Acoustic Research Reveals New Insights into the Distribution of Whales in the Gully Marine Protected Area
As human activities continue to increase in the offshore areas of Atlantic Canada, so do potential impacts on the marine environment. On the Scotian Shelf, there has been recent renewed interest in oil and gas exploration and production. This, along with commercial shipping and other human activities, can generate underwater noise of concern for marine mammals, including several species at risk (SAR).
“We generally don’t have much information about when, where and how marine mammals are using the offshore environment, or how much noise they are being exposed to from human activities,” says Fisheries and Oceans Canada research scientist Dr. Hilary Moors-Murphy.
To address this knowledge gap, she is collaborating with JASCO Applied Sciences Ltd. in Dartmouth, Nova Scotia to gather baseline data on the occurrence and behavior of cetaceans—an order of marine mammals including whales and dolphins—in the Gully Marine Protected Area (MPA) and surrounding areas on the Scotian Slope. The findings will inform recovery efforts for species at risk by identifying important habitat, and supporting the development of ecosystem monitoring indicators for the Gully MPA.
“Whales, and beaked whales in particular, are sensitive to underwater noise,” says Moors-Murphy. “Depending on the type and duration, the effects of underwater noise can vary from disturbing animals and causing changes in behavior to actually causing physical harm such as damaging their hearing. Underwater noise can also interfere with communication. For example, the vocal signals of baleen whales can be masked by boat noise and other low frequency sounds that can propagate through the ocean over very long distances.”
The research team deployed deep-water Autonomous Multichannel Acoustic Recorders (AMAR)—developed by JASCO—at depths of 1,500 metres in three locations within and near the Gully MPA. Each recorder gathered acoustic data almost continuously for two years from October 2012 to September 2014, except for short interruptions every six months to retrieve the data and replace the hard drives and batteries before redeploying them from Canadian Coast Guard ships during scientific research cruises. In collaboration with JASCO, the recordings are being analyzed to determine when, where and for what purpose various species roam these waters.
Coast Guard deck crew and DFO technicians deploy a deep-water acoustic recorder from the CCGS Hudson. Three acoustic recorders, deployed in the Gully marine protected area and surrounding areas on the Scotian Slope from October 2012 to September 2014, gathered baseline data on the occurrence and behavior of cetaceans—an order of marine mammals including whales and dolphins.
Credit: Hilary Moors-Murphy
“One of the most challenging aspects of studying whales offshore is that it’s almost impossible to gather any information in the winter, because the sea state and visibility are usually poor. Most visual studies occur from about June to September,” says Moors-Murphy. “Acoustic research provides year-round data, enabling us to analyze the daily and seasonal occurrence of cetaceans within an area and sometimes more specific behavior such as foraging patterns.”
A second component of the study, led by Fisheries and Oceans Canada research scientist Dr. Norman Cochrane, will characterize the natural (ambient) background noise caused by wind, precipitation and so on, as well as noise produced from shipping, seismic surveys for oil and gas deposits, and other human activities.
The findings of Moors-Murphy’s and Cochrane’s research will be used to:
- assess the year-round occurrence of cetaceans in the Gully MPA and surrounding areas and the relevant importance of these areas to various species, including Scotian Shelf Northern Bottlenose Whales and Blue, Fin, Sei, Humpback, Sperm, and Pilot whales, as well as dolphins.
- assess ambient and anthropogenic noise levels in these areas;
- potentially examine changes in vocal behavior in the presence of specific sources of anthropogenic noise.
Northern Bottlenose Whales
“One of the species we targeted was the Northern Bottlenose Whale, a rare beaked whale that can grow up to 10 metres in length and typically inhabit depths of more than 500 metres,” says Moors-Murphy. “Because they’re a deep-water species, frequently diving to depths of more than 1,000 metres, they occur far offshore and can be difficult to study.” The population off the coast of Nova Scotia, which numbers around 140 individuals, is listed as endangered under the Species at Risk Act (SARA). Relatively little is known about a second population in Davis Strait—assessed as Special Concern—mainly because there haven’t been as many dedicated studies of this more northern population.
The research is investigating how Northern Bottlenose Whales use shelf-break areas between the Gully, Shortland and Haldimand canyons in relation to how they use their critical habitat in the Gully. It may also help to identify other critical habitat for the population, which is one component of the Fisheries and Oceans Canada recovery strategy for this species.
“We know the whales travel between these canyons, but we need to know if these between-canyon areas are more than just migration routes and may actually constitute critical habitat for Bottlenose Whales,” says Moors-Murphy. “My previous studies indicate that these between canyon areas may also be foraging grounds. Bottlenose Whales produce distinctive echolocation clicks to find their food and feed, so I can determine whether they’re feeding in the migratory corridors by listening for foraging vocalizations.”
JASCO uses specialized computer software to automatically detect whale calls in the dataset. This helps Moors-Murphy target specific recordings to examine for the presence of whale calls using spectrographic analysis software, which produces visual representations of the sounds called spectrograms.
“I get more information from looking at the spectrograms than listening to the recordings because a lot of whale vocalizations occur at frequencies outside the human hearing range. I can see sounds even when I can’t hear them,” says Moors-Murphy. “We’re still in the process of assessing the presence of vocalizations from the various species, however the findings so far indicate that Bottlenose Whales frequent and forage in all three areas including those between the canyons throughout the year.”
The data also revealed the presence of clicks produced by another species of beaked whale that has yet to be confirmed, because these clicks are not well described in the literature.
“One theory is the mystery clicks may be from Sowerby’s Beaked Whales, the only other species of beaked whale regularly observed in this area, but we can’t confirm that at this point,” says Moors-Murphy. “We need an opportunity to record these whales when they’re at the surface to compare with the vocalizations of the unidentified species.”
The Atlantic population of Blue Whales, which numbers in the low hundreds, is also classified as endangered. On the Scotian Shelf, vocalizations of this species were detected primarily in winter and sometimes in the summer months, providing important information on their seasonal occurrence, about which little is currently known. The recorders also picked up Fin Whales, a baleen whale classified as Special Concern under the Species at Risk Act.
Findings show there are more Fin Whale calls detected in the winter than in summer, which could suggest that at least some individuals occur offshore throughout the winter rather than migrating elsewhere as previously suggested. Analyses have also detected vocalizations from Sei Whales in offshore areas most commonly during summer months.
“This research will vastly increase our knowledge of cetaceans in East Coast waters and, along with determining areas of importance, will inform the development of strategies to minimize the impact of human activities, including noise, on at-risk species of cetaceans,” says Moors-Murphy. Her monitoring program continues to expand, and she will be placing more acoustic recorders at other sites off Nova Scotia starting in April 2015.
- Date modified: