LYNN – Dave Winchester has taken a career in biology and trisected it to reveal an aquarist, a teacher and a teacher of teachers.”My career has blended into one that I can do in two different places,” said the Classical High School biology teacher.Winchester, a lifelong Lynner, said he spent 10 years working for the New England Aquarium before switching gears to install high-end aquariums, but he was toying with yet another career.”My whole career was the ocean and fish, and I would run into teachers all the time and they kept telling me I should teach, that I’d be good at it,” he said.He went so far as to check out what he had to do to be certified but still wasn’t sure if teaching was for him. A chance meeting with a Lynn teacher changed that, he said. Winchester said the woman called about installing an aquarium in her classroom. He said he would do it for free if she let him hang out in her classroom to see if teaching was his path.View photos from the trip”That was it,” he said. He’s been teaching in Lynn seven years.On Friday morning Winchester led 22 Advanced Placement marine biology students down to Marshview Park, just two blocks from the school, to look for critters, gather water samples and view life in a salt marsh up close and personal.Student Esther Mawhinney held out a large cup as Rene Perez dumped in tiny shrimp he caught in a net. David Medina balanced on rocks as he tried to scoop up a crab nearly the size of the palm of his hand.”Where’s its butt?” he said. “I don’t want to get pinched.”Further down the marsh teens squealed with surprise when Jaime Conroy came upon what she thought was a dead horseshoe crab but quickly realized it was actually two, and they were very much alive.Winchester gently picked up the crabs, deftly flipped them over and explained how to tell the male from the female, and how they used their tails to right themselves when they got upside down.”I love this so much,” said senior Angela Erelli.Erelli plans to become an elementary school teacher but said she could see herself taking her future students on field trips such as this.If Winchester hasn’t retired, he can help.About three years after he began teaching, Winchester started working part time back at the New England Aquarium during the summer and later added Saturdays to his rotation. He said it wasn’t long before they asked him to share his teaching knowledge with others.”They asked me to help teach teachers during the summer on how to take kids outside,” he said. “We’d go to Bell Isle Marsh in Revere and I’d show them how to have a field trip ? I’d tell them not to be intimidated.”The Aquarium has a Teacher Resource Center where teachers can sign out whale bones, sea turtle shells and even complete lesson plans to use in the classroom, he added.Winchester said he also began offering a workshop on how to set up a simple classroom aquarium. His room on Classical’s second floor has no fewer than seven. In them he keeps the shrimp, snails, occasional soft shelled clam and even fish his students bring back from their marsh adventures.Once back in the classroom the students will test water samples for salt content, nitrate levels and other items, Winchester said. They will also examine the critters with a camera or carefully under the microscope. The horseshoe crabs will only visit for a few days, he added, then he will return them to the marsh.In his spare time, Winchester is a part-time aquarist at the Northeastern University Marine Science lab in Nahant and works with Girls Inc., where he is making another urban connection to the natural environment.Despite his heavy work schedule, Winchester said he loves what he does.”I seem to collect jobs,” he said. “All these things seem to cross through (me).”And his fresh air approach with his students seems to be working.”It is the funnest thing we do all year,” said Jeanette Mordaunt. “We’re not just sitting in a classroom.”Moises Ramirez agreed. He said he plans to study chemistry or biol