(CNN)-Somali pirates successfully attacked an Iranian and a Thai fishing vessel over the past 24 hours, although one crew escaped, an anti-piracy expert said.

There were another two unsuccessful attempts this month.

In March, another two vessels, both Iranian, called the Jaber and the Siraj, were captured just off the Somali coast. The crew of the Jaba escaped by overpowering their captors, but the Siraj crew was taken ashore in September. It was the first successful attack in the Gulf of Aden in two years, Steed said.

According to anti-piracy expert John Steed of Oceans Beyond Piracy, which runs a support program to help hostages, the attacks occurred more than 200 nautical miles off Somalia's coastline. The pirates were using small skiffs, a clear indicator of range.

"The attacks are on fishing vessels, which shows because of the high levels of illegal fishing off Somalia, there are lots of potential fishing boat targets. That's what started the Somali piracy problem in the first place," Steed said from Nairobi.

Now, with potential reductions in international naval patrols, more risks taken by shipping companies and a reduction in the high-risk area, "there is more scope for the pirates to find a target," Steed said.

Pirates used to have hundreds of hostages, including Americans, Britons, Indians and South Africans, who they used to extort ransom money from family members or governments.

But the presence of international navies such as the European Union's Navfor and NATO, and the presence of on-board security teams, had dramatically reduced that number.

Now, there are fewer than 40 hostages in pirate hands. However, Steed says a regression is a possibility.

"The potential is quite high for Somalia's piracy problem to come back altogether if we are not very careful," he said. "And we have failed to build the right sort of capacity for Somalia to police its own waters."

The level of Illegal fishing off Somalia has increased 20 times over since 1981, according to a recent Secure Fisheries report.

In 2011, American Jessica Buchanan was kidnapped while working in Somalia for the Danish Refugee Council. She was held for three months but was dramatically rescued by the U.S. Navy's SEAL Team 6. German-American journalist Michael Scott Moore was the most recent, held for 977 days and released by pirates after ransom was paid in 2014.

The longest-held hostages to date are 26 Asian crew members from the fishing vessel Naham 3, who have been held for more than four years. Negotiators are still working to secure their release.

By CNN