Marine Mammal Entanglement
Large Whale Entanglements
The Threat
Humpback whale entangled in gillnet in lower Chatham Strait.
The primary cause of anthropogenic mortality in humpback whales and many marine animals is entanglement in active fishing gear, derelict gear, and other types of marine debris. The International Whaling Commission recently listed by-catch as a primary concern, and it has been estimated that over 300,000 cetaceans die each year worldwide as a result of entanglements (Reid et al, 2006). The sources of these entanglements are extensive and diverse. Actively fished gear, marine debris, constituting lost or abandoned fishing gear, and non-fishery-related gear have been implicated in marine animal entanglements. Since 1998, NOAA Fisheries’ Alaska Protected Resources Division has received at least 139 confirmed reports of entangled marine mammals.* However, the number of entanglements is certainly much greater since many entanglements go unreported. Scar analysis done on humpback whales in northern Southeast Alaska indicated that 78% (maximal estimate) of the population have scars indicating that the animal had been recently entangled (Neilson, 2007).
Deceased humpback whale with gillnet caught around its tail.
The Impact
For many pinnipeds and small cetaceans, drowning in the gear is typically the cause of death. For large whales whose great size allows them to pull gear towards the surface and even break away from all or parts of the entangling gear to return to the surface for air, this is generally not the case. However, the risk of death still exists if the animal remains entangled. The animal may starve to death, experience physical trauma from the gear, develop infections resulting from wounds, and be susceptible to other threats like ship-strikes. In addition, the impacts of entanglement may be non-lethal, as in the reduction of reproductive success.
Stranding network team using "kegging" technique to free a humpback
Disentanglement
Since the threat of entanglement to large whales is not typically immediate, there is time to cut the animal free. However, disentangling a 45-foot, 40-ton, and typically free-swimming animal is not easy, and involves a modification of an old whaling technique called “kegging” to make the animal more approachable. Historically, kegging involved attaching barrels or kegs to whales by harpooning them. The extra drag and buoyancy of the kegs would tire the whale out and keep it at the surface where it could eventually be lanced to death. For disentanglement purposes, rescuers throw grapples or use hooks on the end of poles to attach to the gear entangling the animal. Instead of barrels, rescuers use large polyballs (buoy floats) for buoyancy and drag to keep the whale at the surface, slow it down and generally tire it out. The desired result is a whale that is more approachable, allowing rescuers to safely assess the animal and entanglement, and attempt to free the animal. Specially designed hooked knives on the end of poles are then used to cut the animal free of entangling gear.
Technology
Telemetry buoy, housing a GPS transmitter, tracks an entangled whale. The buoy is attached to the gear entangling the animal.
In addition to specially designed tools that help responders get hold of and cut free large entangled whales, there are transmitters and receivers that allow NMFS to automatically and remotely track an entangled animal over time. The science is called telemetry and it is an important tool in helping us rescue whales. The Alaska Response Network uses telemetry to track and re-locate entangled whales that cannot be disentangled during the initial response due to limited resources (experience of personnel, proper equipment), and/or condition restraints (weather, sea state, time of day, remoteness of location). In addition, telemetry is useful in those cases where an effort has been initiated, but terminated early when condition considerations or the behavior of the animal makes it dangerous for the rescue team to proceed. Thus in all regards, telemetry increases the safety of disentanglement operations, and may assist in its overall success.
The Network uses a pair of transmitters – an Argos/ GPS-based transmitter along with a VHF radio transmitter. Both transmitters complement each other and are placed together on a telemetry buoy that is specially designed to hold the tags and be attached to the entangling gear trailing behind the animal. Telemetry buoys, like the disentanglement tools, are strategically placed throughout the state with trained personnel.
Nine-day track of an entangled whale in southeast Alaska. Animal successfully freed.
In August 2006, Network members tagged an entangled humpback in lower Stephens Passage in Southeast Alaska. The next day the Network was able to respond, re-locate the animal using the transmitters, and cut all wraps of gear from the animal. Unfortunately, lines remained embedded in wounds and thus attached to the animal. The telemetry buoy had to be re-attached to track of the animal. Over the next 9 days and 215 nautical miles, the animal was tracked as it swam southwest along Frederick Sound, south down Chatham Straits, and out to Coronation Island. However, on the 10th day the animal moved back into the sheltered waters of Chatham Strait and conditions cooperated to mount another rescue operation. This time the Network was able to finish the job and completely free the animal from the large mass of trailing gill net gear.
Trained stranding network members assess an entangled whale before attempting to cut it free.
Network and Authorization
Response to disentanglements is coordinated by NOAA Fisheries’ Alaska Region Protected Resources Division, and receives authorization under the agency’s national Marine Mammal Health and Stranding Response Program (MMHSRP) permit (#932-1489). Disentanglement network response is dependent on upon the commitment of many state and federal agencies (e.g. NOAA Fisheries Office of Law Enforcement, the U.S. Coast Guard, the Alaska Department of Fish and Game), private non-governmental organizations, fishermen, and other individuals working together. Whale rescue is complex and dangerous for the whale rescuers as well as the animal. Network response to entangled whales may only be attempted by authorized persons who are experienced, trained, knowledgeable, and have proper support and equipment, working under NOAA Fisheries’ MMHSRP permit.
Response and Outcome
Stranding network members with the assistance of the US Coast Guard free an entangled humpback whale.
The Alaska network to respond to entangled whales has grown since its inception in 1998, and now comprises over 100 participants who have received different levels of training in order to support disentanglement efforts statewide. The network now has 8 caches of specialized equipment strategically distributed throughout the state. Since 1998, the network has mobilized several dozen responses, many of which successfully released animals from life threatening entanglements.
While disentanglement may help save some of these animals, it is not the long-term answer. The value of disentanglement is that it provides information that might help managers, fishermen and other ocean users with the ultimate goal of lowering or at least mitigating the entanglement risk to large whales.
NOTE: These are draft numbers and are subject to change.
How to Report Marine Mammal Strandings and Entanglement
Stranding network members receive training on whale disentanglement. Training, proper equipment and authorization is necessary for a safe response.
Let us know if you see injured, entangled or dead marine mammals in the water or on the beach. The most important information to collect is the date, location of stranding (including latitude and longitude), number of animals, and species. Please don't move or touch the animal
Online Reporting Form(for the general public)
Stranding Report Phone Numbers
- Protected Resources Office:
- Juneau: (907) 586-7235
- Anchorage: (907) 271-5006
- NMFS 24 Hour Hotline: (800) 853-1964
- Alaska SeaLife Center Stranding Hotline: (888) 774-7325
More Information
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