ABSTRACT

Īnanga (Galaxias maculatus) is a widespread freshwater fish, found around coastal New Zealand, Chatham Islands, southern Australia and southern South America, exhibiting both diadromous and land-locked life history patterns. We assessed population size structure, size at maturity, timing of reproduction, and post-reproductive survival in the Waikouaiti and Kakanui rivers, two regionally important G. maculatus populations in southern New Zealand. Size at maturity varied between rivers and sexes, with males generally maturing at smaller sizes than females. The timing of reproduction and recruitment was observed to vary across a relatively small spatial scale. Population length-frequencies indicated that both populations exhibited annual population dynamics, with most individuals spawning in their first year, then apparently dying soon afterwards (as indicated by a marked drop in post-spawning abundance). However, a few individuals with recently spent or resting gonads were present over the winter months, indicating some post-spawning survival. There was a lower frequency of exceptionally large (putatively 1+) individuals than reported for other populations around New Zealand and elsewhere, suggesting over-winter survival following spawning varies. Based on the variation in life history characters over small spatial scales, we suggest that management of regionally important G. maculatus populations should be based on catchment level information.

摘要

Īnanga ( Galaxias maculatus ) 是一种分布广泛的淡水鱼，分布于新西兰沿海、查塔姆群岛、澳大利亚南部和南美洲南部，表现出水产和内陆生活史模式。我们评估了 Waikouaiti 河和 Kakanui 河（两条区域性重要的G. maculatus）的种群规模结构、成熟期规模、繁殖时间和繁殖后存活率新西兰南部的人口。河流和性别之间的成熟尺寸有所不同，雄性成熟时的尺寸通常小于雌性。据观察，繁殖和补充的时间在相对较小的空间范围内有所不同。种群长度频率表明，两个种群都表现出年度种群动态，大多数个体在第一年产卵，然后显然很快就死亡（如产卵后丰度显着下降所示）。然而，一些性腺最近耗尽或处于休眠状态的个体在冬季出现，表明有一些产卵后的存活。与新西兰和其他地方报告的其他种群相比，异常大（推测为 1+）个体的频率较低，这表明产卵后的越冬生存率存在差异。G. maculatus种群应基于流域级别信息。