In some ways, the dolphin deaths along the East Coast this summer have a feeling of deja vu. We have been here before.

The deaths of more than 330 dolphins in the mid-Atlantic this year seem to echo 1987 and 1988, when 742 dolphins died in the same general area, 93 of them off New Jersey. This year's total is more than nine times the historic average for dolphin deaths in July and August.

The 1987 and 1988 deaths were eventually blamed on cetacean morbillivirus, a virus similar to measles. On Tuesday, the National Oceanic and Atmospheric Administration said the same virus is the tentative cause of this year's dead dolphins, but we may never know for sure. Earlier this month, NOAA declared this an "unusual mortality event." But of the 60 such events since 1991, a definitive cause has been found for only 29 of them.

But while there are similarities with the dolphin die-off in the 1980s, it is worth noting what's different this time.

The biggest difference is the ocean. Twenty-five years ago it was easy to jump to the conclusion, as many people did, that human activity was responsible for killing the dolphins. Our near-coastal waters were a very different place then.

Inefficient sewage systems in New Jersey and New York routinely dumped human waste into the ocean. And there was a trash-dumping site - now closed - off the New Jersey coast. Beach closings and reports of trash and medical waste washing up on beaches were common.

Things are different now. In many ways, we have cleaned up our act. Researchers will continue to try to see whether toxins and pollutants are contributing to the current dolphin die-off - perhaps by weakening immune systems - but they are not considered the prime suspects they once were.

The other big change is that we now have better systems in place to try to find the answer. In 1987, it wasn't even clear where tissue samples from the dead dolphins should be sent. Now there is a network of veterinary pathologists and researchers working on the problem.

But some things haven't changed, such as the reasons we should care.

Some are altruistic. Many people feel a connection to these intelligent animals. And our cleaner ocean waters have made sightings of pods of dolphins a more frequent occurrence, deepening that connection. If this is, as some experts believe, a naturally recurring disease cycle, we may be able to make a difference in the next die-off.

And some reasons are selfish. Like dolphins, we are mammals. And like them, we are all dependent on the ocean - increasingly so - for our food. That's reason enough to want to better understand this complex ecosystem and reason enough to hope we can get to the bottom of this epidemic.