Can dolphins survive winter in NJ rivers?

December 28, 2008 6:12:29 AM PST
Six months after a group of dolphins took up residence in two rivers near the Jersey shore, temperatures have plummeted and winter has arrived. Animal advocates worry that the bottlenose dolphins will meet the same fate as four who died in the Shrewsbury River in 1993 when ice closed in on them and they drowned.

Three of the original group of 15 that spent this summer and fall in the Shrewsbury and Navesink rivers, waterways just north of Asbury Park, have died.

Federal wildlife experts say the remaining 11 or so dolphins are healthy, and should be able to make it through the winter if they choose to stay. They cite the cases of dolphins who successfully spent winters in Massachusetts, Virginia and even northern Scotland.

On the other hand, more than two dozen froze to death in a Texas bay when it froze over.

So can New Jersey's wayward dolphins survive until spring?

The answer is an emphatic "yes," according to the National Oceanic and Atmospheric Administration, which has jurisdiction over the dolphins. That agency doesn't plan to intervene unless the dolphins appear to be in imminent danger.

"This is a normal sort of way of life for these critters," said David Gouveia, marine mammal program coordinator for the agency's fisheries service. "We're optimistic that things are going to work out just fine."

Others are not as confident.

"It would seem to me that the natural habitat for dolphins in the winter when it gets cold is much farther south in warmer waters," said U.S. Rep. Frank Pallone Jr., D-Long Branch. "Isn't it stressful for them to be in this colder environment? Since they are mammals, what happens if the ice freezes over and they can't breathe?"

Looming over this debate is the dismal history of dolphins who have wound up in the Shrewsbury in years gone by. In at least two previous instances, dolphins lingered too long in the river and died when rescue attempts went awry.

"We have seen the disastrous consequences when dolphins remain in the area during the winter months," said state Sen. Sean Kean, R-Wall. "Now it's up to NOAA to determine a course of action to try to get the dolphins back to the ocean before it's too late."

Not so, according to Randall Wells, dolphin research program manager for Chicago Zoological Society.

"There are examples of the Navy using dolphins in very cold situations with ice around, and a naturally occurring population of dolphins off the coast of northern Scotland, where ice reaches into the water and snow is in the mountains nearby, and these animals get by fine," he said. "Blubber is a pretty amazing substance in these animals; it's able to maintain body temperatures quite well."

Virginia's coastal waters are usually home to bottlenose dolphins from April through November, when they leave for warmer climes south of Cape Hatteras, N.C. But during the winter of 1996-97, one bottlenose dolphin stayed in a Broad Bay off Virginia Beach, making it through 43-degree water in February. It was seen the following June with a healthy calf.

Five others joined the pair that October, and stayed through the winter of 1997-98. In March 1998, they were all examined and found to be healthy.

In 1990, two bottlenose dolphins spent the winter in Cape Cod Bay, off Plymouth, Mass., where the water was 30-35 degrees.

And in 1940, when the temperature in St. Charles Bay on the Texas coast fell from 64 degrees to 25 degrees in four hours, two porpoises stuck there in low tide did not die, and made it out when the tide returned sufficiently.

Those are the success stories. The outcome was different in Matagorda Bay, Texas, where a sudden freeze killed 26 dolphins in January 1990.

A helicopter pilot there flew overhead in late December 1989 and saw 12 dolphins swimming and breaking ice, trying to keep surfacing and breathing. By Jan. 20, authorities had collected the carcasses of 26 dead dolphins.

Scientists determined that four days of freezing temperatures devastated the dolphins' main food source, striped mullet, 2.6 million of which died when the temperatures plummeted.

That is a concern for the New Jersey dolphins. Scientists had hoped that when the animals' summer food source, menhaden, left the area in late October or early November, the dolphins would follow them out to sea.

But that didn't happen. Instead, the dolphins have switched to other, smaller fish such as alewife, a species of herring that they continue to consume.

"The food may be plentiful now, but it won't be plentiful in February," said Andrew Mencinsky, executive director of the Surfers' Environmental Alliance who lives in Sea Bright and watches the dolphins almost every day.

In four of the last five years, he said, the Shrewsbury River has frozen solid.

Teri Rowles, lead veterinarian for the Fisheries Service and leader of the National Marine Mammal Health and Stranding Response Program, predicted the Shrewsbury dolphins will be able to keep part of the river open by their constant surfacing to breathe.

She said there is no reason to undertake a risky intervention like netting the dolphins or trying to coax or scare them out, especially while they are acting normally and appear to be healthy.

"We are letting these dolphins be wild dolphins," Rowles said. "If they follow the path of the Massachusetts or the Virginia dolphins, we could expect that they would be there for another year. They may become frequent residents in this area.

Gouveia is also optimistic about the New Jersey dolphins' chances.

"If they're there, they're feeding, they're happy, they're in good, healthy condition, they're within their habitat - that's the best we can ask for," he said.

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On The Web:

NOAA NJ dolphins' Web site: http://www.nefsc.noaa.gov/njdolphins Surfers' Environmental Alliance: http://www.seasurfer.org

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