North Atlantic right whales and the dangers and effects of entanglement

By Haley Kilgour, SRC intern

Mysticetes (baleen whales) arguably fall under the category of charismatic marine megafauna, capable of drawing the public’s attention to their conservation concern. However, many species are in quite a bit of trouble. Injury and mortality from entanglement with fishing gear is a problem that affects whales worldwide (Knowlton et al, 2016). It is perhaps one of the greatest concerns for the North Atlantic right whale, and is the second largest leading cause of death (Knowlton and Kraus, 2001). With only about 500 individual North Atlantic right whales left (Stills, 2017), conservation is urgently required to ensure the survival of the species.

Number of North Atlantic right whales with minor or moderate-severe entanglements (Knowlton et al, 2016).

Much of the conservation for these whales surrounds lessening the amount of entangled gear on the whales that have already been entangled and lessening the amount of gear in which they may get entangled. Thus far, the United States has had limited success (Stills, 2017) and observed deaths of both right and humpback whales have exceeded the potential biological removal levels defined by the United States government (Knowlton et al, 2016). Figure 1 depicts the increasing number of North Atlantic right whales that are becoming entangled. While minor entanglements make up the majority of entanglements, the increasing number of moderate-severe entanglements is also increasing. With so few individuals remaining, every death is devastating. Deaths from entanglement are caused from instantaneous drowning, delayed death from impaired feeding, increased energy demands due to the drag of gear, and stress (Knowlton et al, 2016). Figure two shows in depiction A) a whale that would experience impeded feeding and in depiction B) a whale that would experience increased swimming efforts due to the drag of gear. Pettis et al (2014) found that stress responses to entanglement can affect the health of a whale even after gear has been removed. Van der Hoop et al (2013) found that entangled gear increased the power requirements of North Atlantic right whales by 70-102%.

Two possible configuration of gear on entangled North Atlantic right whales. Dashed lines are used to depict line on the underside of the animal (Van der Hoop et al, 2016).

The current efforts have focused on the reduction of rope within the water column (Knowlton et al, 2016). Knowlton et al (2016) studied the effects of fishing rope strength on large baleen whales, focusing on North Atlantic right whales and humpback whales. The purpose of the study done by Knowlton et al (2016) was to analyze the properties of ropes removed from whales and to examine rope characteristics in relation to species, age, and injury severity. Knowing rope deterioration rate and breaking strength is important because a certain amount of drag from entangled gear can be used by a whale to free itself (Van der Hoop et al, 2016), thus this knowledge can be used to create reduced breaking strength ropes that can effectively be used for fishing but will lessen the morality of large baleen whales.

Gear samples analyzed in this study were recovered by the Atlantic Large Whale Disentanglement Network, with most samples being taken from free-swimming or anchored entangled whales (Knowlton et al, 2016). The gear was assessed for the following characteristics: diameter, material and fiber type, condition, estimated breaking strength, and strength of a new rope of the same type and diameter (Knowlton et al 2016). The severity of entanglement and the configuration of the gear, for the most part, were assessed by photographs (Knowlton et al, 2016).

Per each whale used in this study, there was an average of 1.83 ropes and the condition of the rope for the majority of cases was classified as good to very good (Knowlton et al, 2016). The average breaking strength of rope entangling a North Atantic right whales was 19.30 kN, for humpback whales was 17.13 kN, and for minke whales was 10.47 kN (Knowlton et al, 2016). Knowlton et al (2016) found no adult North Atlantic right whales entangled in ropes below a breaking strength of 20.02 kN, which suggests that they can break free or disentangle themselves from the weaker ropes.

Several of the most dangerous aspects of entanglements for whales are infections caused by the rope cutting into their bodies, increased demands in energy requirements of swimming, and restricted feeding (Van der Hoop et al, 2016). Knowlton et al (2016) suggest that the use of reduced breaking strength rope could reduce mortality. While entanglements may not be prevented, the stress and numbers of mortality could lessen if ropes are easier for the whales to break free from. Knowlton et al (2016) do note that reduced breaking strength ropes would not prevent lethal entanglements in some areas such as calving grounds. Thus a conservation plan that reduces gear on already entangled whales, reduces the amount of gear in the water, and enforces use of reduced breaking strength ropes will be the most effective.

Works Cited

Hoop, Julie M. Van Der, et al. “Drag from fishing gear entangling North Atlantic right whales.” Marine Mammal Science, vol. 32, no. 2, Sept. 2015, pp. 619–642.

Hoop, Julie Van Der, et al. “Behavioral impacts of disentanglement of a right whale under sedation and the energetic cost of entanglement.” Marine Mammal Science, vol. 30, no. 1, 2013, pp. 282–307.

Amy Knowlton, and Scott Kraus. “Mortality and serious injury of northern right whales (Eubalaena glacialis) in the western North Atlantic Ocean.” Journal of Cetacean Research Management, no. 2, 2001, pp. 193–208.

Knowlton, Amy R., et al. “Effects of fishing rope strength on the severity of large whale entanglements.” Conservation Biology, vol. 30, no. 2, Jan. 2015, pp. 318–328.

Pettis, Heather M, et al. “Visual health assessment of North Atlantic right whales (Eubalaena glacialis) using photographs.” Canadian Journal of Zoology, vol. 82, no. 1, 2004, pp. 8–19.

Stills, Jennifer, editor. “North Atlantic right whales in danger.” Science, 10 Nov. 2017, pp. 730–731.

Effects of fishing rope strength on the severity of large whale entanglements

By Leila AtallahBenson, SRC Intern


Figure 1. A free swimming humpback whale, that managed to avoid fishing gear entanglements.

Figure 1. A free swimming humpback whale, that managed to avoid fishing gear entanglements.

On top of whales being majestic giants that are exciting to watch, they are also an important animal for marine ecosystems. They enhance primary productivity in nutrient lacking areas and ocean surfaces, and their carcasses provide habitat and energy sources for deep-sea species1. In both these instances, whales fix carbon, turning inorganic carbon to organic compounds. This not only makes more room for carbon to be absorbed, helping with global warming, but contributes to the available amount of organic matter that marine organisms utilize. Whales are also important to the economy, drawing in around $2 billion per year through whale-watching businesses2.

Unfortunately, these species are prone to human fishing gear entanglements, since they are so large and often spend time in prime fishing areas. Once a whale is entangled the individual can drown quickly, or may be able to breath but later dies from starvation, injuries endured by the fishing gear, increased energetic demands, or stress3. These entanglements often come from pot/trap and gillnet fisheries4. Protecting these species not only helps whales, but helps protect our oceans and economy.

Between 1994 and 2010, Knowlton et al. explored the breaking strength of 132 fishing ropes that were found on 70 whales. This included 30 right, 30 humpback, 2 fin, and 8 minke whales, all along the east coast of the United States. In the U.S., fin and humpback whales are protected, and both in the US and Canada, right whales are protected by law. All of the whales that rope was collected from were categorized by species. Right and humpback whales were also separated by age group. The severity, configuration, and any injuries of the entanglement were recorded with pictures.

Most of the gear sampled was retrieved by the Atlantic Large Whale Disentanglement Network. The entangled rope strength was determined. The majority of entangled rope was found to be in good or very good condition. The rope material, its diameter, breaking strength, condition, and how many of that rope found were considered (table 1).

AtallahBenson_Table 1

The authors asked a few questions from this information. One question was if injury severity is related to rope strength? For right whales this proved to be true. With increased rope strength, right whales had more severe injuries. However, this was not true for humpback whales, whose injuries did not get worse with rope strength, but their injuries seemed to be more randomized.

Another important question asked was if rope strength correlated with whale species or age (see figure 2)? Some of these correlations were clear to see in the evidence. Both right and humpback whales were found with ropes of higher breaking strength than minke whales. Adult right whales were found in significantly stronger rope than juvenile right whales, and both adult and juvenile humpback whales. The average breaking strength was 19.30 kilonewton (nK) for right whales, 17.13 kN for humpback whales, and 10.47 kN for minke whales. The 2 fin whale ropes were 11.12 and 31.14 kN.

AtallahBenson_Figure 2

This information helps us take a better look at the fishing gear we use now, and allows us to make changes to better protect these magnificent creatures. There were only limited numbers of whales that were entangled in rope strengths below 7.65 kN. The use of special ropes, called reduced breaking strength (RBS) ropes, of 7.65 kN or less could reduce whale entanglements at least by 72%. Fisherman in the study area haul about 2.24-3.11 kN for lobster, 2.45-3.11 for stationary gillnets, and at most 6.38 nK for dragging gillnets. These RBS ropes of 7.65 would work for these normal fishing endeavors, and save the whales at the same time. So the next time you’re going out fishing, be sure to grab some RBS rope and help save the whales!


Knowlton AR, Robbins J, Landry S, McKenna HA, Kraus SD, Werner TB. 2015. Effects of fishing rope strength on the severity of large whale entanglements. Conservation Biology: 1-11.

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