Spawning energetics of the whitemouth croaker Micropogonias furnieri (Desmarest, 1823), and implications for exploitation in Trinidad, West Indies

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Biology and Fisheries

First Committee Member

Nelson M. Ehrhardt - Committee Chair


The whitemouth croaker is one of the most economically important demersal species in Trinidad. The high level of fishing and small mesh size used on trawlers by which croakers are caught have resulted in recruitment overfishing of this species. The lack of adequate data has prevented the development of management regulations. The major objectives of this study were to determine the temporal spawning pattern and the energy budget of female croakers, the effects of fishing on the spawning stock biomass, and to recommend a suitable level of fishing effort and age at first capture.Monthly variations in the frequency of females with hydrated ovaries and in the gonadosomatic index indicated that the peak spawning season is staggered, being progressively later in the year as females become older. Spawning frequency determined from the frequency of females with hydrated eggs was fifteen times per year. The relationship between batch fecundity (BF) and total length (TL cm) was BF = 2.94 TL$\sp{\rm 3.2}$.The diet of the croaker consisted mainly of penaeid shrimps and portunid crabs. Gastric evacuation, determined from field data, was 0.27h$\sp{\rm -1}$, and daily ration 3.45% body weight. Energy was stored mainly in the liver and musculature, and was utilized for reproduction, although most of the energy for reproduction was obtained from the direct assimilation of food. Average growth efficiency was 7.90$\sp\circ$ and exceeded reproductive effort until age three, after which the reverse occurred. Reproduction effort increased steadily with age, and averaged 8%.The present level of fishing mortality (0.8) and age at first capture (2 years) in the fishery for the croaker in Trinidad result in a spawning potential ratio (ratio of spawning stock biomass per recruit in the fished to that in the unfished population) below the critical level of 0.1. To ensure an adequate spawning stock level, fishing effort must be reduced by 47.5% and the age at first capture increased to three years. Since growth efficiency is equal to reproductive effort at age three, an age at first capture of three years will also ensure a balance of energy flow to growth and reproduction.


Biology, Oceanography; Agriculture, Fisheries and Aquaculture

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