Contrasting Patterns of Larval Recruitment in River–Lake Systems in Migratory and Nonmigratory Galaxias Species

Abstract

Many aspects of the ecology, life history and distribution of fishes differ between their larval and adult life-history stages. Identifying the critical habitats and migration pathways required by each life cycle stage is crucial for effective conservation and ecological management. Using microchemical analysis of otoliths, we examined the influence of larval habitat and migration on the composition and population structure of migratory and nonmigratory Galaxias species collected from tributaries upstream of inland lakes and streams lacking downstream lake connections in the Waitaki River basin, New Zealand. Larval (core) and adult (edge) layers of each individual otolith were analysed to compare otolith trace signatures formed during larval and adult life-history stages. The results revealed considerable variation between larval and adult otolith chemical signatures of migratory (Galaxias brevipinnis) species. Classification analysis indicated that populations of G. brevipinnis upstream of each lake shared a common larval habitat, most likely the lake, with 100% of individuals from each lake-riverine system having larval signatures that were distinct from adult signatures. In contrast, relatively consistent patterns of elemental concentrations were detected across the otoliths of nonmigratory species suggesting both their larval and adult life-history stages had occurred in the same stream from which the adults were collected. These findings provide a framework for understanding how larval-rearing environments can influence the distribution of stream fish across the landscape. Furthermore, identifying the source of recruits can help to improve conservation efforts to protect naturally land-locked populations of G. brevipinnis.