Abstract
Modelling the environmental factors influencing the spatial variation of fish early life stages density and their drift history can identify the key biological and physical processes for the recruitment variability. Distance-based linear multivariate techniques were used to characterize the spawning areas of the European anchovy Engraulis encrasicolus in the Gulf of Cadiz (GoC). Chlorophyll is the environmental variable that best characterized its spawning areas with a time-lag of three days. The use of Lagrangian models to simulate the dispersal of small pelagic species more dependent on advection such as the European anchovy early life stages (early larvae and eggs) in the GoC could provide the degree of connectivity between spawning and nursery areas and identify the physical drivers of the recruitment variability. The larval final destination is critical for the survival of a marine species which is coastal-dependent during its early life stages. Simulations with a Lagrangian transport model in the Southwest Iberian Peninsula were performed during the most intense spawning peak of 2016, when a strong and persistent countercurrent event developed. Most of the simulated early life stages were transported to the western Portuguese coast and, to a lesser extent, to the Atlantic oligotrophic waters, suggesting an increase in the connectivity between the subdivision 9a South and West components. Although different environmental processes occurring during ontogenetic stages, as well as overfishing, among others, can explain part of the variability observed in recruitment, events such as the development of coastal countercurrents during the spawning season could partly account for an increase of anchovy on the western Portuguese coast and a decrease in the Gulf of Cadiz one year later.
Highlights
Understanding how physical–biological interaction mechanisms affect marine life early stages is key to know the processes influencing recruitment success in fish stocks (Sundby and Kristiansen, 2015)
The anchovy eggs density obtained during the ECOCADIZ 2016 campaign (31/7/2016–11/08/2016) ranged between 0.09 and 87.89 eggs m−3, with the lowest values (
Higher chlorophyll-a values were observed in the coastal zone (Fig. 3c), especially in the areas associated with the Guadalquivir River (~5.0–16.9 mg m−3) and Cape San Vicente (~0.6–2.5 mg m−3)
Summary
Understanding how physical–biological interaction mechanisms affect marine life early stages is key to know the processes influencing recruitment success in fish stocks (Sundby and Kristiansen, 2015). In terms of anchovy eggs mortality, it is temperature-driven, with temperatures above 26 °C or below 14 °C resulting in high egg mortality rates (Bernal et al, 2012) Anchovy larvae in this region start having some effective horizontal swimming capacity at a standard length of around 6 mm (~10 days after spawning), mainly depending on the ambient temperature (Morais et al, 2012; Huret et al, 2011). The analysis of their vertical distribution indicates that larval drift in the GoC mainly occurs in the first few meters of the water column (0–10 m) before they develop the diel vertical migration capacity, i.e., before they reach a standard length of 10 mm (Morais et al, 2012) This suggests that, during the first 10 days after spawning, the horizontal dispersion of anchovy early stages in the GoC is mainly determined by the surface currents (Catalán et al, 2006). This could indicate a change in the connectivity between the GoC and the western Portuguese region as a result of the observed change in the spawning location, as reported in other regions (Huret et al, 2010)
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