Co-authored by Heather Delanty of NRDC's Oceans Division
It can be difficult to imagine what entanglement in fishing gear really means for a North Atlantic right whale. How it feels in the moments after entanglement or after months or years of dragging around heavy gear.
But one group of scientists understand this all too well: the veterinarians who respond to right whale stranding events and determine the cause of death (through a procedure called a “necropsy” that is similar to an autopsy in humans).
A team of scientists, led by veterinarian Dr. Sarah Sharp who works for the International Fund for Animal Welfare, recently released a report describing the necropsy findings for all documented right whale deaths from 2003 to 2018.
What they found was shocking and harrowing in equal measure.
No adult or juvenile right whale had died from natural causes during this time period—all were a result of human actions. The two major causes of death were identified as entanglement in fishing gear and vessel collisions. Both were found to “inflict profound physical trauma and suffering” on right whales.
Entanglements in particular cause both short-term (“acute”) and long-term (“chronic”) harm, and are driving the long-term decline of the species. Here are some insights from Dr. Sharp’s study that help explain why entanglements are such a serious problem for right whales.
How do right whales become entangled?
Right whales are unlikely to see or detect fishing gear before it’s too late and, in many cases, they swim directly into it. To a right whale, contact with fishing gear feels like contact from a predator, and so their natural instinct is to start to roll to try and escape. Tragically, this means that the whale ends up wrapping the gear around its entire body, sometimes including its mouth, fins, and tail. Once entangled, the weight of the gear often causes it to wrap around even more tightly, making it practically impossible for the whale to break free.
What does a right whale experience when it becomes entangled in the short and long-term?
In some cases, the whale may be so weighed down by the fishing gear that it cannot return to the surface to breathe. Despite its struggles, the whale drowns within just a few minutes. Calves and young whales that haven’t yet developed their full strength are the most likely to die this way.
Whales that can reach the surface and continue to swim while still dragging gear may suffer a number of painful injuries in the coming days and weeks. The rough ropes slowly and painfully chafe into a whale’s skin and, over time, may cut deeply into the muscle and even down into the bone. These agonizing wounds also make the whale vulnerable to infections.
Entanglement may also make it difficult for a whale to feed or breathe. Their baleen—the long fibrous plates used to filter out food from the seawater—may be broken as the rope becomes ensnared around their mouths. Not only painful, broken baleen prevents a whale from eating properly for the rest of its life, contributing to malnutrition and/or prolonged starvation. Their blowhole, the airway located on the top of their head, can also be restricted as the rope carves into the skin, slowly cutting off their air supply and making every breath a struggle.
Right whales may continue to drag gear for months or even years, their injuries continuing to worsen like a slow death sentence. The deep wounds caused by the ropes may eventually lead to amputations of the fins or tail, or secondary infections may take hold from which the whales are too weak to recover.
If they have not succumbed to their injuries or related infections, the fate of entangled whales is often slow starvation. They simply cannot eat enough to keep up with the extra energy needed to drag around the heavy fishing gear. Due to their low body weight, deceased entangled whales are more likely to sink beneath the waves never to be found.
Whales may also suffer deformities that eventually lead to their death even if they escape the gear. A two year old male right whale that had stranded was found to be suffering from traumatic scoliosis—the abnormal curvature of the spine as a result of physical trauma to the vertebrae—due to a prior entanglement from which he had escaped. Tragically, the entanglement had compromised his mobility and ability to feed for over a year after he was free of the gear, eventually leading to his live stranding. In the end his injuries were so severe that he needed to be euthanized.
Females are also less likely to successfully produce a calf for years after an entanglement event even if they shed the gear due to the extreme levels of stress experienced, as well as other health impacts. Given that over 86 percent of surviving right whales bear scars of previous entanglements, these insidious effects are undoubtedly playing a significant role in the population’s worrisome decline.
What are the major causes of right whale entanglements?
Entanglements can occur in many types of fishing gear, but the most serious result from entanglement in thick vertical lines that attach fishing gear deployed on the seafloor (e.g., lobster and crab pots and traps) to buoys at the water’s surface that mark the location of the gear. Entanglements in vertical lines occur in both the U.S. and Canada, primarily the American lobster and Canadian snow crab fisheries.
Rope strength is significantly correlated with severity of entanglements. The number of moderate and severe injuries caused by entanglement significantly increased from the year 2000 onwards. This trend coincides with a number of gear modifications in the American lobster fishery towards more durable ropes and heavier traps. An additional variable is represented by the groundfish collapse in the U.S. in the early 1990s that resulted in an increase in lobster fishing. The extra energy required to drag the heavier ropes and traps around, combined with the more severe wounds this gear is likely to cause, lead to a greater likelihood of the whales experiencing serious injuries and, potentially, drowning or dying from their wounds, from starvation, or from other health issues brought on by the entanglement.
What is the most effective way to end entanglements?
Whales are at risk of becoming entangled any time fishing line is present within the water column in their proximity. The most effective way to end entanglements is therefore to remove vertical lines from the water—be it through line reductions (i.e., reducing fishing effort or increasing the number of traps per vertical line), seasonal or dynamic fishing closures, or ropeless fishing.
Previous management actions taken throughout the course of Dr. Sharp’s study, including gear modifications (e.g, weak links, sinking groundlines, minimum trap number per trawl, gear marking) and seasonal fishery closures, did nothing to decrease right whale entanglement deaths; in fact, their number increased over this time period.
While updating seasonal fishery closures to reflect areas of new right whale habitat holds promise, there is little evidence to suggest that previous gear modifications like weak links or reduced breaking-strength rope will be effective in freeing entangled whales. Two weak links were found attached to the gear of a dead right whale examined as part of the study; both were still intact (i.e., had not released). And while breaking-strength rope may help decrease deaths and serious injuried from entanglement in adult right whales, it will have little benefit for calves or juveniles, and would still have negative impacts on adult reproductive health, energetic costs, and chronic stress levels, all of which are contributing to the overall decline of the species.
There are now only around 400 surviving right whales and only 95 of those are breeding females. We’ve lost at least 30 animals in a little over two years. This is not the time for half measures. We need to pursue the most effective strategy for reducing all entanglements. We need to get the rope out of the water.