•Underwater noise was recorded from an operating drillship in deep water in the Arctic.•Noise was detectable above ambient at ranges up to 38km.•Back-calculated source levels were up to 190dB re 1μPa ...(rms), depending on activities on the ship.•The noise contained substantial energy at frequencies audible to marine mammals, especially large baleen whales.
Wideband sound recordings were made of underwater noise emitted by an active drillship, Stena Forth, working in 484m of water in Baffin Bay, western Greenland. The recordings were obtained at thirty and one-hundred meters depth. Noise was recorded during both drilling and maintenance work at ranges from 500m to 38km. The emitted noise levels were highest during maintenance work with estimated source levels up to 190dB re 1μPa (rms), while the source level during drilling was 184dB re 1μPa (rms). There were spectral peaks discernible from the background noise to ranges of at least 38km from the drillship with the main energy below 3kHz. M-weighted sound pressure levels were virtually identical to broadband levels for low-frequency cetaceans and about 5dB lower for high-frequency cetaceans. Signals from the dynamic positioning system were clearly detectable at ranges up to two km from the drillship.
The grey seal became locally extinct in the southern Baltic Sea, Danish Straits and Kattegat in the early 1900s after prolonged culling campaigns. Here, we combine national monitoring and anecdotal ...data from Denmark, Sweden, Germany and Poland to report on the grey seal's recolonisation of those areas and the initial reestablishment of breeding colonies. Grey seal occurrence has steadily increased since year 2003 as evidenced by the coordinated Baltic Sea moult censuses. At the first census in 2003, there were 146 grey seals along the southern Baltic coasts of Sweden and Denmark, ca 1% of the total Baltic Sea population count. Since 2015, this has increased to 2000–2600 grey seals, or ca 7% of the total population count. Since the local extinction, there have been sporadic breeding events in the 1940s on sea ice around Bornholm and in the 1980s and 1990s on haul-outs in Kattegat. In 2003, the first two pups in the southern Baltic Sea were recorded at Rødsand, Denmark. This is to date the only site in the southern Baltic Sea with regular annual pupping since the recolonisation. Since 2000, there have also been sporadic breeding events in Danish Kattegat, southern Sweden, Poland and Germany. At Rødsand, there have been at least 3–10 pups recorded every year since initiation of monitoring in 2011, with an increasing tendency until 2017 with 10 pups counted, which subsequently decreased to 5–6 pups annually in 2018–2020. Compared to recolonising events in the Atlantic, the numbers of pups are low. This may be caused by differences in population dynamics, recolonisation distances, habitat and mortality and effects of rehabilitation programmes. It is likely that the breeding distribution will spread throughout the southern Baltic, Danish Straits and Kattegat if appropriate protection measures of seals and haul-outs are installed.
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.
One of the largest ever passive acoustic monitoring studies has been carried out by eight Baltic Sea nations to estimate the abundance of the critically endangered 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, an abundance of 71–1105 individuals (95% CI, point estimate 491) was estimated during May–October within the population's proposed management border. The small abundance 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.
Monitoring abundance and population trends of small odontocetes is notoriously difficult and labor intensive. There is a need to develop alternative methods to the traditional visual line transect ...surveys, especially for low density areas. Here, the prospect of obtaining robust density estimates for porpoises by passive acoustic monitoring (PAM) is demonstrated by combining rigorous application of methods adapted from distance sampling to PAM. Acoustic dataloggers (T-PODs) were deployed in an area where harbor porpoises concurrently were tracked visually. Probability of detection was estimated in a mark-recapture approach, where a visual sighting constituted a "mark" and a simultaneous acoustic detection a "recapture." As a distance could be assigned to each visual observation, a detection function was estimated. Effective detection radius of T-PODs ranged from 22 to 104 m depending on T-POD type, T-POD sensitivity, train classification settings, and snapshot duration. The T-POD density estimates corresponded to the visual densities derived concurrently for the same period. With more dataloggers, located according to a systematic design, density estimates would be obtainable for a larger area. This provides a method suitable for monitoring in areas with densities too low for visual surveys to be practically feasible, e.g., the endangered harbor porpoise population in the Baltic.
Several studies have shown that pingers mitigate porpoise bycatch and thus pinger use is now mandatory in some fisheries—although the long-term effects of pinger exposure on porpoises have not been ...well studied. The effects of 2 types of pingers (Airmar: 10 kHz tone; SaveWave Black Saver: 30–160 kHz sweep) on the presence of wild harbour porpoises, Phocoena phocoena, were investigated in 2 areas. Pinger spacing within the areas was similar to that used in commercial fisheries. Two scenarios were tested: (1) pingers were periodically activated and deactivated during 6 periods resembling the deployment and recovery of nets in a gillnet fishery, and (2) pingers were active continuously for 28 d. Acoustic dataloggers (T-PODs) were deployed, 4 within the pinger areas and 3 in control areas, and detected porpoise echolocation activity throughout the entire study. During the periodic-exposure scenario, the porpoise detection rate was reduced by 56% when pingers were active. The reduction was larger for the SaveWave pingers (65%) than for the Airmar pingers (40%). There was a tendency for the encounter rate to increase after the first 2–4 periodic exposures, which could indicate gradual habituation. During the continuous-exposure scenario, the detection rate was reduced by 65% throughout the 28 d with no sign of habituation. In the control areas (2.5, 3 and 5 km distant), neither a decrease nor an increase in detection rate was observed, suggesting that porpoises were displaced either <2.5 km or >5 km away. If pingers are used as deterrent devices, the impact of habitat exclusion must therefore be considered concurrently with mitigation of bycatch, especially when regulating fisheries in Marine Protected Areas.
The critically endangered Spitsbergen stock of bowhead whale (
Balaena mysticetus
) seems to be increasing. However, research effort has also been increasing confounding a firm conclusion. A ...systematic aerial survey for walrus (
Odobaenus rosmarus
), applying distance sampling methodology in part of the Northeast Water Polynya (NEW), revealed a ‘bycatch’ of several observations of bowhead whales, which resulted in an estimated abundance of 102 (95 % CI 32–329) individuals. This is the largest abundance of bowhead whales reported from the Greenland Sea since the days of whaling in the sixteenth to seventeenth centuries. The NEW was inaccessible to vessels during the whaling period because of heavy pack ice, and it is only recently that researchers have visited this area; thus only a few sightings of bowhead whales within the NEW exist prior to the survey in 2009. The NEW may nevertheless be one of the most important summering grounds for the Spitsbergen stock, and the whales may benefit from advection of calanoid copepods from the productive deep basins along the coast of Svalbard east of the NEW. This discovery provides renewed hope for the Spitsbergen stock of bowhead whales that until now has shown only inconclusive signs of recovery despite more than 100 years of protection from whaling.
•We investigated mercury health risks in the Baltic, Greater North Sea and North Atlantic.•23% of the marine mammals had Hg-concentrations in the High & Severe Risk Category.•The corresponding ...percentages for birds, fish and bivalves were 2.7, 25 and 8.0%•The estimated risk for Baltic populations was not higher that the bordering waters.•Baltic Sea has improved with respect to mercury exposure over the last decades.
A wide range of species, including marine mammals, seabirds, birds of prey, fish and bivalves, were investigated for potential population health risks resulting from contemporary (post 2000) mercury (Hg) exposure, using novel risk thresholds based on literature and de novo contamination data. The main geographic focus is on the Baltic Sea, while data from the same species in adjacent waters, such as the Greater North Sea and North Atlantic, were included for comparative purposes. For marine mammals, 23% of the groups, each composing individuals of a specific sex and maturity from the same species in a specific study region, showed Hg-concentrations within the High Risk Category (HRC) and Severe Risk Category (SRC). The corresponding percentages for seabirds, fish and bivalves were 2.7%, 25% and 8.0%, respectively, although fish and bivalves were not represented in the SRC. Juveniles from all species showed to be at no or low risk. In comparison to the same species in the adjacent waters, i.e. the Greater North Sea and the North Atlantic, the estimated risk for Baltic populations is not considerably higher. These findings suggest that over the past few decades the Baltic Sea has improved considerably with respect to presenting Hg exposure to its local species, while it does still carry a legacy of elevated Hg levels resulting from high neighbouring industrial and agricultural activity and slow water turnover regime.
The white-beaked dolphin (Lagenorhynchus albirostris) is the second most frequently stranded cetacean species along the Danish coastline. The northern North Sea, the Skagerrak, the Kattegat and the ...Danish straits are part of the species distributional range. Here, we present eight incidents of breeding activity for the white-beaked dolphin in the inner Danish waters, reviewed from yearly reports made by the National Contingency Plan concerning strandings of marine mammals in Denmark from 2009 to 2023, Danish Wildlife Diseases Surveillance reports from 2014 to 2023 and the citizen science database Naturbasen in the period 2002 to 2023. Three pregnant females, three lactating females and one calf were found stranded in the inner Danish waters. Besides this, there have been live sightings of a female with a newborn calf. We conclude that the white-beaked dolphin is breeding in the inner Danish waters.
Pile driving of large steel monopiles in offshore waters has increased rapidly in recent years due to the expanding development of offshore wind energy. In particular, Phocoena phocoena (harbor ...porpoise) has been the focus of attention with respect to a possible negative impact. Impact pile driving, where a large steel monopile is driven 20-30 m into the seabed, is capable of generating very loud sound pressures, exceeding 230 dB re 1 μPa peak-peak in source levels and detectable at distances of tens of kilometers (Bailey et al. 2010). Such high sound pressures, coupled with the repetitive emission of sounds (1–2 strokes/s) at a high duty cycle (10%) gives the potential for exposing nearby animals to very high and potentially damaging sound exposure levels (Gordon et al. 2009). Besides the potential to inflict acute injury, the pile-driving noise has the potential to affect behavior of marine mammals over an even larger area.
The rapidly changing Arctic marine ecosystems face new challenges and opportunities that are increasing and shifting governance needs in the region. A group of economists, ecologists, biologists, ...political scientists and resource managers met in Stockholm, SE, Sept 4–6, 2014 to discuss the governance of Arctic marine resources in a spatial context. We report on the findings here.
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