Lopez et al.: A model for estimating biomass of fish species associated with fish aggregating devices 
175 
jD 
< 
Manufacturer's 
New method 
Figure 6 
Error variability when converting acoustic backscatter into bio- 
mass by two different methods analyzed in the present work: the 
manufacturer’s original method and the GAM corrected biomass 
estimations obtained with the new method developed in this study. 
Acoustic data and real catches were collected by a commercial 
Spanish purse seiner in the central and eastern Atlantic Ocean 
between 2009 and 2011 to illustrate the use of the new method. 
Black dots are outlier points. The box show the quartiles, with the 
bars extending to the most extreme data point which is no more 
than ±1.5 the interquartile range. The heavy line across the box 
is the median. 
The new remote-target classification method opens 
a broad range of future lines of research in the area 
of FAD-related fish ecology and behavior. Because the 
model can group species, every acoustic sample given 
by the buoy could return specific biomass-index esti- 
mates for nontuna and tuna species. This raises the 
possibility of computing a wide range of statistical and 
mathematical analyses by fish group, such as modeling 
environmental preferences of each species and groups 
or estimating fish biomass fluctuations in relation 
to FAD trajectories, time of the day or soaking time, 
among other variables. 
One of the most interesting and promising lines of 
investigation derived from this study is the possibility 
of obtaining fisheries-independent indices of relative 
abundance for tuna and nontuna species, a major and 
urgent challenge that would certainly complement cur- 
rent data on target and nontarget species populations. 
Significant effort has been recently conducted by fish- 
eries scientists in this field, who have started to design 
the first promising steps to carry out this kind 
of study (Capello et al. 14 ; Santiago et al. 15 ). 
Sustainable fishing practices with echosounder 
buoys 
Nontuna biomass data provided by the new 
method, when validated by observational data 
in the specific regions of interest, may have at 
least two different applications for conserva- 
tion issues. First, nontuna-to-tuna biomass ra- 
tios can be remotely estimated, helping fishing 
crews to avoid setting on undesirable DFADs 
with a high proportion of nontarget individuals. 
As Dagorn et al. (2012) suggested, the smaller 
the nontuna-to-tuna ratio, the lower are the 
impacts on nontarget species. In this context, 
echosounder buoys may contribute, from virtu- 
ally unlimited distances, to the selection of the 
best DFAD to fish from a conservation point of 
view. Fishermen could benefit by saving fuel 
and time, optimizing their effort, catch and 
profits, by carefully planning their FAD-fishing 
routes in advance. Second, potential nontuna 
hotspots could be discovered, which could aid 
setting conservational measures, such as tem- 
poral or permanent marine protected areas or 
DFAD closures, if necessary. Hotspots obtained 
by this approach should be ground-truthed 
to those found through analysis of observer 
data, keeping in mind that the information of 
observers is based on fishing operations and 
hence, limited by fishing effort and fishing cov- 
erage constraints. Both sources of information 
should be, therefore, complementary. Although 
the nontuna biomass given by this study has 
not been specifically validated due to a lack of 
scientific biological sampling during the fish- 
ing operations used for testing the model, the 
results seem to be in accordance with values 
found by unpublished studies in the Atlantic Ocean 
(Amande 13 ). Future studies should take into account 
more detailed information on species composition (e.g., 
observers’ data) to better understand the performance 
capability of this new method, especially in relation to 
nontuna species. 
It is important to note that the original idea of this 
article was to include tuna size in the biomass estima- 
tion models, which would provide interesting informa- 
14 Capello, M., J.-L. Deneubourg, M. Robert, K. Holland, K. 
Schaeffer, and L. Dagorn.. 2013. A new fisheries indepen- 
dent method to estimate abundances of tropical tunas. In- 
dian Ocean Tuna Commision (IOTC). Working Party Tropi- 
cal Tuna ( WPTT) IOTC-2013-WPTT15-12, 30 p. [Available 
at website.] 
15 Santiago, J., J. Lopez, G. Moreno, H. Murua, I. Quincoces, 
and M. Soto. 2015. Towards a tropical tuna buoy-derived 
abundance index (TT-BAI). International Council for the 
Conservation of Atlantic Tunas (ICCAT) SCRS/2015/90, 12 p. 
ICCAT, Corazon de Maria, 8, 28002 Madrid, Spain. 
