Kimura et a I.: Stock structure and movement of Anoplopoma fimbria 
463 
summer of their first year (still 0-yr-old) (Rutecki and 
Varosi, 1997a), and usually become demersal in outer 
coastal waters during their second year of life at age 
1 yr (Rutecki and Varosi, 1997a, 1997b). From there, 
it is believed that they undergo a protracted ontoge- 
netic migration to greater depths (Saunders et al., 
1997). 
Adult sablefish recruit to offshore demersal fish- 
eries at about age 3-4 yr (Sasaki, 1985; McFarlane 
and Saunders, 1997). Routine trawl, longline, and 
trap surveys by the National Marine Fisheries Ser- 
vice principally cover depths from 200 to 1000 m 
(Parks and Shaw, 1988; Lauth et al., 1998). These 
surveys in Alaska, and along the west coast typically 
indicate sablefish are abundant at the maximum 
depths fished. Spawning off California occurs at 
depths beyond 800 m (Hunter et al., 1989). In 
Monterey Bay, Parrish 2 measured dissolved oxygen 
and noted that peak longline catches occurred in the 
oxygen-minimum zone at around 730 m. A special 
longline survey targeting deeper waters (Wilkins 3 ) 
and deep trap sets (Parks and Shaw, 1988) has shown 
that sablefish along the west coast occur to depths of 
up to -1500 m. Beamish et al. (1979) reported ex- 
ploratory catches of sablefish to depths of 2740 m. 
Pearcy et al. ( 1982) noted the occurrence of sablefish 
in the Astoria and Cascadia abyssal plains down to a 
depth of 2560 m. Deepwater trawl and photographic 
work by Wakefield (1990) showed that sablefish oc- 
cur as far down as -1500 m but appear to become 
scarce beyond this depth. Former naval dumping 
sites off San Francisco, at depths from 2000 to 3200 
m, showed an absence of sablefish (Cailliet et al. 4 ). A 
reasonable interpretation might be that although 
sablefish can occur at depths beyond 1500 m, sable- 
fish abundance can be expected to decline consider- 
ably beyond this depth. 
Because of the many interesting questions raised 
by their broad geographic and bathymetric distribu- 
tions, sablefish have become one of the most tagged 
demersal fish species in the northeast Pacific. On 
the basis of tagging studies, authors have empha- 
sized both the resident nature of some sablefish 
2 Parrish, R. H. 1975. The relationships of oxygen concentra- 
tion and depth of capture with size and abundance of sablefish 
( Anoplopoma fimbria) in Monterey Bay, California. Current 
address: Pacific Fisheries Environmental Lab., 1352 Lighthouse 
Ave., Pacific Grove, CA 93940. Unpubl. manuscript. 
3 Wilkins, M. E. 1997. RACE Division, Alaska Fisheries Sci- 
ence Center, Natl. Mar. Fish. Serv., NOAA, 7600 Sand Point 
Way NE, Seattle, WA 98115. Personal commun. 
4 Cailliet, G. M., W. W. Wakefield, G. Moreno, and K. Rhodes. 
1992. The deep-sea fauna from the proposed navy ocean dis- 
posal site, using trap, otter and beam trawl, and camera sled 
samples. Navy CLEAN Contract No. N62474-88-D-5086, pre- 
pared for PRC Environmental Management, San Francisco, CA, 
and Honolulu, HI, 69 p. 
(Wespestad, 1983; Beamish and McFarlane, 1983, 
1988; Maloney and Heifetz, 1997) and the proclivity 
of other sablefish to be highly migratory (Bracken, 
1983; Dark, 1983; Heifetz and Fujioka, 1991; McFar- 
lane and Saunders, 1997). Generally fish tagged in- 
shore, off the west coast of Vancouver Island, or off 
the U.S. west coast were more likely to be character- 
ized as resident and nonmigratory. 
In this paper we examine several hypotheses con- 
cerning the movement of sablefish, using recapture 
data gathered from offshore tagging of sablefish from 
throughout the northeast Pacific Ocean. The first 
hypothesis is that sablefish off Alaska and Canada, 
i.e. north of 50°N latitude, are a separate population 
from the sablefish south of 50°N latitude found along 
southern Canada and the U.S. west coast. The sec- 
ond hypothesis is that Alaska sablefish tend to mi- 
grate much farther than west coast sablefish. An- 
other question is whether sablefish migrate to greater 
depths as they become older. Such hypotheses are of 
practical importance because they can affect the way 
resource assessment survey results are interpreted. 
A study in which growth curves were estimated 
from a sablefish tag data set has been completed 
(Kimura et al., 1993). In that study differences in 
the growth curves of Alaska and west coast popula- 
tions were reported. In this paper, we examine the 
effects of El Nino-Southern Oscillation (ENSO) 
events on the growth of sablefish in the northeast 
Pacific Ocean. 
Finally, we examine the migration of fish tagged 
in Alaska to areas along the west coast. Upwelling 
along the west coast (42-48°N latitude) appears to 
be positively correlated with these migrations, and 
possible explanations are given for why a correla- 
tion exists. 
Materials and methods 
In this paper we analyze tag recoveries of the sable- 
fish tagging program conducted by the National 
Marine Fisheries Service (NMFS). Tagging occurred 
during surveys designed to measure relative abun- 
dance of sablefish throughout its range in offshore 
U.S. waters. From 1971 to 1993, approximately 
218,255 fish were captured with trawl, trap, and 
longline gears and later released after having been 
tagged with anchor tags (Table 1). With the excep- 
tion of Canadian waters, sablefish were tagged from 
southern California to the Bering Sea. Analyses of 
sablefish tagged in Canadian waters have been pre- 
viously reported (e.g. Beamish et al. 1979; Beamish 
and McFarlane, 1983, 1988; McFarlane and Saunders, 
1997). 
