Catch Composition of Bottom Trawl Fisheries in Düzce Coast, southwestern Black Sea

NESciences, 2017, 2 (3): 158-166 -RESEARCH ARTICLECatch Composition of Bottom Trawl Fisheries in Düzce Coast, southwestern Black Sea Tuba Öğreden1,2, Deniz Yağlıoğlu1,3* 1 2 Department of Biology, Faculty of Arts and Science, Düzce University, Düzce, Turkey Üsküdar Directorate of District Food Agriculture and Livestock, Republic of Turkey Ministry of Food Agriculture and Livestock Üsküdar, İstanbul, Turkey 3 Biodiversity Implementation and Research Center (DU–BIYOM), Düzce University, Düzce, Turkey Abstract This study was performed to identify the catch composition of Düzce coast (southwestern Black Sea) at depths of 30-110 meters by bottom trawl between September 2014 and August 2015. In the catch compositions of the Düzce coast, the abundance of the first, second and third species were Merlangius merlangus with 73.12% (1290.29 kg / km2), Gobius spp. with 9.30% (164.04 kg/km2) and Mullus barbatus with 9.05% (159.61 kg / km2), respectively. The other 33 species make up 8.53% of total fish biomass. When seasonal distribution was examined, the total catch of fish were 1038.54, 2552.37, 1068.72, 5132.96 kg/km 2, of which economic (target) fish species (Merlangius merlangus) constitute 745.72, 1726.14, 724.58, 4910.15 kg/km 2 in autumn, winter, spring and summer respectively. In this study, fishing a very high rate of discard whiting in little sizes draws the attention. Whiting constitutes 56% of discard. Single or sporadic captures were also recorded for Acipenser stellatus, Trachurus trachurus, Spicara smaris, Lophius piscatorius, Serranus hepatus and Hippocampus hippocampus. Moreover, in this study, red list status for 36 fish species belonging to 27 family in Düzce coasts were considered with the Red List published by the International Union for conservation of Nature and Natural Resources (IUCN). As a result of this comparison, it was determined that 2 species Critically Endangered (CR), 5 species Vulnerable (VU), 22 species Least Concern (LC), 4 species Not Evaluated (NE), 2 species Data Deficient (DD). Keywords: Southwestern Black Sea, Düzce coast, Bottom Trawl, Catch Composition, Turkey * Corresponding Author: Deniz Yağlıoğlu, e-mail: Natural and Engineering Sciences 159 Article history: Received 21 November 2017, Accepted 23 November 2017, Available online 30 November 2017 Introduction Düzce is a prominent segment of Black Sea with its 35 km coast line along the Akçakoca district. It also stands as a major observation point to monitor the general issues of Black Sea. Extreme investment being made in the sector with developed technologies lately makes fish stocks to be exposed to extreme fishing pressure. Fishing equipments not having selective specification also makes bycatch rates to be high and jeopardize the future of fishery. Determining the changes in production quantity in catch composition and average product lengths, assessing the effect of fishery on storages, specifying the measurements to be taken by authorities in order to reduce this effect, if necessary, collecting and analyzing regional fishing composition and bycatch data regularly is necessary in order fishery data to be used effectively for many years. In the detailed literature analysis made, it was noticed that there is no study that reveals the composition of trawl fishing at Düzce coasts and it was aimed to close this gap in the literature by this planned study. It is thought that sandy deep structure of Düzce coasts makes other region trawls to prefer this region and this makes Düzce coasts to be the key area for such studies and it is planned that this study reveal important output for intended planning to be done for the future of regional fishery. Thus in the present study, the effects of bottom trawl fishery on the fishes and trawl catch composition and target, by-catch and discard composition and fish stock biomass of bottom trawl fishery were examined for the first time in the Düzce coast, (southwestern Black Sea), Turkey. Material and Methods Total biomass, species composition, seasonal distribution and abundance were examined for 12 months (September 2014- August 2015), with trawling on the lines shown on the map (Figure 1) from the Düzce, western Black Sea coast of Turkey. Experiments were carried out on the commercial trawler (21-24 m and 420 hp main engines) during daytime in stable weather and sea conditions. The diamond mesh cod-end size was 40 mm, head-rope length of the trawl net was 24 m and trawling speed was 1.8-2.0 nm/h. In this study, a total of 33 commercial bottom trawl operations were performed with at 50-60 m depth ranges in the Düzce coast. Seasonal distribution of the number of operations were as 6 in autumn, 12 in winter, 11 in spring and 4 in summer. Species were identified according to Turan et al. (2007) and Eschmeyer et al. (2017), and the number of individuals and the total weight of samples were also detected. Natural and Engineering Sciences 160 Figure 1. Map of Study area (Düzce Coast) (trawling lines are shown with bars) The biomass was estimated based on the swept area method (Sparre & Venema, 1998). The catch per unit area was calculated by using the formula given by Pauly (1980) and Sparre & Venema (1998). The total catch amount occurring in each of these areas was determined separately, and areas with different amounts were then combined into a total. In this method, simple and clear mathematical calculations were used in estimating the existing stock. The estimate of biomass was made by following steps; The swept area (Sparre & Venema, 1992) for each haul was calculated using the formulas; a = D ∗ h ∗ X2, D= V∗t Fraction of the head rope which is equal to the width of the path swept by the trawl, (x2) was taken as 0.4 following Shindo (1973), Somvanshi et al. (2004). Pauly (1980) have arrived at the value of x2 = 0.5 to be the best compromise for the trawl vessels, and this value has been used for the present study. Cw/t= CPUE- kg/h (The Catch-Per-Unit Effort); Catch in units of weight per trawling hour a/t = area swept per trawling. Cw/t Cw = 𝑎/𝑡 𝑎 the Catch Per Unit of Swept Area (CPUA-kg/km2); Natural and Engineering Sciences b= ( / ) 161 kg/km2 In Black Sea waters, value for X1 for M. merlangus, 1.0 (Suer, 2016) have been used, with 1.0 possibly being the best compromise. At the same time a frequency analysis of the frequency of species availability for each season was made (F=Na / N * 100) (Blanchard et al., 2004). As a result of the analysis, the species were grouped according to their frequency in terms of the seasons and the frequency analysis results were visualized on the table. Result and Discussion In the study, Düzce coast trawl catch composition were composed of 36 fish species from 27 family. In the previous study on West Black Sea trawl fishery by Baskaya (2012), 27 fish species, two of which being cartilaginous species, were catched in 34 trawling operation. In the other study related to marine fish fauna o (...truncated)