208 



Fishery Bulletin 91(2), 1993 



higher than those of towed nets. Sampling of local- 

 scale surface features requires the degree of spatial 

 precision and replication provided by small purse-seines 

 (Kingsford & Choat 1985 and 1986, Kingsford et al. 

 1991), but purse-seines cannot sample deeper than the 

 upper few meters of the water column, and are diffi- 

 cult to operate in any but the best conditions. Local- 

 ized replicated sampling may also be obtained by free- 

 fall plankton nets (Kobayashi 1989) which, however, 

 obscure vertical patterns and also have a small vol- 

 ume sampled. 



Investigation of the patch size of pelagic organisms 

 requires the ability to sample simultaneously over sev- 

 eral spatial scales. Large-scale deployment of arrays 

 of automated light-traps will increase replication and 

 allow investigation of phenomena at several spatial 

 scales without risk of temporal confounding, provided 

 the traps can be retrieved over the same time-period. 

 Also, both light-traps and purse-seining with aggrega- 

 tion devices may detect temporal pulses in the density 

 of larger larvae and pelagic juveniles with greater reli- 

 ability and precision than towed nets. 



In addition to the sampling properties of the differ- 

 ent devices, there are a number of more pragmatic 

 considerations. Sorting and identification of samples 

 may be a major bottleneck. This will be influenced by 

 the size of the sample, the amount of organic material 

 included, and condition of the fishes themselves. In 

 this context, large samples taken by finer-mesh nets 

 may be particularly difficult to process. Smaller or more 

 selective samples are more readily processed, and those 

 from purse-seines and light-traps yield living fishes 

 suitable for rearing and experimentation. Further, the 

 smaller the larva the more difficult it is to identify; 

 thus, methods like the light-trap, which samples larger 

 fishes, simplify identification. 



It is clear that studies of the biology of small pelagic 

 fishes require the use of both nets and aggregation 

 devices either separately or in combination, depending 

 on the type of question posed. No single method can 

 provide a comprehensive picture of the larval and pe- 

 lagic juvenile fish fauna, and few programs could cover 

 the expense and logistic effort of the simultaneous de- 

 ployment of a variety of methods. The picture one ob- 

 tains of the larval and pelagic juvenile fish fauna is 

 highly method-dependent. Which picture or combina- 

 tion of pictures is suitable for answering a given ques- 

 tion varies with the question, the taxon, and the size- 

 range of the fishes. 



Acknowledgments 



This project was supported by funds from the URG 

 Griffith University to PJD, the Australian Marine Sci- 



ences and Technology funding panel to JHC and JML, 

 and internal funds from the Australian Museum (JML) 

 and James Cook University (JHC). Field facilities were 

 provided by the Lizard Island Research Station and 

 the Australian Museum. We wish to thank M. and 

 M. Jumelet (RV Sunbird) and M. Milicich, M. Meekan, 

 M. McCormick, N. Preston, and M. Doherty for assis- 

 tance with the sampling program; D. Furlani, 

 R. Birdsey, S. Reader, and S. Thompson for assistance 

 in the lab; and M. Kingsford and M. Milicich for dis- 

 cussion of the program and critical reading of the manu- 

 script. The manuscript benefited from the comments 

 of anonymous reviewers. 



Citations 



Barnes, H., & D. J. Tranter 



1965 A statistical examination of the catches, numbers, 

 and biomass taken by three commonly used plankton 

 nets. Aust. J. Mar. Freshwater Res. 16:293-306. 

 Brander, K., & A. B. Thompson 



1989 Diel differences in avoidance of three vertical pro- 

 file sampling gears by herring larvae. J. Plankton 

 Res. 11 (4):775-784. 

 Clarke, T. A. 



1983 Comparison of abundance estimates of small fishes 

 by three towed nets and preliminary results of the 

 use of small purse seines as sampling devices. Biol. 

 Oceanogr. 2:311-340. 

 1991 Larvae of nearshore fishes in oceanic waters near 

 Oahu, Hawaii. NOAA Tech. Rep. NMFS 101, 19 p. 

 Clutter, R. I., & M. Anraku 



1968 Avoidance of samplers. In Zooplankton sampling, 

 p. 57-76. UNESCO Monogr. Oceanogr. Method. 2. 

 Doherty, P. J. 



1987 Light-traps: selective but useful devices for quan- 

 tifying the distributions and abundances of larval 

 fishes. Bull. Mar. Sci. 41:423-431. 



Doherty, P. J., & D. McB. Williams 



1988 The replenishment of coral reef fish popula- 

 tions. Oceanogr. Mar. Biol. Annu. Rev. 26:487-551. 



Frank, K. T. 



1988 Independent distribution of fish larvae and their 

 prey: natural paradox or sampling artifact. Can. J. 

 Fish. Aquat. Sci. 45:48-59. 



Gartner, J. V. Jr., W. J. Conley, & T. L. Hopkins 



1989 Escapement by fishes from midwater trawls: a 

 case study using lantern fishes. Fish. Bull., U.S. 

 87:213-222. 



Green, R. H. 



1979 Sampling design and statistical methods for 

 environmental biologists. Wiley Interscience, NY, 

 257 p. 

 Gregory, R. S., & P. M. Powles 



1988 Relative selectivities of Miller high-speed samplers 

 and light traps for collecting ichthyoplankton. Can. 

 J. Fish. Aquat. Sci. 45:993-998. 



