Nationales Fischereidatenerhebungsprogramm: Aktivitäten und Ausblick

Within the frame of the EU Data Collection Regulation (DCR), Germany is obliged since 2002 to collect basic fisheries data to support the Common Fisheries Policy. Various governmental institutions are involved in the collection of landings and effort data, biological and economic data of the German fisheries. About 200 trips on commercial fishery vessels were sampled from 2002 to 2006. Additional stock data are collected on research surveys. The landings of cod in the recreational fisheries in the North and Baltic Seas were recorded within a pilot study. In order to assess the economic situation of the fishing fleet and processing industry, economic data were collected. The collected data are being stored in a national database and being made available for scientific working groups. At present, the legal regulations within the DCR framework are being reviewed and adapted to the changing requirements of fisheries management.

Auswirkungen von größeren Steertmaschen bei Grundschleppnetzen auf Plattfischfänge in der Nordsee

The present fishing effort regulation for bottom trawls in the North Sea (EU 40/2008) reduces the fishing effort with larger co-dend mesh sizes (> 100 mm mesh opening) to 86 fishing days per year. The aim of this technical measure is the protection of the weak cod stock usually harvested with this mesh opening. By combining the results of our selectivity investigations on plaice during a commercial fishing trip and the samples taken within the frame of the EU data collection regulation (DCR) we could draw conclusions on commercial and non-commercial fish species. When using codend meshes with larger mesh opening the discard was reduced remarkably. In the reference codend with 80 mm mesh opening the undersized bycatch was 47 % of the total catch of plaice, in the experimental codends with 120 mm mesh opening it was only 7 % and with 130 mm mesh opening just 3 %. On the other hand however, the applied mesh openings in the experimental codends let escape marketable plaice to some extent. The loss of catch was assessed on the basis of fish numbers per length class using a length-weight conversion rate from the DCR. The loss by weight of marketable fish with 120 mm codend mesh opening was 18 %, and 28 % with 130 mm codend mesh opening. To assure the protection of young round and flatfish with one general mesh size, a new regulation should prescribe a minimum mesh opening of 120 mm, accompanied by an expansion of the fishing effort.

Verringerung der Dorschbeifänge in der Schleppnetzfischerei auf Plattfische mit einem im Oberblatt reduziertem Grundschleppnetz

Trials with the “topless” version (with reduced upper panel) of the bottom trawl resulted in a 63 % reduction of cod bycatch in numbers, compared to the complete trawl. Flounder catches increased by 120 % on average. Further modification of the net opening height to optimize the trawl performance are underway.

Simulierte Auswirkungen des mehrjährigen Bewirtschaftungsplans für die Dorschfischerei in der westlichen Ostsee und die Möglichkeit einer technischen Alternative

The cod stock in the Western Baltic Sea is assessed to be overfished regarding the definitions of the UN World Summit on Sustainable Development at Johannesburg in 2002. Thus, the European Fisheries Council enforced a multi-annual management plan in 2007. Our medium term simulations over the future 10 years assume similar stock productivity as compared with the past four decades and indicate that the goals of the management plan can be achieved through TAC and consistent effort regulations. Taking account of the uncertainty in the recruitment patterns, the target average fishing mortality of age groups 3 – 6 years of F = 0.6 per year as defined in the management plan is indicated to exceed sustainable levels consistent with high long term yields and low risk of depletion. The stipulated constraint of the annual TAC variations of ±15% will dominate future fisheries management and implies a high recovery potential of the stock through continued reductions in fishing mortality. The scientific assessment of sustainable levels of exploitation and consideration in the plan is strongly advised, taking account of uncertainties attributed to environmental and biological effects. We recommend our study to be complemented with economic impact assessments including effects on by-catch species, which have been disregarded in this study. It is further demonstrated, that the goals of the management plan can alternatively be achieved by mesh size adaptations. An alternative technical option of mesh size increases to realize the required reductions in fishing mortality provides avoidance of discards of undersized fish after a few years by means of improved selectivity, another important element of the Common Fisheries Policy. However, it is emphasized that technical regulations since 1990 failed to affect the by-catch and discards of juvenile cod. In any way, the meaningful implementation of the multiannual management plan through stringent control and enforcement appears critical.

Auswirkungen der Wassertemperatur auf die Missbildungshäufigkeit pelagischer Fischembryonen

Malformation rates in embryos of dab, whiting, cod, flounder and plaice have been monitored for several years (1984-2006) in the Southern North Sea. For embryos of all species investigated trends for the fluctuation of malformation rates over the time were registered in the areas showing intermediate prevalences at the beginning of the studies in 1984 and maxima in 1987. Thereafter for all species a decrease of malformation rates was found until 2006 excepting an increase in 1996. A significant negative correlation existed between surface water temperature and prevalences of malformed embryos of dab and other species.

Begrenzung des Fischereiaufwandes oder Erhöhung der Mindestmaschenöffnung – Ein Vergleich der Alternativen bei der Dorschfischerei in der Ostsee

The basis for a long-term profitable fishery is a precautionary and environment-compatible use of fish stocks. The fishery management presently models the exploitation through the parameters of fishing mortality and the age at first capture. These two parameters are translated into the technical measures of fishing effort and mesh openings and quotas, which are then used in practice for controlling the fishery. Stock protection can be achieved by reducing the fishing effort, by assigning smaller quotas, by reducing the number of days at sea, or by increasing the mesh opening. The respective protection measures have different effects on the development of the stocks but also on the revenue obtained by the fishery. These alternatives have been examined taking as an example the cod stock in the western Baltic. The optimization goal was the maximization of profit observing at the same time the prerequisites for stock protection according to the precaution approach. For these calculations the same models and data have been used as are beeing used in the stock management of the ACFM of ICES. The response of altered technical measures to the recruitment of cod stock was considered, and a proposal to overcome overfishing of cod in the western Baltic Sea was derived.

Entwicklung eines selektierenden Aalschleppnetzes

In eel catches with special small-mesh trawls the proportion of by-catch is unjustifiably high. From 2003 to 2005 eel trawls with various types of separation panels were designed, constructed, and tested under real fishing conditions. Tests were carried out using cover cod-ends and an underwater TV equipment. It was possible to reduce the amount of by-catch to one tenth of its usual amount. However, a decline of the catch efficiency for the target species eel could not be avoided.

T90-Steert: Letzte Untersuchungen vor der Übernahme ins EU-Regelwerk

After due consideration the EU Commission has decided in December 2005 to admit cod-ends made of netting turned 90 de-grees (T90) as an allowable alternative for the cod fishery of the Baltic. The construction was included as one of two admissibles versions into the newly issued EU regulation 2187/2005 on technical measures for the conservation of fishery resources of the Baltic. This contribution describes some of the investigations preceeding that decision with which some of the previous demurs could be dispelled. In the course of these experiments it was detected that the cod-end netting material plays an important role for the mesh selection of a T90 cod-end, whereas the netting twine diameter is negligible. Problems with modern twine mate-rial have to be taken in consideration for constructional changes of T90 cod-ends. A relation of 1 to 2 in the circumferences in meshes at the joining round between last row of the belly and extension/cod-end turned out to be acceptable. Both the hauling technique (sidetrawler or sterntrawler) and an extensive use in the commercial fishery proved to be of no relevance for to the selection of T90 cod-ends. Taken alone, the different hydrodynamic conditions in a cod-end are insufficient to fully explain the selection phenomena. This was demonstrates by the material-related differences in selectivity of T90 cod-ends.

Gewinnmaximierung der Fischerei schützt den Dorsch der westlichen Ostsee vor Überfischung – Nur ein theoretischer Ansatz ?

Profit maximization in fishery protects cod of western Baltic Sea against overfishing – Only a theoretical approach? The frame for the management of fish stocks politically given contains – apart from ecological and social goals – also an economic goal, which is considered here in particular. From the point of view of fishery enterprises the main management goal for the exploitation of fish stocks is the maximization of profit. There are models for the yield optimization since long time. They are mainly used so far to optimize fishing mortality. Here the Beverton and Holt yield model was used. Apart from the optimization of fishing effort the model was used to optimize age of first capture and thus mesh opening. Starting point of the considerations is a given age group of a fish stock. If this age group is completely fished the yield obtained from this age group is maximized. The investigations show that the term overfishing is not exclusively linked as frequently assumed with a too large fishing mortality, but likewise with a mismatch of the mesh opening. For the calculated example Baltic cod data are used. At present the cod is caught far from reaching its mass optimum. Therefore, the profit of fishery enterprises can in the long term be considerably increased by the optimization of the mesh opening. During the conversion from the state of the art to fishing with optimised mesh sizes, however, a loss of profit has to be expected. The title of the paper sounds provocative. However, the stock of the Baltic Sea cod is better protected by a long-term maximum-profit oriented exploitation than by the precautionary approach applied now.

Die Fischerei im Nordostatlantik im Jahre 2004

Since 1990 North-east Atlantic fish species – arctic cod, saithe, haddock, redfish and Greenland halibut – have been investigated by on-board observers on the German commercial trawler FMS Kiel. These investigations are part of the national data collection regulation established by the European Union in recent years. Collected data are basic data for the scientific assessment of these important fish stocks of the European fisheries. The results of the observed cruises are used by the Arctic Fisheries Working Group of the International Council for the Exploration of the Seas (ICES). Biological investigations were carried out in Norwegian waters and the Barents Sea (ICES Divisions IIa and IIb) on board FMS Kiel in January to March and in August/September 2004. This report presents results of these cruises and an overview about the general fishery situation in 2004.

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L. ) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil I: Allgemeiner Verlauf des jährlichen Reifeprozesses und der Laichaktivitäten in den verschiedenen Gebieten

From 1993 to 2003 special surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea. The ICES advice for cod in the Baltic Sea is based on yearly stock assessments of two separate stocks the western (SD 22 – 24) and the eastern stock (SD 25 – 32). Both stocks are characterized by different spawning seasons. The general progression of the maturity suggests that two types of development can be distinguished. In the western Baltic Sea (SD 22) the maturity development is temporal stable, with a relative short, main spawning period from March to April - spring spawner. In the Arkona Sea and Bornholm Basin the main spawning season starts in June and probably finishes in September - summer spawner. The proportion of spawners in summer is significantly higher than in spring in the Arkona Sea and Bornholm Basin. This again underlines the importance of the Arkona Sea for the reproduction success of the eastern Baltic cod stock. The analysis furthermore show, that the proportion of male spawners was significantly higher than the proportion of female spawners in all areas and the investigated months. This observation suggests that the reproductive success is only limited by the number of female cod which participates in the spawning process.

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L.) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil II: Statistische Analysen zum Anteil reproduktiv aktiver Dorsche in Bezug auf gebietsspezifische Unterschiede und Gemeinsamkeiten, sowie deren mögliche Ursachen.

Surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea from 1993 to 2003. Part I of the article describes the general maturity development and the spawning activities in the western Baltic Sea, the Arkona Sea and the Bornholm Sea. The studies suggest that two types of spawner can be distinguished, the spring spawner in the western Baltic Sea and the summer spawner in the Arkona Sea and the Bornholm Basin. The descriptive analysis is supported by statistical studies presented in this article. It is shown, that the proportion of spawning individuals is significantly higher in summer than in spring in the ArkonaSea and the Bornholm Sea. Furthermore, it is shown that reproductive mixing of both types of spawner is possible in the Arkona Sea in May/June due to the hydrographical conditions in the Arkona Sea which were suitable in 8 of 10 years for successful reproduction of both Baltic cod stocks, and that spatial expansion of spawning activities of the eastern Baltic cod stock into the Arkona Sea is positive correlated with the size of spawning stock in the Bornholm Sea.

Wer fischt was? – Gemischte Bodenfischereien und ihre Auswirkungen auf die wichtigsten Nutzfischbestände in der Nordsee

Cod, haddock, whiting, saithe, plaice, sole and Norway lobster are 7 main target species of the demersal mixed fisheries in the North Sea, Skagerrak and Eastern Channel. Gadoids and Norway lobsters are mainly taken in the nor-thern North Sea by towed gears except beam trawls while the flatfish fisheries are conducted in the southern North Sea mainly using beam trawls. Recently, the central North Sea appears less fished by demersal gears. Towed nets including seines and beam trawls equipped with meshes of more than 100 mm resp. more than 80 mm were identified as the main gears effecting the depleted cod and reduced plaice stocks. The saithe sector, using towed nets with meshes of more than110 mm, longlines, gill nets and others, appears to affect the 7 species to a lesser extend. These results support the interim effort limitations by gear types, vessel and month as enforced by the European Commission since 2003. TAC regulations alone are considered inefficient to sustainably harvest stocks by mixed fisheries. A fleet-effort management method is developed estimating the fleets’ effects based on the sum of partial exploitation rates of the species in mixed fisheries weighted by the ratio of the precautionary reference Bpa and the actual SSB size as ecological quality objective. Applying such fleet effort management could result in increased catch possibilities of some stocks by fleets selecting mainly few and non-overexploited stocks while respecting precautionary management constraints in minimum SSB or maximum exploitation rates at the same time.

Warum Fischereiwissenschaftler nicht mit kommerziellen Netzen fischen

“Wrong trawl, wrong rigging – that’s why research ship cannot find cod” – in a polemic article in the April number of “Fishing News International” British fishermen accuse fishery scientists of using the wrong trawl for their bottom trawl surveys in the North Sea. They wrote the GOV is unsuited to catch cod and therefore the cod stock could be in a much better shape than assessed by the scientists. In this paper the characteristics of a scientific survey trawl and the results of comparison fishing experiments are listed.

Bestandskundliche Untersuchungen an wirtschaftlich wichtigen Grundfischbeständen im Nordost-Atlantik

For many years the assessments of the commercially most important demersal fish stocks of cod, haddock, saithe, redfish and Greenland halibut have annually been carried out by the "Arctic Fisheries Working Group" of ICES. The most important results of the actual assessment are given in this report. It shows that the gadoid stocks of cod, haddock and saithe are in good and stable conditions and that the stocks are harvested within safe biological limits. The stocks of redfish and Greenland halibut are still at a low level and outside safe biological limits. Greenland halibut shows a slightly positive trend in spawning stock biomass, several year-classes and recruitment.