Assessment of natal origin of pike (Esox lucius) in the Baltic Sea using Sr:Ca in otoliths

Abstract

Spawning habitat of pike (Esox lucius) in the Baltic Sea include brackish water bays, brooks and rivers. Elevated salinity concentrations are one of several stressors that might increase the use and importance of freshwater habitats for spawning. In the Baltic Sea, one of the largest brackish seas in the world, freshwater species like pike, perch (Perca fluviatilis), whitefish (Coregonus sp), bream (Abramis brama), ide (Leuciscus idus), roach (Rutilus rutilus) and burbot (Lota lota) all undertake spawning migrations to freshwater. However, over the last decades populations densities of these species have declined, and recruitment failure has been argued to be at least part of the problem. The importance of brooks and rivers as spawning areas for these species have not been quantified and set in relation to spawning success in brackish bays. In this study, we collected 175 adult pike (Esox lucius) on their foraging grounds in the sea. Fish were collected in two regions on the Baltic coast, more than 600 km apart. Subsequently we determined their origin (freshwater or marine) using otolith chemistry. Sagittal otoliths were analysed for strontium using the PIXE-method. The results show that 80 of the 175 pike were recruited in freshwater, and several of the larger specimens showed reoccurring migration behaviour. Data show that freshwater is an important recruitment habitat for Baltic Sea pike, suggesting that habitat improvements in rivers entering the Baltic Sea might significantly contribute to population restoration.

Life history of anadromous burbot (Lota lota, Linneaus) in the brackish Baltic Sea inferred from otolith microchemistry

“…Although widespread in salmonids (e.g., Thorpe 1994), it is only recently when such examples amongst nonsalmonid fish have emerged (Daverat et al 2006(Daverat et al , 2012Feutry et al 2012). Similar results are also reported for pike from the Baltic Sea (Engstedt et al 2010;Rohtla et al 2012). Similar results are also reported for pike from the Baltic Sea (Engstedt et al 2010;Rohtla et al 2012).…”

Temporally stable, weak genetic structuring in brackish water northern pike (Esox lucius) in the Baltic Sea indicates a contrasting divergence pattern relative to freshwater populations

“…Rather, the differences likely reflect true dissimilarities in gene flow between the two types of pike. Anadromous populations of Baltic pike have been demonstrated to exhibit homing behavior to a limited number of creeks and outlets for spawning, creating isolated populations similar to those of salmonids and coregonids (Engstedt et al 2010;Dierking et al 2014). As a contrast, gene flow in brackish spawning pike might be higher because of a more continuous dispersal of suitable spawning grounds in coastal waters without obvious geographic barriers.…”

“…A proportion of the feeding population of pike in the Baltic Sea spawn in brackish coastal areas (Müller and Berg 1982;Westin and Limburg 2002;Engstedt et al 2010), where fewer barriers to dispersal and gene flow appear to occur. Earlier tagging studies indicate a high degree of philopatry in pike both in freshwater habitats (Miller et al 2001) and in the Baltic Sea (Karås and Lehtonen 1993).…”

Essential fish habitats (EFH)

“…Otolith Sr:Ca profiles were used to determine the hatching biome. Regarding adult pike, 90% hatched in freshwater and only 10% in brackish water (Rohtla et al 2012), which may be compared with results from the Swedish waters, where 45% hatched in freshwater and 55% in brackish water (Engstedt et al 2010). In another study from southern Sweden, no pike hatched in brackish water (Olsson et al 2013b).…”