Contrasted optimal environmental windows for both sardinella species in Senegalese waters

Abstract

We investigate Sardinella aurita and Sardinella maderensis recruitment success relative to the variability of oceanographic conditions in Senegalese waters using generalized additive models (GAM). Results show that recruitment of both species is marked by a strong intra‐annual (seasonal) variation with minimum and maximum in winter and summer, respectively. Their interannual variations are synchronous until 2006 (recruitment decreasing), while from 2007 there is no synchrony. The model developed shows that sardinella recruitment variability is closely related to the tested environmental variables in the study area. However, the key environmental variables influencing the recruitment success are different for both species: the Coastal Upwelling Index and the sea surface temperature for S. aurita and S. maderensis, respectively. We report that recruitment success of S. aurita and S. maderensis are associated with distinct ranges of sea surface temperature, upwelling intensity, wind‐induced turbulence, concentration of chlorophyll‐a and north Atlantic oscillation index. Considering food security and socio‐economic importance of both stocks, we recommend that consideration is given to the environmental variability in the small pelagic fish national management plans, particularly in the context of climate change.

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

“…All statistical analyses were performed using the stats, mgcv and Hmisc packages in R (De Mendiburu, 2014;Harrell Jr, 2017;Wood & Wood, 2017), with a significance level of α < 0.05. Sex Female 219 135 170 276 229 401 113 112 86 113 244 168 2266 Male 209 115 167 227 199 362 119 93 91 140 255 154 2131 Total 428 250 337 503 428 763 232 205 177 253 499 322 4397 Stage* I 22 60 18 56 110 160 98 56 6 27 56 4 673 II 33 27 45 66 105 184 38 51 9 12 56 21 647 III 28 31 34 36 39 135 17 11 1 7 35 13 387 IV 91 58 73 75 40 114 39 33 22 29 122 78 (Diankha et al, 2018;Tiedemann & Brehmer, 2017;Zuur et al, 2010). A VIF < 2 for all tested explanatory variables was considered adequate (Zuur et al, 2010).…”

“…Multi‐collinearity of explanatory variables was tested using the variance inflation factor (VIF) on SST, CUI (Tiedemann & Brehmer, ). The VIFs were calculated for all environmental variables to detect possible high dimensional collinearities (Diankha et al ., ; Tiedemann & Brehmer, ; Zuur et al ., ). A VIF < 2 for all tested explanatory variables was considered adequate (Zuur et al ., ).…”

“…() has predicted there is an increase in SST in general. In either case, changes in the upwelling intensity of the Senegal–Mauritanian system will influence the abundance of small pelagic fish, including round sardinella Sardinella aurita Valenciennes 1847 and flat sardinella Sardinella maderensis (Lowe 1838) (Diankha et al ., ; Thiaw et al ., ). Thiaw et al .…”

“…() and Diankha et al . () report that abundance and recruitment success of S. aurita are associated with distinct ranges of SST, upwelling intensity, wind‐induced turbulence, concentration of chlorophyll‐a and North Atlantic oscillation (NAO) index in Senegal.…”

“…Bakun (1990) hypothesised that climate change may lead to an intensification of coastal upwelling in response to increasing favourable upwelling wind and Barton et al (2013) has predicted there is an increase in SST in general. In either case, changes in the upwelling intensity of the Senegal-Mauritanian system will influence the abundance of small pelagic fish, including round sardinella Sardinella aurita Valenciennes 1847 and flat sardinella Sardinella maderensis (Lowe 1838) (Diankha et al, 2018;Thiaw et al, 2017). Thiaw et al (2017) and Diankha et al (2018) report that abundance and recruitment success of S. aurita are associated with distinct ranges of SST, upwelling intensity, wind-induced turbulence, concentration of chlorophyll-a and North Atlantic oscillation (NAO) index in Senegal.…”