MEPS prepress abstract  -  DOI:

Variable utilization of shelf break-associated habitats by chick-brooding rhinoceros auklets In the California Current system

Bradley P. Wilkinson*, Jaime Jahncke, Pete Warzybok, Russell W. Bradley, Scott A. Shaffer


ABSTRACT: Identifying frequently complex and dynamic spatial distributions of marine predators via the modeling of at-sea observations can be inherently challenging, especially when attempting to predict habitats of specific populations. Remotely-sensed tracking devices provide a viable alternative to gathering this information. We collected fine scale spatiotemporal movement data for a small seabird, the rhinoceros auklet Cerorhinca monocerata, in the California Current System. Chick-brooding adults nesting on Southeast Farallon Island were outfitted with GPS loggers during the 2015 and 2016 breeding seasons (n = 15). Along with basic movement parameters, kernel density and residence time analyses were conducted to characterize at-sea distribution and identify areas of intensive use. Binomial generalized linear mixed modeling (GLMM) was used to assess foraging habitat. Compared to previous distributional models based on at-sea censuses, we found a greater utilization of areas beyond the shelf break than predicted. Interannual variation was noted as an increase in outer break foraging in 2015 compared to elevated shelf and inner break exploitation in 2016, despite likely using the same habitat intrannually for self- and chick-provisioning. Prey availability and local oceanographic conditions may have influenced foraging decisions, with rockfish (Sebastes spp.) abundances and submesoscale SST fronts potentially acting as mediating factors. Results of mixed modeling highlighted a composite three-way interaction between environmental variables facilitating auklet behavioral state switching, with an additional non-linear SST term being significant. Overall, foraging effort within the regional shelf break system appears to be variable at fine spatial scales depending on concomitant oceanographic conditions and related resource dynamics.