Spatially explicit estimates of length and biomass of Micromesistius poutassou (Blue Whiting) from acoustic and trawl surveys in the North-East Atlantic in May 2004@en

Acoustic estimates of herring and blue whiting abundance were obtained during the surveys using the Simrad ER60 scientific echosounder. The allocation of NASC-values to herring, blue whiting and other acoustic targets were based on the composition of the trawl catches and the appearance of echo recordings. To estimate the abundance, the allocated NASC -values were averaged for ICES-squares (0.5° latitude by 1° longitude). For each statistical square, the unit area density of fish (rA) in number per square nautical mile (N*nm-2) was calculated using standard equations (Foote et al., 1987; Toresen et al., 1998). To estimate the total abundance of fish, the unit area abundance for each statistical square was multiplied by the number of square nautical miles in each statistical square and then summed for all the statistical squares within defined subareas and over the total area. Biomass estimation was calculated by multiplying abundance in numbers by the average weight of the fish in each statistical square then summing all squares within defined subareas and over the total area. The Norwegian BEAM soft-ware (Totland and Godø 2001) was used to make estimates of total biomass.本次调查采用Simrad ER60科学回声测深仪（Simrad ER60 scientific echosounder）获取了鲱鱼与蓝鳕资源量的声学评估数据。基于拖网渔获物组成及回声记录特征，将NASC值（Nautical Area Scattering Coefficient，单位面积散射系数）分配至鲱鱼、蓝鳕及其他声学目标体。为估算资源量，对国际海洋考察理事会（ICES）海区格网（单格规格为0.5°纬度×1°经度）内分配得到的NASC值求取平均值。针对每个统计格网，采用标准公式（Foote等，1987；Toresen等，1998）计算得到以尾/平方海里为单位的鱼类单位面积密度（rA）。为估算总资源量，将各统计格网的单位面积资源量乘以该格网对应的平方海里数，随后在划定的子区域及全研究区域范围内对所有统计格网的结果进行求和。生物量估算则通过将资源量数值与各统计格网内鱼类的平均体重相乘，再在划定的子区域及全研究区域范围内对所有格网的计算结果求和得到。本研究使用挪威BEAM软件（Totland与Godø，2001）完成总生物量的估算工作。