Movements Of Seals Research Articles

Biologging reveals rapid movements of harbour seals between freshwater and marine habitats in the subarctic

Biologging tools can provide invaluable information on the movement and behaviour of animals, facilitating the elucidation of ecological dynamics, especially for wide-ranging species, and supporting conservation and management efforts. Harbour seals (Phoca vitulina) exhibit extensive habitat plasticity in their vast range across the northern hemisphere, with likely recent increases in abundance at northern latitudes, yet details of their movement behaviour in subarctic areas remain largely unknown. We used satellite-telemetry data, including nearly 5,000 locations and over 12,000 dives, obtained from six harbour seals tagged in western Hudson Bay from 2021 to 2023, to address the knowledge gap on their movement behaviour between marine and freshwater habitats in subarctic regions. We document the behavioural patterns, transit speeds, and diverse aquatic system usage, including detailed records of a harbour seal track traversing over 170 km upriver on three separate trips along the Seal River, Canada. Notably, we observed a rapid downstream transit from the Seal River to Hudson Bay, covering 214 km within a single day. Additionally, we highlight the prevalence of short dive durations in the Seal and Churchill Rivers, in contrast to longer dive durations in Hudson Bay. These insights complement existing evidence of harbour seal occurrences and river use at northern latitudes, as well as enhance our understanding of harbour seal movement ecology within Hudson Bay which can be used to better inform conservation and management strategies between connected freshwater and marine environments in the Arctic.

Foraging habits of Northwest Atlantic hooded seals over the past 30 years: Future habitat suitability under global warming.

The Arctic is a global warming 'hot-spot' that is experiencing rapid increases in air and ocean temperatures and concomitant decreases in sea ice cover. These environmental changes are having major consequences on Arctic ecosystems. All Arctic endemic marine mammals are highly dependent on ice-associated ecosystems for at least part of their life cycle and thus are sensitive to the changes occurring in their habitats. Understanding the biological consequences of changes in these environments is essential for ecosystem management and conservation. However, our ability to study climate change impacts on Arctic marine mammals is generally limited by the lack of sufficiently long data time series. In this study, we took advantage of a unique dataset on hooded seal (Cystophora cristata) movements (and serum samples) that spans more than 30 years in the Northwest Atlantic to (i) investigate foraging (distribution and habitat use) and dietary (trophic level of prey and location) habits over the last three decades and (ii) predict future locations of suitable habitat given a projected global warming scenario. We found that, despite a change in isotopic signatures that might suggest prey changes over the 30-year period, hooded seals from the Northwest Atlantic appeared to target similar oceanographic characteristics throughout the study period. However, over decades, they have moved northward to find food. Somewhat surprisingly, foraging habits differed between seals breeding in the Gulf of St Lawrence vs those breeding at the "Front" (off Newfoundland). Seals from the Gulf favoured colder waters while Front seals favoured warmer waters. We predict that foraging habitats for hooded seals will continue to shift northwards and that Front seals are likely to have the greatest resilience. This study shows how hooded seals are responding to rapid environmental change and provides an indication of future trends for the species-information essential for effective ecosystem management and conservation.

Haul-out patterns of the Baltic grey seal (Halichoerus grypus) in the suburbs of a metropolis

In this study, we investigated the haul-out patterns of the Baltic grey seal in the coastal area adjacent to the metropolitan city, Saint Petersburg, during the ice-free seasons of 2017-2022. Grey seals occupied stony banks near Kotlin Island, in the easternmost part of the Gulf of Finland. The censuses were carried out from the island shore during evening hours. The number of seals reached 70 during the survey. Contrary to the common trend reported in similar studies, the annual minimum in seal abundance (May and June) coincided with the peak of moulting. Active use of the haul-out site was observed between July and November, implying that eastward movements of the grey seals take place in the Gulf of Finland in the post-moulting period. Wind speed and sea state interfered with the seal hauling out throughout the year, whereas the relationship with air temperature varied seasonally. Cloud cover, atmospheric pressure, wind direction and sea level had no impact on the seal number, though the fluctuations in sea level reduced the haul-out space. The tendency of the seals to haul out towards and after the sunset was determined. The most frequent sources of human disturbance were light planes (0.45 ± 0.12 confidence interval, per count) and powerboats (0.41 ± 0.14 confidence interval, per count), but only the powerboats significantly decreased the seal number. We found that the seals used the banks concurrently with seabirds. The area of Kotlin Island presumably attracts the seals by the diversity of prey items in the estuary of the Neva River. Establishing of a marine protected area and physical marking of the water space around the haul-out site are recommended.

Movements and spatial usage of harbour seals in the Elbe estuary in Germany

Harbour seals are top predators in the North Sea and regarded as sentinels for ecosystem health. A few hundred also occur in adjacent estuaries, such as the Elbe estuary, Germany. However, only little is known about how these animals use this dynamic tidally influenced habitat, which has been under high anthropogenic pressure for decades. In this context, nine harbour seals (Phoca vitulina) from the Elbe estuary were equipped with biotelemetry devices to track their movements over multiple months. Harbour seal movements were characterised by short trips (trip length outside pupping season for females: 9.0 ± 1.12 km, males: 7.0 ± 1.24 km) as well as small home ranges (median 50% home range for females: 16.3 km2, males: 36.1 km2) compared to harbour seals from marine regions. Within the estuary, the animals utilised the fairway, river branches and tributaries. During the pupping season in June and July, four seals showed strongly reduced trip lengths and durations, increased daily haul out durations as well as smaller home ranges. Even though a continuous exchange with harbour seals from the Wadden Sea likely occurs, most individuals in this study spent the entire deployment duration inside the estuary. This indicates that the Elbe estuary provides a suitable habitat for harbour seals, despite extensive anthropogenic usage, calling for further studies on the consequences of living in such an industrialised habitat.

Linking movement and dive data to prey distribution models: new insights in foraging behaviour and potential pitfalls of movement analyses

BackgroundAnimal movement data are regularly used to infer foraging behaviour and relationships to environmental characteristics, often to help identify critical habitat. To characterize foraging, movement models make a set of assumptions rooted in theory, for example, time spent foraging in an area increases with higher prey density.MethodsWe assessed the validity of these assumptions by associating horizontal movement and diving of satellite-telemetered ringed seals (Pusa hispida)—an opportunistic predator—in Hudson Bay, Canada, to modelled prey data and environmental proxies.ResultsModelled prey biomass data performed better than their environmental proxies (e.g., sea surface temperature) for explaining seal movement; however movement was not related to foraging effort. Counter to theory, seals appeared to forage more in areas with relatively lower prey diversity and biomass, potentially due to reduced foraging efficiency in those areas.ConclusionsOur study highlights the need to validate movement analyses with prey data to effectively estimate the relationship between prey availability and foraging behaviour.

High levels of inbreeding with spatial and host-associated structure in lice of an endangered freshwater seal.

Host‐specialist parasites of endangered large vertebrates are in many cases more endangered than their hosts. In particular, low host population densities and reduced among‐host transmission rates are expected to lead to inbreeding within parasite infrapopulations living on single host individuals. Furthermore, spatial population structures of directly‐transmitted parasites should be concordant with those of their hosts. Using population genomic approaches, we investigated inbreeding and population structure in a host‐specialist seal louse (Echinophthirius horridus) infesting the Saimaa ringed seal (Phoca hispida saimensis), which is endemic to Lake Saimaa in Finland, and is one of the most endangered pinnipeds in the world. We conducted genome resequencing of pairs of lice collected from 18 individual Saimaa ringed seals throughout the Lake Saimaa complex. Our analyses showed high genetic similarity and inbreeding between lice inhabiting the same individual seal host, indicating low among‐host transmission rates. Across the lake, genetic differentiation among individual lice was correlated with their geographic distance, and assignment analyses revealed a marked break in the genetic variation of the lice in the middle of the lake, indicating substantial population structure. These findings indicate that movements of Saimaa ringed seals across the main breeding areas of the fragmented Lake Saimaa complex may in fact be more restricted than suggested by previous population‐genetic analyses of the seals themselves.

Movements of southern elephant seals (Mirounga leonina) from Davis Base, Antarctica: combining population genetics and tracking data

Marine animals such as the southern elephant seal (Mirounga leonina) rely on a productive marine environment and are vulnerable to oceanic changes that can affect their reproduction and survival rates. Davis Base, Antarctica, acts as a moulting site for southern elephant seals that forage in Prydz Bay, but the mitochondrial haplotype diversity and natal source populations of these seals have not been characterized. In this study, we combined genetic and animal tracking data on these moulting seals to identify levels of mitochondrial haplotype diversity, natal source population, and movement behaviours during foraging and haul-out periods. Using partial sequences of the mitochondrial control region, we identified two major breeding mitochondrial lineages of seals at Davis Base. We found that the majority of the seals originated from breeding stocks within the South Atlantic Ocean and South Indian Ocean. One seal was grouped with the Macquarie Island breeding stock (South Pacific Ocean). The Macquarie Island population, unlike the other two stocks, is decreasing in size. Tracking data revealed long-distance foraging activity of the Macquarie Island seal around Crozet Islands. We speculate that changes to the Antarctic marine environment can result in a shift in foraging and movement strategies, which subsequently affects seal population growth rates.

Should I stay or should I go? Behavioral adjustments of fur seals related to foraging success

Abstract Understanding foraging strategies and decision-making processes of predators provide crucial insights into how they might respond to changes in prey availability and in their environment to maximize their net energy input. In this work, foraging strategies of Antarctic fur seals (Arctocephalus gazella, AFS) and Northern fur seals (Callorhinus ursinus, NFS) were studied to determine how they adjust their foraging behavior according to their past prey capture experiences. AFS on Kerguelen Islands are exclusively oceanic divers, while NFS population of St Paul Island shows both oceanic and neritic divers. We thus hypothesized that the two species would respond differently to a change in prey capture success depending on their foraging strategy. To test this, 40 females were equipped with tags that measured tri-axial acceleration, dive depth, and GPS coordinates, from which we derived prey capture attempts and behavioral metrics. Influence of prey capture success on horizontal and vertical movements of seals was investigated at different time scales: multi-dive, night, and trip. Both AFS and NFS traveled further during the day if they encountered low prey capture periods during the previous night. However, at the multi-dive scale, neritic NFS differed from oceanic NFS and AFS in terms of decision-making processes, e.g., both AFS and oceanic NFS dived deeper in response to low prey capture rate periods, while neritic NFS did not. Similarities in decision-making processes between NFS and AFS foraging on pelagic prey suggest that pelagic vs. neritic prey type is a key factor in defining foraging decisions of diving marine predators.

A vast icefish breeding colony discovered in the Antarctic

A breeding colony of notothenioid icefish (Neopagetopsis ionah, Nybelin 1947) of globally unprecedented extent has been discovered in the southern Weddell Sea, Antarctica. The colony was estimated to cover at least ∼240km2 of the eastern flank of the Filchner Trough, comprised of fish nests at a density of 0.26 nests per square meter, representing an estimated total of ∼60 million active nests and associated fish biomass of >60,000 tonnes. The majority of nests were each occupied by 1 adult fish guarding 1,735 eggs (±433 SD). Bottom water temperatures measured across the nesting colony were up to 2°C warmer than the surrounding bottom waters, indicating a spatial correlation between the modified Warm Deep Water (mWDW) upflow onto the Weddell Shelf and the active nesting area. Historical and concurrently collected seal movement data indicate that this concentrated fish biomass may be utilized by predators such as Weddell seals (Leptonychotes weddellii, Lesson 1826). Numerous degraded fish carcasses within and near the nesting colony suggest that, in death as well as life, these fish provide input for local food webs and influence local biogeochemical processing. To our knowledge, the area surveyed harbors the most spatially expansive continuous fish breeding colony discovered to date globally at any depth, as well as an exceptionally high Antarctic seafloor biomass. This discovery provides support for the establishment of a regional marine protected area in the Southern Ocean under the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) umbrella. VIDEO ABSTRACT.

Failure evaluations for packers in multistage fracturing technology with immobile strings

With the development of unconventional oil and gas resources, the multi-stage fracturing technology with immovable string has been developed rapidly due to its advantages of large construction capacity and multiple fracturing stages. But the failure of packer has become a bottleneck restricting the development of technology. In this paper, the mechanical properties of corroded ((under the environment of I(North Troyes),II(Jeannajor) and III(Khasib)) ) and uncorroded rubber of the packer were tested by designed experiments at first. The experimental values showed that elastic modulus, shear strength and tensile strength decreased when packers were corroded. Then, according to packers' structure and load characteristics, taking the rubber cylinder, rubber support, center pipe, tubing and string as research object, the dynamic model was established for tubes and packers in fracturing layers. Based on conditions of the shear strength, pressure seal and axial movement for rubber cylinder, the safety evaluation method was proposed for packer sealing system. And the failure evaluation of multistage fracturing packer in Gao182-151 well in Daqing Field was carried out by the method established in this paper. At last, we could get the following results: the sealing safety coefficients of upper and lower packers were all greater than 1.0 during the fracturing process of layer I to IV. The axial displacement of the packer's rubber of the non-corrosive and corrosivewere all 0.00. So the packers were sealed well in each stage of fracturing, and no leakage accidents occurred during the entire fracturing process of Gao 182-151 Well. But in the fracturing layer I, the shear safety factor of the corroded (under corrosive environment of I(North Troyes),II(Jeannajor) and III(Khasib)) rubber were is 1.00, 1.10, 0.99 respectively. The shear strength was less than or equal to 1.10 and it didn't not satisfy the shear strength. Therefore, we could get the conclusion that the corroded rubber did not meet the shear strength and rubber tearing was prone to occur in the fracturing layer I. So it is recommended to replace the rubber with a new one before the construction of Gao 182-151Well.

Vagrant sub-Antarctic fur seal at tropical Ascension Island, South Atlantic Ocean

Knowledge of extra-limital movements of seals improves our understanding of species’ dispersal and dispersion abilities and patterns, and perhaps environmental changes. Canvassing and internet literature searches revealed the sighting of a vagrant adult male sub-Antarctic fur seal Arctocephalus tropicalis on the coast adjacent to George Town (7° 56′ S, 14° 25′ W), Ascension Island, in 2010. Although finer details of the sighting are sketchy, this is the first sighting of any seal at Ascension Island, and the northernmost sighting on record for the species on the mid-Atlantic Ridge islands. The likely source of the vagrant is the population at Gough Island (40° 20′ S, 9° 54′ W) some 3624 km further south in the Atlantic. The vagrant likely moved westward from Gough Island to the Brazilian coast, then northwards in coastal waters, eventually reaching Ascension Island.

Geographic variation in at-sea movements, habitat use and diving behaviour of female Cape fur seals

Knowledge of animal foraging behaviour has implications for management and conservation. While Cape fur sealsArctocephalus pusillus pusilluscomprise a major proportion of the southern African marine predator biomass, little is known about their at-sea movements. We investigated foraging distribution, habitat use and diving behaviour for 35 adult female Cape fur seals from 3 breeding colonies experiencing contrasting oceanographic regimes. Animals from Black Rocks, the smallest and eastern-most colony, undertook shorter foraging trips and utilised shallower waters over the shelf. In comparison, animals from the larger west coast colonies, at Kleinsee and False Bay, travelled further and utilised deeper shelf and shelf-slope waters. However, across colonies, females typically preferred depths of <500 m and slopes of <5°. Kleinsee and False Bay seals selected sea surface temperatures within the range typically preferred by pelagic prey species such as round herring, sardine and anchovy (14-19°C). Black Rocks individuals showed bimodal preferences for colder (16°C) and warmer waters (>22°C). Dive behaviour was similar between Kleinsee and False Bay individuals (unavailable from Black Rocks), with both pelagic and benthic foraging evident. Diel patterns were apparent at both sites, as dive depth and benthic diving increased significantly during daylight hours, likely reflecting vertical movements of prey species. We provide the first assessment of Cape fur seal movement behaviour for the South African component of the population. Observed geographic differences likely reflect the availability of suitable habitat but may also indicate differences in foraging strategies and density-dependent effects throughout the range of this species.

Harbour seals responded differently to pulses of out-migrating coho and Chinook smolts

There is increasing evidence that predation by harbour seals on out-migrating salmon smolts may be responsible for the low return of adult coho and Chinook salmon in the Salish Sea. However, little attention has been given to understanding where and when this predation occurs and the extent to which it might be conducted by few or many seals in the population. We equipped 17 harbour seals with data loggers to track seal movements and used accelerometry to infer prey encounter events (PEEs) following the release of ~384000 coho (May 4, 2015) and ~3 million Chinook (May 14, 2015) smolts into the Big Qualicum River. We found a small proportion (5.7%) of all PEEs occurred in the estuary where salmon smolts entered the ocean—and that only one-quarter of the seals actively fed there. PEE counts increased in the estuary after both species of smolts were released. However, the response of the seals was less synchronous and occurred over a greater range of depths following the release of the smaller-bodied and more abundant Chinook smolts. Harbour seals feeding in the estuary appeared to target coho smolts at the beginning of May but appeared to pursue predators of Chinook smolts in mid-May. PEE counts in the estuary increased as tide height rose and were higher at dusk and night—especially during full moonlight. Such fine-scale behavioural information about harbour seals in relation to pulses of out-migrating smolts can be used to design mitigation strategies to reduce predation pressure by seals on salmon populations.

Movement, diving, and haul-out behaviors of juvenile bearded seals in the Bering, Chukchi and Beaufort seas, 2014–2018

Bearded seals (Erignathus barbatus) are abundant in the Pacific Arctic and are an important subsistence resource for many Alaska Native communities. The Pacific Arctic is warming rapidly with substantial consequences predicted for ice-associated marine mammals, such as the bearded seal, which led to its 2012 listing as Threatened under the U.S. Endangered Species Act. We provide the most comprehensive description of juvenile bearded seal movement, diving, and haul-out behaviors for the Pacific Arctic, obtained from 24 seals tagged with satellite-linked data recorders along Alaska’s coast from 2014 to 2018. Most seals (19 of 24) made north–south movements with the seasonal extent of sea ice, however, all three seals tagged north of Bering Strait made minimal north–south movements and two seals tagged in the Bering Sea moved north as sea ice advanced south. All seals primarily occupied shallow coastal waters and areas with intermediate-concentration pack ice or that were near the ice edge. Seals spent half their time near the sea floor. Hauling out occurred less in the winter and increased during spring and summer, coinciding with the annual molting period. When ice was at its minimum extent, seven seals frequently hauled out on land. Juvenile bearded seals made use of much of the continental shelf in the Bering, Chukchi and Beaufort Seas, and their use of a broad range of ice concentrations and willingness to haul out on land suggests some resilience to changing sea ice conditions. However, whether the behaviors we documented in juveniles are similar for adult bearded seals remains unclear.

Daily and seasonal movements of Cape Cod gray seals vary with predation risk

White sharks Carcharodon carcharias and gray seals Halichoerus grypus are re-establishing their ecological roles within the Northwestern Atlantic Ocean, presenting an opportunity to understand gray seal movement and at-sea behavior under predation risk. As with other shark-seal hotspots, movements to and from terrestrial haul outs can be risky for gray seals, thereby eliciting antipredator strategies. We investigated the movement and coastal behavior of gray seals on Cape Cod (USA) in relation to seasonal and diel changes in white shark activity. Analyzing 412 trips to sea by 8 seals and more than 25000 acoustic detections from 23 individual white sharks, we observed seasonally homogeneous movements in seal behavior during months with greater shark presence. During riskier months, seal behavior manifested in near-exclusive nocturnal foraging, reduced offshore ranging, and limited at-sea activity. On these nocturnal trips to sea, seals returning to haul outs tended to avoid daybreak and traversed during diel minima in shark activity. However, seals tended to depart haul outs at dusk when shark presence was maximal. As conservation efforts succeed in rebuilding depleted populations of coastal predators, studying re-emerging predator-prey interactions can enhance our understanding about the drivers of movement and behavior.

Projected shifts in the foraging habitat of crabeater seals along the Antarctic Peninsula

Crabeater seals exhibit extreme dietary specialization, feeding almost exclusively on Antarctic krill. This specialization has inextricably linked habitat use, life history and evolution of this pinniped species to the distribution of its prey. Therefore, the foraging habitat of crabeater seals can be used to infer the distribution of Antarctic krill. Here, we combined seal movements and diving behaviour with environmental variables to build a foraging habitat model for crabeater seals for the rapidly changing western Antarctic Peninsula (WAP). Our projections show that future crabeater seal foraging habitat and, by inference, krill distribution will expand towards offshore waters and the southern WAP in response to changes in circulation, water temperature and sea ice distribution. Antarctic krill biomass is projected to be negatively affected by the environmental changes, which are anticipated to manifest as a decrease in krill densities in coastal waters, with impacts on the land-/ice-based krill predator community, particularly in the northern WAP. Crabeater seals feed predominantly on Antarctic krill. Combining seal tracks and diving behaviour with environmental variables allows the future foraging habitat, and therefore krill distribution, to be predicted, suggesting a shift offshore and south along the western Antarctic Peninsula.

Vocal behavior in spotted seals (Phoca largha)

Captive studies can inform passive acoustic monitoring efforts by describing fundamental features of species-typical vocalizations emitted by known individuals. These include acoustic parameters as well as developmental, seasonal, and sex-based patterns in vocal behavior. Here, two male spotted seals were studied in captivity from age 3 months through 8 years. Vocal behavior was scored daily and opportunistically recorded. The production of underwater calls emerged with presumed sexual maturity (age 4). To evaluate vocal repertoire and fine-scale temporal patterns of sound production in adult seals, an underwater acoustic recorder was continuously deployed with these seals at age 7–8 years. The spotted seals produced a variety of underwater calls—including roars, knocks, and moans—with dominant energy below 1 kHz. There was a marked annual peak in vocal activity in spring, prior to the yearly molt. This period coincided with increased aggressive behavior and musky odor indicative of heightened reproductive activity. These results from developing male spotted seals, obtained in the absence of conspecific females, confirm the production of recognizable, stereotypic underwater calls associated with the breeding season. These findings can be used to inform the use of autonomous acoustic recorders to track the presence and movements of free-ranging seals in remote habitats.

At-sea spatial usage of recently weaned grey seal pups in Iceland

Although grey seals (Halichoerus grypus) are the focus of considerable research effort throughout much of their North Atlantic breeding range, little is known about grey seal movement ecology in Iceland. This is surprising given the long history of grey seal exploitation in Iceland and because grey seals are common bycatch in commercial fisheries. Here, for the first time, we deployed satellite tags on five grey seals in Iceland to quantify the at-sea spatial usage of recently weaned pups during their first year of life. Maximum foraging trip distance ranged from 20 to 160 km for individual pups, while maximum duration ranged from 4.3 to 20.8 days. Individual differences in foraging trip metrics indicated two broad strategies. Specifically, pups either remained near the deployment location or dispersed to the east of Iceland, reaching a total distance of > 300 km from the deployment location. Foraging trips were, however, typically restricted to the continental shelf, which presumably reflects a preference for benthic foraging, as is reported for grey seals at other breeding locations. Our preliminary findings highlight the importance of near-shore waters to recently weaned grey seal pups in Iceland and suggests that coastal fisheries are a prevalent threat. However, additional research is required to quantify interactions between grey seals and commercial fisheries, which in turn, would improve the efficacy of conservation and management efforts.

Measuring responses of harbour seals to potential aversive acoustic mitigation signals using controlled exposure behavioural response studies

Abstract Some anthropogenic activities pose acute risks for marine species. For example, pile driving could damage the hearing of marine mammals while underwater explosions can also result in physical damage or death. Effective mitigation is required to reduce these risks, but the exclusion zones specified in regulations can extend over hundreds or thousands of metres and seals pose particular problems because they are difficult to detect at sea. Aversive sound mitigation aims to exclude animals from high‐risk areas before dangerous activities take place by broadcasting specific acoustic signals. Field research is needed to identify signals that might be effective in eliciting short‐term avoidance by marine species such as harbour seals (Phoca vitulina). A series of controlled‐exposure experiments (CEEs) were undertaken to measure seal movements in response to acoustic deterrent devices (ADD) and predator calls, and to assess the effectiveness of candidate signals for aversive sound mitigation. Seals were fitted with UHF/GPS transmitters providing continuous high‐resolution tracks and real‐time transmissions of their locations. A tracking/playback vessel located seals at sea and transmitted either ADD signals or orca (Orcinus orca) calls over a range of distances while seals were foraging or moving between sites. Behaviour before, during and after exposure was analysed to assess responses. One‐hundred and ten CEEs were assessed as being of at least ‘adequate’ quality. Of the 71 adequate trials with the Lofitech ADD, all 38 at ranges of <1 km (predicted received level 134.6 dB RMS re 1 μPa) elicited a response. The maximum response range was 3123 m (predicted RL: 111 dB RMS re 1 μPa). However, the responses observed did not always result in substantial movements away from the source, especially for seals that were travelling at the time of the exposures. More work is needed to better understand how exposure risks would be reduced in different scenarios. The mean net speed of horizontal movements for seals responding to aversive sounds (1.15 m s−1) was only 7% higher than their mean travel speed. Responses to broadcasts of orca calls were highly variable. The results suggest that signals similar to those generated by a Lofitech ADD could be used to reduce risks to harbour seals from pile driving and underwater explosions in coastal waters. More work will be needed to develop systems that match the requirements of industry and regulators and to explore whether these results can be generalized to offshore waters and to other phocids.

Classifying grey seal behaviour in relation to environmental variability and commercial fishing activity - a multivariate hidden Markov model

Classifying movement behaviour of marine predators in relation to anthropogenic activity and environmental conditions is important to guide marine conservation. We studied the relationship between grey seal (Halichoerus grypus) behaviour and environmental variability in the southwestern Baltic Sea where seal-fishery conflicts are increasing. We used multiple environmental covariates and proximity to active fishing nets within a multivariate hidden Markov model (HMM) to quantify changes in movement behaviour of grey seals while at sea. Dive depth, dive duration, surface duration, horizontal displacement, and turning angle were used to identify travelling, resting and foraging states. The likelihood of seals foraging increased in deeper, colder, more saline waters, which are sites with increased primary productivity and possibly prey densities. Proximity to active fishing net also had a pronounced effect on state occupancy. The probability of seals foraging was highest <5 km from active fishing nets (51%) and decreased as distance to nets increased. However, seals used sites <5 km from active fishing nets only 3% of their time at sea highlighting an important temporal dimension in seal-fishery interactions. By coupling high-resolution oceanographic, fisheries, and grey seal movement data, our study provides a scientific basis for designing management strategies that satisfy ecological and socioeconomic demands on marine ecosystems.