WOODS HOLE OCEANOGRAPHIC INSTITUTION Woods Hole, Massachusetts REFERENCE NO. 68-58 CERATOSCOPELUS MADERENSIS: PECULIAR SOUND-SCATTERING LAYER IDENTIFIED WITH THIS MYCTOPHID FISH by R. H. Backus J. M. Teal J. E. Craddock A. S. Wing R. L. Haedrich G. W. Mead 0 L. Shores W. D. Clarke
October 1968
with supplementary notes by Richard H. Backus
•. TECHNICAL REPORT Submitted to the Office of Naval ReseaPch Wtder Contracts Nonl'-3484 (00) ~ NR 260-107~ Nonr-4029(00)~ NR 260-101; with National Science Foundation Grant GB-4431.
Reproduction in whole or in paPt is pe~itted for any purpose of the United States Govern ment. In citing this report in a bibliography~ the referenae given should be to "Saienae~ Vol. 160~ No. 3831, 1968, pp. 991-993." This document has been approved for public release and sale; its distribution is Wtl.imited.
Earl E. Hays, Chairman Department of Geology d Geophysics i
ABSTRACT
A sound- scattering layer, composed of discrete hyperbolic echo-sequences and apparently restricted to the Slope Water region of the western North Atlantic, has been identified from the Deep Submergence Research Vehicle ALVIN with schools of the myctophid fish Ceratoscopelus maderensis. By diving into the layer and using ALVIN's echo-ranging sonar, we approached and visually identified the sound scatterers. The number of echo sequences observed with the surface echo-sounder (1 /23. 76 x 105 cubic meters of water) checked roughly with the number of sonar targets observed from the submarine (1/7. 45 x 105 cubic meters) . The fish schools appeared to be 5 to 10 meters thick, 10 to 100 meters in diameter, and on centers 100 to 200 meters apart. Density within schools was estimated at 10 to 15 fish per cubic meter. Reprinted with permission from SCIENCE, May 31 , 1968; Vol. 160, No. 3831. Pgs. 991-993 Page 991
Ceratostopelus maderensis: Peculiar Sound.Scattering Layer Identified with This Myctopbid Fish
Abstract. A sound-scattering layer, composed of discrete hyperbolic echo sequences and apparently restricted to the Slope Water region of the western North Atlantic, has been identified from the Deep Submergence Research Ve hicle Alvin with schools of the myctophid fish Ceratoscopelus maderensis. By diving into the layer and using Alvin's echo-ranging sonar, we approached and visually identified the sound scatterers. The number of echo sequences observed with the surface echo-sounder (1 I 23.76 X 103 cubic meters of water) checked roughly with the number of sonar targets observed from the submarine (117.45 X 101 cubic meters). The fish schools appeared to he S to 10 meters thick, 10 to 100 meters in diameter, and on centers 100 to 200 meters apart. Density within schools was estimated at 10 to 15 fish per cubic meter.
A peculiar sound-scattering layer, ap places, the layer in the Slope Water has parently restricted to the Slope Water been continuously recorded for tens of region off northeastern United States kilometers; at others, only in small and eastern Canada (1} (Fig. 1), differs patches or not at atl. An examination of from typical deep scattering layers of the broadband sound-scattering proper oceanic echo-sounder records in the ties of the layer (2} during an evening structure of the echo-sequences. Suc ascent showed that the layer best scat cessive trains of echoes do not form the ters sound at progressively lower fre usual homogeneous band of reverbera quencies as the layer shoals. It best tion such as that which results from the scattered sound at about 12 khz when receipt of sound scattered by numerous near its midday depth (accounting for objects of low target strength. Instead, the high intensity of the echo-sequences they form discrete hyperbolic echo on 12-khz echo-sounder records during sequences such as those which result daytime); at 30 m the layer best sce.t from the receipt of sound scattered by tered sound at about 3 khz. a few objects of high target strength. The layer was present at 39°48'N, The layer makes a diurnal vertical mi 70°33'W, in a depth of about 1800 m gration. Midday depth to the shallowest Page 992 echo sequences on the echo-sounder record is commonly about 330 m. Dur south of Woods Hole, when we began ing the evening ascent, the layer has a series of exploratory dives in the been traced to depths as shallow as mesopelagial there with DSRV Alvin 20 m. on 3 October 1967. We dived to near The layer has been observed in all the bottom of the layer, as shown by parts of the Slope Water, but is irregu the echo-sounders of Alvin's tender, larly developed. A similar and possibly Lulu, and the support ship, R.V. Gos related sound-scattering feature has nold. There, Alvin's echo-ranging sonar been occasionally observed east of (3) showed a number of sound-scat Newfoundland. At some times and tering groups nearby (Fig. 2). Turning
\ I Page 992 out Alvin's lights, we chose one such volume of water registered by the two group and approached it. When the so systems. nar indicated "range zero," we turned on Assuming a 15° vertical beam width, the lights and found we lay in the middle we ~ounted targets on photographs of of a dense school of Ceratoscope/us Alvin's sonarscope at times when the maderensis (Lowe) 1839 (4) (Figs. 3 whole sonar beam was within the layer. and 4). Driving through the school, we Using six sonarscope photographs made captured several liters of fish with a net on three different days and at various that had been rigged on the front of depths, we calculated an average water the submarine. volume per target of 7.45 X 105 m3, Except for the collection of speci Using echo-sounder records made by mens, this procedure was repeated Lulu ( Gifft Depth Recorder) and about 25 times in the course of eight Gosnold (Litton Precision Depth Re 3- to 4-hour dives during 3 to 6 Octo corder), we noted the number of hy ber, and always gave the same result. perbolic echo-sequences that intersected Each time that a target was chosen from a single sweep of the echo-sounder Alvin's sonarscope and approached, a stylus. We computed the radial thick· Ceratoscopt!lus school was viewed. The ness of the figure containing the targets vertical distribution of the sound-scat by taking the minimum soundings to tering groups seen by the surface echo the shallowest and deepest targets sounder corresponded closely with the counted, even though these soundings vertical distribution of those seen from generally did not occur at the instant the submarine. Although it seems evi of the count. A beam width of 60° dent that the sonar targets seen by both was used (5). Thirty calculations gave are the Ceratoscopelus schools, we have an average water volume per target attempted to check this by compar of 23.76 X 105 m3• Undoubtedly, the ing the number of targets per unit Page 991
E' -.s:: ~ 400 ~
Fig. l. Portion of 12-khz echo-sounder record made from R.V. Gosnold with Litton PDR near 39. 48'N, 70.33'W late in the morning of 6 October 1967. Page 992
Fig. 2. Photograph of Alvin's sonarscope [500-yard scale (457-m)] made near 39"48'N, 70" 33'W late in the afternoon of S October 1967 at a depth of about 300 m.
Fig. 3. Photograph of Ceratoscopelus maderensis school made from Alvin near 39"48'N, 70"33'W on the morning of 3 October 1967 at a depth of about 600 m. Page 992
Fig, 4. cz~r~IOSCOP_elu: mod~r~nsis, a S4-mm male collected by .Alvin on 3 October 1967 ncar 39 48 N, 70 33 W at a depth of about 600 m. [Drawing by Martha Howbcrt].
oriented with respect to one another. Page 993 Although this species is well fitted with continuously recording surface echo light organs, no bioluminescence was sounder gives a better estimate of water observed save from specimens in the volume per target than the instantane net, which emitted blue flashes from an ous sonarscope photos do. There is no undetermined source. The dusky dorsal chance of confusing signal with noise lobe of the caudal fin was prominent in the first, but this is unavoidable in and is a useful field mark. There was the latter. This fact probably accounts very little variation in the size of fish for the smaller average water volume in the schools. The 774 specimens col per target computed from the sonar lected by Alvin from 3 to 6 October scope photos. and measured to the nearest millimeter When Alvin approached a Cerato had a mean length of 62.4 mm, a scop~lus school and turned on her lights, standard deviation of 2.9 mm, and a the fish reacted in a characteristic way, range of 52 to 73 mm. swimming vigorously for a few strokes, We estimated the density of fish in coasting for about an equal period, and, little-disturbed schools to be from 10 alternating thus, rapidly moving down to IS per cubic meter of water. There and away from the submarine. Schools was considerable variation in the diam deep in the layer appeared to react eter of schools. We tended to pick large more slowly and less vigorously to the sonar targets for examination and ap submarine than shallower schools. The proached some schools whose diameter submarine's lights appeared to be her was as great as 100 m. A common di most disturbing element. Using flash ameter of the targets displayed on the lights, we made some observations in sonarscope was about 25 m. Some of schools with the submarine's lights out. the targets seen may not have been Cera These and observations made immedi to:rcopelus schools, of course, although ately after the submarine's lights were all targets approached were, including a turned on showed that the fish in the few deliberately chosen for their small schools were at rest. They hung motion diameter (about 10m). We could make lessly in the water, sometimes horizon neither visual nor sonar estimates from tally, but often a little obliquely. They Alvin of the vertical dimension of appeared to be neutrally buoyant. They schools. Surface echo-sounder observa were pointed in random directions, un- tions indicate that they were commonly ., Page 993 In the course of a dozen years of intensive exploration with the echo from S to 10 m thick. Thus, the schools sounder in most parts of the oceanic appeared to be disk-shaped. North Atlantic, we have observed deep It was also difficult to estimate the scattering layers composed of hyper distance between schools. We often bolic echo-sequences only in the Slope noted upon seeking another target, hav Water region and in the waters east of ing made observations of one, that the Newfoundland (7). The principal ques nearest was about 200 m away. How tion that arises from the identification ever, some observations indicated that of Ceratoscopelus maderensis with such the lighted submarine was repellent to a deep-scattering layer, then, is this: Why the schools out to about this radius. are such layers so restricted geograph Furthermore, a school as near to the ically? Not only does C. maderensl.r submarine as 100 m need only have inhabit a wide range in the northern been 25 m deeper or shallower than the North Atlantic, but some, at least, of submarine to have been outside the the dozens of other species in the ubiq purview of the sonar. Because of the uitous oceanic family Myctophidae (in nature of the sonar beam, the separa cluding the abundant, widespread Cera tions shown in the sonarscope photos toscopelus townsendl) might well be ex cannot be taken at face value. Perhaps pected to cause similar acoustic effects the best estimates of the mean distance in many or all parts of the world's deep between schools are the ones derivable ocean. from the water volumes per school es R. H. BACKUS, I. E. CRADDOCK . timated above. A sphere whose volume R. L. HAEDRICH, D. L. SHORES • is 23.76 X 10~ m3 has a diameter of J. M. TEAL, A. S. WINO • 166 m; one whose volume is 7.45 X Woods Hole Oceanographic Institution, 5 3 10 m , a diameter of 112 m. Other Woods Hole, Massachusetts estimates of school separation do not G.W.MEAD violently disagree with these. Museum of Comparative Zoology, Why do these aggregations of Cera Harvard University, loscopelus maderensis form? No feed Cambridge, Massachusetts ing activity was observed, nor did there W. D. CLARKE seem to be any concentration of food Ocean Research Laboratory, organisms within the schools. No spawn Westinghouse Electric Corporation, ing activity was observed; the gonads of San Diego, California 71 specimens collected by Alvin were examined and found to be little devel Rdereaca pd Nola oped. The ratio of males to females in 1. This repon extends from lbo edse of lbo continental shelf to the nonhero cdae of lbe these 71 fish was about 3.4 to 1. It has Gulf Stream betwee~t Cape Haneras and lbo been suggested that schooling, in some tall o( lbe Gr1111d Bllllks. The Slope Water hu been deftncd lllld described b)' C. O'D. Iselin, fishes at least, minimizes predation; Pap. Phy$. Oc:ranoKr. Mrtrorol. 4, t:Z (1936). individuals are less often found by l. Followlns In scneral the melbods described by 1. B. Heney, R. H. Backus, 1. D. Hell· predators when aggregated than when wl1, Drrp-Sra R.rs. I, 196 (1961). The ob dispersed (6}. Perhaps it is for this rea aervatlons were made at 38"45'N, 68"58'W on 15 May 1961. son that C. maderensis schools. We 3. StrDZD Industries Modd 500 Continuous Trans mlctlns Frequency Modulated Scannlna and observed no predators feeding in the Navlaatlon Sonar. which operates over tho schools, although squids (Loligo or Om band from 87 to 72 khz. The horlzonlal beam width Is :z• {between half-power points), and mastrephes sp.) on a few occasions the vertical beam wldlb Is 15". The 10aar seized individuals close to the subma sweeps throush a 270" sector centered on the fore and aft axis or lbo submarille and Is DOt • rine's lights . trainable In lbo vertical plane. Page 993
4. Crrt~loscopellll lfllldrrrnsl.t has a well-devel· oped, sas-lllled swimbladder. In a 61.1-mm male~ uamined by us, the relaxed orsu meu ured 5.7 bY 1.9 by 1.3 mm. The structure or the awimbladder in the c:onsener C. rowmrndl has been described by N. B. Marshall (DIJ· COI'tr1 Rtp. 3l, 41 (1960)}. 5. This Is not the value ordinarily assumed ror the tranaduc:cr used, the UQN-1b, whose beam width between half-power points is 30", but was calculated from our records from the minimum and maximum soundin1s recorded from slnalc hyperbolic echo-sequences. 6. C. M. Breder, Jr., Zoolorlct~ (N.Y.) 52, lS (1967). 7. To Judp from the literature, such laycn are extremely rare for the world ocean as a whole. One has been reported from olf Lower Call· fomia by E. 0 . Barham and I. E. Davia, NIJ\·al Electron. Lab. Rrp. 1361, 9 (1966) (Conlldcntlal). This layer has a rHdlan midday depth or about 200 m and has been asaodated with the Pacific hake, MrrlucciU.t productus, Another such sound-scattcrlna feature has been observed olf the coast of South Arabia, lntrr tu!tlont~l Indian OCI!'an Expedition, Crube Re port, Cr11lse I RRS Discovery (Royal Society, London, 1963), p. 16. No orsanlsm was as sociated with this layer, whose midday depth was about 300 m. 8. This paper Is Contribution No. 2061 from the Woods HoJe Occano.,aphfc Jnatltutlon. Supported in part by contrDCts Nonr-3411-4(00) and Nonr-4029(00) and by NSF arant OB-4431. We thank the many shipmates who have helped us, particularly Alvin pilots W. 0. Raln nle, M. J. Mc:Camls, and E. L. Bland, Jr. I January 1968: revised 14 February 1968 SUPPLEMENTARY NOTES
The scattering layer described in the enclosed paper is the one 11 that has been known at WHOI for some years as "Alexander's Acres • The layer is characterized not only by the teepee·- like structure of the echo sequences. but also by various behavioral properties such as the depths occupied by day and by night. Scattering layers composed of teepee-like echo sequences are rare in the deep ocean, but are common over the continental shelves . None of the shallow- water layers should be confused with Alexander' s Acres . The fish responsible for the latter, Ceratoscopelus maderensis. is never found in water shallower than !00 or 200 fathoms except by accident.
Not too much is known yet about the acoustic properties of Alexander's Acres. However, a set of observations using explosions as sound sources showed that the layer when at a midday depth of about 150 fathoms scattered sound best at a frequency near 12 kHz. When the layer moved up close to the surface at night, the frequency at which it best scattered sound dropped to near 3 kHz. Because 3 kHz is close to the operating frequency of modern high- power sonars and because the fish causing the layer can be very abundant, it is easy to see that when this layer is present night-time operation may well be difficult.
Alexander ' s Acres has been observed with certainty only in the Slope Water region of the western North Atlantic (densely stippled area of Fig. A) . On the other hand. the fish responsible for the layer is known to have a much wider distributwn (cross- hatched area of Fig. A). Why the layer is not to be found wherever the fish is to be found is an mtrigumg question, but the several possib1e answers need not be explored here. A sound- scattering feature similar if not identical with Alexander 1s Acres has been seen now and again on echo-sounder records made between Newfoundland and Ireland (lightly stippled area of Fig. AL and this may also be caused by Ceratoscopelus.
Naval vessels operating in the Slope Water region or in the wide area between Newfoundland and Ireland can determine whether such layers are present by operating their UQN or other deep water ec ho- sounder during • '
Ceratoscopelus moderensls
AREA OF CERTAIN OCCURRENCE OFALEXANOERSACRES
AREA OF POSSIBLE OF ALEXANDERS ACRES
Fig. A . Distribution of Alexander's Acres and of the fish responsible for the layer, Ceratoscopelus maderensis. The wavy margins and question marks indicate where the boundaries are most open to question. - 2 -
daylight hours1. (During the night the layer is so close to the surface as to be indistinguishable from other near-surface sound· scattering. ) One might, then, on the basis of daytime echo-sounder observations better choose the area for a certain operation on the basis of the presence or absence of the layer. At the very least the presence of the layer during hours of daylight would tell the operator that during the coming night active sonar operations at frequencies in the neighborhood of 3 kHz will be more than normally difficult. (It must be remembered, of course, that the layer can be very sporadically developed. In such a case, sonar conditions can change drastically with a relatively small change in ship's position. )
Considerable variation in the density of the layer has been observed. At times as many as 15 or 20 schools may be within the cone of the echo sounder all returning echoes during a single sweep of the recorder. At other times only one or two schools are present. Obviously reverberation levels will be much higher in the first case.
This report can be summarized as follows:
1) Nighttime reverberation levels in the band around 3 kcps will be considerably higher than usual when the scattering layer called Alexander's Acres is present.
2) This layer is composed of teepee- like echo sequences, generally has a midday depth to the top of the layer of 150- 200 fathoms ~ and moves up to near the sea surface at night.
3) The layer occurs in the Slope Water region and possibly in the waters between Newfoundland and Ireland~ but is sporadically developed.
4) Whenever it is useful to anticipate the extra nighttime increase in volume reverberation, a vessel can determine the presence or absence of the layer by operating its echo· sounder during daylight hours. 1 Operators using the echo-sounder for examining the midwater sound scattering should remember to operate the sounder at a much higher gain than is necessary simply to make a good recording of the bottom.
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~~:.~~!err~~·:a.~aphlc lnstttutton WoOf!s Hole Oceanographic Institution 1. Sound-scattering ~ Reference No. 68-58 1. 2. llyctophld Fish 2. llyctophld FIsh~ CEAATOSCOI'!LUS IIADEII£HSIS: PECUliAR SOOIIO-SCAnERIHC CEAATOSCOI'ElUS IIADER£NSIS : PECUI.IAA SOUIIO-SCAn£RIIIG ·-··" ..... I lAYER IOEIITIFIEO IIJTH THIS HYClOPHID FISH by R.H. Bockus , 3. Ceroto
Woods Hole Oceonographlc Institution =~:.~~!·H~e:&.,a"phlc Institution Reference llo, 68-58 1. '•"'·•a••••• 1. 2. Hyctophld Fhh ~ 2...... llyctophtd Ftsh I CEAATOSCOI'Eli/S IIADE~EitSIS: PECUliAR SOOND-SCAnERING CEAATOSCOI'£LUS IIADEREHSIS: PECUliAR SOOHO-SCAnERING lAYER IOEHllFI£0 WITH THIS HYCTOPHIO FISH by R.H. Bockus, 3. CerotoscopelU$ naderensh LAYER IOEHliFI£0 WitH tHIS HYCTOPHID FISH by R.H. Bockus, 3. CerAtoscopelus Mdertns h J .£. Craddock, R.l. Hoedrtch, O.L. Shores, J ,ll. leal, A. S. Win~. J.E. Croddock, P.t. Hoedrtch, O. L. Shores, J .H. lui, A. 5. lllf19, G.v. Head ond W.O. Clorte. Vol- 160. Pp. !191-993. Septeober 1968. G.V. Head and v.o. Clarke. Vol- 160. Pp. 991-993. Stpttoober 1968. Contract Honr-3181(00), lril 260-107 and llcnr-4029(00), UR 260-101. I, Backus, A. H, Y. lui, J. H. Contract Nonr-3184(00), 1111 260-107 and Honr-4029(001, fiR 260-101. I. Badus, R.. H. v. Teal, J. H. HSF Grant GB-U)l. NSF Grtnt GB-1431. II. Craddock, J. £. VI. Wing, A. s. II. Cre~do c k, J, E. VI. Wing, A. 5. ~ sound-scotterlng layer, tDI'C>Ostd or dl ..rete hyperbolic echo A sound-scotterlng layer, c(J:;OOsed of discrete hyperbolic echo sequences and opporently restricted to the Slooe Water r.glon of Ill, lloedrlch, R. l. VII. Plead, G. v. soquencts ond apparently restricted to the Slooe Vater region of Ill. llatdrlch, R. L. VII. Hea4, G. v. Ulo western NorUI Atlantic, has bttn Identified fr..,. the Deep the western NorUI Atlantic, has been Identified fr..,. tho Deep Sut.lergence Reseorch Vehicle AlVIN with schools ofthe ".Yctophld IV. Shores, o. L. VIII. Chrkt, W. 0. Sub-.1'11•••• Re~earch Vehicle AlVIN with schools oftho 01yctophld IV. Shores. D. L. VIII. Chrko, II. D. fish Ceratoscooolus <~oderensls. By divino Into tile layer and fish Cerotoscooo1us <~lderensh. By dhlnq Into the laytr and using ALVIN's echo-ro~lng sonar, we aoproached ond •h~lly oslng ALVIN's echo-ro~l119 sonor, we ooprooclled tnd vhuolly Identified Ulo sound scotterers, The n...C.r of echo •equences 11. Nonr-348-1(00), IIR 260-107 Identified tho sound scatterers. The n...C.r or echo soquances IX. Honr·liB-1(00), IIR 260-107 observed with the surface edlo-sounder 11/23.76 • to5 cubic ob•erved wiUI tile surface echo-sounder 11/23.76 • loS cubic .,.ters of water) cllecked roughly with th~ nlfter of sonor targets X. llonr-4029(00), HA 260-101 ..ters of voter) cllecke4 roughly with ~~ .....t>er or sonar target< l. Honr-4029(00), HA 260-101 observed fi"CCC tile su.,.,arlne {l/7.15 x 10 cubic 010tors). The observed '"""the sulllqrtne 11/7.15 x 10 cubic ..ters). Tllo fish schools IPPflrtd to be 5 to 10 fitters thick, 10 to 100 XI. GB-1431 fish schools t ppeared to be 5 t o 10 ""tors thick, 10 to 100 XI. GB-1431 llleters In diUieter, and On centers 100 to 200 ... ten opart. ...tors In dl ...ter, and on centers 100 to 200 Nters epart. Density within schools vas estiNted ot 10 to 15 fish per cubic thh cord h UIICLASSIFJED Density within schools was ••tiNttd at 10 to 15 fish per collie this urd h UNCLASSIFI EO ""tor. I rll!trr. L _jL _j