Summary1. Life-history theory predicts that organisms will provide an optimal level of parental investment for offspring survival balanced against the effects on their own survival and future reproductive potential. 2. Optimal resource allocation models also predict an increase in reproductive output with age as expected future reproductive effort decreases. To date, maternal investment in sharks has received limited attention. 3. We found that neonatal dusky sharks (Carcharhinus obscurus) are not independent from maternal resource allocation at the point of parturition but instead are provisioned with energy reserves in the form of an enlarged liver that constitutes approximately 20% of total body mass. 4. Analysis of long-term archived data sets showed that a large proportion of this enlarged liver is utilized during the first weeks or months of life suggesting that the reported weight loss of newborn sharks signifies a natural orientation process and is not necessarily related to prey abundance and ⁄ or indicative of high mortality rates. 5. Interrogation of near-term pup mass in two carcharhinids, the dusky and spinner shark (Carcharhinus brevipinna), further revealed an increase in reproductive output with maternal size, with evidence for a moderate decline in the largest mothers. 6. For the dusky shark, there was a trade-off between increasing litter size and near-term pup mass in support of optimal offspring size theory. 7. For both the dusky and spinner shark, there was a linear increase in near-term pup mass with month, which may indicate variable parturition strategies and ⁄ or that carcharhinids are able to adjust the length of the gestation period. 8. The identification of optimal size-specific reproductive output has direct implications for improving the reproductive potential of exploited shark populations and for structuring future management strategies.

Measuring fish condition has become a standard practice in the management of fishes, both at the individual and population level. The comparative application of several condition indices to sharks, however, has not yet received a rigorous evaluation. Data for a total of 2120 dusky sharks Carcharhinus obscurus (Lesueur, 1818), ranging in size from newborns (≤ 79 cm precaudal length [PCL]) to mature adults (≥210 cm PCL), were used to calculate seasonal trends in condition and to facilitate index comparisons. Four commonly used condition measures were selected, including a somatic measure, hepatosomatic index (HSI), and 3 morphometric measures, condition factor (CF), relative condition (Kn) and residual condition (Rr PCL ). The effect of month was significant for most condition analyses by size class, sex and reproductive state. HSI was found to be the most sensitive index and rapid indicator of condition, but its appropriate use requires the disaggregation of data by clearly defined life stages and reproductive states. The relatively large liver size of neonates and the relatively small liver size of pregnant and postpartum females may otherwise bias interpretations of seasonal variations in condition. HSI was also affected by increasing size of the animal, which confounds inter-size-class comparisons and may require the further division of life-stage data into additional size classes. The results of the 3 morphometric measures were comparable but were not correlated with HSI. CF, Kn and Rr PCL lagged behind HSI, were unable to differentiate between neonate and juvenile animals and were insensitive to short-term variations. The effect of increasing size did not affect calculated CF and Rr PCL , but Kn demonstrated a negative correlation. The fact that large predators may consume large volumes of food in a single feeding event was identified as a possible complicating factor in interpreting condition indices. 380: 199-212, 2009 dition index to use and the type of analysis to be undertaken (Bolger & Connolly 1989, Springer et al. 1990, Jakob et al. 1996, Pope & Kruse 2007. KEY WORDS: Hepatosomatic index · Condition factor · Morphometric condition indices · Carcharhinus obscurus · Ontogenetic variation Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerSharks, members of the class Chondrichthyes, have received limited attention with regard to the application of condition indices. Under most circumstances the required data for large and/or highly migratory species are difficult to obtain, restricting comparative condition analyses. Considering the volume of published literature on the use of condition indices for the management of teleost fishes, coupled with the important biological and ecological information that can be elucidated through this approach, it is appropriate to address the subject for this large group of fishes.The most widely applied measure of condition in sharks is HSI, which expresses liver weight relative to body weight, and is often used as ...

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