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Fishery Bulletin 120(1) 
Time (min) 
Figure 4 
Putative spawning rises, meaning abrupt movements of fish to shallower 
depths, identified in archival tag data for 3 female Greenland halibut (Rein- 
hardtius hippoglossoides) tagged in 2004, 2006, and 2012 (tag nos. 5282, 4551, 
and 383, respectively) in the eastern Bering Sea. Black and gray circles indi- 
cate depths recorded during spawning rises. Lines indicate depth profiles 
before, during, and after spawning rises and apexes of those rises (apexes were 
estimated by using simple linear models with data from tags with sampling 
intervals >1 min). The time at the apex of the rise has been set to 0 min, 
and horizontal dashed lines indicate the minimum and maximum depths esti- 
mated for the apex of putative spawning rises (217-326 m). 
indicate that Greenland halibut in the BSAI region spawn 
from January through February, with eggs being released 
217-326 m below the surface (inferred from interpolated 
apexes of spawning rises of females), although they nor- 
mally inhabit deeper water. Because our study involved a 
small sample of individuals from the population and 
because tags recorded at intervals of 1-15 min, we believe 
that it is prudent to assume that eggs are released at a 
broader depth range of 200-350 m. The notions that 
Greenland halibut are total spawners and are capable of 
spawning annually are also supported by identification of 
singular spawning rises made by females in consecutive 
years. The depths at which females initiated spawning 
rises may provide evidence of depth (or site) fidelity. For 
example, a fish (tag no. 5282) began rises at depths of 
859 m, 972 m, and 886 m in 3 consecutive years, and 
another fish (tag no. 383) initiated rises at depths of 619 
m, 526 m, and 527 m in 38 consecutive years (Table 1). 
The consistency in the time between annual spawning 
rises identified for females in this study was remarkably 
close to 1 year; therefore, the timing of spawning of an 
individual female likely can be predicted from the time it 
spawned the previous year. This hypothesis has been put 
forward for lumpfish (Cyclopterus lum- 
pus), another species with this trait (Ken- 
nedy and Olafsson, 2019). Consistency 
in the timing of spawning for the BSAI 
Greenland halibut stock indicates that 
spawn timing for populations in other 
regions should be reexamined. Consider- 
ing that the 2-year oocyte development 
of this species was not well understood 
until recently (Kennedy et al., 2011; 
Rideout et al., 2012), it is possible that 
misspecification of maturity could lead 
to incorrect conclusions across the entire 
range of the Greenland halibut. 
Temperature and currents may play a 
role in regulating development time and 
dispersal of the eggs and larvae of Green- 
land halibut. Greenland halibut are 
known to overwinter at depths >600 m 
(Siwicke and Coutré, 2020), in contrast 
to the depths where Pacific (<600 m) and 
Atlantic (<500 m) halibut overwinter 
(Loher and Seitz, 2008; Murphy et al., 
2017), and the commonly held assump- 
tion is that Greenland halibut release 
their eggs at these depths (Alton et al., 
1988; Sohn et al., 2010; Duffy-Anderson 
et al., 2013). Our results indicate that 
Greenland halibut may release eggs at 
depths that are much shallower than 
previously thought, possibly affecting 
interpretation of egg and larval incu- 
bation and distribution. Spawning rises 
identified for females in the winter con- 
sistently peaked just below the mixed 
layer, which in the Bering Sea is deeper 
and cooler during the winter than during other seasons, 
reaching depths of approximately 200 m; a permanent 
halocline exists below the maximum depth of the mixed 
layer, and the subsurface temperature maximum is cen- 
tered at 200-300 m (Johnson and Stabeno, 2017). 
Because embryo development of Greenland halibut, and 
therefore the timing of the hatch, depends upon water 
temperature (Dominguez-Petit et al., 2013) and because 
temperature is correlated with depth, back-calculations 
of spawn timing from egg and larval development can be 
incorrect if assumptions of the depth at which spawning 
occurs are wrong. Another large deepwater flatfish spe- 
cies, the Pacific halibut, it has been assumed, spawns 
on the bottom (Bailey et al., 2008), although evidence of 
spawning rises indicate that eggs are plausibly released 
at depths higher in the water column (Seitz et al., 2005; 
Loher and Seitz, 2008). Results of analysis of archival tag 
data indicate that similar misspecification of spawning 
depth may be occurring for Greenland halibut, and this 
problem should be resolved in future modeling efforts. 
The sex-specific differences observed in the spawning 
behavior of Greenland halibut in this study indicate that 
females spawn a single batch when fully developed and 
