Siwicke et al.: Spawning behavior of Reinhardtius hippoglossoides in the Bering Sea and Aleutian Islands 65 
spawning has been suggested for Greenland halibut 
(Fedorov, 1971); however, this behavior seems an unlikely 
explanation because it would mean that these small fish 
were already mature at an even smaller size. Given the 
more recent interpretation of gonad development of female 
Greenland halibut and the lack of spawning evidence for 
small females, the L;, currently used in stock assessments 
may be an underestimate, and the maturity classifications 
for Greenland halibut in the BSAI region should therefore 
be revisited. 
Tagging research focused on spawning behavior should 
consider several aspects of study design. When archival 
tags have a temporal data resolution that is too coarse 
(e.g., hourly), they are unlikely to capture behaviors of 
short durations such as spawning (Fisher et al., 2017). Tag 
sampling intervals must be set appropriately to capture 
the behavior of interest. For spawning of large flatfish, 
1-min intervals are appropriate, but if multiyear data are 
desirable, a longer interval may be necessary to extend 
battery life. Type of tag is another consideration; pop-off 
satellite archival tags are often chosen because fish do not 
need to be recaptured to retrieve data, whereas the use 
of archival tags that had to be implanted in fish in this 
study required a large number of tags to be deployed rel- 
ative to the number of tags recovered with usable data. A 
drawback in several studies of spawning in which pop-off 
satellite archival tags were used is the lack of sex informa- 
tion associated with the tag data retrieved (unless the fish 
is recaptured and visually inspected); this issue could be 
remedied through genetic sampling at the time of release 
(e.g., Goetz et al., 2018). Tags that provide data that can 
be used to confirm these presumed behaviors are becom- 
ing available. The previously mentioned SeaTag-SP could 
be used to corroborate the assumption that spawning has 
occurred and to aid estimation of the location and timing 
of spawning. 
Conclusions 
Tagging studies can be used to generate and test hypoth- 
eses related to fish behavior; for example, analysis of tag 
data can determine spawning timing and location. Tag data 
also can be used in concert with data from other sources to 
provide a more complete view of the life history for large 
species that are difficult to sample. The findings from our 
analysis of data from tags implanted in Greenland halibut 
in the BSAI region are as follows: 1) spawning occurs in 
January and February; 2) eggs are released at depths of 
200-350 m below the surface; 3) females are total spawners, 
releasing eggs only once during a year; and 4) a female can 
spawn in consecutive years. Data from deployment of addi- 
tional tags could also support a revised L;, for Greenland 
halibut based upon dimorphic rising behavior or could also 
be used to infer a minimum size at spawning, information 
that could aid in defining lengths in maturity tables. The 
use of archival tags should therefore be considered as a 
complement (when appropriate) to other methods when 
designing future research on fish behavior. 
Acknowledgments 
We would like to thank the numerous researchers, observ- 
ers, and fishermen that have contributed to the success- 
ful tagging and recapture of Greenland halibut, including 
the captains and crews of the FV Ocean Prowler and FV 
Alaskan Leader for their contributions over many years 
tagging fish during Alaska Fisheries Science Center 
longline surveys. Thanks to J. Ianelli for providing some 
of the archival tag data and noting the potential of rises 
in spawning behavior. Thanks to B. Williams, M. Bryan, 
J. Lee, and 2 anonymous reviewers for suggestions that 
helped improve this manuscript. 
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