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We estimated sex- and age-specific apparent survival of harbor seals (Phoca vitulina richardii) born at Tugidak Island, Alaska, from 2000 to 2007 using mark-recapture models and photographs of ventral pelage markings to identify individuals. Estimates of annual apparent survival (1 - (mortality + emigration)) of females were from 0.05 to 0.10 higher than those of males and were 0.820 for weaning (~1 month) to 1 year, 0.865 for 1-3 years, and 0.929 at 3-7 years. Annual survival of males was 0.717, 0.782, and 0.879 for the same ages. Highest mortality occurred preweaning, with cumulative mortality to 4 weeks of age of 0.259, indicating this is the most vulnerable period for Tugidak harbor seals. Estimates of survival, not biased by misidentification, required that an individual had at least 2 good-quality, matching photographs in the photograph library. The number of photographs available for matching improved resighting probabilities from 0.43 for seals with 2 photographs to 0.69 for seals with 8 photographs, but this heterogeneity did not affect survival estimates. Survival estimates based on photograph-identification data were nearly identical to those based on resightings of flipper-tagged seals using mark-recapture models with a preliminary double-tag-loss estimate of 2.5% per year. Photograph identification of natural pelage markings provides a viable method for estimating vital rates of harbor seals even at large haul-outs (> 1,000 animals) and may be useful for populations of conservation concern that require low disturbance of animals or where capturing sufficient numbers of seals for artificial marking is not feasible. [ABSTRACT FROM AUTHOR]

Climate change is having profound impacts on animal populations, and shifts in geographic range are predicted in response. Shifts that result in range overlap between previously allopatric congeneric species may have consequences for biodiversity through interspecific competition, hybridization, and genetic introgression. Harbor seals ( Phoca vitulina) and spotted seals ( Phoca largha) are parapatric sibling species and areas of co-occurrence at the edges of their range, such as Bristol Bay, Alaska, offer a unique opportunity to explore ecological separation and discuss potential consequences of increased range overlap resulting from retreating sea ice. Using telemetry and genetic data from 14 harbor seals and six spotted seals, we explored the ecological and genetic separation of the two species by comparing their utilization distributions, distance from haul-out, dive behavior (e.g., depth, duration, focus), and evidence of hybridization. Firstly, we show that harbor and spotted seals, which cannot be visually distinguished definitively in all cases, haul-out together side by side in Bristol Bay from late summer to early winter. Secondly, we observed subtle rather than pronounced differences in ranging patterns and dive behavior during this period. Thirdly, most spotted seals in this study remained close to shore in contrast to what is known of the species in more northern areas, and lastly, we did not find any evidence of hybridization. The lack of distinct ecological separation in this area of sympatry suggests that interspecific competition could play an important role in the persistence of these species, particularly if range overlap will increase as a result of climate-induced range shifts and loss of spotted seal pagophilic breeding habitat. Our results also highlight the added complexities in monitoring these species in areas of suspected overlap, as they cannot easily be distinguished without genetic analysis. Predicted climate-induced environmental change will likely influence the spatial and temporal extent of overlap in these two sibling species. Ultimately, this may alter the balance between current isolating mechanisms with consequences for species integrity and fitness. [ABSTRACT FROM AUTHOR]

Satellite telemetry devices collect valuable information concerning the sites visited by animals, including the location of central places like dens, nests, rookeries, or haul-outs. Existing methods for estimating the location of central places from telemetry data require user-specified thresholds and ignore common nuances like measurement error. We present a fully model-based approach for locating central places from telemetry data that accounts for multiple sources of uncertainty and uses all of the available locational data. Our general framework consists of an observation model to account for large telemetry measurement error and animal movement, and a highly flexible mixture model specified using a Dirichlet process to identify the location of central places. We also quantify temporal patterns in central place use by incorporating ancillary behavioral data into the model; however, our framework is also suitable when no such behavioral data exist. We apply the model to a simulated data set as proof of concept. We then illustrate our framework by analyzing an Argos satellite telemetry data set on harbor seals ( Phoca vitulina) in the Gulf of Alaska, a species that exhibits fidelity to terrestrial haul-out sites. [ABSTRACT FROM AUTHOR]

Monitoring the dynamics and status of populations of harbor seals (Phoca vitulina richardii) requires efficient methods for estimating population parameters from mark--resight data. We used a test set of photographs from 182 individuals identified by flipper tags, scars, or unique pelage markings to test whether individuals could be identified accurately by their ventral pelage markings; to document efficiency and misidentification error rate associated with a computer-assisted photograph-matching system; and to test for bias in mark-recapture survival estimates resulting from misidentification errors. Pelage patterns of seals that were not of dark-intermediate or intermediate color phase were unique and stable from birth until 6-8 years, and from year to year as adults. The computer-assisted system greatly improved efficiency of photograph matching: 93.3% of good photographs and 69.9% of all photographs ranked 1st, and 95.2% of good photographs ranked in the top 0.3% of the ordered list for visual checking. Additional visual matching error averaged <3.0% for good photographs, and overall misidentification error rate was low at 1.8%, due to the availability of multiple photographs for matching. Inclusion of poor-quality photographs reduced ranking success by ~20% and increased additional visual matching error up to 20%. Bias in survival estimates was -7.0% for a misidentification rate of 8.8%, but was ≤1.1% for misidentification rates of <2.7%, achieved by restricting data to only good photos. Our study suggests that estimation of misidentification error rate, inclusion of only high-quality photographs, or use of models that account for misidentification error, are required to prevent bias in mark-recapture survival estimates when using data from natural-marking studies. [ABSTRACT FROM AUTHOR]

Multiple factors complicate the analysis of animal telemetry location data. Recent advancements address issues such as temporal autocorrelation and telemetry measurement error, but additional challenges remain. Difficulties introduced by complicated error structures or barriers to animal movement can weaken inference. We propose an approach for obtaining resource selection inference from animal location data that accounts for complicated error structures, movement constraints, and temporally autocorrelated observations. We specify a model for telemetry data observed with error conditional on unobserved true locations that reflects prior knowledge about constraints in the animal movement process. The observed telemetry data are modeled using a flexible distribution that accommodates extreme errors and complicated error structures. Although constraints to movement are often viewed as a nuisance, we use constraints to simultaneously estimate and account for telemetry error. We apply the model to simulated data, showing that it outperforms common ad hoc approaches used when confronted with measurement error and movement constraints. We then apply our framework to an Argos satellite telemetry data set on harbor seals (Phoca vitulina) in the Gulf of Alaska, a species that is constrained to move within the marine environment and adjacent coastlines. [ABSTRACT FROM AUTHOR]

In recent years, concerns have increased regarding accumulation of persistent, lipophilic contaminants by marine mammals. We quantified blood levels of the two most prevalent organochlorine (OC) contaminants of the marine ecosystem in a model species, the harbor seal (Phoca vitulina) from three north-central California populations and a population in Bristol Bay, Alaska. Intensive sampling (n = 190) produced robust quantification of blood concentrations of selected PCBs and DDE, and allowed us to investigate factors affecting levels of these contaminants in seal populations with distinct environments and exposure histories. In the Alaskan samples, PCB and DDE levels were most strongly related to sex and age; OCs increased with age in males and decreased with age in females, likely due to cumulative exposure in males and load-dumping during lactation in females. Among females, an inverse relationship was observed between condition and PCB blood levels. In contrast, in the California seals, in which loads were generally much greater, pups had greater levels of PCBs and DDE than subadults and adults, suggesting stable to decreasing environmental contaminant levels. Spatial heterogeneity and seasonal differences also contributed substantially to variation among harbor seals in contaminant loads. These findings underscore the importance of accounting for demographic, geographic, seasonal, and physiological effects in toxicological studies of marine mammals. [ABSTRACT FROM AUTHOR]

Abstract: Springer et al. [Springer, A.M., Estes, J.A., van Vliet, G.B., Williams, T.M., Doak, D.F., Danner, E.M., Forney, K.A., Pfister, B., 2003. Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling? Proceedings of the National Academy of Sciences 100 (21), 12,223–12,228] hypothesized that great whales were an important prey resource for killer whales, and that the removal of fin and sperm whales by commercial whaling in the region of the Bering Sea/Aleutian Islands (BSAI) in the late 1960s and 1970s led to cascading trophic interactions that caused the sequential decline of populations of harbor seal, northern fur seal, Steller sea lion and northern sea otter. This hypothesis, referred to as the Sequential Megafaunal Collapse (SMC), has stirred considerable interest because of its implication for ecosystem-based management. The SMC has the following assumptions: (1) fin whales and sperm whales were important as prey species in the Bering Sea; (2) the biomass of all large whale species (i.e., North Pacific right, fin, humpback, gray, sperm, minke and bowhead whales) was in decline in the Bering Sea in the 1960s and early 1970s; and (3) pinniped declines in the 1970s and 1980s were sequential. We concluded that the available data are not consistent with the first two assumptions of the SMC. Statistical tests of the timing of the declines do not support the assumption that pinniped declines were sequential. We propose two alternative hypotheses for the declines that are more consistent with the available data. While it is plausible, from energetic arguments, for predation by killer whales to have been an important factor in the declines of one or more of the three populations of pinnipeds and the sea otter population in the BSAI region over the last 30 years, we hypothesize that the declines in pinniped populations in the BSAI can best be understood by invoking a multiple factor hypothesis that includes both bottom–up forcing (as indicated by evidence of nutritional stress in the western Steller sea lion population) and top–down forcing (e.g., predation by killer whales, mortality incidental to commercial fishing, directed harvests). Our second hypothesis is a modification of the top–down forcing mechanism (i.e., killer whale predation on one or more of the pinniped populations and the sea otter population is mediated via the recovery of the eastern North Pacific population of the gray whale). We remain skeptical about the proposed link between commercial whaling on fin and sperm whales, which ended in the mid-1960s, and the observed decline of populations of northern fur seal, harbor seal, and Steller sea lion some 15 years later. [Copyright &y& Elsevier]