The iconic whale shark, the largest fish in the sea, was reclassified as an endangered species earlier this month, due to recent declines in its population.

The number of whale sharks (Rhincodon typus) has more than halved over the last 75 years, with legal and illegal fishing, entrapment in fishing gear, and collisions with boats responsible for the most deaths, according to the International Union for the Conservation of Nature (IUCN).

No one knows how many whale sharks are left, but rough estimates put their numbers somewhere in the tens of thousands worldwide.

Fishing for the large, slow-moving sharks is particularly prevalent in China and Oman, though the species is showing some recovery in the Western Hemisphere and in India, the Philippines and Taiwan, thanks to legal protections.

“While international whale shark trade is regulated through the species’ listing on the Convention on International Trade in Endangered Species (CITES), more needs to be done domestically to protect whale sharks at a national level,” Simon Pierce, who led IUCN's assessment, said in a statement.

Whale sharks can reach a length of 40 feet (12 meters). They feed by scooping huge amounts of tiny plankton and small fish from the water, particularly near the surface and in warm water. The huge but docile fish—sometimes called gentle giants—have long thrilled divers and are the stars of growing ecotourism operations around the world. (Learn about how they move in mysterious ways.)

To learn more about whale sharks, we spoke with Greg Stone, an executive vice president and marine biologist with Conservation International (learn more about the group's efforts with whale sharks).

What is the prognosis for whale sharks?

They are struggling, particularly where they live near people. In parts of Asia there is quite a demand for products made out of them. They are considered a gold mine for fishermen because there is so much shark there. They are harvested for their meat, fins, and other parts used in traditional medicinal products.

Whale sharks are doing better in the Gulf of Mexico because there's not a lot of demand for the dead animal there. It's not the kind of product you can easily ship half way across the world, thanks to practical and legal restrictions.

Here's another way to look at it: Are whale sharks threatened in a variety of ways? Yes. Are people doing things to help them? Yes.

Whale Sharks Rescued From Wildlife Traffickers

What protections for whale sharks are making an impact?

People aren't allowed to catch them in any U.S. waters. Other countries have some protections as well, including Indonesia and in various marine sanctuaries. (See how an investigation led to the rescue of whale sharks.)

What more should be done?

We need to apply pressure to try to stop the market for whale shark products. Making that easier, now there are portable kits that can tell you what a shipment of seafood actually contains. You can easily see if it is swordfish or shark, and even the species. There is a whole movement around improving the traceability of seafood now [thanks to past reports of fraud and mislabeling]. Ultimately, if fishermen can't ship whale shark products anywhere then there will be no incentive to catch it.

There are also efforts underway to improve tracking and security in ports and to catch illegal fishermen. There have been tremendous breakthroughs in integrating data sets and tracking suspicious vessels. It's an exciting time for conservation.

What about whale sharks caught as unwanted bycatch, by fishermen going for other species?

That's a big problem, particularly with large gill nets. Better gear technology can help.

Some conservationists are also compensating fishermen when they do catch whale sharks, incentivizing them to donate the bodies to science instead of selling it on the market [where it can fetch tens of thousands of dollars]. We don't want them stimulating the market.

How important is ecotourism to the survival of whale sharks?

One study found that a live manta ray is worth more than a million dollars during its lifetime, based on revenue generated from ecotourism. Whale sharks would probably be similar. They're really fun to swim with. In the old days we used to catch rides by hanging onto their fins, though you probably shouldn't do that.

Watch: Putting a Camera on a Whale Shark Nat Geo explorers deploy Crittercams on whale sharks to get a glimpse of the sharks’ underwater world and to better understand their behavior along the reef.

Can ecotourism operations also threaten the sharks, through crowding them or by people harassing them?

There's always that risk.

Part of my PhD research was studying how habituation to people affects dolphins. Marine mammals who get too friendly with people can approach boats, which can lead to collisions. Or they can spend more time interacting with people than other more natural activities, such as foraging.

You might find purists out there who feel strongly about the impact of tourism on whale sharks, but I don't think they are going to become habituated the way dolphins can. Whale sharks are not the brightest fish in the sea; they have a brain the size of a pack of cigarettes. They might be curious but they probably wouldn't be entertained by people. They probably don't pay them much attention.