Some of the modern methods of fishing, especially in the tuna industry, have had a great toll on dolphins. The use of up to 40 mile long monofilament drift nets to encircle and trap tuna has killed numerous dolphins. Fortunately in 1992 the drift nets were banned. This move was partly initiated by a video tape made by Samuel LaBuddle onboard a tuna fishing boat which showed the horrific number of dolphins slaughtered using this method. Pollution from toxins are probably of the greatest concern for both dolphin and man.
Marine toxins are either biological or chemical, and both have contributed to dolphin deaths.
PCBs are dangerous non-biodegradable chemicals found in paint thinner, batteries and electrical transformers that have made their way to the sea. It is believed that the PCBs are lowering the immune system of dolphins and other marine mammals which leads to diseases such as skin lesions, brain tumors and cutaneous herpes. Even though PCBs and other hazardous chemicals have been banned from major polluting countries, these are still present in dumps and can leach into the sea through the rivers. Many will argue that there are enough problems on earth without having to worry about the health of dolphins but because dolphins are higher up on the marine food chain, they are accumulating a greater amount of toxins. If dolphins are contracting more and more diseases and are being affected by more and more pollutants then this is an indicator as to the state of the sea and the future of an important resource to man.