This photo of an unusual sailfish was taken recently by super-keen billfish angler Terence ‘Bomber’ Farrell of Groote Eylandt in the Northern Territory. One of 97 sails he released for the season, this individual stood out because of its obviously forked bill. Bomber was interested as to whether or not the double bill might be a natural occurrence, and if it would affect the normal lifestyle of the sailfish.
Over many years of observing hundreds of live and dead billfish, I have seen only a handful with forked or split bills, so it is obviously quite a rare phenomenon. On the other hand, billfish with healed, broken bills are not that uncommon, with many observed to be missing the ends of their bills, and some having lost the entire bill to the level of the lower jaw, or even further.
Forked bills are almost certainly the result of injuries to the bill when the fish are very young – probably through collision with a floating object. In the days of timber sailing ships, it was not uncommon to find bills of marlin and swordfish deeply embedded in hulls, and while early mariners imagined that these fearsome fish had been attacking their vessels, it is now believed that the snapped-off bills were the result of misdirected attacks on baitfish aggregating around the slowly moving ships. And in the absence of man-made floating structures, no doubt collisions between billfish and floating logs have been happening for aeons.
Very young billfish have delicate bills that may well split on impact – like a greenstick fracture – after which the two tips continue to grow. And to the question of whether or not damaged bills can regrow, the answer seems to be yes, if the fish is young enough (perhaps in the first year of life), but after that, such injuries appear to be permanent.
In all these cases of forked or missing bills, the fish have obviously survived, and from angler accounts, appeared to behave normally during capture. However, it is quite likely that billfish with deformed or missing bills are at a disadvantage since the bill is primarily needed for maximum streamlining and hence maximum burst speed. This would mean that even though billfish carrying such injuries are still able to feed, they may not be as well conditioned as fully intact fish.
– Dr Julian Pepperell