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 Entwicklung des atlantischen Kabeljaubestandes vor Grönland in der zweiten Hälfte des 20. Jahrhunderts

Based on the results of an analytical assessment, the Atlantic cod stock off Greenland collapsed already in the late 60s and, since then, reached rarely the 10 % level of its size in 1955. Applying the concept of a self-sustaining stock, the drastic harvesting strategy of the past four decades must be considered inadequate. The stock collapse was therefore found consistent with annual exploitation rates being not adjusted to conservative management options and exceeding the productivity of the stock by far. The results of a multiplicative model explained the following recruitment failure based on significant effects of spawning stock size as well as temperature. Certainly, cold periods have negatively affected the recruitment process and consequently contributed to the stock collapse. However, such ecological effects should not be itemized causal but must be taken into account regarding appropriate stock management. Till today, the spawning stock remained severely depleted causing a low probability of a successful recruitment and a substantial stock recovery.

Die deutsche Fischerei vor Nordnorwegen und bei der Bäreninsel im Dezember 1996 und im ersten Halbjahr 1997

Biological investigations were carried out onboard the German factory trawlers “Wiesbaden” and “Kiel” off the Norwegian coast and at Bear Island from December 1996 to June 1997. Data will be contributed to the assessments of the ICES “Arctic Fisheries Working Group”. Information on distribution and fishery of cod, haddock, saithe, redfish and Greenland halibut are given. Biological aspects of length- and age distributions, and stomach- and gonad investigations are represented. Some aspects of the function of sorting grids used in the Bear Island fishery are discussed.

Situation wirtschaftlich wichtiger Grundfischbestände vor Norwegen, Spitzbergen und in der Barents-See

Assessments on NE-arctic stocks of cod, haddock, saith, redfish and Greenland halibut were carried out by the ICES 'Arctic Fisheries Working Group' in August 1996. Whereas stocks of cod, haddock, and saithe are presently in fairly good and stable condition the assessments show the stocks of beaked redfish and Greenland hailibut to be just the opposite. The status of the golden redfish stock seems to be stable. More detailed information is given in this report.

Keine Hoffnung auf ertragreiche Fischerei vor Westgrönland

Nach dem Zusammenbruch der Kabeljaufischerei vor Westgrönland im Jahre 1990 erreichte der Bestand im Herbst 1991 seine geringste Bestandsgröße seit 1982. Im Vergleich zum Vorjahr verringerte sich der Bestand bis zum Dezember 1992 nochmals deutlich. Das regelmäßige aber geringe Vorkommen von Jungfischen deutet auf eine nur mäßige Rekrutierung. Einige ökologisch wichtige aber fischereilich nicht interessante Fischarten weisen auf niedrigem Niveau stagnierende oder schwach zunehmende Bestandszahlen auf. Die Einrichtung umfassender Schonmaßnahmen für den Kabeljau erscheint dringend geboten.