.( \. , . • DISTRIBUI'IOO AND ABUNDANCE OF FLOISAM, LARVAL FISH AND JUVBNILB FISH OFF BARBAim WITII PAilfiCULAR REFEimNCB 'IO 'llm EXcx::x:>R~IDAB By Mario Ronmel T. Lao Institute of Oceanography, ( ~JcGill University, Nontreal • April, 1989 A thesis submitted to the Facu1 ty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science. copyright@ r-1a.rio Rommel T. Lao 1989 Since flyingfish are believed to spawn on floating substrates, the composition and seasonal abundance of flotsam was surveyed by neuston tows at stations 3 nmi, 6 nmi and 9 nmi offshore of Barbados. A total • of 431 tows were conducted between October, 1987 and September, 1988 • ThE~ flotsam was of coastal marine and terrestrial origin. Only 38% of tows contained flotsam, and only 1% of tows produced flotsam with flyingfish eggs. Flotsam was most abundant between March and September, whtm water reaching Barbados originates primarily from the South American mainland. This period does not correspond with the spawning season of the commercially exploited flyin.gfish, Hirundichthys affinis, near Barbados ( December-May) • Fish larvae of 34 and 24 families were collected in day and night neuston tows respectively, and larval abundance was higher by day til.al1 night. The larvae ranged from oceanic families (myctophids and istiophorids), to offshore families (hemiramphids and exocoetids) to coastal families (mugilids and mullids). Hemiramphids ( 46% of day catch) and myctophids (51% of night catch) dominated the catches. In both day and night samples, larvae were n~st abundant between February and Jw1e. When families were considered separately, larvae were either most abundant between February and June or least abundant between February and June. Families in the first category included the myctophids, hemiramphids 1 exocoetids and dactylopterids; families in the second category included the istiophorids, scombrids, carangids and mullids. Seasonal variation in abundance of exocoetid larvae (February to Jw1e) corresponds well with the seasona.lity of spawning in !J.. affiuis (December to 1'1ay} . For all larvae combined, and separately for the myctophid.s, {1emiramphids, dactylopterids, exocoetids and carangids (in night samples), larval abundance differed significantly between Stations 1, 2 and 3 ( 3, 6, and 9 nmi offshore) • Larvae were less abundant at Station 1 than at Station 2 and/or Station 3. The high larval abundance offshore may indicate that larvae are aggregated and retained in eddies downcurrent of the island. For 8 of the 10 coomon families collected, larval size varied significantly between stations. Larvae were largest and most abundant at Station 3 and smallest and least abundant at Station 1. This is consistent with the suggestion that larvae are retained in downcurrent eddy systems; larval retention leading to both higher larval abundance and larger size through growth. A total of 2,204 juvenile flyingfish were captured in the 49 nightlight trips made during the 1-year study. Juveniles of Parexocoetus brachyPterus, Exocoetus voli tans, Hirundichthys affinis and Oxyporhamphus micropterus dominated the catch. Adults of !:· brachyPterus and Q. micropterus were also caught, suggesting that the sampling procedure is less size-selective for these species. This is the first record of juvenile ~. voli tans and Q. micropterus off Barbados. In "E· brachypterus, ~. volitans and Q. micropterus, juveniles appeared in February - March, and remained abundant through summer (t-larch - July for ~· brachYPterus, February - August for !f. volitans, February - July for Q. mibropterus). Juveniles of H· affinis appeared in December-January, and abtmdance increased from February to August. The results suggest that all life history stages of H. affinis are sequentially present year-round near Barbados. This does not support the hypothesis of large-scale migration of !!· !!ifl.!lis from and towards the island. Puisqu'on croit que les poissons volants fraient sur des surfaces flottantes, la composition et 1 'abondance saisonniere des objets flottants ont ~u; mesure par des filet de neuston a des stations situes a 3, 6, et 9 mille nautiques au large de la Barbade. En tout, 431 echantillons, utilisant un filet de neuston, ont ete ramasses entre octobre, 1987 et septembre, 1988. Les objets flottants etait soit d'origine te:rreatre ou coti~re. Seulement 38% des echantillons contenait des objets flottanta et seulement 1% des echantillons conte1mit des objets flottants avec des oeufs de poissons volants. L'abo~tce des objets flottants etait le plus eleve entt~ les mois de mars et septenilire, quand l'eau atteignant la ~·bade est principalement d'origine Sud-Americaine. Cette periode ne correspond pas avec la saison de fraie de l'espece de poisson volant exploite commercialement, Hirundichthys affinis pres de 'la Barbade (decembre - mai). Les larves de 34 et 24 families de poissons ont ete ramassees respectivement1 dans des filet de neuston de jour et de nuit, et l'abondance des larves etait plus haut le jOU1' que la nuit. Les larves representaient des families oceaniques (Myctophidae, et Istiophoridae), des familles au large (Hemiramphidae et Exocoetidae), ainsi que des familles cotiere (Mugilidae et Mullidae). Hemiramphidae (46% de l'eclmntillon de jour) et Myctophidae (51% de l'echantillon de nuit) dominaient les echantillons. Panni les echantillons de jour ainsi que CeUX de nuit, les larves etaient les plus nombt~UX entre fevrier et juin. Quand les familles etaient analysees separemment, les larves etaient soil les plus nombreux entre fevrier et juin ou les moins nombreux entre fevrier et juin. Les familles dans la premiere categorie comptaient en.tre-eux Myctophidae, Hemiramphidae, Exocoetidae, et Dactylopteridae; et parmi les families de la deuxieme cat~gorie se trouvaient Istiophoridae, Scombridae, Carangidae, et Mullidae. La variation saisonniere dans 1 'abondance des larves dans 1 'Exocoetidae (de fevrier a juin) correspond bien. avec la saisonalite de reproduction dans !!· affinis (de decembre ~ mai). Pour 1 'ensemble des 1arves et aussi pour Myctophidae, Hemiramphidae, Dacty1opi:eridae, et Exocoetidae consideres seuls et pour Carangidae dans 1es echanti11ons de nui t, 1 'abondance de 1arves demontrait une difference significative entre 1es stations 1, 2, et 3 (3, 6, et 9 milles nautiques au large de la rive). Les larves etaient mains nombreux a la station 1 qu'a la station 2 et/ou 3. L' abondance eleve au large peut indiquer que les larves sont groupes et retenues dans des contre-courants en aval de 1 •isle. Pour 8 des 10 families communes echantillolmees, la taille des larves variait significativement entre les stations. Les larves ;;;taient les plus grandes et 1es plus nombreuses a la station 3, et les plus petites et mains nombreuses a la station 1. Cela est consistante avec la suggestion que les larves sont retenues dans des systernes de contre-courant; la retention de larve resultant en des abondances de larve elevees ainsi qu, une plus grande taille,suivant la croissance. // En tout, 2204 juveniles de poissons volants ont ete captures en les 49 sorties de nui t (en utilisant des lumiE~res) pendant la periode d'etude d'un an. Les juveniles de Parexocoetus brachYPterus, Exocoetus voli tans, Hirw1diohthys affinis, et Oxyporhwupl!IJS__!!!ieropterus dominaient la prise. Les adultes de ~· P_!J:lPhypterus et Q. J!!_.i,cropt~rus ant aussi et~ captures, qui suggere que la methode d'~haiitillonna.ge est rnoins selective selon la taille pour ces especes. Ceci est la premiere documentation de juveniles de ~· volitans et de Q. micropterus pres de la Barbade. Pour f. brachyPterus, ~· volitans, et Q. micropterus, les juveniles apparaissaient en fevrier-mars et restaient abondantes durant l'ete (mars - juillet pour f. brachyPterus, fevrier - ao'Ut pour ~. volitans, fevrier - juillet pour Q. micropterus). Lea juveniles de H· affinis apparaissaient en decembre-janvier, et 1 'abondance montai t de fevrier a aout. Les resultats suggerent que toutes lea ~tapes de cycle vital de H· affinis sont trouvees en sequence le long de l'ann~e pres de la Barbade. Cela ne soutenir pas 1: hypothese de migration de grand.e echelle de H· affinis de et vera l'!sle. The completion of this thesis would not have been possible witl1out the supervision and support of my adviser, Dr. Wayne Hunte. His comments and suggestions on earlier versions of the thesis are gratefully acknowledged. His moJral support when Murphy's Law repeatedly struck is equally appreciated. Dr. Hazel Oxenford made sure that the thesis was finished before I left Barbados. I thank her for her COIIIIlents on early versions, pa.t:ience during the most trying times and help in production of the final version. Dr. Robin l'tahon provided valuable comments on several sections of the thesis and helped in the survey of the most suitable neuston gear to be used. He also helped in resolving problems with computer software. Dr. Jolm Lewis gave helpful advice and encouragement during the early stages of the study and his ~sional visits to Bellairs were always eagerly anticipated. He made my stay in Montreal enjoyable. From start to finish, these people have always provided their time and energy in resolving unexpected problems and shared their knowledge and expertise in numerous discussions. I would like to thank Mr. Somkiat Khokiattiwong for his help dLn·ing the first few months of sampling 1 particularly when I was absent on a tagging trip for a week. His companionship during the entire study and the discussions we had together were extremely valuable. The fishermen who accompanied me in the field surveys, Emerson and Gabby, eased some of the difficult work at sea. Mr. Victor Small helped in procuring the materials for the neuston gear and in its construction. He also helped in constructing a boom for the original neuston gear. I thank him for his help and friendship. Students who were in Bellairs during the final stages of this study helped in one way or another in providing encouragement, giving me unlimited access to computers, BID in making my departure memorable.