OCCURRENCE OF PHRONIMA SEDENTARIA (FORSKÅL, 1775) (AMPHIPODA, HYPERIIDEA) IN THE STOMACH OF THE LONGNOSE LANCETFISH, ALEPISAURUS FEROX (LOWE, 1833) (AULOPIFORMES, ALEPISAUROIDEI) IN THE NORTH AND TROPICAL ATLANTIC OCEAN

BY

KEISUKE SATOH National Research Institute of Far Seas Fisheries (NRIFSF), 5-7-1, Shimizuorido, Shizuokashi, Shizuoka 424-8633, Japan

ABSTRACT Longnose lancetfish (Alepisaurus ferox) were caught in a longline survey and from their stomach contents Phronima sedentaria were observed to be associated with a gelatinous organism that occurred at a high frequency. A simple regression analysis was performed between the number of barrels and the number of P. sedentaria, and a highly positive correlation resulted (r2 = 0.978, p<0.001, n = 118). Although the quantitative prevalence of the association of Phronima sedentaria and barrels in the zooplankton community of the study area can not be discussed from these limited seasonal data, it is clear that the association was an important food item for the dominating mesopelagic species, Alepisaurus ferox during the survey period in the North and tropical Atlantic Ocean. The distribution of the association is here reported because of the scarcity of the knowledge on this issue.

RÉSUMÉ Des lanciers long-nez (Alepisaurus ferox) ont été capturés au cours d’une campagne au long cours, et dans leurs contenus stomacaux, ont été observés des Phronima sedentaria associés à un organisme gélatineux qui était présent en grand nombre. Une simple analyse de régression a été calculé entre le nombre de “tonnelets” et le nombre de P. sedentaria, et une corrélation hautement positive en est résultée (r2 = 0,978, p<0,001, n = 118). Bien que la fréquence de l’association de Phronima sedentaria et des tonnelets dans la communauté zooplanctonique de la région étudiée ne puisse être discutée à partir de ces données saisonnières limitées, il est clair que l’association était une composante alimentaire importante pour l’espèce mésopélagique dominante, Alepisaurus ferox, au cours de cette période d’investigations dans l’Atlantique nord et tropical. La répartition de cette association est ici rapportée, en raison du manque de connaissance sur ce sujet.

INTRODUCTION Phronima sedentaria (Forskål, 1775) is known to live in barrels made from salps or pyrosomes by the amphipod (Madin & Harbison, 1977; Laval, 1978). © Koninklijke Brill NV, Leiden, 2004 Crustaceana 77 (6): 729-739 Also available online: www.brill.nl 730 KEISUKE SATOH

Some amphipods use the barrel as a nursery house to enhance progeny survival in rearing experiments (Thiel, 1999). Observations of the association in the field by divers are limited to relatively shallow depths. In the mesopelagic realm, the distribution of the hosts and of Phronima sedentaria is not well documented. The longnose lancetfish, Alepisaurus ferox (Lowe, 1833) is a mesopelagic species with a worldwide distribution and often has a high CPUE (catch per unit effort) among the species collected by longline surveys (Matsumoto et al., 2002), as also observed in this study. The stomach contents of lancetfish have been are well studied (Kubota, 1973; Fujita & Hattori, 1976; Matthews et al., 1977; Chow, 2000; Moteki et al., 2001; Romanov & Zamorov, 2002) because these contents often include rare deep-sea species that remain in relatively good, undigested condition, and from these studies the fish has been determined as an opportunistic feeder. A lot of longnose lancetfish were caught in our longline surveys, and P. sedentaria associated with barrels (fig. 1) have been found to occur at a high frequency in the lancetfish’ stomach contents.

Fig. 1. Gelatinous barrel collected from a stomach of Alepisaurus ferox (Lowe, 1833), caught by longline.