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



105 



tic, Caribbean, and Hawaiian species (Grimes, 1987). 

 However, the pattern observed in the present study seems 

 common in the Indo-Pacific where males frequently ( Davis 

 and West, 1992; McPherson and Squire, 1992; Newman et 

 al., 1996, 2000). but not universally (Hilomen, 1997), are 

 the larger sex. As noted above, these differences are consis- 

 tent with predictions based on energetic costs of producing 

 sperm and eggs. 



Lutjanus carponotatus spawning patterns identified by 

 using both GSI and ovarian stage frequencies show pro- 

 nounced seasonal differences: there are at least five months 

 of very limited or no spawning activity from April through 

 August. This finding supports Grimes's ( 1987) observation 

 that continental lutjanid populations tend to have more 

 restricted spawning seasons than populations associated 

 with oceanic islands, which spawn more or less continu- 

 ously throughout the year. Although seasonal patterns ex- 

 ist, the prominence of ripe gonads over seven months from 

 September through March suggests an extended spawning 

 season and supports the general observation that tropical 

 reef fishes spawn over longer periods within the year than 

 do cooler water species (Lowe-McConnell, 1979). However, 

 a study with finer temporal resolution is needed to verify 

 that spawning actually occurs in months with a high pro- 

 portion of stage-IV ovaries. 



Female L. carponotatus mature on average at approxi- 

 mately 75% of their mean asymptotic size, 54% of their 

 maximum observed size, and 119c of their maximum 

 longevity. The relative size at maturity contrasts with 

 Grimes's ( 1987) observations that shallow-water continen- 

 tal lutjanid populations like those of L. carponotatus on the 

 GBR typically mature at smaller relative sizes (=42% maxi- 

 mum size) compared to deep-water populations associated 

 with oceanic islands (=50% maximum size). Two sympatric 

 shallow -water species, L. russelli (Sheaves, 1995) and L. 

 fulviflamma (Hilomen, 1997), likewise contrast with the 

 general familial trend and mature at approximately 50% 

 and 75% of their maximum size, respectively. Hence, a 

 general pattern of relative size at maturity might exist 

 among shallow-water lutjanids in the GBR region that 

 is different from those regions covered by Grimes's ( 1987 ) 

 review. Lutjanids on the GBR are generally lightly fished 

 (Mapstone et al. 1 ); therefore the geographic difference in 

 sizes at maturity might be due to fishing pressure selecting 

 for smaller sizes at maturity in other regions. 



The relative age at maturity of L. carponotatus cannot be 

 as readily placed in a broader familial context given that 

 ages at maturity were not widely estimated for lutjanids 

 at the time of Grimes's (1987) review. However, an array 

 of published studies suggests that many tropical and sub- 

 tropical demersal fishes share the absolute, but not relative, 

 ages of L. carponotatus at 50% and 100% maturity at 2 and 

 4 years, respectively. These include other small gonochores 

 on the GBR (Sheaves, 1995; Hart and Russ, 1996; Hilomen, 

 1997), as well as a range of gonochores in other regions 

 (Grimes and Huntsman, 1980; Davis and West, 199.3; Ross 

 et al., 1995 ) and hermaphrodites on the GBR and elsewhere 

 (Ferreira, 1993, 1995; Bullock and Murphy, 1994). The 

 ubiquity of this maturity schedule, despite a wide array of 

 maximum body sizes (160-1200 mm) and longevities (6-56 



years) among these species, perhaps suggests a common 

 physiological threshold toward which many species gravi- 

 tate in order to maximize lifetime reproductive success. 

 More comprehensive analysis of life history trade-offs (e.g. 

 Roff, 1992) is needed to test this hypothesis. 



Fisheries management 



Harvest of L. carponotatus is currently restricted to fish 

 greater than 250 mm total length ( approximately 233 mm 

 FL) with the aim of allowing 50% offish to spawn at least 

 once, and this regulation is proposed to remain after revi- 

 sion by the GBR fishery management plan (Queensland 

 Fisheries Management Authority 3 ). The estimated size 

 at 50% maturity of 190 mm FL suggests that the regula- 

 tion is meeting its objective. However, the objective itself 

 might not adequately protect the reproductive potential of 

 L. carponotatus and similar species if individuals require 

 multiple spawning years to ensure sufficient replenish- 

 ment of the stock. The extensive longevities of many reef 

 fishes have been hypothesized to be a mechanism for coping 

 with low and irregular recruitment rates through a process 

 dubbed the "storage effect" (Warner and Chesson, 1985). 

 The rationale behind the storage effect hypothesis is that 

 fish must reproduce during many breeding seasons in order 

 to endure poor recruitment years and realize high repro- 

 ductive success during the unpredictable and intermittent 

 good recruitment years. If this process is important for 

 population dynamics of L. carponotatus and other species, 

 management will need to protect an intact natural popula- 

 tion structure in some areas within the fishery. Protecting 

 older age classes cannot be achieved by using maximum 

 size limits for species like L. carponotatus that have a pro- 

 nounced asymptote in the growth trajectory because body 

 sizes are similar over a broad range of age classes and size 

 is therefore poorly correlated with age. Protecting natural 

 age structure could be accomplished through a system of 

 strategically designed marine protected areas that allow 

 some populations to experience natural survival free of 

 fishing mortality. 



Proposed closures of the GBR line fishery during nine- 

 day periods around the new moon in October, November, 

 and December are aimed at protecting spawning activity 

 and particularly spawning aggregations of P. leopardus 

 and other harvested species (Queensland Fisheries Man- 

 agement Authority 3 ). Lutjanus carponotatus shares a peak 

 spawning period during these months with P. leopardus 

 (Ferreira, 1995; Samoilys 1997) and several other sym- 

 patric exploited species (McPherson et al., 1992; Sheaves, 

 1995; Hilomen, 1997; Brown et al. 5 ). In addition, the 

 larger ovaries of the Lizard Island group fish, which were 

 collected closer to the new moon, may indicate that, like 

 P. leopardus (Samoilys, 1997), L. carponotatus spawns at 



5 Brown, I. W., P. J. Doherty, B. Ferreira, C. Keenan, G. McPher- 

 son, G. Russ, M. Samoilys, and W. Sumpton. 1994. Growth, 

 reproduction and recruitment of Great Barrier Reef food fish 

 stocks. Final report to the Fisheries Research and Development 

 Corporation, FRDC Project 90/18, Queensland Department of 

 Primary Industries, 154 p. Southern Fisheries Centre, GPO 

 Box 76. Deception Bay, Queensland 4508, Australia. 



