Seasonal and life‐phase related differences in growth in Scarus ferrugineus on a southern Red Sea fringing reef

Abstract

Temporal trends in growth of the rusty parrotfish Scarus ferrugineus were studied on a southern Red Sea fringing reef that experiences seasonal changes in environmental conditions and benthic algal resources. Length increment data from tagging and recapture were compared among periods and sexes and modelled using GROTAG, a von Bertalanffy growth model. The growth pattern of S. ferrugineus was highly seasonal with a maximum occurring between April and June and a minimum between December and March. Body condition followed the seasonal variation in growth, increasing from April to June and decreasing from December to March. The season of maximum growth coincided with high irradiation, temperature increases and peak abundance of the primary food source, the epilithic algal community. There was a decline in growth rate during summer (July to October) associated with a combination of extreme temperatures and lowered food availability. There were strong sexual size dimorphism (SSD) and life-history traits. Terminal-phase (TP) males achieved larger asymptotic lengths than initial-phase individuals (IP) (L(∞) 34·55 v. 25·12 cm) with growth coefficients (K) of 0·26 and 0·38. The TPs were growing four times as fast as IPs of similar size. Three individuals changed from IP to TP while at liberty and grew eight times faster than IPs of similar size, suggesting that sex change in S. ferrugineus is accompanied by a surge in growth rate. The SSD in S. ferrugineus thus coincided with fast growth that started during sex change and continued into the TP. Faster growth during sex change suggests that the cost associated with sex change is limited.

Size and Age of Stonecats in Lake Champlain; Estimating Growth at the Margin of their Range to Aid in Population Management

“…While this model has been used in other studies (e.g., Francis ; Wilde and Sawynok ; Afeworki et al. ), it is used rarely and those studies have been primarily with marine species that were largely of commercial or recreational interest. We showed that the model can be used to derive useful estimates of growth rates and growth model parameters for an imperiled species for which individuals cannot be legally or ethically sacrificed to remove calcified structures for estimating age.…”

Alternative male mating tactics of the endemic Red Sea parrotfish Scarus ferrugineus

“…This is valid if reproduction reduces growth or increases mortality of the STPs (Iwasa, ). The present study, however, shows that transitional individuals and STPs have the fastest growth in S. ferrugineus (Afeworki et al ., ) suggesting that their reproductive activity does not affect their growth negatively. This is plausible since STPs do not spend energy for territorial defence.…”