Entanglement in fishing gear is a known source of large whale injury and mortality. CCS collects data during its disentanglement efforts that have been essential to understanding this problem. Additionally, the Humpback Whale Studies Program undertakes the important task of identifying the individual humpback whales that have been involved in entanglement events. For each individual found entangled along the US East Coast, we attempt a match against the Gulf of Maine Humpback Whale Catalog. Matching an entangled humpback is no easy task because the features that we use for identification are often held underwater, obscured by the entangling gear or altered by entanglement injuries. Photo-identification matches are often based on the dorsal fin alone and in some cases we have had to rely on a genetic match. However, when we are able to link an entangled whale to a previously cataloged individual, then we can learn a great deal more about the event. For example, we can better bound the maximum duration of entanglement, determine demographic factors that might have contributed to the entanglement and monitor the ultimate fate of the individual. This information is used in our own research and shared with the NOAA Northeast Fisheries Science Center for Federal determinations of the impact of fisheries on whale stocks (see Henry et al. 2016).
Our research focuses on the frequency of entanglement, the nature of these events and their impacts on individuals and populations. Much of the data comes from entanglement reports and disentanglement responses. However, we also study injuries on free-ranging humpback whales as an alternate way of tracking entanglement rates. We developed systematic protocols for data collection and our methods of scar interpretation have been modeled on and successfully tested with eye witnessed entanglement events. This research indicates that more than half of the humpback whales in the Gulf of Maine exhibit scarring that was likely to have resulted from a prior entanglement. Scar acquisition rates indicate that an average of 12% of the population becomes entangled annually. Juveniles appear to be at highest risk, although whales continue to become entangled when mature. Fewer than 10% of the whales that acquire new entanglement injuries were actually seen and reported while entangled. These techniques are also being applied in other populations and oceans to better understand entanglement.
Entanglement is a more frequent occurrence than observed cases would suggest. The most effective management initiatives are therefore those that focus on prevention, rather than intervention for witnessed events. Nevertheless, disentanglement can improve the outcome for individuals that are witnessed entangled and generates critical data for understanding and thereby preventing future events. Learn more about our disentanglement efforts here.