Search

The vertical distributions of early developmental stages of oceanic fishes were investigated across the tropical and equatorial Atlantic, from oligotrophic waters close to the Brazilian coast to more productive waters close to the Mauritanian Upwelling Region. Stratification of the water column was observed throughout the study region. Fishes were caught with a MOCNESS-1 net with mouth area of 1 m 2 at 11 stations. Each station was sampled both during the day and at night within a single 24-h period. The investigation covered both larvae and transforming stages from the surface to 800 m depth. Distribution patterns were analysed, and weighted mean depths for the larvae and transforming stages of each species were calculated for day and night conditions. Forty-seven different species were found. The highest number of species occurred in the three stations south of Cape Verde Islands, characterized by a mixture of South Atlantic Central Water (SACW) and Eastern North Atlantic Central Water (ENACW). There was a marked drop in species richness in the three stations closer to the African upwelling, dominated by ENACW. The highest abundances occurred in the families Myctophidae, Sternoptychidae, Gonostomatidae and Phosichthyidae. Day and night vertical distributions of larvae and transforming stages showed contrasting patterns, both in the depths of the main concentration layers in the water column, and in the diel migration patterns (where these were observed). Larvae generally showed a preference for the upper mixed layer (ca. 0–50 m) and upper thermocline (ca. 50–100 m), except for sternoptychids, which were also abundant in the lower thermocline layer (100–200 m) and even extended into the mesopelagic zone (down to 500 m). Transforming stages showed a more widespread distribution, with main concentrations in the mesopelagic zone (200–800 m). Larvae showed peak concentrations in the more illuminated and zooplankton-rich upper mixed layers during the day and a wider distribution through the upper 100 m during the night. For most species, transforming stages were concentrated in the mesopelagic layers both day and night, although in some species ( Diaphus cf. vanhoeffeni and Vinciguerria nimbaria ), the transforming stages displayed vertical migration into the upper 100 m at night, in a manner similar to their adult stages. [ABSTRACT FROM AUTHOR]

In this investigation we analysed the changes in fish species occurrences and relative abundances across the tropical and equatorial Atlantic, and their vertical distribution patterns in relation to the different environmental scenarios. The study covers a wide region encompassing different water masses, and marked differences in productivity, from an oligotrophic zone close to the Brazilian coast, to a very productive upwelling region close to the Northwest African upwelling. Fishes were collected with a medium-sized midwater trawl (Mesopelagos), complemented by hauls made with a macrozooplankton net (MOCNESS). Species richness in the region was higher than in subtropical, temperate and cold regions. The total number of species and their overall abundance was lower in the stations closer to the Brazilian coast. Abundant species across the entire region were the gonostomatids Cyclothone alba , Cyclothone acclinidens , Cyclothone pallida and Cyclothone pseudopallida , the myctophid Lampanyctus alatus , the sternoptychid Sternoptyx diaphana , and the phosichthyid Vinciguerria nimbaria. The occurrences and abundances of C. parapallida , Lampanyctus nobilis and Lepidophanes guentheri were related to zones where AAIW waters occupied the mesopelagic layers, while other species such as Cyclothone livida and Polyipnus polli increased their abundance when AAIW disappears from their living depths. The presence of Eastern North Atlantic Central Water (ENACW) was associated with the occurrence of several myctophids ( Benthosema glaciale , Ceratoscopelus maderensis , Diaphus holti , Diaphus rafinesquii , Hygophum hygomii , Lampanyctus crocodilus , Myctophum punctatum , Symbolophorus veranyi) , and the gonostomatid Cyclothone braueri. In spite of the important differences in hydrographic features across the tropical and equatorial Atlantic, all stations showed either the general night migration into the epipelagic layers carried out by myctophids, phosicthyids, and some stomiids, or the presence of the several species of Cyclothone , sternoptychids and melamphaeids that remain in the mesopelagic layers, both day and night. The oxygen minimum zone (OMZ) at mesopelagic depths in the north-eastern sector does not seem to disrupt diel vertical migration. Day-night distributions in our study proved that mesopelagic migratory species are capable of crossing these wide hypoxic layers, and that some species such as Diaphus vanhoeffeni remain in these layers during the day. Other non-migratory fishes ( Cyclothone spp. and S. diaphana ) proved to be widely tolerant to these low oxygen concentrations, as shown by their high numerical abundances in the OMZ. [ABSTRACT FROM AUTHOR]

This study examines vertical distribution of the early stages of mesopelagic fishes in the south-eastern Indian Ocean and oceanographic factors that may affect it. This investigation along the 110 °E transect formed part of the second International Indian Ocean Expedition (IIOE-2). Depth-stratified samples to 500 m depth of early stages of mesopelagic fishes were obtained by means a multinet EZ-1 m2. This net captured larvae and transforming stages, but juveniles and adults were also caught, particularly at night. Diel vertical patterns of the different species and stages were analysed relative to the oceanographic conditions encountered at the 20 stations along the transect. This paper provides the ranges of vertical occurrence and weighted mean depth for larvae (135 taxa), and post-metamorphic stages (75 taxa) of fishes caught during the survey. Despite the varying vertical profiles of oceanographic parameters encountered, there were consistent patterns within species and families along the transect, with broader vertical distribution of larvae at the southern stations, where the upper mixed layer was deeper. During both day and night, larval stages of all the species were concentrated in the epipelagic zone, with some differences in terms of weighted mean depth (WMD) between taxa, but with no significant differences in vertical location between day and night. Transforming and juvenile-adult stages, however, presented a wider vertical distribution range than larval stages, and showed important differences among families and species. For example, Myctophidae and Phosichthyidae species presented the highest concentrations in the upper 50–100 m at night, and a much deeper distribution during the day, thereby indicating night vertical migration behaviour of transforming and juvenile-adult stages. By contrast, during these stages the Gonostomatidae Cyclothone spp. and the Sternoptychidae Argyropelecus spp. occurred deeper than the epipelagic layer during both day and night. Although these vertical patterns concur with results from other oceans, the WMD along 110 °E was slightly deeper than that observed in other areas, such as the eastern Atlantic, possibly related to water transparency in this oligotrophic part of the world's oceans. • Mesopelagic fish larvae were concentrated in the epipelagic zone during both day and night. • Transforming-adult stages of Myctophidae and Phosichthyidae migrated towards the surface at night. • Transforming-adult stages of Gonostomatidae and Sternoptychidae did not migrate towards the surface at night. • Vertical distribution patterns were influenced by temperature and dissolved oxygen in the water column. [ABSTRACT FROM AUTHOR]

The distributions of micronekton layers in the Balearic Sea (western Mediterranean) were investigated by acoustic methods. Two multidisciplinary surveys were carried out in late autumn 2009 and summer 2010, recording acoustic, biological, and hydrographic data. We described acoustic layers, migratory behavior, sampled species, and water masses processes. Acoustic modeling of gas-bearing organisms was employed to explain differences between acoustic estimates and sampled abundances. The influence of environmental variables on the vertical distribution and migration pattern of these organisms was analyzed. The thermocline depth was related to the preferred depth for migrating myctophids, while nonmigrant species dwelled in the oxygen minimum zone of the water column both in late autumn and summer periods. [ABSTRACT FROM AUTHOR]

The timing, sources and pathways for incorporation of larval fishes into a developing anti-cyclonic eddy off south-western Australia were investigated. Larval fish assemblages within the study region were structured by location (shelf, eddy and oceanic) and water mass. The larval fish assemblage within the eddy was significantly distinct from that characterizing the surrounding oceanic water. The eddy assemblage, which was comprised largely of larvae of oceanic meso-pelagic fishes (especially Diaphus spp. and Vinciguerria spp.) and less abundant neritic taxa, reflected its Leeuwin Current (LC), shelf and oceanic source waters. The occurrence of neritic taxa in the eddy confirmed the hypothesis that these larvae were incorporated as it developed in proximity to the shelf break. The significantly larger larval size of temperate neritic taxa (e.g. Sardinops sagax, Engraulis australis) in the eddy compared with the shelf suggests that these larvae were transported from the shelf adjacent to the developing eddy. The occurrence of tropical neritic taxa (e.g. Acanthuridae, Lutjanidae, Pomacentridae) highlighted the LC as an important transport route to higher latitudes. Coupling the sampling of larval fishes with the trajectories of Lagrangian drifters provided insight into how larval fish assemblages changed during development of the eddy. [ABSTRACT FROM AUTHOR]