bluuebunny/crossref_metadata_2025 huggingface dataset:
PHYLOGENETIC RELATIONSHIPS OF BRYDE'S WHALES IN THE WESTERN NORTH PACIFIC AND ADJACENT WATERS INFERRED FROM MITOCHONDRIAL DNA SEQUENCES1
Authors: Yoshida Hideyoshi , Kato Hidehiro
Published: August 2006

Abstract

To clarify phylogenetic relationships of Bryde's whales, we examined the nucleotide sequence of the mitochondrial control region and cytochromebgene in 33 animals: 12 from offshore waters of the western North Pacific, five from off the Solomon Islands, and 16 from the East China Sea and coastal waters of Kochi in southwestern Japan. For reference purposes, homologous sequences from fourBalaenopteraspecies including four Bryde's whales collected in the eastern Indian Ocean were added. We found whales from the three sampling areas to be genetically distinct. The control region sequences suggested that the whales from the three areas separate at higher than the populational level from one another. The cytochromebdata indicated that genetic differences between whales off the Solomon Islands and animals in the other two areas are equivalent to values found among recognizedBalaenopteraspecies, although such a relationship was not observed between the other two areas. We conclude that whales in the East China Sea and coastal waters of Kochi separate from Bryde's whales in offshore waters of the western North Pacific at higher than the populational level but lower than the specific level (i. e., at the subspecific level) and that whales off the Solomon Islands do not belong genetically to the Bryde's whale as previously recognized.
DARK ADAPTATION AND VISUAL SENSITIVITY IN SHALLOW AND DEEP‐DIVING PINNIPEDS1
Authors: Levenson David H. , Schusterman Ronald J.
Published: August 2006

Abstract

Pinnipeds forage almost exclusively underwater. Consequently, observing them is difficult and relatively little is known of how they use their senses to locate prey, avoid predators, and navigate while diving. Vision has been presumed to be of primary importance, although previous measurements of visual functioning in pinnipeds have been restricted to just a few shallow‐diving species. As diving pinnipeds experience rapid changes in light levels during descent/ascent and low light levels at depth, it has not been clear whether they possess visual capabilities adequate for use while diving, particularly in the case of deep‐diving species. To examine this issue, behavioral psychophysics have been used to assess and compare the dark adaptation rates and relative light sensitivities of a deep‐diving pinniped (northern elephant seal, Mirounga angustirostris), two shallow‐diving species (California sea lion, Zalophus californianus, and harbor seal, Phoca vitulina), and a human subject.

In comparison to the human subject, both the California sea lion and the harbor seal dark‐adapted relatively quickly and were more light sensitive. These findings suggest that both of these species are well suited for vision in the moderately dim shallow‐water environments in which they dive to forage. In contrast, the elephant seal reached complete dark adaptation in less than half the time taken by the other pinnipeds, and it was significantly more light sensitive. Unlike the shallower‐diving species, the visual abilities of the elephant seal are commensurate with the extreme conditions experienced while deep diving. Thus, we conclude that elephant seals are sufficiently adapted to rely on vision underwater, even while diving to depths in excess of 1000 meters where bioluminescence may be the sole source of ambient light.
OCCURRENCE, PHOTO‐IDENTIFICATION AND PREY OF PACIFIC WHITE‐SIDED DOLPHINS (LAGENORHYNCUS OBLIQUIDENS) IN THE BROUGHTON ARCHIPELAGO, CANADA 1984–1998
Authors: Morton Alexandra
Published: August 2006

Abstract

This study summarizes occurrence of Pacific white‐sided dolphins (Lagenorhyncus obliquidens) in the Broughton Archipelago on the west coast of Canada, from October 1984 through December 1998. Dolphins were detected on 472 d. The annual percent of total occurrence rose from 0.4% in 1984 to 19% in 1994 and then declined to 2% in 1998. Seasonal occurrence peaked from 1 October through January. Dolphin group size ranged from 2 to 1,000; the most common range was 11‐50. While unreported for the Broughton Archipelago prior to 1984, the species is represented by teeth distributed throughout the past 2,000 yr of First Nations midden sediment, suggesting sporadic long‐term occurrence. Increased water temperature from the 1937–1984 mean of 8.6°C, to the 1985–1998 mean of 9.3°C and increased abundance of two fish populations in the study area are considered potential factors in the recent increase in occurrence. Of the 675 naturally marked dolphins that were photo‐identified, 214 were resighted. A pair of dolphins was photographed swimming in tandem, fourteen months apart. Tight groups, of five or fewer extensively scarred dolphins with extremely falcate dorsal fins were seen within every aggregation of over 50 animals, suggesting the existence of all‐male associations. Prey species were collected from 25 encounters with feeding dolphins; they included herring (Clupea harengus), capelin (Mallotus villosus), and Pacific sardine (Sardinops sagax). Predation on eulachon (Thaleichthys pacificus) is suspected. Unreported for the Broughton Archipelago, the capelin sampled in this study may belong to the Bering Sea population. Pacific sardines returned to commercial viability on the British Columbia coast in 1997 after a 60‐yr population collapse. Dolphin frequency of occurrence declined following introduction of underwater acoustic deterrent devices into the study area.
BACULAR AND TESTICULAR GROWTH AND ALLOMETRY IN THE CAPE FUR SEALARCTOCEPHALUS P. PUSILLUS(OTARIIDAE)
Authors: Oosthuizen W. H. , Miller E. H.
Published: August 2006

Abstract

The baculum inArctocephalus p. pusillusreaches up to 14.1 cm in length, 13.5 g in mass, and 1.3 g/cm in density (= mass/length). A pubertal growth spurt occurs between 2 and 3 yr of age, when bacular length increases by 28%, mass by 124%, and density by 77%; concurrently, body length increases by 14%. A second, weaker spurt occurs at social maturity (9‐10 yr of age). Testes grow most rapidly between 1 and 2 yr of age, when testicular length increases by 29%. After 3 yr of age, growth in bacular and testicular length slows, and bacular mass continues to increase approximately linearly. Bacular and testicular lengths average 6.8% and 3.4% (respectively) of body length in adults, compared with 9.9% and 5.7% in the promiscuous harp seal (Pagophilus groenlandicus). Bacular length, mass, and density, and testicular length, are positively allometric to body length over growth; bacular length is isometric to testicular length. Among animals of the same age, bacular length and mass are positively allometric to body length in young animals, with negative allometry or isometry thereafter; testicular length is isometric to body length in young animals and negatively allometric thereafter. Patterns of early growth and allometry of the baculum and testes are interpreted as adaptations for mating opportunities, years before territoriality is possible. The baculum and testes of adult Cape fur seals and other otariids are small compared with those of most phocids, because sperm competition among male otariids is weak.
ATTENDANCE PATTERNS OF CALIFORNIA SEA LION (ZALOPHUS CALIFORNIANUS) FEMALES AND PUPS DURING THE NON‐BREEDING SEASON AT SAN MIGUEL ISLAND
Authors: Melin Sharon R. , Delong Robert L. , Thomason James R. , Vanblaricom Glenn R.
Published: August 2006

Abstract

The attendance patterns of California sea lions were studied during the non‐breeding seasons from 1991 to 1994. Lactating females frequented the rookery to nurse their pups until weaning; most non‐lactating females left the rookery for the season. Females spent over 70% of their time at sea except in 1993 when they spent 59% of their time at sea. The mean foraging trip length in the winter and spring ranged from 3.3 to 4.6 d; the mean nursing visit ranged from 1.2 to 1.4 d. The duration of foraging trips and nursing visits was variable over the season for individuals but no pattern of change was detected. Interannual and seasonal differences were not significant for time at sea, visits ashore, or foraging‐trip duration before, during, or after the 1992‐1993 El Niño event. Pups spent an average of 66.6% of their time ashore and up to three days away from the rookery during their mother's absence. Most females and pups stayed associated until April or May. The results suggest that seasonal movement of prey is more important in determining attendance patterns late in the lactation period than increasing energy demands of the pup.
AGE‐ AND SEX‐SPECIFIC MORTALITY AND POPULATION STRUCTURE IN SEA OTTERS
Authors: Bodkin James L. , Burdin Alexander M. , Ryazanov Dmitry A.
Published: August 2006

Abstract

We used 742 beach‐cast carcasses to characterize age‐ and sex‐specific sea otter mortality during the winter of 1990‐1991 at Bering Island, Russia. We also examined 363 carcasses recovered after the 1989 grounding of the T/V Exxon Valdez, to characterize age and sex composition in the living western Prince William Sound (WPWS) sea otter population. At Bering Island, mortality was male‐biased (81%), and 75% were adults. The WPWS population was female‐biased (59%) and most animals were subadult (79% of the males and 45% of the females). In the decade prior to 1990‐1991 we found increasing sea otter densities (particularly among males), declining prey resources, and declining weights in adult male sea otters at Bering Island. Our findings suggest the increased mortality at Bering Island in 1990‐1991 was a density‐dependent population response. We propose male‐maintained breeding territories and exclusion of juvenile females by adult females, providing a mechanism for maintaining densities in female areas below densities in male areas and for potentially moderating the effects of prey reductions on the female population. Increased adult male mortality at Bering Island in 1990‐1991 likely modified the sex and age class structure there toward that observed in Prince William Sound.
REPRODUCTIVE RATES OF HUMPBACK WHALES OFF CALIFORNIA
Authors: Steiger Gretchen H. , Calambokidis John
Published: August 2006

Abstract

From 1986 to 1996 we examined the reproductive rates, calving rates, and reproductive histories of mature females as part of photo‐identification studies of humpback whales that feed off California, Oregon, and Washington during summer and fall. Annual reproductive rates were measured by two methods: proportion of all whales that were calves based on sightings (0.6%‐5.9% per year, mean = 3.6%, SD = 1.6) and based on individually identified animals (1.1%‐8.0% per year, mean = 4.1%, SD = 1.8). The reproductive rate based on sightings varied significantly by year (G test, P < 0.001), region (G test, P < 0.001), and by month (G test, P < 0.05). Seventy‐nine sexually mature females were identified with 97 calves out of a total of 844 known individuals over the 11‐yr study. Mother‐calf separation on the feeding grounds was recorded in several instances. The apparent reproductive rates of this population are considerably lower than rates of 4%–15% reported from other feeding areas for this species. Our estimates are likely biased downward because this population has been increasing at about 5% per year. Calves may have been missed due to early weaning and because of our sampling from small boats late in the season. We also found evidence of geographic segregation of mother‐calf pairs within our large study area. Despite these factors, we conclude the reproductive rate of this population appears to be lower than has been reported in other areas.
POLYDACTYLY AND OTHER FEATURES OF THE MANUS OF THE VAQUITA, PHOCOENA SINUS
Authors: Ortega‐Ortiz Joel G. , Villa‐Ramírez Bernardo , Gersenowies Jorge R.
Published: August 2006

Abstract

The vaquita (Phocoena sinus) manus was examined in 16 individuals. The carpus has a proximal row of three bones and a cartilaginous accessory carpal element distocaudal to the ulna. Five metacarpal bones are present. A process in distocaudal aspect of Metacarpal III and an additional digital ray were present in all individuals examined. The number of phalanges in the additional digital ray varied among individuals and, sometimes, between the left and the right flipper of the same individual. The suggested phalangeal formula is I‐1, II‐7‐8, III‐6‐7, IV‐0‐3, V‐3‐4, VI‐1. The presence of this particular form of polydactyly may be the result of genetic drift in the small vaquita population.
RIGHT WHALES (EUBALAENA GLACIALIS) ON JEFFREYS LEDGE: A HABITAT OF UNRECOGNIZED IMPORTANCE?
Authors: Weinrich Mason T. , Kenney Robert D. , Hamilton Phillip K.
Published: August 2006

Abstract

North Atlantic right whales (Eubalaena glacialis) are known to spend the majority of the year between the Great South Channel southeast of Cape Cod, and the Nova Scotian shelf. We examined sightings of right whales on and around Jeffreys Ledge, a 54‐km‐long glacial deposit off the coast of northern Massachusetts, New Hampshire, and Maine. Sightings on Jeffreys Ledge were extracted from three data sets: (1) a systematic survey of the entire northeastern continental shelf between 1979 and 1982, (2) whale‐watch and research‐cruise sighting data from 1984 to 1997, and (3) a collaborative database of sightings collected by organizations conducting right whale research and all other available sources. Each database supported two seasonal sighting peaks. During summer (especially July and August) sightings were primarily of mother‐calf pairs. Several cow‐calf pairs were seen over several days to weeks. Several females were resighted in more than one year, but only when calves were present. During October, November, and December, sightings included all age classes, surface‐feeding behavior was frequently observed, and some animals were resighted over several weeks. Given the relatively reduced sighting effort during fall, this number of sightings is surprising. During the 20 yr of observations, 52 of 374 photo‐identified North Atlantic right whales (13.9%) were seen at least once on Jeffreys Ledge. We suggest that Jeffreys Ledge may be a more important right whale habitat than previously believed, and that it may play an important role in annual movements and distribution of this population.
STELLER SEA LION BODY CONDITION INDICES
Authors: Pitcher K. W. , Calkins D. G. , Pendleton G. W.
Published: August 2006

Abstract

We evaluated various measurements of mass, morphology, and blubber thickness as indices of fatness for Steller sea lions by correlation with the percentage of total body mass comprised by the sculp (%SCULP). We concluded LMD‐index was the best index evaluated because it had a relatively high r2 (0.58), had a linear relationship with %SCULP, and the intercept term was not different from O. We suggest the development of a LMD‐index for otariids would likely reduce the unexplained variation in the index. We developed a multiple regression model (r2= 0.745, P < 0.001) for predicting %SCULP with LMD‐index and functions of sex, age, and season as predictor variables. Steller sea lions < 5 yr of age had higher %SCULP values than those ≥ 5 yr. %SCULP declined with age for sea lions < 5 yr. Both younger and older males were fatter during the winter/spring period than during summer/ fall. Females of both age classes had similar %SCULP values throughout the year. Steller sea lions are relatively lean pinnipeds; estimates of blubber and total body lipids ranged from 5% to 17% of total body mass.
ANALYSIS OF MITOCHONDRIAL DNA DIVERSITY WITHIN AND BETWEEN NORTH AND SOUTH ATLANTIC RIGHT WHALES
Authors: Malik S. , Brown M. W. , Kraus S. D. , White B. N.
Published: August 2006

Abstract

DNA sequences of the mitochondrial control region of 180 North Atlantic right whales (Euhalaena glacialis) and 16 South Atlantic right whales (E. australis) have been determined using a combination of direct DNA sequencing and single stranded conformation polymorphism (SSCP) analysis. Five haplotypes were found in E. glacialis, and 10 in E. australis, but none were shared, supporting the reproductive isolation and separate species status of the North and South Atlantic right whales. One haplotype in E, glacialis was found in only three males born before 1982 and this matriline will likely be lost soon. The nucleotide diversity estimates for the five North Atlantic right whale haplotypes was 0.6% and 2.0% for the 10 haplotypes found in the South Atlantic right whales. The average haplotypic diversity was 0.87 in E. glacialis and 0.96 in E. australis, which is consistent with other studies showing a lower level of genetic variation in the North Atlantic right whale. Phylogenetic analysis identified two major assemblages of haplotypes in E. australis from the samples collected from Peninsula Valdes, suggesting a mixing of two historically divergent populations. Using genetic distance measurements with a divergence rate of 0.5%–1.0%/myr, we estimate E. glacialis diverged from E. australis 3–12.5 mya.
MIGRATION AND POPULATION STRUCTURE OF NORTHEASTERN PACIFIC WHALES OFF COASTAL BRITISH COLUMBIA: AN ANALYSIS OF COMMERCIAL WHALING RECORDS FROM 1908‐1967
Authors: Gregr Edward J. , Nichol Linda , Ford John K. B. , Ellis Graeme , Trites Andrew W.
Published: August 2006

Abstract

Data recorded from 24,862 whales killed by British Columbia coastal whaling stations between 1908 and 1967 revealed trends in the abundance, sex ratios, age structure, and distribution of sperm (Physeter macrocephalus), fin (Balaenoptera physalus), sei (Balaenoptera borealis), humpback (Megaptera novaeangliae), and blue (Balaenoptera musculus) whales. The catch data were analyzed using annual and monthly mean values. Monthly and annual variation in whaling effort was deduced from accounts of the history of British Columbia coastal whaling, and biases arising from changes in effort were considered in the interpretation of the results. During the later years of whaling (1948‐1967), the mean lengths of captured whales declined significantly and pregnancy rates dropped to near zero in fin, sei, and blue whales. Monthly patterns in numbers killed revealed a summer migration of sei and blue whales past Vancouver Island, and confirms anecdotal suggestions that local populations of fin and humpback whales once spent extended periods in the coastal waters of British Columbia. Furthermore, the data strongly suggest that sperm whales mated (April‐May) and calved (July‐August) in British Columbia's offshore waters. The historic whaling records reveal much about the migratory behavior and distribution of the large whales species as they once were, and may continue to be, in the northeastern Pacific. Verifying the persistence of these trends in the remnant populations is a necessary and logical next step.
THE RELIABILITY OF SKINFOLD‐CALIPERS FOR MEASURING BLUBBER THICKNESS OF STELLER SEA LION PUPS (EUMETOPIAS JUBATUS)
Authors: Jonker Remco A. H. , Trites Andrew W.
Published: August 2006

Abstract

Twelve dead Steller sea lion pups (Eumetopias jubatus) aged 3‐14 d were recovered from rookeries in Southeast Alaska. They had a wide range of body sizes and conditions (small to large and fat to no fat). The ability of calipers to estimate the thickness of their blubber layer was assessed with a set of skinfold calipers. Average error of measurement for skin and blubber thickness was an acceptable 5.4%, but the skin and blubber of the pups were highly compressible. Skinfold thickness increased with body mass but did not necessarily reflect the development of blubber, given that pups with no blubber also showed an increase in skinfold thickness with increases in body mass. Skinfold thickness of sea lion pups appears to predict body size better than it predicts blubber thickness, making it difficult if not impossible to develop a simple index of body condition or a calculation of percent body fat for Steller sea lion pups from skinfold caliper measurements.
TWO APPROACHES TO COMPRESSING AND INTERPRETING TIME‐DEPTH INFORMATION AS AS COLLECTED BY TIME‐DEPTH RECORDERS AND SATELLITE‐LINKED DATA RECORDERS
Authors: Fedak Michael A. , Lovell Phil , Grant Susanna M.
Published: August 2006

Abstract

Time‐depth recorders sample information about the three‐ dimensional behavior of diving animals over time and reduce this into just two dimensions, depth and time. Even so, interpretation of the data may still be difficult because of the volume of data and the detail that remains. Comparison of dive “shape” across individuals, geographical locations, or species presents problems because its analysis may involve subjective judgments or arbitrary distinctions. More constraints may be imposed if a telemetry system is used to transmit the data. Here we present two approaches for dive data compression and analysis. The first (applied before storage and transmission) selects the most important time‐depth points in a profile where depth Vs. time trajectories change most significantly. The second (used to either preprocess or postprocess dive information) creates a dimensionless, depth, and duration independent index (TAD), which encapsulates the relevant information from dive profiles on where the diver centers its activity with respect to depth during a dive. Its use facilitates comparison across dives performed at different times or places, within or between individuals or species, irrespective of the duration and depth of their dives. Both can be used to reduce the amount of information sent or stored about dive behavior and can facilitate dive analysis.
COUNTING STELLER SEA LION PUPS IN ALASKA: AN EVALUATION OF MEDIUMFORMAT, COLOR AERIAL PHOTOGRAPHY
Authors: Snyder Gary M. , Pitcher Kenneth W. , Perryman Wayne L. , Lynn Morgan S.
Published: August 2006

Abstract

Estimates of Steller sea lion (Eumetopias jubatus) pup production are valuable for estimating population trend and size. Currently in Alaska, pups are counted by visiting rookeries, driving older animals into the water, then walking through the rookeries and counting the pups, a highly disruptive procedure. At smaller rookeries, with good vantage points, pups are occasionally counted from the periphery of rookeries without disturbing the sea lions. We evaluated counts made from medium‐format, color, aerial photographs as an alternative to drive counts and peripheral counts. Neither the peripheral counts nor the aerial photographic counts disturbed animals on the rokeries. There were strong 1:1 linear relationships between photographic counts and drive counts (r2= 0.966, P < 0.001) and between photographic counts and peripheral counts (r2= 0.999, P < 0.001). Precision was similar for all three methods of counting. We suggest that medium‐format, color, aerial photographs is appropriate for routine surveys of Steller sea lion pups in Alaska because it is not disruptive to the hauled‐out sea lions and provides comparable estimates with similar precision to drive and peripheral counts. Large areas canbe rapidly surveyed during periods of good weather with a minimum of manpower.
SEX DIFFERENCES IN BODY SIZE AND BODY CONDITION OF CALIFORNIA SEA LION (ZALOPHUS CALIFORNIANUS) PUPS FROM THE GULF OF CALIFORNIA
Authors: Luque Sebastián P. , Aurioles‐Gamboa David
Published: August 2006

Abstract

The Gulf of California harbors about 15% of the total California sea lion (Zalophus californianus californianus) population. We studied pup morphometrics from eight Gulf of California rookeries during the 1996 and 1997 reproductive seasons to describe sex differences in body size and body condition indices. Newborn pup body size was not different from previous reports. Male pups were heavier and larger than female pups in terms of all linear dimensions. Morphometric relationships, however, showed that males were 3%‐4% denser, and that after removing the effects of length, they were about 2% heavier than females. Sculp depth adjusted for length was 12% larger in female than in male pups. Our data provide further evidence that male otariid pups may allocate a larger fraction of milk energy to muscular and skeletal growth compared to female pups.
STATUS, RELATIONSHIPS, AND DISTRIBUTION OF MESOPLODON BOWDOINI ANDREWS, 1908 (CETACEA: ZIPHIIDAE)
Authors: Baker Alan N.
Published: August 2006

Abstract

The specific status of Mesoplodon bowdoini Andrews is reviewed and new information on its morphology, reproduction, and distribution is presented. This species of beaked whale, known only from 35 specimens, has a southern, circumpolar distribution north of the Antarctic convergence, between 32° and 54°30′S. It shares with M. bahamondi Reyes, Van Waerebeek, Cárdenas and Yáñez from the south Pacific Ocean including New Zealand (this paper) and M. carlhubbsi Moore from the north Pacific, a number of morphological features such as prominential notches in the maxillary bones in the skull. It is less similar to M. stejnegeri True from the north Pacific and M. ginkgodens Nishiwaki and Kamiya from the tropical Indo‐Pacific. Mesoplodon bowdoini can be distinguished from all other species of Mesoplodon by the shape of its teeth (male and female), and differences in the morphology of its skull, especially the proportions of the rostrum, separation of the nasals, the shape of the prominential notches, and the nature of the antorbital processes. The species' distinguishing external characteristics are: a robust body up to about 4.50 m long; a low melon and short, thick beak; an elevated jawline posteriorly; and a low, blunt‐tipped, triangular dorsal fin. The occurrence of fetuses of M. bowdoini in May and September, and perinatal juveniles in May and June, indicates a summer‐autumn breeding season in the New Zealand region; the length at birth is estimated at about 2.20 m.
SHARK ATTACKS ON BOTTLENOSE DOLPHINS (TURSIOPS ADUNCUS) IN SHARK BAY, WESTERN AUSTRALIA: ATTACK RATE, BITE SCAR FREQUENCIES, AND ATTACK SEASONALITY
Authors: Heithaus Michael R.
Published: August 2006

Abstract

Shark predation may have been a central factor influencing the evolution of sociality in dolphins, as well as a determinant of dolphin habitat use and behavior. To understand the role of predation in driving interpopulation differences in behavior and sociality, it is important to quantify differences in predation risk among populations. This study describes the frequency of shark‐inflicted scars and estimates the shark attack rate on bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia. Shark bite scars were found on 74.2% (95 of 128) of non‐calves, and most of these scars were inflicted by tiger sharks (Galeocerdo cuvier). Although there were no differences among age/sex classes in the frequency of scarring, significantly more adult males than adult females bore multiple scars. The rate of unsuccessful shark attack was estimated to be between 11% and 13% of dolphins attacked each year. Large sharks (>3 m) were responsible for a disproportionate number of attacks. However, bites from small carcharhinid sharks on 6.2% of dolphins suggest that some of these small sharks may be dolphin ectoparasites. Both the scar frequencies and attack rate suggest that Shark Bay dolphins face a greater risk of predation than bottlenose dolphins in other locations.
UNOBSERVED KILL OF NURSING DOLPHIN CALVES IN A TUNA PURSE‐SEINE FISHERY
Authors: Archer Frederick , Gerrodette Tim , Dizon Andrew , Abella Karen , Southern ŠÁRKA
Published: August 2006

Abstract

The kill of dolphins (Stenella attenuata and S. longirostris) in the eastern tropical Pacific tuna purse‐seine fishery has been underestimated because of unobserved deaths of nursing calves due to separation from their mothers during fishing. Based on an analysis of dolphins killed from 1973 to 1990, and depending on the length at which calves are assumed to become independent, there was a deficit of calves relative to the number of lactating females killed in 24%–32% of 1,847 spotted‐dolphin sets and in 13%–19% of 563 spinner‐dolphin sets. We found a deficit of 0.31–0.45 spotted dolphin and 0.15–0.26 spinner dolphin calves per set. If these missing calves were added to the observed kill, it would represent an increase in the kill of 10%–15% for spotted dolphins and 6%–10% for spinner dolphins in the sets we examined. We did not attempt to estimate the actual number of unobserved calf deaths due to purse‐seine fishing on dolphins, either in the sets we examined or in all dolphin sets. The actual number of unobserved calf deaths is likely to be higher than the calf deficit we found. Separation of dolphin mothers from calves could occur at any of several points in the fishing process, but most of these would be invisible to us and not produce a calf deficit. Estimation of the actual number of unobserved calf deaths would require further information on how frequently permanent mother‐calf separations occur, the fraction of calves that survive after separation, the fraction of lactating females set upon that are carrying calves, and the fraction of calves killed that are actually related to lactating females killed in the same set. In any case, the observation of a calf deficit indicates that the reported dolphin kill fails to measure the full impact of purse‐seine fishing on spotted and spinner dolphin populations.
SUMMER DIVING BEHAVIOR OF MALE WALRUSES IN BRISTOL BAY, ALASKA
Authors: Jay Chadwick V. , Farley Sean D. , Garner Gerald W.
Published: August 2006

Abstract

Pacific walruses (Odobenus rosmarus divergens) make trips from ice or land haul‐out sites to forage for benthic prey. We describe dive and trip characteristics from time‐depth‐recorder data collected over a one‐month period during summer from four male Pacific walruses in Bristol Bay, Alaska. Dives were classified into four types. Shallow (4 m), short (2.7 min), square‐shaped dives accounted for 11% of trip time, and many were probably associated with traveling. Shallow (2 m) and very short (0.5 min) dives composed only 1% of trip time. Deep (41 m), long (7.2 min), square‐shaped dives accounted for 46% of trip time and were undoubtedly associated with benthic foraging. V‐shaped dives ranged widely in depth, were of moderate duration (4.7 min), and composed 3% of trip time. These dives may have been associated with navigation or exploration of the seafloor for potential prey habitat. Surface intervals between dives were similar among dive types, and generally lasted 1–2 min. Total foraging time was strongly correlated with trip duration and there was no apparent diel pattern of diving in any dive type among animals. We found no correlation between dive duration and postdive surface interval within dive types, suggesting that diving occurred within aerobic dive limits. Trip duration varied considerably within and among walruses (0.3–9.4 d), and there was evidence that some of the very short trips were unrelated to foraging. Overall, walruses were in the water for 76.6% of the time, of which 60.3% was spent diving.
STOCK STRUCTURE OF SEA OTTERS (ENHYDRA LUTRIS KENYONI) IN ALASDA
Authors: Gorbics C. S. , Bodkin J. L.
Published: August 2006

Abstract

Sea otters in Alaska are recognized as a single subspecies (Enhydra lutris kenyoni) and currently managed as a single, interbreeding population. However, geographic and behavioral mechanisms undoubrably constrain sea otter movements on much smaller scales. This paper applies the phylogeographic method (Dizon et al. 1992) and considers distribution, population response, phenotype and genotype data to identify stocks of sea otters within Alaska. The evidence for separate stock identity is genotypic (all stocks), phenotypic (Southcentral and Southwest stocks), and geographic distribution (Southeast stock), whereas population response data are equivocal (all stocks). Differences in genotype frequencies and the presence of unique genotypes among areas indicate restricted gene flow. Genetic exchange may be limited by little or no movement across proposed stock boundaries and discontinuities in distribution at proposed stock boundaries. Skull size differences (phenotypic) between Southwest and Southcentral Alaska populations further support stock separation. Population response information was equivocal in either supporting or refuting stock identity. On the basis of this review, we suggest the following: (1) a Southeast stock extending from Dixon Entrance to Cape Yakataga; (2) a Southcentral stock extending from Cape Yakataga to Cape Douglas including Prince William Sound and Kenai peninsula coast; and (3) a Southwest stock including Alaska Peninsula coast, the Aleutians to Attu Island, Barren, Kodiak, Pribilof Islands, and Bristol Bay.
AN ESTIMATION OF CARRYING CAPACITY FOR SEA OTTERS ALONG THE CALIFORNIA COAST
Authors: Laidre Kristin L. , Jameson Ronald J. , Demaster Douglas P.
Published: August 2006

Abstract

Carrying capacity (K) for the California sea otter (Enhydra lutris nereis) was estimated as a product of the density of sea otters at equilibrium within a portion of their existing range and the total area of available habitat. Equilibrium densities were determined using the number of sea otters observed during spring surveys in 1994, 1995, and 1996 in each of three habitat types where sea otters currently exist. Potential sea otter habitat was defined as from the California coastline to the 40‐m isobath and classified as rocky, sandy, or mixed habitat according to the amount of kelp and rocky substrate in the area. The amount of habitat available to sea otters in California was estimated using a Geographic Information Systems (GIS) program. The estimated mean number of sea otters that could be supported by the marine environment to a depth of 40 m in California was 15,941 (95% CI 13,538–18,577). The GIS‐based approach incorporated detailed bathymetric contours, produced repeatable and accurate estimates, and served as an innovative method of measuring sea otter habitat. We believe the approach described in this paper represents the best available information on how a sea otter population at equilibrium would be distributed along the California coast.
REPRODUCTION IN FEMALE MANATEES OBSERVED IN SARASOTA BAY, FLORIDA
Authors: Koelsch Jessica K.
Published: August 2006

Abstract

Resightings of recognizable individual Florida manatees, Trichechus manatus latirostris, in Sarasota Bay provided information on life history and reproductive parameters. These parameters have been documented at winter aggregation sites, but few data existed for Florida's west coast at non‐winter sites. Life history data are needed to estimate annual reproduction and survival rates and construct population models for manatees along west central Florida. Observations of 113 recognizable manatees of known sex sighted between 1993 and 1997 indicated a 1: 1 sex ratio. Fifty‐three females produced at least 55 calves during five years of observation. Two large, presumably sexually mature females were never observed with calves in over five years of monitoring. Not surprisingly, several reproductive parameters matched those measured in previous studies at winter sites with a mean of 1.8 seasons of calf dependence, 2.2 seasons between births, and age of sexual maturity at 3–4 yr. Birth rates, fecundity, and proportions of females with calves varied only slightly among investigations.
ACOUSTIC DETECTIONS OF SINGING HUMPBACK WHALES IN DEEP WATERS OFF THE BRITISH ISLES
Authors: Charif Russell A. , Clapham Phillip J. , Clark Christopher W.
Published: August 2006

Abstract

From October 1996 through September 1998, we used bottom‐mounted hydrophone arrays to monitor deep‐water areas north and west of the British Isles for songs of humpback whales (Megaptera novaeangliae). Singing humpbacks were consistently detected between October and March from the Shetland‐Faroe Islands south to waters west of the English Channel. Temporal and geographic patterns of song detections, and movements of individually tracked whales, exhibited a southwesterly trend over this period, but with no corresponding northward trend between April and September. These results, together with a review of historical data from this area, suggest that the offshore waters of the British Isles represent a migration corridor for humpbacks, at least some of which summer in Norwegian (and possibly eastern Icelandic) waters. The migratory destination of the detected animals remains unknown, but the limited data suggest that these whales are bound primarily for the West Indies rather than historical breeding areas off the northwestern coast of Africa. Humpbacks detected in British waters after early to mid‐March probably do not undertake a full migration to the tropics. These data provide further evidence that singing is not confined to tropical waters in winter, but occurs commonly on migration even in high latitudes.
MOVEMENTS AND POPULATION STRUCTURE OF HUMPBACK WHALES IN THE NORTH PACIFIC
Authors: Calambokidis John , Steiger Gretchen H. , Straley Janice M. , Herman Louis M. , Cerchio Salvatore , Salden Dan R. , Jorge Urbán R. , Jacobsen Jeff K. , Ziegesar Olga Von , Balcomb Kenneth C. , Gabriele Christine M. , Dahlheim Marilyn E. , Uchida Senzo , Ellis Graeme , Mlyamura Yukifumi , de guevara Paloma Ladrón P. , Yamaguchi Manami , Sato Fumihiko , Mizroch Sally A. , Schlender Lisa , Rasmussen Kristin , Barlow Jay , Ii Terrance J. Quinn
Published: August 2006

Abstract

Despite the extensive use of photographic identification methods to investigate humpback whales in the North Pacific, few quantitative analyses have been conducted. We report on a comprehensive analysis of interchange in the North Pacific among three wintering regions (Mexico, Hawaii, and Japan) each with two to three subareas, and feeding areas that extended from southern California to the Aleutian Islands. Of the 6,413 identification photographs of humpback whales obtained by 16 independent research groups between 1990 and 1993 and examined for this study, 3,650 photographs were determined to be of suitable quality. A total of 1,241 matches was found by two independent matching teams, identifying 2,712 unique whales in the sample (seen one to five times). Site fidelity was greatest at feeding areas where there was a high rate of resightings in the same area in different years and a low rate of interchange among different areas. Migrations between winter regions and feeding areas did not follow a simple pattern, although highest match rates were found for whales that moved between Hawaii and southeastern Alaska, and between mainland and Baja Mexico and California. Interchange among subareas of the three primary wintering regions was extensive for Hawaii, variable (depending on subareas) for Mexico, and low for Japan and reflected the relative distances among subareas. Interchange among these primary wintering regions was rare. This study provides the first quantitative assessment of the migratory structure of humpback whales in the entire North Pacific basin.
MOVEMENTS OF SATELLITE‐TAGGED SUBADULT AND ADULT HARBOR SEALS IN PRINCE WILLIAM SOUND, ALASKA
Authors: Lowry Lloyd F. , Frost Kathryn J. , Ver Hoep Jay M. , Delong Robert A.
Published: August 2006

Abstract

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 km2to >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.
INVESTMENT IN SONS AND DAUGHTERS BY SOUTHERN ELEPHANT SEALS, MIROUNGA LEONINA, AT MARION ISLAND
Authors: Wilkinson Ian S. , van Aarde Rudi J.
Published: August 2006

Abstract

The southern elephant seal, Mirounga leonina, exhibits extreme sexual dimorphism and polygyny and is thought to be an ideal subject to test maternal investment theory. Predictions concerning differential investment in offspring by sex were tested on M. leonina breeding at Marion Island over three austral summers. Large females produced more male pups, while small females produced more female pups, providing tentative support for the Trivers and Willard (1973) hypothesis. Maternal size had a greater influence on growth rate and weaning mass than on the sex of offspring. Differential reproductive costs to adult females were not evident in terms of future fecundity or survival. In keeping with other studies on this species, we could not demonstrate any differential investment in the two sexes. We suggest that before discounting maternal investment theories, further studies need to be undertaken to determine the benefits, if any, of size at weaning on long‐term survival and reproductive success.
MAXIMUM SWIM SPEEDS OF CAPTIVE AND FREE‐RANGING DELPHINIDS: CRITICAL ANALYSIS OF EXTRAORDINARY PERFORMANCE
Authors: Rohr J. J. , Fish F. E. , Gilpatrick J. W.
Published: August 2006

Abstract

Research into dolphin swimming historically was guided by false assumptions pertaining to maximum speed. Accurate measurements on swimming speed and duration of effort of free‐ranging dolphins are rare. To examine the variance of maximum swimming speeds, nearly 2,000 speed measurements were obtained for both captive and free‐ranging dolphins, including Tursiops truncatus, Pseudorca crassidens, Delphinus capensis, and Delphinus delpbis. Measurements were made from videotapes of dolphins trained to swim fast around a large pool or jumping to a maximum height, videotapes of captured wild dolphins immediately after release, and sequential aerial photographs of a school of free‐ranging dolphins startled by a passing airplane. Maximum horizontal speeds for trained animals were 8.2 m/sec for T. truncatus, 8.0 m/sec for D. delphis, and 8.0 m/sec for P. crassidens. Maximum speeds for T. truncatus swimming upwards, prior to vertical leaps ranged from 8.2 to 11.2 m/sec. Wild T. truncatus demonstrated a maximum speed of 5.7 m/sec. Maximum swimming speed of free‐ranging D. capensis responding to multiple passes by a low flying airplane was 6.7 m/sec. There was no evidence that the freeranging dolphins have superior swimming capabilities to captive animals. The results of this study imply that realistic maximum swimming speeds for dolphins are lower than previous reports which were based on sparse data and imprecise measurement techniques.
HOW DO SPERM WHALES CATCH SQUIDS?
Authors: Fristrup Kurt M. , Harbison G. Richard
Published: August 2006

Abstract

Vision may play a central role in sperm whale predation. Two complementary hypotheses regarding the detection and capture of prey items are presented, based on a review of mesopelagic ecology. The first hypothesis postulates that sperm whales locate their prey visually, either silhouetted against the midwater “sky,” or by searching for bioluminescence produced by the movements of their prey. The second hypothesis postulates that sperm whales create a zone of stimulated bioluminescence around the mouth, which attracts squids and other visual predators. Studies of midwater fishes and invertebrates document the importance of vision in mesopelagic communities. If sperm whales search for silhouetted prey, they should be oriented upside‐down to improve visual coverage and to facilitate the transition from search to prey capture. Prey capture events should be marked by excursions toward the surface. If they lure their prey, they should swim at a steady pace, with little rapid acceleration, and spend most of their time foraging at depths with the greatest potential for stimulated bioluminescence.
CLICK CHARACTERISTICS OF NORTHERN BOTTLENOSE WHALES (HYPEROODON AMPULLATUS)
Authors: Hooker Sascha K. , Whitehead Hal
Published: August 2006

Abstract

Sounds produced by northern bottlenose whales (Hyperoodon ampullatus) recorded in the Gully, a submarine canyon off Nova Scotia, consisted predominately of clicks. In 428 min of recordings no whistles were heard which could unequivocally be attributed to bottlenose whales. There were two major types of click series, initially distinguished by large differences in received amplitude. Loud clicks (produced by nearby whales socializing at the surface) were rapid, with short and variable interclick intervals (mean 0.07 sec; CV 71%). The frequency spectra of these were variable and often multimodal, with peak frequencies ranging between 2 and 22 kHz (mean 11 kHz, CV 59%). Clicks received at low amplitude (produced by distant whales, presumably foraging at depth) had more consistent interclick intervals (mean 0.40 sec, CV 12.5%), generally unimodal frequency spectra with a mean peak frequency of 24 kHz (CV 7%) and 3 dB bandwidth of 4 kHz. Echolocation interclick intervals may reflect the approximate search distance of an animal, in this case 300 m, comparable to that found for sperm whales. The relationship between click frequency and the size of object being investigated, suggests that 24 kHz would be optimal for an object of approximately 6 cm or more, consistent with the size range of their squid prey.
ESTIMATED SOURCE LEVELS OF FIN WHALE (BALAENOPTERA PHYSALUS) VOCALIZATIONS: ADJUSTMENTS FOR SURFACE INTERFERENCE
Authors: Charif Russell A. , Mellinger David K. , Dunsmore Katherine J. , Fristrup Kurt M. , Clark Christopher W.
Published: August 2006

Abstract

We recorded a series of 34 fin whale vocalizations using four calibrated hydrophones in a towed array. The whale's location was determined using arrival‐time differences of each call at the hydrophones. The recordings showed evidence of interference between signals propagating along direct and surface‐reflected paths (the “Lloyd Mirror”). We made preliminary estimates of source level (SL) using a spherical spreading model of transmission loss. We then applied a conservative correction for the effect of interference by subtracting the maximum possible signal enhancement from the preliminary SL estimate. These adjusted spherical spreading estimates had a median of 171 dB re 1 μPa at 1 m, with a range of 159–184 dB. These are the first SL estimates that explicitly attempt to correct for possible interference effects. We also propose a method that simultaneously estimates SL and source depth by fitting a Lloyd Mirror transmission loss curve to the measured received level, known receiver depth, and source‐to‐receiver range. Attempts to apply this method to the present data set yielded inconsistent results, probably because of the small number of hydrophones available. With more hydrophones in the interference field, this new method should produce reliable estimates of SL and depth of vocalizing whales.
ESTIMATION OF AGE‐SPECIFIC PROBABILITIES OF FIRST RETURN AND ANNUAL SURVIVAL RATES FOR THE MALE GRAY SEAL (HALICHOERUS GRYPUS) ON SABLE ISLAND FROM CAPTURE‐RECAPTURE DATA
Authors: Manske Micheline , Stobo Wayne T. , Schwarz Carl J.
Published: August 2006

Abstract

We used a longitudinal capture‐recapture study to estimate the age‐specific probabilities of first return to the breeding colony and annual survival rates for male gray seals (Halichoerus grypus), based on resightings of seals branded as young on Sable Island. We estimated that the average age of first returns for seals born in 1969–1970 to be 9.1 (SE 0.4) yr; for seals born in 1973–1974 it is estimated to be 9.8 (SE 0.2) yr. The estimated annual survival rate of these males was estimated to be 0.976 (SE 0.003).