Seasonal Activity Budget of Adult Baltic Ringed Seals

Although ringed seals are important components in oceanic and fresh water ecosystems at high latitudes, little is known about how they exploit these harsh environments. Seasonal activity and diving behaviour of 19 adult Baltic ringed seals were studied by satellite telemetry. We elaborated an activity budget for ten months of the year, extending over the period from moult to the breeding season. Seals from three main regions showed explicit site fidelity and the distributions of animals tagged from different areas did not overlap, suggesting separate stocks. Both the mean duration and the mean depth of dives peaked in June and July. Seals spent 70% (females) to 85% (males) of their time diving in June and July which decreased to 50% in late autumn. Less than one percent of dives exceeded 10 min in females, while 10% of male dives lasted longer than 10 min in June to September. Less than one percent of dives lasted for more than 25 min. Both females and males were most active during day time and hauled out predominantly during the night. Activity patterns during the summer are suggested to be correlated to energy accumulation and prey availability. The information on seasonal activity budget is crucial for developing population energetic models where interactions between ringed seals and other trophic levels can be evaluated

Estimating the abundance of the critically endangered Baltic Proper harbour porpoise (Phocoena phocoena) population using passive acoustic monitoring

The SAMBAH project was funded by the LIFE+ program of the European Commission (LIFE08 NAT/S/000261) and co-funded by Bundesamt für Naturschutz, Germany (SAMBAH II 5 Vw/52602/2011-Mar 36032/66); Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit, Germany (COSAMM FKZ 0325238); Carlsbergfondet, Denmark (CF16-0861); European Association of Zoos and Aquaria, The Netherlands; Główny Inpektorat Ochrony Środowiska, Poland; Havs-och Vattenmyndigheten, Sweden; Instytut Meteorologii i Gospodarki Wodnej - Państwowy Instytut Badawczy, Poland; Japanese Science and Technology Agency-CREST, Japan (7620-7); Kolmårdens Djurpark, Sweden; Maailman Luonnon Säätiö (WWF) Suomen Rahasto, Finland; Miljøministeriet, Denmark; Miljø- og Fødevareministeriet, Denmark (SN 343/SN-0008); Narodowy Fundusz Ochrony Środowiska i Gospodarki Wodnej, Poland (561/2009/Wn-50/OP/RE-LF/D); Naturvårdsverket, Sweden; SNAK Ph.D. School, Aarhus University, Denmark (91147/365); Tampereen Särkänniemi Ltd., Finland; Turun ammattikorkeakoulu Oy, Finland; Uniwersytet Gdański, Poland; Wojewódzki Fundusz Ochrony Środowiska i Gospodarki Wodnej w Gdańsku, Poland; and Ympäristöministeriö, Finland.Knowing the abundance of a population is a crucial component to assess its conservation status and develop effective conservation plans. For most cetaceans, abundance estimation is difficult given their cryptic and mobile nature, especially when the population is small and has a transnational distribution. In the Baltic Sea, the number of harbour porpoises (Phocoena phocoena) has collapsed since the mid-20th century and the Baltic Proper harbour porpoise is listed as Critically Endangered by the IUCN and HELCOM; however, its abundance remains unknown. Here, one of the largest ever passive acoustic monitoring studies was carried out by eight Baltic Sea nations to estimate the abundance of the Baltic Proper harbour porpoise for the first time. By logging porpoise echolocation signals at 298 stations during May 2011-April 2013, calibrating the loggers' spatial detection performance at sea, and measuring the click rate of tagged individuals, we estimated an abundance of 71-1105 individuals (95% CI, point estimate 491) during May-October within the population's proposed management border. The small abundance estimate strongly supports that the Baltic Proper harbour porpoise is facing an extremely high risk of extinction, and highlights the need for immediate and efficient conservation actions through international cooperation. It also provides a starting point in monitoring the trend of the population abundance to evaluate the effectiveness of management measures and determine its interactions with the larger neighboring Belt Sea population. Further, we offer evidence that design-based passive acoustic monitoring can generate reliable estimates of the abundance of rare and cryptic animal populations across large spatial scales.Publisher PDFPeer reviewe

Population size and distribution of the Baltic ringed seal (<i>Phoca hispida botnica</i>)

The study reviews earlier investigations on the distribution and abundance of ringed seals (Phoca hispida botnica) in the Baltic and presents the first statistically robust results for the entire area. A critical review of earlier counts of ringed seals from the Gulf of Riga and the Gulf of Finland reveals grossly exaggerated population estimates in these regions. This is confirmed by results from the first comprehensive surveys in the entire area carried out during 1994-1996. The estimated hauled-out Baltic population in 1996 was about 5,510 ± 42% (± 95% confidence interval). Of this estimate 3,945 ± 1,732 (70%) were in the Gulf of Bothnia, 1,407 ± 590 (25%) in the Gulf of Riga and about 150 (5%) in the Gulf of Finland. Numbers in the Gulf of Bothnia have increased since 1988, but there are no data on trends in other areas, although numbers are low and half the local population in the Gulf of Finland may have died in a mass mortality in the autumn of 1991

Estimates of the size of the Baltic grey seal population based on photo-identification data

The size of the year 2000 summer population of grey seals in the Baltic Sea was estimated using identification of individual seals from photographs taken over a period of 6 years. Photos were taken at haul-out sites within all major grey seal areas in the semi-closed Baltic Sea. The point estimate is 15,631, based on a value for annual survival of identification markings of 0.904, which was also estimated using the photo-id data, with 95% confidence limits from 9,592 to 19,005. The estimate is subject to an unknown, but probably small, upward bias resulting from the risk of failure to identify all individuals in the photographs used for the analysis. An estimated minimum of 15,950 seals were counted at moulting haul-outs in 2003, which thus provides a lower bound on the population size in that year and represents 80% of the photo-id point estimate

Diurnal haul-out behaviour of male and female ringed seals in the Gulf of Finland and Estonian coastal waters.

<p>Data from “Timelines” pooled for main seasons: Summer (May–Aug), Autumn (Sep–Nov) and Winter (Dec–March).</p

Weight of ringed seal females caught in the open water season.

<p>Filled circles refer to data from this study (PS), and open circles are data compiled from the seal data base at the Swedish Museum of Natural History (NRM). A linear regression of pooled data (y = 9.16x−7.97, R² = 0.83) suggest that ringed seal females gain 9.2 kg per month from May up to December.</p

Activity budget for male and female ringed seals in the Gulf of Finland and Estonian coastal waters (pooled data).

<p>The proportion of time diving deeper than 2 m, time spent at surface, and time hauled out from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002006#pone-0002006-g006" target="_blank">figs 6</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002006#pone-0002006-g008" target="_blank">8</a>, and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002006#pone-0002006-g011" target="_blank">11</a>. “Shallow” denotes dives in the interval 1–2 m, and is given by 100% minus the sum of all other activities.</p

Activity budget for female ringed seals in the Bothnian Bay.

<p>Data pooled for four animals. Percentages of time diving (>2 m) extracted from time-at-depth data, and proportions of time hauled out from the “SLR”.</p

Duration (min) of dives of Baltic ringed seals (excluding females from the Bothnian Bay).

<p>About 70% of male dives lasted longer than 2 min in early summer, which decreased to 30% in October. An increase to about 50% was seen up to December, after which dive durations decreased markedly up to March. A similar pattern was seen in females, but dives lasted longer in December and January. About 10% of male dives lasted longer than 10 min in the period from June to September, compared with 0.8% for females.</p