Foraging Behaviour of Juvenile Female New Zealand Sea Lions (Phocarctos hookeri) in Contrasting Environments

Abstract

Foragers can show adaptive responses to changes within their environment through morphological and behavioural plasticity. We investigated the plasticity in body size, at sea movements and diving behaviour of juvenile female New Zealand (NZ) sea lions (Phocarctos hookeri) in two contrasting environments. The NZ sea lion is one of the rarest pinnipeds in the world. Most of the species is based at the subantarctic Auckland Islands (AI; considered to be marginal foraging habitat), with a recolonizing population on the Otago Peninsula, NZ mainland (considered to be more optimal habitat). We investigated how juvenile NZ sea lions adjust their foraging behaviour in contrasting environments by deploying satellite-linked platform transmitting terminals (PTTs) and time-depth recorders (TDRs) on 2–3 year-old females at AI (2007–2010) and Otago (2009–2010). Juvenile female NZ sea lions exhibited plasticity in body size and behaviour. Otago juveniles were significantly heavier than AI juveniles. Linear mixed effects models showed that study site had the most important effect on foraging behaviour, while mass and age had little influence. AI juveniles spent more time at sea, foraged over larger areas, and dove deeper and longer than Otago juveniles. It is difficult to attribute a specific cause to the observed contrasts in foraging behaviour because these differences may be driven by disparities in habitat/prey characteristics, conspecific density levels or interseasonal variation. Nevertheless, the smaller size and increased foraging effort of AI juveniles, combined with the lower productivity in this region, support the hypothesis that AI are less optimal habitat than Otago. It is more difficult for juveniles to forage in suboptimal habitats given their restricted foraging ability and lower tolerance for food limitation compared to adults. Thus, effective management measures should consider the impacts of low resource environments, along with changes that can alter food availability such as potential resource competition with fisheries.

Climatic anomaly affects the immune competence of California sea lions

“…There is some indication that this is indeed the case, as CSL pups born in 2015 in the Mexican north Pacific had lower mass than those born in 2014, when the SST anomaly was less pronounced in that region [ 5 , 18 ]. While there are published studies on the effects of maternal condition, foraging requirements and fasting times on milk quality [ 24 – 26 ], we are unaware of any study on variations in quality of otariid maternal milk caused by atypical oceanographic conditions. However, seasonal hunger has been shown to lead to a temporary decrease in production [ 27 ] and quality [ 28 ] of human milk, and maternal nutritional status can hinder neonatal development, growth, and survival [ 29 ].…”

The benthic‐pelagic continuum: Age class and sex differences in the use of the vertical dimension by a rare pinniped

“…Developing a thorough knowledge of marine predator foraging behaviour is integral to understanding the important role they play within their biological communities (Leung et al., 2013; Raymond et al., 2015; Roman et al., 2014) as integrators and indicators of ecosystem variability (Hazen et al., 2019). Knowledge of foraging behaviour (where, when and what individuals eat and how they search for prey) is required to determine how a species will be influenced by a changing environment.…”