Start with high-confidence marine biology books, then narrow by subgenre or adjacent topics.
Eels
James Prosek
The Book of Eels
Patrik Svensson
Chasing Shadows
Greg Skomal, Ret Talbot
The Log From the Sea of Cortez
John Steinbeck, Richard Astro
Every Last Fish
Rose George
Spying on Whales
Nick Pyenson
The Illlustrated Encyclopedia of Fish & Shellfish of the World
Derek Hall, Daniel Gilpin
A Field Guide to Coastal Fishes
Valerie A. Kells, Kent Carpenter
Marine Mercury Bioaccumulation
Luiz Drude de Lacerda PhD
A Field Guide to Tropical Reef Fishes of the Indo-pacific
Gerald R. Allen, Roger Swainston
Kraken
Wendy Williams
Valerie A. Kells, Luiz A. Rocha
Shark Biology and Conservation
Daniel C. Abel, R. Dean Grubbs
Secrets of the Whales
Brian Skerry, James Cameron
Secrets of the Octopus
Sy Montgomery, Warren K. Carlyle IV
The Soul of an Octopus
Sy Montgomery
The Abyss Stares Back
Stacy Alaimo
The Great White Shark Handbook
Greg Skomal
The World Beneath
Richard Smith
Galapagos
Pierre Constant