FISHERY BULLETIN: VOL. 75. NO. 2 



transmitters, and tracking of the fish were done 

 aboard Linda by three NMFS scientists with 

 assistance from the crew of Linda. Albacore 

 ranging in size from 74 to 87 cm fork length with 

 estimated weights of 8.2 to 13.6 kg were caught on 

 hook and line baited with anchovy. The fish was 

 played an average of 5 min before being brought 

 on board by dip net. Without removing it from the 

 net, the fish to be tagged was placed on its side on a 

 plastic covered foam measuring pad on the deck 

 where it was measured to the nearest lower 

 centimeter and the transmitter was attached. A 

 wet burlap bag was placed over its head to keep 

 the fish calm. No anesthetic was used. 



The ultrasonic transmitter was attached to the 

 back of the fish, immediately in front of the second 

 dorsal fin, with two sutures through the skin and 

 muscle tissue in that area. Upon completion of 

 tagging, fish were immediately replaced in the 

 water. Total elapsed time for fish out of water was 

 between 1 and IV2 min. Within 2 to 4 s after being 

 released, each tagged fish was observed righting 

 itself and actively swimming downward and out of 

 sight. One fish was tracked at a time. The three 

 fish tracked longer than 24 h were tagged in the 

 manner described above. Several fish tracked for 

 shorter periods early in the cruise were tagged by 

 inserting the transmitter into the stomach 

 through the mouth. This latter method was 

 abandoned when it appeared that acoustic signal 

 attenuation caused by internal implacement was 

 resulting in an inadequate receiving range. 



Tracking Equipment 



The transmitter tags and hydrophone used were 

 built by the Northwest and Alaska Fisheries 

 Center, Seattle, Wash. The tags were cylindrical 

 measuring 8.2 by 1.9 cm, weighing 67 g in air and 

 43 g in water, and emitted a 45 or 50 kHz signal at 

 a pulse rate of 120 pulses/min. Acoustic source 

 level of the tag was 63 dB (reference to 1 £ibar at 1 

 m in fresh water). 



The hydrophone was a tuned 6-element array 

 (sensitivity - 69 dB, reference to 1 /xbar at 1 m) 

 with a beam width of 20° horizontally and 40° 

 vertically at the 3-dB point. This was attached to 

 the lower end of a 3-cm aluminum pipe, bracketed 

 to the starboard rail amidship of the tracking 

 vessel. A geared electric motor at the top of the 

 pipe rotated the hydrophone, which was remotely 

 controlled from the tracking station in the 

 wheelhouse. Signals picked up by the hydrophone 



were fed into a Lawson VLF-1 5 superheterodyne 

 receiver. 



Tracking Procedure 



With the hydrophone remote-control unit 

 installed in the pilothouse of Linda alongside the 

 engine and steering controls and the receiver 

 placed about 2 m away, one person was able to 

 operate the tracking system and control the vessel 

 simultaneously. Directing the hydrophone for 

 maximum signal, the operator moved the vessel 

 on that heading until satisfied, on a basis of signal 

 strength, with his proximity to the fish. The 

 receiving range varied widely according to sea 

 state, but on the average Linda was kept an 

 estimated 500 m from the tagged fish. The fish 

 moved continuously and so, consequently, did the 

 vessel, but vessel speed of more than 2 knots was 

 seldom necessary to keep up with the fish. Position 

 of the tracking vessel was determined approx- 

 imately once an hour and was taken also to 

 represent the position of the fish at that time. Most 

 of the navigation for Linda was done by the 

 nearby David Starr Jordan , with a combination of 

 Loran, radar, and Omega systems. 



Oceanographic Observations Made 

 From Ship 



Detailed oceanographic observations were 

 made aboard David Starr Jordan in support of 

 the ultrasonic tracking experiments. These in- 

 cluded continuous monitoring of surface temper- 

 ature and salinity and measurements of sub- 

 surface temperature and salinity at selected 

 stations. Observations were also made to evaluate 

 biological factors of the marine environment. 

 These included continuous monitoring at the 

 surface and subsurface measurements at selected 

 stations of chlorophyll a by fluorometric tech- 

 niques (Holm-Hansen et al. 1965), measurements 

 of primary productivity by 14 C methods (Owen 

 and Zeitzschel 1970), and estimates of the 

 standing stocks of potential albacore food organ- 

 isms. 



The estimates of potential albacore forage were 

 derived from hauls made with a 1.8-m Isaacs-Kidd 

 midwater trawl (IKMT) lined with a 58-mm mesh. 

 The hauls were taken during hours of darkness 



5 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



348 



