Implications of overlooked seasonal growth dynamics in tropical fisheries assessment: A test case of an oyster (Crassostrea tulipa) fishery in the Densu Delta, Ghana
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Date
2021-09-09
Journal Title
Journal ISSN
Volume Title
Publisher
ELSEVIER B.V
Abstract
Tropical fish stocks are perceived not to exhibit seasonality in growth. For this reason the standard von Bertalanffy
growth function (VBGF) has been used widely to fit the growth of tropical fish populations compared to the
seasonally-oscillating VBGF (soVBGF), which is seldom used in tropical fisheries. To advocate for the use of the
soVBGF in assessment of tropical fish stocks, this study compared the outputs of the two methods using ELEFAN_
GA_boot on oysters from the Densu Delta, Ghana. Sampling of mangrove oyster, Crassostrea tulipa covered a
period of 12 months and the data were analysed for VBGF growth parameters and its prediction models. The
intensity of growth oscillation showed that C. tulipa exhibited seasonal growth (C = 0.50), and the soVBGF fitted
the growth of the oyster better than the standard VBGF method. Estimates of some of the stock parameters (t50,
tmax, Fcur, Ecur and Ycur) were comparatively higher for the standard VBGF than the soVBGF approach. In both
approaches, the oysters were underexploited (Ecur < Emsy). However, unlike the soVBGF method where Fcur < F0.5,
the standard method indicated that Fcur > F0.5. In view of the disparities, studies which adopt standard VBGF on
tropical stocks that exhibit seasonality would likely generate comparatively higher outputs for relevant biological
reference points, which may ultimately mislead management decisions. Given the sedentary nature of oysters
which could render the organisms more susceptible to seasonal variations in environmental conditions to show
seasonality as observed in this study, we recommend further works on tropical shell- and finfishes to corroborate
the current findings or otherwise.
Description
Fisheries Research, 244, 106118
Keywords
Isaac Okyere, Oyster growth, TropFishR, SoVBGF, Tropical fisheries assessment, Standard VBGF, Fisheries management, University of Cape Coast, Ghana, ACECOR
Citation
Osei, I. K., Yankson, K., Obodai, E. A., & Okyere, I. (2021). Implications of overlooked seasonal growth dynamics in tropical fisheries assessment: A test case of an oyster (Crassostrea tulipa) fishery in the Densu Delta, Ghana. Fisheries Research, 244, 106118.