Body fat and condition in sperm whales,Physeter macrocephalus,from southern Australian waters

Blubber thickness (n=102) and lipid content (n=37) were measured in sperm whales from three mass stranding events on the west and north-west coasts of Tasmania, Australia in February 1998. Blubber thickness was highly variable, ranging from 43.0 to 168.0 mm (mean 98.4+/-18.4 mm) while lipid fat content, also highly variable, ranged from 16.19 to 89.34% (mean 49.2+/-17.9%). Blubber thickness was significantly and positively related to total length, but a blubber thickness index based on the residuals of this relationship was not related to age, sex or reproductive condition. No relationship was found between blubber thickness index and blubber lipid content, indicating that blubber thickness may not provide a comprehensive indication of body fat condition in sperm whales when only measured at a single site. Blubber lipid content was not related to total length, age or sex. Blubber lipid content was stratified vertically throughout the blubber layer, suggesting that the inner blubber layer may be a more active site for lipid deposition and mobilisation, while the outer blubber layer may serve in a structural or thermoregulatory role. The social structure and foraging ecology of this species may serve to minimise the need to rely on stored energy reserves to meet reproductive energy requirements. In addition, the broader role of blubber for structural, buoyancy and insulative functions coupled with high individual variability may cause a lack of obvious relationships between these variables and body size, age, sex and reproductive state in this species.     

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.     

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.     

Structural fiber reinforcement of keel blubber in harbor porpoise (Phocoena phocoena)

This study investigated the functional morphology of the blubber that forms the caudal keels of the harbor porpoise (Phocoena phocoena). Blubber is a pliant biocomposite formed by adipocytes and structural fibers composed of collagen and elastic fibers. Caudal keels are dorsally and ventrally placed triangular wedges of blubber that define the hydrodynamic profile of the porpoise tailstock. Mechanical tests on carcasses demonstrate that when keels are bent, they strain nonuniformly along their lengths, with highest strains just caudal to the dorsal fin and lowest at the insertion of the flukes. Therefore, caudal keels undergo nonuniform longitudinal deformation while maintaining a stable, triangular cross-sectional shape. Polarizing and transmitted light microscopy techniques were used to investigate blubber's 3D fiber architecture along the length of the dorsal keel. The triangular cross-sectional shape of the keel appears to be maintained by structural fibers oriented to act as tensile stays. The construction of the blubber composite is regionally specific :structural fiber densities and diameters are higher in the relatively stiff caudal region of the keel than in the more deformable cranial keel region. The orientations of structural fibers also change along the length of the keel. Cranially, no fibers are oriented along the long axis, whereas a novel population of longitudinally oriented fibers reinforces the keel at the insertion of the flukes. Thus, differences in the distribution and orientation of structural fibers contribute to the regionally specific mechanical properties of the dorsal keel.     

Identifying a reliable blubber measurement site to assess body condition in a marine mammal with topographically variable blubber,the Pacific walrus

Pacific walruses may be unable to meet caloric requirements in the changing Arctic ecosystem, which could affect body condition and have population‐level consequences. Body condition has historically been monitored by measuring blubber thickness over the xiphoid process (sternum). This may be an unreliable condition index because blubber at other sites along the body may be preferentially targeted to balance energetic demands. Animals in aquaria provided an opportunity for controlled study of how blubber topography is altered by caloric intake. Morphology, body mass, blubber thickness (21 sites), and caloric intake of five mature, nonpregnant, nonlactating female walruses were measured monthly (12 month minimum). Body condition (mass × standard length^?1) was described by a model that included caloric intake and a seasonal effect, and scaled positively with estimates of total blubber mass. Blubber thicknesses (1.91–10.69 cm) varied topographically and were similar to values reported for free‐ranging female walruses. Body condition was most closely related to blubber thickness measured dorsomedially in the region of the anterior insertion of the pectoral flippers (shoulders); sternum blubber thickness was a relatively poor indicator of condition. This study demonstrates the importance of validating condition metrics before using them to monitor free‐ranging populations.     

Stratification and age-related differences in blubber fatty acids of the male harbour porpoise (Phocoena phocoena)

Fatty acid composition of blubber was determined at four body sites of 19 male harbour porpoises. A total of 65 fatty acids were quantified in each sample. The array of fatty acids contained in harbour porpoise blubber was similar to those found in other marine mammals. While chemical composition of total blubber was uniform over the body, with the exception of the caudal peduncle, vertical stratification was evident between the deep (inner) and superficial (outer) blubber layers. Fatty acids with chain lengths shorter than 18 carbons were present in significantly greater amounts in the outer blubber layer, while the longer-chain unsaturated fatty acids were more prevalent in the inner layer. This distribution suggests that the inner blubber layer is more active metabolically than the outer layer in terms of lipid deposition and mobilization. The degree of stratification between the two layers appears to increase with age, indicating a predictable turnover in the blubber layer of male porpoises. Harbour porpoise blubber contained high levels (2–27%) of isovaleric acid in the outer blubber layer, and these levels were positively correlated with age.Abbreviations Caud caudal dorsal body site - GC gas chromatograph - FA fatty acid(s) - IUPAC International Union of Pure and Applied Chemistry - PUFA polyunsaturated fatty acid(s) - II dor II dorsal body site - III dor III Dorsal body site - II Ven II ventral body site     

Blubber development in bottlenose dolphins (Tursiops truncatus)

Blubber, the lipid-rich hypodermis of cetaceans, functions in thermoregulation, buoyancy control, streamlining, metabolic energy storage, and locomotion. This study investigated the development of this specialized hypodermis in bottlenose dolphins (Tursiops truncatus) across an ontogenetic series, including fetuses, neonates, juveniles, subadults, and adults. Blubber samples were collected at the level of the mid-thorax, from robust specimens (n = 25) that stranded along the coasts of North Carolina and Virginia. Blubber was dissected from the carcass and its mass, and the depth and lipid content at the sample site, were measured. Samples were prepared using standard histological methods, viewed by light microscopy, and digital images of blubber captured. Images were analyzed through the depth of the blubber for morphological and structural features including adipocyte size, shape, and numbers, and extracellular, structural fiber densities. From fetus to adult, blubber mass and depth increased proportionally with body mass and length. Blubber lipid content increased dramatically with increasing fetal length. Adult and juvenile blubber had significantly higher blubber lipid content than fetuses, and this increase was reflected in mean adipocyte size, which increased significantly across all robust life history categories. In juvenile, subadult, and adult dolphins, this increase in cell size was not uniform across the depth of the blubber, with the largest increases observed in the middle and deep blubber regions. Through-depth counts of adipocytes were similar in all life history categories. These results suggest that blubber depth is increased during postnatal growth by increasing cell size rather than cell number. In emaciated adults (n = 2), lipid mobilization, as evidenced by a decrease in adipocyte size, was localized to the middle and deep blubber region. Thus, in terms of both lipid accumulation and depletion, the middle and deep blubber appear to be the most metabolically dynamic. The superficial blubber likely serves a structural role important in streamlining the animal. This study demonstrates that blubber is not a homogeneous tissue through its depth, and that it displays life history-dependent changes in its morphology and lipid content.     

Demonstration of the deposition and modification of dietary fatty acids in pinniped blubber using radiolabelled precursors

Radioisotopes are commonly used to study the in vivo metabolism and deposition of dietary fatty acids in adipose tissue. The application of this approach to pinnipeds is problematic because of their large mass and blubber fat content. We have developed a method where labelled lipids can be fed to seals at financially feasible levels, with the radioactivity in individual fatty acids isolated from blubber detected with standard laboratory equipment. A combination of techniques including argentation thin layer chromatography, high performance liquid chromatography with ultraviolet detection, and independent liquid scintillation counting were employed. Juvenile gray seals (Halichoerus grypus) were fed either 0.5 mCi (3)H-labelled triolein (18:1n-9, n=2) or palmitic acid (16:0, n=2). Blubber samples were taken 12 h later, and the radioactivity in individual fatty acids was determined. Radioactivity was detected in only 18:1 from the animals fed (3)H-labelled triolein, indicating direct deposition without modification. Both animals fed (3)H-labelled palmitic acid showed clear peaks of radioactivity in 16:0; however, there was also significant activity (23%-29%) found in the desaturation product 16:1. Our results demonstrate that this method is sufficiently sensitive to track the deposition of labelled dietary lipids as well as modification products of ingested fatty acids and will be important in the application of fatty acid signatures to study predator diets.     

Patterns of blubber fat deposition and evaluation of body condition in growing southern right whale calves (Eubalaena australis)

Marine mammals rely on blubber mainly for energy storage, buoyancy, and streamlining. Mysticetes are born with a relatively thin fat layer that grows rapidly during nursing. However, little information on blubber deposition patterns is available for baleen whale calves. We measured blubber thickness at nine body locations in 350 southern right whale (Eubalaena australis) newborn to 4–6-month-old calves that died on the Península Valdés (Argentina) calving ground from 2003 to 2019, to document changes in blubber thickness with growth. Additionally, we looked for differences in blubber thickness and lipid content of the outer/superficial blubber in calves that died in years with high (2003, 2005, 2007–2013) and low calf mortality (2004, 2006, 2014–2019) to test whether the former were suffering from gross nutritional stress. Blubber thickness increased at all body locations with calf length. Along the cranio-caudal axis, blubber increased in the dorsal and ventral planes, but decreased laterally towards the peduncle, possibly to improve streamlining. We found no difference in blubber thickness and lipid content between high and low mortality years, suggesting that individuals were not undernourished. This is the first study to describe progressive increases in calf blubber during growth and contributes knowledge to right whale health and ontogeny.     

Stratification and intra- and inter-specific differences in fatty acid composition of common dolphin (Delphinus sp.) blubber: implications for dietary analysis

Sixty-five fatty acids were quantified in the blubber of common dolphins (Delphinus delphis, D. capensis) incidentally caught off the coast of southern California. Dolphins were grouped by sex, reproductive status and species, and a blubber sample was collected at a mid-lateral site located caudal to the trailing edge of the dorsal fin. Samples were divided horizontally into inner, middle and outer layers and gradients in fatty acid content (mass percent) were observed across the depth of the blubber. Levels of monounsaturated fatty acids were greatest in the outer layer, whereas levels of saturated and polyunsaturated fatty acids were greatest in the inner layer. Degree of stratification was greatest in sexually mature dolphins. Blubber of sexually immature, but physically mature, male dolphins was also highly stratified, suggesting that this difference may be attributed to differences in diet. Classification and regression tree analysis resulted in the fewest misclassifications when dolphins were grouped by species, possibly indicating that these closely related animals forage on different prey species. Dietary-derived fatty acids were typically selected as splitting criteria in classification and regression tree analyses, suggesting that the observed differences in fatty acid composition between the various groups of dolphins may be attributed to differences in diet.     

Organochlorine residue concentrations and burdens in grey seal (Halichoerus grypus) blubber during the first year of life

Between 1988 and 1991 grey seal ( Halichoerus grypus ) pups at various developmental stages were sampled at Sable Is., NS, and blubber samples were analysed for lipid content and organochlorine (OC) residue concentrations. Blubber lipid content increased significantly between birth and 12 d, and then stayed relatively constant. Blubber OC residue concentrations were fairly constant during the first 12–16 d of life. From weaning (approx. 16 d) until four months, the pups are learning to feed but are relying on blubber fat reserves; thus, during this period blubber weight declined to minimum levels, and OC residue concentrations in blubber lipid increased significantly. Blubber lipid OC concentrations then declined slightly as the pups gained weight, until at the end of one year they were about twice those immediately post-weaning. Blubber lipid residue burdens calculated from these data showed that at weaning, about 98% of the seal's residues were accumulated from maternal milk. After weaning, there were no significant changes in the burdens of any residue until the end of the first year of the pup's life, and the organochlorine concentration changes reflected a fairly constant organochlorine burden around which lipid contents varied. These data suggest that the capacity of the seal to degrade the residue inherited from its mother is very limited. Furthermore, the absence of any significant accumulation of organochlorines during the second six months of the seal's life suggests that the juvenile seal must feed at a low trophic level which is not highly contaminated with organochlorines.     

Vertical fatty acid profiles in blubber of a freshwater ringed seal — Comparison to a marine relative

We investigated the vertical stratification pattern of fatty acids in the blubber of the freshwater Saimaa ringed seal (Phoca hispida saimensis; n = 35). Blubber was dissected vertically into 3 mm thick sequential subsamples, and the fatty acid composition was analyzed separately for each subsample. The combined vertical fatty acid profiles (expressed as numerical gradients) showed that the blubber of > 1 year old individuals is stratified into three distinguishable layers: superficial (~ 1.5 cm), middle and deep (~ 1 cm). Thickness of the middle layer varied according to the total blubber thickness. We suggest that the observed layering is related to the differences in the tissue temperatures and metabolic activity in the blubber column. The dissimilarity in the fatty acid composition (measured as Euclidean distance) between the different blubber layers and the 5 most important fish prey species available in Lake Saimaa was largest in the superficial blubber. In fact, the fatty acid composition of superficial blubber resembled more that of marine ringed seal (Phoca hispida hispida) blubber than any of the analyzed fish species. The composition closest to that of the prey was found in the deep blubber of the Saimaa ringed seal. The large vertical differences in the fatty acid composition of blubber lipids, which likely affect the vertical distribution of other endogenous or exogenous lipophilic substances as well, will set conditions for the sampling of blubber for biomonitoring and dietary studies. Thus the knowledge on the potential layers with different composition and the depths they span in different individuals (e.g. young versus old; with thin versus thick blubber) is crucial for improving the validity and reliability of monitoring methods utilizing the blubber tissue.     

Brown Adipose Tissue in Cetacean Blubber

Brown adipose tissue (BAT) plays an important role in thermoregulation in species living in cold environments, given heat can be generated from its chemical energy reserves. Here we investigate the existence of BAT in blubber in four species of delphinoid cetacean, the Pacific white-sided and bottlenose dolphins, Lagenorhynchus obliquidens and Tursiops truncates, and Dall’s and harbour porpoises, Phocoenoides dalli and Phocoena phocoena. Histology revealed adipocytes with small unilocular fat droplets and a large eosinophilic cytoplasm intermingled with connective tissue in the innermost layers of blubber. Chemistry revealed a brown adipocyte-specific mitochondrial protein, uncoupling protein 1 (UCP1), within these same adipocytes, but not those distributed elsewhere throughout the blubber. Western blot analysis of extracts from the inner blubber layer confirmed that the immunohistochemical positive reaction was specific to UCP1 and that this adipose tissue was BAT. To better understand the distribution of BAT throughout the entire cetacean body, cadavers were subjected to computed tomography (CT) scanning. Resulting imagery, coupled with histological corroboration of fine tissue structure, revealed adipocytes intermingled with connective tissue in the lowest layer of blubber were distributed within a thin, highly dense layer that extended the length of the body, with the exception of the rostrum, fin and fluke regions. As such, we describe BAT effectively enveloping the cetacean body. Our results suggest that delphinoid blubber could serve a role additional to those frequently attributed to it: simple insulation blanket, energy storage, hydrodynamic streamlining or contributor to positive buoyancy. We believe delphinoid BAT might also function like an electric blanket, enabling animals to frequent waters cooler than blubber as an insulator alone might otherwise allow an animal to withstand, or allow animals to maintain body temperature in cool waters during sustained periods of physical inactivity.     

Temporal variation in the vertical stratification of blubber fatty acids alters diet predictions for lactating Weddell seals

Fatty acid signature analysis of blubber has been used to study the foraging ecology of some marine mammals. However, species-specific information on fatty acid (FA) deposition, distribution and mobilization is required to develop further the application of FA as trophic markers within the marine environment. Blubber samples were collected from adult female Weddell seals post-parturition and end of lactation, and were divided into inner and outer half sections. We determined the degree to which there was vertical stratification in FA composition, and how this changed over the lactation period. Inner and outer layers of post-parturition blubber cores separated into two distinct groups. Sixty-two per cent of the dissimilarity between the two layers was accounted for by a higher abundance of monounsaturated fatty acids (18:1ω9c and 16:1ω7c) in the outer blubber layer, and more saturated fatty acids (16:0 and 14:0) in the inner layer. By end of lactation, the FA composition of the inner layer was different to post-parturition samples, and 20:5ω3 had the highest fractional mobilization of all FA. In contrast, the proportion of FA in the outer layer did not change, and there was more variability in the fractional mobilization of FA indicating mobilization was not uniform across the blubber layer. Dietary predictions changed considerably when highly mobilized FA were removed from analyses, and predictions were more consistent with previous dietary studies. The lack of uniformity in FA mobilization adds problems to the future use of FASA in dietary predictions, highlighting the need for more detailed information on FA mobilization.     

Microvascular patterns in the blubber of shallow and deep diving odontocetes

Blubber, a specialized form of subdermal adipose tissue, surrounds marine mammal bodies. Typically, adipose tissue is perfused by capillaries but information on blubber vascularization is lacking. This study's goals were to: 1) describe and compare the microvasculature (capillaries, microarterioles, and microvenules) of blubber across odontocete species; 2) compare microvasculature of blubber to adipose tissue; and 3) examine relationships between blubber's lipid composition and its microvasculature. Percent microvascularity, distribution, branching pattern, and diameter of microvessels were determined from images of histochemically stained blubber sections from shallow‐diving bottlenose dolphins (Tursiops truncatus), deeper‐diving pygmy sperm whales (Kogia breviceps), deep‐diving beaked whales (Mesoplodon densirostris; Ziphius cavirostris), and the subdermal adipose tissue of domestic pigs (Sus scrofa). Tursiops blubber showed significant stratification in percent microvascularity among the superficial, middle, and deep layers and had a significantly higher percent microvascularity than all other animals analyzed, in which the microvasculature was more uniformly distributed. The percent microvasculature of Kogia blubber was lower than that of Tursiops but higher than that of beaked whales and the subdermal adipose tissue of domestic pigs. Tursiops had the most microvascular branching. Microvessel diameter was relatively uniform in all species. There were no clear patterns associating microvascular and lipid characteristics. The microvascular characteristics of the superficial layer of blubber resembled the adipose tissue of terrestrial mammals, suggesting some conservation of microvascular patterns in mammalian adipose tissue. The middle and deep layers of blubber, particularly in Tursiops, showed the greatest departure from typical mammalian microvascular arrangement. Factors such as metabolics or thermoregulation may be influencing the microvasculature in these layers. © J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Changes in the sensitivity to glucagon of lipolysis in adipocytes from pregnant and lactating rats.

1. Rates of lipolysis were measured at different concentrations of glucagon in adipocytes prepared from parametrial adipose tissue of fed or starved rats in different reproductive states. All experiments were performed in the presence of a high concentration of adenosine deaminase (1 unit/ml). 2. Maximal rates of lipolysis (elicited by 25 nM-glucagon in each instance) were higher in adipocytes from peak-lactating rats than those from pregnant animals in both the fed and starved states. 3. Of adipocytes from fed animals, those from peak-lactating rats were the most sensitive to glucagon, whereas those from late-pregnant and early-lactating rats were 1-2 orders of magnitude less sensitive. 4. Adipocytes from 24 h-starved rats showed a much smaller stimulation of lipolysis by glucagon, making the assessment of sensitivity difficult. Therefore, rates of lipolysis were also measured in the presence of a maximally anti-lipolytic dose of insulin. The presence of insulin did not alter the relative sensitivities to glucagon of adipocytes from fed animals in different reproductive states, although all dose-response curves were shifted to the right. When lipolysis in adipocytes from starved animals was measured in the presence of insulin, it became evident that starvation for 24 h markedly increased the sensitivity of adipocytes from late-pregnant rats to glucagon, but did not affect that of cells from animals in the other reproductive states. 5. It is concluded that the large changes in sensitivity to glucagon that occurred during the reproductive cycle may enable the modulation of adipose-tissue lipolysis in vivo to satisfy the different metabolic requirements of the animal in the transition from pregnancy to peak lactation.     

Stratification, composition, and function of marine mammal blubber: the ecology of fatty acids in marine mammals

Abstract This study of vertical fatty acid profiles, based on analysis of 58 fatty acids sampled at 3-mm intervals throughout the blubber column of a model marine mammal, the ringed seal (Pusa hispida), revealed three chemically distinct layers. The average depths of the outer and inner layers were quite consistent (approximately 1.5 and approximately 1 cm, respectively). Consequently, the middle layer varied greatly in thickness, from being virtually absent in the thinnest animals to 2.5 cm thick in the fattest. The relative consistencies of the thickness and composition of the layers as well as the nature of the fatty acids making up each layer support the generally assumed function of the various layers: (1) the outer layer is primarily structural and thermoregulatory, (2) the inner layer is metabolically active with a fatty acid composition that is strongly affected by recent/ongoing lipid mobilization/deposition, and (3) the middle layer is a storage site that contracts and expands with food availability/consumption. The remarkable dynamics of the middle layer along with the discrete pattern of stratification found in the vertical fatty acid profiles have important implications for methodological sampling design for studies of foraging ecology and toxicology based on analyses of blubber of marine mammals.     

Temporal variability in organochlorine contamination in blood and blubber of captive Steller sea lions (Eumetopias jubatus)

Three adult captive Steller sea lions (SSL; two females, one male) housed in Alaska were longitudinally sampled for organochlorine contaminant (OC) analysis in both blubber (n= 19) and blood (n= 69) over a 2 yr period (March 2001 to March 2003). Blood OC concentrations were similar between individuals, and exhibited significant increases in summer months (July through September) relative to winter (January through March). Additionally, paired blood and blubber sample (n= 18) OC were significantly related for all animals. The relationship of blubber OC concentrations to lipid content was significant in all animals. Although limited to a small number of animals, our study results indicate that in SSLs, blood OC were both consistent among all animals and likely changed in association with physiologically driven metabolism of blubber.     

Transfer of fatty acids from female seal blubber via milk to pup blubber

Fatty acids were determined by gas chromatography followed by principal component analysis (PCA) and soft independent modelling of class analogy (SIMCA) in the blubber of 18 female grey seals, Halichoerus grypus, in their milk and in the blubber of their 1-week-old nursing pups. Large individual differences were observed in both blubber and milk content of fatty acids. The fatty acid composition of the milk was systematically different from the composition in maternal blubber, with higher relative amounts of the saturated acids, the monounsaturated with 20 carbon atoms and the n3 polyunsaturated, except 18:3n3. The composition of the fatty acids in the blubber of the pups was different from that of the milk. The same fatty acids that were enriched in the milk were depleted in the blubber of the pups. Therefore the fatty acid composition in the blubber of the pups was similar to that in the adults, although not identical. The results from this investigation imply that the composition of the fatty acids in the blubber of female seals and in the blubber of their pups cannot be determined directly by analysis of fatty acid composition of milk. Accepted: 16 February 2000     

Body regional distribution and stratification of fatty acids in the blubber of New Zealand sea lions: implications for diet predictions

Fatty acids (FAs) from blubber are often analysed to assess the diet of marine mammals. However, distribution of blubber FAs is not necessarily uniform along the body. It is therefore important to understand the deposition of dietary fat to be able to estimate the diet. We analysed the FA compositions of the thoracic ventral (T region) blubber of 28 New Zealand (NZ) sea lions Phocarctos hookeri by-caught by the southern arrow squid Nototodarus sloani fishery. Each blubber sample was divided into an inner and an outer layer. For 16 of these 28 animals, the pelvic dorsal (P) region was also sampled. The influence of body region and layer was statistically tested on the distribution of blubber FAs. We found minimal differences between the P and T regions (3 out of 29 FAs). The outer blubber layer was more concentrated in short-chain monounsaturated FAs, and less concentrated in saturated FAs, but the degree of stratification was small. Diet predictions from quantitative FA signature analysis (QFASA) applied on different body regions were similar. When applied to different blubber layers, QFASA gave some variation in the contribution of rattails (~25 % in outer blubber vs. ~12 % in inner blubber). Nonetheless, diet predicted from both layers was dominated by similar prey species: octopus, hoki and rattails. Hoki and rattails shared a similar ecological niche. Therefore, feeding ecology of NZ sea lions inferred from the inner or the outer blubber would lead to the same conclusions. In the case of NZ sea lions, the outer layer of blubber, if the only sample accessible, could be a useful tissue for diet inference from FAs.