Southern Resident Killer Whales (SRKW) have been in the news a lot lately (well the scientific and environmental news). A pregnant female washed up dead on a beach in British Colombia at the beginning of December and even more tragically was pregnant at the time which, has brought them further into the public eye.
All the SRKW belong to one clan – or “extended family” – therefore they are all related. This clan – J Clan – is made up of three pods – J, K , and L – with 77 individuals of which, only 12 are reproductive females. Four individuals of the population were lost this year which is a big blow for this small clan.
The populations is struggling to recover their numbers back to a viable level and in this post I will discuss why.
SRKW favour Chinook Salmon almost exclusively feeding on it. The problem is that Chinook salmon are struggling to spawn and their numbers are also dwindling due to unsuitable habitats to spawn in. This means that SRKW are facing a depleted prey source and nutritional stress.
Nutritional stress has been shown to affect Glucocorticoids (cortisol) and thyroid hormone in killer whales. Glucocorticoids affect glucose metabolism for a quick response to an immediate threat over a short time frame (indicator of a short term stress), while thyroid hormone lowers metabolism to conserve energy stores over a longer time frame (indicator of long term/sustained stress).
Chinook salmon decline has been caused by activities such as logging and road construction have reduced the habitat condition degrading, fragmenting and eliminating key areas. To turn around their decline river habitats need to be restored to encourage spawning of salmon. This includes the removal/modification of dams on streams and the improvement of water quality and flow.
This issue can be fixed and would be a positive for both the killer whales and local fishermen.
In the middle of the last century the SRKW populations took a large hit when many members and sometimes whole families were removed in the live-capture industry.
Individuals/groups were removed to be put on display. With the removal of whole family groups the structure and populations numbers were severely disrupted. The SRKW were the most affected populations with 36 whales collected and at least 11 dying. There is nothing we can do now to correct this however there is a ban on the removal of all individuals in North America.
Pollution – High Levels Persistent Organic Pollutants (POPs)
Being at the top of the food chain killer whales are particularly susceptible to bioaccumulation of organic pollutants such as Polychlorinated biphenyls (PCBs) and Polybrominated diphenyl ethers (PBDEs). PCBs were used in a variety of adhesives, sealants, and electric transformer insulating fluids, but are now banned. However PBDEs are used as a flame retardant and are still in production and use despite the impacts they may have on wildlife. These Persistent Organic Pollutants have been shown to have toxic effects on marine life including marine mammals. They can disrupt endocrine function that can impeded hormone mediated processes, reproduction and development of individuals as well as increasing the susceptibility of affected animals to diseases and cancers.
The SRKW are highly polluted with Persistent Organic Pollutants from accumulation thought their prey consumption. These pollutants are stored in the blubber layer of killer whales and at times of nutritional stress, which these whales are currently in due to the chinook salmon shortage, they will metabolise their blubber layer for energy. When the blubber layer is metabolised the pollutants are released into the bloodstream. The pollutants are also passed through the mothers fat rich milk to their calves continuing the contamination of the species.
We can’t reduce the pollutants in the blubber layers however, hopefully by reducing nutritional stress and pushing for a ban on PBDEs so that they do not continue to be accumulated in marine mammals. Further to this new pollutants need to be monitored to ensure they have a minimal effect.
SRKW live in a highly anthropogenically impacted environment. There is high vessel traffic including both commercial and recreational vessels. Vessel traffic and its associated noise can disrupt important behaviours such as feeding and socialising in killer whales. This noise also affects the ability of killer whales to detect prey over greater distances and communicate with conspecifics. Loud and/or very persistent sounds can increase stress hormones in marine mammals and over long periods chronic stress could develop. In terrestrial mammals chronic stress is known to induce detrimental physiological conditions such as lowered immune function.
All these factors together may cumulatively impact SRKW in an increasingly negative way much more than each individual factor alone. This sadly does not give SRKW a great starting point for recovery. Their numbers are low, there has not been a successful reproduction and recruitment of any calves in the last few years and the number of reproductively active females is only around 12.
The window of opportunity for action is now and we really don’t have much time. If prey populations are successfully recovered, their anthropogenic interaction mitigated and the populations manages to successfully reproduce there is a chance for recovery. We have to hope that we don’t see this distinct population go extinct.