WARE, Mass. — To the biologist Tom French, the 3.5-mile uninhabited island was a conservationist’s dream. Where better, he thought, to bring a locally endangered species so it could thrive far from existential threats like car tires or humans?

The species in question, though, was a venomous snake, and Mr. French’s plan set off a cascade of anger and a clash between science and politics. Petitions piled up. Worried constituents emailed videos of swimming snakes to state legislators. The objections became so vociferous that lawmakers held an oversight hearing, where Massachusetts’ top environmental official apologized and promised to convene a committee that could at least consider other options.

The plan’s sinuous path has confounded Mr. French, the assistant director of the State Division of Fisheries and Wildlife’s Natural Heritage and Endangered Species Program.

“I’ve got a pretty thick skin, but this one is unique,” Mr. French said in an interview before the hearing on May 10, which went on for more than four hours. He added, “It disappoints me that people don’t think more highly of our native species.”