Identifying female foraging ecotype and fisheries impacts through pup whisker stable isotopes

1. Individual specialization in the foraging behaviour of marine predators can affect the ecology, evolution, and ability of a population to respond to environmental variability and human impacts.
2. Here, blood serum and whisker stable isotope values from New Zealand (NZ) sea lion pups (Phocarctos hookeri) are compared with their mother’s values to identify whether they can be used as proxies to identify their mother’s isotopic niche and foraging strategy.
3. Female NZ sea lions have been identified, both through telemetry and stable isotope research of blood serum and whiskers, to have two distinct foraging ecotypes (mesopelagic or benthic), consistent across their adult life. Females who are mesopelagic foragers have higher overlap and a greater risk of harmful interactions with fisheries.
4. Stable isotope analysis of adult females can be used to determine the proportion of the female population exposed to these detrimental interactions. However, the capture, restraint, and removal of a whisker or blood from an adult female NZ sea lion is an expensive, time-consuming, and invasive undertaking. Instead, by comparing the blood serum and whisker δ¹³C and δ¹⁵N values of 12 NZ sea lion mother-and-pup pairs, for whom the foraging behaviour of the female is known, the question as to whether a pup’s blood serum or whisker isotope value can be used as a proxy to identify female foraging ecotype was investigated.
5. The δ¹³C and δ¹⁵N values for the blood serum and whiskers of pups and their mothers were correlated and differed significantly between foraging ecotypes. This research validates that pup blood serum and whisker stable isotope values from 1-month-old pups can be used as indicators of female isotopic niche and therefore foraging ecotype.
6. This tool can be used across all NZ sea lion colonies to indicate female NZ sea lion foraging ecotypes. For the Auckland Islands, it could determine the proportion of breeding females exposed to negative interactions with fisheries, leading to a better understanding of the level of these effects and helping to implement appropriate management to mitigate impacts.

     

Dispersal of breeding, adult male Phocarctos hookeri: Implications for disease transmission, population management and species recovery

Dispersal impacts on a range of population parameters making it a key piece of information in species conservation. Despite its importance, dispersal is poorly characterized for many species: pinnipeds are no exception. Understanding dispersal patterns of the New Zealand sea lion Phocarctos hookeri is crucial in the conservation management of the species as its recovery to a non-threatened status hinges on range recolonisation. In this study, we examined the movements of breeding adult male New Zealand sea lions within and following the breeding season of the 2002/03 austral summer using a novel multi colony approach. Based on resightings of 202 individually identifiable adult males, we found (1) a previously unappreciated, high level of dispersal by adult territorial males between breeding colonies during the pupping period and (2) that breeding males disperse to the extremes of the species’ range at the end of female oestrous. Our findings are contrary to the current paradigm of otariid breeding behaviour, which is believed to consist of prolonged, uninterrupted male territoriality based on intense male-male competition and sustained fasting. Adult male dispersal between colonies and across the species range has important implications for adult males as vectors of disease in three recent epizootics, species management and species recovery via recolonisation as males are apparently remaining part of a localized, vulnerable breeding population.     

Behavioural plasticity and population connectivity: Contributors to the establishment of new pinniped breeding colonies

1. Understanding the ecological and evolutionary processes that occur during range shift or (re-)colonization is of critical importance for species whose ranges are changing due to human-induced climate change or species such as New Zealand sea lions where their established colonies are significantly declining due to human impacts.
2. The mechanisms underlying colonization are poorly understood. Observations are required to determine the processes that change individual's behaviour associated with colonization, but such observations are rare.
3. Here, the establishment of a new breeding colony of New Zealand sea lions, Phocarctos hookeri, as they recolonized mainland New Zealand, an area from which they had been absent for ~200 years was investigated.
4. There are differences in breeding location behaviour and population connectivity between established and establishing colonies of New Zealand sea lions. The recolonizing population is more dispersed with breeding locations that change annually and have more connections with other populations compared with established colonies and populations.
5. The establishment of a new colony and the greater numbers of resightings between colonies means that for species' management, considerably more public education, habitat management, and protection is needed to ensure the safe return of New Zealand sea lions back on to mainland New Zealand.