We’re not the only mammals to notice the oil tanker entering the Gulf of Amvrakikos.

Some of the dolphins we’re watching notice it too, and several of them change course to intercept it. We follow alongside, and see the animals bow-surfing and spectacularly leaping 5 meters out of the water. Speeding alongside the tanker in our inflatable, it feels more like we’re Greenpeace activists than dolphin researchers.

It was the beginning of July, and as I chased dolphins in this part of the Ionian Sea in Greece’s northwestern province of Epirus, which borders Albania, cinemas across Japan had finally begun showing “The Cove,” the Academy Award- winning U.S. documentary about dolphin hunting in Taiji, Wakayama Prefecture.

Of course, I wasn’t driving the animals into shallow water to spear and hack them to death: I had joined a scientific census of the marine mammals run by the Earthwatch Institute. This international nonprofit organization offers volunteers the opportunity to join scientific field research projects all over the world, and in our case we were monitoring the population of bottlenose dolphins in the Gulf of Amvrakikos, which has the highest known density of the animals anywhere in the Mediterranean.

The 400-sq.-km gulf is almost landlocked, and with an opening into the Mediterranean that is only 300 meters across, it is like the Med in miniature, with its narrow opening into the Atlantic at the Straits of Gibraltar. In effect, the gulf is a giant bathtub — which is both an advantage and a curse.

“Amvrakikos is a natural laboratory for researchers,” said Joan Gonvalzo of the Tethys Research Institute in Milan, Italy, the lead researcher of the Amvrakikos dolphin project. “But the rate of water recycling is very low. It means the dolphins are extremely vulnerable because they rely so much on an increasingly degraded ecosystem.”

Whatever the perils those mammals face, though, this one spent an exhilarating week with the dolphins in Greece, where — unlike Japan — there is no culinary tradition of eating cetaceans.

However, the dolphins in the Mediterranean and around the Japanese coast do face similar threats from pollution. Many studies have shown that dolphin meat on sale in Japan can be contaminated with heavy metals, particularly mercury — sometimes in concentrations high enough to make it potentially dangerous for human consumption.

In the Mediterranean, the pollution has a disturbing consequence for dolphin reproduction. Female bottlenose dolphins become reproductively mature between 5 and 13 years old. In the years before that, traces of the pollutants in the fish they eat build up in their blubber. Small amounts, gradually accumulated, the animals can tolerate — but it’s a different story when they get pregnant.

When a female dolphin gets pregnant for the first time, much of the volume of toxins built up in her body is inadvertently passed on to her fetus. Gonvalzo told me that dolphins’ first-born young are sometimes sick, and may even die. He has seen newborn dolphins with heavily blotched skin: one of the signs of poisoning.

When “The Cove” was screened in Japan, the Taiji fisheries union complained that it could spread misunderstanding about dolphin hunts. Although the film makes no attempt to tell the story from the point of view of the fishermen, it is likely that coming face-to-face with the bloody reality of a dolphin drive-fishery will awaken compassion in many people — no matter what economic hardships the fishermen may incur if the slaughter was stopped.

Of course many people in Japan do already understand that cetaceans are intelligent animals capable of suffering. But it seems that the attitude of a certain proportion of the public to cetaceans is markedly different from that in almost all other developed countries — fellow whale-hunting nations Iceland and Norway excepted.

Yet attitudes can and do change. In research that has a bearing on the Taiji situation, Gonzalvo’s colleague Giovanni Bearzi conducted a survey of attitudes of the Italian public to stranded whales. The idea that animals experience suffering is a relatively new one, and Bearzi and colleagues from the Milan-based Tethys Research Institute questioned more than 100 members of the public who had turned up at a stranding of seven sperm whales on the Adriatic Coast of Italy in December 2009. Of those interviewed, 69 percent expressed feelings of compassion or care toward the stranded and dying whales.

Bearzi and colleagues report that those results are in stark contrast to information obtained from accounts of similar events that have occurred in historical times, and up until the first half of the 20th century.

In the 1970s and ’80s, there was a sharp turnaround in public views about whaling. Until then, cetaceans were portrayed, at least in the Italian media, as “animals to be harassed and killed whenever possible,” writes Bearzi’s team in the journal Aquatic Conservation: Marine and Freshwater Ecosystems.

What happened to change the public perception of cetaceans? The discovery of whale songs, along with growing appreciation of the animals’ complex behavior and high intelligence, has all helped. Documentaries and photographs in books and magazines have also showcased the charismatic animals, while the realization that decades of hunting had pushed several species to the brink of extinction also caused many people to sit up and take notice of whales and dolphins.

Nonetheless, one man protesting outside a Yokohama theater showing “The Cove” was this week reported as saying that the content of the documentary is “anti-Japanese,” and that it “tramples on Japanese culinary culture.”

I can understand how some people in Japan will feel patronized and offended by foreigners telling them what they should do. However, more important is that the terrible suffering of dolphins in Taiji and of whales during so-called “scientific whaling” is halted.

What I hope happens is that Japanese people will themselves tell their government and advocates of whaling and dolphin-drive fisheries that those practices are morally wrong and should be stopped forever.

Rowan Hooper’s trip was organized by the Earthwatch Institute (www.earthwatch.org) Follow Rowan Hooper on Twitter at twitter.com/rowanns. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human).”