Return Customers: Foraging Site Fidelity and the Effect of Environmental Variability in Wide-Ranging Antarctic Fur Seals

Abstract

Strategies employed by wide-ranging foraging animals involve consideration of habitat quality and predictability and should maximise net energy gain. Fidelity to foraging sites is common in areas of high resource availability or where predictable changes in resource availability occur. However, if resource availability is heterogeneous or unpredictable, as it often is in marine environments, then habitat familiarity may also present ecological benefits to individuals. We examined the winter foraging distribution of female Antarctic fur seals, Arctocephalus gazelle, over four years to assess the degree of foraging site fidelity at two scales; within and between years. On average, between-year fidelity was strong, with most individuals utilising more than half of their annual foraging home range over multiple years. However, fidelity was a bimodal strategy among individuals, with five out of eight animals recording between-year overlap values of greater than 50%, while three animals recorded values of less than 5%. High long-term variance in sea surface temperature, a potential proxy for elevated long-term productivity and prey availability, typified areas of overlap. Within-year foraging site fidelity was weak, indicating that successive trips over the winter target different geographic areas. We suggest that over a season, changes in prey availability are predictable enough for individuals to shift foraging area in response, with limited associated energetic costs. Conversely, over multiple years, the availability of prey resources is less spatially and temporally predictable, increasing the potential costs of shifting foraging area and favouring long-term site fidelity. In a dynamic and patchy environment, multi-year foraging site fidelity may confer a long-term energetic advantage to the individual. Such behaviours that operate at the individual level have evolutionary and ecological implications and are potential drivers of niche specialization and modifiers of intra-specific competition.

Cross-seasonal foraging site fidelity of subantarctic fur seals: implications for marine conservation areas

“…The different characteristics of winter and summer foraging areas have important implications for the conservation of Subantarctic fur seals, and potentially other marine top predators such as Antarctic fur seals at Marion Island as shown by Arthur et al (2015). Therefore marine spatial planning, for the purposes of designating Marine Protected Area"s (MPA's), needs to consider habitats important to seals throughout the year and therefore include Subantarctic fur seal winter foraging areas.…”

“…Other habitat utilization studies, based on kernel density estimation, would discard "travelling" locations produced by SSMs (e.g. Arthur et al 2015).…”

“…In summer, prey aggregations are more predictable and productivity is higher, especially in high-latitude seasonal environments. Few studies on winter foraging site fidelity exist, such as on Antarctic fur seals (Arctocephalus gazella, Arthur et al 2015) and King penguins (Aptenodytes patagonicus, Baylis et al 2015). Antarctic fur seal females have a short lactation period (and are therefore free in winter from the constraints imposed by a pup, but the opposite is true for other otariids that have lengthy lactation periods (e.g.…”

Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

“…As such, the data can be used to examine repeatability in foraging destinations (i.e. site fidelity), migration schedules (timing and duration of events), fidelity to wintering areas and routes, and consistency in habitat use or preference , Guilford et al 2011, Thiebot et al 2011, Baylis et al 2015a, Yamamoto et al 2014, Arthur et al 2015.…”

“…The recurrent use of similar areas may increase familiarity with feeding conditions, including fine-scale resource availability and distribution (Hamer et al 2007, Ramírez et al 2016. Marine predators will often target regions characterised by local physical features or processes, including eddies, frontal systems, upwelling zones and shelf breaks, that increase primary production or serve to aggregate various types of prey (Kappes et al 2010, Louzao et al 2011, Pinet et al 2011, Baylis et al 2012, Arthur et al 2015, Wakefield et al 2015. Foraging behaviour and diet specialisations may therefore emerge as a result of the spatial and temporal availability and predictability of prey (Woo et al 2008, Navarro & González-Solís 2009, Patrick et al 2015, Sommerfeld et al 2015.…”