Posted by: The ocean update | May 20, 2015

New study may help free whales from fishing rope entanglement

This four-year-old male right whale entangled in heavy fishing rope was spotted in February 2014, 40 miles east of Jacksonville, FL. Florida Fish and Wildlife biologists removed the fishing rope. (Florida Fish and Wildlife Conservation Commission image, taken under NOAA research permit #15488)

This four-year-old male right whale entangled in heavy fishing rope was spotted in February 2014, 40 miles east of Jacksonville, FL. Florida Fish and Wildlife biologists removed the fishing rope. (Florida Fish and Wildlife Conservation Commission image, taken under NOAA research permit #15488)

May 20th, 2015 (John Barrat). New data just published in the journal Marine Mammal Science may help save the whales, or at least a good many of them.

Using vertebrae and muscle measurements taken from dozens of whale skeletons in museums and research facilities around the country, a team of marine biologists has created a new chart estimating the maximum pulling force that different whale species can create with their tail flukes. Knowing these values may someday aid in designing fishing rope that whales can break or nets with built-in weak links that come apart when a whale becomes entangled.

“There is this idea that large whales are the strongest animals on the face of the earth and that nothing can stop them,” says William McLellan, a marine mammal expert at the University of North Carolina Wilmington and co-author of the paper. “While they have a lot of strength in their axial tail muscles, whales are not infinitely strong. There are actually some upper limits to their strength and the type of line they can break.”

“Critically endangered whale populations are struggling to recover and one of the things holding them back is entanglement in fishing gear,”  says Charles Potter, a whale expert at the Smithsonian. “It’s a very slow and painful death.”

Representative vertebrae from several cetacean species, shown at the same scale and viewed from the cranial face.

Representative vertebrae from several cetacean species, shown at the same scale and viewed from the cranial face.

One way to estimate the maximum force a muscle can produce is to simply measure its size. Starting with known values of force and thrust measured during trials with live bottlenose dolphins, the team used a cross section of a stranded bottlenose dolphin’s axial muscles (which power the tail flukes) taken near the dorsal fin and calculated the cross-sectional area of the dolphin’s muscle in this region of the vertebral column. With this known ratio between force and muscle area in bottlenose dolphins, the team next applied it to whales, taking measurements of museum whale vertebrae to get an estimate of a species’ average adult axial muscle size. With this measurement the scientists were able to estimate how much force the animal could produce.

For example, the study determined a 16.4-foot-long, short-finned pilot whale can produce a maximum force of roughly 1,131 pounds. A 12-foot whale of the same species can create a maximum force of 701 pounds.

Whale scientist Logan Arthur takes the measurements of a sperm whale vertebrae in the Smithsonian’s collection. (Photo by Ann Pabst)

Whale scientist Logan Arthur takes the measurements of a sperm whale vertebrae in the Smithsonian’s collection. (Photo by Ann Pabst)

“We started off with bottlenose dolphins and went up the size tree through to right whales, blue whales and sperm whales, estimating total force production. This is the first time we know of that this has been done,” says McLellan, who conducted the work with researchers from the University of North Carolina Wilmington, the Smithsonian’s National Museum of Natural History, the University of Maine and New River Kinematics.

To verify the accuracy of their estimates of axial muscle cross-sectional area in different whale species “we did a lot of dissections on stranded animals, so we had direct connection with the tissues of the large whales while we were on the beach,” McLellan says. Team members also took measurements from large whales that are on exhibit up and down the east coast, such as the right whale on exhibit at the New Bedford Whaling Museum.

One surprising aspect of the study, according to principle author Logan Arthur, a recent graduate at UNC Wilmington, is that the force a whale produces begins to drop off in scale to its body size the larger it gets. In other words, “per unit body length, the larger whales were actually weaker than a dolphin,” Arthur says.

Another possible use for this data, McLellan says, is “we’ve been looking at the strength of the big offshore hooks used to catch bluefin tuna and swordfish and how much force a pilot whale would need to produce to be able to bend one of these hooks, straighten it and release itself.”

“It is fascinating to me,” Potter says, “that some whale specimens collected by the Smithsonian at the turn of the 19th century are being used to help with conservation issues that are confronting us today. In a sense museum specimens never stop giving. This is the kind of data that we biologists can produce and turn over to the fishing gear-tech folks to help create fishing gear that is safer for whales.”

Citation : Arthur, L. H., Mclellan, W. A., Piscitelli, M. A., Rommel, S. A., Woodward, B. L., Winn, J. P., Potter, C. W. and Ann Pabst, D. (2015), Estimating maximal force output of cetaceans using axial locomotor muscle morphology. Marine Mammal Science. doi: 10.1111/mms.12230

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