Elke Burkhardt

Real-time underwater sounds from the Southern Ocean

Marine sound, natural or anthropogenic, has long fascinated scientists, mariners, and the general public. The haunting songs of humpback whales and the pings of antisubmarine sonar, among other sounds from the oceans, convey allure and suspense. Recently, that suspense has moved from television screens to courtrooms, where navies, scientists, and environmentalists have clashed over the effects of anthropogenic sound on marine mammals [Malakoff, 2002]. Triggered by atypical mass strandings of primarily beaked whales in concordance with naval sonar exercises off Greece in 1996 and the Bahamas in 2000, substantial efforts to obtain baseline data to understand the possible effects of anthropogenic sound on marine mammals have commenced. Recent advances include dive and vocalization records of beaked whales [Johnson et al., 2004] and detailed observations of the behavioral response of sperm whales on seismic signals [Jochens et al., 2006].

Automatic round-the-clock detection of whales for mitigation from underwater noise impacts.

Loud hydroacoustic sources, such as naval mid-frequency sonars or airguns for marine geophysical prospecting, have been increasingly criticized for their possible negative effects on marine mammals and were implicated in several whale stranding events. Competent authorities now regularly request the implementation of mitigation measures, including the shut-down of acoustic sources when marine mammals are sighted within a predefined exclusion zone. Commonly, ship-based marine mammal observers (MMOs) are employed to visually monitor this zone. This approach is personnel-intensive and not applicable during night time, even though most hydroacoustic activities run day and night. This study describes and evaluates an automatic, ship-based, thermographic whale detection system that continuously scans the ship’s environs for whale blows. Its performance is independent of daylight and exhibits an almost uniform, omnidirectional detection probability within a radius of 5 km. It outperforms alerted observers in terms of number of detected blows and ship-whale encounters. Our results demonstrate that thermal imaging can be used for reliable and continuous marine mammal protection.

Calling in the cold: pervasive acoustic presence of humpback whales (Megaptera novaeangliae) in Antarctic coastal waters.

Humpback whales migrate between relatively unproductive tropical or temperate breeding grounds and productive high latitude feeding areas. However, not all individuals of a population undertake the annual migration to the breeding grounds; instead some are thought to remain on the feeding grounds year-round, presumably to avoid the energetic demands of migration. In the Southern Hemisphere, ice and inclement weather conditions restrict investigations of humpback whale presence on feeding grounds as well as the extent of their southern range. Two years of near-continuous recordings from the PerenniAL Acoustic Observatory in the Antarctic Ocean (PALAOA, Ekström Iceshelf, 70°31’S, 8°13’W) are used to explore the acoustic presence of humpback whales in an Antarctic coastal area. Humpback whale calls were present during nine and eleven months of 2008 and 2009, respectively. In 2008, calls were present in January through April, June through August, November and December, whereas in 2009, calls were present throughout the year, except in September. Calls occurred in un-patterned sequences, representing non-song sound production. Typically, calls occurred in bouts, ranging from 2 to 42 consecutive days with February, March and April having the highest daily occurrence of calls in 2008. In 2009, February, March, April and May had the highest daily occurrence of calls. Whales were estimated to be within a 100 km radius off PALAOA. Calls were also present during austral winter when ice cover within this radius was >90%. These results demonstrate that coastal areas near the Antarctic continent are likely of greater importance to humpback whales than previously assumed, presumably providing food resources year-round and open water in winter where animals can breathe.

Input of Energy/Underwater Sound

Underwater sound is ubiquitous throughout the world’s oceans. Evaluating its impact and relevance for the marine fauna is highly complex and hampered by a paucity of data, lack of understanding and ambiguity of terms. When comparing sound (an energetic pollutant) with substantial pollutants (chemical, biological or marine litter) two notable differences emerge: Firstly, while sound propagates instantaneously away from the source, it also ceases immediately within minutes of shutting off the source. Anthropogenic noise is hence per-se ephemeral, lending itself to a set of in-situ mitigation strategies unsuitable for mitigation of persistent pollutants. Secondly, while pollution with hazardous substances can readily be described quantitatively with few parameters (concentration as the most important one), the description of sound and its impact on aquatic life is of much higher complexity, as to be evidenced by the issue’s multifaceted description following hereinafter.

Detection and Tracking of Whales Using a Shipborne, 360° Thermal-Imaging System

Shipborne, quasi-continuous visual marine mammal observations for mitigation or research require, while being restricted to daylight hours, the utmost concentration by observers as well as large teams when conducted during month-long cruises. To overcome such limitations, the use of thermal imaging has first been examined in the context of offshore oil exploration by Greene and Chase (1987). The approach exploits the thermal signature of a whale’s blow, which, at least at high latitudes, is warmer than the environment. Their study and additional research by Cuyler et al. (1992) recorded thermal images of both odontocete and mysticete blows at ranges up to 100 m. Significantly larger detection ranges were achieved by Perryman et al. (1999) who detected gray whale blows at several kilometers range in thermal images taken from ashore. Most recently, Baldacci et al. (2005) tested a handheld naval infrared (IR) camera in the Mediterranean Sea, reporting detections of various species at typically 1–2 nautical miles.

Strategic Assessment of the Risk Posed to Marine Mammals by the Use of Air Guns in the Antarctic: Concepts, Methods, Results, and Controversies

During the past two years, the Alfred Wegener Institute (AWI) prepared a comprehensive, strategic assessment of the risk posed to marine mammals by the use of air guns for scientific, geophysical research in the Southern Ocean around Antarctica (Boebel et al. 2009). This strategic risk assessment focuses not only on a single activity (e.g., a specific expedition) as a risk assessment would but more generally considers the use of research air guns in this region’s typical operational and environmental contexts, which show little interannual variation. The study attempts distinguishing between aspects of analysis (based on scientific knowledge and numerical calculations) and evaluation (based on a set of risk criteria and associated thresholds). The term assessment is used to describe the overall process, involving both analysis and evaluation.