Showing papers in "Marine Mammal Science in 1987"
TL;DR: This paper critically examines the nature and magnitude of the effects of these factors on organochlorine tissue loads in marine mammals and advice is provided about sampling and strategies for selection of variables that will improve the reliability of the comparisons between populations.
Abstract: ALEX AGUILAR* A-008, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92038 ABSTRACT Organochlorine pollutants are potentially useful for identifying discrete pop- ulations of marine mammals that overlap in geographic distribution However, many factors unrelated to geographical distribution may affect the chemical burden of individual animals or of entire population components even within a homogeneously distributed population These factors include, among others, nutritional state, sex, age, trophic level, distance of habitat from mainland and pollution source, excretion, metabolism, and tissue composition Sample storage and analytical methodology may also be an important source of variation These, and any other factors, must be identified and their effect ascertained before attempting any comparison between populations This paper critically examines the nature and magnitude of the effects of these factors on organochlorine tissue loads in marine mammals Pollutant concentrations can be strongly biased if carefully designed sampling regimes are not followed, but they are affected only moderately by sample treatment after collection Conversely, ratios between concentrations of compounds, such as the DDE/tDDT or the tDDT/PCB ratios, seem less dependent on sampling regime but more affected by storage, analytical procedures and ecological variations such as distance from pollutant source or trophic level Taking these effects into account, advice is provided about sampling and strategies for selection of variables that will improve the reliability of the comparisons between populations Key words: marine mammals, cetaceans, pinnipeds, pollutants, organochlorines, techniques, population discreteness, distribution, stock identity 1 Made while at the Southwest Fisheries Center, National Marine Fisheries Service, NOAA, Ia Jolla, California 92038, USA 2 Present address: Department of Zoology (Vertebrates), Faculty of Biology, University of Bar- celona, Barcelona 0807 1, Spain 242
107 citations
TL;DR: Study of the haul-out patterns and movements of harbor seals on San Miguel Island, California, from 23 October through 6 December 1982 by attaching a radio transmitter to each of 18 seals and monitoring their presence ashore with continuously scanning receivers estimated absolute abundance at about 2,168 seals.
Abstract: We studied the haul-out patterns and movements of harbor seals (Phoca vitulina richardsi) on San Miguel Island, California, from 23 October through 6 December 1982 by attaching a radio transmitter to each of 18 seals and monitoring their presence ashore with continuously scanning receivers. Seals hauled out at all hours although, on average, the largest proportion of tagged seals was ashore between 1300 and 1500 h. Median durations of haul-out bouts of individual seals ranged from 4.7 to 21.8 h; 81% of all haul-out bouts were less than 12 h and 3% were longer than 24 h. Eighty-one percent of the seals that were resighted at least twice used only the sites where they were tagged; two seals used two sites and one seal used three. Most seals were hauled out on fewer than 51% of the days sampled. On average, about 41% of tagged seals hauled out each day whereas an average of about 19% was hauled out during peak afternoon hours. Using telemetry data to correct a count of 412 seals made during an aerial survey, we estimated absolute abundance at about 2,168 seals; a modified Peterson mark-recapture model produced an estimate of about 1,445 seals.
107 citations
TL;DR: Stomach lavaging was used to study the feeding habits of northern elephanr seals found on San hliguel Island, California, during the spring of 1984, and 12 of which have not been previously reported as prey of the northern elephant seal were identified.
Abstract: Stomach lavaging was used to study the feeding habits of northern elephanr seals (Mirounga angustirostris) found on San hliguel Island, California, during the spring of 1984. Fifty-nine elephant seals were chemically immobilized with an intramuscular injection of ketamine hydrochloride. Once immobilized, an animal's stomach was intubated, filled nith 3-4 liters of water to create a slurry of the undigested food items, and evacuated into a collection device. The sromachs of 57 (96.6%) of the animals lavaged contained identifiable parts of prey. Twentynine differenr food items were identified, 12 of which have not been previously reported as prey of the northern elephant seal: tu'o teleost fish. Corypbaenoides acrolepis (Pacific rattail) and another unidentified macrourid; nvo crustaceans, Paszpbaea pacifica (glass shrimp) and Enpbausia sp.; six squid, Abraliopsii /e/is. Gonatus benyj, Hisri0teutbi.f dofleini. Crancbia srahra, Taonius pavo. and Galiterrthis sp. and rwo octopi. Ortopus doj4eini and OC~O~~J rube5cen~. 308
96 citations
TL;DR: Comparison of air and water audiograms shows Callorhinus is no exception to previous behavioral findings demonstrating that the „pinniped ear” is more suitable for hearing in water than in air.
Abstract: Aerial and underwater audiograms for two young female northern fur seals (Callorhinus ursinus) and one young female California sea lion (Zalophus californianus) were obtained with the same procedure and apparatus. Callorhinus hears over a larger frequency range and is more sensitive to airborne sounds than Zalophus or any other pinniped thus far tested in the frequency range of 500 Hz to 32 kHz. Sensitivity of Callorhinus to waterborne pure tones, ranging from 2 to 28 kHz, is equal or superior to all other pinnipeds tested in this same frequency range. Like Zalophus, the upper frequency limit for underwater hearing (as defined by Masterton et al. 1969) in Callorhinus is about one-half octave lower than the three phocid species thus far tested. Callorhinus' upper frequency limit in air is about 36 kHz and under water it is about 40 kHz. Comparison of air and water audiograms shows Callorhinus is no exception to previous behavioral findings demonstrating that the „pinniped ear” is more suitable for hearing in water than in air. Similar to Zalophus and Phoca vitulina, Callorhinus shows an anomalous hearing loss at 4 kHz in air. The basis for this insensitivity to airborne sounds at 4kHz and not at lower or higher frequencies is presumably caused by specialized middle ear mechanisms matching impedance for waterborne sounds. Critical ratio curves for Callorhinus are similarly shaped to ones obtained for humans but are shifted upwards in frequency. Compared to all other marine mammals thus far evaluated, the critical ratios for Callorhinus are the smallest yet reported.
75 citations
TL;DR: There is evidence for a powerful control of thermoregulatory mechanisms by the anterior hypothalamic/preoptic region of the brain in two species and Thermoregulation in marine mammals during exercise remains paradoxical.
Abstract: A review of thermoregulation in marine mammals led to the following conclusions: very little is known about thermoregulation in large cetaceans. The only measured value for the metabolic rate of a whale, albeit a young one, was substantially higher than the predicted value for a terrestrial mammal of similar size. Very small and newborn marine mammals rely on a high metabolic heat production to sustain their body temperature during exposure to cold or in the water. The considerable insulation of some adult marine mammals may absolve them from the need for a high level of heat production. One marine mammal in tropical or subtropical waters is hypometabolic. There is evidence for a powerful control of thermoregulatory mechanisms by the anterior hypothalamic/preoptic region of the brain in two species. Thermoregulation in marine mammals during exercise remains paradoxical.
73 citations
TL;DR: Bowhead whales summering in the eastern Beaufort Sea in 1983 were measured through aerial stereophotogrammetry and significant segregation by bowhead whale length was found between four broad regions, confounds an accurate assessment of overall size-class composition of the population.
Abstract: Bowhead whales (Balaena mysticetus) summering in the eastern Beaufort Sea in 1983 were measured through aerial stereophotogrammetry. Photos were taken from a turbine Aerocommander 690 with wingtip-mounted, calibrated 35-mm cameras. Photos were measured on an analytical plotter with scale data provided by radar altimeter and focal length of the lenses. Coefficient of variation of known-sized targets 12 m long was 1.7 percent (n = 25). Potential duplicate photographs of whales were removed from consideration through an algorithm based on whale swim speed and elapsed time between sightings. Significant segregation by bowhead whale length was found between four broad regions (P < 0.001, ANOVA, Chi square). Also an inverse correlation appeared between longitude and size of animals (P < O.OOl), with the larger animals occurring farther east. This unequivocal size-class segregation confounds an accurate assessment of overall size-class composition of the population as well as recent attempts to determine calving rate from aerial survey data.
58 citations
TL;DR: From observations of the spatial distribution of humpback whales in the Mexican Pacific between 1981 and 1986, it is possible to recognize four subregions: 1) the southern coast of Baja California; 2) the northern Gulf of California, including the Midriff Islands; 3) the mainland coast of Mexico, including Isla Isabel and Islas Tres Marias and 4) the Revillagigedo Archipelago as discussed by the authors.
Abstract: From observations of the spatial distribution of humpback whales in the Mexican Pacific between 1981 and 1986, it is possible to recognize four subregions: 1) the southern coast of Baja California; 2) the northern Gulf of California, including the Midriff Islands; 3) the mainland coast of Mexico, including the Isla Isabel and Islas Tres Marias and 4) the Revillagigedo Archipelago. The seasonal distribution of whales near the Mexican mainland and the Revillagigedo Archipelago extends from November to May and is similar to that of other winter breeding grounds, including the Hawaiian Islands. Along the southern coast of Baja California, whales have been observed from September to April, possibly indicating a shorter migratory route. In the northern Gulf of California, however, humpback whales have been reported throughout the year and are occasionally observed feeding during both summer and winter months. The degree of individual movement between the four subregions is still unknown. The number of individual humpback whales identified photographically in recent years suggests that there ate more whales in the Mexican Pacific than previously
58 citations
TL;DR: The results suggest that relative densities of different school types are strongly related to physical environmental parameters, the most important being sea surface temperature, depth of the thermocline and thickness of the oxygen minimum layer.
Abstract: The relative abundance of the most common cetacean schools in the eastern tropical Pacific Ocean for 1977–1980 are estimated based on encounter rates with tuna purse-seiners. No temporal trends were apparent in the relative abundance estimates. The geographic distributions for eight different school types are described. Multivariate statistical techniques are used to investigate interrelations between species and relationships to parameters of the physical environment. The results suggest three major species groupings: (1) an inshore grouping of bottlenose dolphins (Tursiops truncates), Risso's dolphin (Grampus griseus), pilot whales (Globicephala macrorhynchus) and, to a lesser extent, common dolphins (Delphinus delphis); (2) an offshore pelagic grouping of spotted and spinner dolphins (Stenella attenuate and S. longirostris); and (3) an association between pilot whales and common dolphins that overlaps the first grouping in inshore areas and also tends to be segregated from the second grouping. The results also suggest that relative densities of different school types are strongly related to physical environmental parameters, the most important being sea surface temperature, depth of the thermocline and thickness of the oxygen minimum layer.
50 citations
TL;DR: Compared to the anterior surface of the normal human cornea, all Tursiops showed pronounced random, local curvature changes typical of old keratitis and scarring, and Zalophus corneas showed no reliable regular astigmatism, which accounts for equivalent marine and aerial visual resolution in this species.
Abstract: Compared to the anterior surface of the normal human cornea, all Tursiops showed pronounced random, local curvature changes typical of old keratitis and scarring Comparable but less severe findings apply to Zalophus These irregularities were superimposed on the mild regular astigmatism of the spoon-shaped Tursiops cornea (mean central power is 268 D, SD = 38, N = 82) All Zalophus corneas showed no reliable regular astigmatism (overall mean power is 217 D, SD = 44, N = 53) but exhibited a flat, circular region about 65 mm in diameter along the nasal aspect of the horizontal meridian Refraction through this cornea1 region showed aerial emmetropia, which accounts for equivalent marine and aerial visual resolution in this species
44 citations
TL;DR: Evidence is found that belukhas in the wild deposit more than one growth layer groups (GLGs) per year, and captive environments are less variable than natural ones.
Abstract: Growth layer groups (GLGs) were counted in teeth from an adult male belukha whale (Delphinapterus leucas) that had lived for 23 yr in captivity and was estimated to have been 14 mo at capture. As defined here, GLGs are repeating areas of alternating opaque (denser) and translucent (less dense) dentin or cementurn, or nodes at the dentin-cementum interface. A GLG involves at least one change from opaque to translucent, dense to less dense or ridge to groove, but may be further subdivided by incremental growth layers or laminations. Teeth were prepared by two techniques. Thick sections (longitudinal half sections) were examined with a dissecting microscope under reflected light. Thinner cross and longitudinal sections were x-rayed and the plates scanned with a microdensitometer. Scanning electron photomicrographs were prepared from thick sections, but SEM proved to be the least useful technique. Counts of GLGs were variable because the laminations were numerous and some surface layers had been lost from wear. Thick- and thinner-section techniques gave comparable results, and approximately 40 GLGs were counted consistently. Although captive environments are less variable than natural ones, our findings are further evidence that belukhas in the wild deposit more than one—and probably two—GLGs per year.
41 citations
TL;DR: The external appearance of P. sinus was unknown until 13 fresh specimens were recently examined, and the most striking features of the pigmentation pattern are the large black eye patches and the black upper and lower lip patches.
Abstract: The vaquita, Phocoena sinus, is a porpoise in the family Phocoenidae that lives only in the Gulf of California. The external appearance of P. sinus was unknown until 13 fresh specimens were recently examined. The most obvious morphological feature distinguishing P. sinus from its two congeners is the proportionately higher dorsal fin. The most striking features of the pigmentation pattern are the large black eye patches and the black upper and lower lip patches. In both areas, the pigmentation contrasts sharply with the surrounding light gray coloration. The total lengths of the specimens ranged from 70.3 cm (a neonate) to 143.5 cm (an adult female).
TL;DR: Surprisingly, the young seals were able to maintain weight and store protein while energy intake was below metabolic needs; this was possible because animals gained weight as water; they retained wellhydrated proteinaceous tissue while losing poorly-hydrated adipose tissue.
Abstract: We studied energetics and food utilization in young elephant seals as they were first introduced to solid food following their long post-weaning fast. Using radioactive tracer techniques, we monitored changes in body composition, protein metabolism, and metabolic rate during fasting and initial feeding. In fasting animals, fat stores supplied nearly all energetic requirements. In feeding animals, 49% of protein ingested was retained as body tissue, allowing protein mass to increase. Body fat was lost at rates comparable to rates in fasting animals and continued to fuel the bulk of metabolism. Weight loss was arrested when animals consumed 786 g/d, or 40 kcal/kg0.75/d, which was far less than their metabolic rates (63–206 kcal/kg0.75/d). Surprisingly, the young seals were able to maintain weight and store protein while energy intake was below metabolic needs. This was possible because animals gained weight as water; they retained wellhydrated proteinaceous tissue while losing poorly-hydrated adipose tissue.
TL;DR: Examples, broadly mimicking the life history of polar bears, were used to identify potential qualitative errors that may occur from using overly simplified projection models.
Abstract: Adults of long-lived, birth-pulse populations (e.g., many cetaceans, polar bears and walrus) may not breed every year because of parental care, long gestation periods or nutritional constraints. Estimates of adult annual recruitment rates for such populations are necessarily an oversimplification since these rates are applied to both breeding and non-breeding females.
The weighted mean of age-specific recruitment is insufficient for non-stable age projections of multi-annual populations beyond the first time interval. Restated, conventional or collapsed Leslie matrix and life-table projections are not adequate for non-stable age simulations of populations with multi-annual reproduction cycles.
These difficulties may be avoided by employing a parameterization that accommodates a dynamic age structure and proportion of breeding females within a given age class. This parameterization is a true description of the multiple-year reproduction schedule.
Examples, broadly mimicking the life history of polar bears, were used to identify potential qualitative errors that may occur from using overly simplified projection models.
TL;DR: The prevalence of scarring on the black and white animals suggescs sexual dimorphism and that these larger, more conspicuously marked animals are adult males, while the smaller, browner, unscarred animals are females and young.
Abstract: Multiple sightings of a distinctive but unidentified species of beaked whale have been made in the eastern tropical Pacific. The unidentified whale has two color morphs: a conspicuously marked black and white form (judged to be larger), and a uniformly gray-brown form. Maximum length estimates have been 5-5.5 m. Other features include a relatively flat head, with a small, distinct melon; a moderately long beak; and a low, wide-based, triangular dorsal fin. On most animals the trailing edge of the dorsal fin is only slightly falcate and often appears straight. On the black and white morph, a broad white or cream-colored swathe originates immediately posterior to the dorsal surface of the head and runs posterio-ventrally on either side of the animal. The prevalence of scarring on the black and white animals suggescs sexual dimorphism and that these larger, more conspicuously marked animals are adult males, while the smaller, browner, unscarred animals are females and young. Possibilities for identification include: 1) a well-marked race of a known Mesoplodon sp., 2) Mesoplodon (Indopacerus) pacificus or 3) an undescribed species.
TL;DR: The 12 Tursiops eyes were consistent for vascular structure, optic papillae, dimensional components and tapetal coloration and there was a difference between species in the short wavelength regions of the spectrum.
Abstract: We provided a water-cornea interface to correct the usual aerial myopia encountered in fundus photography of marine mammal eyes. The 12 Tursiops eyes were consistent for vascular structure, optic papillae, dimensional components and tapetal coloration. Multiple photographs were assembled to produce one ocular fundus typical of Tursiops truncatus and one for Grampus griseus. The eyes have a vestigial hyaloid vessel and an optic disc („blind spot”) that occupies the center of the fundus. The disc is bounded in both species by a vascular structure that is continuous with a (retrobulbar) perineural organ called the ophthalmic rete. The vascular trees of the fundus do not suggest an area of specialization for high resolution. Both species exhibit total tapetalization. Tapetal spectral reflectance did not vary between Tursiops. There was, however, a difference between species in the short wavelength regions of the spectrum.
TL;DR: Reassociation with a previous offspring, as observed once in this study, also may occur most frequently in food-limited populations where reproductive failures are most common and pup survivorship is significantly increased by additional maternal assistance.
Abstract: Eight tagged sea otter (Enhydra lutris) pups in central Prince William Sound, Alaska, weighed 6-15 kg at the time of separation from their mother. Four pups weighing 15 kg were able to forage successfully on their own. Three pups weighing 19 kg had negligible chances of survival and apparently were abandoned by sick females. Abandonment of a pup may reduce the burden on a sick female, enabling recovery and subsequent reproduction. One of the three sick females that abandoned a pup in this study recovered and pupped again. Abandonment of pups should occur most often in populations where females are stressed by poor food resources. Reassociation with a previous offspring, as observed once in this study, also may occur most frequently in food-limited populations where reproductive failures are most common and pup survivorship is significantly increased by additional maternal assistance.
Journal Article•
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TL;DR: The Cape fur seal Arctocephalus pusillus of South Africa and Namibia breeds in 23 colonies and has a significant increase in numbers of seal pups between 1971 and 1976; the rate of increase is estimated to be 3.2% per year as discussed by the authors.
Abstract: The Cape fur seal Arctocephalus pusillus of South Africa and Namibia breeds in 23 colonies. Aerial surveys have been used to estimate numbers of pups during breeding seasons from December 1971 to December 1978, and the results have been presented by Shaughnessy (1987). In this paper we develop statistical methods for estimating these pup numbers, as well as variances of the estimates. We demonstrate a significant increase in numbers of seal pups between 1971 and 1976; the rate of increase is estimated to be 3.2% per annum.