Finding a Resting Place: How Environmental Conditions Influence the Habitat Selection of Resting Batoids

Abstract

Many batoid species will form aggregations while resting on the seafloor; however, the environmental variables that drive resting habitat selection behavior, and how it varies among species are not well understood. Bat rays (Myliobatis californica), shovelnose guitarfish (Pseudobatos productus), and round stingrays (Urobatis halleri) have been observed forming heterospecific aggregations. We investigated the effects of substrata type and seafloor water temperature as two likely variables that would influence resting habitat selection for these species. Spatial distribution patterns of individuals were determined via diver-based surveys over two survey seasons (Fall 2013 and Summer 2014) and related to detailed georeferenced habitat maps. While these batoids were found resting on both soft sediment types available, fine-sand was selected by all three species, whereas bat rays were the only one of the three species to select for vegetated-sand. The varying thermal sensitivities of the batoids likely influenced their responses to daily and seasonal temperatures within the study area. During Fall 2013, the three species were most abundant across a narrow temperature range (18.00 – 18.25°C); during Summer 2014, there were higher densities of bat rays in areas where daily maximum seafloor temperature reached 20°C. Each species demonstrated habitat selection decisions that were indicative of balancing tradeoffs between environmental variables. As K-selected, meso-level predators, aggregating in predictable ways can ultimately make batoids more susceptible to fishing and anthropogenic pressures. Therefore, knowledge of how batoids select their resting habitat and how environmental conditions shape distributions may provide managers with opportunities to implement better protection for resting species.