Threats to Dolphins

Coastal development often leads to increased pollution from runoff. Sewage, toxins, chemicals, and plastics often enter the ocean directly from runoff. These substances are harmful to dolphins and their habitat. Sewage may contain bacteria that are potentially harmful to dolphins. Toxins and chemicals can accumulate in the food chain, with dolphins ending up with high amounts in their bodies.

Plastics are sometimes ingested by animals mistaking them for food, and entanglement is also a problem.

As the human population increases along the coast, so does the potential for boat strikes and harassment of marine mammals. All of these are dangerous for dolphins.

Damming of rivers directly affects the world’s river dolphin species. Damming a river alters the flow or abundance of water and often leads to changes in sedimentation and water quality. Damming creates barriers that impact the movement of both dolphins and their prey. It can also divide and isolate river dolphin populations, which may eventually limit their genetic diversity and impact their long-term survival.

Water pollution knows no boundaries. Pollutants flow with the water all around the globe. Miles and miles of plastics and other trash are collecting in the North Pacific Gyre current around Hawaii. Known as the Great Pacific Garbage Patch or the Eastern Garbage Patch, it was formed gradually as the rotational pattern of the oceanic current collected debris and trapped it in the region. It is estimated that it may contain 100 million tons of debris.

The plastic debris can last for years, causing ingestion and entanglement hazards for marine life both large and small. As the plastic particulates disintegrate, they become small enough to be ingested by aquatic animals. Not only are the plastics themselves harmful because they can cause blockages and create a feeling of fullness without actual nutrition, but they also contain chemicals that build up in the animalsvï bodies over time.

The unseen chemical contamination from compounds like PCBs and DDT is another threatening form of pollution. These compounds are passed through the food chain, accumulating along the way, putting large predatory animals like dolphins at greater risk of possessing extremely high levels in their bodies. Scientists are studying the effects of these chemicals related to dolphin reproduction and immune system impact.

Even freshwater runoff containing excess fertilizer can cause dense algal blooms. This leads to an unbalanced food web, oxygen-deprived dead zones, and changes in marine habitats, all of which affects dolphin habitats.

Increasing amounts of human-produced noise are filling the world's oceans. Boat traffic, construction noise, and drilling are just a few examples.

Scientists are studying how this additional noise affects dolphins and other marine animals. Because sound travels easily through water, additional sound may interfere with the dolphinvïs ability to communicate, navigate, and locate prey (echolocation). It may become too noisy to hear the natural sounds.

Bycatch in fishing nets is a major problem for a number of coastal dolphin species. Dolphins cannot see or easily detect these nets. Dolphins swim into the netting, become entangled, and drown. This continues to be a problem facing the Ganges River dolphin, Irrawaddy dolphin, harbor porpoises in the Black Sea, and the Hector's dolphin off of New Zealand.

Even discarded and abandoned fishing lines, buoys, and nets cause problems for dolphins. Dolphins can easily become entangled. Some drag the gear along with them, draining their strength and impeding their swimming and feeding ability, while others get trapped underwater and eventually drown. Tons of discarded fishing gear has been collected off the coast of northern Hawaii in an effort to protect dolphins and other sea life.

With a number of fish species and fishing grounds being overfished, dolphins find less food available. This may increase the distance they need to travel to find food, alter their feeding choices and nutrition, and change their behavior.

In addition, "drive fisheries" in Japan and the Solomon Islands herd and slaughter dolphins as a threat to fishing operations and for their meat. You can help stop this brutal practice by signing this petition to end dolphin slaughter in Japan.

Feeding wild dolphins is illegal for a reason. It is harmful to dolphins, causing some to rely on begging for food from humans, upsetting their natural role as hunters and altering their diets. Feeding wild dolphins is a threat to humans, too. Dolphins sometimes become aggressive when seeking food and are known to bite when teased.

The health and welfare of wild dolphins is severely compromised when humans feed them. Human-fed dolphins change their normal wild behavior and run a greater risk of being injured by boats, becoming entangled in fishing gear, or ingesting dangerous items such as fishing hooks and contaminated food. Some dolphins have become so accustomed to receiving routine handouts, they are now taking fishing bait and catches from recreational and commercial fishermen.

Feeding and harassing wild marine mammals is illegal under the Marine Mammal Protection Act, and can result in severe penalties with fines up to $20,000 and one year in jail for the most serious violations.