aqua, International Journal of Ichthyology Blue Water Spawning by Moorish Idols and Orangespine Surgeonfish in Palau: Is it a “Suicide Mission”? Mandy T. Etpison1 and Patrick L. Colin2 1) Etpison Museum, PO Box 7049, Koror, Palau 96940. Email: [email protected] 2) Coral Reef Research Foundation, PO Box 1765, Koror, Palau 96940. Email: [email protected] Received: 13 December 2017 – Accepted: 05 March 2018 Keywords am Morgen zu den Laichplätzen, schlossen sich zu Gruppen Predation, aggregation, feeding frenzy, gray reef shark, zusammen und bewegten sich über der Rifffläche auf und lunar periodicity. ab und zogen dabei die Aufmerksamkeit von Beutegreifern auf sich. Um die Mittagszeit steigen sie vom Riff auf und Abstract begeben sich ins freie Wasser jenseits vom Riff. Graue Spawning aggregations of the moorish idol (MI) and or- Riffhaie folgen ihnen, greifen sie an der Oberfläche an und angespine surgeonfish (OSS) were found on the western verzehren viele von ihnen in einem Fressrausch. Ein hoher barrier reef of Palau. MI aggregated around the first quar- Prozentsatz der aufsteigenden erwachsenen HF wird von ter moon from Dec. to Mar., with largest groups in Jan. den Haien gefressen, nur wenige können in die sichere Zone and Feb. Fish arrived near the sites in the morning, des Riffs zurückkehren. KD versammeln sich in denselben grouped together and moved up and down the reef face up Monaten, aber in der Zeit des letzten Mondviertels – wobei in late morning attracting the attention of predators. At es hierüber weniger Berichte gibt. Die Beobachtungen bei mid-day they ascend from the reef out into open water beiden Fischarten, dass sie weit nach oben steigen und sich away from the reef. Gray reef sharks follow them and at- zum Ablaichen vom Riff entfernen, gelten als ungewöhn- tack at the surface in a feeding frenzy. A high percentage of lich; das Verhalten wird als „Blauwasserlaichablage“ bezeich- the ascending adults are eaten and few return safely to the net, und es gibt wenige weitere Beispiele. Bisher hatte man reef. OSS aggregated in the same months, but on the last die Bedeutung von Riffhaien als Einfluss auf das Laichver- quarter moon with fewer observations being made. The halten von Rifffischen als bedeutungslos bis „mäßig“ observation of both fishes ascending high above and mov- eingestuft (nur wenige laichende Fische würden von Haien ing away from the reef to spawn is unusual and is termed gefressen, hieß es bisher). Das Beispiel der HF und KD, bei “blue water spawning” with only a few similar examples denen sehr viele Individuen von Beutegreifern gefressen known. Previously the importance of reef sharks in influ- werden, ist als Extrem zu werten, das man bisher nur von encing reef fish spawning behavior has been reported as Zackenbarsch-Gruppen kennt. Das Auftreten von Haien an non-existent to “moderate” (a few spawning fish taken by den Laichplätzen während der Gruppenbildung und Laich- sharks). This example of many individuals being taken by ablage lässt auf eine enge Beziehung zu den Rifffischen predators represents an extreme only reported previously schließen. Die offensichtlich hohe Erfolgsquote beim Er- for a grouper aggregation. The occurrence of sharks at the beuten von HF und KD mag eine Besonderheit dieser er- site during aggregation and spawning is indicative of a forschten Laichplätze sein, und es ist wahrscheinlich, dass close relationship with reef fishes. The apparent high rate die einzelnen Fische sich grundsätzlich iteropar verhalten, of predation on spawning MI and OSS may be specific to also Verluste durch erneutes Ablaichen ausgleichen können. these study sites and it is likely individual fishes are gener- ally iteropareous. Résumé Les concentrations de frai de l'idole maure (MI) et orange- Zusammenfassung spine poisson chirurgien (OSS) ont été trouvés sur la bar- Am westlichen Barriereriff Palaus konnte an Halfterfischen rière de corail de l'ouest de Palau. Regroupés autour de la MI (HF) Zanclus cornutus und an Kuhkopf-Doktorfischen Premier quartier de lune à partir de Décembre à Mars, avec (KD) Naso lituratus gruppenweises Ablaichen beobachtet des groupes plus importants en Janvier et Février. Les pois- werden. HF versammelten sich etwa zur Zeit des ersten sons sont arrivée en proximité des sites le matin, regroupés Mondviertels von Dezember bis März, mit den größten et déplacé vers le haut et vers le bas le récif de face dans la fin Gruppierungen im Januar und Februar. Die Fische kamen de matinée attire l'attention des prédateurs. À la mi-journée 121 aqua vol. 23 no. 4 - 15 March 2018 Blue Water Spawning by Moorish Idols and Orangespine Surgeonfish in Palau: Is it a “Suicide Mission”? ils montent du récif out simplement dans l'eau loin du récif. few decades (Sadovy de Mitcheson and Colin Les requins gris de récif de les suivre et d'attaque à la surface 2012) but basic information is still lacking for dans une frénésie d'alimentation. Un pourcentage élevé de many species that aggregate or are likely to do so, l'ordre croissant adultes sont mangés et peu de retourner en limiting the understanding of relationships of toute sécurité dans le récif. OSS regroupés dans le même mois, mais le dernier quartier de lune avec moins d'observa- spawning behavior, interspecific relationships and tions effectuées. L'observation des les deux poissons ascen- environmental conditions. In many areas aggrega- dant au-dessus et en s'écartant de la reef pour frayer est in- tions have been heavily fished, often to ecological habituelle et est appelé "l'eau bleue" de frai avec seulement extinction (they no longer form). Palau in the west- quelques exemples similaires connues. Auparavant, l'impor- ern tropical Pacific is an exception, retaining nu- tance des requins de récif à influencer le comportement de merous spawning aggregations, making it an ideal frai des poissons de récif a été rapporté comme inexistant à location for their study. It also has fishermen and "modérée" (un peu de la fraie des poissons pris par les re- tourist dive guides who are observant and often quins). Cet exemple d'un grand nombre de personnes prises par les prédateurs représente un extrême seulement rap- discover new knowledge about fish reproductive portés précédemment pour une agrégation de mérous. L'ap- behavior adding to traditional knowledge known parition de requins sur le site au cours de l'agrégation et la for decades, if not centuries (Johannes 1981, reproduction est l'indice d'une relation étroite avec poissons Sadovy 2007). Many such reports are now validat- de récif. L'apparente taux élevé de prédation sur les frayères ed scientifically by in situ observations with infor- MI et de l'OSS peuvent être spécifiques à ces sites d'étude et mation on aggregating fish species also included in il est probable que les poissons sont en général iteropareous. a number of popular books and publications, such as Colin (2009) and Etpison (2009, 2014). Sommario Presso la barriera corallina occidentale di Palau sono state Most reef fishes with planktonic eggs, both male- osservate aggregazioni di idoli moreschi (MI) e di pesci female pairs and group spawners with 3 or more unicorno arancione (OSS) legate alla fase della deposizione fish, remain within sight of shelter when spawning delle uova. Gli MI si sono riuniti intorno al primo quarto and release their gametes within 5-10 m of struc- di luna da dicembre a marzo, con gruppi più numerosi a tures to which they can quickly retreat for shelter gennaio e febbraio. I pesci sono arrivati vicino ai siti al from predators. They engage in a rapid vertical or mattino, si sono raggruppati e mossi su e giù per la barriera angled movement away from the bottom, the a tarda mattinata attirando l'attenzione dei predatori. A “spawning rush”, with eggs and sperm released at metà giornata sono risaliti dalla scogliera e si sono portati in acque aperte lontano dalla barriera corallina. Gli squali the peak and fishes quickly returning to near the grigi della scogliera li hanno seguiti e attaccati in preda a bottom. This behavior is generally believed to re- una frenesia alimentare. Un'alta percentuale di adulti è sta- duce egg predation from benthic-based plankti- ta mangiata e pochi sono ritornati sani e salvi nella barriera vores (eggs released high above the reef) (Nemeth corallina. Gli OSS si sono ammassati negli stessi mesi, ma 2012) and predation on the spawners by piscivores nell'ultimo quarto di luna si sono fatte meno osservazioni. (Molloy et al. 2012). L'osservazione di entrambi i pesci che risalgono la colonna The aggregation and spawning of two reef fishes, d’acqua e si allontanano dalla scogliera per deporre le uova moorish idol, Zanclus cornutus (Linnaeus, 1758) è insolita e viene definita "deposizione in acque blu" con solo pochi esempi simili noti. Precedentemente l'impor- (hereafter referred to as “MI”) and the orangespine tanza degli squali di barriera nell'influenzare il comporta- surgeonfish, Naso lituratus (Bloch & Schneider, mento di deposizione dei pesci nella barriera corallina è 1801) (hereafter referred to as “OSS”), violate this stata segnalata come inesistente o "moderata" (pochi pesci generality by swimming high above and far away riproduttori catturati dagli squali). Questo esempio di from the reef to release their gametes, even with a molti individui presi dai predatori rappresenta un caso es- high predation risk from sharks. Our information tremo segnalato in precedenza solo per un'aggregazione di predominantly concerns MI, but includes some cernie. La presenza di squali nel sito durante l'aggregazione comparative data on OSS, which use the same e la deposizione delle uova è indicativo di una stretta re- lazione con i pesci della barriera corallina. L'apparente alto spawning sites on a different lunar schedule. We tasso di predazione su MI e OSS durante la deposizione term this reproductive strategy “blue water spawn- delle uova può essere specifico per questi siti di studio ed è ing” in which the spawning fishes range 50-100 probabile che questi pesci siano specie iteropare.