ICES 1990 PA PER C.M.1990/G:62 Demersal Fish Committee

FCX:>D AND CONDITION' OF DAB

.L.ZMANDA .L.ZMANDA (L_)

, FROM THE nc::x:;<;ER BANK AND THE GERMAN BIGHT

Rainer Knust Alfred-Wegener-Institute for Polar- and Marine Research Columbus-Straße 2850 Bremerhaven F.R.G.

- ABSTRACT - From 1984 to1986 feeding, condition and 'the gonadosomatic index of dab (Limanda limanda (L.}) were studied at one station in theGerman Bight and another on the Dogger Bank. In the German Bight all parameters showed a distinct seasonal, periodicity, with a maximum of food, diversi ty, food uptake and condition in summer and a low feeding activity and condition in spring during the spawning season when the gonadosomatic index is highest. On the Dogger Bank only the,seasonal periodicity of the gonadosomatic index is comparable with those from dab in the German Bight. The food uptake, as weIl ~s the condition factor cf dab from . the Dogger Bank remain nearly constant' during the whole year.

- INTRODUCTION - In the last few' years some "peculiarities" were reported from the Dogger Bank: MOLLER (1979) and DETHLEFSEN (1987) found a high prevalence of "disease in dab (Limanda limanda (L.)) from the Dogger Bank. High concentrations of lead and cadmium (CLAUSSEN, 1988) and high concentrations of organo­ chlorine' residues, especially HCB, (BüTHER, 1988) in the liver of dab from the Dogger Bank were found and KRONCKE (1987) measured a high concentration of heavy metals in macrozoobenthic organisms. KRONCKE (1989) 'compared the macrozoobenthos fauna on the Dogger Bank, in the years 1985 . and 1987 with older data from the·fifties and sixties and found changes in total. biomass and in'fauna composition. A higher biomass and an increased abundance of species like filiformis and op~ortunistic polychaetes indicate

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.J J; • ~ .- an increasing hypertrophication in this part of the centra1 . These observations are combined by more or 1ess un­ typica1 . seasona1 variation in the 10wer trophic compart­ ments of the ecosystem. In contrast to other parts of the North Sea on the Dogger Bank high chlorophyll concentration and high primary production were measured . also in winter (BROCKMAN & WEGNER, 1985; 'RICHARDSON &'OLSEN, 1987; ALETSEE & RICK, 1988). This indicates continuous primary production during the who1e year. This paper is a short summary of part of .a greater studY about feeding, condition and the gonadosomatic index of dab in the southern and centra1 North Sea (KNUST, 1990). The intention of this paper is to show the possib1e'inf1u­ ence of this different seasona1 periodicity on higher tro­ phic levels using the examp1e of food uptake and the condi­ tion factor in-dab from the Dogger Bank.

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Figure 1: INVESTIGATION AREA ',_ ~ .... ~ ...". . -.

- MATERIALS AND METHODS -

In 1984, 1985 and in spring of 1986 a half hour fishings were carried out at one station on the Dogger Bank (Stat.II) and another one in the German Bight (Stat.I) (Fig.l). Threehundredandthirtyfive guts in total were dissected from fresh material (female and male dab (18-22cm» and fixed in 10% formaldehyde. Fourhundrcd­ andfiftyone female dab (18-22cm) were deep frozen for

2 determination of condition and gonadosomatic index. In the laboratory the stomach content was investigated by separa­ ting the food organisms according to systernatic groups and species. Wet weight of the main taxa was estimated within 1 mg of accuracy.

- RESULTS - Food uptake .and diversity of food: In the German Bight the feeding parameters showed a di­ stinct seasonal periodicity with low values in spring and maximum values in summer. The mean numbers of ingested prey organisms increased from March (median=O organisms per sto­ mach) .to August (median=94 organisms per stomach). The mean number of prey species increased.in the same time interval from 0 per stornach to 10 prey species per stornach (Fig.2). The mean diversity of food amount in August was 1.84 (Shannon-Weaver Index) (Fig.3). In spring the"main part of food ·was composed of the , Ophiura albida. In summer, dab of the German Bight fed mainly on crustaceans; amphipods were the most dominant taxa group in the food du­ ring this season. On the Dogger Bank the measured feeding parameters are more or less constant during the year. Significant diffe­ rences like in the German Bight cou1d not be found. In spring the me an number of species in the stomach (median 2­ 4 species per stomach) and thediversity index of food (median 0.45-1.39) were distinct1y higher than in the German Bight, while in summer number of prey species and diversity index of food were' lower than in the German Bight.

Condition 'and gonadosomatic index:

Fig. 4 - 5 represent the mean values of the condition and • gonadosomatic index, measured between March 1984 and Janu­ ary 1986. In the German Bight the values for condition ran- . ged .from 0.80 ± 0.06 in the spring to.l.08 ± 0.10 in Au­ gust. The gonadosomatic index ranged from 1.1 ± 0.27 in Au­ gust and October to 14.3 ± 3.72 in spring. Theresults sho­ wed a distinct seasonal periodicity with the highest value for .the gonadosomatic index and the lowest condition in spring (April~ March). After the spawning season the condi­ tion increased to a maximum in August, whereas the gonado­ somatic index reached aminimum. On the Dogger Bank' the gonadosomatic index showed a comparab1e seasona1 periodicity as found in dab from the GermanBight•. Maximum va1ues were measured in spring, 10­ west.values in summer andautumn (Fig.5). In spring the condition factor of dab from the Dogger Bank was' higher than of dab from the German Bight, while in summer the

3 3 , • 1983 German Bigh\ , • 1981 German Bigh\ •• 1981 .. = 1981 11 • 1985 • '" 1995 15 - o • 1986 o e 1996 1l r iII 0 GI 0 - '0 - 2- a.GI '0 iII 10 - x "J' GI GI 1l C I. ~ a. "J' '0 - l- I. in GI I. 5- GI .D ~~ > e ::Jc ~g ~ $ 'Ü 0- .y ~ it1• 0 + + + • M + 0- 'i"';; "t M + 7 • r--r-- 3 •• 1983 Dogger Bank ' • 1983 Doggl'r Bank + • 1581 .. • 1981 11 '" 1985 .. e 1985 15 o • 1986 o Il! 1986 1l 111 0 GI 0 '0 - 2- a.GI '0 111 10 )( "J' GI GI 1l C I.a. H '0 ? H l- I. in GI 5 I. .D GI e > ::J J c ~ ~ ~ ~ 1 'Ü 0 • 0 0 + + 0- 7." '1r + + I I I I I , II I II 11 I 2 3 5 6 7 8 9 10 11 12 I 2 3 5 6 7 8 9 10 11 12

mon\h month

Fiqure 2: NUMBER OF PREY ORGANISMS PER STOMACH Fiqure 3: DIVERSITY OF FOOD (Shannon-Weaver-Index) IN DAB (LIHANDA LIMANDA) (18-22cm) IN DAB (LIHANDA LIHANDA) (18-22cm) 1.20 + • J991 16 German Bighl • .. 1995 Ger man Bi ght o • 1986

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L + 12 0 Ü 10 .. 1.00 • in c:

1.20 •• 1981 Dogger Banl: 16 Dogger Banl: •• 1985 o • 1986

li

L 12 UI 0 Ü .. 1.00 10 c: in 0

2 J i 5 6 7 8 S 10 11 12 2 J 5 6 7 B S 10 11 12

monlh monlh

Figure 4: CONDITION FACTOR (Ks) OF FEMALE Figure 5: GONADOSOMATIC INDEX (GSI) OF FEMALE DAS (LIMANDA LIMANDA) (18-22cm) DAB (LIHANDA LIHANDA) (18-22cm) condition was lower than in the German Bight. However for dab from the'Dogger Bank a smaller range of the condition factor values through the year was remarkable (Fig.4).

- DISCUSSION - Seasonal changes in condition and gonadosomatic indices for dab were reported by Ortegas-Salas (1980) from the coast of the Isle of Man and by Htun-Han (1978)' from the British coast of the North Sea. The periodicity is similar to that of dab of the German Bighti with low condition and a high gonadosomatic index in spring. during the spawning season. In . summer· the condition factor increases and the gonadosomatic index is low. In the literature no references could be found, which'report any similar seasonal constancy forthe condition factor of dab, likewise we found for female dab caught on the Dogger Bank.

Arntz (1971), Lande (1976) and Ortega-Salas (1980) also reported conformity about seasonal changes of feeding behaviour and food composition of dab. Ortega-Salas (1980) found that the wet weight of food ingested is lowest in winter and spring and highest in the months of summer. These observations are comparable to those of dab from the German Bight, which also showeddistinct seasonal differen­ ces in food uptake and food composition. in contrast to the Dogger Bank where the feeding parameter, we measured, are more or less constant throughout the year. This picture of a strongly reduced annual periodicity in feeding and condition of dab from the Dogger Bank fits weIl with other observations of high primary production in winter on the Dogger Bank (BROCKMAN & WEGNER, 1985; RICHARDSON & OLSEN, 1987 ; ALETSEE & RICK, 1988). For the macrozoobenthos on the Dogger Bank no detailed information about seasonal changes are available, but KRONCKE (pers. comm.) found no' remarkable seasonal differences in the ben­ thos abundance between· spring and autumn and KONITZER (1990) described an important food input to a mud-inhabi­ ting fauna during winter near the Dogger Bank tail end.

- REFERENCES -

Aletsee~L. & Rick,H. (1988): Phytoplankton. In: Zirkulation und Schadstoffumsatz in.der Nordsee (ZISCH). AB~ SCHLUSSBERICHT BMFT-PROJEKT MFU 0545, UNIVERSITÄT HAMBURG 1988. Arntz, W.E. (1971): Die Nahrung der Kliesche (Limanda li­ manda (L.» in der Kieler Bucht~ Ber. dt. wisse Kommn. Meeresforsch 22, 129-183. Brockmann, U. H. & Wegener, G.. (1985): Hydrography, nutrient . and chlorophyll distribution in the North Sea in february 1984. ARCH. FISCHWISS~ 36, 27-45.

6 Büther,H. (1538): Regionale Verteilung und geobiochemische Bedeutung der Konzentrationsmuster schwerflüchtiger Organochlorverbindungen in Klieschen (Limanda 1i­ manda) der südlichen und zentralen Nordsee. VERöF• FENTLICHUNGEN DES INSTITUTS FüR KüSTEN- UND BINNEN­ FISCHEREI HAMBURG 99, 237pp. Claussen,T. (1988): Characteristic levels and spatial dis­ tribution of trace metals in (dab, Li­ manda 1imanda) from the German BIght and the southern North Sea. MITT. GEOL.-PALÄONT. INST. UNIV. HAMBURG 65, 115-131. Dethlefsen,V.; Watermann,B.; Hoppenheit,M. (1987): Diseases of the North Sea dab (Limanda limanda L.) in rela­ tion to biological and chemical parameters. ARCH. FISCHWISS. 37(3), 107-237. , Htun-Han, M.(1978): The 'reproductive biology of dab (Liinanda 1imanda (L.» in the North Sea: gonadoso­ matic index, hepatosomatic index and condition fac­ tor. F. FISH. BIOL. 13,269-378 . .e Knust, R. (1990): Ernährung der Kliesche (Limanda 1imnada (L.» in der zentralen und südlichen Nordsee und die Bedeutung des Ernährungszustandes für die Erkrankungen dieses Fisches. VERÖFFENTLICHUNGEN DES INSTITUTS FÜR, KÜSTEN- UND BINNENFISCHEREI HAMBURG 102, 184pp. Künitzer, A. (1990): Zur Verbreitung und Populationsdynamik der Bodenfauna der zentralen Nordsee. PHD.THESIS UNIVERSITY OF BREMEN FRG 1990, 218pp. Krönke,I. (1987): Lead and cadmium concentrations in selec­ ted macrofauna species from the Dogger Bank arid the eastern North Sea. HELGOLÄNDER WISS. MEERESUNTERS. 41, 465-475. Kröncke, I '(1989): Die.Makrofauna auf der Doggerbank. Ein ökologischer Vergleich zwischen den Jahren 1950­ ,1954 und 1985-1987. PHD. THESIS UNIVERSITY OF HAM­ BURG FRG 1989, 258pp. Lande, R.' (1976): Food and feeding habits of the Dab ,(Limanda limanda (L.» in Borgenfjorden, north ,Tro­ endelag, Norway. NORW. J. ZOOL. 24,225-230. • Möller,H. (1979): Geographical distribution of fish ,di­ seases in the NE 'Atlantic. A bibliographie review. . MEERESFORSCH. 27, 217-235. Ortega-~alas, A. A. (1980): Seasonal changes in the common . dab, Limanda 1imanda (L.) in Isle of Man Waters. J. FISH. BIOL. 16,75-82. ' ' Richardson,K. & Olsen,O.V. (1987): Winter nutrient con­ centratioris and primary production in the eastern North Sea. ICES C.M~ 1987/C:23.

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