Project Summary: Numerous studies have demonstrated a link between maternal foraging trip durations (MFTD) of northern fur seals (NFS) in the Bering Sea and various indicators of prey abundance, particularly of walleye pollock. MFTD is also correlated with the transfer of energy to growing pups and their rate of growth, which is an important determinant of postweaning pup survival. We propose to monitor MFTD as an index of foraging conditions for northern fur seals in 3 colonies known to forage in 3 different oceanic domains around the Pribilof Islands: the middle shelf, outer shelf, and shelf break/basin. This study will establish VHF data-logging receiver stations and deploy 75 pulse-coded, multiyear VHF flipper tags on lactating NFS at 3 rookeries to estimate maternal foraging trip durations in late season 2016, and full breeding seasons in 2017 and 2018. The length of the foraging trips will be examined with respect to metrics of environmental and oceanographic conditions, prey availability from NMFS surveys and fisheries data, and pup mass. This will allow us to characterize the spatial and temporal variability in these relationships and test hypotheses about how environmental changes may influence NFS reproductive success. In addition, by establishing the validity and utility of MFTD as a monitoring tool for processes operating at the rookery scale, we will provide a new tool for assessing the health of NFS populations beyond the temporal frame of this grant.