MOVEMENTS OF SATELLITE-TAGGED SUBADULT AND ADULT HARBOR SEALS IN PRINCE WILLIAM SOUND, ALASKA

Satellite-linked tags were attached to 49 subadult and adult harbor seals captured in Prince William Sound (PWS), Alaska, and their movements were monitored during 1992–1997. Seals were tracked for a total of 5,517 seal-days and were located on about 80% of the days that tags transmitted. Most locations were in or near PWS, but some juvenile seals moved 300–500 km east and west into the Gulf of Alaska. While several seals travelled to 50–100 km offshore, virtually all locations were in water <200 m deep. Overall, juvenile seals moved more than adults and had larger home ranges. Movements were significantly affected by month, and age by month and sex by month interactions. In all months, mean distances between successively used haulouts were <10 km for adults and <20 km for juveniles. Mean monthly home ranges varied from <100 km² to >1,500 km², and were smallest during June-July. Mean haul-out to at-sea distance was 5–10 km for adults and generally 10–25 km for juveniles. Satellite-linked tags provided an effective means of monitoring and describing the full range of harbor seal movements in this region, with the exception of late summer when tags were shed during the molt.     

Satellite tracking of ringed seals Phoca hispida off northwest Greenland

We monitored movements and haul-out patterns of four ringed seals Phoca hispida , off Northwest Greenland between 5 June and 31 October 1988 using the Argos Data Collection and Location System When the seals were hauled out on fast ice their locations were accurately determined, but when they were at sea, few accurate locations were obtained, evidently because these seals spent little time at the surface between dives The seals remained within the fjord where they were tagged, and hauled out often to early July Thereafter, as fast-ice disappeared, they dispersed widely and spent less time hauled out Time of day had no significant effect on haul-out patterns Haul-out periods declined significantly from June to August and increased in September-October Satellite contact with one seal was lost after 16 d while the seal was still in the fjord in late June One seal travelled over 200 km southwest and was located 4 July in offshore waters of Smith Sound 30 d after instrumentation Another seal moved southeast along the Greenland coast where contact was lost after 49 d on 23 July The fourth seal moved north along the Greenland coast, hauled out regularly on ice, and returned south along the coast in late September and October after 181 d of contact with the satellite     

AN ALGORITHM TO IMPROVE GEOLOCATION POSITIONS USING SEA SURFACE TEMPERATURE AND DIVING DEPTH

The at-sea movement of marine mammals is an important component of their foraging ecology, but has been difficult to study. Geolocation timed-data recorders (GLTDRs) estimate positions using measured light level to calculate day length and local noon. It is well known that these location estimates are imprecise (mean error of > 1°). Satellite telemetry generally provides a more accurate, but also more expensive means of monitoring movement. We evaluated the accuracy and precision of geolocation positions by comparing these locations with satellite data from Service Argos for eight free-ranging gray seals ( Halichoerns grypus ) equipped with both a satellite-linked data recorder (SDR) and a GLTDR. Geolocation positions differed by 1,026.0 ± 292.28 km from the corresponding Argos locations. We developed an algorithm to correct geolocation positions by comparing surface water temperature (ST) and dive depth collected by GLTDRs with existing sea-surface temperature and bathymetry databases. The corrected positions were significantly closer (P < 0.025) to the Argos locations of these seals (94.2 ± 8.22 km). The original geolocation positions would have led to incorrect conclusions about the use of space by gray seals; however, the corrected positions can be reliably used to study the large-scale spatial distribution of individuals.     

AQUATIC MATING STRATEGIES OF THE MALE PACIFIC HARBOR SEAL (PHOCA VITULINA RICHARDII): ARE MALES DEFENDING THE HOTSPOT?

Compared to the harem and resource defense systems of terrestrial mating pinnipeds, males of aquatic mating species appear unable to monopolize females or resources. We investigated movements, acoustics, and aquatic territorial behavior of male harbor seals, Phoca vitulina richardii , in Elkhorn Slough, California, using VHF telemetry, hydrophones, and acoustic playback experiments. During the mating season 22 males increased time spent in the water and away from haul-out locations, exhibiting activity patterns similar to Atlantic subspecies. Two acoustic display patterns were observed. At one location multiple males aggregated to display with acoustic activity peaking one month before peak estrus. At two other locations, lone males displayed primarily during peak estrus. Acoustic display areas were non-adjacent with a mean ± SE size of 4,228 ± 576 m², similar to harbor seal display patterns in the Moray Firth, Scotland. Underwater playbacks of male vocalizations were used to define territorial boundaries by inducing responses from territory-holding males. Four solitary males defended adjacent territories (mean area 39,571 ± 18,818 m²) along a travel corridor, similar to observations of harbor seals at Miquelon, Newfoundland. Acoustic display stations appeared to be subcomponents of larger territories. Males exhibited site fidelity to territories for at least 2–4 yr. Females moved through territories freely. The establishment of male-display territories along female-traffic corridors resembles terrestrial systems described as hotspot leks.     

The effect of a large Danish offshore wind farm on harbor and gray seal haul-out behavior

This study investigates the effects of the construction and operation of a large Danish offshore wind farm on harbor and gray seal haul-out behavior within a nearby (4 km) seal sanctuary. Time-lapse photography, visual monitoring, and aerial surveys were used to monitor the number of seals on land in daylight hours. Seals were monitored during two preconstruction periods (19 June–31 August 2001 and April–August 2002), a construction period of the wind farm (August 2002–December 2003), and a period of operation of the wind farm (December 2003–December 2004). Monthly aerial surveys were conducted to estimate the proportion of seals in the sanctuary relative to neighboring haul-out sites. From preconstruction to construction and through the first year of operation the number of harbor seals in the sanctuary increased at the same rate as the number of seals at the neighboring haul-out sites. No long-term effects on haul-out behavior were found due to construction and operation of the wind farm. However, a significant short-term decrease was seen in the number of seals present on land during sheet pile driving in or near the wind farm. Acoustic deterrents were utilized simultaneously to avoid hearing damage.     

DIVE DATA FROM SATELLITE TAGS AND TIME-DEPTH RECORDERS: A COMPARISON IN WEDDELL SEAL PUPS

The diving behavior of juvenile Weddell seals, Leptonychotes weddellii , was monitored simultaneously with time-depth recorders (TDRs) and satellitelinked time-depth recorders (SLTDRs). Recovered TDRs provided a complete record of the depth and duration of all dives, while data received from SLTDR tags via the ARGOS satellite system were compressed into the number of dives in each of six depth or duration bins. The dive information from the two types of tags was compared to determine if data compression, processing, and transmission influenced the data received.
While only half of the dive data collected by TDRs was also received from the SLTDR tags, the chance of receiving SLTDR data was independent of when diving occurred, when data was transmitted, and the subsequent dive activity. In addition, the number of dives in each depth and duration bin was an accurate representation of the actual dive behavior. Therefore, SLTDR tags were judged to provide data qualitatively similar to that provided by TDRs. The accuracy of seal locations provided by Service ARGOS was estimated by comparison to Global Positioning System (GPS) locations, and the average position error found to be significantly greater than predicted by Service ARGOS or reported in other studies (LCO locations ± 11.4 km, LC1 ± 5.0 km).     

Movements, diving and foraging behaviour of grey seals (Halichoerus grypus)

This study presents the first direct observations of the movements and behaviour of free-ranging grey seals at sea. Radio and ultrasonic transmitters were attached to three sub-adult male grey seals which were then tracked from a suitable vessel. Behaviour at sea fell into one of three categories: travelling between haul-outs, short duration trips, and resting adjacent to haul-out sites. Travelling was characterized by direct, relatively fast horizontal movement and by V-shaped dive profiles. During short duration trips the seals swam slower and invariably exhibited square-wave dive profiles, spending approximately 60% of total dive duration at the maximum depth. Resting involved shallow dives close to haul-out sites and an absence of directed lateral movement.
The excellent navigational abilities of grey seals are illustrated by the rapid, direct swimming between distant haul-out sites. It is proposed that short duration trips are specifically for foraging because of their association with other piscivores, and because swimming was slow and mostly on or near the sea bed (grey seals are known to feed almost exclusively on demersal and benthic fish). These trips accounted for only 14% of the nine days that seal 1 was tracked. It is also proposed that the habit of diving to the sea bed whilst travelling between distant haul-out sites is to allow opportunistic foraging with only a small increase in total swimming distance.     

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.     

Current population genetics of Japanese harbor seals: Two distinct populations found within a small area

We used microsatellite loci to understand the current population genetics of Japanese harbor seals, and found that they were subdivided into two distinct populations, one in Erimo and the other in eastern Hokkaido, despite being only 150 km apart and having no obvious geographical boundaries between them. Strong population subdivision between the two areas may be due to the small number of haul-out sites and population size, and that a single habitat type is used for haul-out sites in Japan. Also, at Erimo, there are numerous rocky reefs at a single haul-out site that stretch up to 1.3 km offshore from land, while 10 haul-out sites in eastern Hokkaido, separated by a maximum of 30 km, are interspersed along 75 km of the coast. The direction in which the rocky reefs stretch away from land or in which the haul-out sites are facing may be limiting the movement of Japanese harbor seals and causing strong population subdivision between Erimo and eastern Hokkaido. No recent genetic bottlenecks were detected, although the seals in Erimo and eastern Hokkaido were reported to have experienced declines in population size over the past few decades.     

DIEL HAUL-OUT PATTERNS AND SITE FIDELITY OF HARBOR SEALS (PHOCA VITULINA RICHARDSI) ON SAN MIGUEL ISLAND, CALIFORNIA, IN AUTUMN

We studied the haul-out patterns and movements of harbor seals ( Phoca vitulina richardsi ) on San Miguel Island, California, from 23 October through 6 December 1982 by attaching a radio transmitter to each of 18 seals and monitoring their presence ashore with continuously scanning receivers. Seals hauled out at all hours although, on average, the largest proportion of tagged seals was ashore between 1300 and 1500 h. Median durations of haul-out bouts of individual seals ranged from 4.7 to 21.8 h; 81% of all haul-out bouts were less than 12 h and 3% were longer than 24 h. Eighty-one percent of the seals that were resighted at least twice used only the sites where they were tagged; two seals used two sites and one seal used three. Most seals were hauled out on fewer than 51% of the days sampled. On average, about 41% of tagged seals hauled out each day whereas an average of about 19% was hauled out during peak afternoon hours. Using telemetry data to correct a count of 412 seals made during an aerial survey, we estimated absolute abundance at about 2,168 seals; a modified Peterson mark-recapture model produced an estimate of about 1,445 seals.     

HAUL-OUT SELECTION BY PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII): ISOLATION AND PERCEIVED PREDATION RISK

The potential for non-aquatic predators to influence habitat use by harbor seals ( Phoca vitulina ) in a nearshore marine environment was studied by examining haul-out site use and through an experimental approach. Distance from shore, distance to possible foraging depths, peripheral water depth, and haul-out areas were quantified for each haul-out. There was a positive relationship between the number of seals hauled out and the distance from shore for eight known haul-out sites. The hypothesis that harbor seals increasingly hauled out farther offshore to reduce predation risk was tested experimentally by measuring their response to a model of a potential terrestrial predator in comparison to a control object, and to disturbance by a human at one of the study sites. Harbor seals abandoned the haul-out in the presence of the predator model, but showed little response to the controls, suggesting they possess a threat image for terrestrial predators and avoid hauling out when it is perceived. These results support the hypothesis that harbor seals select isolated sites to reduce exposure to terrestrial carnivores.     

Harbor seal population decline in the Aleutian Archipelago

Populations of Steller sea lions, northern fur seals, and northern sea otters declined substantially during recent decades in the Bering Sea and Aleutian Islands region, yet the population status of harbor seals has not been assessed adequately. We determined that counts obtained during skiff‐based surveys conducted in 1977–1982 represent the earliest estimate of harbor seal abundance throughout the Aleutian Islands. By comparing counts from 106 islands surveyed in 1977–1982 (8,601 seals) with counts from the same islands during a 1999 aerial survey (2,859 seals), we observed a 67% decline over the ～20‐yr period. Regionally, the largest decline of 86% was in the western Aleutians (n= 7 islands), followed by 66% in the central Aleutians (n= 64 islands), and 45% in the eastern Aleutians (n= 35 islands). Harbor seal counts decreased at the majority of islands in each region, the number of islands with >100 seals decreased ～70%, and the number of islands with no seals counted increased ～80%, indicating that harbor seal abundance throughout the Aleutian Islands was substantially lower in the late 1990s than in the 1970s and 1980s.     

HOMING BEHAVIOR OF JUVENILE NORTHERN ELEPHANT SEALS

The aim of this study was to determine if juvenile northern elephant seals, Mirounga angustirostris , translocated from their rookery would return to it quickly and reliably. During the spring and fall of 1990 and 1991 we captured 75 seals at Año Nuevo State Reserve, CA, U. S. A. and translocated them to release sites up to 100 km away. Eighty-eight percent of the seals returned to the capture site within 4.7 ± 4.3 d. Homing rate increased with age, but even the youngest seals (8–10 mo) homed at a 73% rate. Homing rate did not vary significantly with sex, season, or year. Data from diving instruments suggested that the seals often followed direct routes home, arrived on the rookery significantly more often at night than during the day, and when released together, returned separately. Mean homing speed of 18 seals with complete diving records was 39 km/d (range 3–70 km/d). Instruments on seals had no detectable effect on homing rate or homing speed. The translocation paradigm provides a powerful tool for conducting intensive shortterm studies on free-ranging seals.     

DIFFERENTIAL MOVEMENTS BY HARBOR SEAL PUPS IN CONTRASTING ALASKA ENVIRONMENTS

Movement patterns of Alaska harbor seal pups were studied using satellite telemetry during 1997–2000. Mean tracking duration was 277.3 d (SD = 105.8) for Tugidak Island pups ( n = 26) and 171.2 d (108.3) for Prince William Sound (PWS) pups ( n = 27). Movements were similar for males and females and were largely restricted to the continental shelf. Multiple return trips of > 75 km from the natal area and up to ∼3 wk duration were most common, followed by movements restricted to <25 km from the natal area; one way movements from the natal site were rare. Distances moved and home range sizes remained relatively stable or increased gradually from July through winter, then decreased markedly through spring. Monthly movements (maximum distance from tagging location, mean distance from haul-outs to at-sea locations, and home range size) were significantly greater for Tugidak vs . PWS pups. Six of seven pups from each region that traveled farthest and were tracked the longest had returned to their tagging site when their last location was recorded, indicating philopatry or limited dispersal during their first year of life. Seal pups exhibited similar movement patterns in the distinct habitats of the two regions, but differed in the spatial extent of their movements.     

THE ABUNDANCE OF HARBOR SEALS IN THE GULF OF ALASKA

The abundance of harbor seals ( Phoca vitulina richardii ) has declined in recent decades at several Alaska locations. The causes of these declines are unknown, but there is concern about the status of the populations, especially in the Gulf of Alaska. To assess the status of harbor seals in the Gulf of Alaska, we conducted aerial surveys of seals on their haul-out sites in August-September 1996. Many factors influence the propensity of seals to haul out, including tides, weather, time of day, and time of year. Because these "covariates" cannot simultaneously be controlled through survey design, we used a regression model to adjust the counts to an estimate of the number of seals that would have been ashore during a hypothetical survey conducted under ideal conditions for hauling out. The regression, a generalized additive model, not only provided an adjustment for the covariates, but also confirmed the nature and shape of the covariate effects on haul-out behavior. The number of seals hauled out was greatest at the beginning of the surveys (mid-August). There was a broad daily peak from about 1100–1400 local solar time. The greatest numbers were hauled out at low tide on terrestrial sites. Tidal state made little difference in the numbers hauled out on glacial ice, where the area available to seals did not fluctuate with the tide. Adjusting the survey counts to the ideal state for each covariate produced an estimate of 30,035 seals, about 1.8 times the total of the unadjusted counts (16,355 seals). To the adjusted count, we applied a correction factor of 1.198 from a separate study of two haul-out sites elsewhere in Alaska, to produce a total abundance estimate of 35,981 (SE 1,833). This estimate accounts both for the effect of covariates on survey counts and for the proportion of seals that remained in the water even under ideal conditions for hauling out.     

Satellite tracking of grey seals (Halichoerus grypus)

Three types of Argos satellite transmitter were attached to grey seals ( Halichoerus grypus ) at Donna Nook (South Humberside, UK) between 1985 and 1989 in order to investigate their movements. With the first two transmitters (A and B) the entire package was attached to the seal's back. Seal A was tracked for 29 days but although it was located on sandbanks up to 150 km south-east of Donna Nook, no locations were obtained at sea. Transmitters B and C used a submergence sensor to regulate transmissions. Seal B was tracked for 51 days and remained within 40 km of Donna Nook. A few locations were obtained at sea but all within 10 km of Donna Nook. Transmitter C incorporated a head-mounted aerial in order to increase the number of location fixes when the seal was at sea. This seal was tracked for 111 days, producing an average of 9·1 location fixes per day while at sea. It used two sites 265 km apart and undertook three transits between them. On the second visit to the northern site it made several trips up to 55 km out to sea. The majority of the remainder of the time was spent within 10 km of the haulout sites. Estimates of swimming speed were consistent with values required for minimum cost of transport.     

Reaction of Harbor Seals to Cruise Ships

Abstract: The largest aggregations of harbor seals (Phoca vitulina) in Alaska, USA, haul out on floating ice in tidewater glacial fjords. Seals use these fjords in peak numbers during the critical periods of pupping, breeding, and molting when visits by tour ships also peak. Documented and suspected declines of harbor seals in fjords with rising vessel traffic underscore the need to better understand possible impacts, particularly in areas where ship visits have risen substantially in the past 2 decades. We examined the interruption of haul-out bouts of harbor seals due to approaching cruise ships in Disenchantment Bay, Alaska. We conducted observations from cruise ships and focused on disturbance of seals as evidenced by seals flushing into the water from the floating ice on which they rested. We investigated rate of flushing in relation to vessel distance, approach angle, group size, and seal type (mother, pup, or other). Using a survival-regression analysis, we found that the risk of disturbing harbor seals increased when ships approached within 500 m; seals approached as close as 100 m were 25 times more likely to enter the water than seals 500 m from a ship. Seals were 4 times more prone to enter the water when ships were approaching directly rather than passing abeam. Seals responded similarly regardless of group size or seal type. Energetic models indicated a potential to disrupt energy balance and cause thermal stress in disturbed pups if they spent >50% of their time in ice-chilled water. Studies at non-glacial sites suggest that pups spend 40–70% of their time in the water. Voluntary guidelines for approaching seals in Alaska recommend that cruise ships approach ≥91 m (100 yards), a distance at which we show 90% of seals would flush into the water. Our findings indicate a need to develop regulations to maintain a 500-m separation between cruise ships and seals in all Alaskan glacial fjords.     

Postrelease dive ability in rehabilitated harbor seals

The efficacy of seal rehabilitation is examined in a postrelease study of dive ability in harbor seal pups (Phoca vitulina) in the Wash, United Kingdom. Six rehabilitated seals were fitted with Sea Mammal Research Unit (SMRU) Argos Satellite Relay Data Logger tags and their individual dive behavior was monitored for an average of 122 d. The upper 90 percentile edge of dive behavior (dive duration [DD₉₀] and percentage of time at‐sea spent in a dive [PD₉₀]), in 7 d bins, was used as a proxy for physiological dive ability. The results are compared with data from five wild adult harbor seals. There was no statistically significant difference between (1) the mean track duration of rehabilitated seals (126.20 ± 27.48 [SD] d) and adult seals (150.2 ± 24.62 d) (P= 0.108), indicating no evidence that short‐term survival was less in the rehabilitated group; (2) the mean mass‐scaled DD₉₀ of rehabilitated seals (3.95 ± 0.37 min) and adult seals (4.09 ± 0.55 min) (P= 0.632); and (3) the mean PD₉₀ of rehabilitated seals (81.62 ± 1.21%) and adult seals (81.48 ± 3.93%) (P= 0.943). These three results all suggest the success of the rehabilitation program in terms of short‐term survival and dive ability.     

The role of Steller sea lions in a large population decline of harbor seals

We provide the first direct evidence that Steller sea lions will prey on harbor seals. Direct observations of predation on marine mammals at sea are rare, but when observed rates of predation are extrapolated, predation mortality may be found to be significant. From 1992 to 2002, harbor seals in Glacier Bay declined steeply, from 6,200 to 2,500 (∼65%). After documenting that Steller sea lions were preying on seals in Glacier Bay, we investigated increased predation by sea lions as a potential explanation for the large decline. In five independent data sets spanning 21–25 yr and including 14,308 d of observations, 13 predation events were recorded. We conducted a fine-scale analysis for an intensively studied haul-out (Spider Island) and a broader analysis of all of Glacier Bay. At Spider Island, estimated predation by sea lions increased and could account for the entirety of annual pup production in 5 of 8 yr since 1995. The predation rate, however, was not proportional to the number of predators. Predation by Steller sea lions is a new source of mortality that contributed to the seal declines; however, life history modeling indicates that it is unlikely that sea lion predation is the sole factor responsible for the large declines.     

EFFECTS OF MEAL SIZE ON OTOLITH RECOVERY FROM FECAL SAMPLES OF GRAY AND HARBOR SEAL PUPS

Recovered otoliths from pinniped feces provide valuable information on diet composition and prey size. We studied the effect of meal size on otolith recovery from the feces of one harbor and eight gray seal pups. Each of 11 experiments comprised a half-ration meal, a period of fecal collection, a 1.5-or double-ration meal again followed by a period of fecal collection. A significantly lower percentage of Atlantic herring otoliths were recovered from half-ration meals (25%± 12.5% in the harbor seal, 8.6%± 6.9% in eight gray seals) than from 1.5- or double-ration meals (62.5%± 3.1 % in the harbor seal, 32.8%± 23.5% in gray seals). Meal size also significantly affected the percentage of Atlantic cod otoliths recovered from gray seal feces (65.0%± 26.3% from half ration, 98.3%± 2.9% from 1.5 ration). For both size meals, recovered cod otoliths were more significantly eroded than herring otoliths. The development of correction factors to account for the effects of digestion will need to consider the distribution of meal sizes of free-ranging pinnipeds.