An Edgartown man is being held on $100,000 bail following a Monday arrest for allegedly trafficking in fentanyl, a deadly narcotic that is used as a substitute for heroin.

Alex Carlson, 30, was arrested at the Vineyard Haven Steamship Authority terminal at 9:15 p.m. Monday by members of the Martha’s Vineyard Drug Task Force, according to a press release from Edgartown police. Police said they seized about 103 grams of suspected fentanyl, a cell phone, and $388 from Mr. Carlson, after he had disembarked from the ferry. He is being charged with trafficking fentanyl (a class B drug). Arraignment is set for Friday at the Edgartown courthouse.

Fentanyl is a powerful painkiller 50 times more potent than heroin and up to 100 times more powerful than morphine. Police and public safety officials say fentanyl is beginning to replace heroin on the Island, as it is around New England, and point to increased fentanyl use as a leading cause of the rise in drug overdoses.

Edgartown Lieut. Christopher Dolby said seizing the fentanyl before it was distributed on the Island likely prevented an untold number of overdoses.

“That’s a lot of fentanyl right there,” he told the Gazette Wednesday. “A lot of stuff to hit the street . . . just by playing the odds, statistically wise, there’s a significant change that it would have resulted in at least overdoses, and if we didn’t get there in time to save them, ultimately deaths.”

Edgartown district court clerk magistrate Liza H. Williamson underscored the drug’s potency in setting cash bail for Mr. Carlson at $100,000. In a statement explaining her reasons for ordering bail, Ms. Williamson said the amount of fentanyl seized would equal about 600 so-called hits.

“The sale of such a high number of fentanyl hits would likely result in death and a potentially legally viable charge of manslaughter,” she said. “As such, the nature and circumstances of the charge are reasonably closer to homicide under the above circumstances. Because fentanyl is such a life-threatening narcotic, appropriate bail must reflect the actual potential charges.”

According to police, at the time of the arrest Mr. Carlson allegedly attempted to pull officers toward the water in an attempt to destroy something in his pocket. He is also charged with resisting arrest.

In her statement, Ms. Williamson also said Mr. Carlson has two prior convictions of possession with intent to distribute heroin and has served jail time as a result of the convictions. He violated probation in his most recent drug possession case, she said.