Reducing Rope Strength Could Reduce Entanglement Severity

With vessel strikes to right whales on the decline since numerous mitigation measures were put into place, the current number one threat to right whales is entanglement in fishing gear. The majority of the entangling fishing gear involves pot or trap gear (for bottom dwellers like lobster and crab, or certain fish species) and gillnet (for groundfish like cod and haddock, and other fish species). Nearly 83% of the North Atlantic right whale population shows evidence of having been entangled in fishing gear at least once, with 59% being entangled more than once (some whales have experienced over five entanglement events!). Entanglement impacts cover a wide range: from residual scarring only (typically minor), to moderate and severe levels, the latter of which includes individuals with attached gear that can lead to reduced health, infection, severing of body parts, starvation... along with what must be an incredible amount of suffering. Unfortunately, in recent years entanglement cases categorized as severe have become more frequent.

Right whale "Bridle" (Catalog #3311) suffered a severe entanglement during which this line sliced through and under the callosity. Despite disentanglement attempts, Bridle most likely died from causes related to his injuries. Photo: Florida Fish and Wildlife Conservation Commission under NOAA Permit # 932-1905/MA 009526.

Steps have been taken to address this chronic problem, such as the creation of seasonal fishing closures, reduction of the number of vertical lines in the water and use of sinking groundline, but it's still too early to determine how these measures have helped. Researchers from the New England Aquarium (Amy Knowlton, Scott Kraus, Tim Werner) and Center for Coastal Studies (Jooke Robbins, Scott Landry), and rope engineer Henry McKenna turned to examining the ropes recovered from disentangled whales or from those found dead and entangled to see if trends would emerge to shape the story of why these entanglements have increased. That's right- the National Marine Fisheries Service maintains a storage facility that houses the ropes pulled off of entangled whales! This is just one of the reasons why disentanglement by professional teams is so important- they know they need to recover the gear to help advance our knowledge and understanding of the entanglement issue.

"Ruffian" (Catalog #3530), photographed with numerous raw wounds all over his body after a severe entanglement. Photo: Florida Fish and Wildlife Conservation Commission, taken under NOAA Permit #932-1489-09.

Amy Knowlton and her colleagues took these recovered ropes (132 different ropes from 70 entanglements of humpback, right, fin and minke whales) and analyzed them to determine polymer type, diameter, and breaking strength. They then combined this information with whatever was known about the individual whales with regards to entanglement configuration, severity of the injury, and life history to get a bigger picture of what is going on. Their newly published paper "Effects of fishing rope strength on the severity of large whale entanglements" thoroughly explains all of this (and includes a download of supporting information such as an example of a case study and how these ropes were analyzed), but in a nutshell here's what they found:

  • Injury severity has increased over the years, and is related to rope strength.
  • Weaker species (e.g.: minke) and younger whales are less likely to successfully break free of stronger rope, resulting in complex and potentially lethal entanglements.
  • Reduced breaking strength rope (breaks at 1700 pounds or 7.56 kN) could reduce the probability of mortality by 72%.
  • Forces applied during normal fishing operations in many areas are lower than 1700 lbs, so presently used fishing line is stronger than what the majority of fisheries need.
The tight line on this whale (Catalog #3279) cuts through the blowholes and into the head, while likely also wrapping through the mouth as the line is seen exiting the top of the lip. The whale's ability to breathe was clearly inhibited. Photo: Canadian Whale Institute/ New England Aquarium.

Rope manufacturing evolved in the 1950's from natural fibers to synthetic, and in the mid 1990's another leap was made in production by using methods which blend different plastics together (creating copolymer ropes like Polysteel and similar brands) which are widely used today. In a similar shift, pot traps made of wood were replaced with wire traps by the early 1980's, which allowed for an expansion of fishing effort both temporally and spatially. Amy Knowlton and her coauthors believe this shift into heavier, stronger gear is responsible for the increased severity of large whale entanglements. The next focus is to work with rope manufacturers to develop ropes that have reduced strength but better degradation resistance, and also to evaluate where such ropes could be used effectively by fishers. Stay tuned for further updates on this important work!

"Bayla" (Catalog #3911) in extremely poor health while severely entangled. She was found dead at sea a couple of weeks after this photo was taken. Photo: Georgia Department of Natural Resources, taken under NOAA Permit #932-1905.

This new paper has received interest from the media, so here are a few links to articles about the research and interviews with Amy:

"Fishing line causing lethal entanglements for right whales," CBC News
"Right Whales: Saving the iconic endangered species, a Q&A," Nature World News
"How To Stop Whales Getting Entangled In Our Nets," IFL Science!
"New Publication On Baleen Whale Bycatch," Consortium for Wildlife Bycatch Reduction

"Gannet" (Catalog #2660) displays severe wounds to her tail stock and flukes after an entanglement. Hopefully injuries like this can become a thing of the past. Photo: New England Aquarium