Seasonal influences on statolith 



growth in the tropical nearshore 



loliginid squid Loligo chinensis 



(Cephalopoda: Loliginidae) 



off Townsville, North Queensland, 



Australia 



George D. Jackson 



Department of Marine Biology, James Cook University of North Queensland 

 Townsville, Queensland 48 1 1 . Australia 



Present Address: Department of Zoology 



University of Western Australia. Nedlands. 



Perth, Western Australia 6009, Australia 



son and Campana, 1992), much of 

 the work with statolith ageing and 

 validation is still preliminary in 

 nature. However, evidence does 

 support daily periodicity in sta- 

 tolith increment production in 

 many species (Jackson, 1994) al- 

 though there is an ongoing need for 

 further validation and ageing stud- 

 ies. Because age and population 

 information is already available for 

 Loligo chinensis 1 (Jackson, 1990b, 

 1993; Jackson and Choat, 1992), 

 this study was undertaken to see if 

 seasonal differences in growth rate 

 are reflected in statolith-size:body- 

 size relationships in this tropical 

 nearshore squid. 



Information is currently accumu- 

 lating on age, growth, and matu- 

 rity rates of squids, with a number 

 of studies focusing on tropical and 

 warm water species (eg. Jackson, 

 1990, a and b; Arkhipkin and Mik- 

 heev, 1992; Bigelow, 1992; Jackson 

 and Choat, 1992; Arkhipkin and 

 Nekludova, 1993; Jackson, 1993; 

 Laptikhovsky et al., 1993; Young 

 and Mangold, 1994; see also Jack- 

 son, 1994, for review). The interpre- 

 tation of growth phenomena in 

 squids is complicated owing to the 

 high degree of temperature depen- 

 dency in growth (O'Dor and Wells, 

 1987; Forsythe and Hanlon, 1989). 

 Moreover, growth is highly variable 

 even within particular temperature 

 regimes (Lipinski, 1986; Natsukari 

 et al., 1988). The use of validated 

 daily increments in statoliths is a 

 convincing tool for determining 

 both the rate of growth and its vari- 

 ance. However, there is also the po- 

 tential that temperature-induced 

 variation in growth rates might be 

 reflected in statolith growth rates. 

 Recent work on the uncoupling 

 between otolith size and fish size 

 ( see Campana and Jones, 1992 ) has 

 indicated that individual variation 

 in growth rates can have profound 

 effects on soma-otolith relation- 



ships. While such features make 

 analysis such as back calculation of 

 individual size less than straight- 

 forward (Campana, 1990), they do 

 provide a mechanism for detecting 

 past growth histories (or perhaps 

 even past environmental histories) 

 to which a fish has been exposed. 

 For example, if two similar-sized 

 fish of the same species show con- 

 siderable disparity in otolith size, 

 it suggests that the individual with 

 the larger otolith has grown slower 

 (e.g. Reznick et al., 1989; Wright et 

 al., 1990). Lipinski et al. (1993) 

 have also documented substantial 

 uncoupling in squid statolith growth 

 and in growth of the mantle in 

 Todaropsis eblanae and Todarodes 

 angolensis off southern Africa. 



Statolith increments are pro- 

 duced daily in Loligo chinensis 

 (Jackson, 1990b) as well as in other 

 loliginid squids such as Alloteuthis 

 subulata (Lipinski, 1986), Loligo 

 opalescens (Yang et al., 1986), 

 Loliolus noctiluca (Jackson, 1990b), 

 and Sepioteuthis lessoniana (Jack- 

 son, 1990a; Jackson et al., 1993). 

 However, compared with fish 

 otolith analysis in which there is a 

 substantial number of ageing and 

 increment validation studies (e.g. 

 Campana and Neilson, 1985; Steven- 



Materials and methods 



Individuals of Loligo chinensis were 

 captured by using paired otter 

 trawls (each net consisted of an 11- 

 m gape and 3.8-cm mesh). Trawls 

 were towed for approximately 20 

 minutes at a speed of 2-2.5 knots. 

 Samples were taken in Cleveland 

 Bay (19°15'S,146°50 , E) in water 

 <20 m deep off Townsville, North 

 Queensland. Statoliths were ob- 

 tained from squid caught during 

 two seasonal periods, 12 January 

 1989 (austral summer, n-35) and 

 13 July 1989 (austral winter, rc=33). 

 Squid were preserved in 10% buff- 



1 It is now known that the species Loligo 

 chinensis which is found in shallow tropi- 

 cal waters off North Queensland is a dis- 

 tinct species from L. chinensis which is 

 found elsewhere in the tropical Indo-Pa- 

 cific. J. Yeatman. 1993. James Cook 

 Univ. of North Queensland. Personal 

 commun. Furthermore, all Loligo species 

 in Australian waters will probably be re- 

 ferred to as Photololigo in the future. Un- 

 til this is resolved, I have referred to the 

 species of this study as Loligo chinensis 

 which is the same species referred to as 

 Photololigo cf. chinensis (east coast form) 

 in Dunning et al. (1994) and Photololigo 

 sp. 3 in Yeatman and Benzie ( 1994). 



Manuscript accepted 19 June 1995. 

 Fishery Bulletin 93:749-752 ( 1995). 



749 



