Comparison of the effects of two bongo net mesh sizes on the estimation of abundance and size of Engraulidae eggs

Abstract Studies of ichthyoplankton retention by nets of different mesh sizes are important because they help in choosing a sampler when planning collection and the establishment of correction factors. These factors make it possible to compare studies performed with nets of different mesh sizes. In most studies of mesh retention of fish eggs, the taxonomic identification is done at the family level, resulting in the loss of detailed information. We separated Engraulidae eggs, obtained with 0.333 mm and 0.505 mm mesh bongo nets at 172 oceanographic stations in the southeastern Brazilian Bight, into four groups based on their morphometric characteristics. The difference in the abundance of eggs caught by the two nets was not significant for those groups with highest volume, types A and B, but in type C (Engraulis anchoita), the most eccentric, and in type D, of the smallest volume, the difference was significant. However, no significant difference was observed in the egg size sampled with each net for E. anchoita and type D, which exhibited higher abundance in the 0.333 mm mesh net and minor axis varying from 0.45-0.71 mm, smaller than the 0.505 mm mesh aperture and the mesh diagonal.

摘要：针对不同网目尺寸网具对鱼卵仔鱼（ichthyoplankton）的滞留特性研究至关重要，可辅助采样规划阶段的采样器选型，并助力校正因子的建立；这些校正因子能够使不同网目尺寸网具开展的相关研究具备可比性。在多数鱼类鱼卵网目滞留率研究中，分类鉴定仅进行至科级阶元，导致详细分类信息丢失。本研究以在巴西东南部湾（Brazilian Bight）172个海洋观测站位使用0.333 mm与0.505 mm网目尺寸的邦戈网（Bongo nets）采集的鳀科（Engraulidae）鱼卵为研究对象，依据其形态计量特征将其划分为四组。对于体积最高的A、B两组鱼卵，两种网具捕获的丰度差异不显著；但对于最具偏倚性的C型（Engraulis anchoita）以及体积最小的D型，二者捕获的鱼卵丰度差异显著。不过，针对E. anchoita与D型鱼卵的采样尺寸，两种网具未观测到显著差异；该两类鱼卵在0.333 mm网目尺寸网具中的丰度更高，其短轴范围为0.45~0.71 mm，小于0.505 mm的网目孔径（mesh aperture）与网目对角线（mesh diagonal）尺寸。