Endocrine changes in harbor seal (Phoca vitulina) pups undergoing rehabilitation.

Rehabilitating pinniped pups are often admitted to care centers as neonates and generally lack maternal investment and are in poor body condition. Upon admittance to a rehabilitation facility, pups are typically fed a milk replacement formula via gavage, which is switched to frozen fish upon weaning. While rehabilitation has been successful in terms of recovery and release, preweaning growth rates in captivity are consistently lower than in the wild. Indicators of stress (cortisol and total thyroxine; TT4), and standard morphometrics, of harbor seal pups in rehabilitation (n = 20) were determined for both preweaned and weaned pups. Hormone concentrations and standard morphometrics from pups in care were compared with free-ranging harbor seal pups (n = 59). Pups in rehabilitation gained mass on both milk and fish diets. Preweaned pups had greater mean serum cortisol and similar TT4 concentrations than weaned pups. Free-ranging harbor seal pups were heavier and longer than preweaned and weaned pups in rehabilitation. The free-ranging pups had the lowest cortisol and highest TT4 concentrations of any of the pups. These results suggest that weaned pups that have undergone rehabilitation are not physiologically equivalent to free-ranging weaned pups. Additional research is needed regarding physiological changes in endocrine values during early development under captive care conditions. This information should be useful to marine mammal rehabilitation centers in their development of care protocols and release criteria for rehabilitating harbor seal pups.

Life under water: physiological adaptations to diving and living at sea.

This review covers the field of diving physiology by following a chronological approach and focusing heavily on marine mammals. Because the study of modern diving physiology can be traced almost entirely to the work of Laurence Irving in the 1930s, this particular field of physiology is different than most in that it did not derive from multiple laboratories working at many locations or on different aspects of a similar problem. Because most of the physiology principles still used today were first formulated by Irving, it is important to the study of this field that the sequence of thought is examined as a progression of theory. The review covers the field in roughly decadal blocks and traces ideas as they were first suggested, tested, modified and in some cases, abandoned. Because diving physiology has also been extremely dependent on new technologies used in the development of diving recorders, a chronological approach fits well with advances in electronics and mechanical innovation. There are many species that dive underwater as part of their natural behavior, but it is mainly the marine mammals (seals, sea lions, and whales) that demonstrate both long duration and dives to great depth. There have been many studies on other diving species including birds, snakes, small aquatic mammals, and humans. This work examines these other diving species as appropriate and a listing of reviews and relevant literature on these groups is included at the end.

Blood rheology in marine mammals.

The field of blood oxygen transport and delivery to tissues has been studied by comparative physiologists for many decades. Within this general area, the particular differences in oxygen delivery between marine and terrestrial mammals has focused mainly on oxygen supply differences and delivery to the tissues under low blood flow diving conditions. Yet, the study of the inherent flow properties of the blood itself (hemorheology) is rarely discussed when addressing diving. However, hemorheology is important to the study of marine mammals because of the critical nature of the oxygen stores that are carried in the blood during diving periods. This review focuses on the essential elements of hemorheology, how they are defined and on fundamental rheological applications to marine mammals. While the comparative rationale used throughout the review is much broader than the particular problems associated with diving, the basic concepts focus on how changes in the flow properties of whole blood would be critical to oxygen delivery during diving. This review introduces the reader to most of the major rheological concepts that are relevant to the unique and unusual aspects of the diving physiology of marine mammals.

Metabolic adjustments to varying protein intake in harbor seals (Phoca vitulina): evidence from serum free amino acids.

Effects of varying dietary protein intake on serum free amino acid (FAA) concentrations were studied in harbor seals (Phoca vitulina) fed two different prey fish diets: either exclusively low-fat, high-protein walleye pollock (Theragra chalcogramma) or high-fat, relatively high-energy-density Pacific herring (Clupea pallasi). Significant differences in FAA concentrations and patterns were observed between the two diets. All essential amino acids (EAA), except methionine and phenylalanine, and two nonessential amino acids (NEAA), glycine and tyrosine, decreased when the diet was switched from herring to pollock and increased on switching back to herring. Both total EAA concentrations and EAA : NEAA ratios decreased with the elevated protein intake typical of a low-fat pollock diet, indicating an inverse correlation between EAA concentrations and dietary protein intake levels. We propose that differing dietary protein intake, caused by differences in macronutrient composition of the two prey fish species, induced a change in protein metabolism that was reflected in blood-circulating amino acids. These findings suggest that surveys of amino acid profiles may be useful to partially determine the protein metabolic status of harbor seals.

Blood rheology of Weddell seals and bowhead whales.

Red blood cell (RBC) aggregation and blood viscosity are important determinants of in vivo blood flow dynamics and, in marine mammals, these parameters may impact diving physiology by altering blood oxygen delivery during the diving response. Weddell seals are superb divers and exhibit age-related patterns in blood oxygen chemistry and diving ability. By contrast, bowhead whales are not long duration divers, and little is known of their blood properties relative to diving. The present study was designed to compare rheological characteristics of blood from Weddell seal pups, Weddell seal adults, and from adult bowhead whales: blood viscosity and RBC aggregation in plasma and in polymer solutions (i.e., RBC "aggregability") were measured. Salient findings included: (1) significant 4- to 8-fold greater aggregation in blood from adult seals compared with pups and human subjects; (2) 2-to 8-fold greater aggregation in bowhead whale blood compared with human blood; (3) compared to human red cells, enhanced RBC aggregability of RBC from adult seals and whales as determined by their greater aggregation in polymer solutions; (4) increasing RBC aggregation and aggregability of seal pup blood over a seven day period following birth; (5) significantly greater blood viscosity for adult seals compared with pups at both native and standardized hematocrits. These results indicate that, for both species, hemorheological parameters differ markedly from those of humans, and suggest progressive changes with seal age; the physiological implications of these differences have yet to be fully defined.

New insights into the physiology of natural foraging.

The purpose of this symposium was to examine how foraging physiology is studied in the field across a diversity of species and habitats. While field studies are constrained by the relatively poor ability to control the experiment, the natural variability in both the environment and animal behavior provides insights into adaptation to change that are usually not tested in the laboratory. Talks in this session examined how foraging energy (both costs and gains) is partitioned over time. "Time," in this case, ranged from evolutionary time (how different animals are designed to most efficiently forage), to long, lifetime periods (development of foraging ability and growth), to short-duration feeding bouts, and ultimately to the minutes to hours following ingestion (metabolic and biochemical changes). From this diversity, two core themes emerged: that foraging strategies and behaviors are limited by physiology and biochemical processes and that time plays a central role in the organization of foraging behaviors and the physiological processes that underlie those behaviors.

Dietary macronutrients influence 13C and 15N signatures of pinnipeds: captive feeding studies with harbor seals (Phoca vitulina).

Metabolic effects of dietary macronutrients on diet-tissue isotopic discrimination factors were investigated in harbor seals. Three seals were fed either high fat/low protein herring (H), or low fat/high protein pollock (P), and switched to the alternative every 4 months. This allowed each seal to be subjected to two dietary treatments in each of three metabolically defined seasons (breeding from May to September, molting from September to January, and late winter/early spring period from January to May) over a 2 year cycle, and function as its internal control regardless of physiological changes over season. One seal was fed a constant equal mix of H and P over the entire trial. Up to 1 per thousand differences in serum delta15N values of one seal fed alternatively on H and P were observed. Progressively more enriched serum delta15N values as diet switching from H to P might link to changes in seal digestive physiology and protein metabolism in response to very high protein intake on P diet. These findings demonstrate that dietary macronutrients of prey species and protein intake level of consumers also play important roles in shaping isotopic patterns of a consumer's tissues, and thus influence accurate data interpretation of stable isotope techniques in ecological applications.

Defining the limits of diving biochemistry in marine mammals.

The field of marine mammal diving biochemistry was essentially untouched when Peter Hochachka turned his attention to it in the mid-1970s. Over the next 30 years, his work followed three main themes in this area: first, most biologists at that time supported the theory that diving mammals utilized enhanced metabolic pathways for hypoxic energy production (glycolysis to lactate) and reduced their metabolic rate while diving. Peter began his work on potential hypoxic adaptations in marine mammals by working out the details of how these pathways would be regulated. By the 1980s, he started to ask how diving mammals balanced the increased demands of exercise with the apparently conflicting demands to reduce aerobic metabolism while exercising underwater. By the 1990s, his work involved complex models of the interplay between the neural, hormonal, behavioral and evolutionary components of diving biochemistry and animal exercise. From a comparative approach, he excelled at bringing themes of hypoxic adaptation from many different types of animals to the field of diving mammal biochemistry. This review traces the history of Peter Hochachka's work on diving biochemistry from the perspective of those of us who spent time with him both inside the laboratory and outside in the field from Antarctica to Iceland.

Spatial aspects of organochlorine contamination in northern fur seal tissues.

Northern fur seals from the Pribilof Islands, Alaska (St. George Is. and St. Paul Is.) were examined for organochlorine contamination (OC) and whether the organochlorine levels differed between the populations and were at levels that may adversely affect their health. Fur seal blubber and milk samples were obtained from pups, sub-adult males, and adult females on both Pribilof Islands. These samples were analyzed for organochlorine contaminants including dioxin-like PCBs and other selected PCBs and pesticides by high performance liquid chromatography/photodiode array. Results showed that there are clear differences between the two islands in the patterns of fur seal OC distribution. Generally, these differences are confined to the PCBs with only minimal differences in the DDTs. There are also clear biological differences in the levels shown between milk, pup blubber, and sub-adult male blubber. When considering blubber, St. George Is. fur seals show higher OC levels than St. Paul Is., for both pups and sub-adults. On the other hand, milk samples from St. Paul Is. showed higher PCB levels than St. George Is. For the milk, the overall OC levels may impact the immune function of the pups, but are probably of only minimal impact to humans. However, for blubber, the overall toxic equivalency shows levels exceeding those levels recommended for human consumption at St. George Is. and approaching those levels at St. Paul Is. The concentration curves suggest that the movement of OC in and out of milk follows a complex set of reactions dependent on how the OC compounds on a congener level are associated with lipid. In fact, there is some evidence that they may not follow the lipid as closely as we had thought and that lipid levels can vary without impacting the total OC level in the milk.

Biochemical aspects of pressure tolerance in marine mammals.

Some marine mammals can dive to depths approaching 2000 m. At these hydrostatic pressures (200 atm), some fish species show alterations in enzyme structure and function that make them pressure-tolerant. Do marine mammals also possess biochemical adaptations to withstand such pressures? In theory, biochemical alterations might occur at the control of enzymatic pathways, by impacting cell membrane fluidity changes or at a higher level, such as cellular metabolism. Studies of marine mammal tissues show evidence of all of these changes, but the results are not consistent across species or diving depth. This review discusses whether the elevated body temperature of marine mammals imparts pressure tolerance at the biochemical level, whether there are cell membrane structural differences in marine mammals and whether whole, living cells from marine mammals alter their metabolism when pressure stressed. We conclude that temperature alone is probably not protective against pressure and that cell membrane composition data are not conclusive. Whole cell studies suggest that marine mammals either respond positively to pressure or are not impacted by pressure. However, the range of tissue types and enzyme systems that have been studied is extremely limited and needs to be expanded before more general conclusions about how these mammals tolerate elevated pressures on a biochemical level can be drawn.