Length-weight relationships of ten fish species from the Bulgarian Black Sea waters

Research Article Turk J Zool 2011; 35(2): 265-270 © TÜBİTAK doi:10.3906/zoo-0912-44 Length-weight relationships of ten fish species from the Bulgarian Black Sea waters Maria YANKOVA1,*, Danail PAVLOV2, Violin RAYKOV1, Veselina MIHNEVA1, Georghe RADU3 1Institute of Fishing Resources, Department of Ichthyology, P. O. Box 72, 4 Primorski Blvd., 9000, Varna - BULGARIA 2Society of Innovative Ecologists in BULGARIA 3NIMRD “Grigore Antipa” - Constanca, ROMANIA 300 Mamaia Blvd. Received: 23.12.2009 Abstract: Length-weight relationships (LWRs) of 16,842 specimens of fish caught in the Bulgarian Black Sea waters, covering 9 families, 10 genera, and 10 species, were studied. Spiny dogfish (Squalus acanthias L.), thornback ray (Raja clavata L.), sprat (Sprattus sprattus L.), pontic shad (Alosa immaculata Eichwald), anchovy (Engraulis encrasicolus L.), whiting (Merlangius merlangus euxinus Pallas), horse mackerel (Trachurus mediterraneus Aleev), bonito (Sarda sarda Bloch), round goby (Neogobius melanostomus Pallas), and turbot (Psetta maxima L.) were collected from May 2006 to December 2008. The fishes were caught by different fishing techniques, such as gill net, trawl net, and trap nets. The slope or allometric coefficient (b) of the functional regression between length and weight values varied from between 2.302 and 3.839 with the mean b = 3.152. The LWRs for S. acanthias and R. clavata have been reported for the first time for the Bulgarian Black Sea waters. Key words: Length-weight relationships, fish species, Black Sea waters, Bulgaria Introduction The Bulgarian Black Sea waters are a significant spawning and growing area for several fish species (Stoyanov et al., 1963). The most important species for industrial fishing are turbot, sprat, and horse mackerel. Depending on the stock states in different periods, this group may also involve pontic shad, bonito, round goby, anchovy, and some others. The knowledge of the biology of commercially important fish in economic terms (size values, i.e. minimum, maximum, and mean; and size relationships, i.e. length-weight) helps for the sustainable exploitation of the Black Sea’s natural resources. Length and weight measurements in conjunction with age data can give information on the stock composition, age at maturity, life span, mortality, growth, and production (Bolger and Connolly, 1989; Diaz et al., 2000). Length-weight relationships (LWRs) allow fishery scientists to convert growth in length equations to growth in weight in stock assessment models (Morato et al., * E-mail: 265 Length-weight relationships of ten fish species from the Bulgarian Black Sea waters 2001; Stergiou and Moutopoulos, 2001), estimate biomass from length frequency distribution (Petrakis and Stergiou, 1995; Dulčić and Kraljević, 1996), and calculate fish condition (Petrakis and Stergiou, 1995). However, the information about the length-weight relationships of fish species in the western part of the Black Sea is very scarce and incomplete. Data about previous investigations of LWRs for fish species from the Mediterranean, Black, and Azov seas are presented in Table 1. In this study, we report the LWR parameters of 10 species that are of economic and ecological relevance in the commercial fisheries off the Bulgarian Black Sea coast. Materials and methods The investigated area includes the Bulgarian Black Sea waters in front of Cape Kaliakra, Varna, Cape Emine, Bourgas, and Sozopol (Figure), and the study was conducted from May 2006 to December 2008. A total of 16,842 specimens from 10 fish species were collected by different fishing techniques (gill net with mesh size 2a = 400 mm; trawl net with an “effective” part of the mouth of 16 m, vertical opening of 4 m, mesh size of the cod end of 6.5 mm; and trap nets). The samples were transported to the research laboratory in polythene bags containing ice blocks to prevent spoilage and were then stored in a deep freezer (-30 °C) to avert deterioration. The total length Table 1. Some of the results of LWR parameters estimated in different localities for the similar fish species targeted in the present study. M. m. euxinus Lmin-Lmax a b Area Sources 9-24 5-40 5-32.5 0.004 0.005 0.004 0.005 3.24 3.14 3.24 3.11 Mid-Black Sea Eastern Black Sea Black Sea Bulgaria Samsun and Erkoyuncu, 1998 Genç et al., 1999 İşmen, 2002 Maximov et al., 2009 0.015 2.984 Adriatic Sea Zorica and Sinovčić, 2008 S. sarda A. immaculata 9-36 11.6-31.6 0.063 0.002 2.55 3.39 Bulgaria Mid-Black Sea Kolarov, 1991 Samsun, 1995 E. encrasicolus 6-15 0.007 2.92 Mid-Black Sea Samsun et al., 2004 S. sprattus 9-17.4 8.6-11.9 7.2-13.2 0.004 0.022 0.002 3.16 2.51 3.46 Adriatic Adriatic Sea Eastern Black Sea Sinovčić et al., 2004 Sinovčić et al., 2004 Şahin, 1999 T. mediterraneus 10.5-17 0.035 0.0051 3.30 3.17 Bulgaria Eastern Black Sea Yankova et al., 2010 Genç et al., 1999 S. acanthias 27.00-70.50 0.0031 0.0040 3.10 2.95 Aegean Sea Southeastern Black Sea Filiz and Mater, 2002 Avsar, 1996 R. clavata 20.50-99.00 0.0016 3.29 Aegean Sea Filiz and Mater, 2002 0.0074 3.22 Black Sea Samsun et al., 2007 2.431 Sea of Azov P. maxima N. melanostomus 266 0.0972 Froese and Pauly, 2009 M. YANKOVA, D. PAVLOV, V. RAYKOV, V. MIHNEVA, G. RADU 28°4ʹE 27°4ʹE Balchik Cape of Shabla43°3ʹN Cape of Kaliakra VARNA Cape of Emine 42°3ʹN BOURGAS Sozopol BULGARIA 41°3ʹN BLACK SEA Figure. Scheme of area investigated. of each fish (measured to the nearest 0.1 cm) was taken from the tip of the snout to the extended tip of the caudal fin using a measuring board. Body weight was measured to the nearest gram using a balance. Five species, Squalus acanthias, Psetta maxima, Raja clavata, Sprattus sprattus, and Merlangius merlangus euxinus, were collected by the research vessels Elis and RK-3 (boat lengths 13.7 and 17 m, engine horsepower 1.7 and 1.8 hp, respectively). After hauling, the catch was removed, and analyses were carried out on the deck of the research vessel and later in the laboratory. The mathematical function suggested by Le Cren (1951) was used in estimating LWRs: W = aLb where W is the total body weight (g), L the total length (cm), and a and b are the coefficients of the functional regression between W and L. An allometric coefficient b value larger or smaller than 3.0 shows an allometric growth, or isometric growth when it is equal to 3.0 (Bagenal and Tesch, 1978). In order to confirm whether the b values obtained in the linear regressions were significantly different from the isometric value (b = 3), t-tests for independent samples were used. Data concerning the t-tests are presented in Table 2. The values of constants a and b were estimated from the log transformed values of length and weight, i.e.: logW = loga + b logL via least square linear regression. The degree of association between the variables was computed by the determination coefficient, r2. 267 268 P. maxima Bothidae N. m (...truncated)