SANTA BARBARA, California (AP) - Marine biologist Kristy Finstad first put on a dive tank at the age of nine.

The 41-year-old co-owner of Worldwide Diving Adventures was leading the scuba tour off Southern California when fire engulfed the dive boat, Conception, early Monday with 39 people on board, including six crew members.

Her brother Brett Harmeling of Houston said Tuesday that Finstad was among 34 people missing and presumed dead off Santa Cruz island, part of California's Channel Islands. Harmeling thanked everyone in a post on his Facebook page for their "unconditional love and support during this incredibly tragic time."

"No final word on my sister Kristy; however, it is likely she has transitioned to be with the good Lord," he wrote.

Finstad was among 33 passengers and one crew member who were sleeping below deck when the fire started. Five crew members were rescued, and the bodies of 20 victims have been recovered so far, though none has been identified publicly. Many need to be identified by DNA analysis, and officials are collecting samples from family members.

Also below deck were students from a Northern California school, Pacific Collegiate School in Santa Cruz. The school posted a statement on its website that said "our hearts and thoughts are with the families of the victims and those yet missing, particularly those of our students and parents on board."

School director Maria C. Reitano declined Tuesday to say how many students went on the trip, which was not school sponsored. The college preparatory public charter school serves grades 7-12.

Finstad knew the area well, having done hundreds of dives in the Channel Islands, where she first swam with her father as a toddler. She first dove with a tank off Mexico, according to her company's website.

Harmeling described his sister to the Los Angeles Times as extremely strong-willed and adventurous.

"If there was a one percent chance of her making it, she would have made it," Harmeling, 31, said.

Their mother founded the diving company in the 1970s.

Finstad studied damselfish and corals in the Tahitian Islands, dove for black pearls in the French Polynesian Tuamotus Islands and counted salmonids for the city of Santa Cruz, where she lived. She also did research for the Australian Institute of Marine Science and wrote a restoration guidebook for the California Coastal Commission.

"My mission is to inspire appreciation for our underwater world," she wrote on her company's website.

She and her husband had just returned from sailing across the South Pacific. It was part of their 10-year plan that started on the back of a napkin in 2006.

They left from the Channel Islands in 2015 on the journey and planned to return in 2018. Before they set off, Finstad wrote: "Our new boss is King Neptune: when it blows we hunker down; when there's surf we paddle in; when there's rain we wash up. In terms of time-lines, the best we can do is point in the right direction."