Sustainable and safe fisheries for Rio de Janeiro, Brazil: Movement patterns and pollutant accumulation by corvina (Micropogonias furnieri)

点击翻译按钮获取中文摘要

Most fish species undertake movement patterns during their life cycle and defining these ontogenetic movements (i.e. where they go and at what life stage) and determining connectivity (i.e. the extent to which they intermix) are key to understanding their ecology for both conservation and exploitation management purposes. This is especially important for commercially-exploited species as this can allow provision of (1) protected areas for key life stages (e.g. nursery, feeding or spawning areas) and (2) local food security and continuity of employment in the local community. Movement patterns can be reconstructed using tag-recapture and radio-tracking of individually-tagged fish but these methodologies are labour-intensive, logistically difficult to implement and/or costly. In addition, their application to small fish can be limited. Recently, based on the observed spatial differences in water chemistry, the trace element chemistry of calcareous structures such as otoliths (calcified "ear stones") has been used to understand movement patterns of fishes among these locations. The advantage of this technique is that it is not size-restricted and each fish already carries its own internal tag. Aquatic systems have been considered ideal final sinks for persistent and bioaccumulative toxicants (PBTs), such as metals and organohalogen compounds. Due to some features that include chemical stability and affinity for proteins or lipids, some PBTs are efficiently bioaccumulated and end up undergoing biomagnification (i.e. are concentrated) with increasing trophic level (i.e. as you move up the food chain). Therefore, large high trophic level predators such as fish and aquatic mammals, are critical groups to study and may accumulate high PBT concentrations in their bodies. If eaten by Man in sufficient quantities, the transfer if these PBTs may present a significant health risk In this study, a dual approach to study PBTs in whitemouth croaker (or corvina), Micropogonias furnieri, from Guanabara Bay (Rio de Janeiro) is proposed. Firstly, the elemental concentrations in the otoliths will be studied in order to examine the movement patterns of corvina and, secondly, muscle PBT concentrations will be measured in fish of different ages/sizes caught in different locations of the Bay in order to determine uptake rate and accumulation of PBTs over ontogeny. Guanabara Bay is an urbanized estuary of utmost social and economic importance but also one of the most polluted in Brazil. Despite this, the fish populations of Guanabara Bay support artisanal fisheries (3700 fishers, landings 19000 tonnes, $4.8M annual first sale) and corvina comprises about 20% of the annual catch value. For temperate regions of Brazil, it has been demonstrated that this fish species displays ontogenetic habitat shifts with the adult fish feeding in coastal waters and moving into estuaries to spawn. The juvenile fish reside in estuaries for several years before moving out to coastal waters to recruit into the adult stock. The project will address the following questions: (1) What are the movement patterns of juvenile corvina in Guanabara Bay? (i.e. do juveniles of all ages/sizes mix freely within the Bay or do they show size-specific changes in salinity/habitat preference?)(2) At what age/size do adolescent corvinas move from the estuary into coastal waters? (3) What are the movement patterns of adult fish between brackish and marine water? (4) What are the muscular PBT concentrations of corvina in Guanabara Bay and coastal waters? (5) How do muscular PBT concentrations change with age/size? (i.e. what is the rate of accumulation during the estuarine residency period? and do concentrations reduce in adult fish once they are feeding in cleaner coastal waters?)