Kritzer: Sex-specific growth and mortality, spawning season, and female maturation of Lut/anus carponotatus 



95 



One of the most prominent secondary species in the 

 GBR fishery is the stripey bass (Lutjanus carponotatus) 

 (Spanish flag snapper. FAO). In relation to other large 

 predators on the GBR, L. carponotatus is highly abundant 

 on inshore reefs, common on mid-continental shelf reefs, 

 and absent from outer-shelf reefs (Newman and Williams, 

 1996; Newman et al., 1997; Mapstone et al. 4 ). Although 

 this affinity for inshore reefs has the potential to make the 

 species more susceptible to recreational fishing, the limited 

 available data do not suggest that it is heavily exploited 

 by the recreational fleet (Higgs, 1993) in relation to the 

 commercial fleet (Mapstone et al. 1 ). Lutjanus carponota- 

 tus has a broad-based diet, consuming a wide variety of 

 smaller reef fishes and invertebrates (Connell, 1998). Its 

 role as a predator coupled with its abundance, particularly 

 on inshore reefs, suggests that the species might have an 

 important ecological function on the GBR in addition to its 

 role as a fishery resource. 



Davies (1995) and Newman et al. (2000) have collected 

 basic demographic data for L. carponotatus on the north- 

 ern and central GBR, respectively. They both reported a 

 pronounced asymptote in the growth trajectory and that 

 most growth occurred over the first three to five years and 

 little subsequent growth over a lifespan that can reach 15 

 to 20 years. Newman et al. (2000) also reported a heavily 

 male-biased sample and larger body sizes among males. 

 Unlike age and growth data, no information on reproduc- 

 tion of L. carponotatus has been available despite that fact 

 that existing (minimum size limits) and proposed (spawn- 

 ing closures) fisheries regulations are based largely on 

 reproductive traits (Queensland Fisheries Management 

 Authority 3 ). 



Specific aims of this study were 1) to estimate sex ra- 

 tios and sex-specific schedules of growth and mortality; 

 2) to estimate age- and size-specific schedules of female 

 maturation; 3) to identify the spawning season; and 4) to 

 determine whether reproductive output is proportional 

 to body size by examining the ovary weight-body weight 

 relationship and the average spawning duration of large 

 and small fish. All traits were estimated at the Palm Island 

 group on the central GBR. Additionally, sex-specific growth 

 and female maturity schedules were also examined at the 

 Lizard Island group on the northern GBR to develop spa- 

 tial comparisons. 



Materials and methods 



Field methods 



Size, age, and reproductive data were obtained for 465 

 L. carponotatus collected by spear fishing on fringing reef 

 slopes during monthly fishery independent sampling at 



4 Mapstone, B. D., A.M. Ayling, and J. H.Choat. 1998. Habitat, 

 cross shelf and regional patterns in the distributions and abun- 

 dances of some coral reef organisms on the northern Great Bar- 

 rier Reef. Great Barrier Reef Marine Park Authority research 

 publication 48, 71 p. GPO Box 1379, Townsville, Queensland 

 4810, Australia. 



Pelorus, Orpheus, and Fantome Islands in the Palm Island 

 group on the central GBR ( Fig. 1 ) from April 1997 through 

 March 1998. No sampling took place in January 1998 

 because of severe flooding in the area. To develop spatial 

 comparisons, samples of 118 and 18 fish were obtained in 

 October 1997 and April 1999, respectively, by spear fishing 

 at the Lizard Island group approximately 400 km north of 

 the Palm Island group (Fig. 1). Fish were collected from 

 depths of 2 to 15 m by teams of two to four scuba divers. 

 Lutjanus carponotatus most commonly inhabits depths less 

 than 15 m (Newman and Williams, 1996); therefore sam- 

 pling efforts encountered the majority of the population. 

 Fish were targeted as encountered, without preference 

 based on size, in order to collect as representative a sample 

 as possible. Fish <150 mm fork length (FL) were rare in 

 the samples because they were infrequently observed on 

 reef slopes (Kritzer, 2002). Therefore, supplemental spear 

 fishing on reef flats targeting smaller fish was conducted 

 at the Palm Island group (n=24) in April and December 

 1999 and at the Lizard Island group (n=25) in May 1999 

 to obtain growth data for size classes against which the 

 primary sampling was biased. 



Total weight (TW, g) and FL (mm) of each specimen 

 were recorded. Ovaries and testes of small lutjanids on 

 the GBR are characterized by a lipid body running along 

 the length of each lobe, akin to that found in tropical 

 acanthurids (Fishelson et al., 1985). Gonads and these 

 associated lipid bodies were removed and preserved in 

 FAAC (formaldehyde 4%, acetic acid 5%, calcium chloride 

 1.3%). Sagittal otoliths were removed, cleaned, and stored 

 for later analyses. 



Gonad processing and ovarian staging 



The lipid body was removed from each ovary or testis after 

 fixation and the weight of the gonad (GW) and lipid body 

 (LW) were measured to the nearest 0.01 g. A gonadoso- 

 matic index (GSI) and lipidsomatic index (LSI; after Lobel, 

 1989) were calculated for each sample as the percentage of 

 TW represented by GW and LW, respectively. Features of 

 whole fixed ovaries including color, speckling, and surface 

 texture were noted as potential criteria for macroscopic 

 staging after comparison with samples processed histologi- 

 cally. Sex of the April 1999 Lizard Island group samples 

 was determined macroscopically only, and was therefore 

 used in sex-specific growth analyses but not in analysis of 

 maturity. Fish <150 mm FL had undeveloped gonads and 

 sex of these specimens was not determined or assigned a 

 reproductive stage. 



A subsample of 131 ovaries spanning the range of gonad 

 sizes and external appearances were prepared for histo- 

 logical examination. Samoilys and Roelofs (2000) found 

 that medial gonad sections were adequate for determina- 

 tion of reproductive status. Therefore, a medial section was 

 removed from one gonad lobe, dehydrated, and embedded 

 in paraffin. Embedded ovarian tissues were sectioned at 

 5 nm and stained with hematoxylin and eosin. Ovaries were 

 staged on the basis of the most advanced oocyte stage pres- 

 ent (West, 1990). Additional features used in histological 

 staging included the presence of brown bodies and atretic 



