the Bundesforschuno'Onr.oIt für Fischerei H~mburg Bibliothek cod tagging experiments by *). **) F. Lamp and K. T~ews

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1 f1. 11 Thin paper not to be cited without prior re~erence to the authors International Council ~or Explor.ation of the,sea the Bundesforschuno'Onr.oIt für Fischerei H~mburg Bibliothek On the initi s in Baltic cod tagging experiments by *). **) F. Lamp and K. T~ews, C.M. 1972/F:10 Demersal Fish (Northern) Committee At the 1968 and 1969 meetings of ICES as weil as on the occasion o~ the Special Meeting on Cod' and Herring in the Baltic in 1971 preliminary results of tagging experiments on Baltic cod, carried: out during , were reported (1, 3-7) Since the b~ginning a.total of 15p51 cod were tagged until today. The interpretation of return results from these experiments be~ came difficult, since no informations on the initial survival rates of the cod were available. So it was feit to be necessary, to carry out special experiments in this respect on the occa~ion of a research cruise of FRV "Anton Dohrn", which was made fram 11 th ~ 23 rd of April 1972 into the Baltic. ' To study the initial survival rates of cod tagged with the so I called "German Spaghetti' tag" a total of 6 experiments was conducted. In each experiment between 105 and 200 tagged fish ware held in 2 containers of'each 0.8 and 2.0 m 3 water content kept through the containers, so guaranting oxygene saturation Ln : on the she1ter deck of the vessel for periods between 15 and:. ' 41 hours (Table 1). Seawater at a rate of approximately 6 times the water volume of the basins per hour was continously pumped the tanks~ For further security measures air was pumped into: the water by 2 Wisa aquarium pumps.,water temperature correspon~ed *) Dr.F.Lamp, Institut für KUsten- und Binnenfischerei, 2 Ham- 'burg 50, Palmaille 9, Germany **) Pro~.Dr.Tiews, Institut für KUsten- und Binnenfischerei~, 2 Hamburg 50, Palmaille 9, Germany ;

2 - 2 - pract1cally w1th the surface temperature of the Balt1c amounting to some 3-5 C. The normal taggingtechniques were applied. That means: immediately after the hauling of the net being dragged fcrl hour more or less the entire cod catch was thrown as rapid as possible by 3-4 men into a 2 m 3 basin with continously ~enewed seawater. After this all fish drifting on the surface or of waak condition were removed by a scocpnet. Normally 40-80fish, depending on the size of the catch,were found to be suitable for tagging. These fish were tagged within the next minutes and placed into the second basin of 0.8 m 3 in size, in which the water was also continously renewedtt In the normal tagging procedure the tagged fish is being kept there for anothe~ minutes before released into the sea. The experiments conducted for the study of survival rates were also used to transport fish from one area to another, in order tostudy the homing of the fish. On an average the 979 fish used for these experiments were kept for about 25 hours under control before release (Tab1e 1). Only 12 fish, i.e. 1.2 %were found to haya died. This means that the initial Burvival rate in our experiments 'is with 98.8 %practically 100 %. Furthermore it could be observed'that other fiah being kept over s1m1lar periods but untagged were found to be unsu1table for tagging because of their great wildness and v1ta11ty after having completely overcome the stress caused by the catch1ng procedure. This seems to indicate that the survival rate study experiments described above are also conclusive for the further future of the fish. In other words,it is not 1ikely that the survival rate would have decreased, if the duration of the experiments would have been extended. It must be mentioned that the wheather conditions were perfeet during the entire research period wlth wind velocities always below 4 Beaufort and that consequently ideal conditions were met for these experiments. At tbe Special Meeting on Cod in 1971it had been suggested to sink net cages tilled with tagged cod tor the same purpose. tt

3 - 3 - Following this suggestion 3 net cages each 2 x 2 x 2 m were occupied with 50 res~ective1y 49 cod each, from which 30 resp. 29 each were tagged and 20 untagged fish.' The cages were anchored at a depth of some 65 m SSE ofbornho1m Island ( 'N; 'E) and 1eft f~om 12 th April- 15~h of April for some 70 hours, while FRV "Anton Dohrn" continued its cruise into the Southern Gotland Basin. When returning, it was unfortunately,detected that 1 cage was stolen and that from a second one several plastic floats, which were attached to the anchor buoy to ease'the hauling of the equipment, were also lost. When hauling the two cages left, it was found that in one cage 50 %of all fish were dead and in the other 12 %. In the first case 16 of the 30 tagged cod were dead and 9 of the 20 untagged fish, while in the second.case 2 of 29 tagged cod had died and, 4 of the 20 untagged fish. We are inclined, however, to reject the results of this experiment for 2 reasons: First1y it cannot be excluded that the cages were lifted to the surface by someone else and secondly the FRV' "Anton Dohrn" turned out to be to large a vessel for suc,h an: experiment, because the cod had to undergo extended additional stress when turning the vessel for minutes before lowering the cages, whereby the fish was pressed heavily against the net~ ting of the cages. It is interesting to note that the fish, ofthe first cage had to suffer o~ously more during the tur~ " ning manoeuvre than the fish in cage 2, as could be seen from above. The turning manoeuvre was made, when all three cages ~ere dipped into the water at the starboard side of the ship, and, was necessary, to turn the ship into the wind. SUMMARY 6 storage experiments with 979 tagged cod aboard FRV "Anton Dohrn" over hours revea1ed that only 1.2 %of the fish died ; resp. that the initial survival rate of tagged cod under the ' tagging conditions met on this research vesse1 is practically1 100 %.

4 1-4 REFERENCES (1) Bagge,O.,K. Tiews and F. Lamp: (2) Lamp,F., 1967: (3) (4) (6) German and Danish cod tagging in the Baltic ICES, C.M. 1971, Special Meeting,Cod No.9 Tagging Programmeof cod in the German Bi~ht. C.M. 1967/F:13 Lamp, F. and K. Tiews:Comparative tagging experim~nts on 1968 Baltic cod in ICES, C.M. 1968, F:I0, 1-4 Lamp,F. and K. Tiews: Vergleichende Markierungse~~erimente 1969 am Ostseedorsch (Gadus morhua) im Jahre Ber. Dtsch.Wiss. Komm. Meeresforsch., 20 (1): (5) Tiews, K. and F.Lamp: Further comparative tagging experi ments on Baltic cod. ICES, C.M. 1969, F:17, 1-6 Tiews, K. and F.Lamp: Preliminary results of cod tagging 1971 experiments in the Baltic ( ) ICES, C.M. 1971, Special Meeting Cod No. 2, 1-30 (7) Lamp, F. and K.Tiews: Progress report on comparative tagging experiments on Baltic cod. ICES, C.M. 1971, Special Meeting Cod No. 1: 1-10

5 - 5 - Tab1e 1 Initial surviva1 rates in Ba1tic codtagging experiments...-, '" - ft. Experim. Date No. of fish Kept in täks for hours No. of fish % of fish Fish.brought No. tagged minim. maxime mean died died, from- to va1ue ---e-n_ IV ,0 22,5~ 18,6 6 3,7 South.Gotld. Depth - Bornholm Basin IV ,0 27,5 23,6 1 0,6 Bornholm Basin - Arkona Basin IV ,0 24,0 20,1 2 1,2 Arkona Basin - Slupsk Furrow IV ,0 26,0 22,3 1 0,6 Slupsk Furrow - South.. Gotld. DeptJ IV ,0 21,0 18,1 2 1,9 South. Got1d. Depth - Bornholm Basin IV ,0 4:1,0 41,0 0 0,0 Bornholm Basin - Kiel Bight ,9 12 1,2

Leibniz Institute for Baltic Sea Research Warnemünde

INSTITUT FÜR OSTSEEFORSCHUNG WARNEMÜNDE an der Universität Rostock BALTIC SEA RESEARCH INSTITUTE Leibniz Institute for Baltic Sea Research C r u i s e R e p o r t r/v "Elisabeth Mann Borgese" Cruise- No.