Variability of key biological parameters of round sardinella Sardinella aurita and the effects of environmental changes

Abstract

We examined growth rates and reproductive characteristics of Sardinella aurita off Senegal and other coastal areas over a 20 year period (1995–2014) to determine how they relate to variations in environmental characteristics of coastal waters. Based on fish length‐frequency data and a coastal upwelling index, we found that S. aurita recruitment tends to occur during the periods of most intensive upwelling (March–April off Senegal). Peak reproduction corresponds to periods of low sea‐surface temperature (in February or March). The sex ratio was remarkably consistent during the 30 year study period and so was not affected by environmental changes. We hypothesise that S. aurita takes advantage of the higher zooplankton productivity that occurs in coastal waters when upwelling brings nutrient‐rich water to the surface (i.e., it increases its growth rate and accumulates energy reserves for spawning). Growth performance appears to be strongly dependent on environmental conditions. The timing of spawning seems to occur when food (zooplankton) is most available for supplying the energy requirements needed by adults for spawning and early development of larvae. Environmental changes seem to have a significant effect on S. aurita growth and reproduction, which endorses their high phenotypic plasticity.

Bonga shad (Ethmalosa fimbriata) spawning tactics in an upwelling environment

“…The number of spawning batches per month was calculated by dividing the days of the spawning month by the number of days that E. fimbriata of a given length spawned that month. In accordance with findings on the closely related clupeid species S. aurita in the shelf waters of Senegal (Baldé et al, ), the obtained biological parameters were considered interannually invariable throughout the sampling period.…”

“…Successful reproduction in marine fishes requires a variety of energetic, ecological, physiological, anatomical and biochemical adaptations (Baldé et al, ; Rocha, Arukwe, & Kapoor, ). These parameters drive some species to develop reproductive strategies that ensure the survival of their offspring (Peck, Reglero, Takahashi, & Catalán, ).…”

“…The plasticity of small pelagic fish species in their growth, survival and other life history characteristics is key to their ability to adapt to environmental changes and makes them a suitable index for gauging the impact of climate variability on marine ecosystems (Baldé et al, ; Brehmer et al, ). Maximum reproductive success is expected when spawning events match with optimal environmental window (OEW) conditions (Cury & Roy, ; Diankha et al, ).…”

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

“…The main modes in the length frequency distributions (LFDs) found for the Mauritanian round sardinellas coincide with those identified off Senegal (Baldé et al ., 2019b). With the exception of 2009 and the pair 2008/2012, the analysis of the landings' length frequencies resulted in similar patterns for all the years, with an overall predominance of greater sizes.…”

“…Regarding the growth characterization of round sardinella in the area, different methods have been used. Length frequency analyses have been performed for the species inhabiting NW African waters (Boëly et al ., 1982 b ; Maxim & Maxim, 1987–88; Amenzoui & Baali, 2018; Baldé et al ., 2019 a , 2019 b ) and waters of the Gulf of Guinea (Amponsah et al ., 2017). In contrast, scales were the main calcified structure used in the first growth studies in the sub-region (Pham-Thouc, 1973; Krzeptowski, 1981; Boëly et al ., 1982b; Chesheva, 1998, 2001) and otoliths have been used in a study in south Morocco (Baali et al ., 2015).…”