Dynamics of Large Whale Entanglements in Fixed Fishing Gear

Large Whale Entanglement Mitigation 

The North Atlantic right whale (Eubalaena glacialis), a species restricted to the coastal northwest Atlantic, numbers fewer than 409 individuals and has been declining since 2010 (Pace et al. 2017; Pettis et al. 2019, in prep.). Entanglement in fishing gear, especially in fixed gear like pots and gillnets, is the leading cause of human-induced mortality and serious injury, occurring at a rate that is not sustainable for maintaining a viable population. Entanglement mortalities and serious injuries consistently exceed the regulatory limits of the Potential Biological Removal rate set under the Marine Mammal Protection Act (presently less than one whale (0.9) per year is allowed to be taken by human activities; see NOAA’s 2018 Stock Assessment Report for North Atlantic right whales). In 2017, 17 North Atlantic right whales were found dead in the U.S. and Canada, compared with an annual average of 3.8 per year. As a result of this elevated mortality rate, NOAA Fisheries declared an Unusual Mortality Event for this species.  In 2018, four right whales were found dead, three as a result of entanglement. Zero calves were born that year. There were also three live entangled right whales with attached gear and one with severe entanglement injuries documented from July – Aug 2018. In 2019, there were ten dead right whales observed, nine in the months of June and July, and one in September. Four actively entangled whales were also observed, one that was seen entangled and later showed up as the tenth dead whale, and one that has since been disentangled. On June 25, 2020, the first dead right whale of the season was found. Cause of death is yet unknown. In short, to avert the near-term possibility of extinction of this species, we urgently need to eliminate the threat to these whales from entanglements in fishing ropes.

Also see

Case Studies in North Atlantic Right Whale Fishing Gear Entanglements

Entanglement in commercial fishing ropes threatens the recovery of the North Atlantic right whale (Eubalaena glacialis), a species largely restricted to waters off of eastern North America. In recent years, serious entanglements have been increasing, and mortality from conflicts with fishing operations exceeds US legal mandates, with 83% of the population showing incidence of scarring as a consequence of these encounters.

What happens when whales encounter fishing gear is complex and poorly understood. The goal of creating the case studies associated with our publication (see: North Atlantic Right Whale Entanglement Case Studies on the Publications Page - scroll all the way down) was to combine what we know to date on the individual whales entangled, the configuration of ropes entangling them, the extent of their injuries, and what can be learned about the gear retrieved from them. There is much to learn about the nature of these conflicts, and increasing our understanding about these events can help point to some of the more promising ways to avoid them or reduce their severity.

The 30 whale entanglement publication case studies are a subset of total whale bycatch that has occurred off the eastern shores of the US and Canada, with a particular emphasis on the waters south and west of Nova Scotia. Featured here are cases involving the endangered North Atlantic right whales for which:

  1. Fishing gear was retrieved and warehoused by NOAA/NMFS;
  2. Gear archived prior to June 2010 was made available for analysis by an independent rope engineer reflecting 30 right whale events which occurred from 1994-2010;
  3. A disentanglement responder team or a necropsy team was able to document how ropes and other gear were attached to the animal; and
  4. A relatively good understanding exists of some or all the injuries produced by entangling ropes (from images, video or assessments made by disentanglers).

Each two-page case study integrates into five main categories a suite of information from a variety of different sources. Together they are intended to provide a comprehensive picture about the entangling gear and its impacts on individual animals. The information contains:

  • Life history information of the individual whale including catalog number/name, gender, birth year if known, age/age class when first seen entangled, and reproductive status before and after entanglement (if known);
  • Timing and duration of the entanglement, wounds acquired from entanglement, disentanglement efforts, the animal’s present status, and the number of prior entanglement events for the individual;
  • A drawing of the gear configuration with explanatory text;
  • Gear type and component if known, rope polymer, measurements of rope diameter, tested and new breaking strengths of ropes; and
  • Photographs of entanglement configuration and injuries.

Appended to each two page case study, when available, are the findings of the gear analysis carried out during this study including images of the gear.

Documentation of each entanglement case originated with the efforts of the Atlantic Large Whale Disentanglement Network, a consortium of researchers, fishermen, government managers and other professional mariners, to provide safe and efficient responses to reports of entangled whales along the North American East Coast. Further assessment was done by the authors after reviewing all sightings data, response actions, photographs and videos of the animal over the duration of its entanglement or at a necropsy. The entanglement configuration diagrams were created by an entanglement case expert who was directly involved in many of the events (Scott Landry/Provincetown Center for Coastal Studies). The diagrams are intended to make as clear as possible the most plausible layout of gear on a whale’s body at the time of its first discovery, and not depict the details of the gear itself or the level of injury to whales.

Life history, sighting, and fate information for North Atlantic right whales was obtained by permission from the North Atlantic Right Whale Consortium Catalog (curated by the New England Aquarium [NEAq]).

Fishing ropes retrieved from the entanglements and warehoused by NMFS were examined by a rope engineer, Hank McKenna, to determine their polymer type, diameter, color, breaking strength, condition, and other properties of their construction. These data supplement reports already compiled by NMFS about these ropes.


These case studies resulted from the work of many individuals who have been involved in whale research, gear research, necropsies, and disentanglement interventions over several decades. The original 30 case studies were prepared by Amy Knowlton and Candace Borutskie of the New England Aquarium, and Scott Landry of the Provincetown Center for Coastal Studies. We would like to thank John Kenney from NMFS for access and assistance with retrieved gear, and Patrice McCarron and Heather Tetreault of Maine Lobstermen’s Association, Stormy Mayo and Brian Sharp of PCCS, and Michael Moore of Woods Hole Oceanographic Institution for their guidance and input in developing the case studies.

This work would not have been possible without the efforts of the Atlantic Large Whale Disentanglement Network. Entanglement response activities were conducted under the authority of NMFS, the NOAA Marine Mammal Health and Stranding Response Program (Permits 932-1489 and 932-1905), DFO Canada and with major support from NMFS.  Most right whale photos were obtained under a permit held by the contributing organization from NOAA or DFO Canada.  Support for the Dynamics of Whale Entanglements Project is from the Consortium for Wildlife Bycatch Reduction at the New England Aquarium under US DOC-NOAA Grant # NA09NMF4520413. Additional support for development of the case studies or the information on which they were based was provided by NOAA grant NA09OAR4320129 through Woods Hole Oceanographic Institution and private donors.

For more information, see also the Conservation Biology paper by Knowlton et al (2016) on the Publications Page, or on the Conservation Biology Website.

All right whale entanglement case studies

Updated May 2022

A full suite of case studies have been developed and can be found below. This includes all right whales observed with attached fishing gear (only a subset of cases had retrieved gear for our 2016 publication). For each case study, we review information found in NOAA Fisheries entanglement reports (see https://www.fisheries.noaa.gov/new-england-mid-atlantic/marine-mammal-p…) to assess whether gear type and country of origin have been determined and include this information. We also assess the timing of sightings pre and post entanglement and if we feel confident about country of origin based on that information, we will include this. If no country is noted under the gear type, it means this information is not available.

These case studies will be edited if additional information becomes available about the whale or the gear. New case studies will be added as they are created. These case studies are provided for information sharing only. Please contact Amy Knowlton with further questions about the case studies or use of the data therein.

It should be noted that right whales with attached gear represent just a subset of entanglements that right whales have experienced. Most entanglements leave scars only. For data assessed from 1980-2019, a total of 1705 entanglements have been documented and 136 of those cases (8%) had attached gear and are presented here.

Modeling Right Whale 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.

Research paper:


Project video:

Saving Whales: Bycatch Solutions from Kate McClellan on Vimeo.

Lobster Gear Configurations

The Maine Lobstermen's Community Association and the Consortium for Wildlife Bycatch Reduction worked with lobstermen in the Gulf of Maine to document the range of fixed-gear lobster fishing methods for the first time. The publication provides new data and illustrations on how lobster trap gear is configured and deployed by season and location. It fills a major gap in our understanig of the characteristics of trap gear, and it is intended to help fisheries managers and scientists better understand the fishery and evaluate the relative impacts of potential regulatory changes involving lobster gear. It is also a tool for further enganging lobstermen in constructive dialog about the kinds of gear and fishing methods that may pose the lowest risk to whales from rope entanglements. 

Project Partner(s)
Anderson Cabot Center for Marine Life, University of New Hampshire, Bellequant Engineering