The dead North Atlantic right whale found off the coast of Virginia last week was a female of reproducing age last seen in the Gulf of St. Lawrence last summer, say U.S. fisheries officials.
"Preliminary observations suggest that the whale died due to the entanglement," the National Oceanic and Atmospheric Administration (NOAA Fisheries) said in a statement.
The entanglement was "chronic," spokeswoman Jennifer Goebel said in an email to CBC News.
NOAA's law enforcement office is investigating the latest death and scientists are analyzing samples collected during a necropsy performed on Sunday.
'After a devastating number of mortalities in 2017, the already critically endangered North Atlantic right whale is in crisis.' - NOAA Fisheries
The necropsy results could take several weeks to months.
"After a devastating number of mortalities in 2017, the already critically endangered North Atlantic right whale is in crisis," the statement said.
"NOAA scientists, resource managers, and partners are co-ordinating closely to solve this urgent conservation challenge."
There are only an estimated 450 North Atlantic right whales left in the world. Of those, only about 100 are reproducing females.
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At least 17 North Atlantic right whales were found dead last year — 12 in Canadian waters and five in U.S. waters. Scientists believe human activity, including shipping and fishing, was the primary cause.
The latest dead whale — the first confirmed death of the year — has been identified as #3893, a 10-year-old female last seen in the Gulf of St. Lawrence on July 29, 2017, said NOAA.
At that time, she was gear-free, the U.S. agency said.
The normal life expectancy of North Atlantic right whales is about 70 years.
"We are of course always sad to lose any right whale, but especially so when it's a female of breeding age, as this one was," said Goebel.
Ten years old is when females typically start to breed, she said.
"With about 100 breeding females in the population, every one is important to the survival of the species."
The 39-foot carcass, reported on Jan. 22 and located by officials on Jan. 26, was in a "moderate" state of decomposition, said NOAA.
"The whale appears to have been wrapped in line in a manner that, based on past observations of entanglements, suggests the whale was alive and swimming when it encountered the line," the statement said.
The lines were removed from the whale for analysis.
"Until we get necropsy results, we won't have more details to share about cause of death," said Goebel.
Four live North Atlantic right whales were spotted in the same general area last week. NOAA is asking mariners travelling 86 nautical miles east-southeast of Virginia Beach to slow down to 10 knots or less or to route around. The voluntary slow-speed zone remains in effect until Feb. 7.
Fisheries and Oceans Canada Minister Dominic LeBlanc announced last week four changes to the snow crab fishery in the southern Gulf of St. Lawrence to protect North Atlantic right whales from entanglement.
The changes, which took effect immediately, include reducing the number of fishing rope floating on the surface and mandatory reporting of all lost gear, as well as using colour-coded rope and sequentially numbered buoys to identify the gear's place of origin.
LeBlanc has also instructed the Canadian Coast Guard to come up with a plan to use ice-breakers to help start the snow crab fishing season earlier than the usual mid-April, in a bid to get the gear out of the water earlier and out of the whales' way sooner.
In addition, Transport Canada will "most likely" impose speed restrictions for vessels again this year, when the whales return to the gulf, LeBlanc has said.