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Swedish National Monitoring program on harbour porpoises

For small cetaceans bycatch in fishing gear is one of the largest threats towards their conservation. In order to effectively manage this threat, an estimation of the maximum number of animals that can be killed by anthropogenic activities each year is required. Such calculations rely on species or population specific information on population dynamics, and information on the current state of the population relative to carrying capacity. Here, we calculate the mortality limit for the Belt Sea population of harbour porpoises (Phocoena phocoena) based on a modified potential biological removal (mPBR) method. We estimate that for the population to reach the conservation objective set by ASCOBANS (the population should reach 80% of carrying capacity (assumed here to be 50,000 animals), with the assumption that this is achieved within 100 years with an 80% probability) a maximum of 29 animals can be removed annually. This removal rate applies a recover factor (Fr) of 0.1 that accounts for many uncertainties in population dynamics, abundance estimates, and the current removal rate and depletion level of the population. However, even using the highest possible Fr value (1.0) (which is not recommended for populations with unknown status and does not allow the population to reach the conservation objective), the mPBR limit of the population is 292, which is still significantly lower than the current estimated levels of bycatch in this population (~700 a year). Therefore, urgent action is required in order to ensure that this population is able to reach the conservation objective and achieve good environmental status under a range of European legislation.

The Baltic Proper harbor porpoise (Phocoena phocoena) is currently listed as critically endangered (CR), with the Static Acoustic Monitoring of the Baltic Sea Harbor Porpoise (SAMBAH) project concluding that only ~500 individuals remain. This population has a distribution that spans the waters of nine countries, making regular abundance estimates and management action challenging. Given the continued decline of other depleted porpoises, namely the vaquita (Phocoena sinus), the question is often raised about whether management action would even have a positive impact, or whether it is too late for population recovery. When abundance estimates are sparse over time, monitoring programs at key sites are likely to serve as the best indication of population trends, and may provide an early indication of changes at the population level. We compared passive acoustic monitoring data from 12 stations that were utilized both in the SAMBAH project (2011–2013) and as a part of the Swedish National Monitoring Program (2017–2020) to determine trends in detection rates. There was a 29% increase in mean daily detection rate during May–October (over the breeding season) between the two study periods. At the three stations with the highest number of detections, log linear regression revealed a yearly increase of 2.4% between 2011 and 2019 (−4.4–9.6, 95% CI). This may be indicative of the beginnings of population recovery, or simply an indication that the decline has stalled. The rate of increase is still well below what is likely to be possible for porpoise populations, and unlikely to buffer against any potential increase in pressures in the future. We therefore call for urgent management action to remove threats and protect this CR population, the only resident cetacean in the Baltic region, in order to give it the best chance of recovery.

Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 37(5), (2020): 807-824, doi:10.1175/JTECH-D-19-0054.1., Marine mammals are under growing pressure as anthropogenic use of the ocean increases. Ship strikes of large whales and loud underwater sound sources including air guns for marine geophysical prospecting and naval midfrequency sonar are criticized for their possible negative effects on marine mammals. Competent authorities regularly require the implementation of mitigation measures, including vessel speed reductions or shutdown of acoustic sources if marine mammals are sighted in sensitive areas or in predefined exclusion zones around a vessel. To ensure successful mitigation, reliable at-sea detection of animals is crucial. To date, ship-based marine mammal observers are the most commonly implemented detection method; however, thermal (IR) imaging–based automatic detection systems have been used in recent years. This study evaluates thermal imaging–based automatic whale detection technology for its use across different oceans. The performance of this technology is characterized with respect to environmental conditions, and an automatic detection algorithm for whale blows is presented. The technology can detect whales in polar, temperate, and subtropical ocean regimes over distances of up to several kilometers and outperforms marine mammal observers in the number of whales detected. These results show that thermal imaging technology can be used to assist in providing protection for marine mammals against ship strike and acoustic impact across the world’s oceans., This work was funded by the Office of Naval Research (ONR) under Award N000141310856, by the Environmental Studies Research Fund (ESRF; esrfunds.org) under Award 2014-03S and by the Alfred-Wegener-Institute Helmholtz Zentrum für Polar- und Meeresforschung. DPZ and OB declare competing financial interests: 1) Patent US8941728B2, DE102011114084B4: A method for automatic real-time marine mammal detection. The patent describes the ideas basic to the automatic whale detection software as used to acquire and process the data presented in this paper. 2) Licensing of the Tashtego automatic whale detection software to the manufacturer of IR sensor. The authors confirm that these competing financial interests did not alter their adherence good scientific practice. We thank P. Abgrall, J. Coffey, K. Keats, B. Mactavish, V. Moulton, and S. Penney-Belbin for data collection or IR image review. We thank S. Besaw, J. Christian, A. Coombs, P. Coombs, W. Costello, T. Elliott, E. Evans, I. Goudie, C. Jones, K. Knowles, R. Martin, A. Murphy, D. and J. Shepherd; and the staffs at the Irish Loop Express, the Myrick Wireless Interpretive Centre, the Mistaken Point Ecological Reserve, and the lighthouse keepers for logistical assistance at our remote field site. We thank D. Boutilier and B. McDonald (DFO) for assisting us in obtaining license to occupy permits for Cape Race. We thank D. Taylor (ESRF Research Manager) for his support.

Marine mammals are under growing pressure as anthropogenic use of the ocean increases. Ship strikes of large whales and loud underwater sound sources including air guns for marine geophysical prospecting and naval midfrequency sonar are criticized for their possible negative effects on marine mammals. Competent authorities regularly require the implementation of mitigation measures, including vessel speed reductions or shutdown of acoustic sources if marine mammals are sighted in sensitive areas or in predefined exclusion zones around a vessel. To ensure successful mitigation, reliable at-sea detection of animals is crucial. To date, ship-based marine mammal observers are the most commonly implemented detection method; however, thermal (IR) imaging–based automatic detection systems have been used in recent years. This study evaluates thermal imaging–based automatic whale detection technology for its use across different oceans. The performance of this technology is characterized with respect to environmental conditions, and an automatic detection algorithm for whale blows is presented. The technology can detect whales in polar, temperate, and subtropical ocean regimes over distances of up to several kilometers and outperforms marine mammal observers in the number of whales detected. These results show that thermal imaging technology can be used to assist in providing protection for marine mammals against ship strike and acoustic impact across the world’s oceans.

Thermographic imaging has been shown to reliably detect marine mammals, both day and night, for operational mitigation in polar and subpolar waters (Zitterbart et al., 2013), with encouraging findings having recently been reported for temperate waters (NOAA Southwest Fisheries Science Center, 2015). As thermographic imaging is based on thermal contrast between whale body or blow and the sea surface, thermographic discriminability is expected to wane with increasing sea surface temperatures. ETAW explored the upper sea surface temperature limit of this approach by deploying high-end thermal cameras on North Stradbroke Island, Queensland, Australia (subtropical conditions) and on both the North and South shore of Kauai, HI, USA (tropical conditions). The study design included both acquisition of thermographic video as well as concurrent visual sightings, including double-blind setups. Our findings show, that cues of humpback whales are thermally discriminable even under the highest sea surface temperatures encountered (26°C / 79°F). Thermal discriminability and performance of computer based automatic detection of cues, appear, as based on the (subjective) experience gained in the field, to be more dependent on covariates such as camera height, sea-state and glare than on sea surface temperature. While increasing sea surface temperatures appear to reduce the operational radius of thermographic images (yet not below typical mitigation radii of 1-3 km), they did not render cues entirely indistinguishable from the background image, while glare and increased sea states caused increased numbers of false alerts. Comparisons of different IR technologies (scanning LWIR 8 – 12µm, focal plane array LWIR 8.0 – 9.4µm, focal plane array MWIR 3.7 – 5.5µm) suggest that the broadband LWIR sensor produced the clearest image least affected by glare. Tests of polarization filters in different orientations revealed that glare is somewhat, but not significantly reduced, for horizontal pola