Hanselman et at: Application of an acoustic-trawl survey design to improve estimates of rockfish biomass 
387 
Sv Color 
Scale (dli) 
sea floor 
Figure 6 
Acoustic backscatter observed (A) during patch detection and (B) after returning to a trawl location. The 
black vertical lines mark 100-m distance intervals, the orange vertical lines mark the distance sampled 
with the trawl, the thick black horizontal lines show the 10-m conformal integration window. 
and goodness of fit (coefficient of determination, r 2 ). The 
range of correlation for the S v measurements was larger 
(~13 km) than the range of correlation for the trawl 
densities (~8 km). The variogram for the trawl CPUE 
data had a relatively larger nugget, or unexplained mi- 
croscale variance, than the variogram for the S v data. 
Discussion 
The study area, Yakutat, and target species, POP, for 
our field study were chosen to increase the likelihood of 
obtaining a strong relationship between acoustic back- 
scatter and trawl CPUE. Several previous studies had 
observed relatively strong relationships for rockfishes 
between S v and trawl CPUE in the GOA (Krieger et al., 
2001; Hanselman and Quinn, 2004; Fujioka et ah, 2007), 
and the Yakutat area was known to have high rockfish 
abundance. Additionally, Hanselman and Quinn (2004) 
and Fujioka et ah (2007) showed that stratifying by 
acoustic backscatter or double sampling could improve 
precision of biomass estimates on the basis of data col- 
lected during previous ACS surveys for rockfishes and 
biennial NMFS GOA trawl surveys. The use of real-time 
processing of acoustic backscatter to determine patches 
was efficient, and POP were the most commonly caught 
species and were found in higher densities than other 
fishes at patch stations. However, the conditions that 
make the TAPAS design more efficient than random 
sampling, as shown in simulation studies (Spencer et 
ah, 2012), did not materialize in the fieldwork described 
here. 
For the TAPAS design to be more effective than SRS, 
the categorization of patch and background areas must 
show a correspondence with trawl CPUE (i.e., CPUE 
values consistently should be higher at the patch sta- 
tions than at the background stations). When this cor- 
respondence does not occur, the use of these categories 
does not improve the precision of biomass estimates 
and increases variability because the sizes of the patch 
