Early life-history of the spiny siganid Siganus spinus (Linnaeus 1758) inferred from otolith microstructure

Abstract

Juveniles of the spiny siganid Siganus spinus were sampled from three sources in April, May and June 2008 for a study of its early life-history through otolith microstructure analysis. Specimens were obtained from bagnet catches in off-reef sites and seine nets in seagrass beds operating in Lagonoy Gulf, Philippines, and from the guts of skipjack tuna Katsuwonus pelamis caught by hand-line in an offshore area about 72 km east of the mouth of the gulf. The core, hatch ring, first feeding rings, and settlement increment of spiny siganid were identified and their widths measured. Mean daily otolith ages were 20.6, 22.1 and 21.7 of specimens from the gut, off-reef site and seagrass bed, respectively. Sagittae of the youngest (17-, 18- and 19-day-old) specimens from the tuna gut do not have settlement marks. Planktonic larval duration is 17 days. Most settlement (59%) occurred at the 20th increment on the evidence of its highest reduction in width and lessening of opacity. During the settlement process the juveniles swim from the fringing coral reefs to the seaweed beds then finally to the seagrass beds, wherein settlement volume is highest on or about the new moon date. The short, pelagic larval duration and restricted settlement timed on or 1–2 days near the new moon are integral elements in the settlement strategy of the fish.