Marine Mammal Illness Linked to Human Activities, Experts Say at AAAS Briefing

Manatee mother and pup.

ST. LOUIS — Cancer is being found at alarming rates among Pacific sea lions. More and more Pacific Coast otters are dying of toxoplasmosis. An increasing incidence of “red tide” is evident off of Florida’s Gulf Coast, and marine scientists are finding manatees that have been gassed to death by exposure to the toxic blooms.

The troubling indicators are coming from a variety of locations, but experts at a AAAS news briefing said they suggest a pattern: The things that humans do on land are having a profoundly harmful impact on the coastal waters, and mammals who live near the waters edge are paying a lethal price.

And if marine mammals are at risk, it’s likely that people are, too, they said.

“The manatee really is a 2,000-pound canary,” said Gregory Bossart, a veterinary pathologist and manatee specialist at Harbor Branch Oceanographic Institution in Ft. Pierce, Fla. “It’s a good sentinel for environmental health.”

Read All About It! For more AAAS news from the 2006 Annual Meeting in St. Louis, Mo., click here.

Bossart, director of the Harbor Branch Division of Marine Mammal Research and Conservation, was among a panel of marine researchers who detailed their recent findings during a briefing Saturday [18 February] at the AAAS Annual Meeting.

While each works in different fields, they shared a common conclusion: Human activities, from the dumping of highly toxic polychlorinated biphenyls (PCBs) to the population boom among pet cats, is having a deadly impact in the world’s oceans. And if we harm the oceans, we inevitably will harm ourselves.

The profusion of aquablooms appears to be an elemental part of the problem in some areas. Bossart cited “a global pandemic” of the blooms, some toxic and some not. But especially in the Gulf Coast, “red tide” is clearly a problem, the researchers said. While it’s not known what causes the blooms, some believe that climate change and warming waters could be contributing factors.

Teri Rowles, a veterinarian with the U.S. National Oceanic and Atmospheric Administration’s National Marine Mammal Stranding program, said that since 1991, 34 marine mammal die-offs have been reported in U.S. coastal waters, and 29 percent of them have involved bottle-nosed dolphins. Among the causes are phytotoxins and infectious diseases. The dolphins also show repeated chronic exposure to toxic aquablooms and high levels of PCBs and fire retardants, among other human-produced toxins.

PCBs are implicated in Pacific Coast mammal deaths too, panelists said.

Frances Gulland

Frances Gulland, a veterinarian at the Marine Mammal Center in Sausalito, Calif., said 10,000 seals and sea lions have been examined over the years; among adult sea lions which die at the center, over 17 percent have cancer. “This is an extremely high rate for any population, especially a wild mammal,” she said.

Closer examination turned up a herpes virus associated with cancer, Gulland said. But PCBs may also have been related: The rate of that toxic compound in the blubber of the dead sea lions was “significantly higher” than the levels found in sea lions who died of other causes, she said.

In waters just off the central Pacific Coast of the United States, sea otters are falling victim to toxoplasmosis, a brain disease conveyed by parasites found in cat feces. The exposure to otters results from a booming population of domestic and feral cats on land, and on storm run-off that carries their feces into the ocean, said Patricia Conrad, a parasitologist at the University of California-Davis.

[Toxoplasmosis can infect humans, too, and pregnant women are routinely warned that changing cat litter boxes can put them at risk of miscarriage or birth defects.]

Populations of the southern otter have fallen in recent years. And studies of dead otters have shown that the single-celled toxoplasma parasite is the primary cause in 17 percent of the deaths; the disease also makes the otters more vulnerable to shark attacks, Conrad said.

A study of otters from 1998 to 2004 found that 38 percent of the live otters have been infected with the parasite, and 52 percent of the dead otters are infected.

“What the sea otters are trying to tell us about this land-sea connection is a very important message,” Conrad told reporters. “It’s not just what we do but what our pets do on the land can affect not only us but animals in the sea, like sea otters.”

Experts at the panel all agreed that the problems affecting sea mammals suggest risks for people, too. The surge in red tide has produced a sharp increase in hospital visits for people who have breathed the aerosolized toxins, said Bossart. The sickness resulting from PCBs suggests further dangers.

“Why we should care about this is that sea lions share a coastal environment with us,” said Gulland. “They share a diet with us — they eat the same fish.”

Edward W. Lempinen

19 February 2006