Vertical distribution of fish larvae in the Canaries-African coastal transition zone in summer

Abstract

This study reports the vertical distribution of fish larvae during the 1999 summer upwelling season in the Canaries-African Coastal Transition Zone (the Canaries-ACTZ). The transition between the African coastal upwelling and the typical subtropical offshore conditions is a region of intense mesoscale activity that supports a larval fish population dominated by African neritic species. During the study, the thermal stratification extended almost to the surface everywhere, and the surface mixed layer was typically shallow or non-existent. Upwelling occurred on the African shelf in a limited coastal sub-area of our sampling. The vertical distributions of the entire larval fish population, as well as of individual species, were independent of the seasonal thermocline. Fish larvae and mesozooplankton were concentrated at intermediate depths regardless of the thermocline position, probably because of its weak signature and spatial and temporal variability. Day/night vertical distributions suggest that some species did not perform diel vertical migration (DVM), whereas others showed either type I DVM or type II DVM. The opposing DVM patterns of different species compensate for each other resulting in no net DVM for the larval fish population as a whole.

Autumn larval fish assemblages in the northwest African Atlantic coastal zone

“…In the north-western part of the Mediterranean sea, sardine larvae mainly concentrate above 30m, during daylight and at night, and are found in deeper layers as they grow (Olivar et al, 2001;Sabatés, 2004). Although, on the West African Atlantic coast, neritic species show a vertical stratifi cation during daylight, only sardine larvae show a signifi cant diel vertical migration (Rodríguez et al, 2006).…”

“…It is composed of multiple species associations that vary in time and depend on the spawning of adults . However, these associations may result from the shared or contrasting responses of diff erent species to their pelagic environment (Somarakis et al, 2002) especially the local hydrodynamics Sabatés et al, 2004;Rodríguez et al, 2006;Olivar et al, 2010;Moyano et al, 2014). Larval fi sh assemblages refl ect the synchrony and overlapping of the spawning pattern of adults (Frank and Leggett, 1983) coupled with larval behavior (Gray and Miskiewicz, 2000).…”

Transport pathways of decapod larvae under intense mesoscale activity in the Canary-African coastal transition zone: implications for population connectivity

“…On the recovery of each sample, the zooplankton was removed from the meshes and was preserved in 4% borax-buffered formaldehyde prepared using seawater. According to Rodríguez et al (2006), at every station the individual 2-min strata were aggregated into nine strata corresponding to the following depth ranges: 0-20, 20-35, 35-50, 50-66, 66-82, 82-100, 100-124, 124-151 and 151-200. At the shallower stations, D2 and LS24, the bottom depth permitted sampling only for 85 and 80 m, respectively.…”

“…However, we should point out that our sampling strategy was not specifically designed for that purpose (Rodríguez et al 2006). Samples were collected at different times of the day and night and at different locations with quite different environmental conditions, thus preventing sample comparisons.…”

Diel variation in the vertical distribution of fish larvae forced by upwelling filaments off Punta Angamos (northern Chile)

“…Thus, results obtained from cruises on 9 September (1998) and 11 January (1999) showed a trend towards a diel vertical migration and/or ontogenetic migration; this behavior would be independent of condition type (upwelling/non-upwelling) as well as from hydrographic conditions observed during active upwelling events off Punta Angamos. However, in another regions with long periods of active upwelling the traditional migratory model (down at day, up during the night) would be partially affected, as evidenced the change in the migratory behavior (down at night, up during the day) seen in some myctophids larvae (Rodriguez et al, 2006;Auth et al, 2007). In general, it is well documented that a large number of fish larvae are visual predators concentrating its feeding rhythms during the daylight hours or during dusk and dawn hours (Hunter, 1984).…”