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Large Whale Entanglements
Entanglement of large baleen whales, including the right (Eubalaena glacialis), fin (Balaenoptera physalus), sei (Balaenoptera borealis), Bryde's (Balaenoptera brydei), minke (Balaenoptera acutorostrata), and humpback (Megaptera novaeangliae) in fixed fishing gear (e.g. pot and gillnet) is a frequent occurrence along the east coast of the United States and Canada. For right and humpback whales, which have detailed photo-identification histories, the records indicate that 78% of the right whale and 66% of the humpback population have evidence of at least one entanglement interaction, with many animals experiencing multiple entanglement events. Entanglement also appears to affect calves and juveniles more frequently than adults, although we are not sure why.
Although most of these animals are able to free themselves from the entangling gear, serious injuries and deaths caused by entanglement occur in numbers that exceed what is sustainable to their populations.
Mitigating bycatch in large whales differs from approaches with other animals because scientists cannot evaluate potential new gear modifications through at-sea trials. Typically, in these trials, catch rates of non-target species are compared between existing fishing techniques and new fishing devices or methods (e.g. comparing harbor porpoise bycatch in gillnets with and without pingers). In the case of the North Atlantic right whale, the species is so endangered, and the entangling events are so rarely observed, that it is not possible to measure the efficacy of new fishing gear using comparative trials.
Instead, scientists, fisheries engineers, and fishermen must link the biology and behavior of whales with the characteristics of a fishery, and infer entanglement likelihood using less tangible methods, such as estimating the level of overlap between whales and fishing gear, monitoring entanglement interaction levels over time, and making educated assumptions about how whales may respond when they first interact with fishing gear. The Consortium is working to 1) identify the characteristics of fishing gear that cause severe and fatal entanglement risk to whales and 2) provide a stronger scientific basis for evaluating the impact of existing, proposed, and future potential fishing methods to whales.
The Consortium and its partners are studying fishing gear retrieved from entanglements, changes in rope manufacturing, and whale scars to better understand how rope type contributes to whale entanglements and injury sensitivity.
Retrieved Fishing Gear Analysis
The National Marine Fisheries Service has retrieved gear from all entangled baleen whales found since 1997. The Consortium is reviewing information on the breaking strength and other characteristics to see how they may relate to entanglement severity.
Changes in Rope Manufacturing
Serious injuries from entanglements have increased numerically since 1980 - one reason for this increase may be changes in ropes used in fisheries over this time period, specifically rope breaking strength. Amy Knowlton, at the New England Aquarium, has been researching the changes that have occurred in rope manufacturing over this time period and found that today's ropes are at least 30% stronger and three times more abrasion resistant than older lines. If higher breaking strength is leading to increased injury severity because gear does not break as quickly, researchers believe that scars will show evidence of sustained interaction.
Scar Severity Analysis
Researchers are examining records for all right whales observed with scarring and all other whale species for which gear was retrieved and scarring data is also available. In an initial assessment, researchers reviewed each entanglement event in which the animal was seen carrying gear, for evidence of a complex entanglement or sustained interaction in two different time periods: 1980-1992 and 1997-2002. A significantly greater number of animals had severe entanglements in the later time period, in many cases, resulting in death or disappearance. Further work is underway to evaluate all entanglement events from 1980-2006, including those just determined by scar evidence (780 unique events), and categorize the scar severity to see if there have been any changes in severity levels over time. This work may help inform researchers and managers as to whether there is a maximum breaking strength of rope that whales can break free from without causing severe injury.
To investigate the potential role of rope parameters on entanglement complexity, wound severity, and outcome to the animal, a suite of case studies was created for 18 right whales and 22 humpback whales for which gear was retrieved and analyzed. An analysis of the findings is underway now.
One of the challenges in addressing gear interactions with endangered whales is the difficulty of conducting meaningful field tests on fishing gear with the animals. Because entanglements are extremely rare for any given location or fishermen, testing the entanglement effects of an innovative fishing gear is not feasible. In the face of this conundrum, we have started to address one specific problem: What happens when a whale's flipper encounters a line in the water column? This may help to develop buoys and or lines that will do less damage to whales and are less likely to entangle them. The Consortium is working on two projects to simulate large whale entanglements in fishing gear.
Field Testing Entanglements
In 2008, the Consortium began testing encounters between a full-scale model right whale flipper and fishing gear. The objectives are to test ropes of different diameters and tensions, measure the duration of entanglement, analyze the data to determine what scenario might cause the whale flipper to shed the gear rapidly, and to use this data to input into a whale entanglement computer model being created by Dr. Laurens Howle at BelleQuant Engineering.
A full-scale model flipper was built and attached to a research vessel by Ken Baldwin, his team at the University of New Hampshire, and Blue Water Concepts. Observations of the flipper-rope interactions indicate that contact inside 80 cm from the body causes the line to snag and stay attached to the flipper. When the contact occurred further toward the end of the flipper, the line slid off the end of the flipper as soon as the rope gained tension.
It was hypothesized that a taut line, or one with higher tension, might reduce the risk of whale entanglements by encouraging the line to slide from the body. Observations of the flipper, after encounters with the taut line, showed damage from the "sawing" action of the line. See full report here.
Computer Modeling Entanglements
In the absence of direct observations of entanglement events involving baleen whales, the goal of this project is to better understand the dynamics of rope entanglements using computer models.
Dr. Laurens Howle is creating a whale entanglement modeling system as an aid to understanding how whale behaviors and the interaction of gear and whales in a fluid environment explain entanglement events and risk under different scenarios. Using an Xbox 360 controller, the user can "fly" a whale though a virtual environment containing multiple traps, vertical trap lines, and horizontal ground lines. These simulations will consider all parts of the whale body involved in entanglements, mouth and flippers in particular. In much the same way that computer models help aerospace engineers evaluate the performance of aircraft designs, computer aided models will help us study the nature of whale entanglements and the relative merit of various proposed gear modifications.
Watch the Large Whale Entanglement Simulator Video
North Atlantic Right Whale Biology
Researchers working on right whales suspect that vision is the primary mode of sensory detection for prey finding and navigation. However, only anatomical studies of baleen whale eyes have been conducted, and none of those have been carried out on right whales. Cetaceans generally appear to have adapted well to the wavelength absorption characteristics of the ocean, and have developed light-gathering and enhancement methods, retained high levels of resolution acuity, and developed special pupillary and retinal mechanisms to adjunct the different light levels and above/below water vision requirements.
Dr. Jeffry Fasick, at Kean University, has completed research which focuses on marine mammal vision, specifically, determining the wavelengths of light (color) to which the eye is most sensitive. His findings indicate that right whale cones have a blue-shifted spectral sensitivity similar to odontocetes, but that the spectral sensitivity of the rod visual pigment is more similar to terrestrial mammals. This research could allow fishing tackle to be constructed or appended with a color that a particular species would be able to detect visually and possibly avoid.
The Consortium is currently conducting several projects in collaboration with the Maine Lobstermen's Association (MLA) to identify potential fishing practices that would mitigate risk to whales from lobster gear. The MLA is working with fishermen to document the range of commercial fishing methods practiced in the Maine lobster industry, identify current fishing methods that might pose the least risk to whales, and identify innovative fishing gears and techniques that may reduce whale entanglement risk and severity. As part of this effort, the MLA has met with Maine lobstermen from Cutler to Kittery to map how, when, and where they fish (as well as when and where they don't fish) on a harbor-by-harbor basis.
The Consortium hope to produce an understanding about the spatial temporal patterns of lobster fishing in the Gulf of Maine and the range of methods used as they pertain to local conditions.