Blubber Layer Research Articles

Head sinuses, melon, and jaws of bottlenose dolphins, Tursiops truncatus, observed with computed tomography structural and single photon emission computed tomography functional imaging

The head sinuses, melon, and lower jaws of dolphins have been studied extensively with various methods including radiography, chemical analysis, and imaging of dead specimens. Here we report the first structural and functional imaging of live dolphins. Two animals were imaged, one male and one female. Computed tomography (CT) revealed extensive air cavities posterior and medial to the ear as well as between the ear and sound-producing nasal structures. Single photon emission computed tomography (SPECT) employing 50 mCi of the intravenously injected ligand technetium [Tc-99m] biscisate (Neurolite) revealed extensive and uptake in the core of the melon as well as near the pan bone area of the lower jaw. Count density on SPECT images was four times greater in melon as in the surrounding tissue and blubber layer suggesting that the melon is an active rather than a passive tissue. Since the dolphin temporal bone is not attached to the skull except by fibrous suspensions, the air cavities medial and posterior to the ear as well as the abutment of the temporal bone, to the acoustic fat bodies of each lower jaw, should be considered in modeling the mechanism of sound transmission from the environment to the dolphin ear.

High concentrations of isovaleric acid in the fats of odontocetes: variation and patterns of accumulation in blubber vs. stability in the melon.

Isovaleric acid (iso5:0) is an unusual fatty acid that is important for echolocation and hearing in acoustic tissues of some odontocetes, but its functional significance in blubber is unknown. We examined patterns of accumulation of this compound in blubber in 30 species of odontocetes ( n=299). Iso5:0 concentrations in blubber varied with phylogeny, ontogeny and body topography. Iso5:0 accumulated in greater quantities in superficial/outer blubber than in deep/inner blubber. In the outer blubber of northern right whale and Hector's dolphins, iso5:0 accounted for one-third to one-half of all fatty acids. Total blubber burden of iso5:0 in harbour porpoises represented up to 15 times the amount deposited in the melon. The composition of the melon does not change during starvation in harbour porpoises, supporting the hypothesis that lipids in melon are conserved for a specific function. Some odontocetes continually deposit iso5:0 in blubber after levels in melon have reached asymptotic levels, suggesting independent control of iso5:0 synthesis and storage in these compartments. Dolphins and porpoises inhabiting cold waters possess higher concentrations of iso5:0 in their outer blubber layers than species from warmer regions. We propose that this relationship represents an adaptive secondary role for iso5:0 in maintaining blubber flexibility in cold environments.

Outbreak of Botulism Type E Associated With Eating a Beached Whale—Western Alaska, July 2002

Botulism is a neuroparalytic illness caused by toxins produced by the bacterium Clostridium botulinum, an obligate anaerobe found commonly in the environment. Intoxication with toxin type E is associated exclusively with eating animal foods of marine (salt or fresh water) origin. Persons who eat raw or fermented marine fish and mammals are at high risk for botulism from type E toxin. On July 17, 2002, the Alaska Division of Public Health investigated a cluster of suspected botulism cases among residents of a fishing village in Alaska. This report summarizes the findings of the outbreak investigation, which linked disease to eating raw muktuk (skin and a pink blubber layer) from a beached whale (Figure). To avoid delays in treatment, health-care providers evaluating patients suspected of having botulism should base treatment decisions on clinical findings. Public health authorities should be notified immediately about any suspected botulism case.

PCBs and organochlorine pesticides in blubber biopsies from free-ranging St. Lawrence River Estuary beluga whales ( Delphinapterus leucas), 1994–1998

For the first time, organochlorine (OC) contaminants were measured in blubber biopsies from free-ranging St. Lawrence River Estuary beluga whales ( Delphinapterus leucas), to compare contaminant levels to those previously measured in dead stranded belugas. PCBs, DDTs, toxaphene and chlordane-related compounds were the major OC contaminants detected in 44 belugas biopsied in 1994–1998. ΣPCB (the sum of 104 congeners) ranged from 2080 to 128,000 ng/g lipid in males ( n=34; minimum estimated ages 8–22 years), and from 148 to 44,100 ng/g lipid in females ( n=10; minimum estimated ages 7–22 years). The concentrations of PCBs and OC pesticides in the blubber of these whales overlapped those observed in stranded belugas from an earlier study, and demonstrated comparable age and sex-related trends. However, lower proportions of mirex, HCB, DDTs, and many of the highly chlorinated PCBs occurred in the biopsy samples compared to results for blubber from stranded carcasses. Most major OC compounds were present at lower concentrations in the biopsies, but this does not appear to be solely related to age differences between the two groups, or to emaciation in the stranded whales. Nor does it appear to be associated with the use of superficial biopsies, and the possible stratification of lipids and OCs in the blubber layer. Nevertheless, given these possible confounding factors, and the uncertainty in age estimates for the biopsied whales, the results point to the need for careful interpretation of biopsy results when comparing with data taken from the full depth of the blubber mantle in stranded whales. Taken together, results from both biopsied whales and previously studied stranded belugas indicate that PCB and OC pesticide contamination of St. Lawrence beluga whales may occur across a broader range of levels than previously thought, at least for males which formed the largest group in this study, possibly due to different degrees of dietary exposure. It also appears that measuring contaminant concentrations only in stranded whales, may overestimate OC levels in the population as a whole, especially for highly chlorinated OCs.

Vertical stratification of fatty acids in the blubber of southern elephant seals ( Mirounga leonina): implications for diet analysis

Fatty acid signature analysis (FASA) is a powerful ecological tool that uses essential fatty acids (FA) from the tissues of animals to indicate aspects of diet. However, the presence of vertical stratification in FA distribution throughout blubber complicates the application of FASA to marine mammals. Blubber biopsy samples were collected from adult female southern elephant seals ( Mirounga leonina) from Macquarie Island ( n=11), and blubber cores were divided into inner and outer sections to determine the degree to which the blubber layer was stratified in FA composition, we found 19 FA from both blubber layers in greater than trace amounts (>0.5%). The inner and outer blubber layers could be separated using principal components analysis based on the relative proportion of FA in each layer. Dietary polyunsaturated fatty acids (PUFA) were also observed in significantly higher proportions in the inner blubber layer. Due to the degree of FA stratification in southern elephant seals, we concur with other marine mammal studies that sampling only the outer blubber layer will result in a loss of recently accumulated information regarding diet structure (as indicated by ‘surplus’ PUFA from the diet). This finding suggests that differential mobilization/deposition of certain FA may result in a modified signature from prey to predator. Thus, sampling animals to recover the inner blubber layer is important for studies attempting to describe aspects of marine mammal diet. This can be achieved in animals such as pinnipeds where the whole blubber layer can be readily sampled.

Dynamics of PCB transfer from mother to pup during lactation in UK grey seals Halichoerus grypus: differences in PCB profile between compartments of transfer and changes during the lactation period

The composition of the PCB mixture which is transferred from mother to pup in grey seals Halichoerus grypus throughout lactation was measured in the successive compartments of transfer: maternal blubber, maternal serum, milk and pup serum. Mother-pup pairs were captured regularly between birth and weaning on the Isle of May, Scotland. The PCB profiles of the different compartments of transfer consisted mainly of congeners 153, 138, 180, 187, 170 and 101, which made up 85% of the total PCB burden. Outer blubber contained higher relative concentrations (R-153) Of hepta-, octa-, and nona-chlorinated congeners (higher chlorinated congeners) than inner blubber, at both early (less than or equal to 5 d) and late (greater than or equal to 11 d) lactation. There was no change in the composition of the outer blubber layer between early and late lactation, while in the inner blubber, there was a slight increase in the R153 of higher chlorinated congeners at late lactation. In maternal serum, profiles changed towards having a higher proportion of higher chlorinated congeners as lactation progressed, but in milk, the PCB pattern stayed constant throughout lactation. Surprisingly, in pup serum profiles also changed towards higher R153 of higher chlorinated congeners at late lactation compared to early lactation, which was different to the pattern observed in milk. In all body compartments, higher proportions of higher chlorinated congeners were associated with higher concentrations of total PCBs. Maternal blubber and pup serum contained a higher R153 of higher chlorinated congeners than milk and, to a lesser extent, maternal serum. Thus biomagnification of the higher chlorinated congeners was recorded in pup serum.

Documented Sighting of a North Pacific Right Whale in the Gulf of Alaska and Post-Sighting Acoustic Monitoring

North Pacific whales lEubalaena japonica) are large whales (15 to 18 m in length) with a robust black body; narrow, high-arched upper jaw; no dorsal fin; and characteristic callosities on their rostrum and lower lips (see Rosenbaum and others 12000] for discussion of scientific names for whales). They are found in all oceans and migrate from hlgh latitude feeding grounds where they spend the summer to temperate waters for the winter (Braham and Rice 1984). They feed primarily on calanoid copepods by skimmingf' with their mouths open usually near the surface. They were given their name by whalers who considered them to be the right whales to catch because of their size and thick blubber layer, slow swimming speed, and the fact that they floated when killed (Braham and Rice 1984). The Gulf of Alaska was an important part of the summer distribution of the North Pacific whale before intensive whaling severely depleted the population (Rice 1974; Braham and Rice 1984; Webb 1988; Scarff 1991). A whaling ground that included the Gulf of Alaska (130° to 170°W) and waters south to 50° N, termed the Northwest or Kodiak Ground (Fig. 1), became a primary hunting area for whales after discovery there by pelagic whalers in 1835 (Townsend 1935; Scarff 1986) This discovery led to the widespread whaling of whales not only in the Gulf of Alaska, but throughout the North Pacific. The original population size for the North Pacific whale is unknown, but Scarff (2001) estimated a total whaling-induced mortality of 26,466 to 37,173 from 1835 to 1909. Almost half of these mortalities occurred in the 5-y period from 1845 to 1849 (Scarff 2001). The mortality dropped quickly for every 5-y period after 1849, with usually <100 taken per 5-y period after 1869. Their ecanomic value remained high, but only 20 whales were reported caught in the Northwest Ground between 1917 and 1935 (Reeves and others 1985; Brueggeman and others 1986). Tomilin (1957) reported that among 31J475 whales taken between 1911 and 1938 along the northwestern coast of North America only 28 were whales. In 1931, whaling nations, except Japan and the USSR, ratified a prohibition on the killing of whales made by the Convention br the Regulation of Whaling (Brownell and others 2001). Japan was restricted in the hunting of whales after World War II by the Supreme Commander for the A1lied Powers in 1945, and the USSR agreed to the prohibition when it joined the International Whaling Commission in 1945 (Brownell and others 2001). Although the whale was afforded protection in 1945J 251 illegal kills, 3 permitted kills, and fewer than 230 sightings have been documented from the Gulf of Alaska since that time (see Brownell and others [2001] for a review of all 20th century sightings and takes in the North Pacific). In 1961, 3 whales were taken on the same day off south Kodiak Island with a special permit to Japanese scientists (Omura and others 1969). Numbers of whales reported from scientific surveys conducted by the USSR in the western part of the Gulf of Alaska in 1959, from surveys throughout the Gulf of Alaska from 1960 to 1962, and in whaling records from 1958 to 1964 (Berzin and Rovnin 1966; Berzin and Doroshenko 1982) range from 88 to 200, due to discrepancies among reports (Brownell and others 2001). Xapanese whaling scoutboats and catcherboats reported a total of 26 whale sightings in the

Blubber fatty acids of minke whales: stratification, population identification and relation to diet

We determined the fatty acids in the blubber of 10 minke whales (Balaenoptera acutorostrata) from the Norwegian Sea and 12 minke whales from the North Sea. The composition of the fatty acids differed between the inner and outer blubber layer. The saturated, the monounsaturated with 20 and 22 carbon atoms and the polyunsaturated fatty acids had higher relative amounts in the inner than in the outer blubber, and the short-chain monounsaturated acids, i.e. with 14, 16 and 18 carbon atoms, had the highest relative amounts in the outer layer. The change in relative concentration was steeper in the outer parts of the blubber than in the inner parts. Whales from the two areas had different fatty-acid profiles in both inner and outer blubber layer, although these differences were smaller than the difference between inner and outer layer. The difference between the whales from the two areas corresponds to the management stocks defined by the International Whaling Commission. Determination of the fatty-acid profile may be used for identification of whale populations. The composition of the fatty acids in the blubber differed from that of the main prey of the whales: sand eel for the North Sea whales and herring for the Norwegian Sea whales. These differences between prey and blubber fatty acids were larger for the outer blubber layer than for the inner.

Quantitative dynamics of PCB transfer from mother to pup during lactation in UK grey seals Halichoerus grypus

PCB contamination was measured in the milk and serum of grey seal Halichoerus grypus mothers and in the serum of their pups sampled from 2 to 5 times between parturition and weaning on the Isle of May, Scotland, in 1998 and 2000. Blubber biopsies were also taken from the lactating females at early and late lactation in 2000. Concentrations of PCBs in milk stayed constant during the first part of lactation (0.31 +/- 0.17 mug g milk(-1)) and then increased at late lactation (0.67 +/- 0.42 mug g milk(-1)). Curiously, it did not follow the changes of milk lipid content, which increased at early lactation and then stayed constant until the end of the nursing period. As a result, even when expressed per unit of milk lipids, PCBs underwent a rise at the end of lactation. The changes in milk PCBs were accompanied by similar dynamics in maternal serum as well as in pup serum. Increased concentrations of PCBs at late lactation in serum and milk may be explained in part by the changes observed in maternal blubber. PCB levels increased significantly between early and late lactation in inner blubber, suggesting that PCBs are less easily mobilised from blubber than lipids. At late lactation, the retention capacity of the reduced blubber layer for PCBs might have reached its maximum. The mobilization of less polar lipids from blubber might also occur at this stage. In both cases, this could result in a higher mobilization of PCBs at this time. While inner blubber was significantly less concentrated than outer blubber at early lactation (1.26 +/- 0.72 mug g lipids(-1) in inner blubber vs 3.16 +/- 1.34 mug g lipids(-1) in outer blubber), these variations disappeared at late lactation (3.24 +/- 2.60 mug g lipids(-1) in inner blubber vs 3.59 +/- 1.46 mug g(-1) lipids in outer blubber). Newborn pups already had significantly higher serum levels of PCBs than their mothers, revealing an important placental transfer (11.9 +/- 7.0 ng ml serum(-1) in pups vs 6.7 +/- 3.5 ng ml serum(-1) in mothers). These differences were even greater in late lactation, due to the ingestion of milk (27.9 +/- 18.1 ng ml serum(-1) in pups vs 12.2 +/- 7.2 ng ml serum(-1) in mothers). As lactation progressed, PCB levels in pup serum increased exponentially as compared to the levels in the serum of their mothers.

Partitioning of persistent organic pollutants in grey seal ( Halichoerusgrypus) mother–pup pairs

Phocid seals have lipid rich milk, which is known to serve as a transfer medium through which persistent organic pollutants (POPs) move from mother to offspring during lactation. However, knowledge on this generational transfer of different POPs and the partitioning of these compounds in maternal and offspring tissues over the course of the lactation are limited. In this study we examined the qualitative and quantitative partitioning of a range of chlorinated POPs in maternal blubber, blood and milk as well as in pup blubber, collected early in the lactation period and late in the lactation period. In the lactating female, the high-chlorinated and hydrophobic compounds were passed less efficiently into the milk than the low-chlorinated compounds and more water-soluble compounds. Significantly, lower maternal blood concentrations than in maternal blubber biopsies suggest a stratification of POP concentrations in the blubber column of lactating female and lower concentrations in the metabolic active inner layers. Over the course of lactation, there was a significant increase in maternal blood and milk concentrations of POPs as opposed to no change in maternal blubber biopsy concentrations. This was most apparent for the hydrophobic and high-chlorinated compounds. The most likely explanation for this is that the metabolic active inner blubber layer, from which the milk lipids are derived from, is in steady state with the circulatory system, while the outer layers are more static and only slowly respond to changes in concentrations elsewhere in the body. The concentrations of the high-chlorinated and hydrophobic compounds were substantially lower in pup blubber than in maternal blubber. This probably relates the combined effect of these compounds stratification in maternal blubber and their slow transfer into the milk. The present study shows that the more hydrophobic and high-chlorinated compounds come to steady state less quickly in the different tissues than the more water-soluble and low-chlorinated compounds in the lactating female and her offspring. This has implications for which matrices to choose when sampling for assessing the toxicological risk of POPs in seals.

Changes in blubber distribution and morphology associated with starvation in the harbor porpoise (Phocoena phocoena): evidence for regional differences in blubber structure and function.

To examine patterns of blubber loss accompanying a decline in body condition, blubber thickness of juvenile harbor porpoises in normal/robust body condition (n=69) was compared with that of starved conspecifics (n=31). Blubber thickness in the thorax of starved porpoises (9-11 mm) was only 50%-60% of that of normal animals (18-20 mm); however, very little tailstock blubber was lost during starvation. Adipocytes in thorax and tailstock blubber were measured in both groups (n=5) to determine whether thickness changes were homogeneous throughout blubber depth. In the thorax of normal porpoises, adipocytes near the epidermis (outer blubber) were smaller (0.11 nL) than inner blubber adipocytes (0.17 nL). Conversely, the size of tailstock adipocytes was uniform. Starved animals had fewer, smaller adipocytes in the inner thorax blubber, suggesting a possible combination of adipocyte shrinkage and loss. Lipids were withdrawn only from the inner layer of thorax blubber during starvation, supporting a hypothesis of regional specialization of function in blubber. Blubber of the thorax serves as the site of lipid deposition and mobilization, while the tailstock is metabolically inert and likely important in locomotion and streamlining. Therefore, some proportion of the blubber of small odontocetes must be considered structural/mechanical rather than an energy reserve.

Ontogenetic allometry and body composition of harbour porpoises (Phocoena phocoena, L.) from the western North Atlantic

AbstractNorth Atlantic harbour porpoises Phocoena phocoena (L.) face considerable energetic challenges, as they are relatively small marine mammals with an intense reproductive schedule and a cold‐water habitat. Post‐natal growth of these porpoises was described using ontogenetic allometry and body composition techniques. The cross‐sectional sample contained robust calves, immature, and mature porpoises (n= 122) incidentally killed in commercial fishing operations between 1992 and 1998. Total mass and the mass of 26 body components were measured using a standard dissection protocol. Most body components grew similarly in female and male porpoises. Blubber, brain and skull were negatively allometric, while muscle and reproductive tissues exhibited positive allometry. Female heart, liver, intestine and mesenteric lymph node grew at significantly higher rates than in males. Male locomotor muscle and pelvic bones grew significantly faster than in females. High growth rates for visceral and reproductive organs in porpoises, relative to other mammals, may underlie their early maturation and support their intensive, annual reproductive schedule. Relative to other cetaceans, porpoises seem to allocate a larger percentage of their total body mass to blubber. This allocation to blubber, which is greatest in calves (37% of body mass), may provide harbour porpoises with the thermal insulation required to live in cold water. The factors influencing growth rates and differential investments in body composition seem to change at various stages of a porpoise's life. Energy allocation in porpoises seems to shift from an emphasis on developing an insulative blubber layer in young animals to preparing the body for annual reproduction at sexual maturity.

Organochlorine and organotin compounds in Caspian seals ( Phoca caspica) collected during an unusual mortality event in the Caspian Sea in 2000

Polychlorinated biphenyls (PCBs), organochlorine pesticides and organotin compounds were determined in the blubber and liver of Caspian seals ( Phoca caspica) found stranded on the coast of the Caspian Sea during an outbreak of canine distemper virus (CDV) in 2000. Among organochlorines analyzed, DDTs were the most dominant contaminants with concentrations ranging from 6.3 to 470 μg/g on a lipid-weight basis. Caspian seals collected in 2000 during the epizootic had higher concentrations of organochlorines than healthy individuals sampled in 1998. However, the blubber layer was generally thinner in the seals collected in 2000 than those in the previous surveys. Although compositions of organochlorine pesticides in seals suggested that the contamination status in the Caspian Sea is improving, the levels found in Caspian seals in 2000 were comparable to those in other marine mammals that have suffered from epizootics. This implies that the present status of contamination found in Caspian seals poses a risk of immunosuppression. Concentrations of butyltin compounds in livers of seals ranged from 0.49 to 17 ng/g on a wet-weight basis and octyltin compounds were below limit of detection in all the samples analyzed, suggesting less contamination by organotin compounds in the Caspian Sea.

Growth and seasonal fluctuations in size and condition of male Northwest Atlantic harp seals Phoca groenlandica: an analysis using sequential growth curves

Pinnipeds have marked seasonal changes in body condition, accumulating energy re- serves prior to the reproduction period, and depleting these reserves during the breeding and molt- ing periods. This cycle is not well described in male harp seals Phoca groenlandica. We obtained mor- phometric measurements for 3167 Northwest Atlantic male harp seals sampled between 1979 and 1995. The part of the yearly cycle covered in this study (November to May) was divided into short blocks around median dates called 'periods'. For each period, a growth curve was calculated for body mass, sculp mass, core mass and standard length. These sequential growth curves were used to cal- culate changes in size-at-age between periods. In addition, seasonal changes in 3 condition indices (general, sculp and core condition), in blubber thickness and in the ratio of sculp to total mass were analyzed using locally weighted regressions. Male harp seals returned from their high-latitude feed- ing grounds heavier, in better condition, and with a thicker blubber layer than when they left the area in the spring. However, maxima in length, mass, condition and blubber thickness were not observed until the February 22 period (February 12 to March 4), or in the case of seals younger than 5 yr, some- time in March. Mass losses associated with the rut began between the periods February 22 and March 15 (March 5 to 25) and were most pronounced in seals older than 10 yr. About 66% of the losses in mass came from the core during this period. We estimated that males lost 39.4 kg during the rut (1.16 kg d -1 or 0.78% of initial mass d -1 , 44% from sculp and 56% from core) and incurred energy expenditures of 840 MJ (24.7 MJ d -1 ). This corresponds to twice the standard metabolic rate (SMR), and suggests that males are feeding during the rut. All males lost mass in April, and again in May. They began to molt April 19 period (April 16 to 22). Fewer than half the seals had completed the shed- ding of old hair when the study ended, in the May 10 period. Rates of mass loss during the molt varied from 1 to 1.8 kg d -1 , depending on the age of the seals. Minima of length, mass, condition and blubber thickness were observed in May. Molting appears to be a period of high energy expenditures (3 to 5 SMR) despite the low levels of activity observed at this time. This study revealed that length also changes seasonally: fat seals in February were longer than lean seals of the same age in late April.

Diet of northern bottlenose whales inferred from fatty-acid and stable-isotope analyses of biopsy samples

The Gully submarine canyon off eastern Canada has been designated a pilot marine protected area largely because of the northern bottlenose whales (Hyperoodon ampullatus) found there. Studies of this species' diet elsewhere in the North Atlantic Ocean have suggested specialization on the deep-sea squid Gonatus fabricii. We found a high proportion of the congener Gonatus steenstrupi in the stomachs of two bottlenose whales stranded in eastern Canada. In 1997, we collected remote biopsy samples from free-ranging bottlenose whales off Nova Scotia; fatty acids were determined from blubber samples and stable isotopes (carbon and nitrogen) from skin samples. Although fatty-acid stratification throughout the depth of the blubber layer was present (determined from blubber samples of stranded animals), the magnitude of stratification was less pronounced than in many other cetaceans, allowing some qualitative inferences to be made from shallow biopsy samples. Fatty-acid patterns and stable-isotope values from whales were compared with those in samples of G. fabricii from the Norwegian Sea. Blubber fatty acid composition was similar in characteristics to that of adult G. fabricii but was markedly distinct from that of juvenile G. fabricii and other recorded prey species. Nitrogen-isotope values implied that bottlenose whales (mean 15.3‰) and adult G. fabricii (mean 13.7‰) occupy high trophic levels. Overall, the results of these techniques concurred in suggesting that squid of the genus Gonatus may form a major part of the diet of bottlenose whales in the Gully.

Cutaneous Heat Flux Models do not Reliably Predict Metabolic Rates of Marine Mammals

Heat flux models have been used to predict metabolic rates of marine mammals, generally by estimating conductive heat transfer through their blubber layer. Recently, Kvadsheim et al. (1997) found that such models tend to overestimate metabolic rates, and that such errors probably result from the asymmetrical distribution of blubber. This problem may be avoided if reliable estimates of heat flux through the skin of the animals are obtained by using models that combine calculations of conductive heat flux through the skin and fur, and convective heat flux from the surface of the animal to the environment. We evaluated this approach based on simultaneous measurements of metabolic rates and of input parameters necessary for heat flux calculations, as obtained from four harp seals (Phoca groenlandica) resting in cold water. Heat flux estimates were made using two free convection models (double-flat-plate and cylindrical geometry) and one forced convection model (single-flat-plate geometry). We found that heat flux estimates generally underestimated metabolic rates, on average by 26–58%, and that small variations in input parameters caused large variations in these estimates. We conclude that cutaneous heat flux models are too inaccurate and sensitive to small errors in input parameters to provide reliable estimates of metabolic rates of marine mammals.

Biomechanics and energetics in aquatic and semiaquatic mammals: platypus to whale.

A variety of mammalian lineages have secondarily invaded the water. To locomote and thermoregulate in the aqueous medium, mammals developed a range of morphological, physiological, and behavioral adaptations. A distinct difference in the suite of adaptations, which affects energetics, is apparent between semiaquatic and fully aquatic mammals. Semiaquatic mammals swim by paddling, which is inefficient compared to the use of oscillating hydrofoils of aquatic mammals. Semiaquatic mammals swim at the water surface and experience a greater resistive force augmented by wave drag than submerged aquatic mammals. A dense, nonwettable fur insulates semiaquatic mammals, whereas aquatic mammals use a layer of blubber. The fur, while providing insulation and positive buoyancy, incurs a high energy demand for maintenance and limits diving depth. Blubber contours the body to reduce drag, is an energy reserve, and suffers no loss in buoyancy with depth. Despite the high energetic costs of a semiaquatic existence, these animals represent modern analogs of evolutionary intermediates between ancestral terrestrial mammals and their fully aquatic descendants. It is these intermediate animals that indicate which potential selection factors and mechanical constraints may have directed the evolution of more derived aquatic forms.

THE RELIABILITY OF SKINFOLD-CALIPERS FOR MEASURING BLUBBER THICKNESS OF STELLER SEA LION PUPS (EUMETOPIAS JUBATUS)

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.

Spatial distribution of persistent organochlorines in ringed seal ( Phoca hispida) blubber

Blubber samples, taken through the entire blubber column, were collected from three different anatomical locations on ringed seals ( Phoca hispida). The outer and inner layers of these samples were analysed for concentrations of ΣPCBs (sum of the analysed congeners, polychlorinated biphenyls) and p,p′-DDE (4,4′-dichlorodiphenyldichloroethylene). No significant differences were found in blubber thickness or in per cent extractable lipid when comparing age- and sex-groups, or in extractable lipid content when comparing anatomical locations of the blubber or blubber depth. No significant differences were found between the three different anatomical locations with respect to the concentrations of ΣPCBs or p,p′-DDE. However, the concentrations of both ΣPCB and p,p′-DDE were significantly higher in the outer blubber layer compared to the inner. Higher levels of both ΣPCB and p,p′-DDE were found in males compared to females and juveniles in both the inner and outer parts of the blubber column. The most commonly used blubber sampling devices are biopsy tools that penetrate only the outer layer of the blubber. Analyses of such samples will not reflect the real body burden of organochlorines. Standard methods for sampling blubber of marine mammals should be developed so that comparative studies and longitudinal monitoring programs of pollutants in marine mammals can be conducted in a meaningful way.

Biomechanics and energetics in aquatic and semiaquatic mammals: Platypus to whale

Abstract A variety of mammalian lineages have secondarily invaded the water. To locomote and thermoregulate in the aqueous medium, mammals developed a range of morphological, physiological, and behavioral adaptations. A distinct difference in the suite of adaptations, which affects energetics, is apparent between semiaquatic and fully aquatic mammals. Semiaquatic mammals swim by paddling, which is inefficient compared to the use of oscillating hydrofoils of aquatic mammals. Semiaquatic mammals swim at the water surface and experience a greater resistive force augmented by wave drag than submerged aquatic mammals. A dense, nonwettable fur insulates semiaquatic mammals, whereas aquatic mammals use a layer of blubber. The fur, while providing insulation and positive buoyancy, incurs a high energy demand for maintenance and limits diving depth. Blubber contours the body to reduce drag, is an energy reserve, and suffers no loss in buoyancy with depth. Despite the high energetic costs of a semiaquatic existence...