title: Spatial segregation in eastern North Pacific skate assemblages.
abstract: Skates (Rajiformes: Rajoidei) are common mesopredators in marine benthic communities. The spatial associations of individual species and the structure of assemblages are of considerable importance for effective monitoring and management of exploited skate populations. This study investigated the spatial associations of eastern North Pacific (ENP) skates in continental shelf and upper continental slope waters of two regions: central California and the western Gulf of Alaska. Long-term survey data were analyzed using GIS/spatial analysis techniques and regression models to determine distribution (by depth, temperature, and latitude/longitude) and relative abundance of the dominant species in each region. Submersible video data were incorporated for California to facilitate habitat association analysis. We addressed three main questions: 1) Are there regions of differential importance to skates?, 2) Are ENP skate assemblages spatially segregated?, and 3) When skates co-occur, do they differ in size? Skate populations were highly clustered in both regions, on scales of 10s of kilometers; however, high-density regions (i.e., hot spots) were segregated among species. Skate densities and frequencies of occurrence were substantially lower in Alaska as compared to California. Although skates are generally found on soft sediment habitats, Raja rhina exhibited the strongest association with mixed substrates, and R. stellulata catches were greatest on rocky reefs. Size segregation was evident in regions where species overlapped substantially in geographic and depth distribution (e.g., R. rhina and Bathyraja kincaidii off California; B. aleutica and B. interrupta in the Gulf of Alaska). Spatial niche differentiation in skates appears to be more pronounced than previously reported.
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, United States of America.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Bizzarro
authors.affiliation: Cooperative Fish and Wildlife Unit, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Broms
authors.affiliation: School of Oceanography, University of Washington, Seattle, Washington, United States of America.
authors.forename: Miles G
authors.initials: MG
authors.lastname: Logsdon
authors.affiliation: Pacific Shark Research Center, Moss Landing Marine Laboratories, Moss Landing, California, United States of America.
authors.forename: David A
authors.initials: DA
authors.lastname: Ebert
authors.affiliation: National Marine Fisheries Service-Southwest Fisheries Science Center-Fisheries Ecology Division, Santa Cruz, California, United States of America.
authors.forename: Mary M
authors.initials: MM
authors.lastname: Yoklavich
authors.affiliation: Monterey Bay Aquarium Research Institute, Moss Landing, California, United States of America.
authors.forename: Linda A
authors.initials: LA
authors.lastname: Kuhnz
authors.affiliation: Friday Harbor Laboratories, University of Washington, Friday Harbor, Washington, United States of America.
authors.forename: Adam P
authors.initials: AP
authors.lastname: Summers
mesh_terms: D000818:Animals; D049628:Body Size; D017753:Ecosystem; D010140:Pacific Ocean; D012044:Regression Analysis; D012860:Skates, Fish / Q000145:classification / Q000254:growth & development; D062206:Spatial Analysis