Elu ääre peal: sisemerede hülged muutuvas kliimas

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Miljonite aastate jooksul on mereimetajad asustanud kogu Maa geograafiliste ja klimaatilised piirkondade mitmekesisuse, paljud tänapäevased hülgeliigid on levinud ühtlaselt kogu polaarmerede ulatuses. Samas on jääaja järgne maatõus või teised muutused vangistanud mitmed hülgeasurkonnas osaliselt või täiesti maailmameredest eraldatud veekogudesse kus nad on kohastunud elama aastaajaliselt väga laialt vahelduvates tingimustes. Ühest küljest pakub selline olukord mitmekesiseid elupaiku kuid teisalt esitab tõsise väljakutse nende hüljeste kohastumisvõimele. Käesolevas väitekirjas analüüsitakse kliimamuutuste võimalikke mõjusid Läänemere hallhülgele (Halichoerus grypus), viigerhülge (Pusa hispida botnica) ning Kaspia hülge (Pusa caspica) kohasusele ja elujäämisvõimalustele. Väitekirja osaks olevad neli teaduspublikatsiooni moodustavad sellele analüüsile tugeva põhja, kuna nendes uuringutes on kaetud ajalisel, ruumiliselt või sisuliselt mitmed kliimamuutustega seotud võtmeteemad. Võimaliku üleilmse soojenemise jätkudes pakuvad nad viiteid aegadesse kui see muutus end veel ei ilmutanud (II, III, IV) või keskenduvad ökoloogilistele väljakutsetele mis Maa soojenedes jõudu koguvad (I, ka II-IV). Kõik käsitletud hülged on enamal või vähemal määral jääga seotud, kuna nende levilad külmuvad talvekuudel täielikult või osaliselt. Jää moodustab uuritud liikidele ajutise kuid kriitiliselt olulise elupaiga. Käesolevas töös on hüljeste levikut, sigimisstrateegiaid ja edukust käsitletud talve karmuse ning selle võimalike muutuste valguses. Tänapäevane looduslik tasakaal on kujundatud pikaajaliste keskmiste ökoloogiliste tingimuste poolt, samas näitavad kliimamudelid lähiajal temperatuuri tõusu. Jääolude muutused soojenevas kliimas toovad kaasa kriitilise olukorra Läänemere lõunapoolsetele viigerhüljestele ja kaspia hüljestele. Jääpuudus suunab hüljeste leviku aladele kus keskkonnatingimused, mõõdetuna nii füüsiliste kui ka bioloogiliste näitajate kaudu, on praegusest ebasoodsamad. Hüljeste sigimisalad surutakse kokku ning konservatiivne, jääga seotud sigimisstrateegia võib osutuda oluliseks negatiivseks teguriks kiirete, vaid mõnd põlvkonda hõlmavate muutuste keerises. Hallhüljes võib tänu oma paindlikumale poegimisviisile olla vähem mõjutatud kuid ka nende puhul ahendab jää puudumine ning merepinna tõus selle liigi tänast poegimisaegset levikuala. Kõigile kolmele vaadeldud hülgeliigile mõjub pärssivalt jää ebastabiilsusega kaasnev järglaste madalam kvaliteet. Jääpindala kahanemine teeb hülged haavatavaks ka maismaakiskjate ja rööveluviisiliste lindude poolt. Kliimast tulenevaid keskkonnamuutusi võimendavad inimtekkelised tegurid, näiteks reostus, intensiivne kalapüük ning häirimine. Lisandudes keskkonnast johtuvale stressile kahandab inimtegevus oluliselt sisemeredes elavate loivaliste tulevikuväljavaateid.Over the millions of years marine mammals have explored the full range of climatic and geographic latitudes of the Earth, at present several seal species show circumpolar distribution ranges. Post-glacial rebounds or other geo-morphological changes during have locked several seal populations into fully or partly isolated water bodies where they are adapted to live in seasonally widely fluctuating environments which in one hand provide diverse habitat but in the other hand challenge the adaptivity of the seals. This thesis is discussing the landlocked seals in their captive habitats and ecological implications therein. In this thesis the possible impacts of climate change on the fitness and survival of the land-locked grey seal (Halichoerus grypus) and ringed seal (Pusa hispida botnica) in the Baltic Sea and the Caspian seal (Pusa caspica), inhabiting the Caspian Sea are analyzed. The four original publications form a firm basis to approach this analysis, as they are covering spatially, temporally or topically several key aspects relevant to the climate change. In the context of probably ongoing global warming they provide reference to the times when the change was not expressed yet (II, III, IV) or focus on ecological challenges which will gather force with warming Earth (I, also II-IV). All the involved species and subspecies are to greater or lesser extent ice-related as their distribution ranges freeze over partially or wholly during the winter months. Ice forms a temporary critical habitat to the study species so winter severity and its potential changes are discussed in the context of seal distribution, breeding strategy and success. The current ecological balance is determined by long term average ecological conditions while climatic models show increasing temperatures in close future. Change of the ice conditions in warming climate would bring about critical conditions for the southern populations of the Baltic Ringed seal and the Caspian seals. Deficit of ice will lead to change of seal distribution to areas where the habitat quality, measured by both physical and biological parameters is lower compared to the present situation. The seals’ breeding area will become restricted and thus the conservative, ice related breeding strategy of the seals appears to become a major negative factor during current changes which take place during only some generations. The grey seal would be less affected due to plasticity in breeding strategies, but loss of the ice platform and access to several current land breeding sites would also restrict the breeding range of the species, all the three species would lose in breeding success through reduced offspring quality on unstable ice. The reduced ice cover makes the seals vulnerable to terrestrial and avian predation. Climatic changes in the environment are amplified by the anthropogenic factors like pollution, intensive fishing and disturbance which add to the environmental stress and challenge further the survival of the land-locked seal populations

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

Assessment of impacts and potential mitigation for icebreaking vessels transiting pupping areas of an ice-breeding seal

Icebreaker operations in the Arctic and other areas are increasing rapidly to support new industrial activities and shipping routes, but the impact on pinnipeds in these habitats is poorly explored. We present the first quantitative study of icebreakers transiting ice-breeding habitat of a phocid seal and recommendations for mitigation. Impacts were recorded from the vessel bridge during seven ice seasons 2006–2013, for Caspian seals (Pusa caspica) breeding on the winter ice-field of the Caspian Sea. Impacts included displacement and separation of mothers and pups, breakage of birth or nursery sites and vessel-seal collisions. The flight distance of mothers with pups ahead was < 100 m, but measurable disturbance occurred at distances exceeding 200 m. Separation distances of pups from mothers were greatest for seals < 10 m to the side of the vessel, and declined with increasing distance from the vessel. The relative risk of separation by ≥ 20 m was greatest for distances < 50 m from the vessel path. Seals on flat ice were more likely to be separated or displaced by ≥ 20 m than seals in an ice rubble field. The relative risk of vessel collisions with mothers or pups was significantly greater at night when breaking new channels (12.6 times), with vessel speeds ≥ 4 kn (7.8 times). A mitigation hierarchy is recommended for the Caspian Sea which could be applied to Arctic pinnipeds, including reducing icebreaker transits during critical periods, and using data from aerial surveys to plan routes to minimise encounters with seals. Where pre-emptive avoidance is not possible, recommendations include maintaining a safe separation from breeding seals at least 50 m beyond the distance at which measurable disturbance occurs, speed limits, use of thermal imaging at night, dedicated on-board Seal Observers, and training of vessel officers to take effective reactive measures

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