Spatially explicit estimates of length and biomass of Micromesistius poutassou (Blue Whiting) from acoustic and trawl surveys in the North-East Atlantic in May 2007

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.本研究在声学调查期间，依托西姆拉德ER60科学回声测深仪（Simrad ER60 scientific echosounder）获取了鲱鱼与蓝鳕的资源量声学估算结果。鲱鱼、蓝鳕及其他声学目标对应的NASC值（NASC-values）分配依据为拖网渔获组成与回声记录特征。为估算总资源量，先对国际海洋考察理事会分区（ICES-squares，纬度0.5°×经度1°）内的分配后NASC值求取平均值。针对每个统计分区，采用标准公式（Foote等，1987；Toresen等，1998）计算得到以每平方海里尾数（N·nm⁻²）为单位的鱼类单位面积密度（rA）。总资源量估算流程如下：将每个统计分区的单位面积资源量乘以该分区对应的平方海里面积数，随后在划定的子区域及全海域范围内，对所有统计分区的计算结果进行求和。生物量估算则通过将尾数资源量与各统计分区内鱼类的平均体重相乘，再在划定的子区域及全海域范围内对所有分区的结果求和得到。本研究使用挪威BEAM软件（Norwegian BEAM software，原文笔误为soft-ware）完成总生物量的估算工作。