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

Abstract

Pike in the western Baltic Sea live on the edge of their salinity tolerance. Under physiologically challenging conditions, organism may respond by moving to environmentally more benign areas during critical periods, such as during spawning. We hypothesised that pike in a brackish lagoon (8-10 ppt salinity) would perform spawning-and feeding-related movements between areas with different salinity regimes. Twenty-two pike were caught prior to spawning, tagged with acoustic transmitters, and their movements were tracked for 18 months. Pike showed two main patterns of movements that were consistent within individuals across two years. Whereas some individuals stayed in the lagoon year-round, most pike left the lagoon for longer periods after spawning and returned to the lagoon prior to following year's spawning season. We found no evidence that probability of moving out of the lagoon co-varied with either length or condition factor. Despite the fact that the lagoon's salinity is close to the reported upper limit for pike egg development, results indicated that all pike spawned in the lagoon. Correspondingly, genetic data showed that all fish belonged to the same reproductive population unit. Movement patterns thus appear to reflect individual variation in home-range and/or resource optimisation following ideal free principles.

Using otolith microchemical analysis to investigate the importance of brackish bays for pike (Esox lucius Linnaeus, 1758) reproduction in the southern Baltic Sea

“…In the Mecklenburg‐Vorpommern coastal area, commercial catches of pike declined from a mean of 172 t/year in the early 1990s to 90.4 t/year in the last five years (Mecklenburg‐Vorpommern State Office for Agriculture, Food safety and Fishery). This decrease is not a local effect: similar negative trends could be observed in several other Baltic Sea areas (Jacobsen et al, ; Jørgensen et al, ; Lehtonen, Leskinen, & Selen, & Reinikainen, ; Nilsson, Andersson, Karås, & Sandström, ). Potential reasons for this decline include anthropogenic factors like eutrophication (Casselman & Lewis, ), overfishing and recruitment failures due to the disappearance of potential spawning areas (Nilsson, Engstedt, & Larsson, ).…”

“…This decrease is not a local effect: similar negative trends could be observed in several other Baltic Sea areas (Jacobsen et al, 2017;Jørgensen et al, 2010;Lehtonen, Leskinen, & Selen, & Reinikainen, 2009;Nilsson, Andersson, Karås, & Sandström, 2004). Potential reasons for this decline include anthropogenic factors like eutrophication (Casselman & Lewis, 1996), overfishing and recruitment failures due to the disappearance of potential spawning areas (Nilsson, Engstedt, & Larsson, 2014).…”

“…The life history profiles of the examined pike show various sharp Sr:Ca increases and decreases. These changes can either be caused by movements between areas with different salinity regimes (Jacobsen et al, ) or by salinity changes of the ambient water (see Figure ) due to saltwater inflows from the open Baltic Sea.…”

“…Pike ( Esox lucius ) are common top predators in freshwater streams and lakes all over Europe. Previous studies, however, show that juvenile and adult specimens tend to migrate into adjacent brackish coastal water areas of the Baltic Sea with an upper salinity limit of 10–12 PSU and that pike can temporarily deal even with salinities up to 14–15 PSU (Jacobsen et al, ; Raat, ). The Baltic Sea is one of the largest bodies of brackish waters in the world and the water salinity of south‐western Baltic may sometimes exceed the upper salinity tolerance of pike, but there are several lagoons and coastal inlets along the German coastline, which pike can inhabit because of their mesohaline conditions between 5 and 10 PSU (Figures & ).…”

Vertical movements of coastal pike (Esox lucius)—On the role of sun basking

“…Studies addressing diel movements of pike have hitherto focused on horizontal movements (Baktoft et al, 2012;Jacobsen et al, 2017;Jepsen, Beck, Skov, & Koed, 2001;Kobler, Klefoth, Wolter, Fredrich, & Arlinghaus, 2008;Vehanen, Hyvärinen, Johansson, & Laaksonen, 2006), and there are no studies on diel vertical migrations (indicative of a basking behaviour; but see Pierce, Carlson, Carlson, Hudson, & Staples, 2013) and few on thermoregulation of pike. Furthermore, pike shows natal homing behaviour (Engstedt, Engkvist, & Larsson, 2014) and it is a repeat spawner which makes it possible to tag fish with data storage tags during spawning and then retrieve tags the following years during spawning at the same location.…”