Rooper: An ecological analysis of rockfish assemblages in the North Pacific Ocean 
3 
Aleutian Islands region since 1980 (Britt and Martin, 
2001; Zenger, 2004). Surveys were conducted triennially 
between 1990 and 2000 and biennially thereafter (Table 
1). For this analysis, the AFSC bottom trawl data from 
1990 through 2005 were combined across years and 
survey areas in order to maximize the number of useful 
data points for each species. A Poly Nor’Eastern high- 
opening bottom trawl (with 24.2-m roller gear equipped 
with 36-cm rubber bobbins that are separated by 10-cm 
rubber disks) was used in these AFSC bottom trawl sur- 
veys. Trawl hauls were conducted at a speed of 5.6 km/h 
(3 knots) for 15 or 30 minutes. Bottom contact and net 
dimensions were recorded throughout each trawl haul 
by using net mensuration equipment. In a few cases, 
net width was not recorded (n = 35); therefore the overall 
average net width (15.84 m, standard error [SE] = 0.01) 
was used. For these analyses, records were used only if 
trawl performance was satisfactory and if the distance 
fished, geographical position, average depth, and bottom 
water temperature were recorded (/? = 6767). Trawl hauls 
were deemed satisfactory if the net opening was within a 
predetermined normal range, the roller gear maintained 
contact with the seafloor, and the net suffered little or 
no damage during the tow (Zenger, 2004). 
All fish captured during a survey tow were sorted by 
species, counted, measured for total or fork length, and 
the total weight of each species in the catch was deter- 
mined. For large catches, the total catch was weighed 
and subsampled for length data. Catch per unit of ef- 
fort (CPUE, no of fish/ha) for each rockfish species was 
calculated by using the area swept computed from the 
net width for each tow multiplied by the distance towed 
recorded with geographical positioning systems. The 
rockfish catch data were transformed by using natural 
log (CPUE + 1) before analyses, hereafter shortened to 
CPUE. 
Environmental variables 
Three environmental variables were included in the 
analyses: depth, temperature, and geographic position 
along the Alaska coastline. Temperature measurements 
were collected throughout each trawl haul with a cali- 
brated Branker bathythermograph, either a SeaBird-19 
or SeaBird-39 microbathythermograph (Sea-Bird Elec- 
tronics, Inc., Bellevue, WA) attached to the net. Depth 
was also recorded during each trawl haul either off the 
vessel echosounder or from the microbathythermograph 
attached to the net. The average bottom temperature 
and average depth from each trawl haul were used in 
the analyses. The final environmental variable included 
in the analyses was the relative position of each trawl 
haul along the Alaska coastline. Because the major 
axes of the Alaska coastline are from south to north 
in the southeastern Gulf of Alaska and from east to 
west in the remainder of the Gulf of Alaska and Aleu- 
tian Islands (Fig. 1), a reference point was chosen to 
standardize the spatial patterns in trawl hauls. The 
reference point was chosen in the central Gulf of Alaska 
at the eastern side of Hinchinbrook Island, (146.08°W, 
Table 1 
Summary of the number of Alaska Fishery Science Center 
bottom trawl survey hauls used in the analysis of rockfish 
(Sebastes spp.) assemblages in the North Pacific Ocean. 
Data from trawl hauls with no temperature, depth, lati- 
tude, longitude, and inadequate gear performance were 
not used in the analyses. The Gulf of Alaska and Aleutian 
Islands bottom trawl surveys were the data source for 
each ecosystem, although in some years (i.e., 1998) a full 
survey of the ecosystem was not conducted. 
Year 
Ecosystem 
Number of trawl hauls 
1990 
Gulf of Alaska 
286 
1991 
Aleutian Islands 
63 
1993 
Gulf of Alaska 
727 
1994 
Aleutian Islands 
389 
1996 
Gulf of Alaska 
716 
1997 
Aleutian Islands 
399 
1998 
Gulf of Alaska 
5 
1999 
Gulf of Alaska 
765 
2000 
Aleutian Islands 
415 
2001 
Gulf of Alaska 
550 
2002 
Aleutian Islands 
417 
2003 
Gulf of Alaska 
795 
2004 
Aleutian Islands 
415 
2005 
Gulf of Alaska 
825 
Total 
6767 
60.37°N). The distance from this point to each trawl 
haul provided the change in spatial distribution (both 
by latitude and longitude) of rockfish species and the 
variable is hereafter referred to as the position of each 
trawl. Thus, a negative position indicates a trawl haul 
occurring in southeastern Alaska, and a positive position 
indicates a trawl haul occurring west of Hinchinbrook 
Island. Although geographical position is not actually 
an environmental variable, it was used as a proxy for 
longitudinal and latitudinal gradients that affect fish 
distribution and ranges. 
Data analyses 
In every bottom trawl haul, the CPUE of each rockfish 
species was divided into adult and juvenile stages by 
fish length (Table 2). The juvenile stage was broadly 
defined to include all subadult fish with lengths less 
than the size at 50% maturity from literature sources 
(Paraketsov, 1963; McDermott, 1994; NPFMC, 1998, 
2005; Love et al., 2002; Pearson and Gunderson, 2003). 
The adult rockfish of each species were further divided 
into male and female CPUE components. Trawl hauls 
from which no length or sex data were collected were 
eliminated from the analyses for that species. Species 
for which catches occurred in fewer than 100 trawl 
hauls were also excluded from the analyses. For each 
trawl haul, these divisions resulted in three estimates 
of CPUE for each species: juveniles, adult females, and 
adult males. 
