A Bayesian hierarchical model of Antarctic fur seal foraging and pup growth related to sea ice and prey abundance

Abstract

We created a Bayesian hierarchical model (BHM) to investigate ecosystem relationships between the physical ecosystem (sea ice extent), a prey measure (krill density), predator behaviors (diving and foraging effort of female Antarctic fur seals, Arctocephalus gazella, with pups) and predator characteristics (mass of maternal fur seals and pups). We collected data on Antarctic fur seals from 1987/1988 to 1994/1995 at Seal Island, Antarctica. The BHM allowed us to link together predators and prey into a model that uses all the data efficiently and accounts for major sources of uncertainty. Based on the literature, we made hypotheses about the relationships in the model, which we compared with the model outcome after fitting the BHM. For each BHM parameter, we calculated the mean of the posterior density and the 95% credible interval. Our model confirmed others' findings that increased sea ice was related to increased krill density. Higher krill density led to reduced dive intensity of maternal fur seals, as measured by dive depth and duration, and to less time spent foraging by maternal fur seals. Heavier maternal fur seals and lower maternal foraging effort resulted in heavier pups at 22 d. No relationship was found between krill density and maternal mass, or between maternal mass and foraging effort on pup growth rates between 22 and 85 days of age. Maternal mass may have reflected environmental conditions prior to the pup provisioning season, rather than summer prey densities. Maternal mass and foraging effort were not related to pup growth rates between 22 and 85 d, possibly indicating that food was not limiting, food sources other than krill were being used, or differences occurred before pups reached age 22 d.

Top‐down and bottom‐up influences on demographic rates of Antarctic fur seals Arctocephalus gazella

“…Although that may be the case, over‐winter foraging conditions will determine if a female can compensate for lost energy reserves due to rearing offspring as well as provide nutrients for a developing foetus (Hiruki‐Raring et al . ). Thus, large‐scale winter conditions far from the breeding colony may have consequences for adult reproductive and survival rates, similar to what is seen in some colonial seabirds (Le Bohec et al .…”

“…Food limitations during a relatively short lactation period may impose fitness costs that reduce maternal survival as well as prevent implantation, the latter resulting in lower pupping rates the following year (Forcada et al 2005;Forcada, Trathan & Murphy 2008). Although that may be the case, over-winter foraging conditions will determine if a female can compensate for lost energy reserves due to rearing offspring as well as provide nutrients for a developing foetus (Hiruki-Raring et al 2012). Thus, large-scale winter conditions far from the breeding colony may have consequences for adult reproductive and survival rates, similar to what is seen in some colonial seabirds (Le Bohec et al 2008;Baylis et al 2012).…”

The Rapid Population Collapse of a Key Marine Predator in the Northern Antarctic Peninsula Endangers Genetic Diversity and Resilience to Climate Change

“…Observations of AFS behavior and diet indicate a reduction in food availability, during the breeding season, since the earlyto mid-2000s. The foraging trip lengths of adult female AFS reflect prey availability (McCafferty et al, 1998), where longer trips result in lower female body condition, slower pup growth, and lower pup survival (Boyd et al, 1994;Vargas et al, 2009;Hiruki-Raring et al, 2012). The anomalously long foraging trip lengths during 2003 provided an opportunity to assess long-term trends and learn how AFS respond to decadally poor conditions.…”

“…Winter food availability determines if a female can simultaneously compensate for the nutritional stress of the previous breeding season and support her developing fetus. Winter food availability is reflected in female body condition upon arrival to the breeding colony (Lunn and Boyd, 1993;Hiruki-Raring et al, 2012). Age plays a role in body condition as well.…”

View From Below: Inferring Behavior and Physiology of Southern Ocean Marine Predators From Dive Telemetry

“…A recent study on Antarctic fur seals (Jeanniarddu-Dot et al, 2017) incorporated information of prey capture attempts into an energetics framework to estimate foraging efficiency and the consequences for reproductive success (pup growth). Such applications, linking individual foraging behavior with demographic consequences (see also Hiruki-Raring et al, 2012), are important avenues for future biotelemetry research in the Southern Ocean.…”