Spawning site selection by two galaxiid fishes, Galaxias anomalus and G. depressiceps, in tributaries of the Taieri River, South Island, New Zealand

Abstract

Recent studies have led to the recognition of Galaxias depressiceps and reinstatement of Galaxias anomalus. The two species maintain near allopatric distributions and it has been suggested that spawning habitat availability, at least partially, controls the distribution of these species. The spawning habitat of each species was determined and an assessment of the influence of spawning habitat availability on the distribution of the two species was carried out. Factors that may have influenced the onset of spawning were also examined. We found that G. depressiceps selected spawning sites with a high proportion of boulder substrata and nests were found on the underside of or between boulders. G. anomalus spawned within the streambed substrata, under boulders or cobbles, in shallow water and narrow channels relative to the available habitat. Suitable boulder spawning substratum for G. depressiceps in the G. anomalus sites was limited and this supports the hypothesis that spawning habitat availability influences G. depressiceps distribution. Conversely G. anomalus spawning habitat was available in G. depressiceps streams, indicating that spawning habitat limitations are not restricting G. anomalus. The onset of spawning, for both species, did not appear to be related to daylight, phase of the moon, or stream water level, but all species started spawning as water temperatures rose. The proximity of G. anomalus spawning sites to the stream edge and their occurrence in poorly consolidated substrata presents two management issues. Water abstraction may expose spawning sites if stream water levels are lowered, and these sites are vulnerable to trampling by stock.