12/06/2014 07:42 EST | Updated 02/05/2015 05:59 EST

Necropsy on killer whale J-32 seeks answers troubling questions

Marine mammal scientists spent most of Saturday performing a necropsy on killer whale J-32 after the female orca's body was towed shore on Vancouver Island Thursday.

A team of scientists from Canada dissected her as she lay on a concrete boat ramp at Bates Beach near Courtenay, B.C.

The death of the 18-year-old juvenile whale, nicknamed Rhapsody, is troubling, said marine mammal researchers: It marks the fourth recent death in the endangered southern resident population.

Two of the whales, L100 and L53, are presumed to have died sometime this summer, while the calf L120 died about eight weeks ago. 

Now, only 77 southern resident killer whales remain in the Salish Sea. 

Marine mammal co-ordinator Paul Cottrell said the discovery of J-32's body is heart breaking.

"It's a magnificent animal. Sixteen feet or so — so it's likely a juvenile. So, it's terrible and we want to figure out what the cause of death was here and how this animal died," Cottrell said.

According to the Orca Network, J-32  was thought to be in the late stages of pregnancy last summer judging by her wide girth, which was visible when she breached.

Most contaminated marine mammals in world

It’s always a concern to lose an individual from a small population of endangered animals, such as the southern resident killer whales, said Vancouver Aquarium marine mammal scientist Lance Barrett-Lennard. 

"But this is even more distressing because it was a female of reproductive age," he said. "Her probability of contribution to the recovery of this population was very high, and her years of maximum importance to the population were still to come.”

​Vancouver Aquarium pollution researcher Peter Ross said a number of factors might have contributed to the whale's death.

"We have long been concerned about very high levels of endocrine-disrupting pollutants in these whales, reduced food supply — notably chinook salmon — and noise and disturbance,” Ross said.

The aquarium said it was Ross's research that determined the southern resident killer whales are among the most contaminated marine mammals in the world.