Harbor Seal Physiological Ecology

My work on harbor seals is focused on three main fronts:

  1. Understanding the rate of physiological development in juveniles 
  2. Determining how condition influences growth and reproduction is related to pregnancy and parturition rates
  4. Determining how harbor seals utilize different habitats for foraging and haulout

The development of diving physiology in harbor seal pups

Harbor seals (Phoca vitulina richardsi) are one of the most precocial of phocid seals. Unlike most pinniped young, harbor seal pups can swim and dive at birth, and in many areas do so regularly throughout the lactation period. As the rate at which pinniped diving physiology develops has been shown to be closely linked with the onset of active diving and independent foraging, it is expected that harbor seal pups are also relatively mature, physiologically, at an earlier age than other phocid pups. Early development of the physiological mechanisms associated with diving would be beneficial for many reasons. As swimming and diving is more energetically expensive than resting on the beach, young seals that could reduce in-water metabolic rates would have a distinct advantage over those that could not. Lower at-sea costs would likely result in higher growth rates, and better condition at weaning.

The development of efficient diving behavior is dependent on the ability to control swimming and diving metabolic rates and the maturation of total body oxygen stores. Work on Weddell and northern elephant seal pups has shown that both the control of metabolic processes such as heart rate during breath-hold and diving change with age throughout the dependent (lactation) period. Heart rate and other metabolic processes approach the pattern seen for adults by the time pups must forage on their own. Simultaneously, oxygen stores develop. Throughout development, hematocrit and hemoglobin increase, as does the myoglobin content of muscle. As harbor seal pups are both more active in the water, and weaned at a younger age than most species currently studied, it is likely that both the physiological processes related to diving, and the diving behavior itself, matures at a more rapid rate than in other species. In addition, it may be that harbor seal pups are born at a more ‘advanced’ level, and that the magnitude of the changes they undergo during the developmental processes are reduced. By revealing whether these hypotheses are true, this research has the potential to reveal important information on the rate at which physiological processes can mature, and the constraints faced by young marine mammals.

This work is quantifying changes in the physiological processes related to diving in young harbor seal pups by collecting information on changes with age in blood chemistry (hemoglobin, hematocrit, complete blood chemistry panels), muscle myoglobin stores, body composition (3HHO), metabolism (VO2), and heart rate patterns (EKG). Cross-sectional samples were gathered from pre- and post-weaned pups in Alaska and California, while Chery Creelman is gathering longitudinal data from pups in the Gulf of the St. Lawrence River in Canada. Cheryl's research is performed in conjunction with Dr. Jason Schreer, University of Waterloo, and Mike Hammill, Department of Fisheries and Oceans. Cheryl is also working closely with Danielle Greaves, a graduate student of Dr. Schreer, who is studying the development of diving behavior in juvenile harbor seals.

            Cheryl Creelman                                                         Danielle Greaves

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Baseline Health and Condition

Harbor seals have been shown to be vulnerable to oiling at several different levels. For example, approximately 36% of the harbor seal population within oiled areas of Prince William Sound (PWS) died as a direct result of the Exxon Valdez oil spill (Frost et al. 1994, 1995, 1997). However, while regional, seasonal, and age-related variation was observed in the size and condition of harbor seals within PWS in the years after the spill, due to methodological and sampling differences there is no pre-spill data with which post-spill samples can be directly compared (Frost et al. 1994, 1996, Fadely 1997). Similarly, while harbor seals within the oiled areas show higher levels of haptoglobin than those in regions where the population is stable, the absence of pre-spill data has made it impossible to determine if this is a regional difference, an effect of continued oil exposure, or a result of some other stressor (Zenteno-Savin et al. 1997). This research proposes to determine baseline values for the health and condition of harbor seals within the Monterey Bay area, so that the status of oiled, rehabilitated, or exposed harbor seals in California can be properly assessed should an oil spill occur.

The first means of assessing the health and condition of a wild animal is to measure animal size and mass. However, while changes in body condition may reflect normal differences due to age and season, changes have also been linked with alterations in foraging success or ability. As a result, it is necessary to establish year-round population normals for both size and condition before it is possible to determine whether animals exposed to oil or other environmental contaminants have been energetically compromised (Hanks 1981, Franzmann 1985, Lukaski 1987, Harder and Kirkpatrick 1994, Fadely 1997). While determinations of body condition typically utilize size (mass or length) relative to age, or mass relative to a size or shape assessment, in pinnipeds these indirect compositional indices have generally proven to be poor predictors of actual body composition, while those that utilize isotopic dilution techniques have been much more successful (Costa 1987, Ryg et al. 1990, Gales and Renouf 1994, Fadely 1997). Because reductions in body condition following a spill may indicate ongoing, long-term effects of oil exposure, we propose to determine baseline condition values for different age classes within the wild population using both morphometric and isotopic methods.

Another useful tool in assessing individual health and status is a simple blood test. Blood chemistries and hematologies provide diagnostic data for determination of acute and chronic conditions, and by examining groups of analytes the organ or metabolic systems being affected can be detected (Rebar and Boon 1983, Duncan et al. 1994, Roletto 1993). Hematological values which may indicate chronic oil effects or environmental contamination include increased activities (levels) of alanine (ALT) and aspartate aminotransferase (AST), and lactate dehydrogenase (LDH), enzymes associated with the liver (St. Aubin 1990, Hartung 1995, Rebar et al. 1995). Changes to the immune system may also result from chronic exposure to environmental contaminants, manifested as neutrophilia and increased white blood cell counts (de Swart et al. 1995, Schumacher et al. 1995). Changes in nutritional status, energy balance, or even diet composition can also be reflected in blood chemistries, providing an avenue to test degrees of nutritional limitation (Castellini and Rea 1992, Rea 1995, Knick et al. 1993, Thompson et al. 1997). Because blood chemistry and hematology values have been shown to be indicative of health status, disease, nutritional status, and even environmental conditions, it should therefore be possible to assess whether individual seals have been compromised as a result of non lethal oil exposure using this technique (Geraci et al. 1979, Medway 1980, Franzmann 1985, Payne and Payne 1987, Kerr 1989, Castellini et al. 1993, Roletto 1993, Harder and Kirkpatrick 1994, Schumacher et al. 1995, Fadely 1997). However, the success of these interpretations depends on access to established reference or ‘normal’ ranges for all blood parameters of interest. This research proposes to determine normal values for all standard metabolites, as well as two metabolites known to change in response to oiling or increased physiological stress: haptoglobin (Hp) and cytochrome P450 1A (CYP 1A).

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Determining whether female condition is related to pregnancy and parturition rates

This study is designed to characterize the health, condition, and reproductive status of Pacific harbor seal (Phoca vitulina) within South-central Alaska, in the hopes of discovering why some populations have continued to decline following the Exxon Valdez Oil Spill. Previous research into the condition of harbor seals within this region has demonstrated that most individuals are healthy, and has suggested that slow recovery rates may be linked to increased mortality due to predation, rather than reduced food availability. Unfortunately, predation is notoriously difficult to observe in the wild. However if predation, rather than food availability, is the main cause of the ongoing decline, two key life-history parameters should differ in comparison to historical data: age at first reproduction should have decreased, and pregnancy rates increased. Because examining these parameters has the potential to shed light on the causes of the ongoing population decline, the specific objectives of the proposed research are:

  1. To determine the pregnancy rate among wild seals captured at different times during the reproductive cycle by measuring estrogen and progesterone values, and to verify these clinical measures by ultrasonically imaging the uterus. This will be the first time that pregnancy rates have been determined for live Alaskan harbor seals, and the first time that the indirect method of determining pregnancy by hormonal levels has ever been validated with direct visual images. Should these techniques prove successful, there are multiple applications for wildlife monitoring and conservation.  Both techniques are necessary because while imaging ultrasound offers the potential to detect pregnancy at a much earlier stage of gestation than can be done with hormone assays alone, it is not always possible to use the ultrasound unit (such as in remote sites where there is no power, or when no trained personnel are available). In addition, verification of the hormonal method will allow blood samples archived over the past decade to be analyzed. Analysis of historical data will allow us to detect long-term trends in pregnancy rates, and compare data across multiple regions.

  2. If we are to understand why pregnancy rates have changed over time, then we must also know how the health, age, and condition of reproductive females has changed over the same period. Therefore, the second objective of this research is to correlate measurements of reproductive status with those of animal age, mass, body composition, and health. This work will reveal whether females are suffering from poor health or condition, reproducing at an older age (as might be expected if the population was experiencing food-stress) or reproducing at a younger age (as might be expected if populations were at levels below the environmental carrying capacity). This aspect of the research is designed to explain the observed reproductive pattern.

  3. Finally, information obtained as part of this research will be directly conveyed to the local management agencies (Alaska Department of Fish and Game and the National Marine Mammal Laboratory, NOAA), so that they can appropriately direct effort for the recovery of declining populations of harbor seals.

This project is being carried out in collaboration with Dr. Shannon Atkinson at the Alaska SeaLife Center, and was initiated with the financial support of the Abercrombie and Kent Global Foundation "For a Better World". 

Historical samples collection (1993-1997) was supported by funding from the Exxon Valdez Oil Spill Trustee Council to Kathy Frost, Alaska Department of Fish and Game, and Dr. Michael Castellini, University of Alaska Fairbanks. 

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Last modified 10/27/2009