Number Of Seals Research Articles

Relationships between estimates of ringed seal (Phoca hispida) and polar bear (Ursus maritimus) populations in the Canadian Arctic

Analysis of estimates of population size of ringed s,eals (Phoca hispida) and polar bears (Ursus maritimus) from several areas indicated that estimates of one predicted the range of expected population size of the other in areas where ringed seals constitute the primary prey. In some areas, the closeness of this relationship indicates where estimates of either seals or bears may be inaccurate. The number of seals required to support a population of polar bears of predetermined size was estimated independently using both behavioral and energetic data. Behavioral estimates of the number of seals killed may overestimate energetic requirements and vice versa. Predation and energy matrices indicated that high levels of predation on seals are sustainable only if most animals killed are young-of-the-year. The field metabolic rate of the polar bear appears to be about twice the basal metabolic rate. Densities of seals vary in response to overall productivity of the ecosystem in different areas, and fluctuations in their numbers and reproductive rates between years can be used to monitor changes in productivity of the ecosystem. These changes also cause variation in productivity of bears, which indicates the sensitivity, at the population level, of the relationship between ringed seals and polar bears.

Seasonal change in the distribution and density of seals in the pack ice off Princess Martha Coast, Antarctica

During the period 9 December 1991–4 February 1992 shipboard and aerial surveys of seals in the pack ice off the Princess Martha Coast were made. All aerial surveys were flown from the MV SA Agulhas at the edge of the fast ice opposite SANAE at 70°19′S, 02°26′W. A total of 18 1/2-nm-wide transects were flown censusing 481.3 nm2 of pack ice within which 1437 seals were counted. The species composition of the seals was 94.4% crabeater, 3.4% Ross, 1.4% leopard and 0.8% Weddell seals. The density of seals nm−2 for the early season surveys (December) in the inner pack was 1.92 for crabeater, 0.0 for leopard; 0.026 for Weddell and 0.057 for Ross seals. The density for the late season surveys throughout the pack was 4.02 for crabeater, 0.10 for leopard, 0.029 for Weddell and 0.122 for Ross seals. These data support the thesis that seal densities increase as the amount of pack ice diminishes with the advance of summer. Leopard seals were largely found near the retreating outer edge of the pack, and Weddell seals associated closely with the inshore fast ice, whilst both crabeater and Ross seals showed no statistically significant preference either for any part of the pack ice or for any particular geographical area covered during the surveys in the present study. The high densities (0.45−2.91 seals nm−2) and percentage species contribution (9.7−32.4%) of Ross seals determined by shipboard censuses in the same area during the early 1970s could not be confirmed in the present study, and it is likely that a real decrease in Ross seal numbers has taken place.

The effects of future consumption by the Cape fur seal on catches and catch rates of the Cape hakes. 3. Modelling the dynamics of the Cape fur sealArctocephalus pusillus pusillus

The current status of and future trends for the Cape fur seal Arctocephalus pusillus pusillus population are assessed using information from aerial counts of pup abundance. The model used in the analyses is age- and sex-structured, and assumes density-dependence in the survival rate of pups. Uncertainty is assessed by conducting sensitivity tests and estimating 90% confidence intervals by the percentile method. The results confirm the increase of the seal population since the introduction of legal controls at the end of the 19th century, and the estimate of 1,7 million animals of Age 1 and older at the start of 1993 is relatively robust to model assumptions and values for biological parameters. The food consumption by the seal population is estimated to have almost doubled between 1973 and 1993, and to be roughly 2 million tons annually at present. Future trajectories of seal numbers and annual consumption of food cannot be determined with great precision and are sensitive to the values assumed for the post-first-year survival rate and the degree of compensation in density-dependence. Depending on such assumptions, the seal population could already have reached its pre-exploitation equilibrium level or still be well below this level. Data from the 1993 aerial survey have considerable influence on the model results, and particularly on inferences concerning whether the population is now approaching its pre-exploitation level. This suggests that further surveys should be conducted to ascertain the reliability of the changed trend in pup abundance indicated by that 1993 count.

Difficulties in assessing population status of ice seals

The best method of monitoring ice seal populations in shifting packice is by aerial censuses. However, there are a number of problems with this method that are difficult to address in the packice and are best addressed on more accessible ice seals such as the Weddell seal. Counts made during the moult are affected by the fact that Weddell seals can leave the fast ice to forage. Seal numbers on the fast ice will therefore differ depending upon the proximity and availability of prey species, with lower numbers being recorded on the fast ice the further the seal has to travel from the ice to find food. In any census the subgroup of the population that is being counted must be known. Southern elephant seals and Weddell seals haul out to moult in sequences on the basis of age, sex and reproductive condition. This leads to periods of high and low counts through the moult. Examination of data on crabeater seals indicates that a putative 60% decline in numbers may have been due to counts being made at different times of the moult and therefore with different subgroups of the population being counted.

Changes in the abundance of New Zealand fur seals, Arctocephalus forsteri, on Kangaroo Island, South Australia

Kangaroo Island was an important seal-harvesting site during the early years of European colonisation of Australia. A recent survey of the New Zealand fur seal, Arctocephalus forsteri, in South and Western Australia indicates that Kangaroo I. is still an important centre for the species. In order to determine changes in the abundance of the population, numbers of pups were determined at four colonies on Kangaroo Island by mark-recapture in up to five breeding seasons from 1988-89 to 1992-93. Clipping was the preferred technique for mark-recapture estimation of pups because it was quick, easy and effective. Recaptures were conducted visually; they were repeated several times in each season to improve precision of the estimates. No pups were marked between recaptures in order to minimise disturbance. Assumptions made in estimating population size by the mark-recapture technique pertinent to this study are reviewed. Pup numbers increased at three colonies: at Cape Gantheaume, from 458 to 867 over five years (with exponential rate of increase r = 0.16, n = 5); at Nautilus North, from 182 to 376 over five years (at r = 0.19, n = 4); and at North Casuarina Islet, from 442 to 503 over four years (at r = 0.043, n = 2). Rates of increase in the first two colonies are similar to those at the most rapidly increasing fur seal populations in the Southern Hemisphere. The Kangaroo I. population is estimated to be 10000 animals in 1992-93. It is likely to be at the recolonisation phase of growth, with high rates of increase at individual colonies (or parts of colonies) resulting from local immigration. As space does not appear to be limiting expansion in these colonies, fur seal numbers may continue to increase there.

Southern elephant seal numbers during moult on Livingston Island, South Shetland Islands

Southern elephant seal numbers during moult on Livingston Island, South Shetland Islands

The status of grey seals Halichoerus grypus in North Norway and on the Murman Coast, Russia

The distribution and abundance of grey seals Halichoerus grypus were studied by aerial and ground surveys in North Norway and on the Murman coast, Russia, during the moulting (March–April) and breeding (October–December) seasons in 1986–1992. Numbers of grey seals may have increased throughout the area of investigation during the past 25–30 years. Based on observations of pup production, crude estimates of 900 and 3400 grey seals are suggested to inhabit colonies in Nordland county, North Norway and at the Murman coast, Russia, respectively. In Troms and Finnmark counties, North Norway, no reliable pup production estimates are available, but nearly 700 grey seals were observed at haul-out sites during the moulting period. Recorded moulting and breeding haul-out sites are noted for most of the study area.

The interaction between offshore cod trawlers and harp Phoca groenlandica and hooded Cystophora cristata seals off Newfoundland, Canada

The direct interaction between the seals and the trawl or dragger fishery results in seals being trapped in trawler nets and either drowned, released, or killed. A study undertaken between 17 and 27 February 1992 showed that more seals interacted with the net whilst fishing for Atlantic cod Gadus morhua in 450 fathoms of water (10–60 seals) than when fishing for witch Glyptocephalus cynoglossus in over 750 fathoms of water (0–6 seals). Seals were captured only whilst fishing for Atlantic cod (eight harp seals and two hooded seals). Harp seals Phoca groenlandica (33.2±21.8) were more plentiful around the trawler than hooded seals (0.8±0.4) and adult male harp seals were most common (73%). The impact of the seals on the caught fish was negligible with less than 0.002% of the catch being taken by the seals. All observations (n=32) of seals eating Atlantic cod showed that they swallowed them head first and whole. The number of seals captured can be reduced by altering setting methods, and the provision of a runway for the seals over the work deck to the side of the trawler would obviate the need to kill them. We hypothesize that the apparent increase in harp sea/trawler interactions is the result of smaller catches of cod, with consequential decrease in spillage from the nets requiring the seals to enter the nets to obtain cod. This results in increased by-catch of seals.

Finely Striated Lip-Seal Surfaces: Part 1—General Effects

The work presented previously by To̸nder and Salant (1992) is extended and generalized. In that work it was shown that the fine, axially oriented striations found on some lip-seals, under certain conditions, could lead to the total suppression of leakage through a fully lubricated seal. In the present work the behavior of the lubricant annulus is studied, as are the conditions required for leakage suppression. If the latter are met, it is shown that when a certain parameter—here called the seal number—is increased, the lubricant annulus width will shrink. This will lead to a reduction of the friction force. It is further shown that the striated roughness will also generate a radial force or load capacity. This effect does not involve local cavitation.

Variation in the Numbers of Shags Phalacrocorax aristotelis and Common Seals Phoca vitulina near the Mouth of an Atlantic Salmon Salmo salar River at the Time of the Smolt Run

In the 3 years 1987-89 the bulk of the Atlantic salmon smolt run in the Lussa River occurred in late April and early May. Peak daily downstream displacement occurred in the early evening as light levels were falling. The numbers of shags and common seals counted in the vicinity of the river mouth were strongly correlated with the numbers of migrating smolts. Peak daily shag numbers occurred aroung midday, confirming their preference for daylight feeding. Peak daily seal numbers coincided with low tide when they were observed hauled out. Aerial surveys confirmed that at the time of the smolt run, shags were concentrating on the area off the Lussa River. The size of smolts leaving the river was such that both shags and seals would be capable of preying on them

BLOOD CHEMISTRIES AND BODY CONDITION OF STELLER SEA LION PUPS AT MARMOT ISLAND, ALASKA

Abstract : This work is part of a large project focused on assessing the blood chemistry and body condition of pinnipeds in and around Alaskan waters. We have utilized a series of blood indices that reflect hydration state, blood oxygen transport, and protein, lipid and carbohydrate metabolism. In addition to total mass, animals are also examined for blubber thickness at several locations around the body These parameters are useful for detecting significant changes in health status that might alter water balance, cause anemia, or compromise basic metabolic status. The Steller sea lion (Eumetopias jubatus) is of particular interest because its population has declined over the last 20 years to such an extent that the species has been designated as threatened under the United States Endangered Species Act (Federal Register, November 26, 1990). The cause(s) of the decline are unknown but may be linked to redistribution, disease, environmental perturbations (which may influence the quality or quantity of prey), the synergistic effects of fisheries, or other unknown causes (Braham et al. 1980, Merrick et al. 1987, Loughlin and Merrick 1989, Loughlin et al. 1992). Calkins and Goodwin (1988) suggested that adult female Steller sea lions in the Gulf of Alaska during 1985-1986 were anemic and smaller in body size than animals sampled ten years earlier, possibly as a result of food limitations. Also, Castellini and Calkins (1993) have shown the latter group was more lean than the animals studied in the 1970s. The best population models currently suggest that the decline in sea lion numbers results from a reduction in survival of juveniles or breeding females, or both (York, personal communication).

Geology and Hydrocarbon Potential of the Oued Mya Basin, Algeria

The Oued Mya hydrocarbon system is located in the Sahara basin. It is one of the best producing basins in Algeria, along with the Ghadames and Illizi basins. The stratigraphic section consists of Paleozoic and Mesozoic, and is about 5000 m thick. This intracratonic basin is limited to the north by the Toughourt saddle, and to the west and east it is flanked by regional arches, Allal-Tilghemt and Amguid-Hassi Messaoud, which culminate in the super giant Hassi Messaoud and Hassi R'mel hydrocarbon accumulations, respectively, producing oil from the Cambrian sands and gas from the Trissic sands. The primary source rock in this basin is lower Silurian shale, with an average thickness of 50 m and a total organic carbon of 6% (14% in some cases). Results of maturation modeling indicate that the lower Silurian source is in the oil window. The Ordovician shales are also source rocks, but in a second order. Clastic reservoirs are in the Trissic sequence, which is mainly fluvial deposits with complex alluvial channels, and the main target in the basin. Clastic reservoirs in the lower Devonian section have a good hydrocarbon potential east of the basin through a southwest-northwest orientation. The Late Trissic-Early Jurassic evaporitesmore » that overlie the Triassic clastic interval and extend over the entire Oued Mya basin, are considered to be a super-seal evaporite package, which consists predominantly of anhydrite and halite. For paleozoic targets, a large number of potential seals exist within the stratigraphic column. This super seal does not present oil dismigration possibilities. We can infer that a large amount of the oil generated by the Silurian source rock from the beginning of Cretaceous until now still is not discovered and significantly greater volumes could be trapped within structure closures and mixed or stratigraphic traps related to the fluvial Triassic sandstones, marine Devonian sands, and Cambrian-Ordovician reservoirs.« less

Beluga Whale and Spotted Seal Use of a Coastal Lagoon System in the Northeastern Chukchi Sea

Aerial surveys were conducted in the northeastern Chukchi Sea during 1989-91 to investigate the distribution and abundance of beluga whales and spotted seals. Emphasis was on the 170 km long Kasegaluk Lagoon, which was known to be regularly used by both species during the open-water season. Belugas were seen on every survey during 3-14 July 1990 and 4-16 July 1991, with numbers ranging from 7 to 1212. Data from other years indicate that whales sometimes arrive as early as 22 June and leave the area by late July. The presence of nearshore gravel beds and warm, low-salinity water probably combine to make this region important as a place for belugas to molt. Spotted seals occur in the area from mid-July through early November. They haul out on particular spits and shoals near Utukok Pass, Akoliakatat Pass, and Avak Inlet. Numbers counted were variable but exceeded 1000 on many days in July, August, and September. Telemetry data suggest that the maximum count of about 2200 represents only a small portion of the total number of seals frequenting Kasegaluk Lagoon. Comparisons with data from previous years suggest that the numbers of belugas and spotted seals using the area have been relatively stable since the late 1970s. Activities associated with oil, gas, coal, and mineral resource development should be regulated to minimize their potential impacts on important beluga and spotted seal habitats. Key words: beluga whale, Delphinapterus leucas , spotted seal, Phoca largha , Chukchi Sea, Kasegaluk Lagoon, distribution, abundance

A Waiting Line Model:

A model using wailing the principles was developed to assist with foodservice facilities design. The number of seals needed is calculated. Using values for area per seat previously published the size of the dining area can then be determined. The number of seats needed is dependent upon the meal patterns served, arrival rates of customers, turnover rates and the market demand. A residence hall food service was studied to develop the model and to compare calculated results with the existing dining area. The results indicate that wailing line principles can be used to calculate the number of seats needed when arrival rates are known.

A Fur Seal Simulation Model to Explore Alternative Management Strategies

A simulation model is formulated for the South African fur seal (Arctocephalus pusillus pusillus) to evaluate the appropriate management action when culling to reduce population growth rate, culling to decrease fish consumption by seals, or harvesting to maximise numbers of seals removed. There is disturbance associated with bull sealing which increases pup mortality and reduces pregnancy rates, but this is not well quantified. Disturbance can be included or excluded from model runs. To reduce population growth, cow removal is most effective, but the population sex ratio becomes severely altered and this may be undesirable ecologically. Reduction of fish consumption is best achieved either by removing cows, with the same caveat regarding sex ratio, or by removing bulls and including disturbance effects. However, the acceptability of a reduction achieved by humans disrupting seals is questionable, and the continued removal of bulls may eventually lead to further decreases in pregnancy rate. To maximise a harvest, the relative commercial value of different seal products is considered, and bull removal, excluding disturbance effects, followed by removal of pups achieves this aim most effectively.

New Zealand fur seals at the Antipodes Islands

Abstract The Antipodes Islands (49° 41′ S, 178° 47′ E) were discovered in 1800, and their once-abundant fur seals exterminated within 20 years. It was over 150 years before these animals were once more regularly found at the islands. Since the 1950s, New Zealand fur seals, Arctocephalus forsteri, have slowly increased in numbers, and now about 2000 (mostly yearlings and older juveniles) visit the islands each year in late-summer, although there are far fewer in winter. Very few breed at the Antipodes; seven pups found in 1985 were the first recorded there this century. The history of fur seals at Macquarie Island is very similar to that at Antipodes, but both contrast with the far more rapid recovery in numbers of fur seals elsewhere in the New Zealand region. It has been argued that the original fur seals of these two island groups may not have been A. forsteri, but a species more vulnerable to sealing, and this suggestion is re-examined and discussed. An alternative hypothesis is presented: that the two...

A "Neo-Babylonian" Seal from Tell Taanach

A seal found on the surface of Tell Taanach 40 years ago may provide additional evidence for occupation of the site in the late Assyrian/Neo-Babylonian period.

Seasonal abundances of the harbor seal (Phoca vitulina richardsi Gray 1864), at Punta Banda Estuary (B.C., Mexico)

In order to know the present abundance and seasonal variability of the seals (Phoca vitulina richardsi Gray, 1864) hauling at the inner northwest portion of Punta Banda Estuary (Baja California, Mexico), 40 counts were carried out between November 1988 and August 1990. The average abundance during the study period was 52 individuals, although a significant seasonal variability was noted. The largest mean abundance occurred in spring (X = 69; n = 12; range = 31-110) and it was the best season to assess the number of seals that use the estuary. The lowest abundance was recorded in summer (X = 28; n = 5; range = 2-72) while in autumn the number of seals was lower than in winter and spring (X = 31; n = 8; range = 18-48). The maximum seal counts were noted in winter, although their average abundance was lower than in spring (X = 58; n = 15; range = 18-151) since the herd increased by the occasional presence of pups and juveniles. No relationship was found between the abundance of seals and the sea level. The seasonal variation in the size of the herd was associated with its breeding season which occurs late in winter and with herd movements to other near haul-out sites.

Thermal constraints on hauling out by harbour seals (Phoca vitulina)

Measurements of the thermal environment were made in conjunction with regular counts of hauled out harbour seals at three sites in the Pacific Northwest. Solar radiation, wind speed, and air temperature were all significantly correlated with numbers of seals on land. These were incorporated into a thermal index of heat flux (expressed in watts per square metre) between the seal and its environment. Numbers of seals hauled out at midday declined sharply as flux increased above 0 W∙m−2 (i.e., when seals theoretically gained net heat from their environment), but remained constant at all measured negative values of flux. This relationship could be described by a nonlinear piecewise regression equation [Formula: see text]. No significant differences in hauling activity were detected between sites throughout most of the year. During the summer, however, one site with significantly higher mean flux than the others also exhibited significantly lower hauling activity. These findings are consistent with the hypothesis that under temperate summer conditions, hauling out can result in overheating. This may be an important constraint on hauling behaviour.

Toxic elements and organochlorines in harbor seals (Phoca vitulina richardsi), Kodiak, Alaska, USA.

Marine and estuarine habitats near urban or industrialized regions are vulnerable to contaminated runoff. Harbor seals (Phoca vitulina richardsi), which occur throughout much of the northern hemisphere, are useful mammalian biomonitors because they feed, reproduce, and rest near or on shore and are high-level trophic consumers. They have often been monitored for contaminants in Europe. To date, no studies have been reported on contaminants in harbor seals from industrialized areas of Alaska. In the vicinity of Anchorage, Alaska's largest urban and industrial city, harbor seals are sedentary and limited to coastal waters; some movements have been documents but there is no evidence of extensive migrations. Although some harbor seals in the Kodiak Archipelago move up to 100 km along the shore, strong fidelity to specific haulout sites is more common. These seals eat mainly non-migratory fishes and octopi. Harbor seal numbers have declined substantially from unknown causes in the southern part of the Kodiak Archipelago. The Alaska Department of Fish and Game (ADF G) suggested that the decline is a trend for the entire Kodiak region and other Alaskan waters. Contaminants have been suggested as a possible reason for the precipitous decline of Steller sea lions (Eumetopias jubatus) in themore » region, and were suspected in the decline of harbor seals. In this study, harbor seals were sampled from throughout the Kodiak Archipelago to determine concentrations of certain metals, metalloids, polychlorinated biphenyls (PCBs), and organochlorine pesticides, and to determine if these concentrations varied by sex or accumulated with age. All seals were collected within 75 km of Cook Inlet, an estuary next to Anchorage. The targeted elements or compounds were known to be toxic to a wide spectrum of organisms. 19 refs., 1 tab.« less