404 



Abstract— Light traps and channel 

 nets are fixed-position devices that in- 

 volve active and passive sampling, re- 

 spectively, in the collection of settle- 

 ment-stage larvae of coral-reef fishes. 

 We compared the abundance, taxo- 

 nomic composition, and size of such 

 larvae caught by each device deployed 

 simultaneously near two sites that dif- 

 fered substantially in current velocity. 

 Light traps were more selective taxo- 

 nomically. and the two sampling de- 

 vices differed significantly in the abun- 

 dance but not size of taxa caught. Most 

 importantly, light traps and channel 

 nets differed greatly in their catch 

 efficiency between sites: light traps 

 were ineffective in collecting larvae 

 at the relatively high-current site, 

 and channel nets were less efficient 

 in collecting larvae at the low-current 

 site. Use of only one of these sampling 

 methods would clearly result in biased 

 and inaccurate estimates of the spatial 

 variation in larval abundance among 

 locations that differ in current velocity. 

 When selecting a larval sampling de- 

 vice, one must consider not only how 

 well a particular taxon may be repre- 

 sented, but also the environmental con- 

 ditions under which the device will be 

 deployed. 



Current velocity and catch efficiency in sampling 

 settlement-stage larvae of coral-reef fishes 



Todd W. Anderson 



Department of Zoology 



Oregon State University 



Corvallis, Oregon 97331-2914 



Present address: Department ol Biology 



San Diego State University 

 San Diego, California 92182 



E-mail address toddam'sunstroke sdsu edu 



Claudine T. Bartels 



Department of Biological Sciences 

 Flonda Institute of Technology 

 150 West University Boulevard 

 Melbourne. Florida 32901 



Mark A. Hixon 



Department of Zoology 

 Oregon State University 

 Corvallis, Oregon 97331-2914 



Erich Bartels 



Department of Biological Sciences 

 Florida Institute of Technology 

 150 West University Boulevard 

 Melbourne, Flonda 32901 



Mark H. Carr 



Department of Ecology and Evolutionary Biology 

 University of California 

 Santa Cruz, California 95064 



Jonathan M. Shenker 



Department of Biological Sciences 

 Florida Institute of Tecfinology 

 150 West University Boulevard 

 Melbourne, Flonda 32901 



Manuscript accepted 23 January 2002. 

 Fish. Bull. 100:404-413 (2002). " 



With few exceptions, benthic marine 

 organisms exhibit a complex life cycle 

 in which larvae are dispersed pelagi- 

 cally and undergo a planktonic exis- 

 tence before they settle to the sea floor. 

 The vagaries of dispersal by currents 

 and unpredictable mortality of larvae 

 in the plankton contribute to tremen- 

 dous variation observed in recruitment 

 (here defined broadly as the input of 

 young) to adult populations. For reef 

 fishes, the relative importance of varia- 

 tion in the supply of settlement-stage 

 larvae versus postsettlement density- 

 dependent mortality of recruits to the 

 size and structure of local populations 

 has been debated for some time, with 

 evidence provided for both points of 

 view (Doherty and Williams, 1988; 

 Doherty, 1991; Hixon, 1991; Jones. 

 1991; Doherty and Fowler, 1994; Hixon 

 and Carr, 1997; Schmitt and Holbrook, 

 1999). In order to determine the rela- 

 tive contributions of presettlement and 

 postsettlement processes to the popula- 

 tion dynamics of reef fishes, knowledge 

 of spatial and temporal variation in the 

 delivery of settlement-stage larvae to 

 local populations is essential. 



Various methods have been employed 

 to assess the local abundance of pelagic 

 larvae and juveniles of coral-reef fishes 



(Choat et al., 1993, and references there- 

 in). Two common but relatively recent 

 sampling devices developed to sample 

 settlement-stage reef fish larvae are 

 light traps (Doherty 1987; Thorrold 

 and Milicich 1990; Milicich et al. 1992; 

 Thorrold. 1992; Meekan et al., 1993; 

 Thorrold, 1993; Milicich and Doherty 

 1994; Doherty et al., 1996; Sponaugle 

 and Cowen, 1996a, 1996b; Thorrold and 

 Williams, 1996; Doherty and Carleton, 

 1997; Sponaugle and Cowen, 1997; Leis 

 et al., 1998; Munday et al. 1998; Meekan 

 et al. 2000) and stationary nets, includ- 

 ing channel nets (Shenker et al.,1993; 

 Thorrold et al., 1994a, 1994b, 1994c) 

 and crest nets (Dufour and Galzin, 

 1993; Dufour et al., 1996). Light traps 

 are active sampling devices in that fish 

 are attracted to, swim towards, and 

 enter a transparent or semitransparent 

 trap with a light source. By contrast, 

 channel nets and crest nets passively 

 catch larvae that are carried into them 

 by currents or wave action, respectively. 

 Unlike a previous study that compared 

 light traps with towed nets (Choat et 

 al., 1993), the goal of this study was to 

 compare light traps and fixed-position 

 nets, two commonly used methods for 

 collecting settlement-stage fish larvae 

 near coral reefs. 



