Comprehensive monitoring efforts are integral to marine ecosystem management and to predicting and mitigating the effects of anthropogenic change on marine biodiversity. Traditionally, fish occupancy is determined using a combination of fishery-dependent (i.e., catch data) and fishery-independent (e.g., remote underwater video, satellite imagery, hydroacoustics, visual transects, point-count surveys, roving diver surveys) monitoring (Murphy & Jenkins, 2010). The efficacy of a given monitoring technique depends on the target species and its unique characteristics, including size, behavior, crypticity, swimming speed, preferred habitat, and position in the water column (Holt et al., 2013; Harmelin-Vivien & Francour, 1992). Additionally, as observational methods vary in cost, invasiveness, and ease, choosing the appropriate monitoring tool depends on budgets and specific objectives of managers or researchers. It is useful to assess the benefits and disadvantages of different techniques to identify combinations that can maximize surveillance of target species, communities, or habitats while adhering to financial and other constraints.
Underwater visual census (UVC) is a minimally invasive, fishery-independent method in which snorkel or SCUBA is used to assess biodiversity and/or biomass in marine habitats (Pattengill-Semmens & Semmens, 2003). The roving diver technique (RDT; Schmitt & Sullivan, 1996) is a type of UVC especially suited for detecting shy, cryptic, or demersal fishes difficult to assess with other monitoring tools (Murphy & Jenkins, 2010). During RDT surveys, divers swim freely throughout a dive site while recording each observed fish species and a corresponding log-scale categorical abundance. The method can be conducted in a variety of habitats in depths up to 30 m (and beyond with specialized gear). As such, RDT is valuable for assessing frequencies of occurrence, spatial distributions, abundance estimates, and information on status and trends for a broad array of species. Data collected with other visual methods, such as belt transects, can be combined with RDT data to provide a holistic picture that includes species densities and size distributions (Holt et al., 2013).
Across the globe, citizen science programs train recreational divers to effectively monitor marine fishes, invertebrates, and algae (Branchini et al., 2015; Cerrano et al., 2016). The Reef Environmental Education Foundation (REEF) Volunteer Fish Survey Project trains volunteer divers and snorkelers to independently conduct RDT surveys, creating a system by which thousands of standardized surveys are conducted annually and recorded in a publicly accessible database (Pattengill-Semmens & Semmens, 2003). Within such a large pool of trained volunteers lies the potential for scientists and managers to increase their census capabilities by alleviating constraints on equipment, personnel, time, and accessibility to certain areas or habitats. Since 1993, the REEF Volunteer Fish Survey Project has been used worldwide to assess biodiversity and advance the conservation of threatened fishes and invertebrates, both alone and in combination with professional research efforts (Holt et al., 2013; Thorson et al., 2014). Data collected by REEF surveyors have informed numerous conservation and management efforts, including to detect and remove invasive species (Smith et al., 2017), discover new species (Allen et al., 2020), contribute to the recovery of threatened species (Tolimieri et al., 2017), document the impact of human population density on fish communities (Stallings, 2009), and trace the impacts of enigmatic marine diseases (Harvell et al., 2019).
To determine if RDT is an appropriate monitoring tool for a fish species, multiple factors surrounding the species of interest must be considered. This includes, but is not limited to, whether the species occurs at recreational diving depths, is cryptic or conspicuous, and if it can be discerned from closely related species without a specimen in hand (e.g., for meristic counts). Identifying the species that volunteers can potentially encounter and visually identify can improve the interpretation of data provided by this no-cost, high-value monitoring tool (Schmitt & Sullivan, 1996).
The Salish Sea is a 16,925 km2 inland sea bordered by Washington, USA, and British Columbia, Canada. In 2019, relying on preserved specimens in archival institutions, published records, and, especially for within-basin distributions, unpublished field notes and logbooks, Pietsch and Orr (2019) published species accounts for 260 fish species found in the Salish Sea, including distributions across sub-basins. As many of these taxonomic records were generated over a century ago, this compilation focused on providing a comprehensive, cumulative registry of Salish Sea ichthyofauna in addition to a current picture of biodiversity. Records were based on collections of specimens using an array of gear and techniques, including beach and purse seines, trawls, gillnets, traps, spearfishing, hook and lines, poisoning, stomach contents, and beach casts (e.g., Miller & Borton, 1980). Data from RDT or other visual surveys were not included. This compilation provides the best available baseline of the total fish that use, or have used, the Salish Sea ecosystem. While no one method will be suitable to capture all species, individual techniques such as RDT can be evaluated against this list to elucidate the scope of the survey tool.
Since 1998, REEF divers have conducted RDT surveys in the Salish Sea. We compiled REEF RDT surveys recorded over a span of 21 years (1998–2019) and compared these data to the Pietsch and Orr (2019) records of 260 Salish Sea fish species. Because relatively few specimens are collected and preserved from rocky reefs and rock walls (Pietsch & Orr, 2019), often a focus area for recreational divers, we hypothesized that observations by REEF surveyors would expand the geographic range and number of species documented in the Salish Sea based on Pietsch and Orr (2019). Certain fish species are inherently better suited than others for identification by RDT. Therefore, to identify Salish Sea fish species that can be monitored by REEF divers, we developed a categorization system based on the potential for recreational divers and snorkelers to encounter them, and on whether they can be visually identified to species with or without a high-quality photograph if encountered (i.e., a specimen in hand is not required for identification).