The mechanism of retention of pelagic tomcod, Microgadus tomcod, larvae and juveniles in the well-mixed part of the St. Lawrence Estuary
The mechanism of retention of pelagic tomcod, Microgadus tomcod, larvae and juveniles in the well-mixed part of the St. Lawrence Estuary
复制标题
圣劳伦斯河口混合部分中上层真鳕、小真真鳕、幼虫和幼鱼的滞留机制
DOI：
10.1007/bf00001186
复制
发表时间：
1990
影响因子：
1.4
通讯作者：
J. Dodson
中科院分区：
文献类型：
--
作者：
R. Laprise;J. Dodson
我们验证了这样一种假说，即在圣劳伦斯河口混合良好的部分，鳕鱼、小鳕鱼、仔鱼和仔鱼的滞留机制类似于同域鱼种，它们在涨潮时活跃地迁移到水面，在退潮时活跃地迁移到海底，从而使下游净移位减少到最小。1986年6月和7月，在两个锚点站的两个98h采样序列中，记录了鳕鱼仔稚鱼的垂直分布。考虑到白天在表层水域避网的情况下计算的水柱中鱼类质心的每小时指数表明，鳕鱼在水柱中仍然很深，它们在河口顶部的积累是净剩余环流的被动上游运输的结果，而不是主动的潮汐迁徙。对于这两个系列，鱼的深度与水的密度呈负相关，这表明鱼的浮力影响了它们的垂直分布。鳕鱼幼体和幼体受到潮流的影响。6月份，在低静水中发现了较大的幼虫，表明它们位于较小幼虫的上游。在7月份，较大的幼鱼位于较小幼鱼的下游，低静水和高静水之间的平均长度差达到20毫米。个体发生浮力的变化可能是造成这些差异的垂直分布的原因。在相同的水动力条件下，对在同一区域保留的鳕鱼和鳕鱼的早期生活史阶段的比较表明，在一个混合良好的河口，不止一种机制允许保留，所观察到的特定物种的垂直分布模式不能简单地解释为适应保留。
We tested the hypothesis that the mechanism of retention of tomcod,Microgadus tomcod, larvae and juveniles in the well-mixed part of the St. Lawrence Estuary is similar to that of sympatric smelt,Osmerus mordax, larvae who actively migrate to the surface during flood tides and to the bottom during ebb tides so as to minimize net downstream displacement. The vertical distribution of tomcod larvae and juveniles was documented during two 98-h sampling series at 2 anchor stations in June and July, 1986. An hourly index of the center of mass of fish in the water column calculated to take into account daytime net avoidance in surface waters suggested that tomcod remained deep in the water column and that their accumulation at the head of the estuary was the result of passive upstream transport by net residual circulation rather than active tidal migrations. For both series, depth of fish was inversely related to density of the water suggesting that the buoyancy of fish influenced their vertical distribution. Tomcod larvae and juveniles were advected by tidal currents. In June, larger larvae were found at low slack water indicating that they were located upstream of smaller larvae. In July, larger juveniles were located downstream of smaller juveniles, the difference in mean length between low and high slack water attaining 20 mm. Ontogenetic buoyancy changes may be responsible for these differences in the vertical distribution of tomcod. Comparisons of the early life-history stages of tomcod and smelt retained in the same area under the same hydrodynamical conditions indicate that more than one mechanism permits retention in a well-mixed estuary and that the observed species-specific patterns of vertical distribution are not simply interpretable as adaptations to retention.