Demographic rates of northern royal albatross at Taiaroa Head, New Zealand

Demographic rates, such as annual survival rate, are generally difficult to estimate for long-lived seabirds, because of the length of time required for this kind of study and the remoteness of colonies. However, a small colony of northern royal albatross (Diomedea sanfordi) established itself on the mainland of New Zealand at Taiaroa Head, making possible regular banding and monitoring of its individuals since the first chick fledged, in 1938. Data on the presence/absence of birds, as well as on breeding outcomes, were available for the period from 1989-90 to 2011-12, and included 2128 annual resightings of 355 banded individuals of known age. The main goal of the present study was to estimate the annual survival rate of juveniles, pre-breeders, and adults at Taiaroa Head. These rates were estimated simultaneously in a single Bayesian multi-state capture-recapture model. Several models were fitted to the data, with different levels of complexity. From the most parsimonious model, the overall annual adult survival rate was estimated as 0.950 (95% CI [0.941-0.959]). In this model, adult survival declined with age, from 0.976 (95% CI [0.963-0.988]) at 6 years, the minimum age at first breeding, to 0.915 (95% CI [0.879-0.946]) at 40 years. Mean annual survival of pre-breeders was 0.966 (95% CI [0.950-0.980]), and 0.933 (95% CI [0.908-0.966]) for juveniles. There was no discernible difference in survival between males and females, and there was no apparent trend in survival over time. Estimates of other demographic rates were also obtained during the estimation process. The mean age at first return of juveniles to the colony was estimated as 4.8 years (95% CI [4.6-5.1]), and the mean age at first breeding as 8.9 years (95% CI [8.5-9.3]). Because all the birds of the colony were banded, it was possible to estimate the total population size. The number of northern royal albatross present annually at the Taiaroa Head colony has doubled since 1989-90, and the current total population size was estimated to be over 200 individuals. The ratio of the total population size to the number of annual breeding pairs varied from 5 to 12 among years, with an overall mean of 7.65 (95% CI [7.56-7.78]), and this high variability highlights the need for a sufficient number of surveys of seabird breeding populations before reliable conclusions on population trends can be made. Although long-term data allowed estimates of demographic rates of northern royal albatross at Taiaroa Head, the location of the colony and the ongoing management by staff mean that the population dynamics may differ from those of the main population on the Chatham Islands.

Strong phylogeographic structure in a sedentary seabird, the Stewart Island Shag (Leucocarbo chalconotus)

New Zealand's endemic Stewart Island Shag (Leucocarbo chalconotus) comprises two regional groups (Otago and Foveaux Strait) that show consistent differentiation in relative frequencies of pied versus dark-bronze morphotypes, the extent of facial carunculation, body size and breeding time. We used modern and ancient DNA (mitochondrial DNA control region one), and morphometric approaches to investigate the phylogeography and taxonomy of L. chalconotus and its closely related sister species, the endemic Chatham Island Shag (L. onslowi). Our analysis shows Leucocarbo shags in southern New Zealand comprise two well-supported clades, each containing both pied and dark-bronze morphs. However, the combined monophyly of these populations is not supported, with the L. chalconotus Otago lineage sister to L. onslowi. Morphometric analysis indicates that Leucocarbo shags from Otago are larger on average than those from Foveaux Strait. Principal co-ordinate analysis of morphometric data showed substantial morphological differentiation between the Otago and Foveaux Strait clades, and L. onslowi. The phylogeographic partitioning detected within L. chalconotus is marked, and such strong structure is rare for phalacrocoracid species. Our phylogenetic results, together with consistent differences in relative proportions of plumage morphs and facial carunculation, and concordant differentiation in body size and breeding time, suggest several alternative evolutionary hypotheses that require further investigation to determine the level of taxonomic distinctiveness that best represents the L. chalconotus Otago and Foveaux Strait clades.

A Northward Spread In The Breeding Distribution Of The New Zealand Sea Lion (Phocartos Hooeri)

The primary objective of the population management plan for New Zealand sea lions, Phocarctos hookeri, is to move the species from its current conservation status of ‘Threatened’ to ‘Non-threatened’. The mechanism by which this will occur is through the establishment of new breeding colonies away from the only existing colonies at Auckland Islands and Campbell Island. Otago, on the southeast coast of the South Island of New Zealand, is one of only three locations where breeding has been recorded away from these islands in modern times. We found only one female at the initiation of our surveys here in 1991, an individual that had been tagged as a pup at Auckland Islands. This female has remained resident at Otago and is now breeding. Her first live birth, in the 1993/94 breeding season, represented the first record of a P. hookeri pup on the New Zealand mainland since the elimination of the species here by humans c. 150 years ago. Up to and including the 2000/01 breeding season she had produced six pups. Her surviving pups have remained at Otago and her eldest two daughters have started breeding, producing a further three pups. From this total of nine live births, two pups have died. Although 6 - 8 other migrant females have been recorded, to our knowledge none have bred at Otago. We conclude that the initiation of breeding by P. hookeri at Otago has been a serendipitous event attributable to atypical behaviour by a single female.

Pattern Of Immigration Of New Zealand Sea Lions Phocarctos Hookeri To Otago, New Zealand: Implications For Management

The present management strategy for New Zealand sea lions Phocarctos hookeri assumes that kills in a squid trawl fishery around Auckland Islands, the species population base, have prevented an increase in abundance of sea lions. This strategy also assumes that emigration will be initiated as the population reaches carrying capacity, and that emigration rates will be density dependent. We used the combination of photographic identification of individuals and diagnostic features of age classes to estimate immigration rates of P. hookeri to Otago, South Island, New Zealand. Most immigrants were males = 2 years old at arrival, and included animals tagged as pups at Auckland Islands. Estimates for total numbers of immigrants to Otago from four consecutive cohorts, 1991/92 - 1994/95, varied three-fold through a period of constant annual pup production at Auckland Islands. The greatest influx was from the 1993/94 cohort, a breeding season that predated the enforcement of early closures of the squid fishery. We suggest published records from the Auckland Islands indicate that this population is already at carrying capacity. If so, then factors other than, or in addition to, pup production and fishery mortality have an impact on emigration rates.

Pup density related to terrestrial habitat use by New Zealand fur seals

Features of the terrain are important in the selection of terrestrial habitat by otariid seals. Fur seals use rocky shorelines where terrain features such as crevices and ledges may provide shelter for pups. New Zealand fur seals (Arctocephalus forsteri) are increasing in number and expanding their range, requiring them to select new habitat for breeding. Predicting population expansion is important for assessing potential conflicts with commercial fisheries. We quantified terrain features at 25 breeding colonies and 8 nonbreeding colonies around South Island. Univariate tests demonstrated some differences in terrain between breeding and nonbreeding colonies, although principal components analysis (PCA) did not reveal any obvious differences. We suggest that the power to detect differences is reduced by the tendency for nonbreeding colonies to become breeding colonies over time as the population increases. We found a significant relationship between pup density and terrain (i.e., PCA variables) within breeding colonies. The terrain occupied by high-density colonies contained more and smaller rocks, more crevices and ledges, less-pronounced slopes, higher cliffs, and a more westerly exposure than that occupied by low-density colonies. Smaller rocks may provide more spaces in which pups can find shelter; less-pronounced slopes may facilitate pup mobility and higher cliffs may increase shading. We suggest that in addition to terrain features, other phenomena are also involved in breeding-site selection.

Seasonal oscillation in shore attendance and transience of New Zealand fur seals

The New Zealand fur seal (Arctocephalus forsteri) appears to show regular shore attendance in the form of seasonal oscillations. This phenomenon should be quantified to properly interpret counts of fur seals >1 year old (i.e., non-pups). Here we test the predictability of peaks in the annual shore-attendance oscillation on Otago Peninsula using an autoregressive sine model and >2 years of intensive survey data. We predicted that the peak in fur seal numbers ashore would lie between 14 January - 4 April (1996) and 8 January - 2 April (1997), although this low predictability is undesirable when attempts are made to monitor population trends. Estimating population size from counts of non-pups also requires knowledge of the rate of turnover of individuals. Therefore, we tested the hypothesis that tagged animals from other colonies are immigrants to Otago Peninsula. With sightings on Otago Peninsula of fur seals tagged elsewhere in New Zealand, we used a Monte Carlo approach to simulate the expected frequency of single and multiple sightings of individuals. We found that the observed frequency of multiple sightings was significantly less than predicted by the model (P < 0.0001), indicating that tagged animals were transients. We also discovered that the sex ratio of tagged animals varied with breeding colony of origin (G1 = 52.07, P < 0.0001), suggesting that the impetus for emigration differs among colonies. We concur with the view that counting pups is the only way to estimate the relative abundance of New Zealand fur seals. In addition, we showed that counts of non-pups cannot be used to estimate population size because an unknown proportion of individuals is transient. However, counting of pups does not address the issue of estimating relative abundance for locations with large numbers of nonbreeding individuals and few or no breeders. With few or no pups it is impossible to estimate relative abundance using counts of pups.

Seasonal variation in the diet of New Zealand fur seals (Arctocephalus forsteri) at Otago Peninsula, New Zealand

We examined the diet of New Zealand fur seals (Arctocephalus forsteri) at a rookery on Otago Peninsula, New Zealand, by analysing diagnostic remains from 500 faecal samples and 84 regurgitates collected between July 1993 and September 1994. In total, 27 taxa (species or genera) were identified. Small fish were numerically dominant in faecal samples, with five fish species (three species of lanternfish (Myctophidae), ahuru (Auchenoceros punctatus) and juvenile red cod (Pseudophycis bachus)) accounting for over 90% of prey items. Regurgitates occurred only seasonally and contained predominantly cephalopod remains (99% of prey items). Numerical analyses may prove misleading as an indicator of the composition of seal diet because the contribution of large fish that dominate estimates of prey biomass are underrepresented. Estimates of prey biomass were made by combining estimates from both faecal and regurgitate samples. Possible biases created by using this method are considered. A seasonal variation in prey composition was apparent, with arrow squid (Nototodarus sloanii) dominant in summer and autumn, replaced by a combination of barracouta (Thrysites atun), mackerel (Trachurus sp.) and New Zealand octopus (Octopus maorum) in winter and spring.