A Study on possible variant forms of anchovy in the black sea

Download
2014
Şahin, Ezgi
The anchovy in the Black Sea is a commercially important fish source for Turkey, which is represented by two different subspecies in the basin. Spawning and feeding occurs in northern coasts where food supplies are more abundant. When the water temperature starts to decrease, the anchovy migrate toward the warmer waters of the southern coasts. The schools formed during this migration make them a primary target for fishing fleets. Due to morphological similarities, it is not possible to report the catches by subspecies which creates crucial problems in stock assessment and consequently fisheries management. Even if discrimination is carried out by methods such as genetics, blood types and parasitism rate, these are either impractical or very costly. Therefore, in the present study we aimed to establish more practical methods which can be applied for stock assessment studies. In order to achieve this purpose, sampling was carried out at overwintering grounds, with the notion that differences in feeding and nursery grounds may cause variation in size frequency distribution of age groups and length-weight relationships. Other than dissimilar environmental conditions, distances and different routes used to reach the wintering areas may affect the condition factor. An additional aim of this study was to test if shape analysis of otoliths, generally used for ageing in stock assessment studies, could be an effective method to discriminate between mixed anchovy stocks. Furthermore, various otolith shape parameters were studied contrary to adopting only otolith length/width ratio (aspect ratio) for stock discrimination. Biological data were collected by midwater trawls in Autumn-Winter (November to January), in 2011/12 and 2012/13 during the fishing season, in the area covering the southern Black Sea region from İğneada to Hopa. Length, weight and otolith shape variables were measured in the laboratory. In addition, environmental parameters; monthly averages of sea surface temperature (SST) and surface chlorophyll concentrations (Chl-a) were derived from satellite data for the entire study period. Study results indicate dissimilarities among stations in the allometric growth coefficient of length-weight relationship- slope (b), an indicator of well-being of fish, condition factor (CF), and also length frequency distribution of individuals in anchovy schools sampled. However, the stations showing similarities did not always show geographic proximity, and significant geographical patterns could not always be observed. In general, results indicate the presence of two groups, even though condition factor analysis illustrated the existence of an alternative third group. While, the clustering analysis (k-Means), which tests the feasibility of the applied methods for stock discrimination, supports the presence of two groups, ANOVA results indicate that the constants of length-weight relationship (a), and condition factor are not effective variables in grouping. Otolith shape, body length and length-weight parameters were used for principal component analysis (PCA), and those variables justifying most of the variance were later used for discriminant analysis. PCA results indicate that several variables related to otolith shape, as well as aspect ratio, account for most of the variance. However the variables significantly contributing to the discrimination differed in different age groups. 84.15% and 88.51% of fish belonging to 0 and I age classes respectively, were successfully classified via discriminant analysis. Cluster analysis carried out over otolith shape variables evaluated independently from the rest, produced similar results. Although clustering pointed out the existence of two groups, individuals from the same station were not distributed in the same cluster. According to the results of cluster analysis, clusters were explained by different parameters for each age group. So, within 0 age class, parameters such as aspect ratio and ellipticity did not significantly contribute grouping, while within the age I age class, total length of fish and roundness were excluded. As observed in the literature, the results denote the presence of two distinct groups. Hence, approaches already being used could be effective in separating anchovy stocks. However, contrary to this, condition factor results point out the presence of another additional group which may represent a hybrid fraction in the stocks. Therefore, to test the accuracy of group separation and determine whether or not a hybrid stock does exist, it is suggested to support the sampling and analyses carried out in this study with further sampling from the feeding and spawning grounds (the north-western Black Sea basin and Sea of Azov) before wintering, where the subspecies would in theory be isolated.

Suggestions

A box model for the basic elements of the northeastern Mediterranean Sea trawl fisheries
Gücü, Ali Cemal (1995-01-01)
A box model has been constructed for the northeastern Mediterranean Sea, where there is no reliable information on the total removal of fish by fisheries. The model utilizes survey data of biomass and these initial values are improved by a series of population dynamics methods. Once absolute values for the system components (length-weight relational growth parameters, mortality estimates, selection ogives, stomach content analysis) are established, biomass transfer within the ecosystem compartments is estim...
Stock assessment of the Black Sea anchovy
Tutar, Özge; Gücü, Ali Cemal; Department of Marine Biology and Fisheries (2014)
The Black Sea anchovy (Engraulis encrasicolus) is economically the most important fish species in Turkey since it provides 60% of the total fish catch. The Turkish fleet catches 90% of the anchovy stock in the Black Sea due to the anchovy winter migration to the Turkish coast. Over the last 50 years, the Black Sea basin has been subjected to pollution due to human sourced nutrient accumulation in the NW basin via the rivers Danube, Dniester and Dnieper and transportation. The ecosystem has been destroyed by...
Genetic structure of modern and ancient swordfish populations from coasts of Turkey
Yüncü, Eren; Togan, İnci Zehra; Department of Biology (2017)
In this study, partial mitochondrial DNA (mtDNA) and 8 microsatellite loci of swordfish collected from Northern Levantine Sea and Northern Aegean Sea were analyzed. Also same mtDNA region of ancient swordfish samples unearthed from Yenikapı excavation were sequenced. Obtained sequences were evaluated comparatively with the sequences from Balearic Sea, Ligurian Sea, Ionian Sea and Southern Aegean Sea, available in databases. Analysis of the molecular variance revealed a significant differentiation between We...
Current distribution of the small pelagic fish populations in the North Eastern Levantine Sea in relation to environmental conditions and predicting the impacts of temperature rise on their future distributions
Sakınan, Serdar; Gücü, Ali Cemal; Department of Marine Biology and Fisheries (2014)
Stocks of traditionally targeted fish species are in decline in the north eastern Levant Sea due to overfishing during recent decades, while catch statistics show a simultaneous increase in landings of commercially less valuable small pelagic species. Moreover, the number of species in the eastern Mediterranean is increasing due to Lessepsian migration and the response of native species to the continuous migration of lessepsian species is in question. Additionally, warming associated with climate change is ...
Optimization of growth characteristics for the potential probiotics to be used in fish aquaculturing
Aytekin, Nihal Destan; Hamamcı, Haluk; Büyükkileci, Ali Oğuz; Department of Food Engineering (2013)
The aquaculturing of marine and fresh water fish is continually increasing in the world and in Turkey. Of the three fish species; sea bass (Dicentrarchus labrax), seabream (Sparus aurata) and trout (Oncorhynchus mykiss), the latter has the highest share in Turkey, with a current production rate of 170000 tons per annum. The use of antibiotics in true feed is being phased out in the world. Probiotics have emerged one way of making up for the lack of antibiotics in the feed. In order to increase the probiotic...
Citation Formats
E. Şahin, “A Study on possible variant forms of anchovy in the black sea,” M.S. - Master of Science, Middle East Technical University, 2014.