Gray whales continue to wash up dead and emaciated, but causes remain elusive
A research team at Woods Hole Oceanographic Institution, led by oceanographer Elizabeth Hillman, has found that the condition of the whales is likely linked to their foraging and feeding behaviour.
Although it is possible that some are suffering from diseases, there are many factors that may be contributing to the condition of the whales washed ashore around the world.
“Despite decades of research, the causes and effects of deaths remain largely unknown,” said Elizabeth Hillman, a marine biologist at the Woods Hole Oceanographic Institution and the study’s lead investigator. “Because the death process is an inevitable part of its life cycle, these dead individuals may be better suited for detailed study than have been whales so far.”
The group observed dead whales in five locations around the US, including New York, North Carolina and the Canadian West Coast.
While in the past many factors have been held responsible for the cause of death of whales, the present findings suggest that many are dying from diseases because of a complex of pathogens. Diseases included diseases previously associated with marine mammals, bacteria and parasites, which have been identified in the study by identifying the presence of specific genes in the whale’s DNA.
Bacterial infections linked to disease in aquatic mammals
The research found that bacteria were present in high numbers in the cesarean sections of whales that died in New York, with as many as 10,000 bacteria per gram of tissue.
“We suspect that the bacteria are being transferred from the mother to the calf during delivery and, over time, overgrow in the gut, leading to a condition known as entero-hemorrhagic Escherichia coli (EHEC) infection,” said Hillman. “We see the exact same bacteria in the stomachs of healthy whales that we see in those with signs of EHEC infections.”
The group tested for EHEC in the stomachs of dead whales in the eastern North Pacific Ocean. When they compared the whales that died from causes that have been previously