John P. Y. Arnould

Foraging behaviour of Antarctic fur seals during periods of contrasting prey abundance

1. Foraging behaviour of Antarctic fur seals rearing pups at Bird Island, South Georgia, was assessed using at-sea activity patterns measured by electronic time-depth recorders. Information was obtained for a total of 75 individuals and 191 foraging trips to sea over five reproductive seasons from 1988/89 to 1992/93; this included one season (1990/91) of low prey abundance. A method was developed to divide the diving record up into logical units or bouts which differed from past methods used for defining bouts of behaviour. 2. Foraging trips were significantly longer in 1990/91 than in the other years. There were significant differences between years in the proportion of time spent foraging when at sea and in the distribution of foraging through the day and night. These differences probably represent behavioural responses to changes in prey distribution and abundance and were reflected in the frequency of occurrence of different types of foraging behaviour. 3. Four types of foraging bout were recognized using a cluster analysis. Type I (short) bouts were of short duration (17 min) and occurred mainly during daytime and at dusk. They probably represented exploratory behaviour. Type II (long) bouts occurred mainly at night and were of long duration (80 min). They increased in frequency in 1990/91 when food was scarce and 61-73% of time spent foraging was in these bouts. Type III (shallow) bouts occurred mainly at night, were of short duration (12 min) and represented feeding close to the surface, possibly in association with other, surface-feeding krill predators. Shallow bouts accounted for 8-14% of time spent foraging. Type IV (deep) bouts were of medium duration (19 min) and represented feeding at greater depth (40-50 m) than other bout types. They were most abundant around dawn. 4. Mean dive duration during bouts exceeded the theoretical aerobic dive limit on > 30% of occasions for short, long and deep bouts. There were positive correlations between mean dive duration and surface interval duration for most of these bout types in most years. This suggested that long dives incurred a cost in terms of the amount of time spent at the surface between dives. 5. The study demonstrated that female fur seals invest a significantly greater effort in foraging during periods of low prey abundance by both increasing the time spent foraging and by increasing activity during foraging. This could represent a 30-50% increase in the costs of foraging during years of low food abundance.

The diet of Antarctic fur seals Arctocephalus gazella during the breeding season at South Georgia

The diet of lactating female Antarctic fur sealsArctocephalus gazella at South Georgia was investigated during the pup-rearing period (January/March) of 1991–1994. Antarctic krillEuphausia superba was the main prey item, occurring in 88% of all scats (n=497), whereas fish occurred in 47% and squid in 5% of all scats. There was considerable intra- and inter-annual variation in the characteristics of krill taken by fur seals. The distribution of krill sizes taken suggests that fur seals are not actively selecting particular sizes of krill and, therefore, that the krill in the diet reflects the krill available around South Georgia. The absence of group 3 krill (44–48 mm in length) in the South Georgia area, as indicated by their absence in the diet of seals, is suggested as a possible reason for low availability of krill and the subsequent reproductive failure among krill predators. The frequency of occurrence of fish was much higher than in previous studies; the pattern of fish consumption showed a consistent seasonal pattern in 3 of the 4 years studied. Of the total number of the myctophidProtomyctophum choriodon, the most numerous fish taxon, 98% were taken between early February and the middle of March.Champsocephalus gunnari andLepidonotothen larseni agg., which both feed on krill, dominated the fish component of the diet outside this period and together constituted 94% of the total estimated biomass of fish consumed. The intra- and inter-annual variability in the diet of Antarctic fur seals emphasise the need for diet studies to be conducted during the entire pup-rearing periods of several years.

Accuracy of ARGOS locations of Pinnipeds at-sea estimated using Fastloc GPS.

Background ARGOS satellite telemetry is one of the most widely used methods to track the movements of free-ranging marine and terrestrial animals and is fundamental to studies of foraging ecology, migratory behavior and habitat-use. ARGOS location estimates do not include complete error estimations, and for many marine organisms, the most commonly acquired locations (Location Class 0, A, B, or Z) are provided with no declared error estimate. Methodology/Principal Findings We compared the accuracy of ARGOS locations to those obtained using Fastloc GPS from the same electronic tags on five species of pinnipeds: 9 California sea lions (Zalophus californianus), 4 Galapagos sea lions (Zalophus wollebaeki), 6 Cape fur seals (Arctocephalus pusillus pusillus), 3 Australian fur seals (A. p. doriferus) and 5 northern elephant seals (Mirounga angustirostris). These species encompass a range of marine habitats (highly pelagic vs coastal), diving behaviors (mean dive durations 2–21 min) and range of latitudes (equator to temperate). A total of 7,318 ARGOS positions and 27,046 GPS positions were collected. Of these, 1,105 ARGOS positions were obtained within five minutes of a GPS position and were used for comparison. The 68th percentile ARGOS location errors as measured in this study were LC-3 0.49 km, LC-2 1.01 km, LC-1 1.20 km, LC-0 4.18 km, LC-A 6.19 km, LC-B 10.28 km. Conclusions/Significance The ARGOS errors measured here are greater than those provided by ARGOS, but within the range of other studies. The error was non-normally distributed with each LC highly right-skewed. Locations of species that make short duration dives and spend extended periods on the surface (sea lions and fur seals) had less error than species like elephant seals that spend more time underwater and have shorter surface intervals. Supplemental data (S1) are provided allowing the creation of density distributions that can be used in a variety of filtering algorithms to improve the quality of ARGOS tracking data.

Dive behaviour, foraging locations, and maternal-attendance patterns of Australian fur seals (Arctocephalus pusillus doriferus)

The dive behaviour, foraging locations, and colony-attendance patterns of female Australian fur seals (Arctocephalus pusillus doriferus ) from Kanowna Island (39°10 ′S, 146°18′E) in Bass Strait, southeastern Australia, were determined throughout lactation during 1997–1999. Foraging-trip durations increased as lactation progressed, being shortest in summer (3.71 ± 0.24 days; mean ± 1 SE) and longest in winter (6.77 ± 0.57 days, P < 0.05), but maternalattendance periods did not differ in duration (1.70 ± 0.10 days, P > 0.5). Individual mean attendance periods and trip durations were positively correlated ( r2 = 0.21,P < 0.005). Diving commenced shortly after seals left the colony (2.6 ± 0.4 h), was continuous for long periods (up to 36 h), occurred mostly during daylight hours, and lacked regular diel variation in depth. The majority of dives (78%) were typically U-shaped and reached depths corresponding to the pre vailing depths in Bass Strait (65–85 m), indicating that these animals forage mostly on the benthos of the shallow con tinental shelf in this region. Such behaviour is unusual for fur seals but is reminiscent of that of some sea lion species. Mean dive durations varied between 2.0 and 3.7 min (maximum 8.9 min) and the theoretical aerobic dive limit (3.91– 4.26 min) was exceeded on 17.3% of dives. Dive frequency (8.3 ± 0.6/h) and the proportion of time at sea spent div ing (40.7 ± 2.1%) were weakly negatively related to the duration of the foraging trip ( r2 = 0.07,P < 0.004, andr2 = 0.13, P < 0.0001, respectively). Data from at-sea locations showed that lactating females forage almost exclusively within Bass Strait during all seasons. Résumé: Nous avons étudié le comportement de plongée, les zones d’alimentation et la présence dans la colonie chez des femelles de l’Otarie d’Australie ( Arctocephalus pusillus doriferus ) dans l’île de Kanowna (39°10 ′S, 146°18′E), dans le détroit de Bass, dans le sud-est de l’Australie, pendant toute la période d’allaitement, de 1997 à 1999. La durée des excursions de quête de nourriture augmente pendant toute la période d’alllaitement et c’est en été qu’elle est le plus courte (3,71 ± 0,24 jours; moyenne ± 1 erreur type) et en hiver qu’elle est le plus longue (6,77 ± 0,57 jours, P < 0,05), mais la durée de la présence maternelle ne varie pas selon la saison (1,70 ± 0,10 jour, P > 0,5). La durée de la présence individuelle et la durée des excursions sont en corrélation positive ( r2 = 0,21,P < 0.005). Les otaries commencent à plonger peu après leur départ de la colonie (2,6 ± 0,4 h), plongent pendant de longues périodes conti nues (jusqu’à 36 h), surtout durant les heures de clarté et la profondeur de leurs plongées ne suit pas de pattern parti culier selon l’heure. La majorité des plongées (78 %) sont des plongées en U jusqu’aux profondeurs correspondant aux profondeurs les plus communes du détroit de Bass (65–85 m), ce qui indique que les otaries cherchent leur nourriture surtout dans le benthos de la plate-forme continentale de cette région. Un tel comportement est inusité chez une otarie, mais rappelle celui de certains lions de mer. La durée moyenne des plongées va de 2,0 à 3,7 min (maximum 8,9 min) et la limite théorique d’une plongée aérobie (3,91–4,26 min) s’est trouvée dépassée dans 17,3 % des plongées. La fréquence des plongées (8,3 ± 0,6/h) et la proportion du temps en mer consacré aux plongées (40,7 ± 2,1 %) sont en corrélation négative faible avec la durée des excursions (respectivement r2 = 0,07,P < 0,004 etr2 = 0,13,P < 0,0001). Les données sur les sites en mer démontrent que les femelles qui allaitent se nourrissent presque exclusivement dans le détroit de Bass, en toute saison. [Traduit par la Rédaction] Arnould and Hindell 48

Marine debris surveys at Bird Island, South Georgia 1990-1995

The Antarctic marine environment has relatively few direct sources of man-made marine debris; however, there is concern over the dangers posed to wildlife by increasing amounts of such debris. Between 1990 and 1995 beached debris was monitored at Bird Island, South Georgia. This was part of a programme developed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) to monitor compliance with waste disposal under MARPOL and the effectiveness of additional regulations to reduce entanglement of marine mammals and birds. Overall, and in all but one year, the highest incidence of debris occurred during the winter months when 75% of all items were collected. The most numerous category overall (76%), and in all samples since 1991, was pieces of synthetic line as used in the long-line fishery for the Patagonian toothfish Dissostichus eleginoides around South Georgia. Packaging bands (6%) and polythene bags (6%) were the next commonest items. There was a substantial increase in the number of items found ashore in 1995 which coincided with an apparent increase in the long-line fishing effort in the area. The increase in the incidence of synthetic line found ashore corresponds to the increase in the proportion of Antarctic fur seal Arctocephalus gazella entangled in this material at South Georgia in a parallel study. An increasing use of environmentally-aware scientific observers on all fishing vessels, leading to an increased awareness of existing legislation, should result in less man-made debris entering the marine environment in the area around South Georgia.

Measuring the Body Composition of Antarctic Fur Seals (Arctocephalus gazella): Validation of Hydrogen Isotope Dilution

We examined the accuracy of hydrogen isotope dilution (tritium and deuterium) as a means of determining total body water (TBW), and hence body composition, by comparison with whole-carcass chemical analysis in five adult female and four pup Antarctic fur seals. On average, tritium isotope (HTO) dilution overestimated TBW by 1.92% ± 1.00% (n = 9). Deuterium isotope (D₂O) dilution also overestimated TBW (1.71% ± 1.74%, n = 5), but this trend was not significant. The following equations were developed for predicting TBW from hydrogen isotope dilution estimates: TBW (kg) = 0.11 + 0.97 · HTO space (kg) (r² = 0.999, n = 9, P < 0.0001) and TBW (kg) = 2.10 + 0.89 · D₂O space (kg) (r² = 0.980, n = 5, P < 0.001). Whole-carcass chemical analysis showed adult females were composed of 14.5% ± 1.0% total body lipid (TBL), whereas pups were composed of only 9.4% ± 1.0% lipid. Adult females had lower TBW contents (60.1% ± 0.7%) than pups (67.6% ± 1.2%) and, consequently, higher energy contents (adults, 10.59 ± 0.30 MJ · kg⁻¹; pups, 8.24 ± 0.41 MJ · kg⁻¹). Pups had higher ratios of TBW to lean body mass (LBM) (0.747 ± 0.009) than adults (0.707 ± 0.004), which indicates they had not yet reached chemical maturity. The following best-fit predictive equations based on TBW and body mass (BM) were developed for TBL, total body protein (TBP), total body ash (TBA), and total body gross energy (TBGE): TBL (kg) = 0.875 · BM (kg) - 1.187 · TBW (kg) - 0.633 (adults); TBL (%) = 66562 - 0.845 · TBW (%) (pups); TBP (kg) = 0.058 · BM (kg) + 0.209 · TBW (kg) + 0.996 (adults); TBP (kg) = 0.267 · BM (kg) - 0.130 · STBW (kg) + 0.087 (pups); TBA (kg) = 0.071 · TBW (kg) - 0.088 (adults and pups); TBGE (MJ · kg⁻¹) = 34.1 - 0.391 · TBW (%) (adults); TBGE (MJ · kg⁻¹) = 31. 7 - 0.347 · TBW (%) (pups). With the use of these predictive equations, hydrogen isotope dilution is an accurate means of determining body composition in live Antarctic fur seals. Differences in these relationships between adults and pups, and in comparison to those in phocids, emphasize the need for the use of equations derived from appropriate data sets when predicting body composition in pinnipeds.

Milk consumption, body composition and pre-weaning growth rates of Australian fur seal (Arctocephalus pusillus doriferus) pups

Pre-weaning growth rates, body composition, milk consumption and mass gain efficiency were measured in Australian fur seal Arctocephalus pusillus doriferus pups born in two consecutive breeding periods. Australian fur seals have the highest birth mass of any fur seal species (male 8.3 kg; female 7.2 kg). While their absolute pre-weaning growth rate (male 62 g·day−1; female 53 g·day−1) is similar to that of other temperate latitude fur seals, they have the longest birth-mass doubling time of any otariid species (134–136 days). Daily milk consumption increased from 400 g·day−1 (5 MJ·day−1) after birth to 675 g·day−1 (13.7 MJ·day−1) at age 210 day. However, mean mass-specific milk consumption (41 g·kg−1) is substantially lower than in other otariid species (58–70 g·kg−1) and, combined with a low mass gain efficiency (0.12 g·g−1), contributes to the low mass-specific growth rates observed. There were no significant differences in either absolute or mass-specific milk consumption between the sexes. Significant differences, however, were found between the sexes in the body composition of pups with females generally having larger body lipid stores than males for any given mass. Peak milk yield by Australian fur seal females is estimated at 0.60 MJkg−0.75, substantially less than in Antarctic fur seals. The low level of maternal energy transfer in Australian fur seals may reflect the relatively low marine productivity of their foraging areas.

Trends in entanglement of Antarctic fur seals (Arctocephalus gazella) in man-made debris at South Georgia

A study conducted at South Georgia in 1988/1989 indicated that several thousand Antarctic fur seals were entangled mainly in man-made material originating from fishing vessels. Consequently, the authority responsible for the management of Southern Ocean marine resources (CCAMLR) actively campaigned for compliance with the MARPOL provisions relating to waste disposal at sea, and for cutting of any material unavoidably jettisoned which could form collars to entangle seals. Five subsequent years of recording entangled fur seals confirms that entanglement is a persistent problem, although its incidence has been halved in recent years. However, the South Georgia fur seal population has approximately doubled in the same period, so that the overall total of animals entangled may even have increased. Nevertheless, because most seals entangled are juvenile males, the current rate of entanglement will have negligible effects on the reproductive rate of the South Georgia population, especially in relation to its current rate of population increase. The reduction in observed entanglement incidence cannot be attributed mainly to improved waste disposal practices because it has coincided with substantial reductions in fishing activity around South Georgia. However, the particular reduction in entanglement due to packing bands and the fact that all such bands washed ashore over the last 2 years have been cut, does suggest a general improvement in standards of waste disposal on Southern Ocean fishing vessels.

Fasting metabolism in Antarctic fur seal (Arctocephalus gazella) pups.

The metabolism of 52-73-day old Antarctic fur seal pups from Bird Island, South Georgia, was investigated during fasting periods of normal duration while their mothers were at sea foraging. Body mass decreased exponentially with pups losing 3.5-3.8% of body mass per day. Resting metabolic rate also decreased exponentially from 172-197 ml (O2) x min(-1) at the beginning of the fast and scaled to M(b)(0.74) at 2.3 times the level predicted for adult terrestrial mammals of similar size. While there was no significant sex difference in RMR, female pups had significantly higher (F(1,18)=6.614, P<0.019) mass-specific RMR than male pups throughout the fasting period. Fasting FMR was also significantly (t(15)=2.37, P<0.035) greater in females (823 kJ x kg(-1) x d(-1)) than males (686 kJ x kg(-1) x d(-1)). Average protein turnover during the study period was 19.3 g x d(-1) and contributed to 5.4% of total energy expenditure, indicating the adoption of a protein-sparing strategy with a reliance on primarily lipid catabolism for metabolic energy. This is supported by observed decreases in plasma BUN, U/C, glucose and triglyceride concentrations, and an increase in beta-HBA concentration, indicating that Antarctic fur seals pups adopt this strategy within 2-3 days of fasting. Mean RQ also decreased from 0.77 to 0.72 within 3 days of fasting, further supporting a rapid commencement of protein-sparing. However, RQ gradually increased thereafter to 0.77, suggesting a resumption of protein catabolism which was not substantiated by changes in plasma metabolites. Female pups had higher TBL (%) than males for any given mass, which is consistent with previous findings in this and other fur seal species, and suggests sex differences in metabolic fuel use. The observed changes in plasma metabolites and protein turnover, however, do not support this.

Continued population recovery by Australian fur seals

Australian fur seals (Arctocephalus pusillus doriferus) are conspicuous, top-level predators in coastal waters of south-eastern Australia that were over-harvested during the 1800s and have had a delayed recovery. A previous species-wide estimate of live pups in 2002 recorded a near-doubling of annual pup production and a 5% annual growth rate since the 1980s. To determine if pup production increased after 2002, we estimated live pup numbers in 2007. Pups were recorded at 20 locations: 10 previously known colonies, three newly recognised colonies and seven haul-out sites where pups are occasionally born. Two colonies adjacent to the Victorian coast accounted for 51% of live pups estimated: Seal Rocks (5660 pups, 25.9%) and Lady Julia Percy Island (5574 pups, 25.5%). Although some colonies were up and some were down in pup numbers, the 2007 total of 21 882 ± 187 (s.e.) live pups did not differ significantly from a recalculated estimate of 21 545 ± 184 in 2002, suggesting little change to overall population size. However, the colonisation of three new sites between 2002 and 2007 indicates population recovery has continued.