An important documentary on billfish airs this week on Public Television stations. “Billfish: A Challenge For Survival,” produced by Diana Udel in collaboration with Dr. Guy Harvey, examines the billfish species—marlin, sailfish and spearfish—their life cycles, and their role in world oceans. The documentary reveals new tagging studies and underwater photography, and explores conservation issues.

In South Florida, tune in to WPBT Channel 2 on Thursday, April 21 at 10 p.m., on Sunday, April 24 at 3 p.m. and Wednesday, April 27, at 11 p.m. For more information, visit www.billfishdocumentary.com