The survival of the remaining 76 Southern Resident killer whale population and the Chinook salmon runs that they depend upon are tied directly to the health of the Salish Sea. This should be a wakeup call to our region that our own health, economy, and culture are at risk if the Salish Sea isn’t thriving.
The single greatest threat to survival of the Southern Resident orca population is depletion of their preferred prey, Chinook salmon. Southern Residents are highly selective in prey choice, opting for bigger, fattier Chinook over other types of fish. The diet of the Southern resident orca is 80% Chinook salmon, a listed threatened species in the U.S. and Canada. Only 22 of at least 37 historic Chinook populations remain. The remaining Chinook salmon are at only 10% of their historic numbers. There is a direct connection between the recovery of Chinook salmon and the survival of Southern Resident orcas.
Persistent Organic Pollutants, including banned toxics like DDT and PCBs, are present in alarmingly high concentration in Southern Resident orcas, making them one of the most contaminated marine mammals in the world. Several of the toxics found in orcas have been known to interfere with gene expression, suppress the immune system, disrupt the endocrine system, cause brain defects, impair reproduction, and lead to birth defects in marine mammals. If whales are starving due to lack of chinook salmon, they metabolize their fat stores in a last-ditch effort to survive, but tragically flood their bloodstreams with toxics: a double whammy.
Vessels increase underwater ambient noise, which may impact orca’s hunting, navigation, and communication efforts. Several studies have shown that the presence of vessel traffic reduces the time orcas spend foraging and reduces prey capture. Vessel traffic was found to impact the orca population, especially during years of low Chinook salmon abundance, with the potential for cumulative and adverse synergistic effects with other stressors. Multiple studies on vessel impacts to orcas have shown that vessel speed is one of the most important contributors of noise levels received by orcas, and indicate that reducing vessel speed around the Southern Residents would likely reduce acoustic exposure to the orcas.