Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Abstract

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9°C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8°C. Spawning occurred in shallow waters, at depths between 0.2-1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469-1829 m -2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.

Effects of Altered Offshore Food Webs on Coastal Ecosystems Emphasize the Need for Cross-Ecosystem Management

“…This is confirmed by small-scale experimental exclusion of larger fish and grazers, showing that declines in larger predators-by inducing a four level trophic cascade-increase filamentous algal growth with rates comparable to those caused by nutrient enrichment alone Sieben et al 2011b). Food competition and egg predation by the high abundances of stickleback may now even contribute to decreased recruitment success of perch and pike (Nilsson 2006;Ljunggren et al 2010), and potentially ''lock'' the coastal food web in an alternative, mesopredator-dominated regime. Thus, overfishing of offshore cod populations may have contributed to a shift in nearshore food web structure.…”

Pike (Esox lucius L.) on the edge: consistent individual movement patterns in transitional waters of the western Baltic

“…In most areas of the Baltic Sea including the Danish straits, commercial catches of pike have declined considerably since the 1970s-1980s suggesting a drastic population decrease (Nilsson et al, 2004;Nilsson, 2006;Lehtonen et al, 2009;Ljungren et al, 2010). Reasons for these declines in the different areas are not well determined, whether due to poor recruitment, habitat deterioration, eutrophication or other reasons.…”

Spawning population characteristics of pike Esox lucius L. in Lake Rubikiai (Lithuania)

“…The spawning period lasted until the end of April. Nilsson [38] investigated the spawning areas of pike along the Swedish coast of the Baltic Proper and noted that spawning peaked during the last week of April in streams and during the first week of May in brackish waters. Treasurer [39] reported that in two Scottish lakes, Kinord and Davan, the spawning of fishes occurred in the first two weeks of April.…”