Although billfish are not typically the target of commercial fishing operations, they are often retained to supplement the diet of fishermen and their families.
In the fishing industry, "bycatch" refers to a species that is caught unintentionally while fishing for a more valuable "target" species. Bycatch is a major contributor to the declines of many species. Some forms of fishing have notoriously high rates of bycatch. In the Eastern Pacific, the major gear types are purse seine and longline fishing. The highest bycatch of sailfish and marlin is recorded within the first 80 miles from the coast.
Bycatch: Tuna's Dirty Little Secret
The Purse Seine industry uses a large net to surround schools of fish. Often, schools of tuna are identified because they are associated with dolphins, which are visible when they surface to breath. The tuna and dolphins are both feeding on "bait balls" of smaller fish. After public backlash against the industry because of the dolphin bycatch, several technological advances have drastically reduced the unintentional harming of marine mammals.
Longlining refers to a fishing industry that sets out a main line with shorter, hooked lines at spaced intervals. The main line can reach several miles in the most advanced fleets. Longlining has little selectivity; it doesn't depend on locating a school, and many species are caught as bycatch. Billfish, in particular, are caught in very high numbers because they inhabit the same area as tunas, and are also feeding on the same prey.
The Japanese Longline industry had fully colonized Central American waters by the 1960's. The Japanese fleet continues to account for a major proportion of the total catches in the region.