The head of the Maine Warden Service abruptly resigned Thursday after a commercial fishing boat that he owns and operates apparently was caught with undersize lobster on board.

Col. Thomas A. Santaguida, a 20-year veteran of the warden service, submitted his letter of resignation Thursday after he was cited for having nine lobsters that were under the legal size during a routine boat inspection last week. He has been chief warden since 2004.

Santaguida, who operates his own lobster boat in addition to his warden service duties, said in the letter that he has kept a “clean record” throughout his 35 years of commercial fishing. But he took full responsibility for the violation, which he described as an honest mistake that “was the result of not paying close attention to the task at hand.”

“For the past 20 years that I have been a game warden, I have fully recognized that it is of the utmost importance for the public to have complete confidence and trust in the Department of Inland Fisheries and Wildlife and the Bureau of Warden Service,” Santaguida wrote in his letter to DIF&W Commissioner Roland “Danny” Martin.

“Even though, as I have explained, this was not a purposeful act, it is of a nature that may create unwarranted and undeserved concern for the Bureau of Warden Service if I remain in my current position.”

In a statement, Martin praised Santaguida’s service and called him an “exemplary officer.” But Martin agreed with the top warden’s decision to step down from his post.

“Given the nature of the allegations, it would not be possible for Colonel Santaguida to continue to lead the Maine Warden Service,” Martin said. “This is the right thing to do to protect the integrity of the warden service, which has the duty to enforce Maine law and to protect its natural resources.”

The incident happened on Oct. 24 during a routine deck-side inspection in Harpswell by patrol officers with the Maine Department of Marine Resources. Santaguida apparently was found in possession of nine “short” lobsters among the 54 pounds of legal lobsters.

The Department of Marine Resources issued him a summons for the violation Wednesday. Violators are subject to fines and, in some instances, can lose their commercial fishing license.

Santaguida could not be reached for comment Thursday.

DMR Commissioner George Lapointe was not familiar with all of the specifics of Santaguida’s case. But Lapointe said the protection of undersize lobsters is an important law that has been on the books for many years.

“When [violations] come along, we treat them seriously,” Lapointe said in a telephone interview Thursday evening.

A member of the warden service since 1987, Santaguida was named Warden of the Year in 1996 and two years later was promoted to the position of major. Wardens are responsible for upholding Maine’s myriad hunting and freshwater fishing laws, a job that Santaguida took seriously.

In 2005, the agency came under fire after a popular fishing guide with an unblemished record in Washington County was charged with keeping one fish more than the legal limit.

The guide, Randy Spencer, ultimately won the case, but Santaguida said he had no reservations about bringing the case. “We hold guides to a very high standard,” Santaguida told The Associated Press in an interview at the time.

Rep. Troy Jackson, an Allagash Democrat who co-chairs the Legislature’s Joint Committee on Inland Fisheries and Wildlife, praised Santaguida for his work to present fish and game laws in a way that people can understand. Jackson said he believed Santaguida was doing a good job as warden chief and was easy to work with.

But Jackson said it also would be awkward for the warden service to carry out its law enforcement responsibilities – including revoking licenses of violators – if the head warden were still on the job after being caught with illegal lobster.

“I’m sorry to see him go, but I understand why it has to be,” Jackson said.

The second-in-command at the warden service, Maj. Gregg Sanborn, will take over leadership of the service until an acting chief is named or Santaguida’s permanent replacement is identified.

“I apologize for any unintended disappointment and embarrassment that this situation has caused the people of Maine, fellow department employees, game wardens, other law enforcement officials and most of all my friends and family,” Santaguida wrote in his letter to Martin.

The Associated Press contributed to this report.