The dolphin die-off
In 1987 large numbers of dead bottlenose dolphins (in excess of 700) were washed up on the coast of New Jersey, in the eastern USA. The dolphins were covered in sores, and their skin had become detached over large areas of their bodies. It was concluded that the dolphin's immune system had been seriously damaged, and that consequently they had succumbed to a variety of pathogens. The question still remains as to the cause of this immunosuppression. The US Government's National Oceanic and Atmospheric Administration (NOAA) declared that the cause was the ingestion of fish which contained toxins produced by a "red tide". A red tide is the result of extremely rapid growth of dinoflagellates, which are a type of plankton, resulting from extreme environmental factors (increased levels of certain fertilisers are known to contribute to such phenomena). They produce a toxin known as brevotoxin, and the NOAA declared that it was this substance entering the food chain that had caused the demise of the dolphins. However, it is widely held that the cause was in fact a high concentration of PCB's (Polychlorinated Biphenyls) which results from the dumping of waste of many different types. The level of PCB's in the dead dolphins ranged from 13 to 620 parts per million (ppm) with one yielding unprecedented levels of 6.800 ppm. Products which contain more than 5 ppm are required by law to be labelled toxic in the USA!
A Congressional Hearing into the disaster was told that attempts to suppress the significance of these toxic levels of PCB's had been made by Government officials.
For a comprehensive picture of ocean pollution by Greenpeace, Follow this link
The modern fishing fleet harvests the seas indiscriminately. It does not distinguish between fish and marine mammals, and in it's quest for increased efficiency, slaughters thousands of dolphins each year drowned in nets. As the world's fish stocks become more depleted from over-fishing, there is a danger that man's pursuit of protein food will lead to a more determined capture of dolphins and whales to satisfy the demand.
Several fishing practices have taken a toll on dolphin populations. Most lethal are drift nets and nets called purse seines, used to fish for yellowfin tuna. Because tuna often swim beneath dolphin schools, dolphins are actively sought. Fishermen then circle the tuna with mile-long (1.6-km) seine nets that trap fish and mammals alike. When this practice started in the 1950s, it killed more than a quarter of a million dolphins a year. Now boat captains are trained to employ manoeuvres that help release the dolphins. The dolphin kill now totals around 20,000 a year.
The drift net, though, is the most indiscriminate killing device yet used at sea. Up to 40 miles (64 km) long, drift nets hang draped from floats, trapping virtually everything in their path. Fishermen haul the nets aboard, store the fish or squid, and discard everything else, including dolphins that have drowned while trapped.
More on the threat from over-fishing.
The dolphin has evolved over a period in excess of 30 million years to be superbly adapted to it's environment. It is a highly streamlined and efficient swimmer, due to it's shape and the composition of it's skin which reduces friction to a minimum. It has a highly developed brain, and if we ignore the mass of blubber under it's skin, it is the only animal to have a greater brain mass/body weight ratio than man. The entertainment industry has been exploiting this adaptation for many years and held dolphins