474 
Fishery Bulletin 96(3), 1 998 
Figure 6 
Average movement of tagged and recovered sablefish aggregated by area of recov- 
ery. Head of arrow lies in one of the 27 areas in which more than two tag recover- 
ies occurred. Rear of arrows lies in the average location where sablefish were tagged 
(where fish were coming from). 
eas 20-24) group appears to have an excess of large 
(>60 cm) sablefish, but we cannot be sure of their 
origin. We were unsuccessful in our attempt to cor- 
relate annual fluctuations in the abundance of large 
sablefish with upwelling, but this may have been due 
to limitations in the samples that were available on 
a biennial basis from the west coast north area. 
Discussion 
Comparison and interaction of Alaska and 
west coast populations 
Our tag-recovery data alone provide compelling evi- 
dence (Table 6) that Alaska and west coast sablefish 
constitute separate populations that, for practical 
purposes, remain largely independent. In the long- 
term, approximately 3.5% of Alaska fish migrate to 
the west coast, and approximately 4.4% of west coast 
fish migrate to Alaska. Short-term migration rates 
will be small and justify the separation of these popu- 
lations for fishery management purposes. However, 
biologically, these exchange rates are probably suffi- 
cient to consider sablefish a single biological popula- 
tion throughout its range, provided these populations 
are not reproductively isolated. Notice that these 
migration rates say nothing of net migration which 
is dependent on the absolute magnitude of the Alaska 
and west coast populations. 
Stock assessment scientists have long felt that 
sablefish constitute two distinct stocks between 
Alaska and the U.S. west coast, largely because their 
von Bertalanffy growth parameters and size-at-ma- 
turity differ so dramatically (Table 9; McDevitt, 1990; 
Kimura et al., 1993). However, early genetic studies 
(Tsuyuki and Roberts, 1969; Wishard and Aeber- 
sold, 1979; Gharrett et al., 1983) indicate that al- 
though the northeast Pacific may support many 
“somewhat discrete” populations, a mechanism for 
gene transfer was expected to explain the observed 
polymorphism. In light of our strong evidence for 
migratory behavior in tagged sablefish, it is not sur- 
prising that significant gene flow occurs throughout 
the range. 
The recapture rate for tagged sablefish appears to 
be remarkably similar for all areas of tagging (Table 
4), especially if the differential survival rate from 
the fishing gears used for initial capture is taken into 
account. These recapture rates cannot tell us much 
