Estimation of Age, Growth Parameters and Mortality Indices in Lutjanus fulviflamma (Forsskal 1775) (Pisces: Lutjanidae) from Kenyan Inshore Marine Waters

Age and growth parameters of the reef fish Lutjanus fulviflamma have been estimated from tri-monthly plots of length frequency data and a knowledge of the spawning time of the fish. The growth parameters, L∞, K and to were derived from the progression of modal lengths as; 35.0 cm (total length), 0.59 and -0.55 years, respectively. These parameters were used to fit a von Bertalanffy growth equation for the species as: Lt = 35.0 [1 - exp(1 - (0.59 (t + 0.55))]. The total mortality (Z), fishing (F) and natural (N) mortality coefficients were derived for the species from length converted catch-curve and Pauly\'s empirical formula as, 1.97, 0.27 and 1.70/year, respectively. The low fishing mortality (on a 0-1 scale), together with low exploitation rate(Eopt) of 0.137, derived for the stock of L. fulviflamma in Kenya\'s nearshore fishery suggests that the stocks are under exploited. The possible reasons for this under-exploitation are discussed. It is recommended that the growth parameters derived in this study be validated further in order to allow the application of this rapid age assessment method for other species in the Western Indian Ocean, given the difficulties of aging tropical fishes. Journal of Agriculture, Science and Technology Vol.3(1) 2001: 53-6

What drives ontogenetic niche shifts of fishes in coral reef ecosystems?

Ontogenetic niche shifts are taxonomically and ecologically widespread across the globe. Consequently, identifying the ecological mechanics that promote these shifts at diverse scales is central to an improved understanding of ecosystems generally. We evaluated multiple potential drivers of ontogenetic niche shifts (predation, growth, maturation, diet shifts, and food availability) for three fish species between connected coral reef and nearshore habitats. In all cases, neither diet compositional change nor sexual maturity functioned as apparent triggers for emigration from juvenile to adult habitats. Rather, the fitness advantages conferred on reef inhabitants (that is, enhanced growth rates) were primarily related to high prey availability on reefs. However, there exists a clear trade-off to this benefit as survival rates for small fishes were significantly reduced on reefs, thereby revealing the potential value of (and rationale behind high juvenile abundances in) nearshore habitat as predation refugia. We ultimately conclude that predation risk functions as the primary early life stage inhibitor of ontogenetic niche shifts towards more profitable adult habitats in these systems. Furthermore, this study provides a case study for how complex, meta-dynamic populations and ecosystems might be better understood through the elucidation of simple ecological trade-offs.I. A. Kimirei, I. Nagelkerken, M. Trommelen, P. Blankers, N. van Hoytema, D. Hoeijmakers, C. M. Huijbers, Y. D. Mgaya, and A. L. Rype