Life history parameters of the round sardinella Sardinella aurita in the Central East Atlantic off north-west Africa

Abstract

Sardinella aurita has become an important source of fish protein-intake in NW African countries, where one stock is considered from Morocco to south Senegal, performing seasonal reproductive migrations along the coast. Although data are limited for the fisheries involved and for life-history knowledge of the species in the area, a precautionary approach is recommended to avoid overexploitation. Commercial landings of round sardinella produced by the European freezer-pelagic trawlers operating in Mauritanian waters were analysed between May 2004 and February 2012. The length-weight relationships (LWRs) (N = 40,725) did not show significant differences between sexes. Ripening round sardinellas were present throughout the year, but spawning effort rose between June and December. The length at first maturity for males and females was estimated at 27.7 cm TL (2.1 years) and 28.1 cm TL (2.2 years), respectively. Ages were interpreted from otoliths, varying from 0 to 8 years. Von Bertalanffy growth parameters resulted in non-statistically significant differences between sexes (P = 0.28). Natural mortality was estimated at ~0.63 year–1. The results provide important biological information for fisheries assessment of a species that plays an important key role in the current climate change scenario and for the economies of the riparian countries.

Reproductive traits of the round sardinella in the Canary Islands (Spain, NW Africa)

“…The annual length frequencies of round sardinella landings in the Canary Islands between 2013 and 2019 did not show any clear pattern. However, length frequencies clearly differed from the demographic structures found in NW African countries, including noticeably larger individuals (up to ~40 cm sized individuals, with modes in ~20–22 cm, ~26 and ~30 cm) (Baldé et al ., 2019; Jurado-Ruzafa et al ., 2020). The growth pattern observed in the present study should be considered as an informative punctual-trait, to be updated ad hoc if necessary in future studies, because (a) statistically significant differences between sexes were rejected, and (b) previous works in the area showed different results as well as significant seasonal variations (Jurado-Ruzafa et al ., 2016).…”

“…The overall sex ratio obtained for the round sardinella in the Canary Islands resulted in a significant unbalance towards males, in contrast with NW African waters where balanced sex ratios have been observed off Mauritania (Wagué & M'Bodj, 2002; Chesheva, 2006), or where females predominated in landings off South Morocco (Baali et al ., 2017), Mauritania (Jurado-Ruzafa et al ., 2020) and Senegal (Boëly, 1982; Ndiaye et al ., 2018; Baldé et al ., 2019). Unbalance to females is also reported in the Mediterranean Sea (Tsikliras & Antonopoulou, 2006; Mustac & Sinovcic, 2012).…”

“…Unbalance to females is also reported in the Mediterranean Sea (Tsikliras & Antonopoulou, 2006; Mustac & Sinovcic, 2012). Regarding the sex ratio variation by length range, the predominance of females in the largest sizes, as well as a balance for the middle length classes, had been observed for both the Atlantic (Wagué & M'Bodj, 2002; Baali et al ., 2017; Amenzoui & Baali, 2018; Jurado-Ruzafa et al ., 2020) and the Mediterranean round sardinellas (Tsikliras & Antonopoulou, 2006).…”

“…Sardinella aurita spawns year-round in NW Africa with a maximum period from June to September–December (depending on the area included) (Boëly et al ., 1982; Chesheva, 2006; Ndiaye et al ., 2018; Baldé et al ., 2019; Jurado-Ruzafa et al ., 2020). Conversely the spawning peak observed in the Canary Islands occurs in winter, matching with the breeding periods found in the other small pelagic species caught by the same fleet, i.e.…”

“…The coincidence of the spawning peaks with upwelling processes is in line with previous observations on breeding of round sardinellas. It seems synchronized with the major upwelling events in the nearby areas off South Morocco (Amenzoui & Baali, 2018), Mauritania (Jurado-Ruzafa et al ., 2020), or with the period when the sea surface temperature reaches the annual minimum values (Baldé et al ., 2019). Furthermore, the coincidence of the spawning peaks in the main target species of the fleet (artisanal purse-seines) should be considered as an advantage by the fishery managers who face the huge challenge of managing mixed fisheries (Penas Lado, 2019), as the one addressed in the present study, and even more for a species in expansion in the current climate change scenario (Baudron et al ., 2020).…”