Vollen and Albert: Pelagic behavior of adult Remhardtius hippoglossoides 
461 
whereas data showing frequent changes in vertical 
position may indicate pelagic swimming behavior. The 
vertical activity was analyzed in two ways: standard- 
ized vertical distance and vertical swimming activity. 
Standardized vertical distance (VD) between succeeding 
observations of ambient depths (D) were standardized 
to equal time intervals: 
VD ( = 3600 x abs (D-D i ^/s, 
where s = the time step (in seconds) between observation 
z'— 1 and i. 
For each individual fish and day, the extent of vertical 
swimming activity (VA) was estimated as 
VA=I(D max r D min i )/12, 
Where D max • and D min ■ represents the maximum and 
minimum depths recorded within a two-hour time inter- 
val z, and the summation is across the twelve two-hour 
time intervals within each day. 
Thus VA is not only dependent on the vertical range 
traveled during a day, but also on the frequency of 
vertical excursions throughout the day. Whereas VD 
measures the speed during a depth change, VA is a 
measure of activity through the day. 
Additional surveys 
Trawl acoustic surveys were conducted in the Barents 
Sea and Norwegian Sea in August 2003-2005, as part 
of a regular monitoring program of pelagic fish stocks 
in these areas. In the present study, data from these 
investigations were extracted for the extended survey 
area. The surveys were conducted with a Simrad EK 
60 echosounder, frequency 38 kHz (Kongsberg Maritime 
AS, Horten, Norway). The acoustic recordings were scru- 
tinized each day by using the Bergen Echo Integrator, 
and allocation of S A (nautical area scattering coefficient) 
values on species was made by trained personnel using 
standard procedures (Korneliussen, 2004). 
Bathymetric distributions of selected species of fish 
in bottom trawls were used for comparisons with the 
pelagic records. Data were gathered from the annual 
Norwegian Greenland halibut surveys in August 2003- 
2005, within the extended study area. In these surveys 
an Alfredo-5 commercial bottom trawl with rockhopper 
ground gear (Engas and Godp, 1989) and a measured 
mean vertical opening of 3.8-4 m was used at towing 
speeds of 3. 5-4.0 knots. Mesh size in the codend was 
60 mm. 
Stomach-contents data were collected from the same 
surveys, as well as on similar surveys in November 
2003 and March 2004. A standard biological sampling 
(length, weight, sex, maturity, and stomach fullness) 
was performed for two individuals in every 5 -cm length 
group. Individuals sampled were chosen randomly, ex- 
cept in August 2005 when only individuals with stom- 
achs containing food were sampled. These stomachs 
were frozen and analyzed in the laboratory. Methods 
were the same as those used for stomachs sampled from 
vertical longline catches. 
Results 
Pelagic catches of Greenland halibut 
Greenland halibut were caught on vertical longlines 
in most parts of the water column, but despite high 
effort, the species was rarely recorded in the upper few 
hundred meters of the water column. Throughout the 
experimental period a total of 283 individuals were 
caught, and the species was recorded during all sur- 
veys but one. Catch depth ranged from 208 to 934 m 
(Fig. 4). Seventy percent of all catches were from the 
main survey in August 2005, when 93% of the indi- 
viduals were caught between 400 m and 800 m depth. 
There seemed to be an upper catch limit which was 
relatively stable across bottom depths. In August 2005 
this limit was 300 m at 600-700 m bottom depth, 400 
m at 800-1000 m bottom depth, and 500 m at 1200 
m bottom depth. The westward distribution boundary 
could not be identified because of inadequate coverage 
of large depths. 
Greenland halibut was caught at shallower depths in 
November than in either March or August. For March 
and August surveys, mean catch depth above 400-700 m 
bottom depth ranged from 484 m to 554 m. For the two 
November surveys, the corresponding numbers were 
378 m and 363 m, respectively, differing significantly 
from all individual March and August surveys (t-tests, 
P<0.001). The two November surveys were also the only 
surveys where fish were captured in the region above 
300 m catch depth (Fig. 4). 
There were no clear or significant changes in length 
composition with catch depth, but rather with bottom 
depth and with distance from the bottom (data from Au- 
gust 2005, Fig. 5). This was partly due to males, which 
are smaller than females, being distributed higher up 
in the water column (Gtests, PcO.001) and partly to a 
significant decrease of female length (linear regression, 
P<0.05). Below 100 m from the bottom, approximately 
50% of the catches were males, whereas above 300 m, 
75% were males. 
The length range of individuals caught on vertical 
longlines was broad (41-85 cm), but the length and sex 
composition seemed to have more in common with bot- 
tom trawl catches than bottom longline catches (Fig.6). 
Bottom longlines caught few fish smaller than 50 cm, 
which were primarily males. Bottom trawls, on the 
other hand, caught fish as small as 30 cm length, indi- 
cating that both sexes were available at the bottom in 
approximately equal shares. 
During individual surveys in March and August, the 
proportion of females in the pelagic longline catches 
varied from 8% to 48% (mean of 35%). In November no 
females were caught — a finding that differed signifi- 
cantly from all March and August surveys (% 2 , df=l, 
