California blue whales have made a significant comeback, unveils new research. Its population, which was once at the verge of extinction, has now recovered back to pre-whaling level.

Cole Monnahan from the Quantitative Ecology and Resource Management at the University of Washington in Seattle, and colleagues stated in the study that the numbers of the Eastern North Pacific (ENP) blue whale are estimated at 2,200. This species is the only blue whale whose population is recovering from whaling.

Regardless of the increasing growth, there are certain factors that continue to affect the California blue whales' recovering number.

For example, conservation groups claim that every year, minimum 11 blue whales get struck along the U. S. West Coast. It is about four times more than the annual "potential biological removal" of 3.1 whales permitted under the U. S. Marine Mammal Protection Act.

Researchers wanted to know whether this collision with ships causes problem in the recovery of the endangered species. With the help of the population dynamic model, researchers found that ships cause minimal threat to the whales' long term population.

Researchers estimated that there is less possibility that the future strikes will have a long-term impact. For instance, even if an 11-fold increase in vessels is witnessed then also, they will cause only 50% risk that the long-term population would be considered as depleted by regulators.

Researchers said that ship collisions do not cause serious threats to the animal's population. Density dependence is the main problem, further stated researchers.

"Even accepting our results that the current level of ship strikes is not going to cause overall population declines, there is still going to be ongoing concern that we don't want these whales killed by ships", said study co-author Trevor Branch, from the School of Aquatic and Fishery Sciences at the University of Washington.