Do Sardinella aurita spawning seasons match local retention patterns in the Senegalese–Mauritanian upwelling region?

Abstract

Sardinella aurita is the most abundant small pelagic fish in the Senegalese–Mauritanian region. The success of its reproduction crucially depends on the local circulation as this determines whether larvae reach coastal nursery areas favorable to their survival or are dispersed into the open ocean. As a first step towards evaluating sardinella vulnerability to climate‐driven hydrodynamical changes, this study aims at underpinning how transport pathways drive optimal spatial and seasonal patterns for sardinella reproduction. We have used two estimates of the Senegalese–Mauritanian coastal seasonal circulation simulated by two hydrodynamical model configurations that differ in their forcing and topography. Nursery areas are determined by evaluating coastal retention with a Lagrangian individual‐based model that accounts for processes such as diel vertical migration and mortality as a result of lethal temperature exposure. Our results suggest that the shelf zones located at the Arguin Bank (19.5°N–21°N) and south of Senegal (12°N–14.75°N) are highly retentive. We find maximum retention rates in July–August and November–December over the Arguin Bank; from February–July and November–December over the southern Senegalese shelf; and lower retention rates over the central region (14.75°N–19.5°N) that are locally maximum in June–July when the upwelling weakens. These retention areas and their seasonality are in agreement with previously reported spawning patterns, suggesting that the Sardinella aurita spawning strategy may result from a trade‐off between retention patterns associated with the seasonal circulation and food availability. Exposure to lethal temperatures, although not well studied, could be a further limiting factor for spawning. The Lagrangian analysis reveals important connectivity between sub‐regions within and south of the system and hence underlines the importance for joint management of the Sardinella aurita stock.

Contrasted optimal environmental windows for both sardinella species in Senegalese waters

“…However, SST was the second most important variable in S. aurita recruitment variability. The role of the upwelling intensity on S. aurita abundance was already well established (Bacha et al., ; Braham et al., ; Diankha, Thiaw, et al., ; Mbaye et al., ). Nevertheless, to our knowledge, studies quantifying the effect of upwelling intensity on S. maderensis abundance have not previously been reported.…”

Environmental effects on the spatio‐temporal patterns of abundance and distribution of Sardina pilchardus and sardinella off the Mauritanian coast (North‐West Africa)

“…However, off NWA, sardine spawning areas are not continuous along the coast and located in areas where the continental shelf broadens or in coastal indentations such as a bay or downstream of a cape (Roy et al ., ; Ettahiri et al ., ). Spawning in such areas reduces the offshore loss of reproductive products and keeps the larvae in a productive area (Mbaye et al ., ). Off Western Sahara, Mauritania and Senegal, spawning is forced to times of upwelling to provide sufficiently low temperatures, but with coincident high production (Binet et al ., ).The increase in upwelling activity, and hence the increase in productivity, benefits the filter‐feeding strategy of sardine with a phytoplanktonic diet.…”

Effect of environmental conditions on the seasonal and inter‐annual variability of small pelagic fish abundance off North‐West Africa: The case of both Senegalese sardinella

“…The positive correlation between the S. aurita abundance and the CUI in spring suggested a direct influence of the duration of the coastal upwelling season, peaking in winter (Lathuilière et al., ). The coastal upwelling intensity was shown to be a source of interannual fluctuations observed in the coastal abundance of S. aurita in West Africa (Braham et al., ; Demarcq & Faure, ; Diankha et al., ; Mbaye et al., ). This pattern is also in accordance with the dynamics exhibited by other important resources in the area (for example, Farfantepenaeus notialis and Octopus vulgaris ), which have similar periodicity (Thiaw, Gascuel, Thiao, Thiaw, & Jouffre, ; Thiaw et al., ).…”

“…In NW Africa, the influence of the environment on fisheries resources has been increasingly studied in recent decades (Cury & Roy, ; Demarcq & Faure, ; Faure, Inejih, Demarcq, & Cury, ; Caballero‐Alfonso et al., ; Braham, Fréon, Laurec, Demarcq, & Bez, ; Mbaye et al., ; ). The changes in hydro‐climatic conditions are likely to be the major cause of the strong variability of coastal pelagic resources, particularly for sardinella.…”