Postrelease dive ability in rehabilitated harbor seals

The efficacy of seal rehabilitation is examined in a postrelease study of dive ability in harbor seal pups (Phoca vitulina) in the Wash, United Kingdom. Six rehabilitated seals were fitted with Sea Mammal Research Unit (SMRU) Argos Satellite Relay Data Logger tags and their individual dive behavior was monitored for an average of 122 d. The upper 90 percentile edge of dive behavior (dive duration [DD₉₀] and percentage of time at‐sea spent in a dive [PD₉₀]), in 7 d bins, was used as a proxy for physiological dive ability. The results are compared with data from five wild adult harbor seals. There was no statistically significant difference between (1) the mean track duration of rehabilitated seals (126.20 ± 27.48 [SD] d) and adult seals (150.2 ± 24.62 d) (P= 0.108), indicating no evidence that short‐term survival was less in the rehabilitated group; (2) the mean mass‐scaled DD₉₀ of rehabilitated seals (3.95 ± 0.37 min) and adult seals (4.09 ± 0.55 min) (P= 0.632); and (3) the mean PD₉₀ of rehabilitated seals (81.62 ± 1.21%) and adult seals (81.48 ± 3.93%) (P= 0.943). These three results all suggest the success of the rehabilitation program in terms of short‐term survival and dive ability.     

Interactions of respiration and the bradycardia of submersion in harbor seals.

Six harbor seals with percutaneous tracheostomies were artificially ventilated while immersed. Changes in the oxygen content of the inspired gas and in the minute-volume altered the magnitude of the bradycardia observed after the animal had been submerged for 30 s. The average heart rate in five seals changed from 16.7 (S.D. = 4.4) beats per minute during artificial ventilation with N2, to 58.7 (S.D. = 10.4) beats per minute while breathing air, but this cardiac chronotropic effect of oxygen was blocked by addition of 7% CO2 to the inspired gas. Ventilatory minute-volumes above approximately 3 litres/min caused cardiac acceleration in a manner related to ventilation; below this, changes in heart rate were inconsistent. While being artificially ventilated with air, the average heart rate in five seals changed from 16.5 beats per minute to 73.4 beats per minute as ventilation was increased from 0 to greater than 8 litres/min. These experiments demonstrate that O2, CO2, and ventilatory minute-volume have significant effects upon the heart rate of seals under water and suggest the presence of chemoreceptor-mediated effects on heart rate during submersion.     

Photo-ID-based estimates of reproductive patterns in female harbor seals

Variations in reproductive patterns offer important insights into the dynamics of pinniped populations, but collecting data on reproduction for species that spend much of the breeding season in the water is problematic. We used land‐based photo‐identification techniques to collect individual‐based data on the timing of pupping, total pup production, and lactation duration in a population of harbor seals in NE Scotland. Capture–Mark–Recapture (CMR) techniques were used to overcome potential biases due to changes in probability of capture, and provide estimates of lactation duration based upon changes in the “survival” of mother–pup bonds. A mean birth date of 20 June is the first direct estimate of parturition date for UK harbor seals. Information on cumulative births indicated that the peak daily haul‐out count accounted for 77% of total pup production. CMR‐based estimates of lactation duration suggest that 50% of mothers had weaned their pups, when pups were 21‐d old. These results highlight the potential for using photo‐ID techniques to study harbor seal reproductive patterns at sites where intensive capture and marking is not possible for logistic, legislative, or ethical reasons.     

Cardiac output and stroke volume in swimming harbor seals

Summary Cardiac output was measured by the thermodilution method in three young harbor seals, at rest and while swimming up to the maximum effort for which they could be trained. Stroke volume was determined by counting heart rate simultaneously with determination of cardiac output. Cardiac outputs varied widely between surface breathing (7.8 ml · kg^–1 · s^–1) and breath-holding while swimming under water (1.8 ml · kg^–1 · s^–1). Stroke volume while at the surface was almost twice the volume white submerged. Surface cardiac output was always near maximal despite work effort, whereas submerged cardiac output gradually increased at higher work efforts. The cardiovascular performance of seals at the maximum MO₂ we could induce from them is equivalent to that of the domestic goat.Abbreviations CO Cardiac output - HR Heart rate - SV Stroke volume - MO ₂ Metabolic rate - FS Forced sumersion - V Velocity - C _DF Frontal drag coefficient - CV Cardiovascular Present address: Institute of Marine Science, University of Alaska, Fairbanks, AK, USA     

Serologic study of phocine distemper in a population of harbor seals in Scotland.

A serologic survey of the prevalence of morbillivirus antibodies was conducted in a population of harbor seals (Phoca vitulina) from northeastern Scotland, where mortality was comparatively low during the 1988 phocine distemper virus outbreak. None of the 12 seals sampled before the epizootic were seropositive. Thirty-five (52%) of 68 seals sampled after the beginning of the epizootic were seropositive, although there were significant age-related differences in both the number of seropositive individuals and in antibody levels. Marking studies showed that most seropositive seals caught during the peak of the epizootic survived for several months. Thus, the low mortality observed in this population did not appear to result from a lack of contact with the virus.     

Survival probabilities and movements of harbor seals in central California

Harbor seal numbers and population trajectories differ by location in central California. Within San Francisco Bay (SFB) counts have been relatively stable since the 1972 Marine Mammal Protection Act, but in coastal areas like Tomales Bay (TB), counts increased before stabilizing in the 1990s. Emigration, poor survival, and environmental effects have been hypothesized as contributors to differences between trajectories; however, basic demographic data were not available to evaluate these hypotheses. We monitored 32 radio‐tagged adult females (SFB n = 17, TB n = 15) for 20 mo (2011–2013), and estimated survival, resight, and movement probabilities using mark‐resight analyses and multistate mark‐resight models. Annual survival probability for both sites was 0.90 (95% CI = 0.18–0.99). Six seals were observed moving between locations resulting in an estimated probability of 0.042 (95% CI = 0.023–0.076) per month equal movement between sites. Resight probability was less in SFB relative to TB, likely due to differential haul‐out access, area surveyed, visibility, and resight effort. Because of wide confidence intervals and low precision of these first estimates of adult female harbor seal survival in California, this demographic must be further examined to dismiss its contribution to differing population trajectories. Using aerial survey data, we estimated 950 harbor seals in SFB (95% CI = 715–1,184) confirming numbers are still stable.     

Kinematics of terrestrial locomotion in harbor seals and gray seals: Importance of spinal flexion by amphibious phocids

Pinnipeds are amphibious mammals with flippers, which function for both aquatic and terrestrial locomotion. Evolution of the flippers has placed constraints on the terrestrial locomotion of phocid seals. The detailed kinematics of terrestrial locomotion of gray (Halichoerus grypus) and harbor (Phoca vitulina) seals was studied in captivity and in the wild using video analysis. The seals exhibited dorsoventral undulations with the chest and pelvis serving as the main contact points. An anteriorly directed wave produced by spinal flexion aided in lifting the chest off the ground as the fore flippers were retracted to pull the body forward. The highest length‐specific speeds recorded were 1.02 BL/s for a gray seal in captivity and 1.38 BL/s for a harbor seal in the wild. The frequency and amplitude of spinal movement increased directly with speed, but the duty factor remained constant. Substrate did not influence the kinematics except for differences due to moving up or down slopes. The highly aquatic nature of phocids seals has restricted them to locomote on land primarily using spinal flexion, which can limit performance in speed and duration.     

Determining a correction factor for aerial surveys of harbor seals in California

Counts of pinnipeds provide a minimal estimate of population size because some unknown proportion of individuals is in the water during surveys. We determined a correction factor (CF) for Pacific harbor seals (Phoca vitulina richardii) by estimating the proportion ashore of 180 seals tagged with flipper‐mounted radio tags throughout California. The mean proportions of tagged individuals ashore during four complete surveys in 2004 were not different between central and northern California (F= 1.85, P= 0.18) or between sexes (F= 0.57, P= 0.45), but a lesser proportion of weaners was ashore than subadults or adults (F= 7.97, P= 0.001), especially in northern California. The CF calculated for the statewide census of harbor seals was 1.65, using transmitters operating during the survey (n= 114). Using a mark‐recapture estimator for tag survival (phi) and the four telemetry surveys the mean CF for central and northern California was 1.54 ± 0.38 (95% CI). A CF for southern California of 2.86 was based on a single survey. Using the mean CF of 1.54 and a statewide count in 2009 we estimated 30,196 (95% CI = 22,745–37,647) harbor seals in California.     

SEALNET: Facial recognition software for ecological studies of harbor seals

Methods for long‐term monitoring of coastal species such as harbor seals (Phoca vitulina) are often costly, time‐consuming, and highly invasive, underscoring the need for improved techniques for data collection and analysis. Here, we propose the use of automated facial recognition technology for identification of individual seals and demonstrate its utility in ecological and population studies. We created a software package, SealNet, that automates photo identification of seals, using a graphical user interface (GUI) software to detect, align, and chip seal faces from photographs and a deep convolutional neural network (CNN) suitable for small datasets (e.g., 100 seals with five photos per seal) to classify individual seals. We piloted the SealNet technology with a population of harbor seals located within Casco Bay on the coast of Maine, USA. Across two years of sampling, 2019 and 2020, at seven haul‐out sites in Middle Bay, we obtained a dataset optimized for the development and testing of SealNet. We processed 1752 images representing 408 individual seals and achieved 88% Rank‐1 and 96% Rank‐5 accuracy in closed set seal identification. In identifying individual seals, SealNet software outperformed a similar face recognition method, PrimNet, developed for primates but retrained on seals. The ease and wealth of image data that can be processed using SealNet software contributes a vital tool for ecological and behavioral studies of marine mammals in the developing field of conservation technology.

In this paper, we describe the successful application of our newly developed automated facial recognition software as a tool for ecological analysis of harbor seals (Phoca vitulina). We outline an emerging method of data collection and analysis that facilitates rapid interpretation of large photo datasets over wide temporal and geographic scales. In addition, we use this machine learning‐based technology in a preliminary ecological study in a wild population of seals in the Casco Bay region of Maine to demonstrate the effectiveness of this non‐invasive method for use in mark‐recapture and site fidelity studies in the field.     

Mycoplasma phocidae sp. nov., isolated from harbor seals (Phoca vitulina L.).

In 1979 and 1980, more than 400 harbor seals (Phoca vitulina) along the New England coast of the United States died of epizootic pneumonia that was attributed to an influenza virus. Six mycoplasma isolates that were recovered from the respiratory tracts of affected seals were investigated and were found to be serologically identical and distinct from previously described species. These isolates required serum for growth, did not possess a cell wall, and did not hydrolyze urea. Arginine was hydrolyzed, glucose was not fermented, film and spots were observed on horse serum agar, phosphatase was produced, tetrazolium was not reduced, and serum and casein were not digested. The guanine-plus-cytosine content of the DNA was 27.8 mol%. We propose the name Mycoplasma phocidae for these isolates. The type strain of M. phocidae is strain 105 (= ATCC 33657).     

Characterization of Otostrongylus circumlitus from Pacific harbor and northern elephant seals

Otostrongylus circumlitus (Railliet, 1899) from Pacific harbor seals (Phoca vitulina richardsi) and northern elephant seals (Mirounga angustirostris) were examined using morphological and molecular methods to determine whether northern elephant seals along the central California coast are infected by the same species of Otostrongylus as are Pacific harbor seals in the same area. Fixed nematodes were examined and measured using light microscopy. The polymerase chain reaction (PCR) was used to amplify and sequence the second internal transcribed spacer (ITS-2) and D3 expansion (26S) regions of ribosomal DNA of O. circumlitus from Pacific harbor and northern elephant seals. The ITS-2 region was also amplified from Parafilaroides sp. from the Pacific harbor seal, northern elephant seal, and California sea lion (Zalophus californianus) and used for restriction fragment length polymorphism (RFLP) analysis. Morphologically, it was not possible to distinguish O. circumlitus from Pacific harbor and northern elephant seals, and over a consensus length of 443 base pairs (bp) for ITS-2 and 321 bp for D3 the sequences of O. circumlitus from both hosts were identical. With the PCR-RFLP assay, it was possible to distinguish O. circumlitus from Parafilaroides sp. The results suggest that O. circumlitus is the same species in Pacific harbor and northern elephant seals, and molecular methods make it possible to distinguish this nematode from related nematodes.     

Metabolic indicators in the skeletal muscles of harbor seals (Phoca vitulina)

The goal of this study was to determine the distribution of citrate synthase (CS), beta-hydroxyacyl coenzyme A dehydrogenase (HOAD), and lactate dehydrogenase (LDH) activities and myoglobin (Mb) concentration in the locomotor muscles (epaxial muscles) and heart of harbor seals. The entire epaxial musculature, which produces most of the power for submerged swimming, was removed and weighed, and three transverse sections (cranial, middle, and caudal) were taken along the muscle bundle. Multiple samples were taken along points on a circular grid using a 6-mm biopsy. A single sample was taken from the left ventricle of the heart. Muscle groups of similar function were taken from three dogs as a control. Mean values were calculated for four roughly equal quadrants in each transverse section of the epaxial muscles. There were no significant differences among the quadrants within any of the transverse sections for the three enzymes or Mb. However, there were significant differences in the mean enzyme activities and Mb concentrations along the length of the muscle. The middle and caudal sections had significantly higher mean levels of CS, LDH, and Mb than the cranial section, which may be correlated with power production during swimming. The enzyme ratios CS/HOAD and LDH/CS exhibited no variation within transverse sections or along the length of the epaxial muscles. Relative to the dog, the epaxial muscles and heart of the harbor seal had higher HOAD levels and lower CS/HOAD, which, taken together, indicate an increased capacity for aerobic lipid metabolism during diving.     

An outbreak of a herpesvirus infection in harbor seals (Phoca vitulina)

During an outbreak of a herpesvirus infection in juvenile harbor seals, 11 out of 23 seals died. The duration of the disease in these 11 animals varied from 1-6 days. Nasal discharge, inflammation of the oral mucosa, vomiting, diarrhea and fever up to 40 degrees C were observed in the first days of the disease. In later stages coughing, anorexia and lethargy occurred. Severe necrosis of the liver and interstitial pneumonia were the most striking histopathological findings.     

Muscle capillary supply in hind limb and diaphragm of the common shrew (Sorex araneus)

Shrew species of the subfamily Soricinae have unusually high metabolic rates when compared to Crocidurinae shrews and other similar-sized mammals. The aim of this study was to clarify whether the high basal metabolic rate of Soricinae shrews is reflected in a high capillary density in their muscles. To this end, the capillary supply of four limb muscles and diaphragm of the common shrew (Sorex araneus) was quantified from cross-sectioned muscles. The capillary densities of the limb muscles were 2575 ± 329, 3111 ± 299, 2812 ± 197 and 2752 ± 173 capillaries mm⁻² fibre area in gastrocnemius lateralis, g. medialis, plantaris and soleus, respectively. Capillary density of the shrew diaphragm (6691 ± 1057) was double that of the limb muscles. This value is among the highest ever measured in mammals. In general, the capillary supply in the hind limb of the common shrew is about 3–4 times higher than commonly found in the leg muscles of the laboratory rat or other bigger mammals, but similar to those in Crocidurinae shrews and some small rodents. Thus the high resting metabolism of the common shrew is not associated with an extraordinarily high capillary density. The apparent disparity between basal metabolic rate and muscle capillary supply in S. araneus is probably due to the small aerobic scope of shrews in the subfamily Soricinae. Accepted: 22 January 1998     

Seroprevalence of Toxoplasma gondii in harbor seals (Phoca vitulina) in southern Puget Sound, Washington.

As part of the Puget Sound Ambient Monitoring Program of the Washington Department of Fish and Wildlife, serum samples from 380 harbor seals (Phoca vitulina) were tested for antibodies to Toxoplasma gondii in the modified agglutination test (MAT) incorporating formalin-fixed tachyzoites and mercaptoethanol. Antibodies to T. gondii were found in 29 of 380 (7.6%) seals with titers of 1:25 in 13, 1:50 in 14, and > or = 1:500 in 2 seals. Results indicate natural exposure of these wild marine mammals to T. gondii oocysts.     

Haul-out behavior of harbor seals (Phoca vitulina) in Hood Canal, Washington

The goal of this study was to model haul-out behavior of harbor seals (Phoca vitulina) in the Hood Canal region of Washington State with respect to changes in physiological, environmental, and temporal covariates. Previous research has provided a solid understanding of seal haul-out behavior. Here, we expand on that work using a generalized linear mixed model (GLMM) with temporal autocorrelation and a large dataset. Our dataset included behavioral haul-out records from archival and VHF radio tag deployments on 25 individual seals representing 61,430 seal hours. A novel application for increased computational efficiency allowed us to examine this large dataset with a GLMM that appropriately accounts for temporal autocorellation. We found significant relationships with the covariates hour of day, day of year, minutes from high tide and year. Additionally, there was a significant effect of the interaction term hour of day : day of year. This interaction term demonstrated that seals are more likely to haul out during nighttime hours in August and September, but then switch to predominantly daylight haul-out patterns in October and November. We attribute this change in behavior to an effect of human disturbance levels. This study also examined a unique ecological event to determine the role of increased killer whale (Orcinus orca) predation on haul-out behavior. In 2003 and 2005 these harbor seals were exposed to unprecedented levels of killer whale predation and results show an overall increase in haul-out probability after exposure to killer whales. The outcome of this study will be integral to understanding any changes in population abundance as a result of increased killer whale predation.     

The role of Steller sea lions in a large population decline of harbor seals

We provide the first direct evidence that Steller sea lions will prey on harbor seals. Direct observations of predation on marine mammals at sea are rare, but when observed rates of predation are extrapolated, predation mortality may be found to be significant. From 1992 to 2002, harbor seals in Glacier Bay declined steeply, from 6,200 to 2,500 (∼65%). After documenting that Steller sea lions were preying on seals in Glacier Bay, we investigated increased predation by sea lions as a potential explanation for the large decline. In five independent data sets spanning 21–25 yr and including 14,308 d of observations, 13 predation events were recorded. We conducted a fine-scale analysis for an intensively studied haul-out (Spider Island) and a broader analysis of all of Glacier Bay. At Spider Island, estimated predation by sea lions increased and could account for the entirety of annual pup production in 5 of 8 yr since 1995. The predation rate, however, was not proportional to the number of predators. Predation by Steller sea lions is a new source of mortality that contributed to the seal declines; however, life history modeling indicates that it is unlikely that sea lion predation is the sole factor responsible for the large declines.     

Behavioral effects of environmental enrichment on harbor seals (Phoca vitulina concolor) and gray seals (Halichoerus grypus)

Zoos and aquariums have been incorporating environmental enrichment into their animal care programs for the past 30 years to increase mental stimulation and promote natural behaviors. However, most attempts to document the effects of enrichment on animal behavior have focused on terrestrial mammals. Staff at the National Aquarium in Baltimore conducted an investigation of the behavioral effects of enrichment on the seven harbor seals and two gray seals housed in the aquarium's outdoor seal exhibit. We expected that enrichment would change the amount of time the animals spent engaged in specific behaviors. The behaviors recorded were: resting in water, resting hauled out, maintenance, breeding display, breeding behavior, aggression, pattern swimming, random swimming, exploration, and out of sight. Activity levels (random swimming and exploration) were expected to increase, while stereotypic behaviors (pattern swimming) were expected to decrease. The frequency and duration of behaviors were documented for 90 hr in both the control phase (without enrichment) and the experimental phase (with enrichment). Statistically significant differences (P<0.05) in the time spent in pattern swimming, random swimming, exploration, and out of sight were observed between the two phases. With enrichment, pattern swimming and out of sight decreased, while random swimming and exploration behavior increased. These findings demonstrate that enrichment can promote behaviors (random swimming and exploration) that are likely to be normal for phocids in the wild, and that may contribute to the behavioral complexity of these seals in captivity. Zoo Biol 21:375–387, 2002. © 2002 Wiley‐Liss, Inc.