Abstract
Understanding the ecological factors that regulate elasmobranch abundance in nearshore waters is essential to effectively manage coastal ecosystems and promote conservation. However, little is known about elasmobranch populations in the western South Atlantic Ocean. An 8-year, standardized longline and drumline survey conducted in nearshore waters off Recife, northeastern Brazil, allowed us to describe the shark assemblage and to monitor abundance dynamics using zero-inflated generalized additive models. This region is mostly used by several carcharhinids and one ginglymostomid, but sphyrnids are also present. Blacknose sharks, Carcharhinus acronotus, were mostly mature individuals and declined in abundance throughout the survey, contrasting with nurse sharks, Ginglymostoma cirratum, which proliferated possibly due to this species being prohibited from all harvest since 2004 in this region. Tiger sharks, Galeocerdo cuvier, were mostly juveniles smaller than 200 cm and seem to use nearshore waters off Recife between January and September. No long-term trend in tiger shark abundance was discernible. Spatial distribution was similar in true coastal species (i.e. blacknose and nurse sharks) whereas tiger sharks were most abundant at the middle continental shelf. The sea surface temperature, tidal amplitude, wind direction, water turbidity, and pluviosity were all selected to predict shark abundance off Recife. Interspecific variability in abundance dynamics across spatiotemporal and environmental gradients suggest that the ecological processes regulating shark abundance are generally independent between species, which could add complexity to multi-species fisheries management frameworks. Yet, further research is warranted to ascertain trends at population levels in the South Atlantic Ocean.
Highlights
Nearshore areas generally comprise shallow, highly productive habitats supporting great abundance and diversity of fish and invertebrates [1], they provide ideal foraging grounds where elasmobranchs can enhance growth [2] and survival [3,4]
This study aims at characterizing the shark assemblage off the Metropolitan Region of Recife and assessing its spatiotemporal dynamics together with the environmental factors that regulate species abundance in order to understand species-specific trends in the use of nearshore areas
The ecological significance of elasmobranchs warrants the sustainable management of their populations, which can only be achieved with adequate information on their ecology
Summary
Nearshore areas generally comprise shallow, highly productive habitats supporting great abundance and diversity of fish and invertebrates [1], they provide ideal foraging grounds where elasmobranchs can enhance growth [2] and survival [3,4]. Nearshore waters typically comprise extremely dynamic ecosystems [15] to which inhabitants must adapt in order to remain in these regions. Vagile species such as sharks may cope with environmental variability by accessing coastal waters only when favorable conditions are met and moving away otherwise. Coastal elasmobranchs are generally exposed to high levels of anthropogenic pressure due to habitat degradation and loss [24,25,26,27] and fishing These anthropogenic impacts will affect elasmobranchs in different ways according to species-specific strategies of habitat use and function
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