barre seng syn re SØ ne ES t egen =75—- 5% rene DEERE gg =" SISSE SEES 5 Se Ås ne å IBN DE Report of The Danish Biological Station to The Board of Ågriculture. XIII. 1903 ana 1904. By C. G. Joh. Petersen, Ph. D, Translated from ,,Fiskeri-Beretning for 1904—05€. AJ Copenhagen. Centraltrykkeriet. 1906. RG j Pi sly n From NET The Danish Biological Station. BEF FE 1903 and 1904. Copenhagen. Centraltrykkeriet. 1906. Eggs and Young of Fishes in the Danish Waters. (Investigations during 1904 and earlier years.) By Andreas Otterstrøm. Contents. az age Introduetion SEENDE RER NESS ENE Tr SE as er HERA PE SEER 3 General Portion: Ebro Ep BYS EEN ESSEN et SE rs Ace nt RENEE SENERE 8 ODENSE EEN SEE IND SEE SEINE ERNA SUEDE ERE ERE ende LET eg Me 10 belagt young os pe des with" per EEN 15 > > > > My demersal "eres IL LATE ERNE SAN AR REDEN 17 Mounoibottom-stareskoR Asked AT TRA ter ET sa AN RE ae 19 Gongudmøkre marks se REN an ENE En Eee E 21 Special Portion: 1. Species with pelagic eggs ES LEES REE ENE Eee Eee Eee EEN 3] VE SEES SEE ERE SE aa FREE SNS ENN SEES FREE 31 Ohe radere gs SE Ens laa SEERE EGE eres lle: 38 EOS ERE EET SE ET 40 HIGEN ORE ESS SEE GERE ne om ENDS en Ta eter Beer E Te SEERE DE 49 DET UL HEE SEES SEERE SEE ESS ED DE ele 50 eng rd al 3 5.) OY St se DERE DS EST EET E EET EET ER SODE RS OG 52 2. Species with demersal eggs Common sea-scorpion and Long-spined sea-scorpion............2222224… 54 ES EET EEN EEN EET EEN GER 60 Creed Blanes sg se REE NE Eee es er Eje 62 np ea SEE Eee EET Eee 62 Gan nel ENE ERE EEN RR Te 67 GL SDR SS RENEE RDS ER SER SR] DRS SERENE SD SANNE, MENE ESS 68 COMMORSNAMESKO DALER SPEGES ET se 5 Niel ARR NE FREE ERNE eee 69 Tab. 1. Pelagic fish eggs and young in the Danish waters during 1904 ...... 72 Tab. 2. Pelagic fish eggs in the Danish waters during 1904. Summary ..….…... 85 Tab. 3 A and B. Pelagic young fishes in the Danish waters during 1903 and OOA SE SS HIT ES ere re es eee SE I ER EEN, 84 Introduction. It is about 14 years since the Director of the Biological Station began investigations on the pelagic life in Danish waters. The method of the inve- stigations and the material were not then so perfect as they are now. The 4 want of a steamer especially was greatly felt, as the vessel at the disposal of the Biological Station at that time, a transport-boat of the fleet called »Stationen«, though well-fitted up with laboratory, well and store-room, had to have a special steamer of the navy to tow it each time it was moved. On account of these difficulties in changing from place to place, the Di- rector in the spring of 1901 decided, to moor »Stationen« in Fænø Sound in the Little Belt. The current runs so strongly there, that townetting can be carried on pelagically by merely hanging the net over the side from the anchored ship, and the surface-water is usually of a sufficiently high salinity to float the pelagic eggs and newly hatched larvæ. From April 1891 until September 1892 the investigations were being carried on in Fænø Sound. They furnished a rich collection of pelagic organismg, as also of the eggs and young of fishes, so that in 1892 the Director was able to publish a review over the pelagic life in Fænø Sound during the twelve months of the year (Biol. Stat. Beretn. II). On the conclusion of the 1891—92 investigations in Fænø Sound, the Biolozical Station was engaged in other directions for a number of years, but in 1899 the Director again took up the interrupted investigations on the pelagic eggs and young of fishes, with the special object in view of carrying out simul- tameous observations at different places in the Danish waters. The method of procee- dure had therefore to be different from that used in 1891—92. The Biological Station was not yet in possession of a steamer, and was thus unable to make the many necessary collections by itself. Other means had therefore to be employed, and most of the gatherings were taken from a number of lightships, which were specially suited for the purpose on account of their proximity to deep channels. Vertical hauls with the pelagic net were taken twice monthly and the gatherings sent in to the Biological Station. When these collections had been continued for two years, Åpril 1899—April 1901, they were brought to an end and the material was then worked out. The results are published in »De danske Farvandes Plankton 1 ÅAarene 1898—1901, I—II« (D. kgl. Vidensk. Selsk. Skrifter, 6. Række, natur- vidensk. og math. Afd. XIII, 3.). The first portion, written by the Director, con- tains a section on fish eggs and young, based on the collections mentioned. The number of eggs and young in each gathering is given in the form of lists, the determinations being added so far as they could be made. In the spring of 1902 Fænø Sound was again chosen as the mooring- place for »Stationen«, but as the Biological Station now had a steamer at its disposal, the investigations were extended so as to embrace, not only the neigh- bouring portions of the Little Belt but the other Danish waters also. The methods were also improved; especially was this the case with an excellent apparatus for the capture of fish young, constructed by the Director and described under the name of Petersen's young-fish-trawl by Dr. Johs. Schmidt in »Fiskeriundersøgelser ved Island og Færøerne i Sommeren 1903« (Skrifter udgivne af Kommissionen for Havundersøgelser Nr. I). From March 4th to the 22nd of May 1902, »Stationen« was at Fænø Sound. »Bobbin« tow-nets were employed, hung from the boat's side in the current and usually emptied and hung out again several times in the day. Now oa and then the »Sallingsund« made short or long excursions, using on those occasions the young-fish trawl. In 1903 and especially in 1904 very comprehensive investigations of the pelagic fish eggs and young were made according to plans drawn up by the Director and carried out under his direction by the author. In 1903 the young- fish trawl was used only to a limited extent, the pelagic tow-nmet being alone em- ployed at many stations, and as the larger specimens of the young fishes are but seldom taken in the pelagic net, we cannot obtain a complete picture of the kind and number of young present, when only this apparatus is used. On the other hand all sizes of the pelagic young, at any rate of the species found in Danish waters, can be taken by the young-fish trawl. It is better therefore to use only the hauls with the young-fish trawl as basis for a view over the occurrence of the fish young. The eggs are therefore investigated hy means of the pelagic townet, the young by means of the young-fish trawl. The Tables 1—3 (see p. 72—84) have been drawn up on this principle; for 1903 only a summary of the hauls in which pelagic young were taken is given (Tab. 3 A), for 1904 both a special table (Tab. 1) and also summary tables showing the hauls of pelagic eggs (Tab. 2) and of young fishes (Tab 3 B). The stations where surface and intermediate hauls were made with the pelagic tow-net and the young-fish trawl are noted in Tab. 1 from the Journal for 1904. For each station is given the date, place and hydrographacal conditions, then the eggs taken, with the pelagic net and the young taken with the young-fish travl. The stations are placed in chronological order for each of the regions” into which the Danish waters are divided. The place is determined by data showing the bearings: distance in nautical miles and depth in fathoms (1 fathom — ca. 2 meters). The water-samples were taken by means of a water-sampler and the salimities determined by areometer on board. The hauls made with the pelagic net”” were partly vertical, partly hori- zontal. The vertical hauls were always taken to the surface, the tables show from what depths. In order to take the pelagic eggs near the bottom we used the "nelagic net on a pole”, that is: the net was fastened to the top of a pole a =£ The boundaries between the regions are shown on Chart I p. 24; they are as follows: Line Hanstholm—The Naze separates North Sea and Skager Rak, »… Skaw lightship—Marstrand > Skager Rak and Kattegat, »… Eisinore—Helsinborg > Kattegat and the Sound. »… South end of Samsø—Refsnæs J Kattegat and Great Belt, »…… Ashoved—Endelave—South end of Samsø > Kattegat and Little Belt, >»… South end of Samsø—Nord-east point of Funen » Great Belt and Little Belt, »…… Copenhagen—Malmø > The Sound and true Baltic, »… South end of Langeland—Albuen > Great Belt and western Baltic, »…… Thorø— Aarø > Little Belt and western Baltic, »…… Gedser—Darsserot > Western Baltic and true Baltic. Thyborøn and Hals are the natural boundaries of the Lim Fjord towards the North Sea and the Kattegat. := Gauze No. 0; opening 90 cm. in diameter. For description, see: "De danske Far- vandes Plankton”, I, p. 233. little more than a fathom long. The pole maintains a vertical position in the water by having an iron weight on its lower end with some glass air-balls on the upper. By towing this pole along the bottom in a crowfoot, the net is always about a fathom's distance from the ground. When the tables indicate horizontal hauls with the pelagic net a fathom's distance from the bottom, that always means hauls with the "pelagic net on a pole”. The horizontal hauls with the pelagic net are continued to the surface on pulling in. The duration of the haul, given in the table in minutes, is the time occupied in fishing at the depth indicated. In the column for the duration the sign 1 denotes the vertical hauls. The pelagie fish eggs were counted immediately after the haul was made. The numbers are only approximate except in the case of the vertical hauls. The determinations were made on board, sometimes by letting the eggs hatch out, but usually by a rapid microscopic examination. We have therefore not been able to determine every single egg, but have restricted ourselves to noting the species we recognised without too close investigation. As a matter of fact, our attention has been mostly directed to the capture and determination of the young fishes.. The methods for the capture of these have been greatly improved by the Director even during the progress of the investigations. Petersen's young-fish trawl has been constantly used and we have made horizontal hauls with it at varying depths. When using it at or near the surface, we fastened an air-bladder on to the upper part at its centre. When using it deeper down, so far as possible at a certain depth below the surface, we made a line fast to the centre of the upper part and tied a buoy to the end of the line. The buoy was thus able to support the trawl and yet remain on the surface when the »Sallingsund« was moving. In this way we know at any rate, that the trawl did not go deeper than the length of the line, in fact scarcely so deep, as the line was towed a little obliquely in the water. We could not use this method however in fishing close to the bottom, as we ran the risk of the trawl touching the ground, and thus of the pelagic catch being covered over and destroyed by bottom-material and larger fish. It was therefore a great gain to the investigations when the Director constructed the so-called