Adaptive plasticity of otolith shape in Scomber colias from the Canary Islands

Abstract

Small pelagic fish in the Canary Islands (CE Atlantic, from 29°27'N to 27°37'N and from 18°12'W to 13°17’W) are mainly targeted by artisanal purse-seiners, whose activity is monitored by the Canary Oceanographic Centre (IEO-CSIC) in the Data Collection Framework since 2013. The Atlantic chub mackerel (Scomber colias) is the main of the four species targeted by this fleet (45% of the total landings), with landings quite stable around a mean value of 850 tons/year. From August 2016 to December 2017, 792 otoliths of S. colias corresponding to monthly analyses of the mentioned fleet’s landings have been launched used to identify the potential presence of different morphotypes inhabiting Canary waters, based on otolith shape analysis. A DIvisive ANAlysis (DIANA) Clustering method using the 4th wavelet obtained from otolith contours resulted in the detection of five different morphotypes or otolith phenotypes. Differences where found mainly in the collicum-antirostrum and the dorsal margin areas of the otoliths’ contours. Two of the morphotypes represented 85% of the samples analyzed, whose individuals were slightly larger than the other morphotypes, considering mean lengths (≥25cm vs. ≤24.5cm). These very preliminary results open many future questions to be explored: 1) Do these results suggest intra-specific variation in the growth rate among phenotypes?; 2) Do phenotypes proportions change in relation to seasonal variations?; 3) May exist different ecological strategies related to each phenotypes?; and 4) Are these otolith phenotypes present in other geographical areas?