Einfluss des Tag-Nacht-Verhaltens von Fischen auf das Ergebnis hydroakustischer Messungen

Echo integration is an established method for stock estimation. However, this method is not free of errors like every other measuring method. Especially the variation between day and night behaviour of fish may lead to large measuring errors. A new method is represented detecting such systematic errors, exemplified by investigations during the international hydroacoustic survey on the spring spawning herring in the Norwegian Sea. For this method all measured sA-values are sorted by starting time of the measuring unit distance. In order to reduce random influences a moving average over five time intervals is computed. When displaying these values in a diagram makes it is very easy to detect systematic errors based on the differences in day-night behaviour. For both species, herring and blue whiting, stock estimations are calculated based on the measured sA-values and the results of the analysed trawl catches. The influence of the differnt day and night behaviour of herring on the results of its biomass estimation is rather low. For blue whiting the measured values were about three time higher during day time than during night time. The result of this investigation should initiate a change of the evaluation procedure for stock estimation based on hydroacoustic measurements.

Einfluss von Größen und Fangzeit auf das Fettsäuremuster von Sardellen

Fatty acid composition of fish changes according to season, the catching area, the size, the sexuality, the physiological condition and the quantity of fat. The fatty acid composition was evaluated according to size and the catching season of anchovies Engraulis encrasicolus (L. 1758). It was observed that polyunsaturated fatty acids increasmed to highest level and saturated fatty acids decreased to lowest level in March. On the other hand, in April, it was observed that the saturated fatty acids increased to its highest level, monounsaturated fatty acids decreased to its lowest level.

Laichen von Dorschen in Gefangenschaft. Teil 2: Eiqualität und Befruchtungsrate

The quality of eggs spawned by cod of the western Baltic Sea, which were kept in captivity, varies during spawning season. These changes were independent of total length, weight and age of the parental individuals. Diameter, dry weight and fertilisation rate of the spawned eggs decreased during the spawning activities. An influence of water temperature and salinity on the variability of these parameters could not be detected. Diameter, weight and fertilisation rate were, however, influenced by the stage of the spawning process of the parental individuals. These results point out that within the first half of the spawning season not only the largest portion of the fertilised eggs was spawned but also those eggs with the best chance of a successful development.

Beurteilung der Frische von Fischen. Ergebnisse und Empfehlungen einer Konzentierten Aktion im Rahmen von FAIR

Von Anfang 1995 bis Anfang 1998 wurde eine Konzertierte Aktion (CA) mit dem Titel „Evaluation of Fish Freshness“ (Bewertung der Frische von Fisch) mit Mitteln der Kommission der Europäischen Union im Rahmen des 4. Europäischen Forschungsrahmenprogramms (FAIR) unter Beteiligung von 18 zumeist staatlichen oder universitären Fischereiforschunginstituten aus 14 europäischen Ländern durchgeführt.

Das deutsche Larvenprogramm im Hauptlaichgebiet des Herings der westlichen Ostsee - eine Forschungsaufgabe von internationaler Bedeutung

The German larvae surveys in the main spawning area of the herring of the western Baltic Sea - an international important program. The article gives an overview over the German herring larvae surveys in the Greifswalder Bodden and Strelasund. This program is performed under ecological points of view annually in the main spawning area of the herring of the western Baltic Sea and delivers indices, which are well suited as independent estimates of the herring year-class strength.

Flexibles Gitter für die Größenselektion von Ostseehering

In the Institute for Fishery Technology in Hamburg a new sorting grid for herring trawl fishery was developed which is more adapted to the commercial fishery than existing constructions. Therefore a flexible design was choosen with braided snoods as grid elements and rubber rings for shape stabilization. First tests were carried out with twin trawlers in the Western Baltic in February 1999. They proved principally the serviceability of this grid construction under commercial fishing conditions. The percentage of small sized herring was essentially reduced. Due to only few hauls more detailed quantitative statements are not possible yet.

Die deutsche Fischerei auf den "ozeanischen" Rotbarsch (Sebastes mentella) von 1995 bis 1998

Recently, the German redfish fishery displayed a pronounced seasonal pattern in geographic effort distribution and depth. The second and third quarters were the main season when 80 % of the effort was exerted. During the second quarter, the fleet activities were concentrated in international waters close to the Icelandic Exclusive Economic Zone (EEZ), fishing at depths exceeding 600 m. In contrast, the catches in the third quarter were taken mainly inside the Greenland EEZ at depths around 300 m. From 1995 to 1998, the annual effort ranged from 14 000 to 18 000 trawling hours, without a trend. This effort yielded about 18 000 to 21 000 t (international catch > 100 000 t) annually. Since 1996, the catch rate (CPUE) decreased during the main season. The decrease in CPUE should be interpreted as the first reaction of the stock to increased exploitation. The fish size also varied seasonally and peaked during the second quarter at depths exceeding 600 m. Here, males were bigger than females and both sexes were equally frequent. The increase of fish size with increasing depth did not contribute to the hypothesis of two separate pelagic redfish stocks above and below 500 m. In contrast, the close relation between fish size and depth point to the so-called “deeper-bigger phenomenon” which was found in numerous fish stocks. Very few redfish in the catches were immature.

Fangtechnische Möglichkeiten zur Reduzierung des Beifangs von Meeresenten in der Dorschfischerei mit stationären Fanggeräten

The present contribution summarizes results of fishery investigations with gillnets and longlines in the winter cod fishery which had been carried out in the western Baltic region from 1996 to 1999 by the Bundesforschungsanstalt für Fischerei with financial aid of the country Schleswig-Holstein. The main goal of these investigations was to point out technological possibilities for a reduction of unwanted bycatches of sea ducks in gillnetting. As it is obviously impossible to reduce the local and temporal bycatch problem by means of different gillnet constructions or tactical measurements, only the temporary avoidance of fishing grounds with high abundance of ducks or the change to longlining as catch method with reduced duck bycatches may be an effective solution.

Qualitat under Verwertung von Fruhjahrshering aus der Ostsee

The utilization of spring herring caught off the eastern German Baltic Sea coast in the waters around Rügen Island has a long tradition. Since 1991 there was a dramatic decrease in herring fisheries in this area. To promote the better use of this typical spring herring stock an exploratory fishery was started from January to May 1999 accompanied by quality investigations. The results show the possibilities of utilization according to length distribution, fat content and quality aspects.

Vergleichende Texturuntersuchungen an Filets von Kliesche (Limanda limanda) und Scholle (Pleuronectes platessa) in Abhängigkeit von Eislagerzeit post mortem, TK-Lagerung und Erhitzen

Instrumental investigations of texture have been performed using texture profile analysis. The following textural parameters have been assessed: hardness, gumminess, chewiness, springiness, cohesiveness and adhesiveness. The fillets of both species have been prepared from deep frozen headed and gutted raw material without fins after frozen storage of 0, 23 and 34 weeks, respectively. Deep freezing of fishes has been performed on board immediately after hauling or after 6 day’s storage in ice. Before texture measurement the raw material has been thawed and the measurement was carriedout on both thawed and microwave-heated fillets. In general, it can be concluded that both fish species are comparable in their texture parameters. The hardness of heated dab has been slightly higher comparing with that one of plaice. All other texture parameters showed a fairly good conformity between both species. While the hardness of dab increased during heating, it was decreasing in plaice. This was the only one significant difference between both fishes during heating. Adhesiveness as well as cohesiveness increased remarkably during heating. Changes effected by ice storage were only slight. Frozen storage, in contrast, caused a significant decrease of adhesiveness measured after heating the fillets of both species.

Klassifizierung von Echogrammanzeigen

The information in the echosignal of marine scattering objects is only partially used up to now. This signal contains also informations on the biological properties of the objects. Some possibilities are described to estimate these properties from the echosignal.

Leistungsmessung an Bord von Fischereifahrzeugen zur Kontrolle der 300-PS-Begrenzung in der Schollenbox

For monitoring of the engine power of fishing vessels permitted for fishery in the plaice box with engine power of 300 HP or less at sea three different portable power measurement systems are developed and tested. A system measuring the twist of the propeller shaft by two divisible gearwheels mounted on the shaft worked well at shafts with roller bearing at both sides of the measured interval of 100–300 mm length. Only at a very few fishing vessels this system is applicable and therefore for monitoring purposes not suitable. The application of a commercial available system measuring the stress at the surface of the shaft was simplified for application by non experts. The torque is measured by strain gauges. The calibration of the system, measuring and recording of the power is done by a PC automatically. A small polished facet on the shaft protected against oxidation is needed for easy and quick application. In this case the system can be used by technical personnel of supervision boats for monitoring of the engine power at sea in a short time. A third power measurement system determinates the torque by measuring the displacement of two supports clamped on the shaft at a distance of 100 mm. The displacement is measured by a micrometer gauge mounted on one of the supports. Readout of the rotating gauge display is possible taking advantage of stroboscopic effect. The system needs no conditioning of the shaft and can be used by non technicians. The development is not finished until now and some additional investigations and tests are required. Additional measures for monitoring of the power on fishing vessels by self recording power measurement systems and sealed fuel racks with limited injection are reported and discussed.

Untersuchungen zur Sensibilität von Seefischen an Bord

First orientating investigations of the sensitiveness of the fish species dab (Limanda limanda), plaice (Pleuronectes platessa) and cod (Gadus morhua) immediately after catch and after different duration of bulk storage were carried out on board the fishing research vessel “Solea”. The aim of the investigations was to get an idea wether or not the central nervous system of the fishes was in function and the fishes could suffer pain. The proportion of sensitive dab, plaice and cod immediately after the catch was higher than 70, 80 and 95 %, respectively. After 30 min of bulk storage the percentage was reduced to 50, 60 and 70 % resp., after 90 minutes to 5, 15 % and 35 %. In cod it decreased further to 5 % after 120 min. An influence of trawling time (0,5 - 2 h) or size of the catch (100 to 1000 kg) on the number of sensitive animals was not found. Although fishing parameters in commercial fishery will in most cases put a stronger mechanical stress on the animals during trawling and handling on board a certain number of sensitive fish can still be expected.

Toxische Wirkung von Schadstoffen auf Fischzellen. Bestimmung von DNA-Strangbrüchen mit dem Comet-Assay

The alkaline comet assay is a method of detecting DNA strand breaks and alkali labile sites in individual cells. The method was used to detect DNA strand breaks in isolated blood cells (leukocytes) of carp (Cyprius carpio). DNA damage have been induced by exposure of the cells to sediment extract. Therefore comet assay can be applied as in vitro bioassay for investigations on toxicity of marine sediments.

Laichen von Dorschen in Gefangenschaft. Teil 1: Verlauf der Laichaktivitäten

Individuals of the western stock of Baltic cod were kept at captivity with different temperatures and salinities until natural spawning. Spawning activities up to 16 weeks were observed between February and June. This time interval agrees weIl with the spawning season of the wild cod stock. Also as in in-situ observations larger individuals started earlier with the spawning process than smaller ones and had significantly larger periods of spawning. Larger cods produced more batches and more eggs than smaller cods within this time interval. The comparison between the actual and potential absolut fecundity showed large differences. Only apart of the potential absolut fecundity, estimated in the phase of prespawning development of ovaries, was developed until their release. These analyses showed that larger cod were able to develop a larger part of the eggs within the ovaries up to the complete development. This result should be considered in the future during estimations of the population fecundity of the western Baltic spawning stock.