We study why the whales' ability to produce offspring (fecundity) and survivorship are compromised. Knowing these reasons can help us design actions that create conditions necessary for the population to recover.

Ability to Produce Offspring

The reproductive life history of Southern Residents occurs on a time scale somewhat similar to people. Female killer whales become sexually mature in their early teens and usually have their first calf about age 15 following a 17-month gestation period. They nurse their calves for about 2-3 years before calving again at roughly five-year intervals. This pattern repeats until these females reach about age 40, at which time the females become post-reproductive. 

Like females, males become sexually mature in their teens, as evidenced by the development of secondary sex characteristics. Researchers collected small skin and blubber biopsy samples from the whales since 2006. They conducted paternity analyses from which we determined that a relatively small number of the males do most of the breeding. Further, we discovered inbreeding may be occurring due to the small population size.

We examined the history of reproductive-age females. We found that many females did not have their first viable calf until they were in their 20s. For some, their inter-calf interval was much higher than the average span observed in growing killer whale populations. Some females were not successfully reproducing at all. 

Similar work by other scientists indicate that most of the reproductive age females regularly become pregnant, but are not carrying their calves to term, are stillborn, or survive only a short time. Even in the last "baby boom" in 2015, when nine calves were born in the span of a year, only three calves survived. 

Researchers estimate calf survival in other killer whale populations to only be about 50%. We find it disconcerting that since 2016 three Southern Resident calves have been born with only two surviving. The cause of such a high level of failed pregnancies remains unclear.

We have documented relatively high contaminant levels in Southern Residents adult females and their offspring. We are concerned about the impact these contaminants might be playing in this population. We have turned to studies of killer whales in managed facilities to answer questions about mothers transfer contaminants to their offspring.

Ability to Survive

We are challenged to assess an individual whale’s health. We cannot yet collect blood samples, a primary tool for evaluating the health of any animal, from free-ranging whale populations. Instead, we turn to health information we can gather through visual assessments (body and skin condition) and biological samples (skin, breath, and feces). 

Reduced prey availability is one known threat to these whales’ recovery. While some whales appeared emaciated before their disappearance (and presumed death), many others have not. Given that prey sharing occurs within matrilines, we find it unlikely that animals would succumb to starvation, even when prey is scarce. Instead, a reduced nutritional intake likely makes the whales more susceptible to disease. Further, their condition could be exacerbated by a compromised immune system, a result of contaminants or living adjacent to urban environments that introduce a wider variety of pathogens into the environment. 

We have recovered the carcasses of eight Southern Resident killer whales since 2003. Only when carcasses are recovered can cause of death be determined. In those cases, the cause of death included blunt force trauma (including a ship strike), neonatal death, female reproductive issues, and health conditions such as infections. This lack of data means we have only a glimpse into the circumstances or underlying health conditions that cause whales to die. 

Contact

Brad Hanson, Marine Mammal Ecology Team

More Information

Overview of our Research on SRKWs in the Pacific Northwest 

Research on Noise and Disturbance on SRKWs

Species Profile: Southern Resident Killer Whales