This is a summary on a primary peer-reviewed paper about organic pollutants found in killer whales.
Introduction
Although the population of killer whales in the pacific north west have been increasing overall since 1974, there has been a steady drop from 1996 to 2001. Possible reasons could be that they had a harder time finding food because of some change in their environment. Other reasons are that they could be getting exposed to Persistent Organic Pollutants (POPs), or marine noise or they just had a lack of prey available to them. Other marine mammals as well as lab animals that were exposed to these POPs were discovered to have developed adverse health problems as a direct result of exposure, raising concerns that the killer whales living in the same regions could possibly be discovered to have the same illnesses.
Some killer whales in the north pacific were biopsied and found to have high levels of POPs in their blubber, but this happened over ten years ago so more tests need to be done to determine what their current risks are regarding these pollutants.
Killer whales are predators, and any contaminates that the smaller fish eat all end up in them, so we can use this idea to figure out where they hunt, by analyzing the amount and types of pollutants present in various areas. Before DDT was banned in the 1970s California used it profusely, and higher levels of it are found in marine species off the California coast compared to other areas. Urban runoff and sewage also found its way into the ocean and increasing levels of it have been found in the local marine ecosystem, it is known as the "urban signature".
Methods
Since 1974, the killer whales used in this study were photo-identified and had a record kept of their movement. They were biopsied for their blubber and epidermis so the samples can be analyzed in a lab to see if they had any contaminants in them. The samples were sealed and preserved in liquid nitrogen until they could be analyzed. The killer whales blubber was analyzed for levels of POPs using procedures that are beyond my understanding. Their results were compared to standardized concentrations and quality assurance was maintained by comparing their results with quality control samples.
Results
A possible reason for population decline is the reduction of quantity and quality of the fish they eat, primarily Chinook salmon. Both pods were found to be eating fish from the same trophic level. POP levels were measured when analyzing the biopsied blubber and used to determine if the POPs levels were high enough to cause any health problems. Males and calves were found to have higher levels since females would transfer the pollutants to their offspring. Older killer whales also had higher levels since they had a longer time to be exposed to them. The highest concentrations of some pollutants were found in the youngest and oldest males but there was no correlation between age and POP levels. The killer whales sampled were found to have very high levels of contaminates in their system compared to other species in that area that already showed side effects of exposure. Even the killer whale with the lowest level of POPs had levels higher than grey seals that had endocrine disruption. They are found to be more toxic to juveniles because of how they can interfere with how hormones regulate their growth.
Conclusion
Very high levels of persistent organic pollutants were found in killer whales residing in the waters off the west coast of north America. They were compared to be higher levels than that of other marine mammals that were known to have significant health problems, however using cross species comparisons should be done cautiously, one species might have different biological responses to a pollutant compared to another. Also, their feeding areas were figured out by comparing the POP levels in their prey in various areas to that in the killer whales.
Question
Why were there more males sampled than females? Were there not as many females or are they just harder to get a hold of? Is the killer whales exposure to these POPs having an effect on what sex the babies end up being or do the females just have a higher risk of dying young?
Source
Persistent organic pollutants and stable isotopes in biopsy samples (2004/2006) from Southern Resident killer whales. Margaret M. Krahn, M. Bradley Hanson, Robin W. Baird, Richard H. Boyer, Douglas G. Burrows, Candice K. Emmons, John K.B. Ford, Linda L. Jones, Dawn P. Noren, Peter S. Ross, Gregory S. Schorr, Tracy K. Collier. Marine Pollution Bulletin. 2007.08.015
