Impact of Depth and Season on the Demersal Trawl Discard

Given that the discard has crucial impact on the coastal ecosystems, various countries around the world adopted various regulations to reduce the discard of non-commercial and undersized commercial species in the trawl catch, such as trawl exclusion depths and closed season. In this work discarded part of the catch of a trawl has been assessed to evaluate impact of depth and season. Monthly trawl-survey data, collected by the same research vessel operating all year round over the entire depth ranges of the same fishing ground, were used in order to minimize the sources of variation. By this mean, potential rather than absolute composition and quantity discarded by a trawl boat were estimated regardless of fishing regulations applied to the fleet. A generalized additive model was used to model the quantity of discarded catch as a function of depth and time. The model outputs were then used to quantify the impact of fishing regulations on the reduction in discard. The results suggested that the quantity of the catch returned to the sea is reduced 49% by trawl closure and 57% by trawling depth limitations. Overall, season and depth regulations reduce the discard by 77% at the expense of a 73% reduction in marketable catch Finally, past trawl-survey data collected in the 1980s at the same site with the same research vessel and with the same net were used to evaluate possible impacts of regulations on the modification of fish composition


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Nitrogen lost from agriculture has altered the geochemistry of the biosphere, with pronounced impacts on aquatic ecosystems. We aim to elucidate the patterns and driving factors behind the N fluxes in lowland stream ecosystems differing about land-use and climatic-hydrological conditions. The climate-hydrology areas represented humid cold temperate/stable discharge conditions, and humid subtropical climate/flashy conditions. Three complementary monitoring sampling characteristics were selected, including a ...
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Lake ecosystems are exposed to a range of anthropogenic pressures, particularly eutrophication, and in some cases also stocking and/or overfishing of top-predator fish species, all factors that have implications for the food web structure and which could lead to dominance of nuisance cyanobacteria. Restoration of degraded lakes demands insight into the relative role of top-down for bottom-up regulating forces. While knowledge about these forces in temperate lakes is extensive, comparatively little is known ...
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Salix alba L. (white willow) is an indicator species of a healthy riparian ecosystem with great renewable energy potential in Turkey though habitats of the species in many river ecosystems are highly degraded or fragmented. Impacts of this degradation of river ecosystems on the magnitude and pattern of genetic diversity are not known. This study was aimed at assessing the genetic structure of S. alba populations in two highly degraded and fragmented river systems (the Goksu and Kzlrmak rivers) in Turkey wit...
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Riparian countries of the Caspian Sea have been evaluating the pros and cons of the predatory ctenophore Beroe ovata as a control agent against the invasive ctenophore Mnemiopsis leidyi, which has enormous adverse impacts on the fishery resources as well as on the biodiversity in this once fertile sea. To assess the viability of B. ovata establishment in the Caspian Sea, the survival and some physiological characteristics (feeding, respiration, reproduction and growth) of the predatory ctenophore were studi...
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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 ...
Citation Formats
A. C. Gücü, “Impact of Depth and Season on the Demersal Trawl Discard,” TURKISH JOURNAL OF FISHERIES AND AQUATIC SCIENCES, pp. 817–830, 2012, Accessed: 00, 2020. [Online]. Available: