Professor University of Washington Seattle, Washington, United States
Abstract: Human-mediated pathways represent a significant and growing driver of species invasions in freshwater ecosystems. Angling and boating activities that entangle invasive organisms on fishing gear, boat hulls, and outboard engines, or use non-native species as live bait, serve as modes of introduction. Shifting scientific inquiry towards a better understanding of human movement behavior may promote effective implementation of vector prevention strategies for suites of invaders. However, angler and boater behavior are currently inferred from sparsely conducted in-person or mail-in surveys, thus generating data with limited spatiotemporal scope. Mobile app-based technologies, including both geotagged posts and photographs uploaded to social media and passively collected cellular location data, offer an opportunity to improve our understanding of human behavior. Furthermore, such data may provide insight into how climate change may modify spatiotemporal patterns in water-based recreation on public lands. Understanding climate impacts on the intensity and spatiotemporal distribution of aquatic recreational activities is considered critical for estimating future risk of aquatic invasive species introductions via human-mediated pathways. Here, we couple user-generated location records from mobile applications and cellular phones with fine-scale weather data and records of invasive species distributions to (i) assess how the magnitude and location of boater and angler activity across lakes in Washington state may change due to shifting temperature and precipitation regimes, and (ii) visualize and quantify connections between waterbodies in terms of the magnitude, direction and timing of angler and boater movements, with the goal of identifying potential invasion hubs. We model lake visitation (according to mobile application and phone user-days) as a function of temperature and precipitation trends and day of the week. In addition, we employ graph-theoretical methods to identify potential invasion hubs from a network model quantifying the magnitude, direction and timing of overland connections between waterbodies from angler and boater movements. Our results indicate that lake use increases with elevated air temperatures and decreases during precipitation events, with larger lakes experiencing the greatest fluxes in visitation. The preliminary network model identified 102 sub-components across more than 8,000 lakes in the state of Washington with an average degree centrality (i.e., lakes connected to a single lake by human movement) of 16, suggesting that movement between Washington lakes is highly clustered. Identification of specific waterbodies at highest risk of invasive species introductions will allow our management partners to prioritize waterbody locations for preventative measures such as educational signage, boat inspection stations, and gear cleaning services.
