Die Anwendung molekulargenetischer Verfahren in der fischereiwissenschaftlichen Forschung - Trennung von Fischpopulationen

The discrimination of stocks and separate reproductive units within fish species to facilitate fisheries management based on biological data has always been a challenge to fisheries biologists. We describe the use of three different molecular genetic techniques to detect genetic differences between stocks and closely related species. Direct sequencing of the mitochondrial ND3 gene describes the relationship between different aquaculture strains and natural populations of rainbow trout and revealed genetic homogeneity within the hatchery strains. Microsatellite analyses were used to explore the differences between redfish species from the genus Sebastes and to verify populations structure within S. mentella and S. marinus. This lead to an un equivocal discrimination of the species and an indication of populations structure within those species in the North Atlantic. The Amplified Fragment Length Polymorphisum (AFLP) methodology revealed genetic differences between Baltic and North Sea dap (Limanda limanda)and a possible population structure within the North Sea.

Der PAH-Metabolit 1-Hydroxypyren in der Galle von Klieschen (Limanda limanda) aus Nord- und Ostsee

Due to their carcinogenic properties, polycyclic aromatic hydrocarbons (PAH) are important environmental contaminants which may lead to increased levels of neoplastic aberrations in fish liver. To measure the PAH contamination of fish, concentrations of PAH metabolites were determined in the bile. The main metabolite 1-hydroxypyrene was determined in concentrations from < 0.8 to 189 ng/ml in bile of dab caught in the North Sea and the Baltic Sea re-spectively. The concentrations are comparable to levels of 1-hydroxypyrene measured in cod and herring from the Baltic Sea. The highest concentrations in dab bile were measured in fish from the inner German Bight and the Kiel Bight.

Die Qualitäts-Index-Methode (QIM), ein verlässliches Instrument zur sensorischen Bewertung der Frische von Fisch

Fish research institutes in Europe have made considerable effort in developing rapid, objective sensory methods for evaluation of fish freshness. The Quality Index Method(QIM) has been recommended for a European initiative regarding standardisation and harmonisation of sensory evaluation of fish. QIM-schemes have been developed for various common European fish species. Research has now provided the industry with a convenient, objective and powerful tool for measuring freshness of fish kept in ice Further research is needed to evaluate the applicability of QIM for fish handled, stored and processed under different conditions. However, for progress and development of QIM it is now very important that the fish sector implements QIM in fish auctions and the quality management system of the fish processing plants.

Fischereisituation, Probennahme und Zustand der Nutzfischbestände im Nordostatlantik im Jahre 2002

NE-arctic cod, saithe, haddock, redfish and Greenland halibut are important fish stocks of the European fisheries. In many European countries national data sampling projects on commercial fisheries have been established in recent years. Since 1990 German investigations in the NE-Atlantic have been mainly carried out on the commercial trawler FMS KIEL. The results of these sea samplings are used as German basic data for stock assessments of the “Arctic Fisheries Working Group” of the International Council for the Exploration of the Seas (ICES). Biological investigations were carried out in Norwegian waters, the Svalbard area and the Barents Sea (ICES Divisions I, IIa and IIb) on board FMS KIEL in March and October/November 2002. This report presents results of these cruises and an overview over the general fishery situation in 2002. Finally, results and recommendations on the scientific stock assessments of cod, saithe, haddock, redfishand Greenland halibut are reported.

Saisonale Aspekte der deutschen Garnelenfischerei

German landings of brown shrimp consisted of 12 081 tonnes of consumption shrimp, 1078 tonnes of undersized shrimp and of 650 tonnes of industrial shrimp. The seasonality showed the typical pattern with very low landings in winter, a first peak of monthly landings in spring and a more pronounced second peak in autumn due to the incoming new year class of young brown shrimp, lasting until December. The comparison of monthly and summed monthly landings for the last fifteen years (1988 to 2002) showed a very high degree of variability not likely to beuseful for an acceptable and reliable prediction scheme. However, the landings of the first half of a year show apositive correlation towards the landings of the preceding six months (p = 0,01). The remaining scatter of 72 percent allows only for imprecise predictions.

Netzmaterial und Selektivität in der Ostseedorschfischerei

Since some time fishing gear scientists express their concern over an observed tendency of the commercial fishery to proceed from codend netting yarns of 3 to 4 mm to higher values or to switch to the use of double instead of single yarn. A recent large EU-financed project collected statistical evidence on the detrimental effect of such behaviour on the selectivity of the codends. In this context data on cod are very scarce. German-Polish experiments in the Baltic from 1999 to 2001 aimed at filling this gap. The investigations prove a clear evidence of a negativ ecorrelation between netting yarn diameter and selectivity factor and/or L50. In addition they demonstrate a clear negative effect on selectivity when switching from single to double yarn The effects are of an order of magnitude that counteracting effects as catch size are masked and support the decision of the IBSFC to define maximum yarn diameters both for single and double yarn netting. A measuring instrument for the enforcement of these new regulations was introduced right in time.

Meeting der WEFTA in Galway, Ireland

Die WEFTA (West European Fish Technologists Association – gegründet 1970) ist ein Zusammenschluß von Europäischen Instituten, die auf dem Gebiet Fischerei, Fischqualität und –verarbeitung arbeiten und forschen. Ziele der WEFTA sind der Informationsaustausch zwischen Wissenschaftlern und Fischindustrie auf Jahrestreffen und Arbeitsgruppen sowie die Ausweitungund Verbesserung der Zusammenarbeit unterschiedlicher Interessengruppen und Instituten in Projekten. Weitere Informationen können der Homepage der WEFTA (www.wefta.nl) zu entnommen werden.

Kabeljaukrise in der Nordsee erfordert neue bestandserhaltende Maßnahmen

The European Commission has claimed a fundamental revision of the European Common Fisheries Policy in its Green Paper (EC 2001) by highlighting the reasons of continued overfishing of a number of valuable demersal fish stocks. Quotas in excess of scientific recommendations, fleet over capacities and poor enforcement of management decisions were identified causal for major stock and yield reductions while gaps in scientific advices were also criticized. The depleted cod stock in the North Sea, Skagerrak and Eastern Channel is the most prominent example. Existing and proposed management regulations were analysed by an expert group which met with fishing industry consultations in Brussels during 28 April – 7 May 2003. Depending on compliance with new technical regulations since 2000, the cod stock and its exploitation was found only marginally effected, while whiting displayed immediately significant losses in yield over long term and short term losses in haddock yields were reversed in substantial gains, also in SSB. However, reduction in fishing effort was found more effective in recovery potential than technical changes including closed areas, for which detailed information about variation in distribution of the stocks and the fisheries are required. Such effort reductions would reduce not only landings but also unregulated discarding, which is believed to be a major reason of the failure of the management measures in mixed fisheries. Recent trends in fishing effort of European fleets could not be quantified due to persistent data deficiencies.

Test von Fanggeräten zur Untersuchung von Grundfischfaunen in Windparkgebieten der Ostsee

With respect to future environmental impact assessment different bottom trawls are presently investigated for their suitability for sampling the fish fauna in potential windpark areas asses. For this purpose the international Baltic Sea Trawl, the Box trawl, two different small beam trawls and small eel fykes were compared on a research cutter in June 2002. The best catchability with the highest abundance of demersal fish species and widest length distribution was obtained with the Box trawl. During another cruise in December 2002 the Box trawl was again compared with the Windpark trawl. As a result the Box trawl performed best, with regard to the overall catchability. However the Windpark Trawl is easier to handle under the conditions onboard small fishing cutters.

Untersuchungen des Zanderbestandes in den deutschen Küstengewässern der Ostsee von 1992 bis 2002

Pike-perch is an important resource for the coastal fishery in the brackish waters of the eastern part of the coast. For the conservation of the stocks regulation measures (minimum landing size, closed season and minimum mesh size) have been introduced since many years. Basic biological material of the last decade sampled from the commercial fishery and for recruitment by a standard trawl survey. For the “Eastern stock” this paper presents the results concerning age distribution, year-class strengths, growth, proportion spawners, natural mortality and yield-per-recruit analyses.

Ein neues Messgerät zur Kontrolle der Maschenöffnung in der Fischerei

At present both the wedge gauge and the ICES mesh gauge are used to examine the mesh opening of trawl cod-ends. A thorough investigation of both instruments by an EU project (MESH) has revealed a number of deficiencies. This has lead to the conclusions to not further recommend the use of both devices but to go for the development of a complete new measurement tool. This is presently progressing in a further EU project named OMEGA. Prototypes of the new device have been produced and a number of introductory tests have already been made. This contribution reports on further laboratory tests carried out at the Institute for Fishing technology and Fish Quality with special emphasis on netting yarn diameters below 4 mm. The results demonstrate further yarn size depending inaccuracies of the wedge gauge and support the rapid introduction of the newly developed measurement instrument.

Einfluss der Umsetzung der ICES-Fangempfehlungen auf den Zustand der Fischbest

The implementation of the precautionary approach in the mid-1990s required commercial fish stocks to be classified into different categories. These are based on the degree to which stocks have been exploited or are threatened by fishing activities. According to current ICES terminology, stocks are classified as being either “within” or “outside safe biological limits”, or as being “harvested outside safe biological limits”. Between 1996 and 2002, the relative share of stocks in these three categories remained relatively stable (at about 20 %, 30 % and 15 %, respectively). Over the same time span, the number of stocks were insufficient data is available to quantify and thus to appropriately classify the state of the spawning stock biomass (“status unknown”) has increased. Neglecting potential impacts of fishing pressure, the combined average proportion of all stocks with sufficiently high spawning stock biomass is at about one third, while only one fifth of the stocks assessed have been managed sustainably. For some important fish stocks in the ICES environment – specifically demersal ones –, science recently had to call for rebuilding plans or even a closure of the fishery to allow recovery, in spite of the management’s agreement to manage the resources according to the precautionary approach. This obvious difference between approach and implementation has a number of potential causes: erroneous or imprecise input data (landings, discard and sampling information), insufficient assessment models, problems in the understanding of the scientific advice, and implementation errors. The latter could be either a difference between advised and implemented total allowable catches (TACs), or an excess of legal TACs. During the fifteen years covered by this analysis (1987 to 2002), the average deviation between the implemented TACs for a specific stock and that recommended by ICES for the same stock was more than 30 %. The overall average deviation (summed over all stocks) for the entire period was 34 %, excluding, however, four extreme outliers in the data, representing cases in which scientific recommendations were exceeded by as much as 1000 to 2500 %. If these were included, the overall average would be as high as 45 %. The annual deviation has substantially increased in recent years (from roughly 20 % in earlier years of the surveyed period). This recently observed high deviation also matches ICES’s estimate that the fishing mortality in the ICES convention area in the 1990s was well above recommended sustainable levels in the pelagic and demersal fishery. A direct comparison of scientifically proposed and politically implemented TACs is problematic in many case

Fischarten der westlichen Ostsee – Untersuchungen von 2000 bis 2002

Ichthyoplankton provides information on the species com-position in an area of investigation and leads to a better understanding of the entire fish community. Every year since 1993 May/June (from 2000 in April/May) an ichthyoplankton survey in ICES Subdivision 22 and 24 has been done to sample the plankton community in the western Baltic Sea. One objective was to acquire indicators of possible changes in the natural structures of the fish com-munity. The time series derived from the Bongo-Net samples is too short to show a trend in larval densities. Up to now samples in the western Baltic Sea yielded only low mean densities. According to the reproductive biology the fish species were divided in three major groups: •Fish species with a long developmental phase in the plankton community •Small short lived species with benthic eggs and a reduced planktonic phase •Guests without local spawning populations. Species were identified, which were absent in the plankton of the western Baltic Sea in the 1960s and 1970s.

Der Fischei-Test: Ein Toxizitätstest für ökotoxikologische Untersuchungen

Zebrafish (Danio rerio) embryos have been used to quantify the teratogenic potential of environmental samples and harmful substances respectively. The short spawning interval renders this species a good test organism in toxicological research. Due to the transparency of the eggs several lethal and non-lethal endpoints can be detected in parallel after 48 h of embryonic development. Zebrafishembryos have been shown to be sensitive to a number of environmental relevant contaminants, as well as to ex-tracts from polluted sediments

Veränderungen sensorischer und instrumenteller Parameter während der Gefrierlagerung von Ostseedorsch (Gadus morhua) bei unterschiedlichen Temperaturen

Changes in sensory and instrumental quality parameter sand in thawing drip, cooking drip and total drip loss of frozen stored Baltic cod fillets (Gadus morhua) at different storage temperatures were investigated. Cod fillets stored at –20 °C and –30 °C exhibited the lowest drip losses and obtained the highest sensory scores. Drip losses were found to be highest in cod fillets stored at –10°C and in double frozen fillets stored at –20 °C. These two experiments also gave the lowest sensory scores. The texture parameters increased during storage parallel with storage time. The waterbinding capacity was lowest at –10 °C and almost constant at –30 °C. There is a good correlation between the sensory scores for “tough” and the instrumental texture measurement for hardness and chewiness.