The 'fins' are sweeps with the path being only approx 200mm long with the profile being the fin shape. I use this process a lot ... including the dolphin shapes and oddball mulions.
The material is plain ol' metal with a 'relief' cut out of it. Access this by going into the 'Appearance Properties' ---> 'Relief Pattern' withinthe material editor. This is part of the joy of been a teacher ... one of my students researched this and told me! Quite often they'll learn something new and pass on the info to me. Nice students.