Ecologia Char

Ecology of Freshwater Fish 2009: 18: 41–51 Printed in Malaysia Æ All rights reserved

Ó 2008 The Author Journal compilation Ó 2008 Blackwell Munksgaard

ECOLOGY OF FRESHWATER FISH

Char ecology. Natal homing in sympatric populations of anadromous Arctic char Salvelinus alpinus (L.): roles of pheromone recognition
Nordeng H. Char ecology. Natal homing in sympatric populations of anadromousArctic char Salvelinus alpinus (L.): roles of pheromone recognition. Ecology of Freshwater Fish 2009: 18: 41–51. Ó 2008 The Author. Journal compilation Ó 2008 Blackwell Munksgaard Abstract – This study revealed that progeny of sympatric Salangen Arctic char, omitted from any kind of imprinting to home water, returned with high precision to the home river and parental locality upon releases intheir native marine environments. Fish did not select river randomly, and the homing precision was the same for progeny whether fertilized in home stream or in foreign water. The progeny studied originate from the lake Øvervatnet and the Salangen River population and were hatched and reared at a hatchery at Voss in southern Norway. Experimental material comprised freshwater resident and smolt releasedfrom parr directly. The freshwater resident is partly anadromous exhibiting about 74% smolt when released directly into the sea. Char at all stages (resident, transformed resident, and smolt released from parr directly) returned in significant numbers to the home river system and the site of the specific parental population.
Hans Nordeng
Department of Biology, University of Oslo, Oslo, NorwayKey words: Arctic char; brown trout; salmon; homing; pheromones Hans Nordeng, Department of Biology, University of Oslo, P.O.Box 1066 Blindern, NO-0316 Oslo, Norway; e-mail: postmottak@bio.uio.no Accepted for publication May 30, 2008

Introduction

Anadromous salmonids are famous for their ability to home from feeding areas to spawn at their birthplace in their natal stream. The hypotheses(over the years 1599–1964) and the underlying principles that explain this sensational phenomenon are reviewed in Nordeng (1989b). Two of these hypotheses related to homing and olfaction have been and are still relevant in research, management and commercial aquaculture activities with genetically manipulated salmon (compare with Sattaur 1989). The imprinting hypothesis (single or sequential) holdsthat homing depends on recognition of specific stream odours that were learned and imprinted during the juvenile stage (Hasler & Wisby 1951), or rather learned sequentially as the smolt moves downstream to the sea (Harden Jones 1968, p.265). Homeward orientation in the sea was earlier proposed to be true navigation by means of celestial bodies or the earth’s doi: 10.1111/j.1600-0633.2008.00320.xmagnetic field (Hasler 1966; Quinn 1982; compare with Braemer 1960) or navigation based on a crude inherited map sense (Hansen et al. 1993; Hansen & Quinn 1998). This implies that at any given moment the fish must ‘know’ its position in the sea relative to the river of origin. The pheromone hypothesis (Nordeng 1971, 1977), on the other hand, states that the entire homeward migration is initiated anddirected by pheromone trails derived from related smolt descending almost continuously from their respective freshwater home localities to the sea during spring and summer. Pheromones are substances secreted by one individual and received by a second one of the same species in which they exert a specific reaction (Karlson & Luscher 1959; Stabell 1984). With respect to local ¨ orientation, fish thathome by the ‘imprinting line’ respond to specific water quality, leading it to a definitive environment, while fish that home by the ‘pheromone line’ respond innately to population 41

Nordeng specific pheromones, leading them to their riverine population – irrespective of water quality (Nordeng 1989a). The two hypotheses differ with regard to the odours that identify home and with regard to...