Lebranche mullet Mugil liza population structure and connectivity patterns in the southwest Altantic ocean using a multidisciplinary approach

Abstract

Previous meristic analysis of the oblique scale counts (OSC) of Mugil liza showed a bimodal pattern within the southern stock, between São Paulo, Brazil (-24oS), and Samborombón Bay, Argentina (-35oS), allowing the identification of two morphotypes (BR1 and BR2). The Brazilian group with lower number of OSC was represented by morphotype 1 (BR1), while the group with higher number of OSC was referred as morphotype 2 (BR2), which could represent distinct subpopulation-units. This study aims at evaluating 1) the population structure of M. liza in Brazilian waters through meristics and body morphometrics from individuals captured by the industrial purse seine fishery, and 2) to assess the possible connectivity between individuals collected off southeast-south Brazil with specimens sampled in Argentinean waters (AR) through otolith shape and microchemistry analyses. Combined meristic and morphometric analyses of fish bodies captured in Brazilian waters allowed to discriminate morphotypes (BR1 and BR2) characterized by different body proportions, head profiles and relative positions of the eye. BR1 presented on average 34 OSC, contrasting with 36 of BR2. For mullets born in two-time distinct intervals, (i) 2008-2011 and (ii) 2011-2014, otolith shape analyses associated AR to BR2, and evidenced a distinct otolith outline from BR1, while multi-elemental otolith core analyses showed no significant differences between AR and BR2. It suggests that the mechanisms responsible for the elemental deposition during the early life history for these two sub-populations (AR+BR2) were significantly different compared to BR1. Univariate analyses of the otolith fingerprints (core and edge) showed higher significant levels in Cd/Ca, Cu/Ca, Fe/Ca, Li/Ca, Mn/Ca, Ni/Ca and Zn/Ca for BR1 compared to AR and BR2. The hereby morpho-meristic data and univariate elemental fingerprints suggest distinct environments inhabited by fish along the western coast of South America. Furthermore, the multi-elemental otolith core results suggested the existence of more than one nursery area for the species. In conclusion, the two morphotypes identified (BR1 and BR2+AR) should be considered as two sub-populations within the mullets southern stock for fisheries management purposes.