Abstract
The objective of this study is to describe the genetic population structure and demographic history of the endangered marine fish, Epinephelus marginatus, within Malta’s Fisheries Management Zone for the purpose of localised conservation planning. Epinephelus marginatus is a long-lived, sedentary, reef-associated protogynous hermaphrodite with high commercial and recreational value that is at risk of extinction throughout its global distribution. Based on global trends, population substructuring and gaps in local knowledge this has led to an increased interest in evaluation of local stock. Assessment of Maltese demography was based on historical and contemporary catch landings data whilst genetic population structure and regional connectivity patterns were evaluated by examining 175 individuals collected within the central Mediterranean region between 2002 and 2009 using 14 nuclear microsatellite loci. Demographic stock assessment of Maltese E. marginatus’ revealed a 99% decline in catch landings between 1947 and 2009 within the Fisheries Management Zone. A contemporary modest mean size was observed, 3 ± 3 kg, where approximately 17% of the population was juvenile, 68% female/sex-changing and 15% were male with a male-to-female sex ratio of 1:5. Genetic analysis describes the overall population of E. marginatus’ within the Fisheries Management Zone as decreasing in size (ƟH = 2.2), which has gone through a significant size reduction in the past (M = 0.41) and consequently shows signs of moderate inbreeding (FIS = 0.10, p < 0.001) with an estimated effective population size of 130 individuals. Results of spatially explicit Bayesian genetic cluster analysis detected two geographically distinct subpopulations within Malta’s Fisheries Management Zone and that they are connected to a larger network of E. marginatus’ within the Sicily Channel. Results suggest conservation management should be designed to reflect E. marginatus’ within Malta’s Fisheries Management Zone as two management units.
Highlights
Molecular conservation genetics seeks to manage biological threats by assessing genetic composition and implementing management strategies aimed at maintaining or restoring natural dynamics in order to protect unique species and their genetic diversity
Demographic results based on ancillary data collected during this study found the observed weight-length relationship of the Maltese dusky grouper was y = 0.0791x2.63 with a correlation coefficient of R2 = 0.95 (Fig 2)
Based on total length it was estimated that approximately 17% of the population was juvenile, 68% female/sex-changing and 15% were male with a male to female sex ratio of 1:5
Summary
Molecular conservation genetics seeks to manage biological threats by assessing genetic composition and implementing management strategies aimed at maintaining or restoring natural dynamics in order to protect unique species and their genetic diversity. A decline in the number of observed individuals, catch size, landings data (kg) or an imbalance in population demography (e.g. sex ratios) would prompt further investigation into the status of these potentially at risk species. Fragmented or isolated populations often show a decline in genetic diversity over time due to inbreeding This results in a decreased ability to evolve in response to deterministic and stochastic events and a decline in population size and biological fitness [2]. For this reason, minimising the loss of genetic diversity from inbreeding and isolation is a major objective in genetic conservation management
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