Sogard and Berkeley: Movement, growth, and survival of Anoplopoma fimbria off Oregon 
247 
Figure 9 
Proportion of all recaptured sablefish (Anoplopoma fimbria) initially captured in 
2 depth zones during the second set of tagging (tagging set 2) for each year fol¬ 
lowing release. Only resident fish that did not disperse more than 200 km from 
their tagging location are included. 
and growth rates overall slowing with time at large. 
Estimated growth rates of males in the full model were 
42% lower than those of females. We were also able to 
document greatly reduced growth for fish of all sizes 
residing at deeper depths (zone 3). The depth effect on 
growth has been suggested by decreasing size at age 
with depth for both males and females (Saunders et ah, 
1997; Head et ah, 2014) and verified here by recaptures 
of fish that presumably spent the time between tagging 
and recapture primarily near the depth of initial cap¬ 
ture. Initial fish sizes of recaptured fish available for 
growth estimation from depth zone 3 ranged from 50 to 
70 cm FL for females and 54 to 66 cm FL for males— 
a size range that includes immature individuals and 
fish not expected to be close to their asymptotic size. 
Our results corroborate those of Head et al. (2014), 
who found a marked decrease in asymptotic size with 
increased capture depth for female sablefish residing 
in west coast slope habitats from Cape Mendocino, 
California, to the U.S.-Canada border. Reduced growth 
at deeper slope habitats could arise from 2 different 
mechanisms. First, individual differences in genetically 
determined intrinsic growth rates could be associated 
with depths selected by fish after settlement such that 
fish with inherently lower growth capacity migrate to 
deeper habitats than those of fish capable of faster 
growth rates. Under this scenario, these individuals 
would have lower asymptotic sizes regardless of their 
habitat. Alternatively, reduced growth rates in deep 
slope waters could reflect environmental conditions 
of low temperature, low dissolved oxygen levels, and 
low productivity. Under this scenario, fish have lower 
asymptotic sizes because of a limited opportunity for 
growth; they are unable to attain the asymptotic sizes 
of fish residing at shallower depths. Although the lat¬ 
ter, environmentally based mechanism is perhaps more 
intuitively appealing, contrasting intrinsic growth ca¬ 
pacity would be consistent with depth-dependent popu¬ 
lation structure as suggested by Fujiwara and Hankin 
(1988) and Norris (1997). 
An additional factor influencing growth was the gear 
used at recapture; fish recaptured in fixed gear grew at 
faster rates than fish recaptured by trawls. Kimura et 
al. (1993) found a similar result and suggested a differ¬ 
ence in selectivity between the 2 gear types. Sablefish 
actively entering baited traps or attacking bait on long- 
lines may be more aggressive than fish captured pas¬ 
sively by trawls. Individual differences in growth rates 
are often associated with behavioral differences in ac¬ 
tivity and boldness, potentially leading to differences 
in susceptibility to fishing gear (Biro and Post, 2008). 
Caveats 
As in any study of tag-recapture data that depend 
on tag returns primarily from commercial fishermen, 
there are several sources of potential error in interpre¬ 
tation of the resulting data. First, tag loss will result 
in recaptured fish not being identified. Prior studies of 
tag loss in sablefish with the use of double tag methods 
derived estimates of 0.02-0.03 for the instantaneous 
tag shedding rate per year (Beamish and McFarlane, 
1988; Saunders et al., 1990; Lenarz and Shaw, 1997). 
Although these estimates are low compared with those 
reported for several other species (Lenarz and Shaw, 
1997), over time the proportion of fish retaining their 
tag will decrease substantially. In our study, tag loss 
may have resulted in an underestimate of migration 
rates away from the tagging area over time, especially 
because the proportion of recaptured fish that were 
classified as dispersers increased over time. Second, 
geographic variation in reporting rates can influence 
interpretation of dispersal patterns. Reporting rates 
are thought to be consistently high in British Colum- 
