An analytical study of the sea water slime with reference to bacterial flora

A detailed study of the primary film of slime with reference to the bacterial flora, its quality and quantity, as observed on different material surfaces exposed to sea water is carried out. A correlation has been established between bacteria and slime deposited on different surfaces.

A mesocosm analytical study on the impact of freshwater mussel (Lamellidens marginalis Lamarck) mediated bioturbation and biodeposition on some ecological factors of a freshwater lake

The biotic potential of the benthic filter feeding freshwater bivalve mollusc Lamellidens marginalis (Lamarck) influencing the nutrient dynamics of the bottom sediments of the lake by means of biodeposition and bioturbation activities were analysed using a lake mesocosm experiment. Five control as well as experimental mesocosms was maintained up to 60 days (d). The factors studied included the percentage of water content of the sediment, percentage of total nitrogen, percentage of organic matter along with the total phosphorus and humic acid content. While total phosphorus and humic acid content of the experimental mesocosoms showed gradual and significant increases from 30d of the experiment to reach the maximum levels after 60d, the percentage of organic matter registered significant increases right from 15d onwards and reached the maximum values after 60d. On the other hand, while the percentage of water content of the sediments of the experimental mesocosoms increased only up to 30d experiment, percentage of nitrogen was increased during the first half and at the fag end of the experiment. All the investigated ecological factors were found to be significantly influenced by the presence of L. marginalis in the experimental mesocosms. The study indicated that the mussel influence the nutrient dynamics of the inhabitant ecosystem through the processes of excretion, biodeposition of pseudofaeces and faeces, along with the bioturbation of the sediments brought about by their ploughing movements. KEYWORDS: freshwater mussel, Lamellidens marginalis, bioturbation, biodeposition, mesocosms.

A study on the growth of Pseudotolithus elongatus, Chrysichthys nigrodigitatus and Cynoglossus goreensis occurring in the Cross River Estuary

Samples of Pseudotolithus elongatus, Chrysichthys nigrodigitatus and Cynoglosus goreensis obtained from the Cross River Estuary (which is most probably the largest estuary water system along the coast of West Africa) between January 1980 and May 1981 were evaluated on basis of population dynamic analytical method postulated by Pauly (1980) for tropical fish stocks. Growth parameters were obtained for the fish species. Wherever possible, these results were compared to those obtained by Longhurst (1964d) and LeGuen (1971) in other West African waters. On the whole, results obtained in this study tend to indicate that the growth of the croaker, bagrid catfish and the sole in the Cross River Estuary is allometric, the third and fourth year-classes of P. elongatus the second and third class-year of C. nigrodigitatus and the fourth, fifth and sixth year classes of C. goreensis dominated in the age distribution of these fish species

A meta-analytic approach to quantifying scientific uncertainty in stock assessments

Quantifying scientific uncertainty when setting total allowable catch limits for fish stocks is a major challenge, but it is a requirement in the United States since changes to national fisheries legislation. Multiple sources of error are readily identifiable, including estimation error, model specification error, forecast error, and errors associated with the definition and estimation of reference points. Our focus here, however, is to quantify the influence of estimation error and model specification error on assessment outcomes. These are fundamental sources of uncertainty in developing scientific advice concerning appropriate catch levels and although a study of these two factors may not be inclusive, it is feasible with available information. For data-rich stock assessments conducted on the U.S. west coast we report approximate coefficients of variation in terminal biomass estimates from assessments based on inversion of the assessment of the model’s Hessian matrix (i.e., the asymptotic standard error). To summarize variation “among” stock assessments, as a proxy for model specification error, we characterize variation among multiple historical assessments of the same stock. Results indicate that for 17 groundfish and coastal pelagic species, the mean coefficient of variation of terminal biomass is 18%. In contrast, the coefficient of variation ascribable to model specification error (i.e., pooled among-assessment variation) is 37%. We show that if a precautionary probability of overfishing equal to 0.40 is adopted by managers, and only model specification error is considered, a 9% reduction in the overfishing catch level is indicated.

A fisheries co-management case study from The Gambia

User involvement in fisheries management has been around for some time, but few analytical papers have been published on the subject in Africa. Most of these initiatives fall under the rubric of co-management. But what is the concept of co-management in theory and how does it work in practice? In reviewing a comprehensive artisanal fisheries development project, we will attempt to answer this question in the context of The Gambia.