Abstract.— Age and growth pa- 

 rameters of the tropical loliginid squid 

 Sepioteuthis lessoniana in eastern 

 Australian waters were determined 

 from statolith growth-ring analysis. 

 Juvenile specimens were captured, 

 maintained alive, and their statoliths 

 were chemically marked in fn'tii with 

 either tetracycline or calcein. These 

 chemicals produced a fluorescent 

 mark within the statolith microstruc- 

 ture when viewed under UV light. 

 Statoliths were mounted in ther- 

 moplastic cement and subsequently 

 ground and polished. This process 

 allowed rings to be visualized with- 

 out any further preparation. It was 

 thus ])ossible to validate that distinct 

 statolith rings were formed daily and 

 that less-distinct thinner rings were, 

 in fact, subdaily rings. 



The results of the age analysis of 

 field-captured individuals revealed 

 that the population of S. lefn^oniiniii 

 in the study area grows at a very fast 

 rate. Maturity in both sexes was 

 achieved in less than 100 days. All 

 specimens aged were less than 6 

 months old. The size of large in- 

 dividuals was within the range of S. 

 lessoniana captured in other areas, 

 with size ranges being 75-213 mm 

 and 75-184 mm for males and fe- 

 males, respectively. 



Growth rates determined for S. 

 lessoniana based on statolith ageing 

 are considerably different from pre- 

 vious estimates based on length- 

 frequency data. 



Age and Growth of the Tropical 

 Mearshore Loliginid Squid 

 Sepioteuthis lessoniana 

 Determined from Statolith 

 Growth-Ring Analysis 



George David Jackson 



Department of Marine Biology, James Cook University of North Queensland 

 Townsville. Queensland 481 I. Australia 



Manuscript accepted 28 .liily 1989. 

 Fishery Bulletin, U.S. 88:113-118. 



Estimation of growth rates along 

 with estimates of age-at-maturity 

 and life span are the key elements in 

 understanding the population dynam- 

 ics of marine organisms. In many 

 instances, such data are difficult to 

 obtain and approximations often 

 have broad confidence intervals. The 

 provision of accurate age estimates 

 is one method by which reliable data 

 on demographic processes can be ob- 

 tained. For example, research into 

 fish demography has developed ra- 

 pidly (for relevant reviews see Pan- 

 nella 1980, Campana and Neilson 

 1985, Jones 1986) following the dis- 

 covery and validation of daily micro- 

 structure increments within the oto- 

 lith (Pannella 1971). 



Pelagic cephalopods have many 

 fish-like features, yet differ consider- 

 ably in fundamental ways with re- 

 spect to metabolism and growth 

 (O'Dor and Webber 1986). Because of 

 their rapid growth and the lack of 

 population statistics in comparison 

 with fish studies, cephalopods are 

 potentially one of the more interest- 

 ing targets of demographic analysis. 

 Ageing techniques of pelagic cephalo- 

 pods, employing statolith microsti-uc- 

 ture analysis, are currently devel- 

 oping along lines similar to those 

 applied to fish biology. Cephalopod 

 statoliths and fish otoliths are physio- 

 logically analogous structures (Rad- 

 tke 1983). Although statolith gi-owth 

 rings were recognized over 20 years 



ago (Clarke 1966), it has not been un- 

 til relatively recently that some de- 

 tailed microstructure analysis has 

 taken place (see Jackson [1989] for 

 relevant literature). 



Ongoing research into cephalopod 

 demography is revealing that many 

 species are short-lived and exhibit 

 rapid growth and early maturity 

 (Saville 1987). These features make 

 cephalopods particularly amenable to 

 ageing using daily growth rings. Re- 

 cent work on growth and ageing on 

 the small tropical sepioid Idiosepius 

 pygmaeus has revealed that very 

 small tropical species can have rela- 

 tively fast growth and maturity rates 

 (Jackson 1989) compared with pre- 

 vious estimates. 



The majority of research on squid 

 demography has taken place in tem- 

 perate waters. Life spans for large 

 temperate squids are generally be- 

 lieved to be annual (Voss 1983, 

 Natsukari et al. 1988, Amaratunga 

 1987). It was thus of interest to ex- 

 amine age, growth and maturity 

 parameters of a large tropical cepha- 

 lopod to see if these parameters 

 paralleled similar work on their tem- 

 perate counterparts. 



The tropical loliginid squid Sepio- 

 teuthis lessoniana was selected for 

 age and growth analysis. This species 

 is one of the larger tropical nearshore 

 squids, reaching lengths of over 30 

 cm and occurs throughout much of 

 the Indo-Pacific (Roper et al. 1984). 



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