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Western Baltic Spring Spawning herring

Main characteristics and peculiarities
• Spawning is mostly confined to a limited, shallow area: the Greifswalder Bodden/Rügen area
• no agreed assessment available mainly due to problems with the stock separation (North Sea autumn spawners vs. Western Baltic spring spawners) in the Kattegat/Skagerak area; data presented here are the results of a data exploration

Assessment Summary
year	2000 (WG 2001)
type	no assessment, but data exploration using ICA
assessment quality	no assessment
main problems	(1) difficult separation between NSAS and Western Baltic Spring Spawners in Div IIIa and Sub-Div IV (2) fisheries independent surveys yield contradictory information (3) hydroacoustic surveys cover only part of the distribution area at a given time
fisheries independent information	(1a) hydroacoustic october survey in 22-24 and the Kattegat, (1b) hydroacoustic summer survey in IIIa (2a) German bottom trawl surveys in 22 and 24, (2b) int'l bottom trawl survey in IIIa (3) larval survey(s) in the Greifswalder Bodden
catch	118'000 t (1999: 98'000 t); OBS: total catch NSAS and WBSS in the Area ca. 162'000 t
spawning stock biomass	138'000-176'000 t (1999: 110'000 t)
fishing mortality	F(adults [3-6])=0.48-0.59
reference points	not defined
state of the stock	uncertain
perspective	uncertain, but stock parameters rather stable

Stock parameters (under construction)

This standard figure can be downloaded as a printable pdf-file (requires Acrobat Reader)

• estimated catch (including discards and unallocated or misreported catch, totals) or commercial landings (official figures, totals)
• spawning stock biomass
• recruitment
• fishing mortality

Distribution
WBSS are distributed in the Kattegat/Skagerak [Div. IIIa], and the Western Baltic [Sub-Div. 22-24] areas, spawning takes place in spring mainly in the Greifswalder Bodden/Rügen area.

Note that there is a difference between Western Baltic Spawning herring (which is Spring spawners only, caught in the North Sea, Div IIIa and the Western Baltic) and herring caught in the Western Baltic and Div IIIa (which is a mixture of WBSS, North Sea Autumn Spawners, local autumn, winter and spring spawners and Central Baltic Spring Spawners, but caught only in Div IIIa and Sub-Div 22-24). Click here for a detailled table on the composition and catches by fleet for WBSS and North Sea Autumn Spawners, which are mixing in Div IIIa and Sub-Div IVa(E).

Migration pattern
The North Sea autumn spawners enter Division IIIa (Skagerrak and Kattegat) as larvae (Anon. 1977/H:3, Bartsch et al 1989, Johannesen and Moksness 1991) and migrate back to the North Sea with an age of 2-3 years (Anon. 1991/Assess 15 and Johansen 1927).
After spawning during their feeding migration in an age of 2 years (Aro 1989, Biester 1979 and Weber 1975), the Western Baltic spring spawners enter Division IIIa through the Sound and Belt Sea and spread out into the Western part of the Skagerrak and the Eastern North Sea.
Towards the end of summer the herring aggregate in the Eastern Skagerrak and Kattegat before they migrate to the main wintering areas in the southern part of the Kattegat, the Sound and the Western Baltic (Anon. 1991/Assess 15).

Spawning
The Western Baltic area is inhabited by a fast growing and migrating herring population with spawning sites around the Danish Islands and along the German coast (Parmane et al. 1994). The main spawning area is the waters around the Rügen Island (Greifswalder Bodden). Depending on the ice coverage the spawning season lasts from around March to May. At the beginning of the spawning season the arriving herring swarms are characterised by older and bigger fish (Klinkhardt, 1996).
The following parameters are characterising the spawning herring in the waters around Rügen island:

Water depth for spawning	1-6 m (Klinkhardt 1996)
Minimum salinity for spawning	4 (Klinkhardt 1996)
Minimum temperature for spawning	4 °C (Klinkhardt 1996)
Fecundity	10,000 - 100,000 eggs (Below 1979)
Time before hatching	about 7 days (Klinkhardt 1986)
Length when hatching	5.5 - 7.3 mm (Klinkhardt 1986)
Manifestation of first day ring on otoliths	4.5 days (Klinkhardt 1996)
Time to spend yolk-sack	6.5 days (8 °C) (Klinkhardt 1996)
Growth of Larvae	0.3 mm/day (Biester 1979)

Stock separation
The herring stocks in the Kattegat and the Skagerrak have traditionally been separated by the average counts in number of vertebrae in herring samples (Rosenberg &Palmen 1982; Gröger & Gröhsler 1995, 1996). North Sea autumn spawners have a mean number of 56.5 vertebra while the Western Baltic spring spawners are represented by a lower mean number, 55, 8 vertebrae.
For 1996 a new method was employed using otolith micro-structure for separating Western Baltic spring spawners from North Sea spawners (Mosegaard & Popp-Madsen 1996).

Management advice
The fisheries on herring in Division IIIa should continue to be managed in accordance with the management advice given on autumn-spawning herring in the North Sea. If a catch limit is required in Sub-divisions 22–24, the catches should not exceed recent catches in that area which are of the order of 50'000 t.

Source
ICES Working Group for the assessment of Herring South of 62°N 2000, ICES CM 2000/ACFM:10, and 2001, ICES CM 2001/ACFM:12

References
Anon. 1977. Review on the distribution in relation to zones of extended fisheries jurisdiction of the following species: North Sea herring; Celtic Sea herring; Division VIa herring; North Sea sprat; Skagerrak, Kattegat and Norwegian fjord sprat; herring in Division IIIa Skagerrak; blue whiting (Micromesistius poutassou). ICES CM 1977/H:3 - APPENDIX.
Anon. 1991a. Report of the Herring Assessment Working Group for the Area South of 62°N. ICES CM 1991/Assess: 15.
Aro, E. 1989. A review of fish migration patterns in the Baltic. Rapp.P.-v.Reun.Cons.int. Explor.Mer, 190: 72-96.
Bartsch, J.; Brander, K.; Heath, M.; Munk, P.; Richardson, K. and Svendsen, E. 1989. Modelling the advection of herring larvae in the North Sea. Nature Vol. 340: 632-636.
Below, M., 1979. Untersuchungen zur Fruchtbarkeit der Rügenschen Frühjahrsheringe (Clupea harengus L.) und die Entwicklung der Fänge von 1967-1978. Diplomarbeit, Universität Rostock.
Biester, E. 1979. Der Frühjahrshering Rügens- seine Rolle in der Fischerei der Ostsee und in den Übergangsgebieten zur Nordsee. Doctoral Thesis. Wilhelm-Pieck Universität Rostock (1979): 236 pp.
Gröger, J. & Gröhsler, T. 1995. On the discrimination of herring stocks in Division IIIa. ICES, C.M. 1995/J:22.
Gröger, J. & Gröhsler, T. 1996. Information updated discrimination of herring stocks in Baltic Division IIIA. ICES, C.M. 1996/J:10.
Jensen, A.I.J., 1957. Danish herring investigations in the Skagerrak, Kattegat, Belts and Baltic. Ann. Biol. 14: 1991-194
Johannesen, A. and Moksness, E. 1991. Herring larvae (Clupea harengus) in the Skagerrak area from December 1987 to April 1988. Fish.Res., 11 (1991): 155-170.
Johansen, A.C. 1927. On the migration of herring. Extrat du Journal du Conseil International pour l’exploration de la Mer. Vol. II, no. 1.
Klinkhardt, M., 1986. Ergebnisse von Untersuchungen zur Schlupf- und Dottersackphase der Larven von Rügenschen Frühjahrsheringen (Clupea harengus L.). Fischerei-Forschung 24 (2): 28-30.
Klinkhardt, M., 1996. Der Hering. Magdeburg: Westarp-Wiss.; Heidelberg: Spektrum Akad. Verl., 1996: 1-230
Mosegaard, H. & K. Popp-Madsen, 1996: Racial dis crimination of herring stocks, comparing vertebral counts and otolith microstructure analysis. ICES C.M. 1996/H:17)
Rosenberg, R. & L.E. Palmen, 1982. Composition of herring stocks in the Skakerrak-Kattegat and the relations of theses stocks with those of the North Sea and adjacent waters. Fish.Res. 1: 83-104.
Weber, W. 1975. A tagging experiment on spring-spawning herring of the Kiel Bay. Ber.Dt.Wiss.Komm.Meeresforsch. 24 (1975): 184-188

Data entered/updated by (Date)
Tomas Gröhsler (18-05-00/01-07-00/26-06-01)

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