Results of instrumental aerial survey of ice-associated seals on the ice in the Okhotsk Sea in May 2013

Populations of ice-associated seals in the Okhotsk Sea are assessed using modern instrumental aerial technique. The aerial survey was conducted over a part of the ice-covered area of the Sea on May 1-9, 2013 by means of thermal scan and visual digital photography from the aircraft-laboratory An-38 «Vostok». The ice covered area of the Okhotsk Sea in the time of survey was estimated as 242,000 km2, and 2,993 km2 of it was covered by survey transects with total length 5,617 km. The number of animals on all transects within the equipment swath was counted. Four seal species were identified: bearded, spotted, ribbon, and ringed seals, and their number and distribution were determined. The infra-red scanner recorded 5,730 seals on the ice and 4,360 these animals were photographed including 844 ringed seals, 453 bearded, 721 spotted, 1,805 ribbon, 435 pups non-identified to the species, and 102 non-identified to species adult seals. These assessments were extrapolated over the whole ice-covered area of the Okhotsk Sea using a linear model framework, and the following estimations of the species total abundance were presented (95 % confidence intervals in brackets): 88,253 (64,120-130,320) ringed seals, 39,743 (27,868-60,026) bearded seals, 181,179 (118,392-316,995) ribbon seals, and 84,356 (55,172-113,540) spotted seals. A database on all recorded seals with their «portrait-photos» and accompanying information is created on materials of the aerial survey. The developed instrumental technology can be used as a basis for wider aerial surveys of ice-associated seals in the North Pacific

Distribution of Hauled-Out Ladoga Ringed Seals (Pusa hispida ladogensis) in Spring 2012

The spatial distribution and habitat selection of the Ladoga ringed seal (Pusa hispida ladogensis), an endangered freshwater seal, are poorly understood, particularly for the ice-covered period. A fixed-wing, strip-transect aerial survey conducted in early April 2012, before the Lake Ladoga breakup, provided data on seal density and distribution throughout the lake in relation to several environmental covariates: depth, distance to shore, recreational ice-fishing activity, and ice type. A predictive model was applied to combinations of covariates to estimate the total number of seals hauled out on ice of Lake Ladoga. The model estimate was 5068 (95% CI: 4026 – 7086) seals over an area of 16 827 km2. The mean observed seal density was 0.29 seals/km2 (SD = 0.351, range from 0 to 8.61), and density was highest (> 1 seal/km2) in regions that were relatively shallow (< 50 m). Densities appeared to increase with distance from shore but dropped off again at the longest distances. The average density was lower in fast ice habitats (0.13 seals/km2) than in drifting pack ice habitats (0.44 seals/km2). Relatively high seal densities observed in “ice edge” zones (0.26 seals/km2) could be explained by the ice formation pattern of large ridged and hummocked areas in the transition zone between shorefast ice and secondary ice. The presence of fishermen had a highly significant negative effect on seal presence (β = −7.8, p = 0.0014), resulting in a nearly twofold decrease in seal density in shorefast ice habitats (0.09 seals/km2 in fishing areas and 0.15 seals/km2 in areas without fishing activity). An extensive winter recreational fishery, in combination with potential negative trends in ice conditions on the lake, might reduce the amount of suitable habitat for the Ladoga ringed seal in the near future.La répartition spatiale et la sélection de l’habitat du phoque marbré de Ladoga (Pusa hispida ladogensis), phoque d’eau douce en voie de disparition, ne sont pas bien comprises, surtout en ce qui a trait à la période d’englacement. Un levé aérien à base de transects en bandes effectué au début du mois d’avril 2012, avant la débâcle du lac Ladoga, a permis d’obtenir des données sur la densité et la répartition du phoque à l’échelle du lac par rapport à plusieurs covariables environnementales : la profondeur, la distance jusqu’au rivage, la pêche récréative sous la glace et le type de glace. Un modèle prédictif a été appliqué à des combinaisons de covariables afin d’estimer le nombre total de phoques qui se hissent sur la glace du lac Ladoga. Le modèle a permis d’obtenir une estimation de 5 068 (IC de 95 % : 4 026-7 086) phoques dans une aire de 16 827 km2. La densité moyenne des phoques observés était de 0,29 phoque/km2 (écart-type = 0,351, écart allant de 0 à 8,61), et la densité était plus élevée (> 1 phoque/km2) dans les régions relativement peu profondes (< 50 m). Les densités semblaient augmenter en fonction de la distance du rivage, mais elles baissaient de nouveau lorsque les distances étaient plus longues. La densité moyenne était moins élevée dans les habitats à glace rapide (0,13 phoque/km2) que dans les habitats à banquises en dérive (0,44 phoque/km2). Les densités de phoques relativement élevées qui ont été observées dans les zones de « lisières de glaces » (0,26 phoque/km2) pouvaient s’expliquer par le modèle de la formation de glace des grandes zones de glaces tourmentées et moutonnées faisant partie de la zone de transition entre la banquise côtière et la glace secondaire. La présence de pêcheurs avait un effet considérablement négatif sur la présence des phoques (β = −7,8, p = 0,0014), ce qui se traduisait par une diminution de presque la moitié de la densité de phoques dans les habitats à banquise côtière (0,09 phoque/km2 dans les zones de pêche et 0,15 phoque/km2 dans les zones où il n’y avait pas de pêche). L’intensité de la pêche récréative en hiver, alliée aux tendances potentiellement négatives en matière d’état des glaces du lac, pourrait avoir pour effet de rapetisser la quantité d’habitat habitable par le phoque marbré de Ladoga dans un avenir rapproché

Data on phocid seals natural history parameters and code for Bayesian hierarchical models

The datafile was compiled based on publicly available published sources cited in Trukhanova et al 2018 Appendix S1. The associated R files contain a code for data analysis. For detailed data description please see README file

Data from: Taxonomy-based hierarchical analysis of natural mortality: polar and sub-polar phocid seals

Knowledge of life‐history parameters is frequently lacking in many species and populations, often because they are cryptic or logistically challenging to study, but also because life‐history parameters can be difficult to estimate with adequate precision. We suggest using hierarchical Bayesian analysis (HBA) to analyze variation in life‐history parameters among related species, with prior variance components representing shared taxonomy, phenotypic plasticity, and observation error. We develop such a framework to analyze U‐shaped natural mortality patterns typical of mammalian life history from a variety of sparse datasets. Using 39 datasets from seals in the family Phocidae, we analyzed 16 models with different formulations for natural morality, specifically the amount of taxonomic and data‐level variance components (subfamily, species, study, and dataset levels) included in mortality hazard parameters. The highest‐ranked model according to DIC included subfamily‐, species‐, and dataset‐level parameter variance components and resulted in typical U‐shaped hazard functions for the 11 seal species in the study. Species with little data had survival schedules shrunken to the mean. We suggest that evolutionary and population ecologists consider employing HBA to quantify variation in life‐history parameters. This approach can be useful for increasing the precision of estimates resulting from a collection of (often sparse) datasets, and for producing prior distributions for populations missing life‐history data

The commercial harvest of ice-associated seals in the Sea of Okhotsk, 1972-1994.

Sealing log books from 75 out of 79 commercial harvest cruises carried out between 1972 and 1994 in the Sea of Okhotsk, Russia, were analyzed to describe spatial and temporal allocation of ice-associated seal harvest effort, species composition of catches, total harvest rates, and related parameters for species including ringed (Pusa hispida), ribbon (Histriophoca fasciata), bearded (Erignathus barbatus) and spotted (Phoca largha) seal. Variations in catch per unit effort were explored in relation to year, sea ice conditions, day of the year, and geographic location. In most years, the harvest was predominantly represented by ringed seals (mean = 0.43, range 0.25-0.67), followed by ribbon (mean = 0.31, range 0.15-0.43), spotted (mean = 0.19, range 0.11-0.35) and bearded seals (mean = 0.07, range 0.03-0.14). The struck-and-lost percentages were as high as 30-35% for ringed, bearded and spotted seals and 15-20% for ribbon seals. Catch per unit effort (number of seals/skiff*day) for ringed, ribbon, and spotted seals had a similar seasonal pattern with a distinct spike in catches for spotted seals in the first week of May, for ribbon seals in the last week of May, and for ringed seals in the second week of June. Catches of bearded seals showed a less pronounced temporal structure with a gradual increase toward the end of the harvest season in the majority of years. Spatial distribution of harvest effort followed closely with seal distribution obtained from aerial surveys. These data could be used as a source of information on seal herd location throughout the breeding and molting seasons and for more complex demographic or life-table models. We did not find any evidence of the decline of catch per unit effort over the study period. Timely introduction of state regulations and efficient harvest management apparently prevented severe depletion of ice-associated seal populations in the Sea of Okhotsk during the periods of their intense exploitation

Observed catch per unit effort for 1972–1994 combined (right Y-axis) plotted against ordinal day.

<p>The boxes show the number and range of 50% of observations in each group; bold horizontal lines in boxes indicate median number of seals caught, dots indicate outliers in the data. The left Y-axis is for the GAM smooths for each year and multi-year mean. Note that both Y-axis scales vary with species.</p

Seal harvest locations in the Sea of Okhotsk in April-July, 1972–1994 combined.

<p>Sea ice extent [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182725#pone.0182725.ref012" target="_blank">12</a>] is provided for illustrative purposes for the year of 1980 (high ice year).</p

GAM fit and 95% CI for mean observed catch per unit effort, 1972–1994.

<p>Note that the Y-axis scales vary with species.</p