SUCCESSFUL USE OF A TRANSLOCATION PROGRAM TO INVESTIGATE DIVING BEHAVIOR IN A MALE AUSTRALIAN FUR SEAL, ARCTOCEPHALUS PUSILLUS DORIFERUS

This study reports some of the first foraging behavior data collected for male fur seals. A nonbreeding male Australian fur seal, Arctocephalus pusillus doriferus , captured at a commercial salmon farm in southern Tasmania, Australia, was relocated 450 km from the site of capture. The animal was equipped with a geolocating time-depth recorder that recorded diving behavior and approximate location for the 14.4 d that it took the seal to travel down the east coast of Tasmania and be recaptured at the salmon farm. During its time at sea, the seal spent most of its time over the relatively shallow shelf waters. It spent 30% of its time ashore on a number of different haul-out sites. The deepest dive was 102 m and the maximum duration was 6.8 min. "Foraging" type dives made up 31.2% of the time at sea and had a median duration of 2.5 min and a median depth of 14 m. The seal performed these dives more commonly during the latter part of its time at sea, while it was on the east coast. Unlike other fur seal species studied to date, there was no evidence of a diurnal foraging pattern; it made dives at all times of the day and night.     

CAN NEAR INFRARED SPECTROSCOPY BE USED TO IMPROVE ASSESSMENT OF MARINE MAMMAL DIETS VIA FECAL ANALYSIS?

We investigated the utility of Near Infrared Spectroscopy as a means to quantify the diet of seals via analysis of feces. A pilot study showed that we could accurately determine the proportion of each species in a mixture of flesh of two species of fish and one squid. Having done so, we then assessed whether the same capacity existed for fecal material. Again we used two species of fish and one squid as the diet components offered to two captive seals (a California sea lion and an Australian fur seal). Five of the six calibrations could accurately and precisely quantify how much of a given diet component the seal had eaten the previous day from an NIR scan of the feces. NIR spectroscopy is theoretically a viable way to quantify seal diets. We discuss the logistical requirements for development of calibration equations for application to a field study. These may be prohibitive in many cases, but in others may be offset by the particular circumstances or objectives of the study. Adoption of NIRS may confer significant benefits in these circumstances.     

INTERACTIONS BETWEEN SOUTH AFRICAN FUR SEALS and THE PURSE-SEINE FISHERY

Operational interactions occur between South African (Cape) fur seals and the purse-seine fishery in South Africa. Seals eat fish from the nets but the main concern is the activity of seals causing fish to sound, resulting in loss, or partial loss of the catch. Detectable loss occurs on approximately 5% of hauls. In addition to this, smaller quantities may be lost on each haul as seals depress the net float line while moving into and out of the net. The cost of seal interference is difficult to quantify because the mass of fish lost is not known, and the loss is essentially one of additional fishing time required to fill the total allowable catch for the fishery. An estimate of the cost is calculated as between 1.6% and 4.1% of the landed value of the fishery. Some seals are killed by fishermen when they pose a potential threat to the safety of the crew aboard, and some may drown if caught in the net or pump. Overall this is probably fewer than a thousand seals per year. It is also known that if seals are thought to be disturbing the fish, these seals near the nets may be deliberately killed by purse-seine fishermen. Overall this mortality, whether deliberate or incidental, is probably negligible in terms of the population size of South African fur seals.     

EVALUATION OF AN EFFECTIVE METHOD TO ESTIMATE AGE OF CAPE FUR SEALS USING GROUND TOOTH SECTIONS

Teeth of known-age Cape fur seals Arctocephalus pusillus pusillus were used to validate age estimated from ground sections. In the canines, dentine growth layer groups (GLGs) reflected age accurately but no reliable readings could be obtained from GLGs in the cementum. Upper canines were the most suitable for age estimation. By contrast, in the postcanines where the cementum is thicker, only GLGs in the cementum could be used for age determination, but not with the same accuracy as for dentine in the canines. Therefore, it is recommended that GLGs in the dentine be used to determine age in the Cape fur seal. However, pulp cavities in canines closed at about 13 yr and consequently GLGs in the cementum of the postcanines should be used where the pulp cavities of canines are closed. Accurate estimation of age is not possible from the dentine of older animals.     

STATISTICAL METHODS FOR ESTIMATING NUMBERS OF CAPE FUR SEAL PUPS FROM AERIAL SURVEYS

The Cape fur seal Arctocephalus pusillus of South Africa and Namibia breeds in 23 colonies. Aerial surveys have been used to estimate numbers of pups during breeding seasons from December 1971 to December 1978, and the results have been presented by Shaughnessy (1987). In this paper we develop statistical methods for estimating these pup numbers, as well as variances of the estimates. We demonstrate a significant increase in numbers of seal pups between 1971 and 1976; the rate of increase is estimated to be 3.2% per annum.     

Analysis of Australian fur seal diet by pyrosequencing prey DNA in faeces

DNA-based techniques have proven useful for defining trophic links in a variety of ecosystems and recently developed sequencing technologies provide new opportunities for dietary studies. We investigated the diet of Australian fur seals ( Arctocephalus pusillus doriferus ) by pyrosequencing prey DNA from faeces collected at three breeding colonies across the seals' range. DNA from 270 faecal samples was amplified with four polymerase chain reaction primer sets and a blocking primer was used to limit amplification of fur seal DNA. Pooled amplicons from each colony were sequenced using the Roche GS-FLX platform, generating > 20 000 sequences. Software was developed to sort and group similar sequences. A total of 54 bony fish, 4 cartilaginous fish and 4 cephalopods were identified based on the most taxonomically informative amplicons sequenced (mitochondrial 16S). The prevalence of sequences from redbait ( Emmelichthys nitidus ) and jack mackerel ( Trachurus declivis ) confirm the importance of these species in the seals' diet. A third fish species, blue mackerel ( Scomber australasicus ), may be a more important prey species than previously recognised. There were major differences in the proportions of prey DNA recovered in faeces from different colonies, probably reflecting differences in prey availability. Parallel hard-part analysis identified largely the same main prey species as did the DNA-based technique, but with lower species diversity and no remains from cartilaginous prey. The pyrosequencing approach presented significantly expands the capabilities of DNA-based methods of dietary analysis and is suitable for large-scale diet investigations on a broad range of animals.     

COMPARATIVE POPULATION DYNAMICS OF FUR SEALS

The population sizes, trends, exploitation, and life history parameters for the ten fur seal species and subspecies are summarized. The largest population is that of Arctocephalus pusillus pusillus with approximately two million seals, and the smallest is A. townsendi with approximately 7,000 individuals. Most populations are legally protected, although controlled harvesting may occur. None of the fur seal populations is currently known to be decreasing. Data are presented for parameters related to the survival of pups, juveniles, adults, and territorial males, and to reproduction, including the age of attainment of territorial status, aggregation sizes, age of first parturition, pregnancy rates, sex ratios of young animals, and information on the birth seasons of the different species. Since pinnipeds are often of concern in fisheries management, their daily consumption rates are of importance, and consequently data on body masses are summarized and the paucity of data on consumption rates as a function of body mass noted. A simplified age-structured model is developed, and the results of this model are compared with results from more detailed models based on two published life tables for Callorhinus ursinus. This comparison shows that the use of the simplified age-structured model is justified to explore changes in population growth rate. However, the simplified model does show exaggerated age structure effects compared to the more detailed models. This model is used to compare the population dynamics of those species for which sufficient data are available. Areas in which limited, or no, data are available for the different fur seal species are highlighted.     

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.     

FATTY ACID COMPOSITION OF FATS FROM THE URUGUAYAN FUR SEAL (ARCTOCEPHALUS AUSTRALIS ZIMMERMANN)

The composition and properties of commercial oil collected from Uruguayan fur seals ( Arctocephalus australis Zimmermann) during 1985, 1986 and 1987 are reported. Oil recovered from some organs (kidney, heart, liver) and blubber were also analyzed. All have compositions similar to oils from other marine animals in commercial use, containing high percentages of long chain and polyunsaturated fatty acids.