Relative body condition of red mullet (Mullus barbatus) and its applicability as an indicator of environmental status

Abstract

This study examines the ratio between length and body weight of 4191 specimens of a prevalent, tertiary tropic level Teleost fish, red mullet (Mullus barbatus) sampled using a standard survey protocol from more than 2500 km by the coasts of Turkey extending along the Mediterranean, Aegean, and the Black Sea. The study's primary aim was to investigate whether there is a correspondence between the body condition of the red mullet and the environmental status independently determined based on lower trophic levels of the water masses the species inhabits. Possible impacts of some intrinsic (fish length), extrinsic factors (bathymetry, abundance, and site), and numerical condition expressions on the outcomes were analyzed and eliminated. The results displayed a strong positive correlation between the fish condition index values and the ecosystem descriptor; the body condition of fish increased as ecological status improved from "bad" to "good/high". Based on this relationship and to facilitate the use of red mullet body condition as an ecosystem indicator, a set of target reference values addressing different ecological states have been proposed. (C) 2021 Elsevier B.V. All rights reserved.