Ontogenetic and intraspecific variability in otolith shape of anchoveta (Engraulis ringens) used to identify demographic units in the Pacific Southeast off Chile

Abstract

The phenotypical variability in otolith shape of anchoveta (Engraulis ringens) was analysed in three zones (I, II and III) from north to south along the Chilean coast, using juvenile and adult fish. Generalised additive models were used to analyse shape indices and canonical discriminant analysis was used to analyse elliptical Fourier harmonics. The form factor and ellipticity indices varied significantly among the three zones, whereas roundness, circularity and rectangularity indices only showed differences between Zones I and III. Fourier reconstructed outlines for five ontogenetic stages suggested important differences among sampling zones, which were larger for sampling Zone III, where, at the same fish length, otoliths were smaller than those sampled in Zones I and II, at least at the pre-recruit stage. Elliptical Fourier descriptors showed significant differences among the three units, with a total percentage of correct classifications for juveniles of 89 and 74% for raw data and cross-validated cases respectively, compared with >85 and ~65% respectively for adult fish. The results support the hypothesis that juveniles and adults of anchoveta have remained segregated throughout their entire, or at least a fraction of, their life cycle, mainly between the extreme northward and southward zones.

Anchoveta Engraulis ringens along the Chilean coast: Management units, demographic units and water masses: Insights from multiple otolith‐based approaches

“…We found evidence of a much greater segregation between both northern units (DU‐I and DU‐II) and the southern unit (DU‐III), than between the two northern units, which is consistent with previous findings based upon parasitological (Valdivia et al, ) and otolith shape markers (Cerna et al, in press). Moreover, it is clearly consistent with the idea that an oceanographic and biogeographic discontinuity exists at the Tropical Convergence, which imposes relevant changes in water masses and community structures (Escribano, Fernández, & Aranís, ; Lancellotti & Vasquez, , ; Navarrete, Lagos, & Ojeda, ; Thiel et al, ).…”

“…The few available studies aimed to clarify the structure of demographic units (DUs) of E. ringens along the Chilean coast have suggested that at least two discrete units exist within the Chilean EEZ (Cerna, Saavedra‐Naveas, Plaza, Niklitschek, & Morales‐Nin, in press; George‐Nascimento & Moscoso, ; Valdivia et al, ). These two DUs appear to be located north from Caldera (25°S) and south from Valparaiso (32°S), respectively, tending to match latitudinal boundaries defined for MU‐I and MU‐III, respectively.…”

Invariant morphological descriptors from otolith shape in environment automatic classification

“…There are morphometric internal descriptors from the whole object and external descriptors from the contour of the object, such as area, perimeter, length of main axes (major axis and minor axis), and Feret distances (length, width, diameter; Bostanci et al., 2015; Iestyn‐Mapp, 2015; Ladroit et al., 2017; Montanini et al., 2017; Ozpicak et al., 2019; Skeljo & Ferri, 2012; Tuset et al., 2003; Zorica et al., 2010). Classic geometric indexes show the relationships between otolith shape and conventional geometric shapes such as circularity, rectangularity, ellipticity, and bounding box (Bostanci et al., 2015; Bostanci & Yedier, 2018; de Carvalho, Spach, et al., 2019; de Carvalho, Volpedo, et al., 2019; Cerna et al., 2019; Iestyn‐Mapp, 2015; Ladroit et al., 2017; Montanini et al., 2017; Ozpicak et al., 2019; See et al., 2016; Skeljo & Ferri, 2012; Tuset et al., 2003; Zorica et al., 2010). Some authors consider aspect ratios, such as the relationship between otolith length and fish size or the otolith mass and fish size (de Carvalho, Spach, et al., 2019; de Carvalho, Volpedo, et al., 2019; Jaramillo et al., 2014; See et al., 2016).…”

Spatiotemporal analysis of the daily growth traits of the prerecruits of a small pelagic fish in response to environmental drivers

“…In this area, intense fishery activity has caused anchoveta landings to reach the highest levels in recent decades, with 4.3 and 3.1 million tons landed by Peru and Chile, respectively, between 2015 and 2016 (Pikitch et al., 2012). Recent studies have addressed the population structure of this species along the Chilean coast with the use of otolith‐based ecological markers (i.e., Cerna, Saavedra‐Nievas, Plaza, Niklitschek, & Morales‐Nin, 2019; Garcés et al., 2019), revealing the existence of three different demographic units (“stocks”) in a northern zone (18º21'S and 24º00'S), a central‐northern zone (24º00'S and 32º10'S), and a central‐southern zone (32º10'S and 41º00'S), which suggest high heterogeneity in the population structure of this species.…”