the quiet gray whale (eschrichtius glaucus)

Deep-Sea Research, 1965, Vol. 12, pp. 869 to 877. Pergamon Prcss Ltd. Printed in Great Britain,

The quiet gray whale (Eschrichtius glaucus)*

R. A. R.,XSMtSSEW', and N. E. HEAl);-

( Receipted 9 AllL, ttst 1965 )

Abstract--Studies conducted during the period De:ember 22, 1964-March 7, 1965 near San Diego, California and at several locations in Baja California failed to confirm the use of acoustic signals by the gray whale. It is concluded that this cetacean rarely transmits subsurface sounds, and that it utilizes methods other than echolocation for navigation in shallower areas during the day.

INTRODL!CTION

VEINY few investigations have been directed toward the detection and classification of acoustic emissions from the California gray whale, and results of these investigations are inadequate to confirm the use of sound by this cetacean for purposes of navigation or comnmnicat ion.

No sounds identifiable with lhe gray ~xhalc were detected during investigations conducted at San lgnacio L~goon, Baja California, in Februa.'y of 1950 (HtmBS and SNODGRASS). h3 1955, o[T Point Loma, Catilk~rnia, P. V. AsA-D~RI,~N (WENz 1964) observed and recorded a series of audible " c l icks" that were believed to be echolocation :~ignals of the grax whale, presumably emitted by the whale to locate the small boat utilized in the observatiors. A spectrum-time plot of these clicks was fotmd to be similar to one obtained for echolocation signals of the sperm whale. In me, re recent studies conducted at Scammon Lagoon, Baja California IEm¢v,H.XRT aqd EVANS, 1962), tWO sounds were ascribed to the gray whale. These werc described ~s °' Iow-f:equency rumbles, like large amounts of air being released underwater," and " croaker-like sounds." The uppe~" frequency limit of H~e spectrum of these sound,; was determined to be 700 c/s, and the average duration of t!lC cmission~ was reported as 0-1 sac.

The principal goals of the investigations reported here were the confirmation of the use of ccholoc~tion sig:~als by the gray whale, the evaluation of the acoustic properties of these signals, and the determination of the conditions under which l!~ey were emitted. It was al~ticipalcd that communicat ion signals might incident- ally be detected, particularly i~ Lhat part of the study conducted ~_tt Scammon Lagoon where the whale population v, as exceptionally large. During the period December 22, 1964-Marc!; 7. 1965, approxilnately 200 whales were acoustically monitored and visually observed under a variety of conditions and at ranges of less than 1000 m. No subsur~hcc sounds, undeniably attributable to the gray whale, were detected.

*This paper represents results of research sponsored by the Office of Naval Research. +University of California, San Diego, Marine Physical Laboratory of the Scripps Institution

of O:canography, San Diego, California 92152. Contribution from Scripps Institution of Oceanography.

869

870 R . A . RASMUSSEN and N. E. HEAD

I N S T R U M E N T A T I O N

In designing the instrumentation system, emphasis was placed on flexibility of operation. The customary, overside hydrophone was therefore complemented by radio-telemetered sonobuoys that could either be tethered to anchored floats or permitted to drift freely. The system was extremely mobile; and the remote monitoring capability afforded by the sonobuoys enhanced the likelihood of detecting " natural" sound emissions, i.e., sounds that might not be emitted in the presence of a monitoring vessel.

A photograph of one of the sonobuoys may be seen in Fig. 1. The buoy is a 1.2 m length of Plexiglass tubing having an outside diameter of 10.2 cm and a wall thickness of 0.31 cm. Plexiglass discs fitted with neoprene " O ' " rings seal the buoy, and watertight connectors extending through the center of these discs permit attachment of the transmitting antenna and the hydrophone cable. Stability of the buoy with respect to rotation about a horizontal axis is achieved by the attachment of a lead weight to the inside surface of the lower sealing disc and by the placement of the battery-pack immediately above this weight. The mass of the weight is determined by the length of the hydrophone cable and is altered so as to maintain a buoy freeboard of approximately 40 cm. The radio range of the sonobuoys was approximately 3 km and the useful battery life was 10hr. Block diagrams showing the sonobuoys and shipboard instrumentation components appear in Fig. 2. It will be noted that the shipboard instrumentation provides for

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SONOSOOY SHIPBOARD Fig. 2. Sonobuoys and shipboard instrumentation diagrams.

the simultaneous recording of signals from two sonobuoys and one overside hydrophone. The electrical frequency response in each of these channels can be made uniform to within 3 db over the range of from 10 c/s to 30 kc/s. Provision in the tape recorder of one amplitude modulation channel and one frequency modulation channel for each of the received signals permits accurate recording over this large frequency range. It should be emphasized that the entire instrumentation system is battery-operated.

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Fig. 6. An oscillogram of one of the emissions recorded at Todos Santos Bay. Note the second arrival of the signal occurring approximately 0-04 sec after the initial arri,,al.

The quiet gray whale (EschrichtitL~ glaucus) 871

Mention should also be made of the use of a remotely monitored microphone to record the breathing sounds of the whale. A highly directional microphone was mounted 2.5 m above the deck of a modified skiff. Signals from the microphone preamplifier were coupled to the connector terminals at the base of a sonobuoy, the sonobuoy being secured to the skiff in a vertical position. In this configuration, the sonobuoy served as the telemetering transmitter for the remote recording of airborne sounds.

OFFSHORE S'[UDIES (DECEMBER 22, 1964-JANUARY 14, 1965)

Earlier Two-Vessel Observations. Initial efforts were directed toward the detection of echolocation signals emitted by the gray whale during its southward passage from Point La Jolla, California to the Coronado Islands which lie 32 km south of Point Loma. Charts showing this part of the annual migration route are sketched in Figs. 3 and 4. The earlier investigations required two vessels : one vessel would

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Fig. 3. Chart of the San Diego area showing routes followed by gray whales m their passage from Pt. La Jolla to Pt. Loma. A region of convergence is indicated by the encircled cross.

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cruise northward from a preselected position until a whale or a group of whales was sighted, whereupon the second vessel was notified of the sighting and the course of the sighting vessel was altered to follow in the path of the whale(s). The second vessel, carrying the acoustic monitoring and recording apparatus, was located at a point 3-5 km to the south. By noting the course of the first vessel and

872 R . A . RASMUSSI:;N and N. E. HEAD

allowing for drift due to wind and current, the observers would to position the second vessel and/or a freely drifting sonobuoy in

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Fig. 4. Chart showing some migratory paths taken by gray wlmles in their passage lrom Pt. Loma to the Coronado Islands. Note the convergence of paths off South Coronado Isiand.

whale(s) at a range o f less than 500 m. Fhis procedure was succcs~ftH m that i,:~: or twelve whalcs (it is not always possible to determine accura teh the number ~.'. whales in a group) were observed to pass the monitoring vessel at ranges of lc,~, than 200 m. On three occasions, whales passed between the overside hydrophor~c and a sonobuoy hydrophone located not more than 100 m distant; and on oH~: occasion, a single whale passed within 20 m of the overside hydrophone. N,> acoustic signals attributable to the gray whale were ever detected during the~u measurements or in later analyses o f the tape recordings. Observations at Migratory Convergence Regions. During the two-ship investiganon,; near the Coronado Islands, it was observed that while the whales utilized variou,, approaches to these islands, the great majority passed through a small region lying approximately 500m west of the southern tip of South Coronado Island (see Fig. 4). It became apparent that a sighting vessel was unnecessary: the monitoring vessel need only to lie in wait at this location with an overside hydrophone and one or two sonobuoys in readiness. Spouts of the approaching whales

The quiet gray whale (Eschrichtius glaucus) 873

were easily visible at ranges as great as 3 kin. This procedure was successfully followed, and during four days of observation, approximately fifty whales were observed to pass within 200 m of either the vessel or the sonobuoy; at least seven whales dived directly under the vessel without changing course. The water depth in this region is approximately 60 m and increases very rapidly with distance from the island. Hydrophone depths ranging from 30 to 55 m were utilized, and occasional ett"orts were made to provoke echolocation by energizing various sound generators (including the ship's engines) while monitoring a sonobuoy well removed from the ship and in the path of the approaching whales. Despite a relatively low ambient noise level, all efforts to detect any acoustic emissions from tile whales met with failure.

Another convergence region was accidentally discovered off Point Loma, this region being located approximately 2 kin offshore, 4 km north of the Point koma light and corresponding to the westernmost edge of the kelp beds (Fig. 3). The water depth at this site is approximately 28 in. On several occasions, whales moving southward from La Jolla on courses both to the east and west were observed to change course and move into this region before continuing southward past Point Loma. It should be emphasized that not all of the whales sigllted passed through this region, nor did all the whales passing through the region alter their course to do so. However, the vessel could be stationed here with the assurance that a majority of the whales sighted would pass within 500 m of the hydrophone.

Early one morning, while measurement preparations were being made at this location, a heavy fog settled over the Point Loma area. Visibility was limited to 1000 m or less and the monitoring vessel was forced to use the western edge of the kelp bed in determining its position. Eight whales passed through the region during a two-hour period. Three of these passed within 100 m of the overside hydrophone and one dived directly beneath the vessel. Again, no whale emissions were detected. It should be mentioned, however, that the ambient noise level in this region is relatively high, the principal noise sources being snapping shrimp.

The fortuitous location of the two convergence regions described above led to speculation concerning the existence of a third such region to the south of the Coronado Islands. On two different days., groups of whales were followed past the tip of South Coronado Island for several miles. The course taken by both groups was approximately 150T, and projection of this course indicated that the whales were headed toward Todos Santos Bay. A two-day visit to this location confirmed only that there was a considerable migratory population in the area. Later, a group cf four whales was followed from South Coronado Island to Todos Santos Bay, the course of the group being indicated in Fig. 5. The group arrived in the Todos Santos Bay area at dusk and was approaching the channel separating the Todos Santos Islands and Punta Banda when visual contact was lost. The ship was stopped and a sonobuoy was launched approximately 10 minutes after the last sighting, the estimated range to the whales at the time of launching being 600 m. A series of intense sounds were detected immediately following the sonobuoy laanching, the last emissions in this series being considerably attenuated and occurring 15 minutes later. An oscillograph showing one of these emissions appears in Fig. 6. The duration of emissions was approximately 0.05 sec and the interval between emissions varied from 1 to 15 sec. Some listencrs have likened the sounds


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Fig. 5. Chart showing the course followed by a group of four whales from South C'oronado Island to Todos Santos Bay. The solid circles denote radar fixes.

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to those produced by hammering against the hull of a wooden ship. However, they might better be compared with the sound produced by a light wooden door. e.g., a window shutter, as it slams against its stops. The sound is not unlike that observed at former Pacific Sofar Stations and referred to as the " carpenter " sound by WENZ (1964). WORTHINGTON and SCHEViLL (1957) reported hearing similar sounds during auditions of the sperm whale.

No sounds resembling the sperm whale " clicks " recorded by SCHEViLL and WATKINS (1962) were detected.

The " c a r p e n t e r " sounds were heard on this one occasion only and cannot definitely be attributed to the gray whale. However, a group of whales was moving into a navigationally hazardous area, it was dark, and the estimated time required for the whales to arrive at the Todos Santos Islands-Punta Banda channel coincided with the period during which the sounds were detected. The interesting possibitits. is that the sounds were echolocation signals and that they were not emitted at any other time simply because the conditions did not necessitate echolocation.

I t was not determined whether the group continued southward or rested in the area overnight. However, a large number of whales was seen in the vicinity of the


Todos Santos Islands on the following morning; hence there is little doubt that these islands represent another convergence region on the migration route for at least some of the herd.

STUDIES IN SCAMMON LAGOON ( F E B R U A R Y 2 3 - M A R C H 7, 1 9 6 5 )

Station 1- The Nursery. A chart of Scammon Lagoon showing the points at which acoustic studies were conducted is sketched in Fig. 7. The Nursery is a region of comparatively shallow water scored by several channels having depths of not more than 15 m. It is so named because the calves are born and receive their early nursing and training in this region. The ambient noise level is extremely

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Fig. 7. Chart of Scammon Lagoon. Encircled crosses designate monitoring stations.

high, being generated principally by snapping shrimp and probably several species of bivalves. The level of noise was sufficiently high to permit unamplified audition of the din in below-deck compartments of the research vessel. During the four- day station at the Nursery, thirty to forty whales, mothers and calves (adult males


apparently do not frequent the Nursery), passed within 200 m of either the overside hydrophone or a tethered sonobuoy hydrophone located 1000 m l¥om the vessel and at a depth of 10 m. Although no waterborne whale sounds were detected.. some rather spectacular recordings of the breathing sounds of both the :~duJt fcma',,. and her calf were obtained using tile directional microphone. In tH~taining th< recordings the small boat was positioned so as to drift toward a mott 'er ,ahale and her offspring. The directional microphone was then aimed at the blowholes of ti>. whales as they passed at ranges o f from 2 to I00 m. Needless to ,;av. anxiou>, moments were suffered by the observer'< Station 2-Stony Island. On two ditl'ercnt days, the ship was stationed m narrow channel bounded by Stony Island and a submerged sandbar. [ h e maximum depth o f this channel was 14 m. and the ship served as an obstacle in the path ~,! the more than thirty whales which passed at ranges of from 20 to 200 nt. Although the ambient noise level ~.a.~ c~msiderabtv below that measured at the Nursery. n~ whale sounds were detected.

A submerged spit extends from the sandbar, curxcs in the direction of Sto,~,~ Island, and parallels the main channel for a distance of approxilna~ciy 1-2 kin. thereby forming what might be termed a "" false "' channel. On several occa~i<>n: whales were seen to enter this cimnnet after passing the ship en r(mte Io ii~, Nursery. Upon discovering thal no through passage existed, these whales proceeded ,< " s p y h o p " : i.e., they extended their heads vertically above the w:~.tcr For period> as great as eight seconds, as if at tempting to visually determine thch- Incat ion Eventually, they retraced their course, circled the end of the spit and continl.lcti on toward the Nursery via the main channel. fhi> behaviour pattern has i)ee;~ observed many times during previous expeditions to the lagoon (N~w~r¢c,r~t. Station 3 771e Deep Chalme/. In this part of the lagoon tile water depli~ exceed- 50 m and the noise level is comparatively tow. The ship remained at anchor ,>r~ this station for 20 hr. Again there was considerable whale activity near .q~e overside hydrophone, and again no whale sounds \~cre heard. However, the [otld ~.,ices c,~ two or three croakers were audible in the period of from 7 : 45 p.m. ~ i i 00 p.n~ and a group of four or live small porpoises was oeca~ioaally heard ~,.~ ciuck :t.qc, chuckle during their three-hour xisit near the ship on the following morning. Station 4 -The LagooH Etltrgtl,{c. All ex!raordinar{ly large number e l ,'~,i~ales \xa,~ observed to pass in and out ,.q' the emrancc channel during the d~31igiil ii~urs The channel appeared to be at once a playground, a training area and ga mating rendezvous. Single whales, mothers and calves, and mating whale> were ~,,li observed in this area. On two successive days, the ship was anchored ~ear tile center o f the entrance channel and slightly seaward of the southea.,tern tip of the Nor th Sand Dunes. The average water depth at this site wa> 13 m. ,\!~ ~er .&ie hydrophone and sonobuoys were simultaneously monitored at this ~tation. l h e sonobuoys were transported upstream from the ship in a small motorboa t a.lld launched at distances exceeding 1000 m. They were then permitted to drift fl'eeI: with the tidal currents until either they drilied into shallow water ~ ih% wen; carried f rom sight, whereupon they were retrieved and relaunched.

On numerous occasions whales were observed at ranges of less thaq 50 ..'n from the overside hydrophone or the sonobuoys. On one occasion a sonobuL:~y was launched 40 m from a mating trio (two males and one female) and remained


within 100 m of these whales for a period o f twenty minutes. Still there were no detectable sonic emissions.

CONCLUSION

The negative results of these studies do not warrant the conclusion that the gray whale is not soniferous. However, they suggest that this cetacean does not find it necessary to transmit echolocation signals in shallower water during the day. There is little doubt that the gray whale can determine its location visually from landmarks, and observations in Scammon Lagoon would indicate that it will " spyhop " out of curiosity as well as f rom navigational necessity (GILMORE, 1955). On the other hand, this visual capability would be of no utility in a heavy fog or under overcast skies at night. It would therefore appear that the gray whale employs other senses to navigate inshore areas, and its passive, acoustic location of the shore (or the kelp beds which harbour noise-making creatures) is certainly a real possibility.

Whales moving southward from points north of La Jolla have been observed to change course abruptly and head toward the shore upon passing into the comparatively deep water (400 m) of the La Jolla Canyon (WALKER). It is possible that these whales sense the change in depth and alter their course to follow a depth contour. However, the group of whales tracked southward f rom the Coronado lslands passed rather abruptly from shallower water into depths exceeding 200 m without deviating from their course. Furthermore, no whales were observed to join or leave the group during their passage from the Coronado Islands to Todos Santos Bay: hence, the use of a " s c o u t " is unlikely.

Acknowledgments--The chart sketched in Fig. 7 was made by Capt. R. C. NEWBEGIN Of the Scripps Institution of Oceanography and is perhaps the most accurate chart available. The track of the whale group followed from South Coronado Island to Todos Santos Bay was recorded by T. J. WALKER of the Scripps Institution of Oceanography and is presented through his courtesy.

REFERENCES

EBERHART R. L. and EVANS W. E. (1962) Sound activity of the California gray whale, Eschrichtius glaucus. J. Audio Eng. Soc., 10, 324-328.

GILMORE R. M. (1955) The return of the gray whale, Sci. Am., 192 (1): 62. HUBBS C. L. and SNODGRASS J. M. Univ. of California, Scripps Inst, Oceanog. (Personal

communication). NEWBEGIN R. C. Univ. of California, Scripps Inst. Oceanog. (Personal communication). SCHEVILL W. E. and WATKINS W. A. (1962) Whale and porpoise voices. A phonograph

record. Woods Hole Oceanographic Institution Contribution Number 1320. WALKER T. J. Univ. of California, Scripps Inst. Oceanog. (Personal communication). WENZ G. M. (1964) Curious noises and the sonic environment in the ocean, pp. 101-119.

In: Marine bio-acoustics, W. N. Tavolga, Ed. Macmillan, New York. WORTHINGTON L. V. and SCHEVILL W. E. (1957) Underwater sounds heard from sperm

whales. Nature, Lond., 180 (4580): 291.

the quiet gray whale (eschrichtius glaucus)

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