Abstract
Size and shape of fish otoliths are species-specific, but some species also display intraspecific variations. The common sardine, Strangomera bentincki , is a small pelagic fish inhabiting a seasonal upwelling ecosystem off central-southern Chile, having two discrete spawning sites along its latitudinal distribution. Otoliths of specimens were collected from commercial catches in Talcahuano and Corral, representing the central and south spawning zones. On the basis of otolith images, size-based shape descriptors were used to detect ontogenetic variation, and morphometric variables (length, breadth, area, perimeter and weight) were used to detect geographical differences in size and shape of otoliths. Outline analysis was studied on the basis of elliptic Fourier descriptors through multivariate statistical procedures. Size-based shape descriptors showed that otolith shape starts to be stable for fish larger than 12 cm total length, which keep an elliptical form. Morphometric variables for fish larger than 12 cm revealed intraspecific variation between central and south zones, which were associated with otolith weight and breadth. Outline analysis did not reveal significant spatial differences, but extreme intraspecific variation was due to the antirostrum, excisure , and posterior part of otoliths. Intraspecific variation in otolith size could be linked to differences in each spawning habitat and related to geographical origin, whose differences are not clearly identified. It is concluded that intraspecific variability in morphometric variables of sardine otoliths revealed geographic differences in size that are not attributable to allometric effects, and that otolith shape was similar between specimens from different geographic origin.
Highlights
Otoliths are polycrystalline hard structures that form part of the inner acoustic system of teleost fish
Morphometric variables for fish larger than 12 cm revealed intraspecific variation between central and south zones, which were associated with otolith weight and breadth
Outline analysis did not reveal significant spatial differences, but extreme intraspecific variation was due to the antirostrum, excisure, and posterior part of otoliths
Summary
Otoliths are polycrystalline hard structures that form part of the inner acoustic system of teleost fish. Otoliths are composed of precipitate calcium carbonate (usually aragonite) and other minerals in small amounts, all of which are immersed in a protein organic matrix (Degens et al 1969). Their shape and form is due to differential accretion of minerals, producing spherical forms in early larvae and the characteristic morphology of otoliths in later stages of a given species (Gauldie 1988, Lagardère et al 1995). Morphology and morphometry of otoliths have been important for trophic ecology studies (Härkönen 1986, Tuset et al 1996, Tombari et al 2000), for taxonomy (e.g. Lombarte and Castellón 1991, Martínez and Monasterio de Gonzo 1991), and for palaeontological studies (e.g. Nolf 1985)
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