Cause of the Month: Spinner Dolphins

The star of a major 1980s conservation controversy, spinner dolphins are the inspiration behind the Dolphin Safe tuna campaign

Jumping, spinning, twisting, flipping—the daring acrobatic feats of the playful spinner dolphin always make a splash! In fact, their common name comes from their unique ability to complete many spins in a single jump—the current record is seven! Scientists believe they spin for practical reasons, like communication, courtship, and to remove parasites like suckerfish, but also just for the sheer fun of it. 

I mean, haven’t we all wished to be a dolphin for this exact reason?

Spinner dolphins live in all tropical and most subtropical waters in the Atlantic, Pacific, and Indian Oceans. There are four recognized subspecies of spinner dolphin and each varies in appearance, range, and social structure: 

• Gray’s spinner dolphin is the most widely distributed subspecies and can be found everywhere in the tropical Atlantic, Indian, and western and central Pacific Oceans; this includes the Hawaiian spinner dolphin, a population that tends to spend more time near the shore than other spinners and is more social with people and boats. Gray’s spinner dolphins have distinctive three-banded coloring that’s dark grey on the back with lighter grey on the flanks and a pale belly.

The eastern spinner dolphin is just one color—dark grey—and is found in the Eastern Tropical Pacific (ETP) off the coast of South and Central America; this includes the waters, coasts, and islands off the shores of Costa Rica, Panama, Colombia and Ecuador. 

The Central American spinner is only found in a narrow strip of habitat along Central America’s Pacific Coast and has a similar tri-color pattern as the Gray’s Spinner Dolphin.

The dwarf spinner is only found in Southeast Asia and northern Australia and also has a tri-color pattern, though it is much smaller than other spinners.

All spinners have a long, skinny beak and a slender body with small, curved flippers that have pointed tips, and a tall, triangular dorsal fin. They’re relatively small compared to other dolphin species and can be identified by the shape, size, and condition of their dorsal fins.

Spinner dolphins travel in large pods that number anywhere from a few dozen to a few thousand individuals. Their social structure can vary, with some populations favoring a fluid arrangement where they join up in groups that separate from time to time while other populations live in stable pods for many years.

Like people, spinners have a daytime and nighttime routine. During the day, they rest, play, socialize, and keep an eye out for predators like sharks in shallow coastal waters. 

You’ll know spinner dolphins are done resting by an abrupt increase in their level of activity including swim speed, aerial behaviors, and vocalizations. The late afternoon and early evening is their favorite time for spinning because they’re well rested and ready to hunt.

At night, they venture out into deeper waters of the open ocean where they feed on small fish, squid, and shrimp that have migrated up from the depths.

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Spinner dolphins are often observed traveling and feeding alongside other species like humpback whales and bottlenose and spotted dolphins. 

In the ETP, dolphins are often followed by yellowfin tuna—a commercially valuable species. This rare relationship is seldom observed in other oceans and, in the 1980s, it put spinner dolphins at the center of a major conservation controversy that led to the dolphin-safe labels seen on tuna packaging today.

Fishers targeting tuna would track spinners by sea and air, chase them by speedboat until they were exhausted, and then lay out a mile-long wall of netting that would capture the tuna and (accidentally) drown whole pods of dolphins. This practice is now illegal in most parts of the world, but scientists estimate that roughly six million spinner and spotted dolphins were killed in tuna nets in the ETP alone.

U.S. tuna fleets were responsible for the majority of dolphin deaths in the 1970s. It’s actually one of the reasons the U.S. passed the Marine Mammal Protection Act (MMPA) of 1972, which not only prohibited the killing, harassment, and capture of marine mammals without a permit, but also required U.S. tuna fishers in the ETP to reduce dolphin deaths “to levels approaching zero.” 

In response. U.S. tuna fishers developed a new technique to prevent the accidental capture and killing of dolphins. While the back-down technique helped decrease dolphin deaths dramatically, the maneuver required skilled boat operators to work and still killed too many dolphins to meet the regulatory standards of the MMPA.

Then, in the 1980s, Mexico and other ETP countries began to build out their tuna fleets but made no effort to reduce dolphin catch with the back-down technique. As expected, dolphin deaths were back on the rise.

By the end of the decade, U.S. and international tuna fleets were responsible for killing roughly 100,000 dolphins each year. It was clear the MMPA was not providing dolphins adequate protection.

In 1987, biologist Sam LaBudde went undercover on a commercial tuna fishing vessel to document the ship’s offshore activities. LaBudde became the first person to capture video proof of the brutal dolphin slaughter happening in the ETP. 

Supported by a major awareness campaign run by the International Marine Mammal Project (IMMP), LaBudde’s secret surveillance lasted five months. The graphic footage he captured was released in 1988, immediately sparking public outrage and demands for a solution. 

The uproar caused by LaBudde’s undercover video and the IMMP awareness campaign led to the creation of the Dolphin Protection Consumer Information Act. Incorporated into the Marine Mammal Protect Act in 1990,  the DPCIA defined Dolphin Safe tuna as “caught without setting nets on or near dolphins.”

The Dolphin Safe label was prohibited for any tuna caught while intentionally chasing or netting dolphins. In 1997, new MMPA amendments clarified that if a net contained accidental dolphin mortalities or serious injuries—a fairly rare event if the tuna vessel was not targeting dolphins—the landed tuna still could not be labeled Dolphin Safe in the U.S.

Since the creation of the Dolphin Safe label, more than 800 tuna companies—about 95% of the global industry—have pledged to fish in a Dolphin Safe manner. Onboard government observers have recorded sharp declines in dolphin deaths by U.S. and most international tuna vessels.

An estimated 100,000 dolphins were killed in the ETP in 1989, the year before the Dolphin Safe tuna label was instituted. In 2020, the reported number of deaths (based on government observer counts) totaled 689 with none linked to U.S. vessels. 

While the Dolphin Safe tuna label has made significant advances for dolphins, a small number of international fleets continue to chase and net dolphins in the ETP. Ultimately, continued study is needed to determine population trends and the conservation status of this incredible species.

Unfortunately, poor fisheries management isn’t the only threat to spinner dolphins. 

• Interactions with plastic pollution and marine debris may lead to ingestion and entanglement. Consuming plastic can introduce chemical pollutants that make dolphins sick or alter their behavior. Entanglement can make it harder to feed and reproduce. It can also cause extreme energy depletion, serious and sometimes fatal injuries, and often leads to drowning.

• Noise pollution interrupts normal behavioral patterns and drives dolphins away from crucial habitats. It can cause serious injuries and even be fatal. For example, the oil and gas industry uses seismology to find underwater reservoirs of natural resources, which directs loud pulses of noise at the seabed. The military uses powerful underwater sonar that can travel up to 300 miles at an intensity of 140 decibels. For reference, the world’s loudest rock bands top out at around 130 decibels.

• Human interactions and pressure from wildlife tours bring people and wild animals close together in ways that can be detrimental to the animals. Because spinner dolphins are so friendly and playful, tour operators will advertise close encounters that set a potentially dangerous expectation with tourists.

Commercial operators and individuals interested in viewing spinners increasingly target their daytime habitats, which is where they go to rest. Closely approaching, swimming with, pursuing, and interacting with the dolphins can disturb the animals and divert time and energy away from normal behaviors that keep them healthy.

Over time, these interactions can have negative impacts. For instance, lack of consistent, undisturbed resting periods can reduce the amount of energy dolphins have for foraging, which in turn can result in poor health. Poor health limits a dolphin’s ability to fight off disease, protect themselves from predators, successfully reproduce, and raise their young.

Human-caused disturbances are an especially chronic problem for Hawaii’s spinner dolphin population, where behavioral changes in spinners’ daytime habitats have already been documented by researchers, including changes to patterns associated with aerial behaviors, residence times, and distribution within the habitat.

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