Publications (20)28.23 Total impact
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Article: Organochloride pesticides in California sea lions revisited: Correction
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ABSTRACT: There has been an error in the publication of this paper [1]; the title should read: 'Organochlorine pollutants in California sea lions revisited'.BMC Ecology 04/2012; 3(1):1-1. -
Article: ESTIMATING POPULATION SIZE IN ASYNCHRONOUS AGGREGATIONS: A BAYESIAN APPROACH AND TEST WITH ELEPHANT SEAL CENSUSES
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ABSTRACT: Many organisms reproduce in temporary aggregations where estimates of colony size can be made by direct counts. When individuals are not synchronous, however, early breeders depart before the last arrive, so counts underestimate the total breeding population. We present a model describing a colony's census as a function of arrival, breeding tenure, and the correlation between them, and we use it to illustrate how variance in arrival and tenure affect the census. Counts of breeding female northern elephant seals (Mirounga angustirostris) from 1975 to 2007 were used to test the model. Four of the model's parameters—population size, mean and variance of arrival date, and the correlation between arrival date and breeding tenure—could be estimated from census data using a Bayesian approach; prior estimates of two other parameters—mean tenure and its variance—had to be used to avoid overparameterization. The model's predictions fit observed censuses well and produced reliable estimates of population size and arrival behavior, showing that the maximum census was 8%–16% below the total number of breeding females. This method could be used for estimating abundance in any asynchronous aggregation, given independent information on one of the defining distributions: arrival, tenure, or departure.Marine Mammal Science 06/2007; 23(4):834 - 855. · 1.61 Impact Factor -
Article: Mobilization of PCBs from blubber to blood in northern elephant seals (Mirounga angustirostris) during the post-weaning fast.
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ABSTRACT: Northern elephant seals (Mirounga angustirostris) are characterized by extended fasting during which they rely entirely on their own body reserves. During fasts, lipids are mobilized from blubber to match the energy requirements of the animal. This transfer frees toxic fat-soluble pollutants into the blood circulation, which may exert adverse health effects, especially in young and developing animals. We investigated the dynamics of mobilization of polychlorinated biphenyls (PCBs) from the blubber of northern elephant seal pups during the post-weaning fast. Longitudinal samples of blubber and serum were collected from free-ranging animals throughout the fast at Año Nuevo, California. Blubber biopsies were separated into inner and outer layers. The PCB profiles of blubber and serum consisted mainly of penta- (PCB-101, -110, -118), hexa- (PCB-138, -153) and hepta- (PCB-180, -183, -187) chlorobiphenyls, which accounted for almost 90% of the total PCB burden. Total PCB concentrations in inner blubber increased significantly between early and late fasting (563.6+/-162.0 microg/kg lipids at early versus 911.6+/-513.1 microg/kg lipids at late fasting) whereas they remained fairly constant in outer blubber (572.6+/-134.8 microg/kg lipids at early versus 659.2+/-158.8 microg/kg lipids at late fasting). A corresponding rise of PCB concentrations was observed in serum during the second half of the fast (3.8+/-1.1 microg/l serum at early versus 7.2+/-0.9 microg/l at late fasting). The longitudinal changes in circulating total PCBs could not be explained by the changes in serum lipid fractions (cholesterol, phospholipids, triacylglycerols and free fatty acids). The increases in total PCB concentrations in inner blubber and serum were more pronounced in leaner animals, which suggests that they might be more at risk to potential toxic effects.Aquatic Toxicology 12/2006; 80(2):149-57. · 3.76 Impact Factor -
Article: Mating system and reproductive success in eastern Pacific harbour seals.
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ABSTRACT: Harbour seals sometimes breed along inland travel corridors where females become clustered in space and time and males establish underwater acoustic display territories similar to terrestrial arenas known as resource-based leks. Under these conditions, we predicted that higher levels of polygyny would be observed than has been previously reported for this species mating in open coast environments without travel corridors. Reproductive success (RS) of 70 males was measured using 20 microsatellite DNA loci and likelihood-based paternity analysis of 136 offspring collected over 3 years. Most males were assigned either zero or one paternity with 80% confidence. The greatest number of pups assigned to one male in a season was two. Variance in RS was higher for males than females (which are biologically limited to one offspring per year) indicating low to mild polygyny. In addition, distributions of relatedness values among pups within year classes did not differ significantly from a simulated distribution with R = 0, indicating that half-siblings were uncommon. Overall, polygyny levels were low relative to terrestrial pinniped mating systems and similar to observations from a harbour seal population along an open coast. Due to large confidence intervals associated with our results, we cannot rule out the hypothesis that a travel corridor might increase the degree of polygyny skew relative to that observed in open coast environments. Habitat appeared to influence male strategies as the most successful males in open coast environments patrolled offshore, while the most successful male in this study defended a territory along the travel corridor.Molecular Ecology 10/2006; 15(10):3023-34. · 5.52 Impact Factor -
Article: Polychlorinated biphenyls, dioxins, and furans in weaned, free-ranging northern elephant seal pups from central California, USA.
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ABSTRACT: The aim of this study was to measure persistent organic pollutants in northern elephant seals ([NES], Mirounga angustirotris). We obtained blubber biopsy samples from six healthy, newly weaned NES pups from Año Nuevo, California (USA). Contaminant levels were lower than those of other pinnipeds studied on the west coast of North America. Blubber concentrations of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans averaged 700 +/- 130 microg/kg, 32 +/- 23 ng/kg, and 17 +/- 5 ng/kg (lipid wt), respectively. These contaminants originate from transplacental transfer and from maternal milk, which, in turn, reflect contaminants acquired by the mother from prey during long-distance foraging trips in the northeastern Pacific Ocean. The PCB profile in the blubber of NES pups mainly was composed of penta-, hexa-, and hepta-chlorobiphenyls, possibly reflecting the deep-sea nature of the mother's diet. Our results suggest that NES pups, in contrast to pups of other pinnipeds in the eastern Pacific Ocean, are exposed to low levels of persistent organic pollutants, reflecting an open ocean signal.Environmental Toxicology and Chemistry 04/2005; 24(3):629-33. · 2.81 Impact Factor -
Article: PCBs and DDT in the serum of juvenile California sea lions: associations with vitamins A and E and thyroid hormones.
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ABSTRACT: Top-trophic predators like California sea lions bioaccumulate high levels of persistent fat-soluble pollutants that may provoke physiological impairments such as endocrine or vitamins A and E disruption. We measured circulating levels of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in 12 healthy juvenile California sea lions captured on Año Nuevo Island, California, in 2002. We investigated the relationship between the contamination by PCBs and DDT and the circulating levels of vitamins A and E and thyroid hormones (thyroxine, T4 and triiodothyronine, T3). Serum concentrations of total PCBs (sigmaPCBs) and total DDT were 14 +/- 9 mg/kg and 28 +/- 19 mg/kg lipid weight, respectively. PCB toxic equivalents (sigmaPCB TEQs) were 320 +/- 170 ng/kg lipid weight. Concentrations of sigmaPCBs and sigmaPCB TEQs in serum lipids were negatively correlated (p < 0.05) with serum vitamin A and T3, potentially reflecting PCB-related toxicity. A slight but not significant negative correlation (p < 0.1) was observed between serum T4 and the levels of sigmaPCBs and sigmaPCB TEQs. Conversely, no relationship was evident between the contaminant concentrations and vitamin E (p > 0.1). As juvenile California sea lions are useful sentinels of coastal contamination, the high levels encountered in their serum is cause for concern about the ecosystem health of the area.Environmental Pollution 03/2005; 134(2):323-32. · 3.75 Impact Factor -
Article: Ocean climate and seal condition.
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ABSTRACT: The condition of many marine mammals varies with fluctuations in productivity and food supply in the ocean basin where they forage. Prey is impacted by physical environmental variables such as cyclic warming trends. The weaning weight of northern elephant seal pups, Mirounga angustirostris, being closely linked to maternal condition, indirectly reflects prey availability and foraging success of pregnant females in deep waters of the northeastern Pacific. The aim of this study was to examine the effect of ocean climate on foraging success in this deep-diving marine mammal over the course of three decades, using cohort weaning weight as the principal metric of successful resource accrual. The mean annual weaning weight of pups declined from 1975 to the late 1990s, a period characterized by a large-scale, basin-wide warm decadal regime that included multiple strong or long-duration El Niños; and increased with a return to a cool decadal regime from about 1999 to 2004. Increased foraging effort and decreased mass gain of adult females, indicative of reduced foraging success and nutritional stress, were associated with high ocean temperatures. Despite ranging widely and foraging deeply in cold waters beyond coastal thermoclines in the northeastern Pacific, elephant seals are impacted significantly by ocean thermal dynamics. Ocean warming redistributes prey decreasing foraging success of females, which in turn leads to lower weaning mass of pups. Annual fluctuations in weaning mass, in turn, reflect the foraging success of females during the year prior to giving birth and signals changes in ocean temperature cycles.BMC Biology 02/2005; 3:9. · 5.75 Impact Factor -
Article: The effect of a low-frequency sound source (acoustic thermometry of the ocean climate) on the diving behavior of juvenile northern elephant seals, Mirounga angustirostris.
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ABSTRACT: Changes in the diving behavior of individual free-ranging juvenile northern elephant seals, Mirounga angustirostris, exposed to the acoustic thermometry of the ocean climate (ATOC) sound source were examined using data loggers. Data loggers were attached to the animals and measured swim speed, maximum depth of dive, dive duration, surface interval, descent and ascent rate, and descent and ascent angle along with sound pressure level (SPL). The ATOC sound source was at a depth of 939 m and transmitted at 195 dB re: 1 microPa at 1 m centered at 75 Hz with a 37.5-Hz bandwidth. Sound pressure levels (SPL) measured at the seal during transmissions averaged 128 dB and ranged from 118 to 137 dB re: 1 microPa for the 60-90 Hz band, in comparison to ambient levels of 87-107 dB within this band. In no case did an animal end its dive or show any other obvious change in behavior upon exposure to the ATOC sound. Subtle changes in diving behavior were detected, however. During exposure, deviations in descent rate were greater than 1 s.d. of the control mean in 9 of 14 seals. Dive depth increased and descent velocity increased in three animals, ascent velocity decreased in two animals, ascent rate increased in one animal and decreased in another, and dive duration decreased in only one animal. There was a highly significant positive correlation between SPL and descent rate. The biological significance of these subtle changes is likely to be minimal. This is the first study to quantify behavioral responses of an animal underwater with simultaneous measurements of SPL of anthropogenic sounds recorded at the animal.The Journal of the Acoustical Society of America 03/2003; 113(2):1155-65. · 1.55 Impact Factor -
Article: Organochlorine pollutants [corrected] in California sea lions revisited.
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ABSTRACT: Dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that have been banned in most countries, but considerable amounts continue to cycle the ecosphere. Top trophic level predators, like sea birds and marine mammals, bioaccumulate these lipophilic compounds, reflecting their presence in the environment. We measured concentrations of tDDT (p,p' - DDT + p,p' - DDD + p,p' - DDE) and PCBs in the blubber of dead California sea lions stranded along the California coast. tDDT and PCB concentrations were 150 +/- 257 ug/g lipid weight (mean +/- SD) and 44 +/- 78 ug/g lipid weight, respectively. There were no differences in tDDT or PCB concentrations between animal categories varying in sex or age. There was a trend towards a decrease in tDDT and PCB concentrations from northern to southern California. The lipid content of the blubber was negatively correlated with levels of tDDT and PCBs. tDDT concentrations were approximately 3 times higher than PCB concentrations. tDDT levels in the blubber of California sea lions decreased by over one order of magnitude from 1970 to 2000. PCB level changes over time were unclear owing to a paucity of data and analytical differences over the years. Current levels of these pollutants in California sea lions are among the highest among marine mammals and exceed those reported to cause immunotoxicity or endocrine disruption.BMC Ecology 01/2003; 2:11. -
Article: Diving behaviour and foraging ecology of female southern elephant seals from Patagonia
Aquatic Mammals. 24(1):1-11. -
Article: Geolocation by light levels: a validation study
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Article: A method for calibrating swim-speed recorders
Marine Mammal Science. 15(3):894-905. -
Article: Diving behavior of juvenile northern elephant seals
Canadian Journal of Zoology. 74(9):1632-1644. -
Article: Swimming speed and foraging strategies of northern elephant seals
Deep-Sea Research II. 54:369-383. -
Article: Evaluating the function of the male harbour seal, Phoca vitulina, roar through playback experiments
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ABSTRACT: The aim of this study was to evaluate the role of vocalizations produced during the breeding season by the male harbour seal, an aquatically breeding pinniped. During the spring of 1999, playback experiments were conducted at eight locations in Elkhorn Slough, California, U.S.A. Through an underwater speaker, we presented male harbour seals with three acoustic stimuli: a long-duration, low-frequency roar (LL), a short-duration, high-frequency roar (SH) and amplified water noise (control). Male responses to the playback boat were characterized by increased approach rates and aggressive flipper slapping during 62.5% of SH sessions (N=8), 25% of LL sessions (N=8) and 0% of control sessions (N=8). No more than one identifiable seal responded during each playback location. We observed no responses by female harbour seals to playbacks. We conclude from these experiments that territorial male harbour seals use roars given by intruders to locate and challenge intruders.Animal Behaviour. -
Chapter: Swim speed and dive function in a female northern elephant seal
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Article: Milk Intake of Elephant Seal Pups: An Index of Parental Investment
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ABSTRACT: Total milk ingested throughout nursing in free-living northern elephant seal pups, derived from the turnover of tritiated water, gives an accurate estimate of the energetic component of parental investment. In 4 wk of nursing, females transferred a mean of 138 kg of milk with a value of 6.04 x 105 kcal, five times the metabolic requirements of pups. The mean rate of energy transfer is more than twice that predicted for the female's size from studies of laboratory and domestic animals. In one month, pups receive sufficient energy and essential nutrients from mother's milk to enable them to fast while continuing to develop for an additional 2 1/2 mo before feeding on their own. Measurement of the energetic component of parental investment makes it possible to test predictions from the theory of parental investment.The American Naturalist. 124(3):416-422. -
Article: Maternal traits and reproductive effort in northern elephant seals
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ABSTRACT: The aim of this study was to determine the effects of maternal traits on reproductive expenditure and energy delivery to the offspring in a capital breeder, the northern elephant seal (Mirounga angustirostris). Changes in maternal and offspring energy reserves and milk-energy delivery were examined in relation to maternal parturition mass, body composition, and age in females and pups breeding at Ano Nuevo State Reserve, California. Maternal body mass and composition had significant effects on maternal energy expenditure over lactation. Path analysis suggested no significant effects of maternal age on reproductive effort of parous females. The efficiency of milk production increased significantly with maternal age. Offspring metabolism was a relatively small component of maternal energy expenditure, with pups storing 84% of the energy obtained from milk. These effects are an important consequence of the phocid strategy for enabling terrestrial parturition despite marine feeding. This strategy has resulted in an abbreviated and highly efficient lactation system that is strongly impacted by body reserves, linking foraging success at sea with reproductive success on land. Maternal size, body composition, and age were important features of reproduction in northern elephant seals. These characteristics are rarely considered concurrently in life history studies.Ecology (Washington D C). 82(12):3541-3555. -
Article: Drift diving in female northern elephant seals: Implications for food processing
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ABSTRACT: We tested predictions from the hypothesis that northern elephant seals, Mirounga angustirostris, drift during the bottom segment of some dives (called C dives) using oxygen saved from reduced locomotion to process food. Sixteen free-ranging dive records were obtained with microcomputer dive recorders attached to 13 adult females from Ano Nuevo, California, during biannual foraging trips when they were in early or late stages of gestation; swim speed was recorded throughout one dive record. Body composition was measured before and after trips to sea. C dives with a bout length of 2-10 dives and a mean duration similar to those of other dive types made up 6.3 plus-minus 1.9% of the dives recorded. Swim speed was near or below the recorder stall speed (0.22 m/s) during the second, drift segment of these dives. The rate of vertical depth change while drifting varied little within bouts, was initially significantly correlated with the ratio of fat to lean body mass at departure, and changed systematically as the seals fed while at sea. Females in early gestation, with initial mean body fat of 24%, drifted down at a mean rate of 0.31 plus-minus 0.04 m/s; females in late gestation, with mean body fat approaching 36%, drifted up at an average rate of 0. 17 plus-minus 0.05 m/s. The frequency, duration, and temporal pattern of drift dives were correlated with foraging behavior, supporting the hypothesis that drifting while diving is associated with the metabolic cost of processing food. This study provides indirect support for the hypothesis that elephant seals suspend active swimming on certain dives, during which a greater proportion of oxygen stores is allocated to the processing of food, without interrupting the seals' normal pattern of continuous diving and allowing them to remain within their aerobic dive limit.Canadian Journal of Zoology 75(1):27-39. · 1.21 Impact Factor -
Article: Swimming speed and foraging strategies of northern elephant seals
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ABSTRACT: We investigated swimming speed, a key variable in both the management of oxygen stores and foraging strategies, and its relationship to diving behaviour in northern elephant seals, Mirounga angustirostris. Swimming speed significantly reduced the dive duration and time at depth for presumed foraging dives, but increased with dive depth. This suggests that the extended duration of deep dives is made possible by physiological adjustments and not by changes in swimming speed or effort. Swimming speeds were similar across sex and age classes despite different predicted minimum cost of transport speeds.All seals exhibited characteristic dive shapes and swimming speed patterns that support their putative functions, but two-dimensional dive shapes and swimming angles varied between sexes and age classes. Mean dive angles on descent were markedly shallow, suggesting use of negative buoyancy to cover horizontal distance while diving. Buoyancy also appeared to affect two-dimensional dive shapes and ability to use extended gliding behaviours between surface and deep foraging zones. Significant differences in diving behaviour between sexes and between young and adult females were evident for various phases of the dive cycle, potentially resulting from physical constraints or differences in dive functionality.Deep Sea Research Part II Topical Studies in Oceanography 54:369-383. · 2.28 Impact Factor
Top co-authors
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Institutions
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2003–2012
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University of California, Santa Cruz
- • Institute of Marine Sciences
- • Department of Ecology & Evolutionary Biology
Santa Cruz, CA, USA
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