Changing Oceanic Conditions on The Foraging Patterns of Cassin’s Auklets, Ptychoramphus aleuticusChanging Oceanic Conditions on The Foraging Patterns of Cassin’s Auklets, Ptychoramphus aleuticus

Abstract

Cassin’s auklet (Ptychoramphus aleuticus) reproductive success has been monitored on Southeast Farallon Island (SEFI) for the past 45 years. Their productivity has varied with oceanic conditions. The purpose of this study is to connect how oceanic conditions affect Cassin’s auklet foraging behaviors. The California Current System (CCS) can normally maintain high plankton productivity, and thus high seabird productivity, because of coastal upwelling. I hypothesized that lower upwelling and/or higher sea surface temperatures (SSTs) lead Cassin’s auklets to spend more time on intensive foraging behaviors such as flying and diving, and have less time to spend resting. I also hypothesized that they would dive more, dive deeper, and spend more time underwater in years of high SST and/or low upwelling. We deployed time depth recorders (TDRs) on 85 Cassin’s auklets on SEFI from 2008-2017 for a total of 268 foraging trips. We programmed the TDRs to record temperature and pressure every 5 seconds, and every 0.5 seconds when diving. I used the Pacific Fisheries Environmental Laboratory derived upwelling index (UI) from three months prior to the early chick-rearing season, and SST measured from SEFI during the days the TDRs were deployed. UI from three months prior and SST were not correlated. I found that in years with higher SSTs and in years with less upwelling, the Cassin’s auklets made deeper dives and stayed underwater longer. Neither higher SSTs nor lower UIs significantly affected the amount of time the auklets spent flying, diving, or resting. These results show that the physical conditions that drive the development of the California current food web influence they diving behavior of top predators