Abstract
The spatial distribution of eggs and larvae of three pelagic species, mackerel, horse mackerel and sardine, in the Bay of Biscay was studied in 1998, 2001 and 2004. The spatial distribution was clearly different between the years studied and corresponds quite precisely to different water circulation regimes. Mackerel and horse mackerel larvae are more affected by the prevailing currents than sardine, as their spawning grounds are located offshore, far from the shelf break where the current velocities are higher. Survival rates for mackerel and horse mackerel were higher in 2001, when the offshore larval transport was stronger. However, for sardine, the mortality rate hardly varied between years. The abundance of 25-day-old larvae, considered as an index of the survival rate, appears to be a good recruitment indicator, at least for 1998, 2001 and 2004. Our results did not support the hypothesis of Bakun (1996), which states that dispersion of early life stages towards open ocean waters should cause high larval mortality. At least under the conditions observed for the years studied, the retention of larvae offshore appears to have a positive effect on larval growth and/or survival.
Highlights
Mackerel (Scomber scombrus, L.), horse mackerel (Trachurus trachurus, L.) and sardine (Sardine pilchardus) populations represent the most important stocks of pelagic fisheries in southern European areas (Spain and Portugal)
Physical and biological processes occurring at the shelf break appear to play an important role in the regulation of some fish populations, as their recruitment depends upon the dynamics during these early life stages (ELS)
The peak of spawning for these species is late in the Bay of Biscay, where mackerel spawns from February to May, with the peak in March-April, while the highest incidence for horse mackerel occurs in May-June (D’Elbée et al 2009)
Summary
Mackerel (Scomber scombrus, L.), horse mackerel (Trachurus trachurus, L.) and sardine (Sardine pilchardus) populations represent the most important stocks of pelagic fisheries in southern European areas (Spain and Portugal). In the Bay of Biscay, these populations partially share spawning habitats, so their pelagic eggs and larvae compete for food and predators. Physical and biological processes occurring at the shelf break appear to play an important role in the regulation of some fish populations, as their recruitment depends upon the dynamics during these early life stages (ELS). Mackerel and horse mackerel show great similarities in their life cycles These small pelagic species are distributed from the southern Norwegian coast to Mauritania. They are batch spawners, with a fairly extended spawning season. Juvenile areas (sardine at age 0) appear off the Iberian Peninsula in the northern and central parts of Portugal between summer and winter (Carrera et al 2006)
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