Effects of seismic surveys on New Zealand fur seals during daylight hours: Do fur seals respond to obstacles rather than airgun noise?

The responses of New Zealand fur seals (Arctocephalus forsteri) during a three‐dimensional marine seismic survey were recorded in the first quantified investigation of the effects of seismic exploration operations on otariid seals. The survey was over the continental slope off southern New Zealand, where fur seals dive to forage at night and rest on the surface during daylight hours. Data were restricted to daylight sightings from the source vessel while towed seismic gear was fully deployed, with comparisons made between fur seal responses when airguns were off and when airguns were operating at full power. Results were inconclusive. Comparisons were confounded because both sighting rate and distance first seen decreased with deteriorating sea state. The key finding of this study was that the source vessel and towed gear created physical obstacles that often generated responses from fur seals. A more thorough investigation is recommended in order to differentiate between responses to airgun noise and responses to physical obstacles, and improvements are suggested to rectify shortfalls in data collection that should generate conclusive outcomes.     

Mitochondrial DNA structure and colony expansion dynamics of New Zealand fur seals (Arctocephalus forsteri) around Banks Peninsula

New Zealand fur seals are one of many pinniped species that survived the commercial sealing of the eighteenth and nineteenth centuries in dangerously low numbers. After the enforcement of a series of protection measures in the early twentieth century, New Zealand fur seals began to recover from the brink of extinction. We examined the New Zealand fur seal populations of Banks Peninsula, South Island, New Zealand using the mitochondrial DNA control region. We identified a panmictic population structure around Banks Peninsula. The most abundant haplotype in the area showed a slight significant aggregated structure. The Horseshoe Bay colony showed the least number of shared haplotypes with other colonies, suggesting a different origin of re-colonisation of this specific colony. The effective population size of the New Zealand fur seal population at Banks Peninsula was estimated at approximately 2500 individuals. The exponential population growth rate parameter for the area was 35, which corresponds to an expanding population. In general, samples from adjacent colonies shared 4.4 haplotypes while samples collected from colonies separated by between five and eight bays shared 1.9 haplotypes. The genetic data support the spill-over dynamics of colony expansion already suggested for this species. Approximate Bayesian computations analysis suggests re-colonisation of the area from two main clades identified across New Zealand with a most likely admixture coefficient of 0.41 to form the Banks Peninsula population. Approximate Bayesian computations analysis estimated a founder population size of approximately 372 breeding individuals for the area, which then rapidly increased in size with successive waves of external recruitment. The population of fur seals in the area is probably in the late phase of maturity in the colony expansion dynamic.     

Fur seals at Macquarie Island: post-sealing colonisation,trends in abundance and hybridisation of three species

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The first breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954–2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is significant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been affected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.     

Key fish species, northern fur seals, Callorhinus ursinus, and fisheries interactions involving walleye pollock, Theragra chalcogramma, in the eastern Bering Sea

The recent decline of the northern fur seal population breeding on the Pribilof Islands has not yet been explained. This study estimates the amounts and sizes of walleye pollock (the fur seal's main prey) removed by predatory fish, fur seals and commercial fisheries in the main fur seal feeding area in the eastern Bering Sea during summer 1985. Fur seals relied primarily on age-1 pollock during 1985, while predatory fish consumed pollock mainly of ages 0-1. The fishery took pollock older than age-3. This indicated no direct effect of fishery removal on fur seal prey abundance, at least during the study period. In the short term, the 1985 pollock fishery may have indirectly affected fur seal prey abundance in a positive manner by removing adult pollock that compete with fur seals for age-1 pollock.     

Multiple mating strategies explain unexpected genetic mixing of New Zealand fur seals with two congenerics in a recently recolonized population

Human impacts on natural systems can cause local population extinctions, which may promote redistribution of taxa and secondary contact between divergent lineages. In mammalian populations that have mating systems shaped by polygyny and sexual selection, the potential for hybridization to ensue and persist depends on individual and demographic factors. At Macquarie Island, a recently formed fur seal population is comprised of both sexes of breeding Antarctic (Arctocephalus gazella) and subantarctic (A. tropicalis) fur seals, and an itinerant collection of male New Zealand fur seals (A. forsteri), presumed to be non-breeders due to their absence from principle breeding areas. The mating system of the three species is described as resource-defence polygyny: males defend beach territories containing breeding females for exclusive mating rights. A recent genetic study identified a high level of hybridization in the population (17-30%), unexpectedly involving all three species. This study examined the source of involvement in breeding by A. forsteri with respect to mating strategies operating in the population. Ninety-five (10%) pups born from 1992 to 2003 were genetically identified as New Zealand hybrids. Most resulted from reproduction within territories by New Zealand hybrids of both sexes, although some were conceived extra-territorially, indicating that males successfully utilize strategies other than territory holding to achieve paternities. Female reproductive status influenced mating partner and mating location, and females without pups were more likely to conceive extra-territorially and with A. forsteri males. This study illustrates an important consequence of low heterospecific discrimination in a sympatric population of long-lived mammals.     

Pup growth of the New Zealand fur seal Arctocephalus forsteri on the Open Bay Islands, New Zealand

Growth of New Zealand fur seal pups was investigated at Taumaka, Open Bay Islands, New Zealand, from November 1974 to September 1976. Pups were weighed and curvilinear length, axillary girth and foreflipper length measured at about ages 55, 190, 235 and 290 days. Males are significantly heavier and larger than females at each age, wtih the exception of axillary girth at 235 days. Pups born during the austral summer of 1974–5 were smaller overall than were pups born during the following summer. This difference was so great that males aged 140 days in 1976 were larger and heavier than males aged 235 days in 1975. Circumstantial evidence suggests that the difference in growth rates of pups born during the two years may have been a consequence, either directly or indirectly, of environmental temperatures. Pups born during the warmer season (1974–5) had the slower growth.     

Aerobic dive limit: how often does it occur in nature?

Diving animals offer a unique opportunity to study the importance of physiological constraint in their everyday behaviors. An important component of the physiological capability of any diving animal is its aerobic dive limit (ADL). The ADL has only been measured in a few species. The goal of this study was to estimate the aerobic dive limit from measurements of body oxygen stores and at sea metabolism. This calculated ADL (cADL) was then compared to measurements of diving behavior of individual animals of three species of otariids, the Antarctic fur seal, Arctocephalus gazella, the Australian sea lion, Neophoca cinerea, and the New Zealand sea lion, Phocarctos hookeri. Antarctic fur seals dove well within the cADL. In contrast, many individuals of both sea lion species exceeded the cADL, some by significant amounts. Australian sea lions typically dove 1.4 times longer than the cADL, while New Zealand sea lions on average dove 1.5 times longer than the cADL. The tendency to exceed the cADL was correlated with the dive pattern of individual animals. In both Antarctic Fur Seals and Australian sea lions, deeper diving females made longer dives that approached or exceeded the cADL (P<0.01, r(2)=0.54). Australian and New Zealand sea lions with longer bottom times also exceeded the cADL to a greater degree. The two sea lions forage on the benthos while the fur seals feed shallow in the water column. It appears that benthic foraging requires these animals to reach or exceed their aerobic dive limit.     

Behavioural Effects of Tourism on Oceanic Common Dolphins,Delphinus sp., in New Zealand: The Effects of Markov Analysis Variations and Current Tour Operator Compliance with Regulations

Common dolphins, Delphinus sp., are one of the marine mammal species tourism operations in New Zealand focus on. While effects of cetacean-watching activities have previously been examined in coastal regions in New Zealand, this study is the first to investigate effects of commercial tourism and recreational vessels on common dolphins in an open oceanic habitat. Observations from both an independent research vessel and aboard commercial tour vessels operating off the central and east coast Bay of Plenty, North Island, New Zealand were used to assess dolphin behaviour and record the level of compliance by permitted commercial tour operators and private recreational vessels with New Zealand regulations. Dolphin behaviour was assessed using two different approaches to Markov chain analysis in order to examine variation of responses of dolphins to vessels. Results showed that, regardless of the variance in Markov methods, dolphin foraging behaviour was significantly altered by boat interactions. Dolphins spent less time foraging during interactions and took significantly longer to return to foraging once disrupted by vessel presence. This research raises concerns about the potential disruption to feeding, a biologically critical behaviour. This may be particularly important in an open oceanic habitat, where prey resources are typically widely dispersed and unpredictable in abundance. Furthermore, because tourism in this region focuses on common dolphins transiting between adjacent coastal locations, the potential for cumulative effects could exacerbate the local effects demonstrated in this study. While the overall level of compliance by commercial operators was relatively high, non-compliance to the regulations was observed with time restriction, number or speed of vessels interacting with dolphins not being respected. Additionally, prohibited swimming with calves did occur. The effects shown in this study should be carefully considered within conservation management plans, in order to reduce the risk of detrimental effects on common dolphins within the region.     

Ménage à trois on Macquarie Island: hybridization among three species of fur seal (Arctocephalus spp.) following historical population extinction

Human-induced changes to natural systems can cause major disturbances to fundamental ecological and population processes and result in local extinctions and secondary contacts between formerly isolated species. Extensive fur seal harvesting during the nineteenth century on Macquarie Island (subantarctic) resulted in extinction of the original population. Recolonization by three species has been slow and complex, characterized by the establishment of breeding groups of Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis) and presumed nonbreeding (itinerant) male New Zealand fur seals (Arctocephalus forsteri). One thousand and seven pups from eight annual cohorts (1992-2003) were analysed using mitochondrial control region data (RFLP) and 10 microsatellite loci to estimate species composition and hybridization. Antarctic fur seals predominated, but hybridization occurred between all three species (17-30% of all pups). Involvement of New Zealand fur seals was unexpected as females are absent and males are not observed to hold territories during the breeding season. The proportion of hybrids in the population has fallen over time, apparently owing to substantial influxes of pure Antarctic and subantarctic individuals and non-random mating. Over 50% of New Zealand hybrids and 43% of Antarctic-subantarctic hybrids were not F(1), which indicates some degree of hybrid reproductive success, and this may be underestimated: simulations showed that hybrids become virtually undetectable by the third generation of backcrossing. While human impacts seem to have driven novel hybridization in this population, the present 'time slices' analysis suggests some biological resistance to complete homogenization.     

Holocene changes in the ecology of northern fur seals: insights from stable isotopes and archaeofauna

The remains of northern fur seals (Callorhinus ursinus) are among the most abundant of pinniped elements recovered from mainland coastal archaeological sites in both California and Oregon. This is surprising as all contemporary northern fur seals breed exclusively on offshore islands, primarily at high latitudes, and the species is otherwise pelagic. The vulnerability of these animals to human predation suggests that either humans were foraging much further offshore than has been presumed or alternatively that the ecology of these animals has shifted during the late Holocene. We used isotopic and archaeofaunal analysis of the remains of pinnipeds from the middle to late Holocene of central and northern California to clarify the breeding and foraging behavior, and migration patterns of these ancient animals. The carbon and nitrogen isotope compositions of ancient northern fur seals reveal that these animals fed as far offshore as they do today, and that they remained at middle latitudes throughout the year. From an archaeological site at Moss Landing, California, we identified 16 skeletal elements from at least 12 very small northern fur seal pups. From another site near Mendocino, California, we identified the remains of at least 6 pups. We estimate the size and age of 5 of the young animals using sex-specific regressions of body length on the short dentary length derived from measurements of modern specimens. Our estimates indicate these ancient pups were substantially smaller, and therefore younger, than modern 3-month-old northern fur seal pups from similar latitudes and their nitrogen isotope compositions suggest they had not been weaned. As present-day northern fur seals do not leave their rookeries until they are at least 4 months old, we consider it highly unlikely that these ancient pups swam to these mainland locations from some distant island rookery. While there are numerous nearshore rocky outcrops along the Mendocino Coast, which may have supported small breeding colonies, the Moss Landing site is centered on a 40-km-long sandy beach, and is more than 120 km from what at the time were the nearest offshore islands. We conclude that northern fur seal adult females, subadults, and pups whose remains were recovered at the Moss Landing archaeological site must have been taken at a mainland rookery. Evidence that northern fur seals once bred on the mainland at this central California location suggests that the abundant remains of these animals at numerous other archaeological sites along the California coast also reflect the presence of nearby mainland rookeries. Based on the relative abundance of their remains in ancient human occupation sites and the widespread distribution of sites where their remains have been found, it appears that northern fur seals were once the predominant pinniped throughout a region where they now only rarely occur. Furthermore, their presence along the central and northern California coasts appears to have once severely limited the distribution of other pinnipeds, which are now common to the region.     

The role of seabirds and seals in the survival of coastal plants: lessons from New Zealand Lepidium (Brassicaceae)

Six of the eight indigenous New Zealand Lepidium species are coastal, and have restricted or reduced distributions. One is extinct and the remainder are considered threatened with extinction. This limited distribution is in marked contrast to their apparent abundance in the eighteenth and early nineteenth centuries (1760s–1830s). Accounts from the voyages of Cook, Surville and d'Urville describe L. oleraceum as an abundant coastal plant which was collected extensively for use as an antiscorbutic. However, by the late 19th century, resident botanists were expressing concern about the marked decline in coastal species of Lepidium, a decline which has continued to the present. Ecologically, coastal species of Lepidium are similar, being restricted to open sites often close to the high tide mark. They are commonly associated with bird colonies, and occasionally with fur seal colonies. Traditionally their decline has been attributed to introduced herbivores. However, wild grazing animals were not common until the end of the 19th century, well after the initial decline had occurred. Other possible reasons for their decline include herbivory and predation by rats, and by fungal and invertebrate pests of cultivated Brassicaceae, overcollecting and coastal development. However, we suggest that a major factor in the decline of coastal Lepidium species was a decline in coastal seabirds through predation and seals through culling. Seabirds and seals are critical for the survival of Lepidium species by keeping sites open through disturbance, dispersing seed, and providing nutrient enrichment for plant growth, and their loss has resulted in decline of habitat for Lepidium.     

Individual Foraging Strategies Reveal Niche Overlap between Endangered Galapagos Pinnipeds

Most competition studies between species are conducted from a population-level approach. Few studies have examined inter-specific competition in conjunction with intra-specific competition, with an individual-based approach. To our knowledge, none has been conducted on marine top predators. Sympatric Galapagos fur seals (Arctocephalus galapagoensis) and sea lions (Zalophus wollebaeki) share similar geographic habitats and potentially compete. We studied their foraging niche overlap at Cabo Douglas, Fernandina Island from simultaneously collected dive and movement data to examine spatial and temporal inter- and intra-specific competition. Sea lions exhibited 3 foraging strategies (shallow, intermediate and deep) indicating intra-specific competition. Fur seals exhibited one foraging strategy, diving predominantly at night, between 0–80 m depth and mostly at 19–22 h. Most sea lion dives also occurred at night (63%), between 0–40 m, within fur seals'' diving depth range. 34% of sea lions night dives occurred at 19–22 h, when fur seals dived the most, but most of them occurred at dawn and dusk, when fur seals exhibited the least amount of dives. Fur seals and sea lions foraging behavior overlapped at 19 and 21 h between 0–30 m depths. Sea lions from the deep diving strategy exhibited the greatest foraging overlap with fur seals, in time (19 h), depth during overlapping time (21–24 m), and foraging range (37.7%). Fur seals foraging range was larger. Cabo Douglas northwest coastal area, region of highest diving density, is a foraging “hot spot” for both species. Fur seals and sea lions foraging niche overlap occurred, but segregation also occurred; fur seals primarily dived at night, while sea lions exhibited night and day diving. Both species exploited depths and areas exclusive to their species. Niche breadth generally increases with environmental uncertainty and decreased productivity. Potential competition between these species could be greater during warmer periods when prey availability is reduced.     

A comparison of Salmonella serotypes isolated from New Zealand sea lions and feral pigs on the Auckland Islands by pulsed-field gel electrophoresis

The Salmonella serotypes S. Cerro and S. Newport were isolated from New Zealand sea lions (Phocarctos hookeri) and feral pigs on the Auckland Islands in the New Zealand subantarctic region. The isolates were typed by pulsed-field gel electrophoresis using Xba1 as the restriction enzyme. The isolates were indistinguishable, which suggests that Salmonella infection cycles between sea lions and pigs in this environment. Apart from a previous isolation from a single New Zealand fur seal (Arctocephalus forsteri), S. Newport has not been recorded in any animals from New Zealand, but it is associated with gastroenteritis in humans. Contamination of the marine environment by human waste is a possible source of infection for marine mammals and warrants further investigation.     

At-sea behavior of South American fur seals: Influence of coastal hydrographic conditions and physiological implication

At-sea behavior and effects of hydrographic conditions on the pelagic habitat use of South American fur seals (Arctocephalus australis) seasonally inhabiting the surrounding waters of shallow rocky reefs off Punta Mogotes (Mar del Plata, Argentina) were analyzed integrating geographic locations of fur seal groups (FSGs) with coastal hydrographic conditions and behavioral data in a Geographic Information System. Punta Mogotes rocky reefs represent a potentially high quality patch foraging area, crucial to a central place foraging species during their pelagic dispersion at sea. Fur seal behavior at-sea was strongly influenced by hydrographic conditions such us bathymetry, Beafourt sea state and sea surface current direction. Fur seals General Use Area (GUA) was associated with the 10 m isobaths, whereas Critical Use Area (CUA) was almost completely enclosed within the 5 m isobaths. A concentration-dispersion dynamic trend according to sea state was evident (GUA Beafourt ≤3 = 3.3 km² vs. GUA Beafourt >3 = 1.7 km²), with a “use area displacement” according to sea surface current direction. A general prevalence of long, at-sea resting periods (passive floating was the most frequently performed behavior, and usually for long periods) and a differential occurrence of each behavior associated with Beafourt sea states were detected. During calm seas (Beafourt ≤3), fur seals exhibit passive floating, occupying extended areas, and drifting according to sea surface current direction. With increasing sea states (Beafourt sea state >3), fur seals tended to perform shallow prolonged immersion and directional movements, and concentrated in restricted areas weakly affected by currents. The importance of floating periods at-sea, probably associated with resting and digestion, was interpreted as an energy conserving strategy that would allow an increase overall foraging efficiency. Results suggested that the ability of fur seals to perform certain behaviors that will allow completing physiological process and ultimately determine reproduction and survival success, would be conditioned by the hydrographic regime at foraging areas. This last could be extrapolated to other fur seal species spending long times at-sea, both as part of migration movements or during typical long foraging round trips.     

Resource-defense Polygyny and Male Territory Quality in the New Zealand Fur Seal

The polygynous New Zealand fur seal, Arctocephalus forsteri, breeds in densely-packed colonies with males defending exclusive territories. The distribution of individuals within a colony of these seals was monitored over three consecutive breeding seasons and behavioural thermoregulation was found to be an important factor influencing the site selection of both males and females. Shaded areas and pools of water were used by both sexes for cooling and use of these cooling substrates increased as rock surface temperature increased, resulting in a clumped distribution on hot days. Substrate preferences were tested experimentally by manipulating the availability of cooling substrates during two seasons. The number of females using an area increased significantly after shade or pools of water were added to that area. For males, pool additions resulted in increased use of those areas, while adding shade had no effect. Cooling substrates had a patchy distribution and could therefore be monopolised by territorial males. Using the number of females on a territory as a measure of male mating success, it was found that female numbers were most strongly positively correlated with the area of shaded substrate on a territory. Total territory area was also positively correlated with number of females. It is argued that thermoregulatory constraints are a major factor affecting female site choice, and that this in turn affects male mating success.     

Tuberculosis in a captive colony of pinnipeds

Tuberculosis was diagnosed in 10 of 16 otariid seals upon post mortem examination. The species involved were New Zealand fur seals (Arctocephalus forsteri), Australian sea lions (Neophoca cinerea) and an Australian fur seal (Arctocephalus pusillus doriferus). Five seals died, four as a direct result of mycobacterial infection. One seal died of unrelated disease. The remaining 10 animals were subsequently tuberculin tested and then killed and necropsied. Tuberculous lesions were seen in five. Gross pathological changes were most commonly seen in the respiratory system. However, a generalized infection, a case with lesions confined to the liver and draining lymph nodes, and a case with tuberculous meningitis also were seen. Histological lesions were characterized by spindle cell proliferation and necrosis without mineralization or giant cell formation. The mycobacteria isolated was identified as belonging to the Mycobacterium tuberculosis complex but it appeared to be unique. Intradermal tuberculin testing showed promise as a diagnostic aid; however, the results were not statistically significant. Circumstances suggest that the initial infection was present when the seals were captured from the wild.     

A panel of new microsatellite loci for genetic studies of antarctic fur seals and other otariids

Nine dinucelotide microsatellite loci were developed in the Antarctic fur seal Arctocephalus gazella. Each locus possessed between 4 and 9 alleles in a sample of twenty individuals sampled from Bird Island, South Georgia, and expected heterozygosity ranged from 0.52 to 0.84. All but one of the loci conformed to Hardy–Weinberg equilibrium and no evidence was found for genotypic disequilibrium. Additionally, all of the loci successfully cross-amplified in the South American fur seal Arctocephalus australis, the New Zealand fur seal Arctocephalus forsteri and the Steller’s sea lion Eumetopias jubatus, and six also yielded products in the more distantly related harbour seal Phoca vitulina and walrus Odobenus rosmarus. These loci should prove useful for studies of the population genetics of Antarctic fur seals and other important otariid species.     

Community reassembly: a test using limestone grassland in New Zealand

To examine community reassembly, we sampled grasslands on calcareous soil (4%–24% CaCO₃) in New Zealand that were largely composed of species introduced from Britain. We tested whether the British species had reassembled on New Zealand limestone into the same communities as they form on limestone in Britain. The vegetation of six New Zealand sites was sampled, each with ten 2 × 2 m quadrats that followed the standard methodology of the British National Vegetation Classification (NVC). Analysing species presence and cover using program TableFit with the full database of British species, the New Zealand species assemblages gave poor to moderate fits (40%–72%) to the communities of the NVC, and even then not to calcareous grassland, though one site did fit to a calcareous spring community. The poor fits can be partly attributed to the absence from New Zealand of many British calcareous-specialist species. On omitting from the NVC database all species not present in New Zealand, the fits increased somewhat to 48%–77%. Using this modified database, two sites fitted British calcareous grassland communities. These two sites are on thinner soil (<10 cm depth), under lower rainfall. Where fits were obtained to calcareous communities, the environment of the community in Britain matched very well that of the New Zealand site. It is concluded that environmental and perhaps biotic filtering has been strong enough in some sites to assort alien species into the same species assemblages as they form in their native range, indicating the Deterministic model of community structure. However, the absence of some species has prevented full reassembly.