The nightscape of the Arctic winter shapes the diving behavior of a marine predator.

Predator-prey interactions in marine ecosystems are dynamically influenced by light, as demonstrated by diel vertical migrations of low-trophic level organisms. At high latitudes, the long winter nights can provide foraging opportunities for marine predators targeting vertically migrating prey closer to the surface at night. However, there is limited documentation of such diel patterns in marine predators under extreme light regimes. To address this, we recorded the diving behavior of 17 harbour porpoises just south of the Arctic circle in West Greenland, from summer to winter. Unlike classical diel vertical migration, the porpoises dove 24-37% deeper at night and the frequency of deep dives (> 100 m) increased tenfold as they entered the darkest months. The daily mean depth was negatively correlated with daylength, suggesting an increased diving activity when approaching the polar night. Our findings suggest a light-mediated strategy in which harbour porpoises would either target (i) benthic prey, (ii) pelagic prey migrating seasonally towards the seafloor, or (iii) vertically migrating prey that may be otherwise inaccessible in deeper waters at night, therefore maximizing feeding activity during extended periods of darkness. Extreme light regimes observed at high latitudes are therefore critical in structuring pelagic communities and food webs.

Characterising underwater noise and changes in harbour porpoise behaviour during the decommissioning of an oil and gas platform.

Many man-made marine structures (MMS) will have to be decommissioned in the coming decades. While studies on the impacts of construction of MMS on marine mammals exist, no research has been done on the effects of their decommissioning. The complete removal of an oil and gas platform in Scotland in 2021 provided an opportunity to investigate the response of harbour porpoises to decommissioning. Arrays of broadband noise recorders and echolocation detectors were used to describe noise characteristics produced by decommissioning activities and assess porpoise behaviour. During decommissioning, sound pressure spectral density levels in the frequency range 100 Hz to 48 kHz were 30-40 dB higher than baseline, with vessel presence being the main source of noise. The study detected small-scale (< 2 km) and short-term porpoise displacement during decommissioning, with porpoise occurrence increasing immediately after this. These findings can inform the consenting process for future decommissioning projects.

Similar susceptibility to temporary hearing threshold shifts despite different audiograms in harbor porpoises and harbor seals.

When they are exposed to loud fatiguing sounds in the oceans, marine mammals are susceptible to hearing damage in the form of temporary hearing threshold shifts (TTSs) or permanent hearing threshold shifts. We compared the level-dependent and frequency-dependent susceptibility to TTSs in harbor seals and harbor porpoises, species with different hearing sensitivities in the low- and high-frequency regions. Both species were exposed to 100% duty cycle one-sixth-octave noise bands at frequencies that covered their entire hearing range. In the case of the 6.5 kHz exposure for the harbor seals, a pure tone (continuous wave) was used. TTS was quantified as a function of sound pressure level (SPL) half an octave above the center frequency of the fatiguing sound. The species have different audiograms, but their frequency-specific susceptibility to TTS was more similar. The hearing frequency range in which both species were most susceptible to TTS was 22.5-50 kHz. Furthermore, the frequency ranges were characterized by having similar critical levels (defined as the SPL of the fatiguing sound above which the magnitude of TTS induced as a function of SPL increases more strongly). This standardized between-species comparison indicates that the audiogram is not a good predictor of frequency-dependent susceptibility to TTS.

TDP-43 and Alzheimer's Disease Pathology in the Brain of a Harbor Porpoise Exposed to the Cyanobacterial Toxin BMAA.

Cetaceans are well-regarded as sentinels for toxin exposure. Emerging studies suggest that cetaceans can also develop neuropathological changes associated with neurodegenerative disease. The occurrence of neuropathology makes cetaceans an ideal species for examining the impact of marine toxins on the brain across the lifespan. Here, we describe TAR DNA-binding protein 43 (TDP-43) proteinopathy and Alzheimer's disease (AD) neuropathological changes in a beached harbor porpoise (Phocoena phocoena) that was exposed to a toxin produced by cyanobacteria called ß-N-methylamino-L-alanine (BMAA). We found pathogenic TDP-43 cytoplasmic inclusions in neurons throughout the cerebral cortex, midbrain and brainstem. P62/sequestosome-1, responsible for the autophagy of misfolded proteins, was observed in the amygdala, hippocampus and frontal cortex. Genes implicated in AD and TDP-43 neuropathology such as APP and TARDBP were expressed in the brain. AD neuropathological changes such as amyloid-ß plaques, neurofibrillary tangles, granulovacuolar degeneration and Hirano bodies were present in the hippocampus. These findings further support the development of progressive neurodegenerative disease in cetaceans and a potential causative link to cyanobacterial toxins. Climate change, nutrient pollution and industrial waste are increasing the frequency of harmful cyanobacterial blooms. Cyanotoxins like BMAA that are associated with neurodegenerative disease pose an increasing public health risk.

Development of a new control rule for managing anthropogenic removals of protected, endangered or threatened species in marine ecosystems.

Human activities in the oceans are increasing and can result in additional mortality on many marine Protected, Endangered or Threatened Species (PETS). It is necessary to implement ambitious measures that aim to restore biodiversity at all nodes of marine food webs and to manage removals resulting from anthropogenic activities. We developed a stochastic surplus production model (SPM) linking abundance and removal processes under the assumption that variations in removals reflect variations in abundance. We then consider several 'harvest' control rules, included two candidate ones derived from this SPM (which we called 'Anthropogenic Removals Threshold', or ART), to manage removals of PETS. The two candidate rules hinge on the estimation of a stationary removal rate. We compared these candidate rules to other existing control rules (e.g. potential biological removal or a fixed percentage rule) in three scenarios: (i) a base scenario whereby unbiased but noisy data are available, (ii) scenario whereby abundance estimates are overestimated and (iii) scenario whereby abundance estimates are underestimated. The different rules were tested on a simulated set of data with life-history parameters close to a small-sized cetacean species of conservation interest in the North-East Atlantic, the harbour porpoise (Phocoena phocoena), and in a management strategy evaluation framework. The effectiveness of the rules were assessed by looking at performance metrics, such as time to reach the conservation objectives, the removal limits obtained with the rules or temporal autocorrelation in removal limits. Most control rules were robust against biases in data and allowed to reach conservation objectives with removal limits of similar magnitude when averaged over time. However, one of the candidate rule (ART) displayed greater alignment with policy requirements for PETS such as minimizing removals over time.

Did algal toxin and Klebsiella infections cause the unexplained 2007 mass mortality event in Danish and Swedish marine mammals?

An unusual mass mortality event (MME) of harbour seals (Phoca vitulina) and harbour porpoises (Phocoena phocoena) occurred in Denmark and Sweden in June 2007. Prior to this incident, the region had experienced two MMEs in harbour seals caused by Phocine Distemper Virus (PDV) in 1988 and 2002. Although epidemiology and symptoms of the 2007 MME resembled PDV, none of the animals examined for PDV tested positive. Thus, it has been speculated that another - yet unknown - pathogen caused the June 2007 MME. To shed new light on the likely cause of death, we combine previously unpublished veterinary examinations of harbour seals with novel analyses of algal toxins and algal monitoring data. All harbour seals subject to pathological examination showed pneumonia, but were negative for PDV, influenza and coronavirus. Histological analyses revealed septicaemia in multiple animals, and six animals tested positive for Klebsiella pneumonia. Furthermore, we detected the algal Dinophysis toxin DTX-1b (1-115 ng g-1) in five seals subject to toxicology, representing the first time DTX-1b has been detected in marine vertebrates. However, no animals tested positive for both Klebsiella and toxins. Thus, while our relatively small sample size prevent firm conclusions on causative agents, we speculate that the unexplained MME may have been caused by a chance incidence of multiple pathogens acting in parallel in June 2007, including Dinophysis toxin and Klebsiella. Our study illustrates the complexity of wildlife MMEs and highlights the need for thorough sampling during and after MMEs, as well as additional research on and monitoring of DTX-1b and other algal toxins in the region.

Phthalate contamination in marine mammals off the Norwegian coast.

Phthalates are used in plastics, found throughout the marine environment and have the potential to cause adverse health effects. In the present study, we quantified blubber concentrations of 11 phthalates in 16 samples from stranded and/or free-living marine mammals from the Norwegian coast: the killer whale (Orcinus orca), sperm whale (Physeter macrocephalus), long-finned pilot whale (Globicephala melas), white-beaked dolphin (Lagenorhynchus albirostris), harbour porpoise (Phocoena phocoena), and harbour seal (Phoca vitulina). Five compounds were detected across all samples: benzyl butyl phthalate (BBP; in 50 % of samples), bis(2-ethylhexyl) phthalate (DEHP; 33 %), diisononyl phthalate (DiNP; 33 %), diisobutyl phthalate (DiBP; 19 %), and dioctyl phthalate (DOP; 13 %). Overall, the most contaminated individual was the white-beaked dolphin, whilst the lowest concentrations were measured in the killer whale, sperm whale and long-finned pilot whale. We found no phthalates in the neonate killer whale. The present study is important for future monitoring and management of these toxic compounds.

Validation of the F-POD-A fully automated cetacean monitoring system.

The F-POD, an echolocation-click logging device, is commonly used for passive acoustic monitoring of cetaceans. This paper presents the first assessment of the error-rate of fully automated analysis by this system, a description of the F-POD hardware, and a description of the KERNO-F v1.0 classifier which identifies click trains. Since 2020, twenty F-POD loggers have been used in the BlackCeTrends project by research teams from Bulgaria, Georgia, Romania, Türkiye, and Ukraine with the aim of investigating trends of relative abundance in populations of cetaceans of the Black Sea. Acoustic data from this project analysed here comprises 9 billion raw data clicks in total, of which 297 million were classified by KERNO-F as Narrow Band High Frequency (NBHF) clicks (harbour porpoise clicks) and 91 million as dolphin clicks. Such data volumes require a reliable automated system of analysis, which we describe. A total of 16,805 Detection Positive Minutes (DPM) were individually inspected and assessed by a visual check of click train characteristics in each DPM. To assess the overall error rate in each species group we investigated 2,000 DPM classified as having NBHF clicks and 2,000 DPM classified as having dolphin clicks. The fraction of NBHF DPM containing misclassified NBHF trains was less than 0.1% and for dolphins the corresponding error-rate was 0.97%. For both species groups (harbour porpoises and dolphins), these error-rates are acceptable for further study of cetaceans in the Black Sea using the automated classification without further editing of the data. The main sources of errors were 0.17% of boat sonar DPMs misclassified as harbour porpoises, and 0.14% of harbour porpoise DPMs misclassified as dolphins. The potential to estimate the rate at which these sources generate errors makes possible a new predictive approach to overall error estimation.

Ship noise causes tagged harbour porpoises to change direction or dive deeper.

Shipping is the most pervasive source of marine noise pollution globally, yet its impact on sensitive fauna remains unclear. We tracked 10 harbour porpoises for 5-10 days to determine exposure and behavioural reactions to modelled broadband noise (10 Hz-20 kHz, VHF-weighted) from individual ships monitored by AIS. Porpoises spent a third of their time experiencing ship noise above ambient, to which they regularly reacted by moving away during daytime and diving deeper during night. However, even ships >2 km away (noise levels of 93 ± 14 dB re 1 µPa2) caused animals to react 5-9 % of the time (∼18.6 ships/day). Ships can thus influence the behaviour and habitat use of cetaceans over long distances, with worrying implications for fitness in coastal areas where anthropogenic noise from dense ship traffic repeatedly disrupt their natural behaviour.

Infection with Pythium flevoense in a harbour porpoise (Phocoena phocoena) as a novel cause of dermatitis in marine mammals.

The oomycete Pythium flevoense was diagnosed as the cause of dermatitis in a young adult female harbour porpoise (Phocoena phocoena) that had been trapped in a pound net in a temperate saltwater environment. Disease from Pythium sp. infection-pythiosis-is infrequently diagnosed in humans, horses, dogs, cattle, and few other mammalian species. Pythiosis is typically associated with exposure to tropical or subtropical freshwater conditions, and typically caused by Pythium insidiosum. However, until now, pythiosis has been reported in neither marine mammals nor temperate saltwater conditions, and P. flevoense is not known as a cause of pythiosis in mammals. This porpoise developed generalised dermatitis despite treatment and euthanasia was necessary. Histopathological evaluation revealed a chronic active erosive dermatitis, with intralesional hyphae morphologically consistent with a Pythium sp. PCR analysis and sequencing of affected skin matched Pythium flevoense with a 100% similarity to the reference strain. Additional diagnostics excluded other pathogens. Based on this case report, P. flevoense needs to be considered as a mammalian pathogen. Furthermore, harbour porpoises and possibly other marine mammals may be at risk of infection with P. flevoense, and pythiosis should be included in the differential diagnosis of dermatitis in marine mammals.

Environmental impact of the explosion of the Nord Stream pipelines.

Armed conflicts have, in addition to severe impacts on human lives and infrastructure, also impacts on the environment, which needs to be assessed and documented. On September the 26th 2022, unknown perpetrators deliberately ruptured the two gas pipelines Nord Stream 1 and 2 with four coordinated explosions near a major chemical munition dump site near the Danish island of Bornholm in the Baltic Sea. While the massive release of natural gas into atmosphere raised serious concerns concerning the contribution to climate change-this paper assesses the overlooked direct impact of the explosions on the marine ecosystem. Seals and porpoises within a radius of four km would be at high risk of being killed by the shockwave, while temporary impact on hearing would be expected up to 50 km away. As the Baltic Proper population of harbour porpoises (Phocoena phocoena) is critically endangered, the loss or serious injury of even a single individual is considered a significant impact on the population. The rupture moreover resulted in the resuspension of 250000 metric tons of heavily contaminated sediment from deep-sea sedimentary basin for over a week, resulting in unacceptable toxicological risks towards fish and other biota in 11 km3 water in the area for more than a month.

Implications of porpoise echolocation and dive behaviour on passive acoustic monitoring.

Harbour porpoises are visually inconspicuous but highly soniferous echolocating marine predators that are regularly studied using passive acoustic monitoring (PAM). PAM can provide quality data on animal abundance, human impact, habitat use, and behaviour. The probability of detecting porpoise clicks within a given area (P̂) is a key metric when interpreting PAM data. Estimates of P̂ can be used to determine the number of clicks per porpoise encounter that may have been missed on a PAM device, which, in turn, allows for the calculation of abundance and ideally non-biased comparison of acoustic data between habitats and time periods. However, P̂ is influenced by several factors, including the behaviour of the vocalising animal. Here, the common implicit assumption that changes in animal behaviour have a negligible effect on P̂ between different monitoring stations or across time is tested. Using a simulation-based approach informed by acoustic biologging data from 22 tagged harbour porpoises, it is demonstrated that porpoise behavioural states can have significant (up to 3× difference) effects on P̂. Consequently, the behavioural state of the animals must be considered in analysis of animal abundance to avoid substantial over- or underestimation of the true abundance, habitat use, or effects of human disturbance.

Wild harbour porpoises startle and flee at low received levels from acoustic harassment device.

Acoustic Harassment Devices (AHD) are widely used to deter marine mammals from aquaculture depredation, and from pile driving operations that may otherwise cause hearing damage. However, little is known about the behavioural and physiological effects of these devices. Here, we investigate the physiological and behavioural responses of harbour porpoises (Phocoena phocoena) to a commercial AHD in Danish waters. Six porpoises were tagged with suction-cup-attached DTAGs recording sound, 3D-movement, and GPS (n = 3) or electrocardiogram (n = 2). They were then exposed to AHDs for 15 min, with initial received levels (RL) ranging from 98 to 132 dB re 1 µPa (rms-fast, 125 ms) and initial exposure ranges of 0.9-7 km. All animals reacted by displaying a mixture of acoustic startle responses, fleeing, altered echolocation behaviour, and by demonstrating unusual tachycardia while diving. Moreover, during the 15-min exposures, half of the animals received cumulative sound doses close to published thresholds for temporary auditory threshold shifts. We conclude that AHD exposure at many km can evoke both startle, flight and cardiac responses which may impact blood-gas management, breath-hold capability, energy balance, stress level and risk of by-catch. We posit that current AHDs are too powerful for mitigation use to prevent hearing damage of porpoises from offshore construction.

Assessing of the use of proteins A, G, and chimeric protein AG to detect marine mammal immunoglobulins.

In recent years, there has been an increase in infectious diseases in marine mammals, including brucellosis, infections of morbillivirus, herpesvirus, and poxvirus. Several serological diagnostic methods, including enzyme-linked immunosorbent assays, immunofluorescence assays (ELISA), and western blotting, have been used to detect antibodies against pathogens in marine mammals. However, options for commercial secondary antibodies used to detect antibodies in marine mammals are limited; therefore, the use of proteins A, G, or chimeric protein AG may provide a suitable alternative. This study aimed to assess the use of proteins A, G, and chimeric protein AG to detect marine mammal immunoglobulins. Currently, there are no comparative studies on the use of proteins A, G, and chimeric protein AG for the detection of immunoglobulins in marine mammals. In this study, we used ten pinnipeds' species (Baikal seal, California sea lion, harbor seal, northern fur seal, ringed seal, South American fur seal, South American sea lion, spotted seal, Steller sea lion, and walrus) and five cetacean species (beluga whale, bottlenose dolphin, harbor porpoise, killer whale, and Pacific white-sided dolphin) and compare binding ability to proteins A, G, or chimeric protein AG by ELISA. The results revealed that the immunoglobulins from pinniped and cetacean species reacted more strongly to protein A than protein G. In addition, the immunoglobulins of pinnipeds and cetaceans showed a strong binding ability to chimeric protein AG. These results suggest that proteins A, G, and chimeric protein AG would be used to help further develop serological assays.

Knowing the fishery to know the bycatch: bias-corrected estimates of harbour porpoise bycatch in gillnet fisheries.

Incidental captures (bycatch) remain a key global conservation threat for cetaceans. Bycatch of harbour porpoise Phocoena phocoena in set gillnets is routinely monitored in European Union fisheries, but generally relies on data collected at low spatio-temporal resolution or over short periods. In Denmark, a long-term monitoring programme started in 2010 using electronic monitoring to collect data on porpoise bycatch and gillnet fishing effort at a fine spatial and temporal scale, including time and position of each fishing operation, together with every associated bycatch event. We used these observations to model bycatch rates, given the operational and ecological characteristics of each haul observed in Danish waters. Data on fishing effort from the Danish and Swedish gillnet fleets were collected to predict fleet-wide porpoise bycatch in gillnets at regional level. Between 2010 and 2020, yearly total bycatch averaged 2088 animals (95% Cl: 667-6798). For the Western Baltic assessment unit, bycatch levels were above sustainability thresholds. These results demonstrate that fishing characteristics are key determinants of porpoise bycatch and that classical approaches ignoring these features would produce biased estimates. It emphasizes the need for efficient and informative monitoring methods to understand possible conservation impacts of marine mammal bycatch and to implement tailored mitigation techniques.

Medium-term acoustic monitoring of small cetaceans in Patagonia, Chile.

Coastal dolphins and porpoises such as the Chilean dolphin (Cephalorhynchus eutropia), the Peale's dolphin (Lagenorhynchus australis), and the Burmeister's porpoise (Phocoena spinipinnis) inhabit the remote areas of Chilean Patagonia. Human development is growing fast in these parts and may constitute a serious threat to such poorly known species. It is thus urgent to develop new tools to try and study these cryptic species and find out more about their behavior, population levels, and habits. These odontocetes emit narrow-band high-frequency (NBHF) clicks and efforts have been made to characterize precisely their acoustic production. Passive acoustic monitoring is a common way to study these animals. Nevertheless, as the signal frequency is usually higher than 100 kHz, storage problems are acute and do not allow for long-term monitoring. The solutions for recording NBHF clicks are usually twofold: either short duration, opportunistic recording from a small boat in presence of the animals (short-term monitoring) or long-term monitoring using devices including a click detector and registering events rather than sound. We suggest, as another possibility, medium-term monitoring, arguing that today's devices have reached a level of performance allowing for a few days of continual recording even at these extremely high frequencies and in difficult conditions, combined with a long-term click detector. As an example, during 2021, we performed a quasi-continuous recording for one week with the Qualilife High-Blue recorder anchored in a fjord near Puerto Cisnes, Region de Aysen, Chile. We detected more than 13,000 clicks, grouped in 22 periods of passing animals. Our detected clicks are quite similar to precedent results but, due to the large number of clicks recorded, we find a larger variability of parameters. Several rapid sequences of clicks (buzz) were found in the recordings and their features are consistent with previous studies: on average they have a larger bandwidth and a lower peak frequency than the usual clicks. We also installed in the same place a click detector (C-POD) and the two devices compare well and show the same number and duration of periods of animals presence. Passages of odontocetes were happening on average each three hours. We thus confirm the high site fidelity for the species of dolphins emitting NBHF clicks present in this zone. Finally, we confirm that the combined use of recording and detection devices is probably a good alternative to study these poorly known species in remote areas.

Highly Pathogenic Avian Influenza A(H5N1) Virus in a Harbor Porpoise, Sweden.

We found highly pathogenic avian influenza A(H5N1) virus clade 2.3.4.4b associated with meningoencephalitis in a stranded harbor porpoise (Phocoena phocoena). The virus was closely related to strains responsible for a concurrent avian influenza outbreak in wild birds. This case highlights the potential risk for virus spillover to mammalian hosts.

Harbor Porpoise Deaths Associated with Erysipelothrix rhusiopathiae, the Netherlands, 2021.

In August 2021, a large-scale mortality event affected harbor porpoises (Phocoena phocoena) in the Netherlands. Pathology and ancillary testing of 22 animals indicated that the most likely cause of death was Erysipelothrix rhusiopathiae infection. This zoonotic agent poses a health hazard for cetaceans and possibly for persons handling cetacean carcasses.

Latencies of click-evoked auditory responses in a harbor porpoise exceed the time interval between subsequent echolocation clicks.

Most auditory evoked potential (AEP) studies in echolocating toothed whales measure neural responses to outgoing clicks and returning echoes using short-latency auditory brainstem responses (ABRs) arising a few ms after acoustic stimuli. However, little is known about longer-latency cortical AEPs despite their relevance for understanding echo processing and auditory stream segregation. Here, we used a non-invasive AEP setup with low click repetition rates on a trained harbor porpoise to test the long-standing hypothesis that echo information from distant targets is completely processed before the next click is emitted. We reject this hypothesis by finding reliable click-related AEP peaks with latencies of 90 and 160 ms, which are longer than 99% of click intervals used by echolocating porpoises, demonstrating that some higher-order echo processing continues well after the next click emission even during slow clicking. We propose that some of the echo information, such as range to evasive prey, is used to guide vocal-motor responses within 50-100 ms, but that information used for discrimination and auditory scene analysis is processed more slowly, integrating information over many click-echo pairs. We conclude by showing theoretically that the identified long-latency AEPs may enable hearing sensitivity measurements at frequencies ten times lower than current ABR methods.

Directional hydrophone clusters reveal evasive responses of small cetaceans to disturbance during construction at offshore windfarms.

Mitigation measures to disperse marine mammals prior to pile-driving include acoustic deterrent devices and piling soft starts, but their efficacy remains uncertain. We developed a self-contained portable hydrophone cluster to detect small cetacean movements from the distributions of bearings to detections. Using an array of clusters within 10 km of foundation pile installations, we tested the hypothesis that harbour porpoises (Phocoena phocoena) respond to mitigation measures at offshore windfarm sites by moving away. During baseline periods, porpoise movements were evenly distributed in all directions. By contrast, animals showed significant directional movement away from sound sources during acoustic deterrent device use and piling soft starts. We demonstrate that porpoises respond to measures aimed to mitigate the most severe impacts of construction at offshore windfarms by swimming directly away from these sound sources. Portable directional hydrophone clusters now provide opportunities to characterize responses to disturbance sources across a broad suite of habitats and contexts.