Ever since the Puget Sound's southern-resident killer whales came under the Endangered Species Act (ESA), scientists have found out where orcas go in winter. They have also learned that these whales can differentiate a chinook from a sockeye by using sonar to detect little differences in the swim bladder of each fish. Researchers have also documented many ways in which these majestic mammals shift their behaviour in response to engine and propeller noise from the boats.

According to a new synopsis of research done by the National Oceanic and Atmospheric Administration (NOAA),despite the vast knowledge about them, the killer whales were still listed as endangered in 2005 and the orca population is still not growing.

Scientists are "trying to understand ... why the whales haven't increased more than they have", said Mike Ford who is with the conservation biology program at NOAA's Northwest Fisheries Science Centre.

A study in whale science reveals that orcas face quite complex and overlapping threats that tend to compound one another.

In the early 1960s, the killer whales were numbered 140 and some scientists also suspect that a century before that there might have been 200 or more than that. By the early 1970s when the entrepreneurs began capturing orcas for sale to marine parks, their population plummeted to barely 71. Then, capture was outlawed after a few years and orca populations reached 99 somewhere in the mid-1990s.

As of 2013, only 82 remain.

There are three main factors that appear to contribute to their decline: lack of food, disturbance due to marine vessels and the build up of pollutants in their bodies.

These majestic mammals are already among the most polluted animals on the Earth due to toxins accumulating in their fat over years. When whales get hungry, contaminants mobilize in their system which potentially affects their health as well as the reproduction.