Stock identification of Mediterranean horse mackerel (Trachurus mediterraneus) using morphometric and meristic characters

ICES Journal of Marine Science, 61: 774e781 (2004) doi:10.1016/j.icesjms.2004.05.001 Stock identification of Mediterranean horse mackerel (Trachurus mediterraneus) using morphometric and meristic characters Cemal Turan Turan, C. 2004. Stock identification of Mediterranean horse mackerel (Trachurus mediterraneus) using morphometric and meristic characters. e ICES Journal of Marine Science, 61: 774e781. Ó 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved. Keywords: Mediterranean horse mackerel, meristics, morphometrics, stock identification, Trachurus mediterraneus. Received 7 November 2003; accepted 5 May 2004. C. Turan: Fisheries Genetics Laboratory, College of Fisheries and Aquaculture, Mustafa Kemal University, 31040 Antakya, Hatay, Turkey. C. Turan: tel.: C90 326 245 58 16; fax: C90 326 245 58 17; e-mail: . Introduction Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner 1868), is one of the most important fishing resources in the Mediterranean Sea. This species is a semipelagic carnivore fish distributed throughout the Mediterranean, Marmara and Black Seas, and along the eastern Atlantic coast from Morocco to the English Channel (SmithVaniz, 1986; Fischer et al., 1987). The contribution of Trachurus mediterraneus to local fisheries differs in each sea; 54% of the total catch in the Black Sea (2919 t), 39% in the Marmara Sea (562 t), 4% in the Aegean Sea (247 t) and 3% in the Northeastern Mediterranean Sea (272 t) (DIE, 2001). The total catches of T. mediterraneus have drastically declined to nearly zero in the Black and Marmara Seas in 1988 due to overfishing in previous years (DIE, 2001). For effective fishery management and implementation of worthwhile stock rebuilding programs, knowledge of stock 1054-3139/$30.00 structure, distribution of fishing effort and mortality amongst the various components are essential, since each stock must be managed separately to optimize their yield (Grimes et al., 1987; Carvalho and Hauser, 1994; Begg et al., 1999). Poor understanding of the fish and fishery management can lead to dramatic changes in the biological attributes and productivity of a species (Altukhov, 1981; Ricker, 1981; Smith et al., 1991). The potential capacity of populations to adapt and evolve as independent biological entities in different environmental conditions is restricted by the exchange of individuals between populations. A sufficient degree of isolation may result in notable phenotypic and genetic differentiation among fish populations within a species, which may be recognizable as a basis for separation and management of distinct populations. Morphological characters, such as body shape and meristic counts, have long been used to delineate stocks (Heincke, 1898), and continue to be used Ó 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved. Morphologic differentiation among stocks of Mediterranean horse mackerel, Trachurus mediterraneus, throughout the Black, Marmara, Aegean and Eastern Mediterranean Seas, was investigated using morphometric and meristic characters. Discriminant function analysis of both morphometric and meristic characters suggested that there is restricted migration of mackerel among the adjacent seas. Overlapping of four Black sea samples on the discriminant space in morphometric and meristic characters suggested that there is one self-recruiting population in the area. The Marmara sea samples were the most isolated samples from all others for both morphometric and meristic characters, which may indicate existence of a distinguishable mackerel stock in the area. The sample from the Aegean Sea was grouped with one geographically close Mediterranean sample based on morphometrics, and separated from all other Mediterranean samples based on meristic characters, suggesting some degree of intermingling between these areas. Examination of the contribution of each morphometric variable to canonical functions indicated that differences among samples seemed to be associated with the anterior part of the body. In meristic analyses, highest contributions to canonical functions were associated with the number of gill rakers and pectoral fin rays. Stock identification of Mediterranean horse mackerel Material and methods Trachurus mediterraneus were collected by commercial fishing vessels from ten fishing ports in the Black, Marmara, Aegean, and Northeastern Mediterranean Seas during the feeding season (Table 1; Figure 1). Following capture, samples were placed individually into plastic bags and were kept deep-frozen (
20(C) for transport to the laboratory. Thirty animals were collected at each site, based on Reist’s (1985) recommendation that at least 25 animals be used for morphological analyses. The age of fish was determined by identifying and counting annuli of otoliths (Waldron and Kerstan, 2001). Multivariate analyses A stepwise multivariate discriminant analysis was used separately for morphometric and meristic data to identify the combination of variables that best separate T. mediterraneus samples, since predictive ability of morphometric and meristic characters are statistically different (Ihssen et al., 1981; Hair et al., 1996). In morphometric analyses, allometric growth, i.e. heterogeneity in body size among samples, can result in heterogeneity of shape without providing information on differences in body proportions among populations (Reist, 1985). In the present study, there were significant correlations with body length for morphometric and meristic characters. Therefore, transformation of absolute measurements to size-independent shape variables was the first step of the analyses. Size-dependent variation for morphometric and meristic characters was removed using the formula by Elliott et al. (1995): Madj ¼ MðLs =Lo Þb where M is the original morphometric measurement, Madj the size adjusted measurement, Lo the standard length of fish, and Ls the overall mean of standard length for all fish from all samples for each variable. The parameter b was estimated for each character from the observed data as the slope of the regression of log M on log Lo, using all specimens. Correlation coefficients between transformed variables and standard length were calculated to check if the data transformation was effective in removing the effect of size in the data. Table 1. Sampling details of T. mediterraneus used in this study. MSL, mean standard length (cm). Standard deviations of MSL are given in brackets. Sample Black Sea (Trabzon) Black Sea (Ordu) Black Sea (Sinop) Black Sea (Zonguldak) Marmara (Istanbul) Marmara (C xanakkale) Aegean Sea (Izmir) N. Mediterranean (Antalya) N. Mediterranean (Mersin) N. Mediterranean (Iskenderun) Abbreviation Date of capture Age Sampling gear MSL BS1 BS2 BS3 BS4 MS1 MS2 AS NMS1 NMS2 NMS3 21 March 2002 24 December 2002 12 February 2002 25 February 2002 11 October 2002 20 April 2002 03 December 2002 1 (...truncated)