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Chemical Contamination
Northwest killer whales are known to be the most contaminated marine mammals in the world, due to the high levels of toxic anthropogenic chemicals that accumulate in their tissues ]. Implicated in the decline of Orca populations in the Pacific Northwest, these widespread contaminants pose a large problem for conservation efforts. While many chemicals can be found in the tissues of Orca, the most common are DDT, an insecticide, polybrominated diphenyl ethers, or PBDEs and polychlorinated biphenyls, or PCBs. Each of these have detrimental physiological effects on Orca, and can be found in such high concentrations in dead individuals that those individuals must be disposed of in hazardous waste site. Correlative evidence shows orca may be vulnerable to effects of PCB’s on many levels. Research has identified PCBs as being linked to restricting development of the reproductive system in orcas and dolphins. High contamination levels leads to low pregnancy rates and high mortality in dolphins. Further effects include endocrine and immune system disruption, both systems being critical to mammalian health and survival. A study examining 35 Northwest orcas found key genetic alterations that caused changes to normal physiological functions. These genetic level interferences, combined with the varied effects of PCBs at other physiological levels, suggest these contaminants may be partially responsible for declines in Orca populations.

Decline in prey
Commercial fishing has depleted large quantities in the marine environments, while personal fishing in the salmon’s upstream spawning grounds have further depleted stock replenishment.

Marine noise
Noise and crowding from tour boats and larger vessels interrupt foraging behavior, or scare away prey. Also, the sonar used by some ships and submarines is enough to cause hemorrhaging, and subsequently, death in some individuals