Pearcy: Movements of acoustically-tagged Sebastes flavidus 



729 



were decoded and displayed by the receiver. The transmitters had 

 a rated range of 500-1500m. 



Pressure-telemetering transmitters with battery durations of 

 4.5 days were used in 1989 and 1990. The pulse rates of these 

 transmitters were linearly proportional to pressure, and individual 

 calibrations were incorporated into the receiver program. The 

 manufacturer claimed accuracy was 5% of the full range, or 5 psi 

 (~3m depth), similar to my test of two tags lowered vertically 

 on a metered line at sea. Data on depths of fish and time of day 

 from these transmitters were printed at regular intervals aboard 

 ship and stored in the receiver. During 1989, depths and times 

 were recorded manually every 5min or less. During 1990, data 

 on time and depth were stored automatically by the receiver every 

 0.5 sec. Median depths were calculated for every 25-sec period and 

 plotted by computer. 



Field procedures 



Research was conducted using either the RV William A. McGaw, 

 a 32 m ship used to support submersible research, or the FV Cor- 

 sair, an 18m trawler. Echosounders were used to scout concen- 

 trations of fish over the shallow (60-90 m) portions of Heceta 

 Bank. When dense midwater schools of fish were detected, 

 weighted fishing lines with jigs were lowered to catch fish. Only 

 yellowtail rockfish were caught from these midwater schools, 

 which were usually at depths of 20-40 m. Often the schools were 

 so compact that our fishing weights bounced off fish at these 

 depths. If yellowtail rockfish were readily caught, our position was 

 recorded and an anchored surface float was released from the 

 Corsair to provide a fixed reference to prevent drifting off-station 

 and assist tracking of fish. 



Transmitter signals were detected with a directional hydrophone 

 attached to the end of a 4 m rotatable pole mounted to the side 

 of'the vessels. The hydrophone pole was rotated through 360° 

 until the signal strength of a transmitter was maximal. Then the 

 vessel headed directly toward the transmitter. Signal strength 

 increased as the range closed. When signal strength was equally 

 high in all directions or when the direction of the signal decreased 

 rapidly, we assumed that the fish was in the vessel's immediate 

 vicinity and our location was then determined by LORAN C. Re- 

 peated positions for stationary transmitters on the bottom were 

 within O.lnmi (~180m) from one another. Repeatable accuracy 

 of Loran C for one vessel is about 100 m (Dugan and Panshin 

 1979). 



Results 



Horizontal movements 



1 988 (Fig. 3) Four yellowtail rockfish were caught near the bot- 

 tom, tagged, and released during September 1988. Three fish were 

 released where they were caught, and the fourth was displaced 

 about 1 nmi seaward of its catch location. Fish 1 was caught and 

 released over a shallow (71m), high-relief rocky area of Heceta 

 Bank on 15 September (Fig. 3). Three locations were determined 



44"02 



44°00' 



43 58' — 



124° 55' 



124° 51' 



Figure 3 



Locations and tracks of yellowtail rockfish 

 Sebastes flavidus tagged and released in 1988. 

 Fish 1, released 15 September at 1919 h ( • ), was 

 located 24 h later (■), and was found within the 

 open circle (O) during seven intervening fixes. 

 Fishes 2, 3, and 4 were released 13 September 

 ( • ) and followed indicated paths. Fish 3 moved 

 less than 200 m. 



immediately after release, three after 12 h, 

 and two after ~24h. All locations were 

 within 0.5 nmi of one another, and the last 

 was O.lnmi from the capture site. Fish 2 and 

 3 were caught, released, and detected once 

 over the southernmost shallow portion of 

 Heceta Bank at a depth of 80 m on 13 Sep- 

 tember. One of these fish was located ~0.75 

 nmi (1400 m) east of its capture location 

 after 7h. The other fish was found within 

 200m of the release site 17h after release. 

 To determine if a stationary transmitter 

 location was the result of a regurgitated tag, 

 the submersible Delta, with a separate 

 hydrophone and receiver, dove on Fish 3, 

 which remained close to the release site. The 

 ship maintained position over this transmit- 

 ter as the submersible was launched. Al- 

 though a strong signal was recorded from 

 the transmitter, its bearing changed fre- 

 quently, indicating that the tag was moving 

 and had not been regurgitated. This was 

 confirmed when the bearing of the transmit- 

 ter changed 180° as a school of several hun- 

 dred fish swam under the submersible. The 

 fish transmitting the signal had two exter- 

 nal Floy tags but was not seen. 



