Hedgepeth J, Gallucci V F, Campos J, Mug M
BioSonics, 4027 Leary Way NW, Seattle, Washington 98107, USA.
Rev Biol Trop. 2000 Jun-Sep;48(2-3):371-87.
A stratified sampling design was used for a hydroacoustic survey of the inner parts of the Gulf of Nicoya in 1987 and 1988. The bottom topography of the inner Gulf was modeled by introducing the concept of a topographical basin model, as the basis for the projection of the sample survey estimates to the entire inner gulf. The bottom depth contours and volumes for the basin model were constructed from nautical charts. The estimates of sample abundance were made for the fish in the inner Gulf using the acoustic methods, EMS (Expectation Maximization and Smoothing) and echo integration. The estimates of population were made by the multiplication of the topographic model's estimate of water volume and a model of fish density dependent on bottom depth. The results showed a general decrease in fish density biomass with bottom depth, and a simultaneous tendency for maximum concentrations over bottom depths of about four meters. The four meter bottom depth includes a broad expanse of the inner Gulf located south of Isla Chira. Overall estimates of volumetric density (0.269 fish/m3) and of areal densities (1.88 fish/m2) are comparable to other estuarine shallow water environments.
1987年和1988年，在尼科亚湾内部进行的水声学调查采用了分层抽样设计。通过引入地形盆地模型的概念，对海湾内部的底部地形进行建模，以此作为将样本调查估计值推算至整个海湾内部的基础。盆地模型的底部深度等高线和体积是根据海图绘制的。利用声学方法、期望最大化与平滑法（EMS）和回波积分法，对海湾内部的鱼类样本丰度进行了估计。通过将地形模型的水体体积估计值与依赖于底部深度的鱼类密度模型相乘，得出了种群数量估计值。结果表明，鱼类密度生物量总体上随底部深度增加而下降，同时在底部深度约为4米处有出现最大浓度的趋势。4米的底部深度涵盖了位于奇拉岛以南的海湾内部大片区域。体积密度（0.269条鱼/立方米）和面积密度（1.88条鱼/平方米）的总体估计值与其他河口浅水环境相当。
