Contribution of the nursery areas to the major fishing grounds of the Brazilian sardine (Sardinella brasiliensis) in Southeastern Brazilian Bight inferred from otolith fingerprints

In the late seventies, studies on the population structure of Sardinella brasiliensis suggested the existence of two stocks (23–25°S and 26°S−28°S) based on distinct regional somatic growth rates and spawning areas. This scenario was recently confirmed by using geochemical signatures of whole otoliths combined with basic biological data from two-year-old individuals collected in southeast-south Brazil. However, information about sardine movements and connectivity between their main juvenile recruitment areas and the adult fishing grounds is currently limited. In this work, otolith natal elemental fingerprints (core section) of recruits (age 0+) and adults (age 2+), collected respectively in the main spawning areas (2019) and fishing grounds (2021) were evaluate. Otolith geochemical signatures (element/Ca) of recruits were compared with those of adult fish from the same cohort to estimate connectivity between juvenile recruitment areas (Rio de Janeiro RJ: 22°S, São Paulo SP: 23°S and Santa Catarina SC: 26°S) and regional adult populations captured in the major fishing grounds (22–23°S, 24–25°S and 26–27°S). Uni and multi-elemental signatures showed significant differences for recruits and adult’s individuals. This variability was mainly driven by Ba/Ca, Cu/Ca and Mg/Ca ratios. Pairwise comparisons associated recruits and adults from the northern distribution area (RJ+SP), but differentiated them from those individual from south (SC). The leave-one-out matrix combining otolith fingerprints reassigned the individuals to their original areas with moderate to high accuracy, for both recruits (RJ: 79%, SP: 73% and SC: 67%) and adults (RJ: 75%, SP: 60% and SC: 69%). A multinomial logistic regression suggested that for the 2019 cohort the replenishment of adult populations of S. brasiliensis along the Southeastern Brazilian Bight was mostly derived from the northern recruitment area (RJ+SP=89%). Nonetheless, minor contribution from the southern counterparts to the northern stock was detected (11%), supporting the hypothesis of meta-population structure for this species.