Rapp. P.-v. Réun. Cons. int. Explor. Mer, 190: 109-112. 1989 The distribution of spring-spawning herring larvae in coastal waters of the German Democratic Republic

Erich Biester

Biester, Erich. 1989. The distribution of spring-spawning herring larvae in coastal waters of the German Democratic Republic. - Rapp. P.v. Réun. Cons. int. Explor. Mer, 190: 109-112.

Thé larvae of spring-spawning herring are found along virtually the whole of the coastline of the German Democratic Republic from the island of Usedom in the east to Wismar in the west between March/April and July/August. The numbers found, however, vary in time and space. Larval studies in the 1930s, 1950s, and 1960s led to the continuous monitoring of herring larvae in Greifswalder Bodden since 1977. The waters adjoining the bodden and the coastal regions east and west of Rügen have also been studied sporadically using the same methods. Larval abundance in these regions can therefore be compared to those in Greifswalder Bodden for the inves­ tigation period. Larval abundance in Greifswalder Bodden is usually higher than in the other regions. However, on one occasion abundances off the east coast of Rügen island were several times higher than at the Greifswalder Bodden spawning ground in May. Direct comparison of larval abundance in Greifswalder Bodden with the total abundance for all other regions investigated east and west of Rügen shows that Greifswalder Bodden accounted for 45 to 85% (Greifswalder Bodden and west Rügen) and 65 to 75% (Greifswalder Bodden and east Rügen) of the abundance.

Erich Biester: Wilhelm-Pieck-Universität Rostock, Sektion Biologie, Wissenschafts­ bereich Fischereibiologie, Universitätsplatz 5, DDR-2500 Rostock, German Demo­ cratic Republic.

the coast of Usedom. Larvae were most abundant in Introduction May and June. The first studies dealing with the larvae of the spring- Studies in the Greifswalder Bodden were not resumed spawning Rügen herring were in 1937 to 1939, whereas until 20 years later (1958/59) (Waldmann, 1961), and the autumn-spawning herring, which predominated in these were continued sporadically in 1960/61. Samples the Baltic during the 1920s, had been the subject of collected in March and early April contained larvae earlier studies. Denmark systematically collected with a length of 26-50 mm and in May of 36-45 mm. samples of larvae from 1925 to 1938 (Nybelin, 1929; These larvae were considered to be offspring of the Johansen, 1930; Poulsen, 1936). Sweden also took part autumn spawners. Larvae of the spring spawners did in these studies up to 1932 and Germany up to 1931 not appear until April, when they were about 6 mm (Altnöder, 1928, 1929, 1932; Kandier, 1952; Weber, long. 1971). The occurrence of herring larvae at the more The systematic larval survey that is still in progress localized spawning grounds off the coast of the western and continues from March/April to July each year in Belt See was also investigated at that time (Kandier, the Greifswalder Bodden started in 1977 (Biester and 1952). Brielmann, 1977; Biester, 1979,1984; Brielmann, 1982, The studies dealing with the larvae of the Rügen and later). The station grid in Greifswalder Bodden herring showed that the Greifswalder Bodden (GB), consists of about 30 stations. Facilities permitted studies Strelasund, and the coast of Usedom island were the to be carried out in the waters west of Rügen island in main spawning grounds. Little spawning took place May and July for the first time in 1981 (Thu, 1983; around the island of Rügen (west, north, and east Ladwig, 1983), and in 1984/85 the coastal waters east coasts). From the length distribution of the larvae it was of Rügen could be included in the survey (Son, 1987). evident that there were two spawning periods in a season Since 1977 the survey in Greifswalder Bodden, the a year. Spawning took place during both periods in principal spawning ground, has also been continued Greifswalder Bodden, but only during the second off year after year using the same methods and sampling

109 MECKLENBURGER BUCHT

STRALSUN

BREITLING

ROSTOCK GREIFSWALD

US.ED.oy WISMÀR

Figure 1. Station grid until 1982. technique, and the additional investigations off the coast of Rügen permit “quasisynoptic” comparison of larval abundances in these regions with those in Greifswalder Bodden. In the following, abundances in the waters off Rügen are expressed as percentages of the abundance in Greifswalder Bodden.

Methods o — Ichthyoplankton samples are collected with a MARMAP-bongo net, double inclined hauls being made for each sample. The layout of the station grid Rügen was designed to yield results that can be considered fairly representative of the whole coastal region with 146 stations (Figs. 1,2). In addition, phytoplankton and zooplankton samples are collected and environmental parameters are recorded at 22 of them. Sampling was also carried out at another 15 stations in the Breitling and stations in the chain of boddens south of Darss-

Zingst. Greifswald Herring larval abundances are expressed in indi­ viduals per unit water surface (n/m2). The lengths of larvae were measured by means of an object micrometer (0-5 mm below).

Figure 2. Station grid since 1983. • Hydrographic stations.

110 Results of the German Democratic Republic to be compared with Greifswalder Bodden at the same time. However, Greifswalder Bodden is the main spawning ground of in May 1981 (12th May to 2nd June) it was possible to the spring-spawning herring. The larvae less than 7 mm study Greifswalder Bodden, the Strelasund, and Kubit- long can be caught there from March/April to July. The zer Bodden at the beginning and the end of a sampling lengths of larvae and juveniles caught in this area vary action for the region west of Hiddensee. In Greifswalder between 5 and 60 mm. Occasional larvae and juveniles Bodden larval abundance on 2nd June (20 x 109) was over 25 mm long are caught in all regions early in the almost seven times as high as from 12th to 13th May season. Larvae of this size are the offspring of autumn (3 x 109). In Table 1 the Greifswalder Bodden is com­ spawners from the previous year and gradually dis­ pared with the waters west of Rügen. appear from the samples. Larvae from the previous year The variability of the values within three weeks natu­ were also found in samples collected in the boddens rally makes comparison difficult, but the data confirm south of the Darss-Zingst peninsula from 1975 to 1977 the outstanding importance of Greifswalder Bodden (Hoffman, 1977), and subsequent studies have shown and its adjacent waters at this time of the year (66-4 and that both larvae and juvenile herring are found there 90-9% of all larvae). If the adjacent waters (Strelasund every year. Weigmann (1982), too, showed that spawn­ and Kubitzer Bodden) are not taken into account, the ing takes place and larvae can be caught in Greifswalder abundance in Greifswalder Bodden in mid-May 1981 Bodden and the adjacent waters in October and Nov­ was exceptionally low at less than 50%, as mentioned ember. before. However, surveys from autumn to the end of 1984 Two surveys (Table 2) performed in the regions east and 1985 in Greifswalder Bodden yielded only several of Rügen in 1985 are also suitable for comparison. larvae between 18 and 29 mm long in 1984 and in 1985. Therefore there is little spawning activity between Sept­ ember and December. Table 2. Signs of spawning activity were also found in the 29th May Breitling (Rostock) in the 1980s despite the nearby to 20th to port. Although abundances here were only 1% of those 6th June 25th June observed in Greifswalder Bodden, the spawn indicates 1985 1985 that herring try every inlet along the coast. This is also A Greifswalder Bodden...... 73-5% 63-2% shown by the spawners caught in the Breitling and K Coast of Usedom ...... 20-3% 22-7% between Zingst (Grabow) and Gellen (Hiddensee) in L Ruden-Greifswalder Oie...... 2-9% 6-4% the approaches to Stralsund. M East of Rügen, south...... 1-8% 2-7% Herring and sprat larvae were found together in this N East of Rügen, north...... 1-5% 5-0% region west of the island of Rügen at the end of the Total...... 100% 100% season. Larvae longer than 6 mm could be distinguished Total larval abundance...... 43-6 x 109 9-3 x 109 by means of the trunk myomers: herring larvae had at least 44 and sprat larvae only 42 or less. It was unfortunately not possible to arrange a sam­ pling schedule that would permit all regions of the coast This comparison, too, shows that larval abundance is far higher in Greifswalder Bodden (73-5 and 63-2% of Table 1. all larvae) even if its adjacent waters are not included. Although abundance was relatively high off the Usedom 20th May coast in 1985, higher abundances were also recorded 12th to to 27th May 2nd June east of Rügen from Nordperd to Sassnitz (East of 1981 1981 Rügen, south) in 1984.

A Greifswalder Bodden...... 45-8% B Strelasund...... 110% Conclusions C Kubitzer B odden...... 9-4% D West of Hiddensee to Darss.... 18-3% 4-9% 1. Regions where spring-spawning herring spawn and E Darss to Warnemünde...... 9-0% 2-4% where the larvae hatch and grow are found all along 1-3% F Warnemünde to Kühlungsborn 4-8% the coastline of the German Democratic Republic. G W ismar...... 1-5% 0-4% C Kubitzer B odden...... 0-5% 2. Greifswalder Bodden and the adjacent waters are B Strelasund...... 5-3% the principal spawning ground. A Greifswalder Bodden...... 85-1% 3. The importance of the regions east of Rügen and south to the coast of Usedom as spawning grounds Total...... 100% 100% can also be considerable, but vary in both time and Total larval abundance...... 6-4 x 101' 23-8 x 10’ space.

I ll Table 3. Herring larvae abundances expressed as percentages zur Feststellung des Vorkommens von Herbstheringslarven of the abundances in Greifswalder Bodden (100%) at com­ in der Laichperiode 1927. Ber. d. Dtsch. Wiss. Komm. f. parable times (May). Meeresforsch (DWK). N.F. 4 (3): 125-194. Altnöder, K. 1930. Bericht über die Untersuchungsfahrten zur % Feststellung des Vorkommens von Heringslarven in den Laichperioden 1928 und 1929. Ber. d. Dtsch. Wiss. Komm. A Greifswalder B odden...... 100 f. Meeresforsch (DWK). N.F. 5 (3): 96-111. B Strelasund...... 16-70 Altnöder, K. 1932. Bericht über die dritte und vierte Unter­ C Kubitzer B odden...... 10-16 suchungsfahrt zur Feststellung des Vorkommens der D West of Hiddensee to Darss 40 Herbstheringslarven in den Laichperioden 1930 und 1931. E Darss to Warnemünde...... 20 Ber. d. Dtsch. Wiss. Komm. f. Meeresforsch (DWK). N.F. F Warnemünde to Kühlungsborn 10 6 (2): 90-106. G W ismar...... 3 Biester, E. 1979. Der Frühjahrshering Rügens - seine Rolle K Coast of Usedom ...... 9-41 in der Fischerei der Ostsee und in den Ubergangsgebieten L Ruden-Greifswalder O ie ...... 10-500 zur Nordsee. Wilhelm-Pieck-Universität Rostock. Dr.sc. M East of Rügen, south...... 3-1000 Thesis, 1-236. N East of Rügen, north...... <10 Biester, E. 1984. Occurrence of herring larvae along the outer coastline of the German Democratic Republic in spring and D -G in May 1981 with unusual low abundances in Greifs­ summer. ICES CM 1984/J: 33, 1-9. walder Bodden. Biester, E. 1986. Heringslarven und -jungfische. 15 Jahre Fischereibiologie Wilhelm-Pieck-Universität Rostock, Sek­ tion Biologie, Fischereibiologische Herbsttagung. 1. 4. The importance of the regions west of Hiddensee to Rostock, 27-37. Wismar (D-G) also varies, but is generally slight. Biester, E., and Brielmann, N. 1977. Occurrence of herring larvae in the Greifswalder Bodden in 1977. ICES CM 1977/ This applies likewise to the eastern part of the bodden P: 21. chain south of the Darss-Zingst peninsula. Hoffman, U. 1977. Clupeidennachwuchs in der Darßer 5. Considerable numbers of young larvae can still be Boddenkette Wilhelm-Pieck-Universität Rostock. Diploma observed in Mecklenburg Bay at the end of the Thesis, 1-94. Johansen, A. C. 1930. On a correlation between the yearly season. This indicates that spawning continues for catch of herring in the Sound and the abundance of herring longer or hatching takes place later in this region. larvae in autumn. Rapp. P.-v. Réun. Cons. int. Explor. Mer, 6. Initial attempts to estimate larval abundances and to 65: 82. express them as percentages of larval abundance in Kandier, R. 1952. Uber das Laichen des Frühjahrsherings bei Greifswalder Bodden show that the region east of Rügen und die Häufigkeit der Brut des Herbstherings in der Beltsee und südlichen Ostsee. Kieler Meeresforsch. 8 (2): Rügen-south, (M) and the Ruden-Greifswalder Oie 145-163. (L) have both had higher abundances than Greifs­ Ladwig, B. 1983. Untersuchungen am Ichthyoplankton küsten­ walder Bodden on one occasion. These regions, the naher Seegebiete der Mecklenburger Bucht unter beson­ coast of Usedom (K) and the Strelasund-Kubitzer derer Berücksichtigung des Herings (Clupea harengus L.). Wilhelm-Pieck-Universität Rostock. Diploma Thesis. Bodden (B, C) region are sometimes of considerable Nybelin, O. 1929. Untersuchungen über Heringslarven im importance in terms of recruitment. They can be Kattegat und in der südlichen Ostsee. Svenska Hydr.-Biol. considered as the boundaries of the main spawning Komm. Skr. Ny Ser. Biologie 1 (3). ground in Greifswalder Bodden (Table 3). Poulsen, E. M. 1936. Yearly variations in the number of larvae of autumn spawning herrings in the southern part of the 7. Annual and regional variations in the importance of transition area. Rapp. P.-v. Réun. Cons. int. Explor. Mer, the different regions compared to Greifswalder 100 (2): 22-23. Bodden may be responsible for the known difficulties Son, D. M. 1986. Untersuchungen an Heringslarvenvor- in estimating year-class recruitment on the basis of kommen in den Gewässern östlich Rügens und ihre Bedeu­ surveys of the larvae of the Rügen spring-spawning tung für die Reproduktion des Bestandes. Wilhelm-Pieck- Universität Rostock. Dr. Thesis, 1-139. herring. Thu, V. H. 1983. Untersuchungen über das Vorkommen von 8. An international larval survey employing several ves­ Heringslarven (Clupea harengus L.) im Frühjahr/Sommer sels for continuously monitoring the waters from an der DDR-Küste, besonders im Jahr 1981. Wilhelm-Pieck- Wismar to Wollin throughout the season could pro­ Universität Rostock. Dr. Thesis, 1-134. Waldmann, J. 1961. Untersuchungen an Heringslarven und vide more conclusive data, because recruitment could Zooplankton des Greifswalder Boddens in den Jahren 1958 then be estimated from the larval abundance through­ und 1959. Z. Fischerei 10: 523-536. out the whole spawning region. Weber, W. 1971. Die Laichplätz des Herings (Clupea harengus L.) der westlichen Ostsee. Kieler Meeresforsch. 27 (2): 194— 206. References Weigmann, M. 1982. Fischereibiologische Untersuchungen an den im Herbst vor Südost Rügen und im Greifswalder Altnöder, K. 1928. Untersuchungen an den Heringen der Bodden laichenden Heringen. Wilhelm-Pieck-Universität westlichen Ostee und Berichte über die Untersuchungsfahrt Rostock. Diploma Thesis, 1-34.

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