Combining W shing and acoustic monitoring data to evaluate the distribution and movements of spotted rat W sh Hydrolagus colliei

Direct and indirect methods have been used to describe patterns of movement of Wshes, but few studies have compared these methods simultaneously. We used 20 years of trawl survey data and 1 year of acoustic telemetry data to evaluate the vertical and horizontal movement patterns of spotted ratWsh Hydrolagus colliei in Puget Sound, WA, USA. Densities of large ratWsh ( ̧30 cm) were higher at the deepest depths trawled (70 m) during daylight hours, whereas densities were similar across depth zones (to 10 m) at night. Acoustic tracking of ratWsh showed distinct diel patterns of movement and activity level; ratWsh moved into shallow, nearshore habitats at night from deeper, oVshore habitats during the day and made »3 times more moves at night than day in shallow habitats. Broader spatial patterns depended on where ratWsh were tagged: one tag group remained in one general location with few excursions, whereas a second tag group moved within a 20-km band with some individuals moving >90 km. These data will help inform food web models’ abilities to quantify interspeciWc interactions between ratWsh and other components of their community. Introduction As ecosystem-based management approaches are implemented, the need to characterize trophic interactions and quantify the interspeciWc interactions within a food web context becomes apparent (e.g., Walters et al. 1997). This is particularly important for species that exert control over the structure of marine communities (e.g., top predators; Estes et al. 1998; Dill et al. 2003; Bascompte et al. 2005) and for species that dominate a community’s biomass. To determine the eVects of species on other components of the system, it is necessary to understand habitat use, residence patterns, and movements over various temporal scales (i.e., diel, seasonal, and ontogenetic). Moreover, the local eVects of consumers on resources can be related to how much time consumers spend moving through various habitats (e.g., Fortin et al. 2005). These patterns of movement often generate the spatial patterns of abundance observed in population surveys (Turchin 1991; Wiens et al. 1993). In addition, mobile organisms link the trophic webs of diVerent habitats and communities, and we need to understand the dynamics of those links over space and time. Over the last decade, technological advances and the commercial availability of tracking equipment have made it relatively easy to study the movements of individual marine Wshes at various spatial and temporal scales using acoustic and satellite tracking methods (e.g., Tolimieri et al. 2009; Weng et al. 2008; Andrews et al. 2010; Lowe et al. 2003). Direct telemetric studies of individual movement have become common for large-bodied species such as sharks and tunas (Andrews et al. 2009; Heithaus et al. 2007; Heupel et al. 2004; Brill et al. 1999) and for species with high commercial value or of interest to marine reserve planning (Heupel and Simpfendorfer 2005; Starr et al. 2004; Parsons and Egli 2005; Tolimieri et al. 2009). However, Communicated by D. Righton. K. S. Andrews (&) Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2725 Montlake Blvd E, Seattle, WA 98112, USA e-mail: Kelly.andrews@noaa.gov T. P. Quinn School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195, USA 770 Mar Biol (2012) 159:769–782 123 information on the movements of species with low commercial value but potentially high ecological value is also important, but often unavailable. Data from various methods such as stable isotope analysis (Maruyama et al. 2001; de la Moriniere et al. 2003), otolith microchemistry (Chittaro et al. 2009; Gillanders and Kingsford 1996), presence of speciWc parasites (Grutter 1998), and taxa-speciWc surveys (Machias et al. 1998; Quinn et al. 1980; Dorel et al. 1991) have been used indirectly to characterize movement patterns for a variety of taxa. The movements captured by these methods are generally at broad spatial scales and occur between discrete periods in the life history of the individual (e.g., movement between juvenile and adult habitat (Gillanders et al. 2003; Machias and Labropoulou 2002)); however, diel movement patterns have been inferred from surveys occurring at both day and night (Pillar and Barange 1997; Gibson et al. 1996; Quinn et al. 1980). These indirect measures of movement generate straightforward hypotheses that can be tested directly with telemetry methods. Some studies have combined direct measurements of movement (e.g., video and telemetry) with traditional survey data (Bach et al. 2003; Gibson et al. 1998) to validate indirect methods to quantify movement. The use of traditional methods allows for large sample sizes and the study of multiple species, age/size classes, and sex that may not be logistically possible with telemetry methods because of cost or size limitations. Bach et al. (2003) validated the use of experimental longlines Wtted with time–depth recorders to quantify the vertical distribution of bigeye tuna Thunnus obesus by comparing distribution data with direct measurements of acoustically tagged tunas. For demersal species, results of bottom trawl surveys have been taken as evidence of movement, based on changes in the catch per unit eVort over various timescales. We conducted this study to (1) determine basic movement patterns of the spotted ratWsh Hydrolagus colliei within Puget Sound, WA, USA, (2) compare the inferences based on trawl survey and telemetry data, and (3) assess the validity of indirect evidence for diel ratWsh movements (Quinn et al. 1980; Moulton 1977; Hixon and Tissot 1992). The spotted ratWsh (“ratWsh” hereafter) is a chondrichthyan that inhabits a diverse range of coastal benthic habitats from southeast Alaska to the Gulf of California (Hart 1973), from the intertidal (Jopson 1958) to >900 m depth (Alverson et al. 1964). In Puget Sound, ratWsh primarily feed on polychaete worms and bivalves (Reum and Essington 2008), but Wshes, crustaceans, and other molluscs are also common prey items (Fresh et al. 1979; Miller et al. 1977). There is no directed Wshery for ratWsh in Puget Sound, and they are categorized “Least Concern” in a conservation context (IUCN Red List; Dagit 2006). Indeed, for decades, ratWsh have been the most abundant Wsh species collected in bottom trawl surveys (accounting for 37–75% of total numbers) in Puget Sound (Quinnell and Schmitt 1991), the southern Strait of Georgia and the San Juan Archipelago (Palsson et al. 2003), and the Strait of Juan de Fuca (Palsson et al. 2002). Thus, the movement of such an abundant species through these ecosystems likely inXuences benthic food web structure. In this study, we combined long-term bottom trawl surveys and acoustic telemetry to examine the abundance, distribution, and coarse-scale movement patterns of ratWsh in Puget Sound, Washington, USA. SpeciWcally, we used 20 years of timeand depth-stratiWed bottom trawl survey data in Port Madison, Washington, to characterize the abundance and vertical distribution of ratWsh over the diel cycle. We then used acoustic telemetry to monitor and quantify the vertical and horizontal movement patterns of individual ratWsh. Finally, we compared the inferences drawn from the two datasets to determine the most accurate overall characterization of movement patterns, and to assess the relative strengths of each scientiWc approach.