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Öğe Body shape and trawl cod end selectivity for nine commercial fish species(Cambridge Univ Press, 2003) Tosunoglu, Z; Ozbilgin, YD; Ozbilgin, HThis study investigates the catch components of a commercially used demersal trawl cod end in Izmir Bay, and reveals some of the morphological characteristics of nine commercial fish species; red mullet (Mullus barbatus), hake (Merluccius merluccius), whiting (Merlangius merlangus euxinus), poor cod (Trisopterus minutus capelanus), tub gurnard (Trigla lucerna), common pandora (Pagellus erythrinus), axillary sea bream (Pagellus acarne), picarel (Spicara smaris) and annular sea bream (Diplodus annularis) in relation to mesh size and shapes. furthermore selectivity of 40-mm polyethylene netting cod end for red mullet, hake, common pandora, axillary sea bream, picarel and annular sea bream is presented. The results are discussed in a way to understand the probable effects of fish body shape on mesh selectivity.Öğe By-catch in a 40 mm PE demersal trawl codend(Scientific Technical Research Council Turkey-Tubitak, 2006) Ozbilgin, YD; Tosunoglu, Z; Ozbilgin, HDemersal trawling in Turkish waters yields a considerable amount of by-catch and discard. Data presented in this study were collected during a demersal trawl codend selectivity trial carried out on board the RV Egesuf (27 m, 500 HP) between August 9 and September 4, 2002, in Izmir Bay. In total, 52 species of fish and invertebrate from 40 mm nominal mesh size commercially used PE codend and 24 mm cover were identified, separately weighed, and classified as commercial and non-commercial. In addition, for red mullet (Mullus barbatus), hake (Merluccius merluccius), common pandora (Pagellus erythrinus), axillary sea bream (Pagellus acarne), annular sea bream (Diplodus annularis), and picarel (Spicare smaris), length measurements were taken to the nearest half centimeter, and percentages of by-catch, in terms of numbers of individuals, were calculated using Minimum Landing Size (MLS) or, if this was not defined, Length at First Maturity (LFM). Levels of by-catch for these species were also calculated in terms of weight, using length-weight relationships reported in the literature. The results showed that, on average, 63% (93 kg) of codend catch was composed of commercial species, while the rest, 37% (56 kg), was unmarketable species. Moreover, although they are commercial species, 5% of red mullet, 92% of hake, 32% of common pandora, and 33% of axillary sea bream were below MLS in terms of weight. In conclusion, it is stressed that the Aegean Sea demersal trawl fishery has a multi-species nature, its by-catch level is rather high, and therefore there is an urgent need for introducing more selective fishing practices.Öğe Comparison of the selectivities of double and single codends(Elsevier Science Bv, 2003) Ozbilgin, H; Tosunoglu, ZThis study investigates the differences in the selectivities of 40 rum mesh size single and double codends. The comparisons were carried out in the Bay of Izmir in the Eastern Aegean Sea between 4 and 18 April 2002. A conventional, 600 meshes around mouth, commercially used bottom trawl was operated. Selectivity data were collected in nine hauls with single, and nine hauls with double codends for red mullet (Mullus barbatus), annular sea bream (Diplodus annularis), and common pandora (Pagellus erythrinus). The hooped covered codend method was used for data collection. The data were pooled due to insufficient numbers of fish recorded in individuals hauls, and the selectivity parameters were obtained using a logistic equation with the maximum likelihood method. The single codend had higher L-50 values than the double codend, while the SRs are similar for both the codends for all the species. L-50's of double and single codends were 9.0 and 10.1 cm, respectively for red mullet; 7.7 and 8.7 cm for annular sea bream; and 8.1 and 10.5 cm for common pandora. The results confirm that the use of double codend impedes the escapements of significant proportions of immature fish. (C) 2003 Elsevier Science B.V. All rights reserved.Öğe Comparison of the selectivities of double and single codends(Elsevier Science Bv, 2003) Ozbilgin, H; Tosunoglu, ZThis study investigates the differences in the selectivities of 40 rum mesh size single and double codends. The comparisons were carried out in the Bay of Izmir in the Eastern Aegean Sea between 4 and 18 April 2002. A conventional, 600 meshes around mouth, commercially used bottom trawl was operated. Selectivity data were collected in nine hauls with single, and nine hauls with double codends for red mullet (Mullus barbatus), annular sea bream (Diplodus annularis), and common pandora (Pagellus erythrinus). The hooped covered codend method was used for data collection. The data were pooled due to insufficient numbers of fish recorded in individuals hauls, and the selectivity parameters were obtained using a logistic equation with the maximum likelihood method. The single codend had higher L-50 values than the double codend, while the SRs are similar for both the codends for all the species. L-50's of double and single codends were 9.0 and 10.1 cm, respectively for red mullet; 7.7 and 8.7 cm for annular sea bream; and 8.1 and 10.5 cm for common pandora. The results confirm that the use of double codend impedes the escapements of significant proportions of immature fish. (C) 2003 Elsevier Science B.V. All rights reserved.Öğe Determination of the appropriate hanging ratios to ease the escape of juvenile red mullet (Mullus barbatus L., 1758) and annular sea bream (Diplodus annularis L., 1758) from a trawl codend(Scientific Technical Research Council Turkey, 2003) Tosunoglu, Z; Ozbilgin, YD; Ozbilgin, HThis study investigates the relationship between total length (TL) and fork length (FL), girth (G), height (H) and width (W) of red mullet (Mullus barbatus) (n = 953) and annular sea bream (Diplodus annularis) (n = 944) collected during trawl selectivity trials carried out in Izmir Bay between July 1996 and February 1997. The FL, G, H and W of red mullet were 89, 53, 20 and 11% of the TL, respectively. For annular sea bream these values were 91, 80, 34 and 11 %, respectively. The ratios for average body thickness (W/H) were 0.573 for red mullet and 0.319 for annular sea bream. The hanging ratios (E-RM and E-AS8) of codends designed to ease the escape of juveniles of these species were 0.497 for red mullet and 0.304 for annular sea bream.Öğe Effect of PA and PE material on codend selectivity in Turkish bottom trawl(Elsevier Science Bv, 2004) Tokac, A; Ozbilgin, H; Tosunoglu, ZThis study investigates the differences in the selective properties of a 40 mm nominal PE, 36 and 44 mm nominal PA codends. The experiments were carried out in Izmir Bay in the Eastern Aegean Sea between 4 February 2002 and 22 March 2002. A conventional bottom trawl was operated onboard R/V Egesuf. Selectivity data were collected for red mullet (Mullus barbatus). annular sea bream (Diplodus annularis), picarel (Spicara smaris) and common pandora (Pagellus erythrinus) by using hooped covered codend method. Selectivity parameters were obtained by using logistic equation with the maximum likelihood method and by taking into account between-haul variation. Three codends were tested in a total of 25 hauls of which 18 were accepted valid for picarel and 23 valid for the other three species. In general. the PA material codends produced much higher L-50 values than the PE codend. However, the SRs of the three tested codends, were very close to each other. L-50'S of 40 mm PE, 36 mm PA and 44 mm PA codends, respectively, were found as 8.8. 8.4 and 10.3 cm for annular sea bream; 10.8, 12.4 and 13.8 cm for common pandora. There were not enough red mullet and picarel retained in the 44 min PA codend to estimate the selectivity parameters. Due to insufficient amount of retained fish selection parameters of 44 mm PA codend could not be obtained for red mullet and picarel. L-50'S of PE 40 mm and PA 36 rum codends. respectively, were 10.7 and 12.8 cm for red mullet and 12.4 and 13.3 cm for picarel. It is thought that 40 mm PE netting. which is commercially used, has rather poor selectivity. On the other hand, 44 mm PA codend causes the loss of marketable fish. Amongst the three tested codends 36 mm PA provides the most appropriate selection. (C) 2003 Elsevier B.V. All rights reserved.Öğe Effect of seasonal temperature changes on the escape behaviour of haddock, Melanogrammus aeglefinus, from the codend(Elsevier Science Bv, 2002) Ozbilgin, H; Wardle, CSSea temperature around the coast of Scotland rises from 7 degreesC in late winter to 12 degreesC in late summer. Recently, it was shown that the selectivity of trawl codend was poorer in late winter than it was in late summer. A change in water temperature is expected to affect the escape speed of fish, and therefore the selectivity of the gear. Four experiments carried out in this study showed the effect of this seasonal temperature change on the ability of haddock, Melanogrammus aeglefinus, to escape from a codend. A temperature increase from 7 to 12 degreesC changed the minimum twitch contraction time of the lateral muscle from 38.8 to 27.6 ms. This gives a maximum tail beat frequency of 12.78 Hz at 7 degreesC rising to 19.12 Hz at 12 degreesC. Escape reflexes of the fish were significantly slower at 7 degreesC than at 12 degreesC (P < 0.001). The shortest time to complete first body bend (stage 1) was 40 ms at 7 degreesC and 20 ms at 12 degreesC. The mean time taken to complete stage 1 at 7 degreesC (63.9 ms, S.E. 1.2) was significantly (t-test, P < 0.001) longer than at 12 degrees C (40.1 ms, S.E. 0.92). The mean time taken to complete the propulsive stroke (stage 2) of the fast start was significantly (t-test, P < 0.001) longer at 7 degrees C (108.5 ms, S.E. 5.3) than at 12 degrees C (72.6 ms, S.E. 2.6). The maximum speed recorded while competitively swimming for food reward was 7.9 L s(-1) at 7 degrees C and 12.5 L s(-1) at 12 degrees C. The observed maximum tail beat frequency used by haddock when leaving the mesh of a codend escape panel changed from 12 to 25 Hz. The general underlying physiological effect of a temperature increase of 10 degrees C was to double the speed of the maximum swimming ability (Q(10 degrees C) = 2). The effect of a change of only 5 degrees C on the ability to manoeuvre out of codend selection devices is discussed. Crown Copyright (c) 2002 Published by Elsevier Science B.V. All rights reserved.Öğe Effects of the protective bags on the codend selectivity in Turkish bottom-trawl fishery(Urban & Fischer Verlag, 2003) Tosunoglu, Z; Ozbilgin, H; Tokac, AThis study investigates the differences of selectivity between a plain codend (C) and a codend surrounded with a protective bag (CP). The experiments were carried out in the Bay of Izmir in the Eastern Aegean Sea between 16 January and 14 February 2002. The experiments were conducted onboard the RN Egesuf (27 in loa, 500 hp main engine) by employing a conventional bottom trawl commercially used in Turkish waters. The hooped covered codend method was used to obtain selectivity data. Eleven valid hauls (45 min towing duration and 2.5 knot average towing speed, 25 to 30 to water depth) were carried out both with C and CP Data were collected for red mullet (Mullus barbatus), annular sea bream (Diplodus annularis), picarel (Spicara smaris), and common pandora (Pagellus erythrinus). Selectivity parameters were obtained by using a logistic equation with the "Maximum Likelihood Method". Selectivity of C and CP was found to be very similar for the species investigated except that the 50% retention length (L-50) of CP was 9% higher than that of C for common pandora, and the selection range (SR) of CP was 32% wider than that of C for picarel. L-50 values obtained for C and CP were 10.7 and 10.6 cm for red mullet, 8.6 and 8.6 cm for annular sea bream, 12.3 and 12.1 cm for picarel, and 10.3 and 11.2 cm for common pandora, respectively. These results show that the protective bags used in Turkish demersal trawling do not have a significant effect on codend selectivity for the species investigated. The codend tested here and commercially used in Turkish waters retains a significant number of immature fish and therefore needs to be modified in order to improve its selectivity.Öğe Effects of the protective bags on the codend selectivity in Turkish bottom-trawl fishery(Urban & Fischer Verlag, 2003) Tosunoglu, Z; Ozbilgin, H; Tokac, AThis study investigates the differences of selectivity between a plain codend (C) and a codend surrounded with a protective bag (CP). The experiments were carried out in the Bay of Izmir in the Eastern Aegean Sea between 16 January and 14 February 2002. The experiments were conducted onboard the RN Egesuf (27 in loa, 500 hp main engine) by employing a conventional bottom trawl commercially used in Turkish waters. The hooped covered codend method was used to obtain selectivity data. Eleven valid hauls (45 min towing duration and 2.5 knot average towing speed, 25 to 30 to water depth) were carried out both with C and CP Data were collected for red mullet (Mullus barbatus), annular sea bream (Diplodus annularis), picarel (Spicara smaris), and common pandora (Pagellus erythrinus). Selectivity parameters were obtained by using a logistic equation with the "Maximum Likelihood Method". Selectivity of C and CP was found to be very similar for the species investigated except that the 50% retention length (L-50) of CP was 9% higher than that of C for common pandora, and the selection range (SR) of CP was 32% wider than that of C for picarel. L-50 values obtained for C and CP were 10.7 and 10.6 cm for red mullet, 8.6 and 8.6 cm for annular sea bream, 12.3 and 12.1 cm for picarel, and 10.3 and 11.2 cm for common pandora, respectively. These results show that the protective bags used in Turkish demersal trawling do not have a significant effect on codend selectivity for the species investigated. The codend tested here and commercially used in Turkish waters retains a significant number of immature fish and therefore needs to be modified in order to improve its selectivity.Öğe Population parameters of Mullus barbatus in Izmir Bay (Aegean Sea), using length frequency analysis(Blackwell Verlag Gmbh, 2004) Ozbilgin, H; Tosunoglu, Z; Bilecenoglu, M; Tokac, AThe growth and mortality of Mullus barbatus from Izmir Bay (Aegean Sea) was investigated based on length frequency data using the FISAT software. Total length of the sampled 110 891 fish ranged from 5.0 to 23.0 cm. The seasonalized von Bertalanffy growth resulted in parameter values of L-infinity = 24.26 cm, k = 0.565, t(0) = -0.305, C = 0.27 and WP = 0.45. Potential lifespan was estimated to be 5.3 years. Total mortality (Z) based on the length converted catch curve was 3.70 (seasonal data) and 3.85 (non-seasonal data). Natural mortality (M) was 1.07 and the exploitation ratio (0.71-0.72) revealed an overfished stock.
