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.

Unterschiedliche Trends beim Fischnachwuchs der Nordsee

During this years’ International Bottom Trawl Survey (IBTS) of ICES, a total of 407 half hour tows were made in the North Sea including Skagerrak in January/ February, 1998. Results indicate except for sprat no outstanding incoming yearclasses for cod, haddock, saithe, Norway pout, whiting, herring, and mackerel. Most of the adult cod and saithe investigated did not show normal gonad development for this time of the year. The abundance of skates and sharks was still low. Results of 68 hydrographical stations of R.V. “Walter Herwig III” showed in contrast to four preceeding IBTS-surveys a warming of the northern North Sea of approx. 1 K.

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.

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.

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.

Hoffnung für einige Nordseefischbestände

In the first quarter of 1997 R.V. “Walther Herwig III” took part in the internationally (ICES) coordinated International Bottom Trawl Survey (IBTS) in the North Sea. A total of 365 half-hour tows using a standardized GOV-net were made by seven research vessels in order to determine the strength of incoming yearclasses of cod, haddock, whiting, Norway pout, herring, sprat, and mackerel. Overall results, though preliminary show a considerable increase of the index figures for cod, Norway pout, herring, and mackerel whereas the indices for haddock, sprat, and whiting indicate lower recruitment figures. Water temperatures and salinity values were unhomogeneously below and above of the longterm mean.

Untersuchungen zur Langleinenfischerei auf Dorsch und Aal in der Ostsee

With the aim to reduce bycatches and discards first investigations were carried out in longlining for cod and eel in the Baltic. In the case of eel fisheries they are compared with small mesh size trawling and in the case of cod fisheries with gillnetting, where during the winter season unwished bycatches of seabirds could be a problem. First results show that these investigations should be continued.

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.

Erste Ergebnisse zum Verlauf der Laichsaison von Dorschen in der westlichen Ostsee 1997

Investigations concerning the intensity and duration of spawning seasons of cod stocks are parts of the work of the reproductions ecology of commercial fish stocks in the Baltic Sea. The Institute of Baltic Fisheries Rostock has sampled and analysed data for this goal since 1992. The first data analyses for the spawning season 1997, sampled in the areas Kiel Bay, Mecklenburg Bay and Arkona Sea showed that the process of the spawning season is different compared to the years before. The spawning process starts earlier than the other years in Kiel Bay and Mecklenburg Bay. The results show that a high proportion of the spawning stock was part of the spawning process in this area. The Arkona Sea cod are regarded by ICES definition as belonging to the western cod stock. In this ICES sub-division only a low number of spawned cod was observed in March, the main spawning time of the western cod stock. Opposite to the theory of the stock units intensive spawning activities were observed in June as in the years before in the Arkona Sea.

Relation between TMAOase activity and content of formaldehyde in fillet minces and bellyflap minces from gadoid fishes

Minced fish is a significant component of a number of frozen fishery products like fish fingers, cakes and patties. Predominately minced fish is produced from gadoid species (Alaska pollack, cod, saithe, hake and others) possessing the enzyme trimethylamine oxide demethylase (TMAOase, E.C. 4.1.2.32) (Rehbein and Schreiber 1984). TMAOase catalyses the degradation of trimethylamine oxide (TMAO) to formaldehyde (FA) and dimethylamine (DMA), preferentially during frozen storage of products (Hultin 1992). In most gadoid species light muscle contains only low activity of TMAOase, the activity of red muscle and bellyflaps being somewhat higher. In contrast, the TMAOase activity in blood, kidney and other tissues, residues of which may contaminate minced fish flesh, may be higher for several orders of magnitude (Rehbein and Schreiber 1984).

Die Entwicklung wichtiger Fischbestände in der Nordsee und im Nordatlantik. Ergebnisse der Herbstsitzung des Advisory Committees for Fishery Management des internationalen Rates für Meeresforschung

The October meeting of the ACFM of ICES gave advice for a number of North-Atlantic fish stocks. The results of the most important stocks are given here from the perspective of German fishery management. The are chiefly North Sea plaice and sole, for which a reduction of 25 % of the fishing mortality (F) is recommended for 1998, North Sea saithe (minus 20 % in F), while North Sea cod is in the process of recovery and North Sea haddock is inside safe biological limits. The mackerel stock of the North Sea has not yet recovered, while the western mackerel stock as an entity has stabilised at a level of about 2.3 million t.

Über die Herkunft des starken Kabeljau-Jahrgangs 1996 in der Nordsee

Cod in the North Sea is expected to reach „Safe biological limit“ due to a strong 1996 year-class. The cod fry was seen first as 5 cm fingerlings in the catches during a hydroacoustic survey in the southeastern North Sea. Back-calculations of the water drift show with high probability that the respective spawning ground was situated in the southwestern North Sea.

Radioaktives Cäsium im Fisch der Barentssee weiterhin abnehmend

A decrease of 137Cs concentration in cod flesh from Barents Sea is shown by six years random sampling. This reduction runs parallel to reduced emissions from the nuclear fuel reprocessing plant Sellafield (Great Britain). It must be emphasized that even the highest values from 1992 are lower than comparable ones from the North Sea and from the Baltic. Although there is no increase of the radiation dose on people by consuming these fishes further monitoring should not be stopped. Potential risk arises from radioactive wastes of the russian nuclear navy in their coastal area. Obviously a safe storage seams almost too expensive.

Norwegens Fischerei 1996: Anlandungen und Erlöse weiter gestiegen

Norway’s sea fishery 1996 ranked 9th world wide. Preliminary data for 1996, as published in the Norwegean journal Fiskets Gang, show a further increase of the total catch by 114 000 tonnes, which now reached 2.63 million tonnes. The value of these landings were 8550 million nkr, up by 381 million nkr. The 5 most caught species were herring, cod, blue whiting and saithe. The 5 highest values, however, were obtained by cod, mackerel, herring, saithe and deepsea prawn. Considerable increases of prices were noted for jack mackerel (+142 %), mackerel (+133 %) and herring (+34 %).

Hinweise auf eine Überfischung grönländischer Grundfischbestände

At present, the severe decline of the fishery off Greenland is being discussed controversially. In contrast to overfishing, climate changes and emigration are itemized causal. Available German data on commercial catches and research cruises are presented for clarification. A few years after the beginning of heavy exploitation during the early sixties, the stocks of cod, golden and beaked redfish reflected a significant rejuvenescence based on catch analysis. Regular scientific surveys• for stock assessment purposes commenced in 1982 when the productivity of the stocks was already adversely affected due to low spawning stocks and extremely irregular recruitment. From this point of view, the results of the latest survey in 1995 showing stagnant fish biomass at record low level since 1991 are not surprising. The status of the cod stock is still considered severely depleted. Taking the high abundance of juvenile redfish into account, recovery of the groundfish stocks is unlikely in short term and depends on the non-predictable recruitment only.