Maloney and Sigler: Age-specific movement patterns of Anoplopoma fimbria 
313 
15 20 25 30 35 
Number at age 2 (millions) 
Figure 7 
Scatterplot of proportion of sablefish ( Anoplopoma fimbria) tag recoveries in 
western areas (Bering Sea, Aleutian Islands, Western Gulf of Alaska) versus 
year-class strength (number at age 2 in millions; Hanselman et al., 2006). 
agement; for example, recoveries at 
depths >700 m were fewer during 
IFQ management (16% of recoveries 
during 2003-05) than during open 
access management (25% during 
1992-94). This result has poten- 
tially substantial implications for 
a stock assessment because “dome- 
shaped” availability influences the 
reliability of abundance estimates 
(Bence et ah, 1993; Sigler, 1999). A 
logical next step for other research- 
ers to understand these effects is 
to complete a migratory catch-age 
analysis (e.g., Quinn et ah, 1990) 
that melds sablefish migration (Heif- 
etz and Fujioka, 1991) and age- 
structured (Sigler, 1999; Hanselman 
et al., 2006) analyses. 
Density-dependent effect 
on migration 
Migration is a prominent feature 
in the life history of many fishes. 
Well-known examples of migratory 
fish are Pacific salmon ( Oncorhyn - 
chus spp.) that return to their natal stream to spawn 
(Burgner, 1991; Heard, 1991) and Pacific herring 
( Clupea harengus ) that consistently follow routes from 
spawning to feeding grounds (Hourston, 1982; Wheeler 
and Winters, 1984; Corten, 2002). Presumably the 
energy expended during migration is compensated for 
by other benefits. Demonstrated benefits include the 
ability to take advantage of seasonally available prey 
(Walters et al., 1986; Livingston, 1993) and avoidance 
of predation (Carlson, 1980). Benefits of migration for 
sablefish are not immediately obvious because they 
are opportunistic feeders and have no need to pursue 
specific prey, and their rapid growth rate in early 
life quickly lessens their vulnerability as prey. Nev- 
ertheless, a substantial proportion of the population 
migrates each year (Heifetz and Fujioka, 1991; Kimura 
et ah, 1998). 
Sablefish are characterized by great variability in 
year-class strength; and occasional strong year classes 
dominate the fishery for several years in a row (Sigler, 
1999; Hanselman et al., 2006). A higher proportion of 
a strong year class may migrate and young fish may 
move farther and faster in order to occupy less crowded 
areas (density-dependent habitat selection; e.g., Mac- 
Call, 1990). Beamish and McFarlane (1988) noted dif- 
fering rates of sablefish movement out of release areas 
from 1977 to 1985 and theorized that increased den- 
sity resulting from recruitment of the large 1977 year 
class may have contributed to an increased rate of 
movement. However, we found no significant effect of 
year-class strength on the proportion of recoveries in 
the western areas, and therefore cohort density does 
not appear to affect the proportion of a cohort that will 
migrate. Although we tested a long time series, this 
time series does not span the full range of observed 
recruitment variability. Some earlier year classes were 
substantially stronger (e.g., the exceptional 1977 year 
class was 44% larger than the strongest year class 
(1984) that we tested). Migration may be stronger for 
year classes of such magnitude. Further, movement 
rates may be affected by total abundance — a possibility 
that could be tested in a sablefish migratory catch-age 
analysis such as we suggested earlier. 
Observed sablefish abundance trends by area during 
the last 25 years can be explained by their counter- 
clockwise migration pattern. Overall sablefish abun- 
dance peaked in the late 1980s and then decreased. 
The western areas of Bering Sea, Aleutian Islands, 
and western GOA decreased quickest, as migrating fish 
matured and turned eastward (Fig. 8). Abundance 
declined more slowly in the eastern GOA, presumably 
because fish that migrated westward returned to the 
eastern GOA. The abundance decline in the central 
GOA was intermediate, probably because migrating 
fish pass through in both directions (westward and 
eastward). This pattern of abundance changes (faster 
in western areas, slower in central and eastern GOA) 
supports the conclusion that the eastern GOA and the 
eastern part of the central GOA are the center of the 
range for Alaska sablefish (Bracken, 1983; Beamish 
and McFarlane, 1988; Sigler et al., 2001). 
Currents and sablefish migration 
Prevailing currents may play an important role in deter- 
mining the direction of migration for most young sable- 
