Management of a pikeperch stock in a long-term biomanipulated stratified lake: efficient predation vs. low recruitment

Abstract

Pikeperch is an efficient predator in the pelagic zone of eutrophic and hypertrophic lakes and has, therefore, been used in several biomanipulation projects. Pikeperch stocking has also been part of the manipulation strategy in Feldberger Haussee, Germany. From 1996 to 1999, population development, growth and diet composition of pikeperch in Feldberger Haussee were studied. From 1996 to 1998, the population was dominated by two cohorts. Only in years with warm summers, recruitment from 0+ fish to older age-classes was successful. It appears likely that due to the relatively high depth of the lake the spawning period is delayed as a result of a slower temperature increase in spring. Therefore, 0+ pikeperch cannot benefit from the spring maximum of the zooplankton. This may be the reason for the slow growth and consequently, hampers the switch to piscivory for the majority of 0+ pikeperch. However, after becoming piscivorous, the pikeperch showed a reasonably good growth. Predation was mainly directed towards roach and 0+ perch, the major planktivores. The results of the present study confirm the role of pikeperch as an efficient predator of zooplanktivorous fish in open-water dominated lakes. Yet, it is suggested that the probability of successful recruitment of pikeperch in deeper, stratified lakes is reduced. Therefore, stable self-sustaining pikeperch populations cannot be expected in such lakes and regular stocking measures may be necessary even if a potential spawning stock exists.