734 



Fishery Bulletin 90(4), 1992 



bottom most of the time. Data from pressure-tele- 

 metering tags show that fish dove toward the bottom 

 but remained there only briefly. Only one fish with a 

 pressure transmitter either rested on the bottom for an 

 extended period or disgorged its transmitter (Fig. 7). 



Little is known about the diel vertical distribution of 

 rockfishes. Schools of S. entomelas and S. proriger are 

 known to rise off the bottom during the night and 

 become more diffuse than dense schools on the bottom 

 during the day (Leaman et al. 1990). Rockfish may 

 intercept vertically-migrating pelagic organisms that 

 constitute their primary prey, feeding closer to the sur- 

 face at night or during crepuscular periods and de- 

 scending with their prey during the day. Sometimes 

 vertically migrating prey, such as euphausiids, are 

 advected onto banks and seamounts and trapped near 

 the bottom during the day where they are devoured 

 by rockfishes (Isaacs and Schwartzlose 1965, Chess et 

 al. 1988, Genin et al. 1988, Hobson 1989). Euphausiids 

 are often the primary prey of adult yellowtail rockfish 

 (Lorz et al. 1983). About 50% of the diet by weight of 

 yellowtail rockfish from Heceta Bank was comprised 

 of euphausiids (Brodeur and Pearcy 1984). However, 

 vertically-migrating mesopelagic fishes and shrimp 

 were the primary food items of yellowtail rockfish col- 

 lected in deeper water (137m bottom depth) along the 

 southern edge of Astoria Canyon (Pereyra et al. 1969). 



Yellowtail rockfish from Heceta Bank did not 

 demonstrate obvious diel changes in their behavior by 

 either rising closer to the surface at night or swimming 

 over deeper water to intercept more oceanic organisms. 

 Such behavior has been observed for other species of 

 rockfishes (Chess et al. 1988, Leaman et al. 1990), and 

 predatory shore fishes are known to migrate offshore 

 at night to feed in midwater (Hobson 1968). One 

 yellowtail rockfish on Heceta Bank with a pressure- 

 telemetering transmitter made more dives to the 

 bottom during night than day. 



The reasons for dives to the bottom are unclear. One 

 possible explanation is that these dives assist the fish 

 in localizing their position on the bank and preventing 

 drift of the school away from their home station. Sur- 

 face currents often set the ship away from tagged fish 

 that appeared to be geostationary. Yellowtail rockfish 

 must be able to orient to a specific site and swim 

 against prevailing currents to maintain their position. 



Tagging-tracking techniques 



Sonic tags inserted into the stomachs of yellowtail 

 rockfish without retention hooks were useful for track- 

 ing fish for several days. Most fish showed detectable 

 movements up to 2 days after release. Horizontal 

 movements greater than the accuracy of fixes were 



found in one fish 10 days later, but this was an excep- 

 tion. Depth sensor tags provided reliable information 

 on the retention of tags since fish were almost always 

 in midwater. Fish with depth transmitters remained 

 in midwater up to 5 days, the rated duration of the 

 batteries. One pressure-sensitive tag (Fish 3. Fig. 7) 

 was apparently regurgitated after 22 h and fell to the 

 bottom. If arm's were employed on tags, fish move- 

 ments were measurable for 1 month after release. One 

 ARM tag dropped to the bottom immediately after the 

 fish was released, demonstrating that restraining hooks 

 are not a guarantee that tags will stay in the stomach. 

 Eight of the twelve fish with non-pressure telemeter- 

 ing ARM tags that were relocated moved significant 

 distances 30 days after the release of fish, indicating 

 long-term retention of transmitters. 



Effects of the transmitter on behavior of the fish are 

 not known. However, one fish apparently schooled soon 

 after release. Although fish dove toward the bottom 

 immediately after release, they rose to typical mid- 

 water depths after less than an hour. These observa- 

 tions suggest that the trauma of being caught, tagged, 

 and released, and the added weight of the transmit- 

 ter, did not have prolonged effects and tagged fish 

 behaved normally. 



Acknowledgments 



This research was supported by the Department of In- 

 terior's U.S. Minerals Management Service (Cooper- 

 ative Agreement 14-12-0001-30445). NOAA's National 

 Undersea Research Program provided supplemental 

 shiptime and submersible support. I thank J. P. Fisher, 

 B.N. Tissot, R. Albright, and the Captain of the FV 

 Corsair, W. Dixon, and his crew for conducting this 

 research at sea, J. P. Fisher for his help with analyses 

 of the data, and J. P. Fisher, A. Schoener, M.A. Hix- 

 on, and two anonymous reviewers for helpful com- 

 ments on the manuscript. A. Ebeling and M.A. Hixon 

 provided the microgasometer and advice to determine 

 the composition of gas escaping from decompressed 

 yellowtail rockfish. 



Citations 



Brodeur, R.D., and W.G. Pearcy 



1984 Food habits and dietary overlap of some shelf rockfishes 



(genus Sebasles) from the northeastern Pacific Ocean. Fish. 



Bull., U.S. 82:269-293. 

 Carlson, H.R. 



1986 Restricted year-class structure and recruitment lag within 



a discrete school of yellowtail rockfish. Trans. Am. Fish. Soc. 



115:490-492. 



