Spatially explicit estimates of length and biomass of Clupea harengus (Norwegian spring spawning herring) from acoustic and trawl surveys in the North-East Atlantic in May 2005@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.本研究在声学调查作业期间，使用Simrad ER60科学回声测深仪获取了鲱鱼与蓝鳕资源量的声学估算数据。将航海面积散射系数（Nautical Area Scattering Coefficient，简称NASC）值分配至鲱鱼、蓝鳕及其他声学目标的依据为拖网渔获物组成与回声记录的形态特征。为估算资源量，对国际海洋考察理事会（International Council for the Exploration of the Sea, ICES）方格（0.5°纬度×1°经度）内的分配后NASC值求取平均值。针对每个统计方格，采用标准公式（Foote等，1987；Toresen等，1998）计算鱼类单位面积密度（rA），单位为每平方海里尾数（N·nm⁻²）。为计算鱼类总资源量，先将每个统计方格的单位面积资源量乘以该方格对应的平方海里面积，随后对划定亚区及全海域内的全部统计方格进行求和。生物量估算则通过将各统计方格内的资源尾数乘以对应方格的鱼类平均体重，再对划定亚区及全海域内的全部统计方格求和得到。本次研究采用挪威开发的BEAM软件（Totland与Godø，2001）完成总生物量估算。