At first glance, it might seem like small marine creatures would be hardest hit by water pollution. In reality, each tiny organism consumes trace amounts of contaminants that lodge in its body as it feeds. In turn, an animal higher up the food chain will devour many of these creatures and absorb their pollutants. This continues until animals at the top have received the highest levels of pollution. Apex predators like beluga whales, killer whales, bottlenose dolphins, common dolphins, and harbor seals rank as some of the most polluted marine species.
St. Lawrence Beluga Whale
The St. Lawrence Seaway provides a concentrated area for both agricultural run-off and industrial waste. The beluga whales that swim in these waters have extremely elevated amounts of such agricultural chemicals as 2,4-D and phosphorus. One result of this is cancer rates higher than any other marine animals in the world.
Also known as orcas, killer whales are one of the most efficient hunters of the seas. What causes them to be such highly polluted marine species beyond cold-blooded predators like sharks is that as warm-blooded mammals, they must consume far larger quantities of food to maintain their temperature. PCBs have been the main culprit in cutting the mammal’s lifespan nearly in half.
Like the orca, the bottlenose dolphin is hit hard by PCB contamination. Among their many other damaging effects, these chemicals reduce the fertility rates of female bottlenose dolphins and sterility in males. In addition, the pollutants concentrate in the female’s milk and lead to high offspring mortality rates.
What makes the harbor seal an especially polluted marine species is that they don’t migrate. These seals remain in protected coastal areas year-round. It’s here where contaminants from waterways and heavy numbers of watercraft create concentrated pollution that the seals are constantly exposed to.
Found throughout the world, the common dolphin suffers similar pollution threats as their relative, the bottlenose dolphin. While PCBs are no longer produced, another group of chemicals called PBDEs show increasing levels in the oceans and appear to have similar damaging impacts on marine wildlife.