Comparative biology of tropical Lethrinus species (Emperors): challenges for multi-species management

Abstract

Species of the family Lethrinidae are often targeted by fisheries and are important components of reef fish communities. Life history characteristics of six tropical emperor species sampled from the Great Barrier Reef World Heritage Area were compared. Two species groups were identified based on fork length (LF): large species with maximum lengths over 640 mm LF (longface emperor Lethrinus olivaceus, yellowlip emperor Lethrinus xanthochilus and spangled emperor Lethrinus nebulosus) and small species with maximum lengths less than 480 mm LF (Pacific yellowtail emperor Lethrinus atkinsoni, pink ear emperor Lethrinus lentjan and ornate emperor Lethrinus ornatus). Longevity was not correlated with body size. Early growth for all species was rapid and similar during the first few years of life but parameters of the von Bertalanffy growth function varied considerably among species. Growth also differed between sexes for L. atkinsoni. Reproductive characteristics varied among species, with peak periods of spawning occurring in November-December for L. atkinsoni, July-August for L. nebulous, September-October for L. olivaceus and a protracted season for L. lentjan, though fewer samples were available for the latter two species. Sex-specific length and age distributions and gonad histology of L. lentjan were suggestive of a functional protogynous reproductive pattern, as observed in some other emperors. Gonad histology indicated non-functional protogynous hermaphroditism for L. atkinsoni and L. nebulosus. The diversity of life-histories among these closely related species emphasises the difficulty in devising single management strategies appropriate for multi-species fisheries and illustrates the importance of understanding species-specific life histories to infer responses to exploitation.