Year-class strength patterns in Baltic perch and pikeperch populations - a basis for development of systems for prognosis
Bulletin of the Sea Fisheries Institute 2 (141) 1997, pp. 3-17

Peter Karas1, Paula BÖHLING2,Leili JÄRV3, Hannu Lehtonen4, Andrey Makarchouk5 and Valdemaras Ziliukas6
1National Board of Fisheries, Institute of Coastal Research, Gamla Slipvägen 19, S-740 71 Öregrund, Sweden.
2Finnish Game and Fisheries Research Institute, FIN-00151 Helsinki, Finland.
3Estonian Marine Institute, 32 Lai street, EE-0001 Tallinn, Estonia.
4University of Helsinki, Department of Limnology and Environmental Protection, FIN-00014 Helsinki, Finland.
5Latvian Fisheries Research Institute, 6 Daugavgrivas street, LV-1007 Riga, Latvia
6Institute of Ecology, Laboratory of Marine Ecology, Akademijos 2, LT-2600 Vilnius,Lithuania
 

Key words: perch, pikeperch, year-class strength, Baltic Sea.

Abstract.
Variations in year-class strength of perch (Perca fluviatilis L.) and pikeperch (Stizostedion lucioperca L.) were analyzed among 11 different Baltic populations from Finland, Estonia, Latvia, Lithuania and Sweden using age distributions and estimates of year-class strength from catches. Similar patterns in year-class strength appeared in perch populations from archipelago areas in the Northern Quark, Archipelago Sea and along the Swedish coast of the Baltic proper. This could be attributed to large-scale weather variations similarly influencing water temperature in similar habitats. Perch year-class stregth variations in the coastal waters of Estonia, Latvia and Lithuania also demonstrated a common pattern, although not as abvious. In general, it was not possible to relate these variations to temperature. The data fot this type of analysis was, however, weaker than for other areas. Also pikeperch demontrated different patterns in year-class strength variations between the Archipelago Sea and coastal populations in Estonia, Latvia and Lithuania. Two populations in the Gulf of Riga were similar in this respect but the one studied in Lithuania deviated. The analyses made showed that there were similarities in year-class strength variations of the two species in different parts and habitats of the coastal areas that are important to understand and use when evaluating monitoring data and making prognoses of stock size variations. It is suggested for the future that joint analyses and prognoses be performed for this purpose.