James T. Harvey

Mortality of sea lions along the central California coast linked to a toxic diatom bloom.

Over 400 California sea lions (Zalophus californianus) died and many others displayed signs of neurological dysfunction along the central California coast during May and June 1998. A bloom of Pseudo-nitzschia australis (diatom) was observed in the Monterey Bay region during the same period. This bloom was associated with production of domoic acid (DA), a neurotoxin that was also detected in planktivorous fish, including the northern anchovy (Engraulis mordax), and in sea lion body fluids. These and other concurrent observations demonstrate the trophic transfer of DA resulting in marine mammal mortality. In contrast to fish, blue mussels (Mytilus edulus) collected during the DA outbreak contained no DA or only trace amounts. Such findings reveal that monitoring of mussel toxicity alone does not necessarily provide adequate warning of DA entering the food web at levels sufficient to harm marine wildlife and perhaps humans.

Foraging behavior of humpback whales: kinematic and respiratory patterns suggest a high cost for a lunge

SUMMARY Lunge feeding in rorqual whales is a drag-based feeding mechanism that is thought to entail a high energetic cost and consequently limit the maximum dive time of these extraordinarily large predators. Although the kinematics of lunge feeding in fin whales supports this hypothesis, it is unclear whether respiratory compensation occurs as a consequence of lunge-feeding activity. We used high-resolution digital tags on foraging humpback whales (Megaptera novaengliae) to determine the number of lunges executed per dive as well as respiratory frequency between dives. Data from two whales are reported, which together performed 58 foraging dives and 451 lunges. During one study, we tracked one tagged whale for approximately 2 h and examined the spatial distribution of prey using a digital echosounder. These data were integrated with the dive profile to reveal that lunges are directed toward the upper boundary of dense krill aggregations. Foraging dives were characterized by a gliding descent, up to 15 lunges at depth, and an ascent powered by steady swimming. Longer dives were required to perform more lunges at depth and these extended apneas were followed by an increase in the number of breaths taken after a dive. Maximum dive durations during foraging were approximately half of those previously reported for singing (i.e. non-feeding) humpback whales. At the highest lunge frequencies (10 to 15 lunges per dive), respiratory rate was at least threefold higher than that of singing humpback whales that underwent a similar degree of apnea. These data suggest that the high energetic cost associated with lunge feeding in blue and fin whales also occurs in intermediate sized rorquals.

Changes in the cetacean assemblage of a coastal upwelling ecosystem during El Niño 1997-98 and La Niña 1999

Abstract We report results of ecosystem studies in Monterey Bay, California, during the summer upwelling periods, 1996–99, including impacts of El Nino 1997–98 and La Nina 1999. Random-systematic line-transect surveys of marine mammals were conducted monthly from August to November 1996, and from May to November 1997–99. CTDs and zooplankton net tows were conducted opportunistically, and at 10 predetermined locations. Hydroacoustic backscatter was measured continuously while underway to estimate prevalence of zooplankton, with emphasis on euphausiids, a key trophic link between primary production and higher trophic level consumers. The occurrences of several of the California Current’s most common cetaceans varied among years. The assemblage of odontocetes became more diverse during the El Nino with a temporary influx of warm-water species. Densities of cold-temperate Dall’s porpoise, Phocoenoides dalli, were greatest before the onset of El Nino, whereas warm-temperate common dolphins, Delphinus spp., were present only during the warm-water period associated with El Nino. Rorqual densities decreased in August 1997 as euphausiid backscatter was reduced. In 1998, as euphausiid backscatter slowly increased, rorqual densities increased sharply to the greatest observed values. Euphausiid backscatter further increased in 1999, whereas rorqual densities were similar to those observed during 1998. We hypothesize that a dramatic reduction in zooplankton biomass offshore during El Nino 1997–98 led to the concentration of rorquals in the remaining productive coastal upwelling areas, including Monterey Bay. These patterns exemplify short-term responses of cetaceans to large-scale changes in oceanic conditions.

Development of Body Oxygen Stores in Harbor Seals: Effects of Age, Mass, and Body Composition

Harbor seal pups are highly precocial and can swim and dive at birth. Such behavioral maturity suggests that they may be born with mature body oxygen stores or that stores develop quickly during the nursing period. To test this hypothesis, we compared the blood and muscle oxygen stores of harbor seal pups, yearlings, and adults. We found that pups had smaller oxygen stores than adults (neonates 57%, weaned pups 75%, and yearlings 90% those of adults), largely because neonatal myoglobin concentrations were low (1.6 ± 0.2 g% vs. 3.8 ± 0.3 g% for adults) and changed little during the nursing period. In contrast, blood oxygen stores were relatively mature, with nursing pups having hematocrit (55% ± 0.2%), hemoglobin (21.7 ± 0.4 g%), and blood volume (12.3 ± 0.5 mL/kg) only slightly lower than the corresponding values for adults (57% ± 0.2%, 23.8 ± 0.3 g %, and 15.0 ± 0.5 mL/kg). Because neonatal pups had relatively high metabolic rates (11.0 mL O2/kg min), their calculated aerobic dive limit was less than 50% that of adults. These results suggest that harbor seals’ early aquatic activity is primarily supported by rapid development of blood, with immature muscle oxygen stores and elevated use rates limiting aerobic diving ability.

The role of body size in individual-based foraging strategies of a top marine predator.

Body size is an important determinant of the diving and foraging ability in air-breathing marine vertebrate predators. Satellite-linked dive recorders were used during 2003-2004 to investigate the foraging behavior of 22 male California sea lions (Zalophus californianus, a large, sexually dimorphic otariid) and to evaluate the extent to which body size explained variation among individuals and foraging strategies. Multivariate analyses were used to reduce the number of behavioral variables used to characterize foraging strategies (principal component analysis, PCA), to identify individually based foraging strategies in multidimensional space (hierarchical cluster analysis), and to classify each individual into a cluster or foraging strategy (discriminant analysis). Approximately 81.1% of the variation in diving behavior among individuals was explained by three factors: diving patterns (PC1), foraging effort (PC2), and behavior at the surface (PC3). Individuals were classified into three distinct groups based on their diving behavior (shallow, mixed depth, and deeper divers), and jackknife resampling of the data resulted in correct group assignment 86% of the time. Body size as an independent variable was positively related to dive duration and time spent ashore and negatively related to time at sea, and it was a key parameter in PC2 used to classify the three distinct clusters. Differences among individual-based foraging strategies probably were driven by differences in body size, which enabled larger animals to dive deeper and forage more efficiently by targeting different and perhaps larger prey items. The occurrence of foraging specializations within a species and age class has implications for quantitative modeling of population-level predator-prey interactions and ecosystem structure.

Contaminant Loads And Hematological Correlates In The Harbor Seal (Phoca vitulina) Of San Francisco Bay, California

An expanding body of research indicates that exposure to contaminants may impact marine mammal health, thus possibly contributing to population declines. The harbor seal population of the San Francisco Bay (SFB), California, has suffered habitat loss and degradation, including decades of environmental contamination. To explore the possibility of contaminant-induced health alterations in this population, blood levels of polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (DDE), and polybrominated diphenyl ethers (PBDEs) were quantified in free-ranging seals; relationships between contaminant exposure and several key hematological parameters were examined; and PCB levels in the present study were compared with levels determined in SFB seals a decade earlier. PCB residues in harbor seal blood decreased during the past decade, but remained at levels great enough that adverse reproductive and immunological effects might be expected. Main results included a positive association between leukocyte counts and PBDEs, PCBs, and DDE in seals, and an inverse relationship between red blood cell count and PBDEs. Although not necessarily pathologic, these responses may serve as sentinel indications of contaminant-induced alterations in harbor seals of SFB, which, in individuals with relatively high contaminant burdens, might include increased rates of infection and anemia. We thank staff, students, and volunteers from Moss Landing Marine Laboratories, the Richmond Bridge Harbor Seal Survey/San Francisco State University, and the Marine Mammal Center for assistance with seal capture and handling. We gratefully acknowledge Judy Lawrence (Marine Mammal Center) for running CBCs and serum chemistries. D. Anderson, B. Sacks, and two anonymous reviewers provided helpful critiques of the article. This project was supported in part by grants to J. Neale from the University of California Marine Council (02 T CEQI 03 0104) and the NIH (5 T32 ES07059-25 Traineeship in Environmental Toxicology).

Hematology and serum chemistry comparisons between free-ranging and rehabilitated harbor seal (Phoca vitulina richardsi) pups

The objectives of this study were to compare the hematology and serum chemistry values between free-ranging and stranded harbor seal (Phoca vitulina richardsi) pups and to ascertain how blood values of stranded pups changed during the rehabilitation process. Coincident with these comparisons, reference values were obtained for free-ranging pups. Stranded harbor seal pups (n=28) recovered from areas between Pebble Beach and Moss Landing, California (USA) were admitted to The Marine Mammal Center, Sausalito, from March to May 1995, 1996, and 1998. Blood samples were collected from harbor seal pups before and after rehabilitation. As a control group, wild harbor seal pups were captured at Pebble Beach and Elkhorn Slough (n=42) during the 1995, 1996, and 1998 pupping seasons. Mean eosinophil and calcium values of wild pups were significantly greater than those of newly admitted pups, whereas mean bands, aspartate aminotransferase, alanine aminotransferase, total bilirubin, and chloride values were significantly lower (P≤0.05). Mean neutrophil, band, lymphocyte, eosinophil, basophil, calcium, phosphorus, blood urea nitrogen, potassium, total protein, and globulin values of rehabilitated pups increased significantly after 2–3 mo in captivity, whereas, mean red blood cell, hemoglobin, hematocrit, cholesterol, and total bilirubin values decreased significantly (P≤0.05).

Evaluating the function of the male harbour seal, Phoca vitulina, roar through playback experiments

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.

Patterns in the vocalizations of male harbor seals

Comparative analyses of the roar vocalization of male harbor seals from ten sites throughout their distribution showed that vocal variation occurs at the oceanic, regional, population, and subpopulation level. Genetic barriers based on the physical distance between harbor seal populations present a likely explanation for some of the observed vocal variation. However, site-specific vocal variations were present between genetically mixed subpopulations in California. A tree-based classification analysis grouped Scottish populations together with eastern Pacific sites, rather than amongst Atlantic sites as would be expected if variation was based purely on genetics. Lastly, within the classification tree no individual vocal parameter was consistently responsible for consecutive splits between geographic sites. Combined, these factors suggest that site-specific variation influences the development of vocal structure in harbor seals and these factors may provide evidence for the occurrence of vocal dialects.

Behavior, Movements, and Apparent Survival of Rehabilitated and Free-Ranging Harbor Seal Pups

Post-release studies are essential to determine the efficacy of wildlife rehabilitation. Although an increasing number of Pacific harbor seal (Phoca vitulina richardsi) pups are admitted to rehabilitation centers, few studies have been conducted to monitor the behaviors and survival of rehabilitated pups released back into the wild. Our objectives were to compare diving behaviors, activity patterns, movements, and survival between rehabilitated pups (n = 29) and wild pups (n = 24). Pups were radiotracked for 5 months after release at Pebble Beach, California, during 1995, 1996, and 1998. Mean duration of dives (t 27 = 0.90, P = 0.37) and surface intervals (U = 52, P = 0.20) of rehabilitated pups did not differ from that of wild pups. Rehabilitated pups spent a greater proportion of their time in the water (t 18 = 2.12, P= 0.047) than did wild pups. Most pups traveled north from Pebble Beach, and movements were variable. Seal group (F 1 31 = 1.33, P= 0.26) or sex (F 1 31 = 0.22, P= 0.64) had no effect on maximum distance traveled. Survival curves between rehabilitated and wild pups were similar during 1995 (X 2 = 0.40, P> 0.05) and 1998 (X 2 = 1.34, P> 0.05), whereas rehabilitated pups had lower survival than wild pups during 1996 (X 2 = 3.94, P 0.05). In summary, the overall behavior, movement, and apparent survival of rehabilitated pups appeared similar to wild pups. Future studies should be conducted to assess the long-term survival of rehabilitated and free-ranging harbor seal pups.