Vollen and Albert: Pelagic behavior of adult Reinhardtius hippoglossoides 
467 
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Length group (cm) Length group (cm) Length group (cm) 
Figure 10 
Prey composition by 5-cm length groups of Greenland halibut ( Reinhardtius hippoglossoides) 
from bottom trawl, all periods combined. Bubble size is proportional to percentage composition 
by numbers (%N), weight (%W), and frequency of occurrence (%FO). Number of stomachs with 
contents is given above left panel. 
The abundance of Greenland halibut in bottom trawl 
was highest between 500 and 800 m, and the species 
was virtually absent below 1000 m. Figure 11 also 
shows that the backscatter from the 10-m high bot- 
tom-zone almost disappeared below 500 m depth, when 
Greenland halibut, which does not have a swim-bladder 
and thus a very low target-strength, dominated almost 
completely over all other fish species. Above 500 m, blue 
whiting and several demersal species were numerous, 
whereas Greenland halibut catches were near zero. 
Discussion 
Greenland halibut caught in pelagic waters ranged in 
length from 41 to 84 cm, which is within the same range 
as that found for those caught on the bottom. This is 
in contrast to a study by Jprgensen (1997), who found 
that although one- and two-year-old Greenland halibut 
from West Greenland nursery areas were found in high 
abundance in pelagic waters, larger fish (>52 cm) were 
not found in the pelagic zone of the area inhabited by 
adult fish. However, Jprgensen commented that the 
pelagic occurrence of larger specimens may have been 
underestimated if these fish were able to avoid the 
pelagic trawl. Support for the ability of large individu- 
als to avoid bottom trawls has subsequently been noted 
(Albert et ah, 2003). 
The influence of gear selectivity processes was ap- 
parent in length-frequency distributions of catches 
from demersal longlines and bottom trawls — distribu- 
tions that closely resembled those found by Huse et 
al. (1999). The results from trawl catches indicated 
that small individuals were present on the bottom 
even though these fish were not caught by demersal 
longlines. The reason for this could be that the com- 
mercial longlines used in the experiment targeted 
large individuals by factors such as hook- and bait- 
size, which are important in the size-selectivity of 
longlines (Bjordal and Lpkkeborg, 1996). Also, dif- 
ferences in swimming speed and in the competitive 
ability between small and large fish may impart a 
selection bias, bringing a relatively high proportion of 
large individuals into contact with the gear (Bjordal 
and Lqkkeborg, 1996). Therefore, because small fish 
were common in pelagic longline catches, this may 
imply that these fish were more abundant than catch 
rates indicated. 
The depth recordings from archival tags supported 
the findings from vertical longline results. The re- 
cordings showed periods of distinctly different verti- 
cal activity, both on a small scale (diurnal) and large 
scale (typically several weeks). Although the depth-re- 
cordings bore no information about the distance from 
the sea floor, it seems reasonable to assume that the 
high vertical activity periods were associated, at least 
partly, with pelagic distribution. The diurnal signal 
was most apparent at shallower depths, but could also 
be interpreted as an increase in migration to lower 
depths during daytime. Depth recordings from the 
