英语听力：自然百科 保护马蹄蟹（三）

Oddly enough, it was the Red Knot decline that made us pay attention to another species in decline. In the past decade, it's been estimated that horseshoe crabs in the Delaware Bay have dropped by 75 percent.

It all began in the 90s, when the growing fishery discovered that horseshoe crabs made good bait. They were easy to collect and free. With no regulations, anyone could scoop crabs right off the beach. At the height of the rush, 2 million crabs were harvested in one year. No one seemed concerned, until Red Knot numbers began to drop. By the time we saw the connection, the Red Knot was in serious trouble.

Getting a handle on horseshoe crab populations has been tricky. One method is to tag crabs and ask the public to report sightings. Dave Smith from the US Geological Survey has been a key player in tracking crab numbers.

There is a lot of demands on this animal and right now it's up to us to find out if there is room for all of those demands, if there is room for using horseshoe crabs for bait as well as biomedical and, and still meet the needs of Red Knots.

Today, efforts are underway to restore a balance that has been lost. To build up crab numbers, there is now a two-year moratorium on harvesting horseshoe crabs in the Delaware Bay.

The regulations that have been put in place for horseshoe crab seem to be working. There is gonna to be a lag and whether this success has occurred in time for Red Knots, we just don't know.

A recovery of the crabs in the Bay will take time. Horseshoe crabs don't mature till they are nine or ten, that's nearly a decade before the next generation is ready to spawn. In the short season, females lay over 80,000 eggs. Out of 80,000 only 10 might survive to adulthood. Theodds might seem low, but it's been a successful breeding strategy for eons.

Protected beneath the sand, the eggs are nurtured by the warmth of the sun and moisture from the tides. By the fifth day, tiny legs become visible inside their watery nurseries. The next day they will move for the first time. They will shed their shells four times while still inside the egg. But their tails won't grow until after they've hatched. It's a remarkable process the horseshoe crab has carried out for 350 million years. But will the population recover in time for the Red Knot? No one knows.