Seal Island Research Articles

Predatory behaviour of white sharks (carcharodon carcharias) at seal island, south africa

between 1997 and 2003, there were 2088 natural predations by white sharks (carcharodon carcharias) on cape fur seals (arctocephalus pusillus pusillus) and 121 strikes on towed seal-shaped decoys were documented from observation vessels at seal island, south africa. white sharks at seal island appear to selectively target lone, incoming young of the year cape fur seals at or near the surface. most attacks lasted <1 min and consisted of a single breach, with predatory success rate decreasing rapidly with increasing duration and number of subsequent breaches. a white shark predatory ethogram, composed of four phases and 20 behavioural units, is presented, including four varieties of initial strike and 11 subsequent behaviour units not previously defined in the literature. behaviour units scored from 210 predatory attacks revealed that, for both successful and unsuccessful attacks, polaris breach was the most commonly employed initial strike, while surface lunge was the most frequent second event, closely followed by lateral snap. examination of video footage, still images, and tooth impressions in decoys indicated that white sharks at seal island bite prey obliquely using their anterolateral teeth via a sudden lateral snap of the jaws and not perpendicularly with their anterior teeth, as previously supposed. analysis of white shark upper tooth morphology and spacing suggest the reversed intermediate teeth of white sharks occur at the strongest part of the jaw and produce the largest wound. white shark predatory success at seal island is greatest (55%) within one hour of sunrise and decreases rapidly with increasing ambient light; the sharks cease active predation on seals when success rate drops to ±40%; this is the first evidence of cessation of foraging at unproductive times by any predatory fish. at seal island, white shark predatory success is significantly lower at locations where frequency of predation is highest, suggesting that white sharks may launch suboptimal strikes in areas of greatest intraspecific competition; this is the first evidence of social influence on predation in any elasmobranch. idiosyncratic predatory behaviours and elevated success rates of known individual white sharks at seal island suggest some degree of trial-and-error learning. a hypothetical decision tree is proposed that models predatory behaviour of white sharks attacking cape fur seals at the surface.

Adult Survival Estimates From Two Atlantic Puffin (Fratercula Arctica) Colonies in The Gulf of Maine

AbstractWe report survival probabilities for 148 breeding adult Atlantic Puffins (Fratercula arctica) monitored through capture-mark-resight at two colonies for 11 years (1992–2003). The colonies, Eastern Egg Rock and Seal Island, are ∼42 km apart in the Gulf of Maine. Support for competing models in the program MARK suggests constant survival of 0.95 ± 0.01 (SE) that is independent of colony. Our high survival probability is consistent with published estimates for Atlantic Puffins and other long-lived seabirds. No time-variance contrasts with many long-term seabird studies, which often report high survival in most years, broken occasionally by low-survival events. However, a post-hoc observation of survival estimates from the time-dependent model suggests that there may have been at least two low-survival events in our time-series; sparse data may have precluded detection by our models. In this study, each bird received an individually engraved, plastic, field-readable leg band, as well as the standard metal band. Using an index of band readability, we show that plastic bands wore rapidly, resulting in accumulating losses of engraved characters through time. Degradation and loss of marks is a common source of overdispersion in capture-mark-re-encounter data and results in underestimated sampling variances. In the presence of a 70% reduction in band readability over eight years, an estimate of the adjusted overdispersion factor (ĉ = 1.14) identified very little overdispersion in our data. Overdispersion was avoided by double banding and intensively resighting metal bands.Estimation de la Survie Adulte de Deux Colonies de Fratercula arctica dans le Golfe du Maine

ADULT SURVIVAL ESTIMATES FROM TWO ATLANTIC PUFFIN (FRATERCULA ARCTICA) COLONIES IN THE GULF OF MAINE

We report survival probabilities for 148 breeding adult Atlantic Puffins (Fratercula arctica) monitored through capture-mark-resight at two colonies for 11 years (1992–2003). The colonies, Eastern Egg Rock and Seal Island, are ∼42 km apart in the Gulf of Maine. Support for competing models in the program MARK suggests constant survival of 0.95 ± 0.01 (SE) that is independent of colony. Our high survival probability is consistent with published estimates for Atlantic Puffins and other long-lived seabirds. No time-variance contrasts with many long-term seabird studies, which often report high survival in most years, broken occasionally by low-survival events. However, a post-hoc observation of survival estimates from the time-dependent model suggests that there may have been at least two low-survival events in our time-series; sparse data may have precluded detection by our models. In this study, each bird received an individually engraved, plastic, field-readable leg band, as well as the standard metal band. Using an index of band readability, we show that plastic bands wore rapidly, resulting in accumulating losses of engraved characters through time. Degradation and loss of marks is a common source of overdispersion in capture-mark-re-encounter data and results in underestimated sampling variances. In the presence of a 70% reduction in band readability over eight years, an estimate of the adjusted overdispersion factor (ĉ = 1.14) identified very little overdispersion in our data. Overdispersion was avoided by double banding and intensively resighting metal bands. Estimation de la Survie Adulte de Deux Colonies de Fratercula arctica dans le Golfe du Maine

Natural mortality of puffadder shysharks due to Cape fur seals and black‐backed kelp gulls at Seal Island, South Africa

Natural mortality of puffadder shysharks Haploblepharus edwardsii due to two species of marine tetrapod, the Cape fur seal Arctocephalus pusillus pusillus and the black‐backed kelp gull Larus dominicanis vetula, is reported. These data constitute the first multiple observations of natural mortality of any cartilaginous fish due to object play or kleptoparasitism by marine tetrapods. Evidence of range extension of the puffadder shyshark to False Bay, South Africa is presented.

Seabirds as indicators of changes in marine ecosystems: ecological monitoring on Machias Seal Island.

Changes in marine ecosystems can be manifested in many different ways, on different temporal and spatial scales. Seabirds are top consumers in marine foodwebs and offer opportunities to detect and assess the biological effects of changes in physical parameters (sea-surface temperature [SST], salinity, depth of thermocline etc.) of the marine ecosystem. We compare six-eight years' of data on the biology (diet, and breeding success) of four species of seabird (arctic tern Sterna paradisaea and common tern S. hirundo, which feed at the sea surface; and Atlantic puffin Fratercula antica and razorbill Alca torda, which dive 30-60 m for their prey) breeding on Machias Seal Island (MSI) in the Bay of Fundy with both our own meteorological and oceanographic measurements, and with standard measurements from conventional sources. These are compared with fisheries data on changes in the main prey of all the seabirds concerned (juvenile or '0-group' herring Clupea harengus) which are the most direct link between the seabirds and the physical properties of the marine system. We explore relationships between seabird productivity and diet, and other aspects of both herring biology (larval surveys, and fat content) and oceanography (SST data from the island, and remotely sensed data from the entrance to the Bay of Fundy). Timing of laying by puffins followed SST variation at neither the local (MSI) nor regional scales, but at the scale of the North Atlantic, following the trend of populations breeding off northern Norway. The proportion of herring in the diet of terns over 6 years varied inversely with herring larval abundance the previous fall; this relationship was not statistically significant in the puffin and razorbill. A major new finding is the considerable (approximately 50%) inter-annual variation in the energy density (fat content) of juvenile herring that are the main seabird prey; breeding success of both species of tern varied in parallel with the energy density of juvenile herring in the diet until the last two years of the study, when sandlance (Ammodytes sp.) and euphausid shrimp predominated in the diet. Our long-term research approach combines traditional population monitoring (of numbers of breeding birds) with demographic, behavioural and environmental monitoring, to provide new understanding of the marine ecosystem as well as of seabirds.

Seasonal shifts in the provisioning behavior of chinstrap penguins, Pygoscelis antarctica.

Whether parents are able to adapt food gathering to rising offspring demands, or if they are controlled largely by extrinsic factors, is important for understanding key limits on fitness. Over seven breeding seasons, we studied the provisioning behavior of chinstrap penguins, Pygoscelis antarctica, at Seal Island, Antarctica, during parents' transition to leave broods of one or two chicks unguarded. By measuring the frequency, duration, and diel timing of foraging trips and the quantity of prey brought to chicks, we examined the extent to which variation in parents' feeding behavior could be attributed to provisioning costs which increase with chick growth. Estimates of the energy content of food loads were combined with foraging patterns and brood requirements to model parents' seasonal provisioning budget. The frequency of foraging trips increased from the guard to post-guard phase and was higher, and the seasonal effect larger, in parents with two chicks. The duration of overnight trips (~16h) increased with seasonally increasing night length; diurnal trip duration (~8h) showed no seasonal pattern. Birds exhibited a seasonal shift to diurnal foraging, a trend that was generally weaker in parents of smaller broods. Food loads increased with chick mass only in parents of one chick; parents of two chicks had larger but more constant food loads. Based on per trip calculations, parents foraging overnight could not have delivered to two-chick broods enough food to meet their demands unless chicks were small. Diurnal foragers (regardless of brood size) and overnight foragers with one chick could meet brood demands at chicks' peak mass. The combined daily effort of parents indicated that mated pairs on average had ample resources to meet chick demands through most of rearing. A brief period when demands could not be met was predicted in two-chick broods just before chicks were left unguarded and again as they neared fledging. Our findings suggest that penguins both increased provisioning frequency and favored foraging under higher light intensity in conjunction with increasing chick demands, tactics which required parents to leave chicks unattended. The ability to maintain intrinsic control over provisioning has bearing on how penguins may be limited by extrinsic constraints. Prey surveys conducted annually near colonies show abundant resources 10-20km offshore with no consistent seasonal shifts in abundance. These findings support a prominent role for intrinsic factors in the foraging decisions of chinstrap penguins.

Hunting and social behaviour of leopard seals (Hydrurga leptonyx) at Seal Island, South Shetland Islands, Antarctica

AbstractThe hunting behaviour of leopard seals Hydrurga leptonyx was monitored opportunistically at Seal Island, South Shetland Islands, during the austral summers from 1986/87 to 1994/95. Leopard seals used several methods to catch Antarctic fur seal pups Arctocephalus gazella and chinstrap penguins Pygoscelis antarctica, and individuals showed different hunting styles and hunting success. One to two leopard seals per year were responsible for an average of 60% of observed captures of fur seal pups. Leopard seals preyed on penguins throughout the summer, but preyed on fur seal pups only between late December and mid‐February. Hunting behaviour differed significantly between different locations on the island; fur seals were hunted only at one colony, and penguins were hunted in several areas. The relative abundance of prey types, size of prey in relation to predator, and specialization of individual leopard seals to hunt fur seal prey probably influence individual prey preferences among leopard seals. On five occasions, two leopard seals were seen together on Seal Island. Possible interpretations of the relationship between the inter‐acting leopard seals included a mother–offspring relationship, a consorting male–female pair, and an adult leopard seal followed by an unrelated juvenile. In two incidents at Seal Island, two leopard seals were observed interacting while hunting: one seal captured fur seal pups and appeared to release them to the other seal. Observations of leopard seals interacting during hunting sessions were difficult to confirm as co‐operative hunting, but they strongly implied that the two seals were not agonistic toward one another. The hunting success of individual leopard seals pursuing penguins or fur seals is probably high enough for co‐operative hunting not to become a common hunting strategy; however, it may occur infrequently when it increases the hunting productivity of the seals.

Hunting and social behaviour of leopard seals (Hydrurga leptonyx) at Seal Island, South Shetland Islands, Antarctica

The hunting behaviour of leopard seals Hydrurga leptonyx was monitored opportunistically at Seal Island, South Shetland Islands, during the austral summers from 1986/87 to 1994/95. Leopard seals used several methods to catch Antarctic fur seal pups Arctocephalus gazella and chinstrap penguins Pygoscelis antarctica, and individuals showed different hunting styles and hunting success. One to two leopard seals per year were responsible for an average of 60% of observed captures of fur seal pups. Leopard seals preyed on penguins throughout the summer, but preyed on fur seal pups only between late December and mid-February. Hunting behaviour differed significantly between different locations on the island; fur seals were hunted only at one colony, and penguins were hunted in several areas. The relative abundance of prey types, size of prey in relation to predator, and specialization of individual leopard seals to hunt fur seal prey probably influence individual prey preferences among leopard seals. On five occasions, two leopard seals were seen together on Seal Island. Possible interpretations of the relationship between the inter-acting leopard seals included a mother–offspring relationship, a consorting male–female pair, and an adult leopard seal followed by an unrelated juvenile. In two incidents at Seal Island, two leopard seals were observed interacting while hunting: one seal captured fur seal pups and appeared to release them to the other seal. Observations of leopard seals interacting during hunting sessions were difficult to confirm as co-operative hunting, but they strongly implied that the two seals were not agonistic toward one another. The hunting success of individual leopard seals pursuing penguins or fur seals is probably high enough for co-operative hunting not to become a common hunting strategy; however, it may occur infrequently when it increases the hunting productivity of the seals.

Northstar-Geology, Exploration History, and Development Status, Beaufort Sea, Alaska

Exploration for oil at Northstar has been long and costly. Northstar leases were first acquired in 1979 at a joint state and federal sale by Shell Oil, Amerada Hess, and Texas Eastern. The Northstar Unit is 6 mi offshore and about 4 mi northeast of the Point McIntyre Field. Oil was first discovered in Shell's Seal Island 1 in 1983. Five additional appraisal wells were drilled (1983-1986) from two man-made gravel islands in 40 ft of water. Early engineering estimates put the cost of development at $ 1.6 billion. In February 1995, BP Exploration (Alaska) acquired a 98 % interest in the Northstar Unit from Amerada Hess and Shell Oil. When developed by BP, Northstar will be the first oil produced from federal leases in Alaska. To date, the oil industry has invested in excess of $ 140 million in exploration and appraisal operations. An additional $ 90 million was spent on lease bonus bids. The giant Prudhoe Bay and Kuparuk Fields lie along the Barrow Arch. This arch is bounded to the north by a rift margin that deepens into the present-day offshore region. Northstar is located among a series of down-stepping faults off this northern rift margin of the Prudhoe Kuparuk high. The structure is a gently south-dipping northwest-trending faulted anticline. The crest of the structure is located near 10,850 ft subsea. The primary reservoir is the Ivishak Formation (325 ft thick) of the Sadlerochit Group. This is the same primary reservoir at Prudhoe Bay, approximately 12 mi to the south. At Northstar the Ivishak is a high-energy, coarse-grained conglomeratic facies of the Ivishak Formation. The primary lithology is a pebbly chert to quartz conglomerate with occasional sandstone. This very high net to gross reservoir appears to contain no regionally continuous permeability barriers. Cementation has reduced primary porosity to less than 15 %. Accurate porosity estimates are difficult to make due to the coarse-grained nature of the lithology and the presence of kaolinite and microporous chert. Permeability is highly variable, but averages 10 to 100 mDarcies. Oil is a very light and volatile 42 API crude with approximately 2,100 ft3 of gas per stock tank barrel of oil. This oil is very different from the heavier oils (26) found to the south in Prudhoe Bay. Estimated recoverable oil reserves range from 100 to 160 million barrels. A free-standing drilling rig is required at Northstar because the reserves are beyond extended-reach drilling techniques from shore-based facilities. The current development plan is to expand the existing Seal Island to about 5 acres. This is significantly less than Endicott's 40-acre island. The proposed drilling and produc tion island will be accessed by summer barges and winter ice roads. Oil, gas, and water will be processed at a stand-alone facility and then sent to shore via a subsurface pipeline. Northstar will have the first Arctic subsea pipeline in Alaska to transport oil to shore facilities (TAPS). Preliminary tests in Spring 1996 were very successful in demonstrating the technology to successfully bury a subsea pipeline safely in the Arctic.

THE IMPACT OF THE FUR SEAL INDUSTRY ON THE DISTRIBUTION AND ABUNDANCE OF CAPE FUR SEALS ARCTOCEPHALUS PUSILLUS PUSILLUS ON THE EASTERN CAPE COAST OF SOUTH AFRICA

SUMMARY The present paper provides a review of the former distribution and abundance of Cape fur seals, Arctocephalus pusillus pusillus, off the Eastern Cape coast of South Africa based on available historical records. It identifies the distribution of Eastern Cape seals before commercial sealing began; documents sealing activities off the Eastern Cape coast during the 19th and 20th centuries, and discusses current population trends in relation to past exploitation regimes. The importance of the Eastern Cape population is discussed in relation to the total population. Cape fur seals were valued primarily for their fine quality furs. Other products included oil from the blubber; leather from skins of old seals; and vitamin A from the liver. Exploitation by Europeans began near the Cape of Good Hope in 1610. By the end of the 19th century more than 20 colonies had been extirpated. On the Eastern Cape coast, Cape fur seals inhabited six islands in Algoa Bay (Stag, Seal, Black Rocks, St. Croix, Jahleel and Brenton) and two sites in Plettenberg Bay (Seal Point on the Robberg Peninsula and Beacon Island). Soon after British settlement of Algoa Bay in 1820, the St. Croix and Bird Islands were leased to individuals by the governor of the Cape Colony (Lord Charles Sommerset) at an annual rental, for fishing and sealing purposes. More than 18 000 seals were killed by commercial sealers in Algoa Bay between 1822 and 1825; > 2 935 between 1831 and 1850; c. 3 516 between 1851 and 1876; > 1 763 in 1907 and 1908; and > 500 between 1943 and 1949. Harvest figures for Plettenberg Bay are unknown. Available evidence suggests that seals had been extirpated from St. Croix, Jahleel and Brenton Islands in the late 1850s; Seal Point between 1857 and 1890; Stag Island in the mid/late 1800s; Seal Island in the early 1900s; and Beacon Island in the late 1800s/early 1900s. Black Rocks was the only colony on the Eastern Cape coast to survive commercial sealing operations. Access to Black Rocks is difficult and for that reason sealing activities were irregular. Sealing operations on Black Rocks were terminated in 1949. At present, Black Rocks supports c. 700 seals. In the last 12 years the population has decreased by 82%. By destroying seal herds through commercial harvesting, and confining the population to Black Rocks, the population is unable to build up its numbers sufficiently to stimulate colonisation on neighbouring islands. Limited space for breeding seals on Black Rocks, and the influence of storms (gale force winds and high swells) restricts the number of pups that can be reared successfully. It is unlikely that the Black Rocks population can increase quickly enough to flow onto Seal and Stag Island, without being depleted by storms. The effect of man on the Seal, Stag and Black Rocks population is therefore a permanent one. Approximately 23 000 Cape fur seals may have occupied the Bird Island group before European exploitation. The current population for the Eastern Cape coast is considerably less than its historical size.

POPULATION GROWTH OF ANTARCTIC FUR SEALS: LIMITATION BY A TOP PREDATOR, THE LEOPARD SEAL?

Antarctic fur seals (Arctocephalus gazella) in the South Shetland Islands are recovering from 19th-century exploitation more slowly than the main population at South Georgia. To document demographic changes associated with the recovery in the South Shetlands, we monitored fur seal abundance and reproduction in the vicinity of Elephant Island during austral summers from 1986/1987 through 1994/1995. Total births, mean and variance of birth dates, and average daily mortality rates were estimated from daily live pup counts at North Cove (NC) and North Annex (NA) colonies on Seal Island. Sightings of leopard seals (Hydrurga leptonyx) and incidents of leopard seal predation on fur seal pups were recorded opportunistically during daily fur seal research at both sites. High mortality of fur seal pups, attributed to predation by leopard seals frequently observed at NC, caused pup numbers to decline rapidly between January and March (i.e., prior to weaning) each year and probably caused a long-term decline in the size of that colony. The NA colony, where leopard seals were never observed, increased in size during the study. Pup mortality from causes other than leopard seal predation appeared to be similar at the two sites. The number of pups counted at four locations in the Elephant Island vicinity increased slowly, at an annual rate of 3.8%, compared to rates as high as 11% at other locations in the South Shetland Islands. Several lines of circumstantial evidence are consistent with the hypothesis that leopard seal predators limit the growth of the fur seal population in the Elephant Island area and perhaps in the broader population in the South Shetland Islands. The sustained growth of this fur seal population over many decades rules out certain predator–prey models, allowing inference about the interaction between leopard seals and fur seals even though it is less thoroughly studied than predator–prey systems of terrestrial vertebrates of the northern hemisphere. Top-down forces should be included in hypotheses for future research on the factors shaping the recovery of the fur seal population in the South Shetland Islands.

Population Growth of Antarctic Fur Seals: Limitation by a Top Predator, the Leopard Seal?

Antarctic fur seals (Arctocephalus gazella) in the South Shetland Islands are recovering from 19th-century exploitation more slowly than the main population at South Georgia. To document demographic changes associated with the recovery in the South Shetlands, we monitored fur seal abundance and reproduction in the vicinity of Elephant Island during austral summers from 1986/1987 through 1994/1995. Total births, mean and variance of birth dates, and average daily mortality rates were estimated from daily live pup counts at North Cove (NC) and North Annex (NA) colonies on Seal Island. Sightings of leopard seals (Hydrurga leptonyx) and incidents of leopard seal predation on fur seal pups were recorded opportunistically during daily fur seal research at both sites. High mortality of fur seal pups, attributed to predation by leopard seals frequently observed at NC, caused pup numbers to decline rapidly between January and March (i.e., prior to weaning) each year and probably caused a long-term decline in the size of that colony. The NA colony, where leopard seals were never observed, increased in size during the study. Pup mortality from causes other than leopard seal predation appeared to be similar at the two sites. The number of pups counted at four locations in the Elephant Island vicinity increased slowly, at an annual rate of 3.8%, compared to rates as high as 11% at other locations in the South Shetland Islands. Several lines of circumstantial evidence are consistent with the hypothesis that leopard seal predators limit the growth of the fur seal population in the Elephant Island area and perhaps in the broader population in the South Shetland Islands. The sustained growth of this fur seal population over many decades rules out certain predator–prey models, allowing inference about the interaction between leopard seals and fur seals even though it is less thoroughly studied than predator–prey systems of terrestrial vertebrates of the northern hemisphere. Top-down forces should be included in hypotheses for future research on the factors shaping the recovery of the fur seal population in the South Shetland Islands.

Foraging modes of chinstrap penguins:contrasts between day and night

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 165:161-172 (1998) - doi:10.3354/meps165161 Foraging modes of chinstrap penguins: contrasts between day and night John K. Jansen*, Peter L. Boveng, John L. Bengtson National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration, 7600 Sand Point Way N.E., Building 4, Seattle, Washington 98115-0070, USA *E-mail: john.jansen@noaa.gov Penguins rely on vision to travel and hunt at sea. Vision in marine predators, particularly those hunting phototactic prey under a broad range of light intensities, must be better understood to realize how these species respond to changes in their environment. We studied the effects of daily cycles in light intensity on visual predators by examining the duration and timing of chinstrap penguins' Pygoscelis antarctica foraging trips and the size, composition, and timing of their meals. We used radio telemetry and stomach-contents sampling to study adult penguins that were provisioning chicks during the summers of 1993 and 1994 at Seal Island, Antarctica. The penguins rarely initiated or terminated foraging trips at night, but otherwise varied the timing and duration of trips to sea. Cluster analyses using departure and arrival times revealed 5 distinct modes of foraging: 3 were strictly diurnal (early, mid-, and late) and 2 were partly nocturnal (overnight and extended). Durations of diurnal trips (4 to 11 h) were shorter than overnight (13 to 14 h) and extended trips (18 to 22 h). Early and mid-diurnal trips and extended trips were significantly shorter in 1993 than in 1994; late diurnal and overnight trip durations did not differ between years. Diurnal foraging was most common in 1993, whereas overnight foraging predominated in 1994. Shortened diurnal foraging in 1993 appears to have increased the frequency of diurnal foraging by allowing more parent birds to alternate diurnal trips within a single day and by reducing the incidence of birds extending diurnal foraging through the night. That penguins foraged more frequently by day when permitted by shorter trip durations (in 1993) suggests that they opted to forage diurnally whenever possible. Returning diurnal and overnight foragers had greater than 99 and 74% Antarctic krill Euphausia superba by weight in their stomachs, respectively. However, overnight foragers also returned with significant amounts of highly digested remains of pelagic fish, suggesting birds were in offshore waters taking fish during the night. In contrast, only 1 out of 40 diurnal foragers from both years combined had evidence of fish. Thus, the daily light cycle affected both the timing and duration of chinstrap penguin foraging as well as the type of prey consumed during trips to sea. Diel activity patterns · Diet composition · Foraging trip duration · Myctophid fish · Ecological monitoring · Pygoscelis antarctica · Euphausia superba Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 165. Publication date: May 07, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Dive bout organization in the Chinstrap penguin at seal island, antarctica

Diving behavior of 2 breeding Chinstrap penguins (Pygoscelis antarctica) was studied focusing first and primarily on dive bouts rather than dives themselves. Analysis of dive bout organization revealed (1) though there are differences between solitary dives and dive bouts in dive duration and dive depth, the first dives of dive bouts do not differ from solitary dives in the dive parameters, (2) mean dive duration during bout correlates positively to both mean dive depth during bout and mean surface interval during bout, while number of dives during bout negatively correlates to both cost (consumed energy) and duration of a dive cycle during bout. These findings suggest the following possibilities on foraging behavior of penguins: (1) their decision to repeat diving depends on the result of the first dive at a site, and the first dives of bouts would tend to be searching or evaluating dives though they would be also successful foraging dives, (2) they repeat diving at a foraging patch until foraging efficiency decrease to a threshold of diminishing returns.

Relationships between brood size and parental provisioning performance in chinstrap penguins during the chick guard phase

Chinstrap penguins (Pygoscelis antarctica) normally lay two eggs, but brood size is often reduced by mortality during incubation or after hatching. We hypothesized that this variation in brood size would affect the parents’ foraging behavior and their chick provisioning performance. We studied patterns of adult foraging trip duration and frequency, food load delivery, and chick growth rates in relation to brood size during the guard phase in four breeding seasons (1991–1994) on Seal Island, Antarctica. Within a given year, parents with two chicks made more frequent foraging trips to sea and may have transported larger food loads to the nest; however, the duration of foraging trips was unrelated to brood size. Overall, parents with two chicks spent ∼15% more time at sea than parents with only one chick. Both the frequency and duration of foraging trips varied between years. Foraging trip duration may partly reflect the birds’ foraging radius, which probably varies with time in response to shifts in krill distribution. Chick growth rate varied betwen years, but was related to brood size only in 1992, when chicks from two-chick broods grew significantly more slowly than chicks from one-chick broods. Food loads transported to chicks, as well as chick growth rates, were highest in 1994, when concurrent hydroacoustic studies indicated that regional krill biomass was severely depressed. This apparent anomaly suggests that the spatial scale of the krill survey may have been too coarse to detect some high-density krill aggregations within the penguins’ foraging range.

Using Animal Behavior for Conservation

To develop successful restoration programs for wildlife, conservation biologists should consider features of animal behavior to help design restoration plans. This paper presents case studies of the first restored colonies of Arctic Terns (Sterna paradisaea), Common Terns (S. hirundo) and Roseate Terns (S. dougallii), Atlantic Puffins (Fratercula arctica) and Leach's Storm-Petrels (Oceanodroma leucorhoa). These restoration projects are based on the use of two fundamental and commonly occurring features of colonial waterbird behavior: social facilitation and philopatry.Social facilitation, the influence of one animal's behavior on that of its associates, was adapted for conservation purposes by placing decoys and sound recordings at historic nesting islands to simulate established colonies. The use of decoys and audio recordings to simulate and encourage social facilitation is referred to as social attraction. Philopatry, the tendency for young birds to recruit to nesting populations at their natal home, was adapted for conservation purposes by translocating puffin chicks from a large colony at the center of the range to historic nesting islands at the southern, historic limit of the puffin's range where they were extirpated nearly a century earlier by excessive hunting for food and feathers. Young puffins, reared and released from artificial burrows at two historic sites learned the location of the release sites and eventually returned to the long-extinct colonies rather than their hatching place.To restore colonies of terns and puffins that were displaced by Herring and Great Black-backed Gulls, nesting population of these gulls were reduced at Eastern Egg Rock and Seal Island National Wildlife Refuge (NWR) to encourage recolonization by terns and puffins. Common, Arctic and Roseate Terns were attracted to island recolonization sites off mid-coast Maine, USA using decoys and 24-hour playback recordings. By 1996, Seal Island NWR was the largest Arctic Tern colony in Maine with 956 pairs and Eastern Egg Rock was the largest Roseate Tern colony in the state with 126 nesting pairs of this endangered species. These successes using social attraction are compared to tern restoration on Petit Manan Island, Maine where gull control alone resulted in recolonization. In this example, terns were absent for only 4 years and many were still living with a memory of nesting on the island. After gull removal, these birds quickly recolonized in the same year that gull control began. In contrast, using gull control and social attraction, it took 3 and 5 years respectively for terns to re-colonize Eastern Egg Rock and Seal Island NWR (where terns had not nested for 44 and 36 years). In these cases, no living terns with a memory of nesting on these islands were available for recolonization.Puffin colonies at Eastern Egg Rock and Seal Island NWR were restored by translocating 3-40 (average 17) day-old puffin chicks from Newfoundland, Canada (approx. 1610km distant). A total of 954 and 950 chicks were translocated to Eastern Egg Rock and Seal Island NWR respectively. These were captive-reared in individual sod burrows which were opened at their entrance after the first week. The chicks were banded and permitted to fledge into the adjacent ocean. Translocated puffins began to return when two years old; many also visited nearby puffin colonies where some eventually nested. Recolonization at the historic nesting sites occurred in 1981 and 1992 respectively at Eastern Egg Rock and Seal Island NWR-in both cases 8 years after initiation of translocations. Four pairs nested in 1981, a number that increased to 19 pairs by 1985 and has remained constant at 16-19 pairs, due to recruitment of native-hatched chicks. At Seal Island NWR, 7 pairs nested in 1992 and increased to 40 pairs by 1996.

Habitat Use, Diet and Breeding Biology of Tufted Puffins in Prince William Sound, Alaska

Habitat use, diet and breeding biology of tufted puffins (Fratercula cirrhata) were studied in Prince William Sound, Alaska, during summer 1995. On Seal Island, 112 puffin bur- rows (71% active) were located. Of 95 accessible burrows, 49% were typical earthen burrows, whereas the remainder were atypical for the species (e.g., under tree roots). Hatching success ('79%), fledging success (282%), chick growth rates (17.7 g/day), asymptotic (600 g) and fledg- ing (563 g) weights, meal sizes (14.2 g), meal delivery rates (5.32 meals/day), and daily rations (75.5 g/day) were all average or above-average for tufted puffins in Alaska. A total of 42 chick meals, comprising 125 individual prey were collected. Meals were composed of juvenile pollock (12.7% of total mass), herring (21.8%), prowfish (32.3%), salmonids (24.1%), and capelin, sand- lance and squid (<5% each). Tufted puffin populations in Prince William Sound are relatively small, and may be limited by low densities of prey in the Sound, nest-site availability, and heavy rainfall.

VARIABILITY IN ANTARCTIC FUR SEAL DIVE DATA: IMPLICATIONS FOR TDR STUDIES

AbstractWe analyzed 19 dive records obtained from female antarctic fur seals (Arctocephalas gazella) during three austral summer breeding seasons on Seal Island, Antarctica, to assess the extent of individual variation and the potential for using time‐depth recorder (TDR) statistics to detect annual changes in six measures of foraging behavior. We report the mean values and typical variability among individuals for dive duration, dive depth, proportion of time submerged, transit time, vertical distance dived, and diving intensity. Dive duration was the least variable and vertical distance dived was the most variable among individual seals. The results were used to estimate the sample sizes required to detect—with acceptable precision and power—differences in the six measures between sites, years, or species. Statistics that vary most among individuals require the largest sample sizes to reliably detect a given percentage difference between annual means. Interestingly, we also observed the most significant interannual differences in those same statistics. These results emphasize that specifying the magnitude of the (interannual, intersite or interspecific) difference that is biologically significant to the study population is an important, though sometimes difficult, component of TDR survey design.

Effects of time–depth recorders on maternal foraging and attendance behavior of Antarctic fur seals (Arctocephalus gazella)

We evaluated the difference in average durations of foraging trips and nursing visits to shore between one group of female Antarctic fur seals (Arctocephalus gazella) carrying radio transmitters only and another group carrying time–depth recorders (TDRs) and radio transmitters during their first five postpartum foraging trip – nursing visit cycles. Data were collected from 105 different fur seals in five breeding seasons (1989 – 1990 to 1993 – 1994) on Seal Island, Antarctica. Average foraging-trip and nursing-visit durations were significantly greater for the seals carrying TDRs and radio transmitters than for seals carrying radio transmitters only (two-way ANOVA, year × instrument type; trip, P = 0.004; visit, P = 0.04). Historically, instrument-effect studies on marine animals have focused on smaller species and larger instrument to body size ratios. Because of small sample sizes (the number of instruments successfully deployed and retrieved) and the typically variable nature of data from TDRs, the statistical power to detect significant differences due to instrument effects has been low. The evidence of instrument effects on Antarctic fur seals has possible implications for studies utilizing devices attached to similar-sized animals: results may not be representative of the natural (non-instrumented) population.

Bias in acoustic biomass estimates of Euphausia superba due to diel vertical migration

The diel vertical migration (DVM) of Antarctic krill ( Euphausia superba) can greatly bias the results of qualitative and quantitative hydroacoustic surveys which are conducted with a down-looking sonar and irrespective of the time of day. To demonstrate and quantify these negative biases on both the estimates of biomass distribution and abundance, a time-depth-density analysis was performed. Data were collected, as part of the United States Antarctic Marine Living Resources Program (AMLR), in the vicinities of Elephant Island, Antarctica, during the austral summers of 1992 and 1993. Five surveys were conducted in 1992; two covered a 105 by 105 n.mi. area centered on Elephant Island, two encompassed a 60 by 35 n.mi. area immediately to the north of the Island, and one covered a 1 n.mi. 2 area centered on a large krill swarm to the west of Seal Island. The 1993 data include repetitions of the two small-area and two large-area surveys. Average krill volume densities were calculated for each hour as well as for three daily periods: day, twilight and night. These data were normalized and presented as a probability of daily average density. With spectral analysis to identify the frequencies of migration, a four-term periodic function was fitted to the probability density function of average daily biomass versus local apparent time. This function was transformed to create a temporal compensation function (TCF) for upwardly adjusting acoustic biomass estimates. The TCF was then applied to the original 1992 survey data; the resulting biomass estimates are an average of 49.5% higher than those calculated disregarding biases due to diel vertical migration. The effect of DVM on the estimates of krill distribution are illustrated by a comparison of compensated and uncompensated density maps of two 1992 surveys. Through this technique, high density kril areas are revealed where uncompensated maps indicated low densities.