Do upwellings produce specific morphologic and chemical signatures in Sardinella brasiliensis otoliths?.

ANDRÉ M. VAZ-DOS-SANTOS; CRISTIANO D. ALBUQUERQUE; DANIELE C. BATALHA; SIMONE PERIN; ALEJANDRA V. VOLPEDO

lausanne

Congreso; XVI European Congress of Ichthyology. FRONTIERS; 2019

European Congress of Ichthyology.

Sardinella brasiliensis is the most important small pelagic fishery resource of the continental shelf between 22°S and 28°36?S, Brazil, Southwestern Atlantic. Historical landings varied from 228,000t to 17,000t, with usual values close to 75,000t. It is quite studied and geographic variations of adult shoals are well known. Younger and small fishes (0-1 years, up to 190 mm TL) are more numerous in the south of its distribution area and the older and bigger (2-5 years, up to 290 mm TL) in the north. Sagitta otoliths present spatial temporal variations in morphology and growth pattern. The spawning extends from October to March in two main areas (23°S-25°S and 26°-28°S), close to important superficial upwellings (Cape Frio 23°S-25°S and Cape of Santa Marta Grande 28°36?S). The hypothesis that upwellings can model otolith morphometric and chemistry was evaluated in the young-of-the-year (YOY) of S. brasiliensis, a key issue to detect the contribution of different nursery areas to adult stock biomass. Samplings were attained during surveys performed in November 2008 and March 2010. A mid-water trawl net was used whenever schools were detected with an echo sounder between 11 and 130m of depth. The specimens of were measured and the otoliths were obtained. The YOY were chosen (<100 mm TL, age 0+) by areas (Area 1 = 22°S to 23°25?S, Area 2 = 23°25?S to 26°30?S, Area 3 = 26°30?S to 28°36?S) and periods. Otoliths measurements were attained: length (Lo, mm), height (Ho, mm), perimeter (Po, mm), area (Ao, mm²), sulcus acusticus length (Lsa, mm), sulcus acusticus height (Hsa, mm), sulcus acusticus perimeter (Psa, mm) and area (Asa, mm2). Aspect ratios Lo/Lt, Lo/Ho, Lsa/Hsa and shape indices (form-factor FF, circularity C, rectangularity Re, ellipticity E, roundness Ro and relative sulcus surface Asa/Ao) were calculated, removing the size effect. A Principal Component Analysis (PCA) was done and the scores of the three first axis were used in a discriminant analysis (DA) with cross-validation (jackknife) and tested with a PERMANOVA followed by the post-hoc pairwise comparisons (areas and periods) (alpha=0.05). Whole otolith microchemistry (OMC) was analyzed following international standard procedures. The concentration of Ba, Sr and Ca were determined (triplicates) using an inductively coupled plasma-atomic emission spectrometry (ICP-OES). The ratios Sr:Ca and Ba:Ca were calculated and corrected in function of otolith weight and total length, and then tested by areas and periods with a Kruskal-Wallis test followed by the post-hoc Mann Whitney test. In November 2008 S. brasiliensis was caught only in Areas 1 and 2, comprising 13 individuals (71).