372 
Fishery Bulletin 1 10(3) 
which environmental variables are appropriate proxies 
for the ambient conditions that influence growth may 
be done best with data from smaller time and space 
scales than with the data available for the purposes of 
this study and that environmental data at fine temporal 
or spatial scales are likely to be difficult to interpret 
for fish species that move long distances (Heifetz and 
Fujioka, 1991; Kimura et ah, 1998). The use of broad 
geographic and time-averaged representations of envi- 
ronmental effects misses short-term changes in tem- 
perature regimes brought on by weather events, such as 
wind-driven mixing and upwelling. In the future, to de- 
termine an appropriate scale, results from the extensive 
tagging studies with sablefish should be examined (the 
Fisheries Agency of Japan and NMFS have been tag- 
ging sablefish throughout the entire geographic range of 
the annual longline survey since 1972). Further, analy- 
sis should be done with the El Nino-Southern Oscilla- 
tion as an environmental variable in a similar manner 
to work done by Kimura et al. (1998) who found growth 
of groundfish species to be significantly enhanced by 
events of the El Nino-Southern Oscillation. 
There appear to be significant differences in growth 
patterns among management regions; the GOA regions 
consistently displayed the largest (in asymptotic length 
and average size) sablefish for both sexes in this study 
and in past research (McDevitt, 1990; Sigler et al., 
1997). Sasaki (1985) reported regional differences in 
mean sizes between young sablefish from the EBS, Al, 
and GOA and a temporal increase in weight-at-age in 
the EBS from the 1960s to the late 1970s similar to the 
temporal increase in growth (length-at-age) reported 
here. Sasaki’s reported differences were minor and not 
significant. McDevitt (1990) reported significant growth 
differences between the EBS and GOA but did not find 
significant differences in growth between the Al and 
EBS and the Al and GOA. She speculated that her 
findings were the result of high variability of the data 
from the Al. Consequently, differences between the Al 
and EBS regions were not detected because of the low 
power of the tests. In accord with our results, Sigler et 
al. (1997) found that female sablefish in the Shumagin 
and Southeast regions of the GOA differed significantly 
in growth, but no regional differences were detected 
for males. 
In both the Al and EBS regions, poor model fits and 
atypical rates of growth and average maximum sizes 
were noted in this and past studies (McDevitt, 1990). 
Both of these regions displayed notably high estimates 
of the growth parameter k, likely because samples from 
these two regions consisted mostly of larger ( >66 cm 
FL) fish, and smaller (<57 cm FL) fish are required 
for an accurate estimate of k. Data from both of these 
regions exhibit the highest variability (large residual 
population variances) and the poorest fit to the growth 
curves, compared with data from other regions in this 
study. The most notable differences among observed 
sablefish were consistently found in the EBS region, 
where smaller asymptotic lengths were reported than 
those for sablefish found in all other regions. 
Alaskan sablefish are assessed by the AFSC as one 
stock, and therefore sablefish found throughout Alaskan 
waters are assumed to display similar growth rates; 
however, this stock is highly mobile (Heifetz and Fujio- 
ka, 1991; Maloney and Sigler, 2008). Younger fish move 
into deeper waters onto the slope, moving from the 
Eastern Gulf of Alaska (EGOA) in a counter clockwise 
direction through the Central Gulf of Alaska (CGOA) 
to the Western Gulf of Alaska (WGOA), returning to 
the EGOA as larger, older fish (Heifetz and Fujioka, 
1991; Maloney and Sigler, 2008). In theory, one would 
not expect there to be many regional differences in 
sablefish growth and average size-at-age because a 
large part of the sablefish population moves each year, 
maintaining a well-mixed population (Heifetz and Fu- 
jioka, 1991). Several competing hypotheses are available 
to explain these observed regional differences: geo- 
graphic differences in food abundance, oceanographic 
condition, or sablefish abundance. Any explanation for 
these regional differences, however, has to be consistent 
with this observed movement pattern. As with observed 
geographical variation for the northern anchovy (En- 
graulis mordax) along the west coast of North America, 
geographical variation in age composition could have 
influenced the observed variation in mean size of sable- 
fish in the 6 management regions (Parrish et al., 1985; 
Saunders et al., 1997). Sablefish in the GOA may have 
displayed apparently faster growth and larger asymp- 
totic lengths and weights than have sablefish in the 
Al and EBS regions because size-dependent migration 
results in a mixture of faster-growing young fish with 
older spawning fish (Heifetz and Fujioka, 1991). In 
contrast, in the EBS region, which primarily comprises 
fish >4 years of age, sablefish might have displayed 
slower growth because of the absence of the youngest, 
fastest-growing fish (Quinn and Deriso, 1999; Sogard 
and Olla, 2001). 
Alternatively, varying growth rates might be ex- 
plained in part by regional differences in abiotic factors, 
such as oceanographic conditions (Sasaki, 1985; McDe- 
vitt, 1990; Saunders et al., 1997; Kuznetsova, 2003). If 
fish are grouped within a highly migratory population, 
environmental effects would appear as growth differ- 
ences between the 6 management regions. Temperature 
differences may explain the divergence in growth rates 
between fish in the EBS region and fish in regions in 
the GOA, such as the Southeast region. Several marine 
species (e.g., northern anchovy; Atlantic cod [Gadus 
morhua L.]; walleye pollock [Theragra chalcogramma]; 
turbot [Scophthalmus maximus I; and blacknose shark 
[Carcharhinus acronotus ]) are of larger sizes and are 
faster growing in the southern extent of their ranges 
than in other areas of their distributions (Parrish et al., 
1985; Imsland et al., 2001; Kuznetsova, 2003; Armstong 
et al., 2004; Driggers et al., 2004; Stark et al., 2007). 
For the purposes of the management of Alaskan sa- 
blefish, updated and corrected growth estimates divided 
into the 2 survey periods, 1981-93 and 1996-2004, 
have been incorporated into the Alaskan sablefish stock 
assessment conducted by the AFSC. We ran the model 
