Title: The use of production models and length frequency data in stock assessments in Jamaican fisheries, building on the Caribbean Spiny Lobster observations

Type:
Final project
Year of publication:
2009
Publisher:
UNU-FTP
Place of publication:
Reykjavík
Number of pages:
55
Supervisors: Gudmundur Thordarson

Abstract

Jamaica has had an active data collection programme since 1996 covering six of its major fisheries. Data are collected by fishery type and landing sites and are primarily catch, effort and biological. Experts outside of the country usually do stocks assessments periodically on the two main fisheries. As part of strengthening the Fisheries Division’s capabilities to conduct independent stock assessment on possibly all fisheries for which there are available data, the use of length-frequency methods and production models was applied to the spiny lobster fishery. The concepts and principles grasped from this will become the platform for future analyses for other fisheries of Jamaica with similar data. After data exploration, length frequency distributions were fitted followed by fitting the data to surplus production model (Schaefer model) and length-based models (Jones’ cohort analysis and the Thompson and Bell prediction model), thereby estimating fishery performance indicators MSY, B(MSY), F(MSY) and EMSY. Given the uncertainties of model outcomes, the effects of alternative management options including those generated by the surplus production model were explored. Data exploration indicated some level of inconsistency with meeting sample targets however, a great portion of landings were below the minimum legal size of 76 mm. Schaefer model for performance indicators estimated MSY at 222 tons, EMSY at 3529 fishing days. However, forward projections showed that fishing at a fixed catch of 222 tons proved to be unsustainable since the estimated biomass was already depleted (that is B<BMSY) whereas fishing at the fixed effort of EMSY showed stock recovery within 3 years. Despite the various limitations of the models used, Jamaica should pay close attention to both the current effort and catch levels imposed on the lobster stock, as there appears to be potential dangers for the fishery if these levels of exploitation are continued.

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