Marine Mammal Science

Haul-out behavior of ringed seals (Pusa hispida) was investigated during the spring molting period of 2003 (May-July) in Kongsfjorden, Svalbard, Norway. Hourly counts were conducted on the land-fast ice in six spatially defined sectors in the inner fjord, from an elevated land-based vantage point from early May through until the ice began to break up in June, from 0600 to 2200 daily (total counts n = 478). Concomitantly, measurements were made of a variety of weather parameters. Multiple regression analyses revealed that time of day (P < 0.001) and date (P < 0.001) significantly affected the number of ringed seals hauled out on the ice surface. Other factors influencing the number of seals counted on the ice were air temperature (P = 0.011) and wind speed (P < 0.001). Daily peaks occurred in the early afternoon between 1300 and 1400 and the seasonal high (n = 385) was registered during the first week in June, after which the number of seals on the ice in the fjord declined. In addition to the visual counts, 24 ringed seals were equipped with VHF transmitters, and the haul-out behavior of individuals was monitored from May through July via an automatic recording station. The VHF-tagged seals exhibited the same diurnal pattern seen in the total counts, with haul-out most frequent from 1300 to 1400. Pups exhibited short and frequent haul-outs, whereas longer haul-out periods were seen in the older age classes; adult females had the greatest number of haul-out periods that exceeded 24 h. The seasonal peak of haul-out for the tagged seals preceded the peak seasonal counts by approximately 3 wk. This may reflect significant out-and influx of seals from and to the area, a phenomenon warranting further attention because of its implications for assessment studies.

In phocid seals, blubber serves as the main thermal insulation instead of fur. The thermal function of fur, at least in adult phocid seals, has therefore been questioned. We measured the relative contribution of fur to the combined thermal resistance (insulation) offered by blubber, skin, and fur in newborn and adult harp (Pagophilus gvoenlandiczls) and hooded (Cystophora cristutu) seals, in air and water, to elucidate the role of fur as insulation in phocid seals. In air the fur contributed 70% of the combined thermal resistance of blubber, skin, and fur in newborn harp seal pups and 27% in adults, whereas in hooded seals the fur contributed 73% in newborn pups and 34% in adults. When submerged the thermal resistance of the fur was reduced by 84%-92%, and contributed 65% to the total insulation in newborn harp seal pups and 3% in adults, and 26% in newborn hooded seal pups and 5% in adults. We conclude that in air the fur of phocid seals makes an important contribution to the insulation of pups, and also contributes considerably to the insulation of adult animals. In water, even though the thermal resistance of the fur is dramatically reduced, the fur still contributes substantially to the insulation of pups, but its contribution in adults is negligible.

Adults of long-lived, birth-pulse populations (e.g., many cetaceans, polar bears and walrus) may not breed every year because of parental care, long gestation periods or nutritional constraints. Estimates of adult annual recruitment rates for such populations are necessarily an oversimplification since these rates are applied to both breeding and non-breeding females. The weighted mean of age-specific recruitment is insufficient for non-stable age projections of multi-annual populations beyond the first time interval. Restated, conventional or collapsed Leslie matrix and life-table projections are not adequate for non-stable age simulations of populations with multi-annual reproduction cycles. These difficulties may be avoided by employing a parameterization that accommodates a dynamic age structure and proportion of breeding females within a given age class. This parameterization is a true description of the multipleyear reproduction schedule. Examples, broadly mimicking the life history of polar bears, were used to identify potential qualitative errors that may occur from using overly simplified projection models.

The first evidence of exposure of free-ranging Florida manatees (Trichechus manatees latirostris) to a morbillivirus is reported. Blood samples were collected from 148 Florida manatees between 1977 and 1994. The sample included manatees that were under rehabilitation (n = 97), free-ranging (n = 40) and fresh necropsy specimens (n = 11). Serum from six animals (4%) neutralized porpoise and dolphin morbilliviruses to a higher titer than any other member of the Morbillivirus genus. Antibodies were not detected in sera from 12 freeranging Antillean manatees (T. manatus manatus) from Guyana sampled in 1992 or from 12 hand-reared Amazonian manatees (T. inunguis) sampled in 1984. Immunoprecipitation studies using radio-labelled canine distemper virus protein and serum from Florida manatees showed precipitation of the nucleocapsid (N) protein. The combination of low antibody titers and absence of clinical disease suggest that the Florida manatee is a dead-end host. Sporadic infection may occur following contact with another species in which infection is enzootic. Morbillivirus could, either by fatal infection or more insidious effects on the immune system or reproduction, pose a problem to this already threatened species.

The social structure of coastal ecotype bottlenose dolphins, Tursiops truncatus, is largely unknown as they inhabit regions far from shore. This study reports on a community of bottlenose dolphins ! 27 km from Grand Bahama Island (May-September, 1993-2002). Resident and non-resident dolphins occurred in the area. Some dolphins traveled over 320 km between communities; others showed longterm site fidelity up to 17 yr. Average group size was 3-5, and was significantly larger with calves present and significantly smaller when traveling. The half-weight index was used to determine coefficients of association (COA) for individuals of known sex annually and for pooled years. Permutation tests revealed non-random associations and presence of preferred/avoided companions in all data sets. Annual COAs were low: female-female x ¼ 0.31, male-male x ¼ 0.30, and mixed-sex x ¼ 0.26. Mother-calf associations showed the highest values. Some males formed strong, long-term bonds. Female COAs fluctuated with reproductive status. Using pooled data, COAs were lower and the same basic trends were evident. However, strong associations seen in the annual data were not evident in pooled data. Bottlenose dolphins that inhabit offshore, shallow water show many of the same social structure characteristics as in well-studied coastal populations.

The marine otter (Lutrafelina) lives exclusively along exposed rocky shorelines on the South American Pacific coast from Peru (6'9, to Cape Horn, Chile (56'S), and Isla de 10s Estados, Argentina. L. felina diet and its relationship to prey availability and energy content was assessed by spraint and prey remains analysis, direct observation, and the use of crab pots and fish traps, at four sites on the Valdivian coast in the south of Chile, between June 1999 and June 2000. Based on spraints analysis, the diet was composed of 25 species; 52% (13/25) of the species identified were crustaceans, 40% (10/25) were fish, and 8% (2/25) were mollusks. Crustaceans were found in 78% of 475 spraints, 100% of 929 prey remains, and 90.8% of prey determined by direct observation, fish in 20% of spraints and 9.0% of prey determined by direct observation, and mollusks in 2% of spraints and 0.2% of prey determined by direct observation. Observed seasonal variation in prey availability was reflected in the otter diet. Fourteen prey species were trapped; 43% (6114) were crustaceans and 57% (8/14) fish, crustaceans were 93% of 566 trapped individuals, fish 7%. L. felina showed opportunistic feeding behavior, selecting prey seasonally according to their availability rather than to their energy input.

Humpback whales (Megaptera novaeangliae) migrate long distances each year on a return journey from low-latitude breeding grounds to high-latitude feeding grounds. Migration is influenced by subtle and complex social behaviors and the assumption that whales transit directly through the migratory corridor off the east coast of Australia requires further investigation. From 2003 to 2005, we followed the movements of 99 individual whales within one migratory cycle from three locations, off Byron Bay during the whales' northern migration and in Hervey Bay and at Ballina during the southern migration. The median sighting interval of whales between Byron Bay and Hervey Bay (n = 26) was 52 d (IQR = 42.5-75.5); between Byron Bay and Ballina (n = 21) was 59 d (IQR = 47.0-70.0); and between Hervey Bay and Ballina (n = 33) was 9 d (8.0-14.0). The overall pattern observed from these resightings suggests that Group E1 humpback whales spend approximately two months in the northern quarter of their range during the austral winter months. Intraseason resightings of whales at Ballina (n = 13, median sighting interval = 7 d) also suggest that some individuals, particularly adult males, may circle back north 1 Corresponding author (e-mail: [email protected]). 562 during their general southward journey along this part of the coast, perhaps in an attempt to increase mating opportunities.

Little is known about the long-finned pilot whale's population size, structure, distribution and dynamics in the Western Mediterranean basin. The research region covered since 1992 in southeast Spain, at the edge of the Alboran Sea, is considered an important oceanographic transition zone between the Mediterranean and the Atlantic. The research ship Toftevaag carried out surveys covering a total of 10,173 nmi (18,840 km) from April to September each year, 1992September each year, -1997 years pooled. Effort for ten-by-ten-mile quadrats was stratified by depth and sea state to ascertain encounter rates. Tracking of animals was used together with photo-identification in order to analyze home range of groups. Behavior was recorded ad libitum, and underwater video taping was used to analyze specific behavior patterns. One hundred and nine sightings of pilot whales were made. The average group size was 41.4 ± 58.4, ranging from 1 to 350. The average depth at encounters was 848.7 ± 281.2 m. ranging from 300 to 1800 m. Comparison of results on encounter rate and group size with those for other Mediterranean regions, together with site fidelity shown by photoidentification and observations of reproductive behavior, reflect the importance of the Alboran Sea to the species in the Mediterranean.

Analyses of skeletal and external morphology of spinner dolphins killed in the yellowfin tuna purse-seine fishery in the eastern tropical Pacific led to the description of two subspecies of spinners from this region, the eastern spinner dolphin and the Central American spinner dolphin (Perrin 1990). However, when we examined lengths of spinner dolphins taken from vertical aerial photographs from the same area, we found three unique morphotypes. Two of these forms correspond, at least in average length and distribution, to the existing subspecies. The third form is intermediate in length between the two recognized subspecies and is found along the edge of the continental shelf north of Cab0 Corrientes, Mexico. We provisionally call this form the "Tres Marias spinner dolphin." Our results demonstrate the value of a mix of fishery and fishery-independent data in studies of stock structure of impacted species.

Quantifying the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographic variation, and social relevance. However, the vocalizations of free-ranging common dolphins (Delphinus sp.) have not previously been described from New Zealand waters. We present the first quantitative analysis of whistle characteristics to be undertaken on the New Zealand population. Acoustic data were collected in the Hauraki Gulf, North Island from 28 independent dolphin group encounters. A total of 11,715 whistles were collected from 105.1 min of recordings. Seven whistle contours were identified containing 29 subtypes. Vocalizations spanned from 3.2 to 23 kHz, with most whistles occurring between 11 and 13 kHz. Whistle duration ranged from 0.01 to 4.00 s (mean ± SD; 0.27 ± 0.32). Of the 2,663 whistles analyzed, 82% have previously been identified within U.K. populations. An additional six contours, apparently unique to New Zealand Delphinus were also identified. Data presented here offer a first insight into the whistle characteristics of New Zealand Delphinus. Comparisons with previously studied populations reveal marked differences in the whistle frequency and modulation of the New Zealand population. Interpopulation differences suggest behavior and the local environment likely play a role in shaping the vocal repertoire of this species.

Two experiments were conducted to determine the effect of vitamin A supplementation on serum vitamin E in adult female northern fur seals (Callorhinus ursinus). In the first experiment five animals received, in addition to their routine dietary multivitamin supplement, a high-level vitamin A supplement (53 pmol retinyl palmitate/d) for 30 d. Five seals consuming their routine dietary supplement served as controls. Serum vitamin E decreased significantly in animals receiving high-level vitamin A supplements. At the end of 30 d serum vitamin E averaged 18.6 pg I mL in the control animals and 13.4 pg/mL in the animals receiving the high-eve1 vitamin A supplement. In experiment 2 ten animals received the high level vitamin A supplement for 60 d. After 30 d, serum vitamin E levels were reduced, but by 60 d had returned to baseline levels. However, the ratio of serum vitamin E to phospholipid, another index of vitamin E status, remained decreased. Although the exact mechanism of interaction is unknown, this study shows that when providing vitamin supplements for captive pinnipeds, vitamin interactions must be considered. The vitamin A supplementation currently used by some institutions seems unnecessary and may have detrimental effects on vitamin E status.

Stable carbon (␦ 13 C) and nitrogen (␦ 15 N) isotopes are used frequently to describe the trophic ecology of top marine mammal predators. Australian sea lions (Neophoca cinerea) are one of the world's rarest otariid seals and exhibit the highest levels of natal site philopatry of any seal. We report the development of a screening technique to identify different foraging ecotypes and assess their relative frequencies in Australian sea lion breeding colonies using stable isotope ratios in pups. Geospatial and dive data from 15 adult females at three breeding colonies revealed alternate foraging strategies (inshore and offshore foraging) that were reflected in significant changes in ␦ 13 C and ␦ 15 N. Isotope fractionation from mother to pup was validated using paired whisker and blood serum samples with no significant difference between ␦ 13 C and ␦ 15 N enrichment of +1.27 (whiskers) and +1.92 (blood serum) from mothers to pups. Isotope ratios from whisker samples representing over 50% of pups born at three colonies revealed significant intercolony differences in maternal foraging ecotype frequencies. These results are unique in that ecological partitioning over such a small spatial scale has not been described in any other otariid species.

Humpback whales feed on a variety of prey, but significant differences likely occur between regional feeding grounds. In this study, the diets of humpback whales were analyzed by comparing stable isotope ratios in animal tissues at three humpback whale feeding grounds in the Russian Far East: Karaginsky Gulf, Anadyr Gulf, and the Commander Islands. Anadyr Gulf is a neritic zone far from a shelf break, Karaginsky Gulf is a neritic zone close to a shelf break, and the Commander Islands represent an open oceanic ecosystem where whales feed off the shelf break. Samples from the Commander Islands had the lowest mean d 13 C and d 15 N values (mean ± SE: d 13 C = −18.7 ± 0.1, d 15 N = 10.4 ± 0.1) compared to the samples from Karaginsky Gulf (d 13 C = −17.2 ± 0.1, d 15 N = 12.7 ± 0.2) and Anadyr Gulf (d 13 C= −17.8 ± 0.1, d 15 N = 14.0 ± 0.4). The samples from Anadyr Gulf had the highest d 15 N values, while the samples from Karaginsky Gulf had the highest d 13 C values. Both d 13 C and d 15 N values differed significantly among all three areas. Our data support the hypothesis that humpback whales tend to feed on fish in neritic areas and on plankton in deep oceanic waters.

Most studies of delphinid-trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal trawl gear. Using video cameras mounted inside trawl nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish trawl fishery in northwestern Australia. Footage from 36 trawls across the fishery was analyzed to determine the extent of dolphin-gear interactions and the behavior of dolphins inside the nets. Interaction rates were high, with dolphins present inside and outside the nets during 29 and 34 trawls, respectively, and for up to 99% of the trawl duration. The proportion of foraging behaviors exhibited inside the nets was higher than the proportions of traveling and socializing behaviors. Twenty-nine individuals were identified inside the net, seven of which returned repeatedly within and between trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering trawl nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of trawler-associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.

Morphometrics from 25 captive killer whales (1 1 captive-born) were collected at SeaWorld parks from 1984 to 1995 to determine age-specific growth parameters. For sexes combined, the body-volume index was the most accurate predictor of body weight. However, predicting weight from total length was appropriate, although it may underestimate weight of pregnant animals. Among captive-born calves, a Gompertz model was the best predictor of weight and length at age. Estimates for length and weight at birth were done using data from in utero and neonatal calves. For ages 1-5 yr, models indicate that males grew in both weight and length at slower rates. Growth rates in males may surpass those of females at approximately 5-6 yr of age.

The vaquita, Phocoena sinlls, is one of two critically endangered cetacean species, and is listed as an endangered species in both the United States and Mexico. These listings result from a small population size, estimated to be 224 animals, and a rapid decline in abundance (18% per annum) thought to be caused by human activities. To characterize the genetic composition of the vaquita, we have sequenced a portion of the mitochondria1 DNA control region from 43 individuals collected between 1985 and 1993. All animals had identical sequences. While low genetic variability has been reported for cetacean species, this complete lack of polymorphism in the control region is unique. This result is concordant with the hypothesis that the evolutionary ' This paper is dedicated to Dr. Ken Norris who, among his many other contributions to * Present address: Patricia Rosel, National Ocean Service, 219 Fort Johnson Road, Charleston, marine mammal science, was one of the first to recognize the vaquita as a new species.

The vaquita, Phocoena sinus, is a porpoise in the family Phocoenidae that lives only in the Gulf of California. The external appearance of P. sinus was unknown until 13 fresh specimens were recently examined. The most obvious morphological feature distinguishing P. sinus from its two congeners is the proportionately higher dorsal fin. The most striking features of the pigmentation pattern are the large black eye patches and the black upper and lower lip patches. In both areas, the pigmentation contrasts sharply with the surrounding light gray coloration. The total lengths of the specimens ranged from 70.3 cm (a neonate) to 143.5 cm (an adult female).

Studies of social differentiation between populations of killer whales (Orcinus orca) are important due to the cosmopolitan nature of the species, both in terms of distribution and feeding habits. The following research provides preliminary findings describing the social structure of the killer whale, Orcinus orca, population at subantarctic Marion Island. We provide evidence for consistent, observable patterns of social interactions with animals associating and disassociating in nonrandom patterns. We show that the social structure of this population may follow a new pattern of association, displaying a blend of the traditional resident/transient model displayed in the Northern Hemisphere. However, we emphasize the critical need for further studies related to the sociality, biology, and life history of Southern Ocean killer whales.

The Baikal seal (Phoca sibirica) is confined to Lake Baikal in southern Siberia. The breeding distribution of seals in winter, when the lake is frozen over, is fairly well known, whereas their movements and foraging behaviors have been relatively unstudied.

North Atlantic right whales (Eubdlaena gZ&alis) make a short, distinctive broadband sound that is produced internally called a Gunshot sound. This sound has been recorded in the Bay of Fundy, Canada from both single whales (n =9) and social surface active groups (n=49). Those single whales producing Gunshot sounds whose sex could be determined (n = 9) were all mature males. Gunshot sounds were produced as part of a stereotyped behavioral sequence by these individuals, including frequent head-lifts and flipper slapping at the surface. In surface active groups, Gunshot sounds were commonly recorded when males were present in the group. The rate of production of Gunshot sounds was weakly correlated with the total number of males present in the group. Given the behavioral context of Gunshot sound production, and production of the sound only by male whales, Gunshots may function in a reproductive context as an advertisement signal to attract females, an agonistic signal directed toward other males, or a combination of the two functions.

Accurate identification of human-induced injuries that lead to death or interfere with reproduction is important for marine mammal management, as deaths exceeding established limits can lead to restrictions on fisheries or vessel operations. The fates of cetaceans last seen swimming with attached gear, particularly in pelagic fisheries, or with vessel strike lacerations, have been difficult to predict. Survival and reproduction data from long-term research on resident common bottlenose dolphins near Sarasota, Florida were examined relative to consequences of fishing gear ingestion, line entanglements, vessel strikes, and amputations of unknown origins. Fishing hooks embedded in the throat, goosebeak, or esophagus, or line wrapped around the goosebeak, generally lead to death. Multiple, constrictive line wraps around fin insertions can lead to amputation, blood loss, impaired mobility, or infection. Dolphins with ingested gear or severe entanglements may swim away with the gear, but likely die later. Propeller injuries involving only soft tissue were often survivable. Some dolphins survived amputations of the distal ends of fins, and continued to reproduce. As a precautionary approach, dolphins with ingested gear or severe constrictive entanglements should be considered mortalities, but extrapolations of findings from coastal bottlenose dolphins to other cetaceans and different gear must be done with caution.

The use of perioral bristles (modified vibrissae) by 17 captive Florida manatees and approximately 20 wild manatees was analyzed. Captive manatees were fed six species of aquatic vegetation normally eaten in the wild (four freshwater species and two seagrasses). Inanimate objects were placed in the holding tanks with manatees at Lowry Park Zoological Gardens (Tampa, FL) to determine the degree to which perioral bristles were used in exploration and to define the range of manipulative behavior. In addition, behavioral observations were made on the use of perioral bristles during social interactions with conspecifics. Observations were recorded using a Hi8-format video camera. Florida manatees possess an unusually large degree of fine motor control of the snout and perioral bristles. The large and robust perioral bristle fields of the upper lip were used in a prehensile manner during feeding. Bristle use by manatees feeding on submerged vegetation differed from that seen during feeding on floating vegetation. Other behavioral use of the perioral bristles shows variation depending upon the situation encountered. The degree of plasticity of perioral bristle use supports our hypothesis that the vibrissal-muscular complex of the Florida manatee has evolved to increase the efficiency of grazing and browsing on aquatic vegetation and to fully maximize the potential of the manatee as a generalist feeder. The manipulative and sensitive nature of the manatee snout is likely a manifestation of a complex sensory and motor system which has evolved for marine mammal aquatic herbivores living in shallow turbid habitats.

Data gathered from both direct observations and from whaling catches indicate that humpbacks do not feed while on their tropical breeding grounds, but instead subsist on the large reserves of fat stored in their blubber (Slijper 1962, Brodie 1975. Examination of thousands of humpbacks caught in tropical regions, or on presumed migratory routes in sub-tropical waters, has consistently shown an absence of, or negligible amount of, prey organisms in the stomach (Chittleborough 1965, Dawbin 1966. Furthermore, whaling catch data clearly show that whales in late winter or early spring weighed significantly less and yielded fewer barrels of oil than animals of similar lengths killed during the summer feeding season (Lockyer 198 1). Stone et al. ( 1987) suggest that the presence of humpbacks at Bermuda, a way-point during the springtime northward migration, may be attributed to increased food availability, providing the first opportunity to feed after the wintering ground fast. These data, in combination with extensive behavioral observations made in the West Indies, demonstrate that humpback feeding behavior is highly seasonal, and a rare occurrence during the period of residency in low-latitude waters. For the record, however, we report here on a humpback whale observed feeding in one of the principal habitats of the West Indies breeding range. We also present more equivocal observations of apparent feeding by four other whales in the same area.

Consistent and well-defined criteria for the classification and measurement of humpback whale song features are essential for robust comparisons between investigators. Song structure terminology has been well-established and used by many authors, though at times inconsistently. This review discusses the development of the nomenclature describing humpback song and explores the potential significance of the often-overlooked variation in song patterns. Within the hierarchical definition of humpback song, the most problematic issues arise from the inconsistent delineation of phrase types, and the use of the metric of song duration without regards to variability in thematic sequence. With regards to the former, a set of guidelines is suggested to facilitate consistent delineation of phrases. With regards to the latter, current research demonstrates that the "song duration" metric has resulted in the disregard of variability at this level, which is more widespread than traditionally reported. An exemplar case is used to highlight the problem inherent in defining and measuring song duration. Humpback song is evaluated within the framework of avian songbird research, and a shift in analysis paradigm is recommended, towards phrase-based analyses in which sequences of phrases are treated as a salient feature of song pattern.

Astronavigation is a possible mechanism of offshore orientation in marine mammals. However, the basic prerequisite for astronavigation is to see enough stars of the night sky. This cannot be taken for granted in seals as, due to adaptations of their dioptric apparatus to the optical properties of water, seals are supposed to be myopic and astigmatic when out of the water under low light conditions. Using various real and artificial stars in a go/no-go response paradigm we therefore determined the minimum brightness at which a harbor seal (Phocu vztulinu) can detect stars. The dark-adapted seal was trained to look through an empty tube ("seal telescope") and to retract its head only when a star appeared at the opposite aperture. The seal reliably detected Venus or Sirius becoming suddenly visible when the telescope was moved across the night sky. Detection thresholds were determined using artificial stars (parallel light identical to starlight coming from the universe) of predefined brightness generated by an optical system installed in front of the seal's telescope. The seal detected artificial stars down to 4.4 stellar magnitudes. Although these results cannot present evidence for astronavigation, they imply that seals should see enough stars to allow such orientation mechanisms.

Sonar target strength measurements of several types of nets and associated gear were made using simulated dolphin echolocation signals. The different types of nets included (a) standard commercial monofilament gillnet used in the salmon mothership fishery, (b) prototype hollow core monofilament net, (c) Macah tribal cord setnet, and (d) multifilament nets. Target strength measurements were made at four angles of incidence, 0° (normal to net), 15°, 30°, and 45°. The standard gillnet had the smallest target strength which was relatively independent of the angle of incidence. The target strength based on the peak-to-peak values of the echoes varied from –59 to – 62 dB. Using echo energy within the integration time of Tursiops truncatus, the target strength was found to be between – 54 and –59 dB. Biosonar detection ranges for different sea state conditions were estimated using the noise-limited form of the sonar equation and target detection data obtained for Tursiops truncatus in Kaneohe Bay, Oahu, Hawaii. The results suggest that an echolocating dolphin should be able to detect a gillnet at ranges long enough to avoid entanglement, even in sea state 6 conditions. Several possibilities for the seeming inability of dolphins to detect gillnets are discussed.

The authors review the literature on bottlenose dolphin ecology, behavior and social organization, focusing on data collected on free-ranging animals. Most bottlenose dolphins studied to date have had definable home ranges, and behavioral, morphological and biochemical information indicates discrete stocks in some areas. Bottlenose dolphins appear to form relatively permanent social groups based on sex and age. Mother-calf bonds are long-lasting. Movement patterns are extremely variable from location to location but are relatively predictable at any given site. Food resources are one of the most important factors affecting movements.

We assessed scientists' ability to detect declines of marine mammal stocks based on recent levels of survey effort, when the actual decline is precipitous. We defined a precipitous decline as a 50% decrease in abundance in 15 yr, at which point a stock could be legally classified as "depleted" under the U.S. Marine Mammal Protection Act. We assessed stocks for three categories of cetaceans: large whales (n = 23, most of which are listed as endangered), beaked whales (n = 11, potentially vulnerable to anthropogenic noise), and small whales/dolphins/porpoises (n = 69, bycatch in fisheries and important abundant predators), for two categories of pinnipeds with substantially different survey precision: counted on land (n = 13) and surveyed on ice (n = 5), and for a category containing polar bear and sea otter stocks (n = 6). The percentage of precipitous declines that would not be detected as declines was 72% for large whales, 90% for beaked whales, and 78% for dolphins/porpoises, 5% for pinnipeds on land, 100% for pinnipeds on ice, and 55% for polar bears/sea otters (based on a one-tailed t-test, ␣ = 0.05), given the frequency and precision of recent monitoring effort. We recommend alternatives to improve performance.

The major challenges in immobilization of free-ranging walruses (Odobenw vosmaras divergem) are to produce a deep level of anesthesia very quickly (to avoid darted animals from entering the water and drowning), and to find a drug or drug combination that requires only a small volume to be delivered by dart, is safe, reversible, and that provides an adequate period of immobilization to permit attachment of instruments, phlebotomy, and measuring. Tiletamine-zolazepam is recommended for immobilization of pinnipeds, with inhalant anesthesia recommended for more extensive procedures requiring better analgesia (Gales 1989