Partial migration of a maraena whitefish Coregonus maraena population from the River Elbe, Germany

M Gerson,A Klügel,V Sarrazin,R Thiel,L Marohn,J Dierking

doi:10.3354/esr01102

Abstract

The maraena whitefish Coregonus maraena is a threatened anadromous species in the North Sea, which in the past was decimated to near extinction. Since the late 1980s, several re-establishment programs have been implemented in rivers draining into the North Sea, but the scientific basis for sustainable conservation measures is often lacking, since little is known about the biology of this species. In this study, otolith microchemistry of fish ranging from 24.6 to 58.4 cm in total length (median 31.3 cm, SD 8.4 cm) was used to characterize the migration behavior of a reintroduced population of maraena whitefish from the River Elbe, Germany. Our analyses revealed the presence of 3 different migration patterns: (1) one-time migration into high-salinity habitat (North Sea) within the first year of life (29.6%), (2) multiple migrations between low- and high-salinity habitats starting in the first year of life (14.8%) and (3) permanent residency within low-salinity habitats, a pattern displayed by the majority (55.6%) of sampled individuals. Not only do these results reveal differential migration behavior, but they also indicate that permanent river residency is common in the River Elbe population of C. maraena. The role of the Elbe as both a feeding and a spawning habitat should thus be considered more explicitly in current conservation measures to support recovery of this species.

Highlights

A major threat for diadromous fish species is habitat alteration, which includes physical and chemical barriers that block natural migration routes, and causes the direct loss of freshwater habitat for spawning or nursery
The study area was located in the lower River Elbe between Hamburg and Cuxhaven in northern Germany (Fig. 1)
Opercula were removed for subsequent age determination

Summary

Introduction

A major threat for diadromous fish species is habitat alteration, which includes physical and chemical barriers that block natural migration routes, and causes the direct loss of freshwater habitat for spawning or nursery (de Groot 2002, Limburg & Waldman 2009). As most diadromous species are of commercial importance, fishing is a contributing factor to the decline of many species (Limburg & Waldman 2009). These threats apply to both anadromous species migrating. Since the consideration of houting in the North Sea is not limited to the possibly extinct species C. oxyrinchus, but rather to the North Sea population of C. maraena (Bloch 1779) or a previously undescribed species (Kottelat & Freyhof 2007), we use the scientific name C. maraena instead of C. oxyrinchus following Mehner et al (2018). Whether whitefish populations from the North Sea should be considered a separate species from those in the Baltic Sea is still subject to scientific discussions There is evidence that the extant form of whitefish from the North Sea should be classified as a separate evolutionarily significant unit for conservation purposes, independent of the actual species status (Dierking et al 2014)

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