Effects of mass fish removal on coregonid larval abundance in a large mesotrophic lake
Urpanen, O.; Keskinen, T.; Marjomäki, T.J.; Sakomaa, V.; Salo, H.; Syrjänen, J.; Viljanen, M.; Karjalainen, J.
It has been proposed that perch populations can regulate the size of vendace (Coregonus albula (L. )) stocks due to predation and prevent the recovery of stocks by prolonging the low stock phase. Thus, the impacts of a mass fish removal on the densities of vendace and whitefish (C. lavaretus L. s. l. ) larvae were examined in a mesotrophic Finnish lake (area 4600 ha) with a Beyond BACI design with four control lakes. The goal of the mass removal was to improve coregonid stocks. Total biomass of fish removed was about 428 tons (33 kg ha-1) during four intensive fishing years (2001–2004). Major proportions of fish removed were roach (Rutilus rutilus) (46%) and perch (Perca fluviatilis) (24%). Newly hatched coregonid larvae densities were estimated for three years before and six years after the beginning of fishing. Regardless of slight increases in larval vendace densities, no significant differences in larval densities between study periods were found. This study confirmed previous results, but did not produce any new support for the perch predation hypothesis. The fish removal may not have been sufficiently high or the fishing period may have not been long enough to strengthen the very low spawning stock and affect the density of larval coregonids.