636 



Abstract.— This study examined the 

 relation between statolith and somatic 

 growth in the tropical squid Sepioteuthis 

 lessoniana. Five separate linear dimen- 

 sions were measured on the statoliths 

 of 103 individuals ( 17-245 mm mantle 

 length 1. In addition the statoliths of 80 

 adults (82-245 mm mantle length) 

 were weighed. Statolith increment 

 analysis provided age estimates for 78 

 individuals. Statolith total length was 

 cprrelated with age for squid less than 

 -60 days of age, although neither sta- 

 tolith total length nor weight was a 

 useful predictor of age in older squid. 

 Combining the five statolith dimen- 

 sions to produce a description of sta- 

 tolith shape provided only slightly bet- 

 ter estimates of age than statolith to- 

 tal length or weight alone. Statolith 

 shape changed during ontogeny, devel- 

 oping from relatively elongate juvenile 

 statoliths into the adult form with more 

 robust dorsal and lateral domes. This 

 development was reflected in wider 

 spacing and superior optical definition 

 of daily growth increments in the dor- 

 sal and lateral domes of adult sta- 

 toliths, in relation to the slower grow- 

 ing rostrum. Growth of S. lessoniana 

 statoliths does not appear to be strongly 

 linked to mantle growth; both statolith 

 total length and weight increase more 

 slowly than mantle length. 



Ontogenetic changes in size and shape 

 of statoliths: implications for age and 

 growth of the short-lived tropical squid 

 Sepioteuthis lessoniana 

 (Cephalopoda: Loliginidae) 



Ross Thomas 



Natalie A. Moltschaniwskyj 



School of Marine Biology and Aquaculture 



James Cook University 



Townsville, Queensland 4811, Australia 



Present address (for N A Moltschaniwskyi, contact author): School of Aquaculture 



University of Tasmania 



PO Box 1214 



Launceston, Tasmania 7250. Australia. 

 E-mail (for N A Moitscfianiwskyj, contact author) natalie moltschaniwskyi aulas edu au 



Manuscript accepted 12 August 1998. 

 Fish. Bull. 97:636-645 (1999). 



Knowledge of the age structure and 

 growth rates in naturally occurring 

 populations is fundamental to esti- 

 mating demographic parameters 

 and evaluating ecological processes. 

 Periodic growth increments in squid 

 statoliths are a reliable and accu- 

 rate tool for determining the age 

 structure of squid populations 

 (Villanueva, 1992;Ai-khipkin, 1993; 

 Bigelow, 1994; Jackson, 1994). 

 Growth-rate calculations based on 

 statolith age estimates indicate that 

 tropical squid are short-lived and 

 gi-ow continuously throughout their 

 lifespan (Jackson, 1990; Jackson 

 and Choat, 1992). Growth rates of 

 tropical squid can be strongly influ- 

 enced by changes in their environ- 

 ment, including temperature fluc- 

 tuations (Forsythe and Hanlon, 

 1989), and availability of food 

 (Forsythe, 1993). Consequently, 

 growth rates, final size, and re- 

 sponse to changing conditions of 

 tropical squid may vary greatly 

 within or between species (Jackson, 

 1990; Jackson and Choat, 1992). 

 Apart from obtaining size-at-age 

 information from statoliths, there is 

 also the potential to obtain ecologi- 

 cal information on past growth his- 

 tories of some squid species (Jack- 



son, 1994). Any attempts made at 

 constructing growth histories of 

 squid based on statolith microstruc- 

 ture will benefit greatly from a thor- 

 ough understanding of growth and 

 development of the statolith and 

 how this relates to growth of so- 

 matic tissue. 



Daily growth increments in fish 

 otoliths, which are analogous to 

 those in squid statoliths (Radtke, 

 1983 ), provide valuable data on the 

 age structure and growth rates of 

 exploited fish species (Campana 

 and Neilson, 1985; Jones, 1986; 

 Stevenson and Campana, 1992). 

 Recent studies of fish somatic- 

 otolith growth relationships may 

 contribute to investigations of so- 

 matic-statolith growth relation- 

 ships in squid. Evidence exists sup- 

 porting the direct relationship be- 

 tween age and otolith weight for 

 several fish species (Boehlert, 1985; 

 Fletcher, 1991), although further 

 validation is required before otolith 

 weight can be used reliably to esti- 

 mate age. Several authors have also 

 demonstrated that slower-growing 

 fish have larger otoliths than simi- 

 lar sized, faster-growing individu- 

 als (Mosegaard et al., 1988; Secor 

 and Dean, 1989; Wright et al., 1990; 



