(CNN) -- Officials are searching for a "mother ship" believed to be used to launch high-speed boats for several recent pirate attacks off Somalia. Since November 5, when pirates tried unsuccessfully to attack a 440-foot cruise liner operated by Seabourn Cruise Lines, at least five other attacks have taken place, most of them northeast of Somalia, said Andrew Mwangura, program coordinator at the Kenyan Seafarer's Association.Overall, he said, seven ships and crews have been taken into captivity in that section of the Indian Ocean.Fishermen in the area spotted a "pirate mother ship" drifting off the Somali coast in July, on November 5 and earlier this week, Mwangura said. Only one mother ship has been spotted, but there may be more in existence. Officials think the smaller boats used in attacks are launched from the mother ship, he said.A crew of more than 10 people, including a captain and engineer, are believed to be on the ship. The crew is believed to be well-organized, Mwangura said."We are trying to call up the coalition forces to track the vessel and to get pictures of the mother ship," he said.Earlier this week, the director of the International Maritime Bureau, appealed to vessels off the Somali coasts to come to the aid of ships under attack in a statement citing an "alarming rise" in the number of piracy attacks in the area."At the very least," said Capt. Pottengal Mukundan, IMB director, "they can prevent the hijackers from taking these ships into Somali waters. Once the vessels have entered these waters, the chances of any law enforcement is negligible."Twenty-five pirate attacks have been reported in the past six months, the statement said. "In one incident, a ship was lured into danger by pirates firing bogus distress flares."In the attempted cruise liner attack, pirates were in two boats and armed with machine guns and rocket-propelled grenades, Deborah Natansohn, president of Seabourn Cruise Lines, told CNN at the time. (Watch passengers recall their encounter with ocean marauders -- 2:34)The northern and southern coastline of Somalia -- Africa's longest -- links trade routes for key commodities like oil, grains and iron ore from the Gulf and Red Sea region down to the Mozambique Channel. Thousands of merchant ships snake down the Somali coast to the Cape of Good Hope every year.Some of the world's leading shipping bodies called on the U.N. to urgently address the issue.The piracy watchdog has warned merchant ships to stay at least 200 nautical miles away from the Somali coast -- an admonition that has gone unheeded.After two years of relative calm, 32 pirate attacks have been recorded since mid-March, including raids on ships carrying supplies for the U.N. World Food Program.Somalia has been ruled by rival warlords since dictator Mohammed Siad Barre was overthrown in 1991. Many of the warlords are believed to run gangs who smuggle drugs, weapons and people by road, sea and air around the region.Piracy is a lucrative and growing offshoot of this trade.On Wednesday, the U.N. Security Council criticized Somalia's squabbling government and urged rival factions to work to confront the chaos and piracy plaguing the lawless nation.The council expressed "serious concern" about the recent wave of pirate attacks off the coast, and urged regional powers and international bodies to address the problem urgently.CNN's Erin McLaughlin contributed to this report.Copyright 2005 CNN. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed. Associated Press contributed to this report.