer sound alternatives for detecting alien species. [Display omitted] •Recreational yacht fouling is an important regional vector for marine alien species.•There is a need to effectively and efficiently monitor yachts for alien species.•Most yachts (79%) supported fouling covering 1–40% of hull surfaces.•Scrape quadrats and niche area inspections by divers detected most alien species.•Scrape sampling incurred the least cost per species detected.