bluuebunny/crossref_metadata_2025 huggingface dataset:
PINNIPED POPULATION DYNAMICS IN CENTRAL CALIFORNIA: CORRELATIONS WITH SEA SURFACE TEMPERATURE AND UPWELLING INDICES
Authors: Sydeman William J. , Allen Sarah G.
Published: August 2006

Abstract

We investigated effects of marine climate variability on pinniped populations and assessed the initial stages of recovery following implementation of the U. S. Marine Mammal Protection Act (MMPA) based on long‐term (1973‐1997) population surveys at the South Farallon Islands and Point Reyes Peninsula, central California. California sea lions increased over the study period, with peak numbers observed during and after major El Niño events. The rate of increase for California sea lions appears to have decreased in recent years. Steller sea lions decreased at the South Farallon Islands and remain depleted at Point Reyes Peninsula. Harbor seal populations increased in a logistic and non‐linear fashion at Point Reyes Peninsula and the South Farallon Islands, respectively. Harbor seals were more abundant at the South Farallon Islands during years of relatively high sea‐surface temperature, which may be related to their inability to find sufficient prey in coastal waters under these conditions. Northern elephant seal abundance increased in a logistic fashion over the study period at both the South Farallon Islands and Point Reyes Peninsula; however, productivity at the South Farallon Islands decreased in recent years. Maximum haulout numbers for elephant seals at the South Farallon Islands increased in the 1970s, maintained an asymptote throughout the 1980s and early 1990s, but recently declined; additional studies are needed to investigate which age classes are associated with this decline. Protection afforded by the MMPA has facilitated partial to full recovery of all populations except for Steller sea lion. Oceanographic relationships do not appear to confound interpretations of population recovery and may help to explain changes in the Steller sea lion population.
MONITORING THE TREND OF HARBOR SEALS IN PRINCE WILLIAM SOUND, ALASKA, AFTER THE EXXON VALDEZ OIL SPILL
Authors: Frost Kathryn J. , Lowry Lloyd F. , Ver Hoef Jay M.
Published: August 2006

Abstract

We used aerial counts to monitor the trend in numbers of harbor seals, Phoca vitulina richardsi, in Prince William Sound, Alaska, following the 1989 Exxon Valdez oil spill. Repetitive counts were made at 25 haul‐out sites during the annual molt period each year from 1990 through 1997. A generalized linear model indicated that time of day, date, and time relative to low tide significantly affected seal counts. When Poisson regression was used to adjust counts to a standardized set of survey conditions, results showed a highly significant decline of 4.6% per year. Unadjusted counts indicated a slight, but not statistically significant, decline in the number of seals. The number of harbor seals on the trend‐count route in eastern and central PWS has been declining since at least 1984, with an overall population reduction of 63% through 1997.

Programs to monitor long‐term changes in animal population sizes should account for factors that can cause short‐term variations in indices of abundance. The inclusion of such factors as covariates in models can improve the accuracy of monitoring programs.
STOMACH CONTENTS OF FALSE KILLER WHALES (PSEUDORCA CRASSIDENS) STRANDED ON THE COASTS OF THE STRAIT OF MAGELLAN, TIERRA DEL FUEGO
Authors: Alonso Mariano Koen , Pedraza Susana N. , Schiavini Adrian C. M. , Goodall R. NATALIE P. , Crespo Enrique A.
Published: August 2006

Abstract

We examined the stomachs of 25 false killer whales collected from a mass stranding of 181 animals along both coasts of the Strait of Magellan, Chile, in March 1989. The 21 stomachs (nine males and 12 females), with food remains contained 11 prey species (nine cephalopods and two fishes) with a total of 442 individuals. Except for one case, food remains were meager, indicating that the animals had not eaten for some time or through stress had vomited on the beach. Eleven of the 21 animals had mud (often with squid beaks) in the esophagus and first stomach. The prey were identified employing squid beaks, fish otoliths and bones, and their wet weights were estimated using regressions between hard parts and known weights of species. The most important prey were the oceanic and neritic‐oceanic squids, Martialia byadesi and Illex argentinus, followed by the neritic fish, Macruronus magellanicus. Of less importance were the oceanic squid, Todaroes fillipovae, the oceanic and epipelagic octopus, Ocytboe sp., and the oceanic squid, Moroteuthis ingens. The rest of the prey were poorly represented and included four oceanic squids and one neritic fish. The prey species of these animals were subantarctic, with two antarctic species, abundant over the Patagonian shelf and adjacent oceanic waters around Tierra del Fuego.
MOTHER‐INFANT SPATIAL RELATIONS IN CAPTIVE BOTTLENOSE DOLPHINS, TURSIOPS TRUNCATUS
Authors: Gubbins Cara , Mcowan Brenda , Lynn Spencer K. , Hooper Stacie , Reiss Diana
Published: August 2006

Abstract

The prolonged nursing period and strong, extended mother‐infant bond observed among bottlenose dolphins may reflect social and physical ontogeny critical for infant survival. This study was conducted to quantify ontogentic changes in mother‐infant contact time and the amount of time infants spent in specific spatial states with their mothers from birth to age 12 mo. These behaviors were studied through a systematic, longitudinal study of six mother‐infant pairs of captive bottlenose dolphins from three different social groups. There was a significant decrease in the time infants spent with their mothers (logistic regression, P < 0.001), following the general mammalian pattern of increasing independence with age. When with their mothers, the probability that infants would be found in “echelon” position, flanking the mother, decreased as the calf aged (logistic regression, P <0.001), possibly due to anatomical and hydrodynamic factors. The probability that infants would be found in “infant” position, underneath the mother, increased with calf age (logistic regression, P < 0.001). Results obtained in this study are consistent with similar studies of wild bottlenose dolphin mother‐infant pairs, indicating a suite of ontogenetically comparable behaviors between wild and captive bottlenose dolphins.
RISK FACTORS AFFECTING THE VAQUITA (PHOCOENA SINUS)1
Authors: Rojas‐Bracho Lorenzo , Taylor Barbara L.
Published: August 2006

Abstract

Despite the vaquita being commonly cited as one of the most endangered marine mammals in the world, there is still disagreement over which factors put the species at greatest risk of extinction. This lack of agreement hinders management decisions needed to reduce the risk to the species. To expedite decision‐making we consider four major risk factors. Habitat alteration from reduced flow of the Colorado River does not currently appear to be a risk factor because productivity remains high in vaquita habitat. Pollutant loads are low and pose low to no risk. Reduced fitness from inbreeding depression and loss of genetic variability are unlikely to pose high risk currently, though risk will increase if vaquitas remain at low abundance over long periods of time. Mortality resulting from fisheries bycatch poses high risk. Thus, short term management should not be hindered by uncertainty in estimating the risk of these factors, and primary conservation efforts should be directed to wards immediate elimination of incidental fishery mortality.
MITOCHONDRIAL DNA VARIATION IN THE CRITICALLY ENDANGERED VAQUITAPHOCOENA SINUSNORRIS AND MACFARLAND, 19581
Authors: Rosel Patricia E. , Rojas‐Bracho Lorenzo
Published: August 2006

Abstract

The vaquita,Phocoena sinus, 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 mitochondrial 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 history of the species includes a bottleneck or founder event, possibly at species inception, followed by a small long‐term effective population size. We recommend parallel studies of nuclear variability, which could provide understanding of the basic biology of the vaquita for use in conservation efforts.
BIASES IN DOLPHIN AGE STRUCTURE DUE TO AGE ESTIMATION TECHNIQUE1
Authors: Hohn Aleta A. , Fernandez Stephanie
Published: August 2006

Abstract

The use of different tooth‐preparation techniques resulted in widely different estimates of age in a sample of bottlenose dolphins, Tursiops truncatus. Teeth from 30 animals were prepared using the two most prevalent techniques reported in the literature for this species, unstained sections and decalcified and stained thin sections, and the resulting paired counts of growth layers were compared. Estimates from the two methods were identical or at least placed the specimen in the same age class in only five cases, ranging in age from 2 to 22 yr. Otherwise, the results fell into one of two categories: when the estimates were close (± 3‐yr difference, n= 15), counts from unstained sections generally were higher (13 cases, age from unstained sections 2‐20 yr); when the counts were more disparate, estimates from stained sections always were higher (6‐31 yr difference, n= 10, age from unstained sections 12‐27 yr and corresponding ages from stained sections of 27‐47). Previous studies of age estimation in known‐age bottlenose dolphins indicate that stained sections allow accurate estimates of age and demonstrate that maximum lifespan approaches or exceeds 50 yr. In contrast, the results herein suggest that using unstained sections for age estimation may result in imprecise or biased age‐structure data.
THE SPERM WHALE'S NOSE: SEXUAL SELECTION ON A GRAND SCALE?1
Authors: Cranford Ted W.
Published: August 2006

Abstract

The world's largest nose belongs to the sperm whale, yet its functional significance remains equivocal. In order to help shed light on its function, the head of a postmortem neonate sperm whale was subjected to CT scanning. Geometric comparisons between homologous cephalic structures in sperm whales and dolphins (normalized for body size) show extreme hypertrophy and size sexual dimorphism in the sperm whale's lipid spermaceti organ. Anatomic geometry, energetics, and behavior suggest that this immense nasal apparatus is a bioacoustical machine. Sexual selection via an acoustic display is suggested as an explanation for the size and continuous (physiologically isolated) energy investment in the construction and maintenance of the male's spermaceti organ.
MOVEMENTS OF NORTH PACIFIC BLUE WHALES DURING THE FEEDING SEASON OFF SOUTHERN CALIFORNIA AND THEIR SOUTHERN FALL MIGRATION1
Authors: Mate Bruce R. , Lagerquist Barbara A. , Calambokidis John
Published: August 2006

Abstract

The satellite‐acquired locations of 10 blue whales (Balaenoptera musculus) tagged off southern California with Argos radio tags were used to identify (1) their movements during the late summer feeding season; (2) the routes and rate of travel for individuals on their southern fall migration; and (3) a possible winter calving/breeding area. Whales were tracked from 5.1 to 78.1 d and from 393 to 8,668 km. While in the Southern California Bight, most of the locations for individual whales were either clumped or zigzagged in pattern, suggesting feeding or foraging (searching for prey).

Average speeds ranged from 2.4 to 7.2 km/h. One whale moved north to Cape Mendocino, and four migrated south along the Baja California, Mexico coast, two passing south of Cabo San Lucas on the same day. One of the latter whales traveled an additional 2,959 km south in 30.5 d to within 450 km of the Costa Rican Dome (CRD), an upwelling feature. The timing of this migration suggests the CRD may be a calving/breeding area for North Pacific blue whales. Although blue whales have previously been sighted in the Eastern Tropical Pacific (ETP), this is the first evidence that whales from the feeding aggregation off California range that far south. The productivity of the CRD may allow blue whales to feed during their winter calving/breeding season, unlike gray whales (Eschrichtius robustus) and humpbacks (Megaptera novaeangliae) which fast during that period.
RELATIVE ABUNDANCE OF LARGE WHALES AROUND SOUTH GEORGIA (1979–1998)1
Authors: Moore M. J. , Berrow S. D. , Jensen B. A. , Carr P. , Sears R. , Rowntree V. J. , Payne R. , Hamilton P. K.
Published: August 2006

Abstract

To assess large‐whale stocks following the cessation of land‐based South Georgia whaling in 1965, we report three independent sighting databases: a cruise in 1997, observations from Bird Island (NW of South Georgia) between 1979 and 1998, and mariner sightings between 1992 and 1997. All species were rare, with sightings of southern right whales being the most common event. Two right whales photographed off South Georgia matched animals known from Peninsula Valdés, Argentina, a population known to be growing at 7%per annum. In contrast, blue and fin whales appeared to be less abundant. A single blue whale mother‐calf pair was observed off the Shag Rocks in February 1997. Extirpation of animals from this particular feeding ground is the most likely reason for ongoing low numbers of all species. Other factors may include competition for krill by traditional predators such as penguins and seals and more recently by humans, an unusually high rate of natural mortality, habitat change such as alteration in sea ice coverage, and/or the impact of ongoing whaling. The history of this critical area of large‐whale habitat and this report demonstrate the need for improved, consistent longterm monitoring of population trends for these depleted stocks.
HARBOR PORPOISE (PHOCOENA PHOCOENA) ABUNDANCE IN ALASKA: BRISTOL BAY TO SOUTHEAST ALASKA, 1991‐1993
Authors: Dahlheim M. , York A. , Towell R. , Waite J. , Breiwick J.
Published: August 2006

Abstract

Between 1991 and 1993, Alaska harbor porpoise (Phocoena phocoena) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line‐transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km2, or approximately 3,531 harbor porpoises (95% C. I. 2,206‐5,651) in Bristol Bay and 0.54 groups/100 km2, or 136 harbor porpoises (95% C. I. 11‐1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km2, or an abundance estimate of 740 (95% C. I. 259‐2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km2 and an abundance estimate of 551 (95% C. I. 423‐719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km2 and an abundance estimate of 3,982 (95% C. I. 2,567‐6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km2, resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746‐11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number.
ASPECTS OF GROWTH IN CAPTIVE KILLER WHALES (ORCINUS ORCA)
Authors: Clark Steven T. , Odell Daniel K. , Lacinak C. Thad
Published: August 2006

Abstract

Morphometrics from 25 captive killer whales (11 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.
CHANGES IN MORPHOLOGY WITH AGE IN MEDITERRANEAN MONK SEALS (MONACHUS MONACHUS)
Authors: Samaranch Roser , González Luis Mariano
Published: August 2006

Abstract

In order to describe the pelage and external appearance of the Mediterranean monk seal (Monachus monachus) and prepare an age‐sex classification guide, 120 seals from the Cabo Blanco Peninsula colony in the Western Sahara/Mauritania were periodically photographed between 1993 and 1996. Analysis of the pigmentation pattern, pelage color and pattern of natural markings of each seal established 48 phenetic types, which were, in turn, arranged in five groups (morphological classes) with multivariate cluster analysis (UPGMA). The variables that best define these groups are size and color. The variation related to relative size, sex and age of 26 identified seals monitored over three years showed that: (1) after each molt, external appearance varied considerably only in non‐adults, while adult appearance was invariable; (2) marked sexual dimorphism exists in adults' external appearance; and (3) a remarkable similarity of adult and neonate pelage exists. With these results, we propose an age‐sex classification guide to facilitate monk seal identification in the field.
PUP SURVIVAL IN THE MEDITERRANEAN MONK SEAL (MONACHUS MONACHUS) COLONY AT CABO BLANCO PENINSULA (WESTERN SAHARA‐MAURITANIA)
Authors: Gazo Manel , Aparicio Fernando , Cedenilla Miguel Angel , Layna Jorge F. , González Luis Mariano
Published: August 2006

Abstract

We surveyed pup survival in Mediterranean monk seals (Monachus monachus), at Cabo Blanco Peninsula (Western Sahara‐Mauritania) colony from May 1993 to December 1997. This species breeds and hauls out on beaches inside two main caves. During the study period we detected a total of 93 pups that died or disappeared. The survival rate of 84 pups through the age of first moult (approximately two months) was 0.47. This value is similar to those reported for other pinnipeds breeding in caves but lower than for those breeding on open beaches. Mortality varied seasonally and appeared to increase as a result of storms, large ocean swells, and high tides. Mother‐pup pair separation (and resulting pup starvation) and physical injury caused by impact against the rock walls of the cave and cliffs were established as the causes of most deaths. Beach surface area inside the caves also appeared to be a mediating factor in the effects of sea conditions. High pup mortality may be a limiting growth factor in this population, although cave dwelling protects the population from predators and human disturbance.
A KINEMATIC STUDY OF SUCTION FEEDING AND ASSOCIATED BEHAVIOR IN THE LONG‐FINNED PILOT WHALE, GLOBICEPHALA MELAS (TRAILL)
Authors: Werth Alexander
Published: August 2006

Abstract

Analysis of videotaped feeding sequences provides novel documentation of suction feeding in captive juvenile long‐finned pilot whales (Globicephala melas). Swimming and stationary whales were videotaped while feeding at the surface, mid‐water, and bottom. The ingestion sequence includes a preparatory phase with partial gape followed by jaw opening and rapid hyoid depression to suck in prey at a mean distance of 14 cm (duration 90 msec), although prey were taken from much greater distances. Depression and retraction of the large, piston‐like tongue generate negative intraoral pressures for prey capture and ingestion. Food was normally ingested without grasping by teeth yet was manipulated with lingual, hyoid, and mandibular movement for realignment; suction was then used to transport prey into the oropharynx. Whales frequently rolled or inverted before taking prey, presumably to avoid grasping and repositioning. Prey were sucked off the bottom or sides of the pool without direct contact; lateral suction was used to ingest items from the sides of the mouth.
TEMPORAL VARIABILITY IN FEATURES USED TO PHOTO‐IDENTIFY HUMPBACK WHALES (MEGAPTERA NOVAEANGLIAE)
Authors: Blackmer Alexis L. , Anderson Scott K. , Weinrich Mason T.
Published: August 2006

Abstract

Photographs of 99 humpback whales of known age were analyzed to assess the temporal variability and recognizability of individually distinctive fluke and dorsal fin features used for photo‐identification. Stable features tended to be morphological in nature (dorsal fin shape and edges, the trailing edge of the fluke, and the raised bumps on the caudal peduncle termed “knobs”). Transitory features typically were superficial marks (scarring, scratching, and pigmentation). The variability of several features was found to be age‐dependent as well. Young animals sometimes experienced substantial change to their fluke coloration patterns, though this feature stabilized with age. Dorsal fin edges and fluke serration peaks tended to undergo more change in males than in females, with most changes occurring following sexual maturation. Peduncle knobs were the most stable feature, with no documented change in any age interval. Given the extreme stability (and hence recognizability) of dorsal fin shape and peduncle knobs, we suggest that photographs combining the dorsal fin and the caudal peduncle provide the most consistent way to reidentify humpback whales, particularly calves following weaning.
MEASUREMENT OF PHOTOGRAPHIC QUALITY AND INDIVIDUAL DISTINCTIVENESS FOR THE PHOTOGRAPHIC IDENTIFICATION OF HUMPBACK WHALES, MEGAPTERA NOVAEANGLIAE
Authors: Friday Nancy , Smith Tim D. , Stevick Peter T. , Allen Judy
Published: August 2006

Abstract

Accurate identification of humpback whales from photographic identification data depends on the quality of the photographs and the distinctiveness of the flukes. Criteria for evaluating photographic quality and individual distinctiveness were developed involving judgments about overall quality or distinctiveness and about specific aspects of each. These criteria were tested for the level of agreement among judges. The distinctiveness scheme was tested for the independence of distinctiveness judgments and photographic quality. Our results show that judges could agree when evaluating specific and overall aspects of photographic quality and individual distinctiveness. The level of agreement varied for different pairs of judges, and less adept judges were identified. Ability to agree on evaluations of photographic quality was independent of the experience of the judges. Overall photographic quality and overall distinctiveness were successfully predicted from more specific variables, but the agreement between judges for these was not significantly greater than the agreement for the overall measures judged directly. There was no correlation between individual distinctiveness and photographic quality for four of the five judges, but the power of this rest may be low. Analyses of photographic identification data frequently require evaluations of photographic quality and individual distinctiveness. To obtain reliable results from such analyses, evaluation schemes and judges should be tested to ensure reliable and consistent evaluations.
A BAYESIAN ANALYSIS TO ESTIMATE LOSS IN SQUID CATCH DUE TO THE IMPLEMENTATION OF A SEA LION POPULATION MANAGEMENT PLAN
Authors: Maunder Mark N. , Starr Paul J. , Hilborn Ray
Published: August 2006

Abstract

This study estimates the effect of a sea lion (Phocarctos hookeri) population management plan on both the sea lion population and the associated squid (Nototodarus sloanii) fishery. The goal of the management plan is to rebuild the sea lion population and involves closing the squid fishery when a threshold level of sea lions have been caught. The threshold level is calculated from a generalized simulation analysis which conservatively allows for adequate population rebuilding for a number of different species and populations. Our analysis uses Bayesian theory to describe uncertainty in the sea lion population site and squid catch under the implementation of the management plan. The priors represent this particular sea lion population, and the analysis represents expectation rather than calculating conservative levels of safe fishing‐related mortality. The results show that the squid catch is very sensitive to whether or not the squid fishery is closed when it exceeds the threshold level for sea lion bycatch. The sea lion population size is much less sensitive to the closure of the squid fishery. For an economically important fishery, the estimates of uncertainty in both loss of catch and increase in sea lion population are needed to allow informed decision‐making about trade‐offs between sea lion conservation and full exploitation of the fishery.
SEASONAL AND DIURNAL TRENDS OF CHORUSING HUMPBACK WHALES WINTERING IN WATERS OFF WESTERN MAUI
Authors: Au Whitlow W. L. , Mobley Joseph , Burgess William C. , Lammers Marc O. , Nachtigall Paul E.
Published: August 2006

Abstract

A portable data logger controlled by a Tattletale 7 microcontroller was used to record humpback whale choruses during the 1998 humpback whale winter season in Hawaii. The data logger sampled the sounds for four minutes every half hour using a digitizing rate of 2 kHz, and the data were stored on a hard disk. The results between January and April showed a peak in the sound pressure level between mid‐February and mid‐March. This peak of approximately 120 dB re 1 μPa coincided with the peak in the number of whales sighted by aerial survey on 7 March 1998. The choruses had spectral peaks at 315 Hz and 630 Hz. Some of the sounds at 630 Hz were second harmonics of the 315 Hz peak and others were not. The data also indicated a diurnal pattern in the sound pressure level, with levels at night significantly louder than the daytime levels. The sound levels began to increase during sunset and remained relatively high until sunrise, when they progressively decreased to a minimum. The nighttime peak occurred within an hour before and after midnight, and the daytime minimum occurred between 1100 and 1500. That more humpback whales appear to sing at night may reflect a switch to sexual advertisement as the primary male mating strategy at this time. It may also indicate that daylight and vision play key roles in the formation of competitive groups. It is suggested that the relative number of humpback whales in a given locale may be estimated by monitoring changes in sound pressure levels.
FUNCTIONAL REDUCTION OF THE SOUTHERN MINKE WHALE (BALAENOPTERA ACUTOROSTRATA) TESTIS DURING THE FEEDING SEASON
Authors: Mogoe Toshihiro , Suzuki Takatoshi , Asada Masatsugu , Fukui Yutaka , Ishikawa Hajime , Ohsumi Seiji
Published: August 2006

Abstract

Seasonal variation in reproductive activity in the male southern minke whales was investigated. The animals were killed and collected during the feeding season (December‐March) in the Antarctic Ocean in the eastern part of Area III (35°E‐70°E, south of 60°S) and Area IV (70°E‐130°E, south of 60°S). Blood samples, testes, epididymides, and vasa deferentia were collected from 62 males, which had testes weighing over 400 g each. Changes in testicular morphology and plasma testosterone, estradiol‐17β and LH concentrations measured by enzyme immunoassay were investigated. Reduction of testicular function associated with different capture periods was found in the summer season. From December to March, body length and body weight remained steady, but decreases in testicular weight, epididymal weight, and testicular volume were found in February. During the same period, plasma testosterone concentration also declined. A significant decrease in the number of germ cells continued during the period of feeding season. An increase in area of seminiferous tubule tended to proceed in a number of germ cells. These changes reflected the percentage of spermatozoa in the vasa deferentia; in particular, motile spermatozoa were observed in December. Based on morphological observation, spermatogenesis had also declined. These results indicate regulation of testicular function by testosterone, as in terrestrial mammals. A gradual decrease of testicular function occurred during December‐January.
DO PHOTOPERIOD AND TEMPERATURE INFLUENCE THE MOLT CYCLE OF PHOCA VITULINA IN CAPTIVITY?
Authors: Mo Giulia , Gili Claudia , Ferrando Paola
Published: August 2006

Abstract

Photoperiod variations are the principal environmental signals entraining circannual activity in mammals, which is also believed to be influenced by changes in temperature and nutrition. Control of the molt in phocids has not been extensively studied with experimental manipulations of environmental factors, but substantial work indicates that photoperiod has a primary influence on mammalian breeding and furring mechanisms. Studies were under taken to reestablish the molt cycle in five harbor seals (Phoca vitulina) previously kept in an enclosed facility with a limited air/water temperature gradient and artificial photoperiod. The seals were exposed to an extended temperature gradient during the first period of study, and no molting was observed. The second period of study was characterized by a natural occurring photoperiod of 8 h 53 min light (L)/15 h 07 min dark (D) and a maximal 15 h 31 min L/8h 29 min D duration, and molting occurred in all individuals. These results suggest a prevalent influence of photoperiod variation on the harbor seal molt.
DIET OF HARP SEALS (PAGOPHILUS GROENLANDICUS) IN NEARSHORE NORTHEAST NEWFOUNDLAND: INFERENCES FROM STABLE‐CARBON (δ13C) AND NITROGEN (δ15N) ISOTOPE ANALYSES
Authors: Lawson John W. , Hobson Keith A.
Published: August 2006

Abstract

Trophic position, and often the source of feeding of predators in food webs, can be estimated using measurements of stable isotope ratios of nitrogen and carbon in predators and their prey. Muscle samples from 60 harp seals (Pagophilus groenlandicus) collected during May 1995 in nearshore waters of New foundland, Canada, were analyzed for δ13C and δ15N values. These values were compared with those for 63 prey samples representing seven species generally collected near the same area. Using diet‐tissue isotopic fractionation factors derived from previous studies using captive animals, we infer a greater dependence of harp seals on lower trophic‐level prey during April compared with results expected from exclusive diets of Atlantic cod (Gadus morhua), Atlantic herring (Clupea harengus), Greenland halibut (Reinhardtius hippoglossoides), or northern shrimp (Pandalus borealis). Our mean δ15N value for harp seals is lower than previous findings for seals collected on the winter whelping patch and may be a function of interannual or seasonal differences in diet. Subadult seals (aged 1‐4 yr) had significantly lower δ15N values than adults (5 + yr), suggesting that older seals were feeding at a slightly higher trophic level.
VOCAL INDIVIDUALITY IN MOTHER AND PUP SOUTH AMERICAN FUR SEALS, ARCTOCEPHALUS AUSTRALIS
Authors: Phillips Alana V. , Stirling Ian
Published: August 2006

Abstract

South American fur seals breeding in Peru are subjected to levels of maternal aggression, and subsequent pup mortality, that are higher than has been reported for any other otariid species. For mothers and pups to maintain contact with each other, a mutual recognition system should exist to facilitate reunion and avoid misdirection of maternal effort. We recorded vocalizations of mothers and pups at Punta San Juan, Peru, during the 1994 and 1995 breeding seasons. Sixteen acoustic variables were measured from a total of 560 calls from 15 mothers and 13 pups. Multivariate analysis showed that calls were variable in several acoustic dimensions. While calls of both mothers and pups showed low variability within and high variability among individuals, mothers' calls were more individualistic. On average, discriminant‐function analysis correctly assigned 60% of pup calls and 70% of mother calls to the individual that produced them. Characteristics of the fundamental frequency were most important for distinguishing among mothers, while pup calls, which typically contained less harmonic structure, could be differentiated by formant‐like frequency ranges. Thus, calls of mother and pup South American fur seals appear to exhibit sufficient stereotypy to allow for recognition and discrimination among individuals.
CHANGES IN THE RELATIVE ABUNDANCE AND DISTRIBUTION OF GRAY WHALES (ESCHRICHTIUS ROBUSTUS) IN MAGDALENA BAY, MEXICO DURING AN EL NIÑO EVENT
Authors: Gardner S. C. , Chávez‐Rosales S.
Published: August 2006

Abstract

The oceanographic changes during the El Niño and La Niña of 1998–1999 have provided an opportunity to document the effects of these events on the migratory patterns of gray whales (Eschrichtius robustus). Magdalena Bay is located at the southernmost point of the gray whale's annual breeding migration along the Baja California Peninsula in Mexico. Standardized surveys were conducted for three consecutive seasons (1997–1999) in Magdalena Bay, enabling an assessment of the changes in the relative abundance of gray whales with altered temperature. The average temperature of the bay in 1998 was 4.2°C higher than in 1997 and 5.8°C higher than in 1999. The number of whale sightings during that time period was inversely related to temperature, with nearly 15 times greater relative abundance observed in 1999 than in 1998. It is hypochesized that the decreasing temperatures associated with the La Niña event of 1999 may have induced more whales to travel farther south along their migration route. Alternative hypotheses are also expiored. Comparisons of the three years are discussed with consideration of the importance of environmental conditionsversusarea fidelity as determining factors in the location of gray whale calving and breeding activities.
DISTRIBUTION OF KILLER WHALE PODS IN PRINCE WILLIAM SOUND, ALASKA 1984–1996
Authors: Scheel D. , Matkin Craig O. , Saulitis Eva
Published: August 2006

Abstract

Thirteen years of encounter data (1984–1996) were used to examine killer whale distribution within Prince William Sound, Alaska. Four patterns of area use were found, which comprised differences between resident pods and transient groups and differences among resident groups. Resident pods frequented large open passages, while transient groups used the narrow passages and bays in the southwest. This dichotomy likely reflects resident use of salmon and transient use of pinniped prey resources, as well as the different foraging strategies required for these prey types. Four resident pods (AB, AI, AJ, and AN) used Knight Island Passage more than other areas of the Sound; two (AE and AK) used all areas of the Sound more evenly. Use of the Sound by the AT1 transient whales declined in the latter part of the study. Nearshore foraging for pinniped prey by the AT1 transient whales was more common in areas where these whales spend a disproportionate amount of time, suggesting that these areas were critical foraging habitat for them. No similar pattern emerged for Open‐water Foraging for cetaceans by AT1 whales, nor for foraging by the resident whales.
LABORATORY DIGESTION OF PREY AND INTERPRETATION OF WALRUS STOMACH CONTENTS
Authors: Sheffield Gay , Fay Francis H. , Feder Howard , Kelly Brendan P.
Published: August 2006

Abstract

A new approach for evaluating the potential biases of walrus (Odobenus rosmarus) diet data derived from stomach contents was examined based on the rates at which different prey types were digested. In this study controlled digestion experiments on polychaetes, echiurid and sipunculid worms, clams, snails, and crabs demonstrated that these prey items did not remain equally identifiable during digestion. Polychaetes, echiurids, and sipunculids were the least persistent prey. All worms became unidentifiable during the six‐hour digestion trials. Over 50% of the clams maintained their diagnostic tissues (i. e., foot and/or siphon). Clam viscera did not survive hour 2. Snails and crustaceans were the most persistent prey. Without a consideration of the state of digestion, a stomach sample may not accurately reflect the species composition and size of prey consumed. Volume is not a reliable measure of a prey's relative importance, as the diagnostic fragments of invertebrate prey in a stomach vary greatly in physical composition. Walruses probably consume all of the soft tissues of clams, not solely the foot and siphon.
INCREASED AVOIDANCE OF SWIMMERS BY WILD BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) DUE TO LONG‐TERM EXPOSURE TO SWIM‐WITH‐DOLPHIN TOURISM
Authors: Constantine Rochelle
Published: August 2006

Abstract

The responses of wild, non‐provisioned bottlenose dolphins (Tursiops truncatus) to swim attempts from commercial swim‐with‐dolphin tour boats were systematically observed during two research periods: 1994–1995 and 1997–1998. A total of 255 groups of dolphins was encountered during boat‐based surveys and 36% (n= 93) were exposed to at least one swim attempt. The operators' success with swim attempts, defined as at least one dolphin milling within 5 m of at least one swimmer, decreased from 48% in 1994–1995 to 34% in 1997–1998, and avoidance responses to swimmers increased from 22% to 31%. Dolphin response was found to vary according to swimmer placement. The greatest increase in avoidance occurred when swimmers were placed in the dolphins' path of travel. Based on sighting records of 266 individually identified dolphins, it was estimated that an average dolphin was exposed to 31 swim attempts per year. This level of exposure suggests that individual dolphins have, with cumulative experience, become sensitized to swim attempts. When a swim attempt was successful, on average it involved 19% of the group. Age‐class differences in interaction rates showed that juveniles were significantly more likely to interact with swimmers than adults. This study highlights the importance of longitudinal studies in evaluating human impact and suggests the urgent need for similar studies of potential human impact on other toothed cetaceans.
DIRECT ESTIMATION OF WITHIN‐GROUP HETEROGENEITY IN PHOTO‐IDENTIFICATION OF SPERM WHALES
Authors: Whitehead Hal
Published: August 2006

Abstract

Heterogeneity in photo‐identification rates among individuals is a potentially serious problem in many studies of cetacean biology, especially the analysis of populations. However, this heterogeneity is usually difficult to identify or measure. Two instances in which closed groups of female and immature sperm whales (Physeter macrocepbalus) were tracked and identified using fluke photographs over periods of days off the Galápagos Islands allowed direct examination of heterogeneity in identification rates. A group of nine animals followed in 1999 provided almost no evidence for heterogeneity (permutation test for heterogeneity, P= 0.48), with an estimated coefficient of variation in identification rates of 0.03 (95% CI from 1,000 bootstrap replications: 0.00–0.10). In contrast, the identification rates of a group of 22 animals followed in 1995 seemed to show potentially important differences (P= 0.058, CV = 0.20, 95% CI = 0.07–0.28). These differences were not related to the internal social structure of the group or to differences in numbers of markings on the flukes, but smaller whales had lower identification rates. Thus, young sperm whales may be underrepresented in photo‐identification studies, but adults within groups seem to have similar identification rates. Situations in which animals are photo‐identified from closed populations of known size are particularly useful for examining heterogeneity. They should be vigorously exploited by those who use photo‐identification to examine population or behavioral biology.
DIVING BEHAVIOR OF SUBADULT AND ADULT HARBOR SEALS IN PRINCE WILLIAM SOUND, ALASKA
Authors: Frost Kathryn J. , Simpkins Michael A. , Lowry Lloyd F.
Published: August 2006

Abstract

Satellite‐linked depth recorders (SDRs) were attached to 47 harbor seals in Prince William Sound, Alaska, during 1992–1996. Parameters describing diving effort, diving focus, and focal depth (depth bin to which diving was focused) were calculated from binned data on maximum dive depth and time spent at depth, and analyzed using repeated‐measures mixed models. This analysis method accounted for individual variability, temporal autocorrelation, and the binned nature of SDR data, which are often ignored using standard statistical techniques. Results indicated that diving effort remained steady from September to April, when seals spent 68%‐75% of their overall time in the water. Time spent in the water declined to 60% in May and to about 40% in July. Seals spent the most time in the water at night and the least in the morning. The diving of all seals in all months was highly focused. Overall, diving was focused to one depth bin approximately 75% of the time. Diving was more focused for females than for males and subadults. Focal dive depth was deepest in winter and shallowest during May‐July. Focal depth and diving focus varied by region. Collinearity between month and region in the focal depth model suggests that seals move in winter to regions where prey are found deeper in the water column. Variations in diving behavior presumably result from combinations of regional bathymetry, seasonal cycles in type or depth distribution of prey, and seal life‐cycle events such as reproduction and molting.
THREE‐DIMENSIONAL DIVING BEHAVIORS OF RINGED SEALS (PHOCA HISPIDA)
Authors: Simpkins Michael A. , Kelly Brendan P. , Wartzok Douglas
Published: August 2006

Abstract

Dives of five freely diving ringed seals were classified into three‐dimentional movement types. Horizontally convoluted dives, defined as dives with angular velocity > 15°/sec, appeared to be foraging or social dives. Simple dives that did not include convoluted movements (angular velocity < 10°/sec) were considered to be exploration dives. Directional dives with nearly linear horizontal travel (horizontal directionality >0.6, on a scale of 0–1) were presumed to be travel dives. Each three‐dimensional dive type was observed with similar frequency in dives with two distinct time‐depth profiles: V‐shaped profiles in which ascent immediately followed descent, and U‐shaped profiles in which >7 sec were spent at depth between descent and ascent. The lack of behavioral differences between dives with distinct time‐depth profiles suggested that time‐depth profiles are not a reliable means of inferring dive behaviors for ringed seals.
DIET OF WEANED PUPS AND SEASONAL VARIATIONS IN BODY CONDITION OF JUVENILE BARENTS SEA HARP SEALS PHOCA GROENLANDICA
Authors: Nilssen Kjell Tormod , Haug Tore , Lindblom Charlotta
Published: August 2006

Abstract

Data on blubber depth, body condition, and diet were collected from young of year and juvenile harp seals (Phoca groenlandica) in the Barents Sea in the periods February‐April and June‐October 1990–1997. Harp seal pups feed independently shortly after weaning. In the southern parts of the Barents Sea the diet of harp seal pups consisted mainly of euphausiids (“krill”) Thysanoessa sp. and amphipods of the genus Parathemisto. The change in body condition of harp seal pups between weaning (mid‐March) and June indicated that considerable amounts of blubber energy, deposited during suckling, were mobilized. This suggests that the early food intake of weaned pups was insufficient to meet the energy requirements. The pattern of low spring and earlysummer body condition, followed by a subsequent rapid improvement in condition during late summer and autumn appeared to occur not only among pups‐of‐the‐year, but also in one‐ and two‐year old harp seals.
MOLECULAR SYSTEMATICS OF RIVER DOLPHINS INFERRED FROM COMPLETE MITOCHONDRIAL CYTOCHROME‐B GENE SEQUENCES
Authors: Yang Guang , Zhou Kaiya , Ren Wenhua , Ji Guoqing , Liu Shan , Bastida Richardo , Rivero Laura
Published: August 2006

Abstract

1,140 bp of the complete mitochondrial cytochrome‐b gene sequences of baiji (Lipotes vexillifer), franciscana (Pontoporia blainvillei), and Ganges river dolphin (Platanista gangetica gangetica) were determined to address the systematic position and phylogeny of extant river dolphins with combination of homologous sequences of other cetaceans. The neighbor‐joining (NJ), maximum parsimony (MP), and maximum likelihood (ML) phylogenetic analyses all identified the river dolphins into three lineages, i. e., Platanista, Lipotes, and Inia+Pontoporia. The Lipotes did not have sister relationship with either Platanista or Inia+Pontoporia, which strongly supported the referral of Lipotes to a separate family, i. e., Lipotidae. There were very high sequence divergences between all river dolphin genera, suggesting a relatively longer period of separation time than those among other odontocete families.
SPERM WHALE DIVES TRACKED BY RADIO TAG TELEMETRY
Authors: Watkins William A. , Daher Mary Ann , Dimarzio Nancy A. , Samuels Amy , Wartzok Douglas , Fristrup Kurt M. , Howey Paul W. , Maiefski Romaine R.
Published: August 2006

Abstract

Dives of a 12‐m sperm whale (Physeter catodon Linnaeus, 1758) were tracked in the southeast Caribbean by long range, 30 MHz radio tag with dive‐profile telemetry over 4.6 d, 26 April‐1 May 1995. Over the 295‐km track, average speed was 0.7 m/sec (2.6 km/h). Of 158 dives (defined as submergences longer than 3 min), 65 were shallow (<200 m). The 93 deep dives averaged 990 m (range 420–1,330 m) in depth, and 44.4 min in duration (range 18.2–65.3 min). Water depth was at least 200 m deeper than the whale dive depth. The whale was engaged in activities at or near the surface, shallow dives, and deep dives during 22.6%, 23.4%, and 54% of the time, respectively. Depth and duration of dives were correlated, but there was little relationship between the length or depth of dives with the duration of surfacings either before or after dives. Deep dives occurred day and night. In 44.4% of the deep dives, the vertical movement of descents and ascents was interrupted at intermediate depths, lengthening these dives by an average of 10.8 min. During dives without stops at intermediate depths, descents averaged 11 min at 1.52 m/sec, and ascents averaged 11.8 min at 1.4 m/sec.
GEOGRAPHIC VARIATION IN SKULL MORPHOLOGY OF ADULT STELLER SEA LIONS (EUMETOPIAS JUBATUS)
Authors: Brunner Sylvia
Published: August 2006

Abstract

Data from cranial specimens of adult E. jubatus were analyzed to compare intraspecific morphology of skulls. Males and females were grouped separately to avoid bias from sexual dimorphism. Geographic variation was observed in adult male E. jubutus, indicating the potential presence of three morphologically disparate groups: those from Alaska, those from California, and those from Japan and Russia. Although sample sizes were small, results from cluster and discriminant function analyses indicated that specimens from eastern and western Alaska were morphologically similar, and that the most divergent specimens for the species appeared to be those from Japan. Skulls from Alaska possessed a typically longer, less robust skull, whereas those from Japan appeared smaller, yet most robust. Skulls from California were intermediate.