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    The effect of mesh size and cod end material on the mortality and yield of the rose shrimp, Parapenaeus longirostris (Lucas, 1846) (Decapoda, Penaeidae) in the Turkish beam trawl fishery
    (Brill Academic Publishers, 2006) Deval, Mehmet C.; Ates, Celal; Bok, Tomris; Tosunoglu, Zafer
    Mortality and yield parameters of the rose shrimp, Parapenaeus longirostris were compared with length frequency data collected from the beam trawl fishery in the Sea of Marmara. Von Bertalanffy parameters were estimated as L infinity=16.28 cm and K=0.490 year(-1). The rates of total (Z), natural (M), and fishing (F) mortalitiy were calculated as 2.83, 0.97, and 1.86 for a 32 mm PE (polyethylene) cod end. The Z and F rates for two other cod ends, 32 mm PA (polyamide) and 36 mm PA, were, respectively, 2.13 and 1.16, versus 1.57 and 0.60. A study on the relative yield per recruit shows that maximum yield can be obtained at an exploitation rate (E) of 0.53, 0.52, and 0.45, respectively, for 32 PE, 32 PA, and 36 PA cod ends, whereas the current E values are 0.65, 0.54, and 0.38. Consequently, 32 mm PE and PA cod ends cause overfishing pressure on the stock of P. longirostris.
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    Length-based estimates of growth parameters, mortality rates, and recruitment of Astacus leptodactylus (Eschscholtz, 1823) (Decapoda, Astacidae) in unexploited inland waters of the northern Marmara region, European Turkey)
    (Brill Academic Publishers, 2007) Deval, Mehmet C.; Boek, Tomris; Ates, Celal; Tosunoglu, Zafer
    The growth parameters, mortality rates, and recruitment pattern of Astacus leptodactylus from an unexploited area in inland waters of the northern Marmara region were investigated based on length-frequency data using FISAT software. Specimens were collected during eight scientific samplings carried out between March 2005 and May 2006. The seasonalized Von Bertalanffy growth function was fitted to the length frequency data (n = 2434) with the following parameters: L-infinity = 80.8 mm, K = 0.405 year(-1), C = 1, and WP = 0.90. The study of functional regressions permits us to conclude that the growth of this population is allometric. Natural mortality (M) was estimated at 0.578 year(-1)and total mortality at 0.589 year(-1). The longevity of the crayfish was calculated as t (max) = 7.4 year. The recruitment pattern shows that there is peak recruitment in May and June. We also estimated the potential instantaneous fishing mortality coefficient at F = 1.53-1.63 year(-1), the instantaneous total mortality coefficient at Z = 2.11-2.21 year(-1), and the exploitation rate E = 0.72-0.73, all through the length-converted catch curve procedure using the length-frequency data of the fyke-nets of 32 mm polyamide (PA) mesh size (stretched mesh).
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    Selectivity of PE and PA material codends for rose shrimp (Parapenaus longirostris) in Turkish twin rigged beam trawl fishery
    (Elsevier Science Bv, 2006) Deval, Mehmet Cengiz; Bok, Tomris; Ates, Celal; Ozbilgin, Hoseyin
    This study investigated the differences in the selective properties of 32 turn nominal polyethylene (PE) and 32, 36, 40 and 56 mm, nominal polyamide (PA) codends in beam trawl fisheries targeting rose shrimp, Parapenaeus longirostris, in the Sea of Marmara, Turkey. Data were collected in spring 2005 onboard a commercial trawler, on commercial fishing grounds. Selectivity data were collected using the covered codend method in two twin beam trawls in every haul. Using this method, four selection curves could be obtained in one haul. Selectivity parameters were calculated by fitting a logistic function using maximum likelihood. The L-50 values of 32, 36 and 40 mm PA codends were found to be 9.1, 10.2 and 12.6 cm, respectively. Due to retention of only a few specimens, realistic selectivity parameters could not be calculated for the 56 mm PA codend. Mean L-50 decreased with a change in mesh material from PA to PE. The lowest L-50 (8.0 cm) was found for the 32 mm PE material codend. This study has shown that for rose shrimp the 32 mm PA diamond mesh codend is not appropriate for the first maturity size (FMS) of 10 cm for rose shrimp in the Turkish twin rigged beam trawl fishery. In addition, the PE netting material provides a significantly lower L-50 value than the PA netting material. (c) 2006 Elsevier B.V. All rights reserved.