Schaeffer and Oliver: Shape, volume, and resonance frequency of the swimbladder of Thunnus albacares 



373 



produced by Stenella and Delphinus, we use the 

 maximum SL measured for jaw pops of Tursiopa 

 truncatus, 163 dB re IpPa (Finneran et al., 2000). 

 Maximum detection range under spherical spread- 

 ing conditions is calculated as: 



Range = 10 iSL,„„^,-SL 



received 



)/20. 



(8) 



In the absence of other sounds (e.g. ambient noise), 

 we estimated that yellowfin tuna in the eastern 

 Pacific Ocean may be able to detect a 500-Hz sound 

 of 163 dB re IpPa out to a distance of approximately 

 10 km. 



Ambient noise in offshore waters results primarily 

 from wind and waves (Richardson et al., 1995) and 

 can mask reception of other sounds. In the region of 

 the eastern Pacific Ocean, where a yellowfin tuna fish- 

 ery exists, the sea surface is characterized by frequent 

 periods of light winds with wind speed less than 5 m/s 

 (sea state 2) more than 609c of the time (Webb, 1998). 

 At 500 Hz and with sea state 2, broadband ambient 

 noise is approximately 85 dB re IpPa (Richardson et 

 al., 1995), and would probably mask the ability of tuna 

 to detect our hypothetical 83-dB dolphin sound at the 

 maximum distance we calculated. We are unaware of 

 any data on critical ratios or critical band widths asso- 

 ciated with tuna hearing, from which we could esti- 

 mate the effective received level required for a tuna 

 to detect our sound in the presence of this ambient 

 noise. However, the source level received by a yellow- 

 fin tuna would have to be higher than ambient noise 

 level, thus reducing detection distance. 



The swimbladder of yellowfin tuna may function 

 as a key mechanism in the formation of the bond 

 between yellowfin tuna and dolphins in the eastern 

 Pacific Ocean. Whether larger yellowfin tuna actively 

 search for dolphins to increase their probability of 

 remaining within food-rich habitat (Fiedler et al., 

 1998) or whether the dolphin's sonar echolocation 

 ability detects yellowfin tuna (Au, 1993), the swim- 

 bladder may play an important role in both sound 

 reception and detectability as an acoustical target. 

 Further research should be conducted on yellowfin 

 tuna bioacoustics, including hearing sensitivity in 

 larger yellowfin tuna, determination of the role of 

 the swimbladder in hearing sensitivity, and mea- 

 surements of source level sounds produced by dol- 

 phins and other marine organisms at frequencies 

 below 1 kHz, referenced to a source. 



Acknowledgments 



We thank R. Deriso and E. Edwards for their encour- 

 agement and support of this investigation. We are 



grateful to F. LoPreste and S. Loomis, and also the 

 crew and passengers of the Royal Polaris, for their 

 invaluable assistance in obtaining these data. We 

 also gratefully acknowledge R. Allen, W. Bayliff, R. 

 Nero, D. Rees, and three anonymous reviewers for 

 helpful suggestions and comments on the manu- 

 script. This paper is dedicated to the memory of 

 James "Rollo" Heyn (1960-1999) who taught me, 

 K. Schaefer, a great deal over the years aboard the 

 Royal Polaris about how to kill large yellowfin tuna 

 with rod and reel, in the name of science. 



Literature cited 



Alexander, R. M. 



1993. Buoyancy, /n The physiology of fishe.s (D. H. Evans, 

 ed. ), p. 75-97. CRC Press, Inc., Boca Raton, FL. 

 Andreeva, I. B., 



1964. Scattering of sound by air bladders offish in deep sound- 

 scattering ocean layers. Sov. Phys, Acoust. 10:17-20. 

 Au, W. W. L. 



1993. The sonar of dolphins. Springer- Verlag New York, 

 Inc., New York, NY, 277 p. 

 Bayliff, W. H. (ed.). 



1998. Inter-Amer. Trop. Tuna Comm., Ann. Rep. for 1996, 

 306 p. 

 Blaxter, J. H. S. 



1980. The swimbladder and hearing. //? Hearing and sound 

 communication in fishes (W. N, Tavolga, A. N. Popper, and 

 R. R. Fay. eds.), p. 61-71. Springer- Verlag, New York, 

 NY. 

 Blaxter, J. H. S., and P. Tytler. 



1978. Physiology and function of the swimbladder Adv. 

 Comp. Phys. Biochem. 7:311-367. 

 Block, B. A., J. E. Keen, B. Castillo, H. Dewar, E. V. Freund, 

 D. J. Marcinek, R. W. Brill, and C. Farwell. 



1997. Environmental preferences of yellowfin tuna iThun- 

 iiu!i albacares} at the northern extent of its range. Mar. 

 Biol. 130:119-132. 



Carey, F. G., and R. J. Olson. 



1982. Sonic tracking experiments with tuna. Interna- 

 tional Commission for the Conservation of Atlantic Tunas 

 (ICCAT), Collective Volume of Scientific Papers 17:458- 

 468. 

 Chang, R. K. C, and J. J. IMagnuson. 



1968. A radiogi'aphic method for determining gas bladder 

 volume offish. Copeia 1968:187-189. 

 Feuillade, C, and R. W. Nero. 



1998. A viscous-elastic swimbladder model for describing 

 enhanced-frequency resonance scattering from fish. J. 

 Acoust. Soc. Am. 103:3245-3255. 



Feuillade, C. R. W. Nero, and R. H. Love. 



1996. A low frequency acoustic scattering model for small 

 schools of fish. J. Acoust. Soc. Am. 99:196-208. 

 Fiedler, P. C. 



1992. Seasonal climatologies and variability of eastern tropi- 

 ical Pacific surface waters. U.S. Dep. Commer., NOAA 

 Tech. Rep. NMFS 109:1-65. 

 Fiedler, P. C, J. Barlow, and T. Gerrodette. 



1998. Dolphin prey abundance determined from acoustic 

 backscatter data in eastern Pacific surveys. Fish. Bull. 

 96:237-247. 



