Examining The Effects of Externally Mounted Biologgers On At-Sea Behavior And Reproductive Success In Adult Female Northern Elephant Seals, Mirounga Angustirostris, Using Computational Fluid Dynamics

Abstract

Over the past five decades, biologgers have been used to study animal behavior, physiology, and ecology. Externally mounted biologgers may have unforeseen effects on behavior, habitat use, foraging success, and reproductive success. Although guidelines exist for the recommended mass of biologgers on terrestrial animals, these guidelines are inappropriate for marine animals, which are more affected by buoyancy and drag. However, drag is difficult to measure directly necessitating the use of proxies based on physical characteristics of biologgers like frontal area. Northern elephant seals are a model species for studying the impacts of biologgers due to an existing long-term dataset collected using numerous types of biologgers. I used Computational Fluid Dynamics to simulate drag from 26 multi-biologger configurations and evaluated biologger characteristics to identify a drag proxy. I determined that the frontal surface area of the head and back-mounted biologgers were the most predictive characteristics for added drag. Analysis of 18 years of data from northern elephant seals at Año Nuevo State Park using these proxies revealed negligible effects of biologger-associated drag on dive behavior during both foraging trips, with only a small amount of variation explained by the frontal area of the biologgers. Postmolt seals with larger biologgers performed marginally shallower dives with departure mass-dependent impacts to drift dive frequency. In contrast, post-breeding seals performed slightly shorter dives, resulting in shorter bottom times in response to increased drag. They also exhibited a small increase in foraging trip duration. However, these behavioral changes are within the normal range of behaviors for northern elephant seals, and no long-term effects were identified