A PROTRACTED FORAGING AND ATTENDANCE CYCLE IN FEMALE JUAN FERNÁNDEZ FUR SEALS

Previous studies of fur seals suggest that the attendance patterns and consequent temporal patterning of energy transfer from mother to pup follows a latitudinal cline. While data from subpolar, tropical, and some temperate latitude species support the postulated cline, data for the temperate latitude Juan Fernández fur seal do not. Maternal foraging trips and associated visits ashore were the longest of all otariids studied to date. The first foraging trip postpartum averaged 10.2 d ( n = 51 females, range 1–22.5), foraging trips combined averaged 12.3 d ( n = 100, range 1.0-25.0), and visits ashore averaged 5.3 d ( n = 91, range 0.3-15.8) over the three seasons of study. Only duration of lactation was intermediate between subpolar and tropical strategies as predicted. Dive records suggest that these females feed almost exclusively at night at depths of less than 10 m and at distances of more than 500 km offshore. The prey species of this fur seal, primarily myctophids and squid, migrate to the surface at night and are patchily distributed. Foraging trip length varied between years in conjunction with shifts in seasurface temperature and type of prey consumed. We suggest that distribution of prey, irrespective of latitude, dictates foraging patterns of fur seals and leads to the exceptionally long foraging trips and visits ashore observed in this species.     

VARIATION IN THE FORAGING LOCATION OF ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA) AND THE EFFECTS ON DIVING BEHAVIOR

This study investigated how female Antarctic fur seals adapt their foraging behavior, over time scales of days, to spatial unpredictability in the distribution of their food. Lactating Antarctic fur seals are central-place foragers that feed on highly patchy but spatially and temporally dynamic food. We measured the foraging distribution of 28 fur seals to test whether variation in foraging trip durations was reflected in variation in the location of foraging and the diving behavior of seals at sea. Based on the maximum distance travelled from the breeding beach, three categories of foraging trips were denned: those to the continental shelf area ( n = 12, median = 71 km), to oceanic water ( n = 11, median =164 km), and to farther offshore oceanic waters ( n = 5, median = 260 km). Trip duration and mean surface speed were positively correlated with the maximum distance travelled from the breeding beach. Seals on longer trips spent proportionally less of their time submerged, but there was no significant difference in the total number of dives or the total time spent foraging by seals in relation to trip duration. Evidence from this study and previous work investigating energy gain suggests that an animal on a longer foraging trip could potentially have a higher mean energy return per dive than a similar animal on a shorter foraging trip. Evidence presented suggests that the type of foraging trip (near or far) is not predetermined by the animal but may be a simple response to the stochastic distribution of the resources available.     

INDICES OF BODY CONDITION AND BODY COMPOSITION IN FEMALE ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA)

An attempt was made to develop simple, inexpensive, rapid means of determining body composition in Antarctic fur seals ( Arctocephalus gazella ). Measurements of total body water ( TBW ) and total body lipid ( TBL ), obtained by hydrogen isotope dilution, were compared to the results of bioelectrical impedance analysis ( BIA ) and morphometric indices of body condition in 52 adult females. TBW was weakly correlated with BIA measurements of resistance ( v = -0.30, P < 0.03). Conductor volume (length2/resistance) was more highly correlated with TBW ( r = 0.75, P < 0.0001) and the inclusion of mass into the predictive equation improved the correlation further ( r = 0.95, P < 0.0001). A body condition index (mass/length) previously used in pinniped studies was positively correlated to TBL ( r = 0.77, P < 0.0001) validating its use as a relative index of condition. However, body mass alone was highly correlated to TBW ( r = 0.94, P < 0.0001) and appears to provide a simple, rapid means of estimating body composition in adult females. This technique may also be applicable to juvenile male Antarctic fur seals.     

ENTANGLEMENT IN MAN-MADE DEBRIS OF ANTARCTIC FUR SEALS AT BIRD ISLAND, SOUTH GEORGIA

Neck collars of man-made marine debris were seen on 208 Antarctic fur seals (and removed from 170) during the 142 days of the 1988–1989 pup-rearing season at Bird Island, South Georgia. This represents at least 0.1% of the total Bird Island population and a minimum of 0.4% of animals in the best covered areas; a maximum value might approach 1%. Polypropylene straps (packaging bands) formed 59% of collars, nylon string (16%), fishing net (13%) and six other materials comprised the rest. Males accounted for 71% of entanglements, 88% of which were of young (1–4 yr old) animals; females accounted for 64% of animals older than this. Obvious physical injury was being caused to 30% of animals and only on 19% of animals was the collar loose enough potentially to come off. The magnitude of the problem at South Georgia is similar to that with northern fur seals at the Pribilof Islands, where a significant population decline has occurred concurrently. Antarctic fur seals are still increasing in numbers but stricter controls on the jettisoning of debris into the Southern Ocean ate needed if the entanglement problem is not to increase beyond the level of a potential threat.     

DIET OF SOUTH AMERICAN FUR SEALS (ARCTOCEPHALUS AUSTRALIS) IN ISLA DE LOBOS, URUGUAY

The diet of Arctocephalus australis was studied through fecal analysis, from September of 1995 to May of 1998, in Isla de Lobos (35°01'50"S-54°53'00"W), Uruguay. A total of 539 scats analyzed indicated that the weakfish ( Cynoscion guatucupa ), the cutlasfish ( Trichiurus lepturus ), the anchoveta ( Engraulis anchoita ), the anchovy ( Anchoa marinii ), and cephalopods were the main prey consumed by these fur seals. Prey richness was higher during January. The diet of A. australis varied between years, apparently related to changes in prey availability. C. guatucupa and E. anchoita decreased while T. lepturus and cephalopods increased from 1996 to 1998. South American fur seals fed on fish ranging in length from 5.4 to 104.8 cm and from 0.7 to 629.9 g in wet mass. However, the mean mass of the main items was never more than 200 g. Observations suggests that A. australis is a trophic generalist with the potential to prey on a wide range of species, although most of the diet is comprised of relatively few species. Fur seals and artisan fisheries both took C. guatucupa , with fur seals taking younger individuals (1–2 yr) than artisan fisheries (> 3 yr).     

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.     

ISLAND BIOGEOGRAPHY OF GALÁPAGOS LAVA LIZARDS (TROPIDURIDAE: MICROLOPHUS): SPECIES DIVERSITY AND COLONIZATION OF THE ARCHIPELAGO

The "lava lizards" ( Microlophus ) are distributed throughout the Galápagos Archipelago, and consist of radiations derived from two independent colonizations. The "Eastern Radiation" includes M. bivittatus and M. habeli endemic to San Cristobal and Marchena Islands. The "Western Radiation" includes five to seven historically recognized species distributed across almost the entire Archipelago. We combine dense geographic sampling and multilocus sequence data to estimate a phylogenetic hypothesis for the Western Radiation, to delimit species boundaries in this radiation, and to estimate a time frame for colonization events. Our phylogenetic hypothesis rejects two earlier topologies for the Western Radiation and paraphyly of M. albemarlensis , while providing strong support for single colonizations on each island. The colonization history implied by our phylogeny is consistent with general expectations of an east-to-west route predicted by the putative age of island groups, and prevailing ocean currents in the Archipelago. Additionally, combined evidence suggests that M. indefatigabilis from Santa Fe should be recognized as a full species. Finally, molecular divergence estimates suggest that the two colonization events likely occurred on the oldest existing islands, and the Western Radiation represents a recent radiation that, in most cases, has produced species that are considerably younger than the islands they inhabit.     

ANALYSIS OF SWIM VELOCITIES DURING DEEP AND SHALLOW DIVES OF TWO NORTHERN FUR SEALS, CALLORHINUS URSINUS

Swim velocities at 15-sec intervals and maximum depth per dive were recorded by microprocessor units on two "mixed diver" adult female northern fur seals during summer foraging trips. These records allowed comparison of swim velocities of deep (>75 m) and shallow (<75 m) dives.
Deep dives averaged 120 m depth and 3 min duration; shallow dives averaged 30 m and 1.2 min. Mean swim velocities on deep dives were 1.8 and 1.5 m/sec for the two animals; mean swim velocities on shallow dives were 1.5 and 1.2 m/sec. The number of minutes per hour spent diving during the deep and shallow dive patterns were 11 and 27 min, respectively.
Swim velocity, and hence, relative metabolic rate, did not account for the differences in dive durations between deep and shallow dives. The long surface durations associated with deep dives, and estimates of metabolic rates for the observed swim velocities, suggest that deep dives involve significant anaerobic metabolism.     

VOCAL INDIVIDUALITY IN MOTHER AND PUP SOUTH AMERICAN FUR SEALS, ARCTOCEPHALUS AUSTRALIS

South American fur seals breeding in Peru are subjected to levels of maternal aggression, and subsequent pup mortality, that are higher than has been reported for any other otariid species. For mothers and pups to maintain contact with each other, a mutual recognition system should exist to facilitate reunion and avoid misdirection of maternal effort. We recorded vocalizations of mothers and pups at Punta San Juan, Peru, during the 1994 and 1995 breeding seasons. Sixteen acoustic variables were measured from a total of 560 calls from 15 mothers and 13 pups. Multivariate analysis showed that calls were variable in several acoustic dimensions. While calls of both mothers and pups showed low variability within and high variability among individuals, mothers' calls were more individualistic. On average, discriminant-function analysis correctly assigned 60% of pup calls and 70% of mother calls to the individual that produced them. Characteristics of the fundamental frequency were most important for distinguishing among mothers, while pup calls, which typically contained less harmonic structure, could be differentiated by formant-like frequency ranges. Thus, calls of mother and pup South American fur seals appear to exhibit sufficient stereotypy to allow for recognition and discrimination among individuals.     

STUDY OF VITAMIN A SUPPLEMENTATION IN CAPTIVE NORTHERN FUR SEALS (CALLORHINUS URSINUS) AND ITS EFFECT ON SERUM VITAMIN E

Two experiments were conducted to determine the effect of vitamin A supplementation on serum vitamin E in adult female northern fur seals ( Callorhinus ursinus ). In the first experiment five animals received, in addition to their routine dietary multivitamin supplement, a high-level vitamin A supplement (53 μmol retinyl palmitate/d) for 30 d. Five seals consuming their routine dietary supplement served as controls. Serum vitamin E decreased significantly in animals receiving high-level vitamin A supplements. At the end of 30 d serum vitamin E averaged 18.6 μg/mL in the control animals and 13.4 μg/mL in the animals receiving the high-Ieve1 vitamin A supplement. In experiment 2 ten animals received the high level vitamin A supplement for 60 d. After 30 d, serum vitamin E levels were reduced, but by 60 d had returned to baseline levels. However, the ratio of serum vitamin E to phospholipid, another index of vitamin E status, remained decreased. Although the exact mechanism of interaction is unknown, this study shows that when providing vitamin supplements for captive pinnipeds, vitamin interactions must be considered. The vitamin A supplementation currently used by some institutions seems unnecessary and may have detrimental effects on vitamin E status.     

BUFFERING CAPACITY OF THE LOCOMOTOR MUSCLE IN CETACEANS: CORRELATES WITH POSTPARTUM DEVELOPMENT, DIVE DURATION, AND SWIM PERFORMANCE

Skeletal muscles of marine mammals must support the metabolic demands of exercise during periods of reduced blood flow associated with the dive response. Enhanced muscle buffering could support anaerobic metabolic processes during apnea, yet this has not been fully investigated in cetaceans. To assess the importance of this adaptation in the diving and swimming performance of cetaceans, muscle buffering capacity due to non-bicarbonate buffers was measured in the longissimus dorsi of ten species of odontocete and one mysticete. Immature specimens from a subset of these species were studied to assess developmental trends. Fetal and neonatal cetaceans have low buffering capacities (range: 34.8–53.9 slykes) that are within the range measured for terrestrial mammals. A lengthy developmental period, independent of muscle myoglobin postnatal development, is required before adult levels are attained. Adult cetacean buffering capacities (range: 63.7–94.5 slykes) are among the highest values recorded for mammals. Cetacean species that demonstrate extremely long dive durations or high burst speed swimming tend to have greater buffering capacities. However, the wide range of body size across cetaceans may complicate these trends. Enhanced muscle buffering capacity may enable small-bodied species to extend breath-hold beyond short aerobic dive limits for foraging or predator evasion when necessary.