Atlantic Fisheries Research Document 1996/058
An evaluation of the acoustic backscatter of western Newfoundland herring with a comparison of classical statistics and geostatistics for the estimation of variance
By I.H. McQuinn; L. Lefebvre
Abstract
A hydroacoustic survey was conducted aboard the F.G. CREED in the fall of 1995 as part of a fishery-independent index of abundance for the west coast of Newfoundland herring stocks. Systematic-parallel transects were chosen along the coast and were surveyed during night-time hours. Biological sampling was accomplished in collaboration with the western Newfoundland large purse seine fleet, which also took temperature, salinity, and depth (STD) profiles. Raw volume backscatter data (Sv) from both 38 and 120 kHz transducers, as well as split-beam phase data were collected. The variances of the abundance estimates were estimated by two procedures: (1) using classical statistics, and (2) using geostatistics (1-D transitive and 2-D intrinsic kridging). The survey revealed that herring concentrations were spread out along the bottom throughout several strata, similar to the distribution found in 1993. The most important concentration, over 1/3 of the total biomass, was found off New Ferrole (stratum 10). The biomass was estimated at 84, 000 t, made up of 38, 000 t of spring spawners and 46,000 t of autumn spawners. Using classical statistics, the coefficient of variation (CV) on the biomass estimates ranged from 22.4 to 84.5% by strata. The estimated CV was significantly reduced using 1-D kridging, resulting in an overall CV for all strata of 16.6%. The estimated CV of 23.9% for stratum 10 using the 2-D kridging was also substantially lower than both the 1-D kridging (37.3%) and the classical statistics (59.6%).
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