Erster Einsatz von Trenngittern in der kommerziellen Garnelenfischerei

Comparative fishing trials were conducted in the river Elbe estuary using 9 m commercial brown shrimp beam trawls. To avoid the bycatch of fish a metal sorting grid of the Nordmöre type was used. The elliptical grid was constructed of 6 mm stainless steel bar with a spacing of 20 mm between the bars and housed in a cylindrical frame of 800 mm diameter. It was installed in the extension piece just in front of the codend. The inclination of the grid was 45 degrees. A fish outlet was provided in the upper panel of the trawl at the upper edge of the grid. A series of 8 tows of 15 min duration at a towing speed of 3 kns was done. For evaluation the catch of the main codend was compared to the portion of the catch escaped through the grid. The presence of the grid caused a 97.4 % reduction of the catch of lump sucker, a 90.6 % reduction of the catch of sea scorpion, a 79.3 % reduction of the catch of cod, a 58.8 % reduction of the catch of armed bullhead, a 39.6 % reduction of the catch of dab, a 34.7 % reduction of the catch of flounder, a 32.3 % reduction of the catch of smelt, a 19.8 % reduction of the catch of plaice and a 14.5 % reduction of the catch of brown shrimp.

Trenngitter - eine Alternative zu den Trichternetzen in der Garnelenfischerei

Experimental fishing trials were conducted in the Elbe Estuary using an experimental 3 m-standard beamtrawl. To avoid the by-catch of fish, a sorting grid was used. The elliptical grid was constructed of 6 mm diameter stainless steel bars with a spacing of 13 mm between the bars and housed in a cylindrical frame of 400 mm diameter. It was installed in the extension piece just in front of the codend angled at 45°, with a fish outlet at the top. A series of 10 tows of 15 minutes duration at a towing speed of 3 kn was done. The catch of the main codend was compared with the catch separated by the sorting grid. This achieved a reduction of 56 % of plaice (Pleuronectes platessa), 75 % of flounder (Platichthys flesus), 99 % of whiting (Merlangius merlangus), 94 % of cod (Gadus morhua) and 49 % of smelt (Osmerus eperlanus) with a mean loss of 43 % of shrimps (Crangon crangon). English grid trials in the Humber estuary using a flapper set or guiding funnel in front of the sorting grid device demonstrated reasonable lower escapement rates for fish and shrimps.

Species identification of family Lutjanidae and separation of populations of John’s snapper (Lutjanus johnii) in Persian Gulf and Oman Sea based on otolith shape analysis

The anatomical and morphometric (shape indices, contour descriptors and otolith weight) characterizations of sagittal otoliths were investigated in 13 species of Lutjanus spp. inhabiting the Persian Gulf. This is the first study that compares the efficiency of three different image analysis techniques for discriminating species based on the shape of the outer otolith contour, including elliptical Fourier descriptors (EFD), fast Fourier transform (FFT) and wavelet transform (WT). Sagittal otoliths of snappers are morphologically similar with some small specific variations. The use of otolith contour based on wavelets (WT) provided the best results in comparison with the two other methods based on Fourier descriptors, but only the combination of the all three methods (EFD, FFT and WT) was useful to obtain a robust classification of species. The species prediction improved when otolith weight was included. In relation to the shape indices, only the aspect ratio provided a clear grouping of species. Also, another study was carried on to test the possibility of application of shape analysis and comparing otolith contour of otoliths of Lutjanus johnii from Persian Gulf and Oman Sea to identify potential stocks. The results showed the otoliths have differences in contour shape and can be contribute to two different stocks.