FISH and VANIA: KILLER WHALE SOUNDS 



was turned on) or keep them from moving- up 

 the river (when the sound was turned on before 

 the whales started upriver) . 



We had an excellent view of the river from 

 the third floor of a building about 25 m above 

 the water at Station A. Frequent low-altitude 

 flights in small planes provided a check on the 

 exact location of the whales when they could 

 not be seen from the building. The white-col- 

 ored whales were easy to see in the muddy brown 

 river. 



In all, there were 14 playback trials plus 7 

 control trials in which the whales were observed 

 but sounds were not transmitted. The number 

 of whales involved in each trial ranged from 50 

 to near 500 with about 100 being the average 

 group size. Because several years of observa- 

 tions indicated the belugas move up the river on 

 every incoming tide, we did not feel it was nec- 

 essary to have an equal number of transmission 

 and control trials. Consequently, we introduced 

 a control after no more than four successive 

 transmissions, primarily to determine if the be- 

 lugas had stopped using the river as a result of 

 the sound playbacks. 



The sound pressure level of the playback 

 sounds transmitted from Station A was mea- 

 sured at 6 locations in the river within 4 km of 

 the source (Table 1). All levels reported in 

 this paper are in db, re 1 fiN/m'. Sandbars pre- 

 vented good transmission across the river, par- 

 ticularly during the early stages of the flood 

 tide when some of the bars were covered by less 

 than 0.5 m of water. For example, the sounds 

 projected from Station A were below the back- 

 ground noise level at Location 6 (Figure 2) . The 



Table 1. — Sound pressure level (db re 1 /xN/m') of 

 playback signals and ambient noise at the indicated 

 locations. 



Location, 

 Fig. 2 



Signal 

 broad- 

 band 



Ambient noise 



Broad- 

 bond 



500-5000 

 Hz bond 



best transmitting channel was downriver toward 

 Telephone Point (Location 2), where a level of 

 132 db was measured for the playback signals. 

 Beyond this area, the signal level dropped off 

 quickly because of the shallow water which ex- 

 tended out a considerable distance from the 

 Point. Most of the energy of the playback 

 sounds occurred in a frequency band from 500 

 to 5000 Hz; thus we measured ambient levels 

 in this band in addition to making broadband 

 ambient measurements. 



RESULTS OF PLAYBACK EXPERIMENTS 



In the first seven transmission trials, we let the 

 whales move up the river on the west side to 

 within approximately 2 km of the sound source 

 before turning on the playback. The first six 

 times, the animals turned immediately when the 

 sound began and swam directly out of the river 

 against the strong incoming tide. Their rate 

 of blowing increased and they spent more time 

 at the surface of the water, making it very easy 

 for us to observe their course. On the 7th trial, 

 some of the animals crossed to the opposite side 

 of the river when the sound started and swam 

 downstream along the sandbar (Location 4). 

 The others remained just ofi" Telephone Point 

 for an hour, then moved out of the river. 



It was difl^cult to see the approaching belugas 

 on the 8th trial because of low light, and they 

 had already moved up to Location 6 before we 

 started transmitting. About half of the 100 

 whales continued up the river; the others turned 

 and swam back out along the sandbar. On the 

 next trial, the animals were first seen moving 

 up the river along the sandbar. Possibly they 

 learned from the previous eight transmissions to 

 avoid the side of the river where the sound pro- 

 jector was located. They continued up to the 

 end of the bar, even after the sound was turned 

 on, but then rounded it and moved back down the 

 river on the other side of the bar (Location 5). 



The belugas similarly rounded the upriver end 

 of the sandbar on the 10th trial; but, instead 

 of turning around, they swam to the shore (Lo- 

 cation 7) and continued up the river very close 

 to the bank. Poor transmission to this location 



533 



