How is sound used to protect marine mammals?
Human impacts on marine animals include entanglements in open-ocean and coastal fisheries, interactions with aquaculture facilities, and ship strike. Acoustic devices are being employed as a tool to reduce risk and decrease these human impacts.
Pingers: Reducing the Risk of Entanglement in Gillnet Gear
Entanglements in fisheries is a global problem that affects at least 40 species of cetaceans. World-wide, over 300,000 cetaceans are estimated to be incidentally caught in fishing gear each year. Some species, such as the Vaquita, are threatened with extinction due entanglement-related deaths.
Small coastal cetaceans, like the Vaquita and their northern relatives, the harbor porpoise are vulnerable to entanglement in gillnets primarily due to overlap between their habitat and gillnet fisheries. Traditionally, gillnet gear consists of nylon nets that are suspended in the water column. Marine mammals may not detect the fine-mesh nets in time to avoid a collision. Cetaceans may also become entangled due to opportunistic feeding on fish that are already captured in the nets. As gillnet operations continue in areas inhabited by coastal cetaceans, methods to reduce entanglement risks are needed.
One technique developed to reduce cetacean bycatch in gillnet gear is to attach acoustic “pingers”. Pingers emit pulsed, high frequency signals that alert animals to gear in the water column. Cetaceans may use echolocation to investigate the pinger sound source and avoid the gear, or they may simply be startled by the sound and avoid the area.
Commercially available pingers broadcast short duration (<1 s) signals at 10 kHz with source levels of 132 underwater dB. It is critical that pingers do not deter fish targeted by the gear, and hence, frequencies should be set outside the auditory range of fish (>2 kHz). It important, and also challenging, to deter pinnipeds (seals and sea lions) from gillnets. Pinger signals may result in the “dinner bell” effect, where sound acts as an attractant to a food source, and in this case, would put seals and sea lions at risk of entanglement in gillnet gear.
Research suggests the effectiveness of pingers may vary widely between species, fishing areas, and fisheries. Both field and laboratory studies have shown that some cetaceans, such as the harbor porpoise, Franciscana dolphin, and several species of beaked whales, avoid nets equipped with acoustic alarms. However, mixed results have been cited for the bottlenose dolphin, and the striped dolphin has shown no reaction to pingers.
The deterring effects of pingers are not clearly understood, and their long-term effects are not well known. Widespread pinger use could exclude marine mammal species from critical habitats. Pinger signals may cause negative physiological and auditory effects on cetaceans and other marine animals, of which current knowledge is limited. There is also concern that animals may habituate to pinger signals, causing the effect of the alarms to be reduced or lost over time. Managers have expressed caution with regards to pinger technology and suggest that its usage be implemented in addition to other risk-reduction measures such as area-closures and/or other gear modifications. Pingers are nonetheless recommended by the International whaling Commission (IWC) as a means to reduce bycatch of harbor porpoise and other small cetacean species.
Longlining is a commercial fishing method that uses hooks and line. Long lines have a horizontal line that are 1-3 miles in length, to which shorter lines are attached that have baited hooks. The longline is left in the water from one hour up to a day or more before it is reeled back onto the boat and hooked fish are harvested. Cetaceans, including false killer whales, pilot whales, sperm whales, and a variety of dolphin species are attracted to longlines because of the opportunity to remove bait or caught fish from the line. Cetacean-longline interactions may include animals being hooked or entangled in the lines, which can seriously injure or kill an animal. Important consequences for the fishermen are that their gear can be damaged or lost.
Commercial fishing for sablefish (also known as black cod) occurs annually in the Gulf of Alaska from March 1-November 15. Sablefish are large, bottom-dwelling fish that live in water deeper than 300 m. They are the highest valued finfish in Alaskan commercial fisheries. The fishery has an estimated annual value of about $100 million (U.S. dollars) with fishermen landing an average of 13,000 metric tons of sablefish each year. In the eastern Gulf of Alaska, sperm whale depredation of sablefish longline fishery has been reported since at least 1978. Working the fish free from the lines without getting injured, sperm whales remove hooked sablefish from the longline gear before it is retrieved. Whales can strip nearly a quarter of the fish catch.
Due to changes in regulations that permit a longer fishing season, the number of sperm whale encounters with longlines in the Gulf of Alaska has increased substantially. Growing concerns for both entanglement and losses to fish catch have prompted more research on sperm whale and longline gear interactions. Using hydrophones and acoustic tags, researchers working on the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) found sperm whales to be vocally active around fishing boats setting out and hauling in longline gear. Whales appeared to be foraging at depths of 50m near the gear, as opposed to their natural foraging depths of 300-400m for the area. Scientists think that certain sounds associated with the fishing vessels may attract the whales to the gear. The engines of the fishing vessels make a very distinct sound as they engage and disengage while gear is hauled back onboard. Scientists hypothesize that this acoustic cue attracts sperm whales to the longline fishing gear.
Future research includes determining how far away a whale can hear a fishing vessel hauling gear, gaining a better understanding of sperm whale depredation rates, testing gear and hauling modifications to prevent depredation, and testing acoustic deterrents. The National Marine Fisheries Service of the National Oceanic and Atmospheric Administration is using acoustic recorders during their sablefish surveys to monitor the interaction between sperm whales and the fishery and more accurately determine depredation rates.
Acoustic Harassment Devices (AHDs): Preventing Aquaculture/Pinniped Conflicts
Marine (and freshwater) aquaculture is one of the fastest growing food industries (global production ~$70billion). It is estimated that 50% of seafood is produced by aquaculture. Fish farms, as potential sources for food, attract marine mammals, predominantly pinnipeds (seals and sea lions), which will bite fish through the nets enclosing the fish pens. Pushing up against and biting at aquaculture nets puts seals and sea lions at risk of entanglement. To prevent attacks, some farm managers have illegally shot seals and sea lions.
Acoustic Harassment Devices (AHDs) can be used to deter pinnipeds. AHDs emit a high frequency, intense noise intended to repel an animal from an area. Commercially available AHDs operate in a frequency range of 8-20 kHz with source levels 187-195 underwater dB. Most fish do not hear well at these frequencies and are not affected by the AHDs.
There are some potential problems with AHDs. Animals may habituate to the sounds or even learn that the sounds are associated with food (the “dinner bell” effect). Some researchers also believe that prolonged exposure to the sound emitted from an AHD may cause a permanent hearing threshold shift (PTS) in the seals/sea lions being targeted. Another concern is that other species in the area that do not attack the pens can also be affected. Harbor porpoise, dolphin, and killer whale densities have decreased in areas near active AHDs. The overall use of AHDs is viewed as an ineffective deterrent method and some locations (e.g. British Columbia) prohibit their use.
Real-time Automatic-detection Buoys: Monitoring Right Whale Locations to Avoid Ship Strike
Entrance channels to busy commercial ports can overlap with habitat for the critically north atlantic right whale, causing collisions with vessels to be the leading human impact on the species. The shipping industry has made efforts to reduce the risk of ship strike, however, it is often difficult to spot a whale in time to change course and avoid collision. Regulations have been passed to implement speed restrictions in specific locations along the U.S. east coast, and shipping lanes have been shifted to reduce the risk of collision between large ships and whales. In addition, passive acoustics is also being explored as a tool in determining right whale locations in real-time to reduce ship strike.
Right whales produce a variety of low frequency sounds. The most common are between 10 Hz and 1000 Hz. One typical right whale vocalization used to communicate with other right whales is the “up call”. It is a short “whoop” sound that rises from about 50 Hz to 440 Hz and lasts about 2 seconds. Detection of up-calls have been the most common means of determining right whale presence from acoustic data.
Real-time Automatic-detection buoys, developed by the Cornell Laboratory of Ornithology’s Bioacoustics Research Program (BRP) and the Woods Hole Oceanographic Institution (WHOI) are an acoustic tool being used to monitor right whales off the coast of Massachusetts. In accordance with the development of an LNG terminal in the Port of Boston, Massachusetts, ten auto-detection buoys were deployed between the port’s inbound and outbound shipping lanes. The buoys are tethered to the sea floor and can detect right whale vocalizations within 5 nautical miles. Onboard computers estimate each sound’s similarity to a right whale up-call, assessing acoustic characteristics such as starting, minimum, and maximum frequencies, and the sound’s duration. Up call detections are transmitted back to shore via a cell phone or satellite link, where they are then verified by trained signal analysts. Information on which buoys detected whale vocalizations are re-transmitted to vessels. Data on right whale detections are available online and are also distributed by e-mail. The information is also incorporated into marine safety bulletins. Captains, other mariners, and the general public can also access the real-time information from the “Right Whale Listening Network” . Time from detection at the buoy to posting on the website can be as short as 20 minutes.
At this time, only LNG tankers are mandated to reduce their speeds in the areas around buoys that have detected whales. All other ships are encouraged to check whale-buoy alerts and slow down if necessary. Managers are able to track the LNG vessels via the Automatic Identification System (AIS) – all large ocean-going vessels as well as tugs and tows and larger passenger boats are required to have AIS transponders to avoid collisions with other ships, as well as assist port authorities to better control sea traffic. Information is received on vessel speed and location approximately every 2 seconds. This allows managers to complete real-time compliance assessments for all LNG tankers entering the Boston shipping lanes. Thus far, all LNG tankers have slowed their ship speed and/or adjusted their locations upon receiving a right whale alert.
The map below is an example of the live feed from the Right Whale Listening Network. The live feed shows the latest detections of right whales in Massachusetts Bay.
Additional Links on DOSITS
- Harbor Porpoise
- North Atlantic Right Whale
- Passive Acoustic Recording Tags
- Real-time Passive Acoustic Sensors
- Sperm Whale
- Cornell Lab of Ornithology, Blue Whale Heard Singing off New York Coast.
- “Consortium for Wildlife Bycatch Reduction- Bycatch Reduction Database.
- Cornell Bioacoustics Program, Endangered whales heard for the first time in waters around New York City.
- NOAA Fisheries, Harbor Porpoise Take Reduction Plan (HPTRP)
- NOAA Fisheries, NOAA Office of Protected Resources Ship Strike Reduction Strategy.
- NOAA Fisheries, Northeast U.S. Right Whale Sighting Advisory System (SAS)
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