Spatially explicit estimates of length and biomass of Micromesistius poutassou (Blue Whiting) from acoustic and trawl surveys in the North-East Atlantic in May 2009

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.

本调查依托Simrad ER60科学回声测深仪开展，获取了鲱鱼与蓝鳕资源量的声学评估数据。研究人员依据拖网渔获物组成与回声记录特征，将NASC值分配至鲱鱼、蓝鳕及其他声学目标类别。为估算资源量，研究人员对完成分配的NASC值在国际海洋考察理事会（ICES）统计海区（纬度0.5°×经度1°）内取平均值。针对每个统计海区，研究人员采用标准公式（Foote等，1987；Toresen等，1998），计算得到以尾/平方海里为单位的鱼群单位面积密度（rA）。为估算总鱼群资源量，研究人员将每个统计海区的单位面积资源量乘以该海区的平方海里面积，随后对划定亚区内及全区域内所有统计海区的结果进行求和汇总。生物量估算则通过将每个统计海区的鱼群尾数密度与该海区鱼类平均体重相乘，随后对划定亚区内及全区域内所有统计海区的结果求和汇总得到。本研究采用挪威开发的BEAM软件（Totland与Godø，2001）完成总生物量的估算工作。