HARBOR SEAL TRACKING AND TELEMETRY BY SATELLITE

We tested a satellite Platform Transmitter Terminal (PTT) in the laboratory (on a float and on captive seals) and on a free-ranging harbor seal in the Southern California Bight to investigate the utility of satellite telemetry in documenting seals'at-sea behavior and movements. We used records from a microprocessor-based time-depth recorder (TDR) to interpret location and diving records from the PTT. For the free-ranging harbor seal, we obtained at least one uplink during 70% (while the seal was at sea) to 82% (while she was ashore) of satellite passes and at least one location each day. Of 62 locations determined by Service Argos for the free-ranging seal, 20 were verified from TDR records to have been at sea; these indicated that the seal may have ranged up to 48 km from the haul-out site, although most locations were within 5 km. The accuracies of locations calculated when the seal was at sea (±15 km) were substantially less than when it was ashore (±1.5 km), thus limiting at-sea tracking of seals by satellite to rather gross movements. Fewer transmissions were detected and locations calculated when the seal was actively diving than when it was swimming near the surface as it departed from or returned to the haul-out site. Consequently, average dive durations indicated by the PTT were substantially shorter than those calculated from TDR records. Documentation of foraging areas and detailed at-sea movements using satellite technology may not be possible for pinnipeds unless PTT-transmission rates are increased substantially from the 1 per 45 set maximum rate now permitted by Service Argos.     

Seals and Man—a changing relationship

Seals were an important resource for coastal communities in prehistoric -times and were hunted in the United Kingdom until recently. Depopulation of remote islands as well as legal protection has allowed British seal stocks to increase greatly. Seals have been regarded by fishermen as serious competitors, but increasingly the public sees them as part of the national and global heritage to be carefully conserved.     

USE OF BIOELECTRICAL IMPEDANCE ANALYSIS TO ASSESS BODY COMPOSITION OF SEALS

Abstract: Bioelectrical impedance analysis (BIA) measures resistance and reactance of a current as it passes through an organism. The validity of using BIA as a tool to measure body water content, and hence body composition and condition, was tested on harp and ringed seals. The resistance and reactance readings from BIA were compared to estimates of total body water (TBW) determined via tritiated water dilution. The relationship between resistance and TBW (% of body mass) was linear after logarithmic transformation and the two variables were highly correlated. We describe the electrode configuration and placements which provide reliable results in these seals. Our findings indicate that BIA has considerable potential as an inexpensive, rapid, and reliable technique for estimating body composition of phocid seals.     

PUPPING IN THE MOST NORTHERLY HARBOR SEAL (PHOCA VITULINA)

The Norwegian high arctic archipelago Svalbard is the home of the world's northernmost population of harbor seals. Due to their limited distribution in isolated areas of the archipelago, little is known about their biology. Until now no information has been published on their pupping or whether it differs from that of harbor seals in other regions. This paper shows that the peak pupping period for harbor seals in Svalbard coincides with that in Europe, i.e., the second half of June. The pups are born with an adult-like pelt and not with a white coat.     

INFRARED SENSING OF THE UNDER-SNOW LAIRS OF THE RINGED SEAL

Airborne sensing of emitted infrared (IR) was tested as a means of detecting under-snow lairs of the ringed seal ( Phoca hispida ) in study areas in Resolute Passage, N.W.T. Lairs and regularly used large breathing holes could in some cases be detected by emitted IR from altitudes of up to 180 m. Lairs were more easily detected if they had thin roofs, and detectability was higher before sunrise, and under conditions of low wind, low ambient temperature and high cloud cover.     

THE DISTRIBUTION, ABUNDANCE AND SELECTED PREY OF THE HARBOR SEAL, PHOCA VITULINA CONCOLOR, IN SOUTHERN NEW ENGLAND

The seasonal distribution and abundance of harbor seals occurring south of Maine were documented by counting the number of seals at traditional haulout locations. The average number of seals counted during each survey in Massachusetts and New Hampshire was 3,560 ± 255 (95% CI), 1983–1987. The maximum number of seals counted on any individual survey was 4,736 individuals. Fifty percent of all the surveys since January 1985 have resulted in counts greater than 4,000 seals reflecting a 27% increase in the abundance of seals in our study area since that date. Seventy-five percent of the seals in southern New England are located at haulout sites on Cape Cod and Nantucket Island. The largest aggregation of seals in the eastern United States occurs mid-winter at Monomoy Island and adjacent shoals. A single high count of 1,672 seals occurred at this site during the study period. An additional 271–374 seals were also counted in Rhode Island, Connecticut and eastern Long Island Sound during surveys conducted in March 1986 and 1987. The American sandlance Ammodytes americanus was the single dominant prey item of harbor seals in waters adjacent to Cape Cod based on the modified frequency of occurrence of each prey species in scat samples collected from three haulout sites on Cape Cod between 1984–1987. During January and February sandlance was the near exclusive prey item at Monomoy (99%, n= 80). During March and April, the frequency of Atlantic herring Clupea harengus increased in the scat samples at this site. Regional differences in the diet of seals reflect distinct prey communities throughout the study area. Since 1986, the percent occurrence and importance of sandlance in the diet of seals has decreased, reflecting an overall decrease in abundance of this prey species in waters adjacent to Cape Cod. In spite of fluctuations in abundance, and regional differences in the diet of seals throughout the study area, sandlance still comprised a minimum 55% of the total prey species of harbor seals throughout the study area.     

DO PHOTOPERIOD AND TEMPERATURE INFLUENCE THE MOLT CYCLE OF PHOCA VITULINA IN CAPTIVITY?

Photoperiod variations are the principal environmental signals entraining circannual activity in mammals, which is also believed to be influenced by changes in temperature and nutrition. Control of the molt in phocids has not been extensively studied with experimental manipulations of environmental factors, but substantial work indicates that photoperiod has a primary influence on mammalian breeding and furring mechanisms. Studies were under taken to reestablish the molt cycle in five harbor seals ( Phoca vitulina ) previously kept in an enclosed facility with a limited air/water temperature gradient and artificial photoperiod. The seals were exposed to an extended temperature gradient during the first period of study, and no molting was observed. The second period of study was characterized by a natural occurring photoperiod of 8 h 53 min light (L)/15 h 07 min dark (D) and a maximal 15 h 31 min L/8h 29 min D duration, and molting occurred in all individuals. These results suggest a prevalent influence of photoperiod variation on the harbor seal molt.     

THE MOST NORTHERLY HARBOR SEAL, PHOCA VITULINA, AT PRINS KARLS FORLAND, SVALBARD

The harbor seal ( Phoca vitulina ) has its northernmost distribution at the Norwegian arctic archipelago of Svalbard. Little information exists on this particular harbor seal population. The present paper summarizes this information, and gives the result of surveys of harbor seals conducted in Svalbard in 1984, 1985 and 1987. These surveys show that harbor seals in Svalbard are limited to the area around Prins Karls Forland, the westernmost island in the archipelago. The harbor seal population at Prins Karls Forland numbers at least five to six hundred animals.     

REBUILDING SEAL STOCKS IN THE KATTEGAT-SKAGERRAK

The harbor seal ( Phoca vitulina ) population in the Kattegat-Skagerrak area has been dwindling for several centuries due to excessive hunting pressure. Corrected hunting statistics during 1890–1976 are used to estimate changes in population size over the past century. After protection was introduced in the 1960s and 1970s the harbor seal population in the area increased at an exponential rate of 0.12 and exceeded 5,000 animals in 1986. The present rate of population growth is used for modelling the influence of fertility and age-specific mortality. It is found that the observed high rate of increase is only realistic if female fertility rate is very high, the range of juvenile mortality rate is 0.33–0.52 and adult mortality is less than 0.15. Commonly cited higher mortality rates are not realistic in the Kattegat-Skagerrak area.     

PLASMA PROGESTERONE CONCENTRATIONS MEASURED USING AN ENZYME-LINKED IMMUNOSORBENT ASSAY USEFUL FOR DIAGNOSING PREGNANCY IN HARBOR SEALS (PHOCA VITULINA)

Wild-caught female harbor seals ( Phoca vitulina ) were classified as sexually mature or immature on the basis of standard body length (< 125 cm immature, > 125 cm mature) and plasma progesterone concentrations measured using an enzyme-linked immunosorbent assay (ELISA), a technique usable in the field. Sexually mature females were classified as pregnant or non-pregnant on the basis of their plasma progesterone concentrations. Of 28 wild mature female harbor seals caught in the Moray Firth, N.E. Scotland, between the end of February and the end of May, 79% had plasma progesterone concentrations greater than 60 nmol liter⁻¹, the lowest plasma progesterone concentration measured in one of eight females later observed with a pup, and were diagnosed as pregnant. A linear discriminant function, calculated to provide a method of distinguishing pregnant and non-pregnant females, predicted 100% of non-pregnant females and 95.8% of pregnant females using plasma progesterone concentration, standard length, and month of capture as parameters. Plasma progesterone concentrations were less than 30 nmol liter⁻¹ in all mature and immature males and immature females. In mature females plasma progesterone concentrations ranged from 0-318 nmol liter⁻¹.     

DIGESTIBILITY OF CRUSTACEANS and CAPELIN IN HARP SEALS (PHOCA GROENLANDICA)

Gross energy intake (GEI), apparent digestible efficiency (%DE), and body-mass change were studied both in recently weaned and in subadult harp seals fed capelin ( Mallotus villosus ) and crustaceans ( Parathemisto libellula and Thysanoessa sp.) ad lib. The median %DE of Parathemisto libellula (with a wet-weight energy density (ED) of 3.9 kJ/g) and Thysanoessa sp. (ED: 2.3 kJ/g) was 81% and 83%, respectively, while the median %DE of capelin (ED: 8.6 kJ/g) was 94% and 93% for subadult harp seals and one harp seal pup, respectively. No correlation between age and %DE was obtained (P > 0.05). Despite ad lib. access to the food, the harp seal pups were unable to maintain body mass while on a crustacean diet, and it is therefore suggested that harp seal pups most likely must supplement their crustacean diets with fish to maintain growth.