Abstract
The Fuegian sprat Sprattus fuegensis represents one of the most important pelagic resources in the Southwest Atlantic Ocean (SWAO), exerting a crucial ecological role as an intermediary link in Patagonian food webs. Otolith microstructure of 217 age-0 sprats were analyzed aiming to characterize growth patterns and possible environmental effects over them. Samples were gathered during three oceanographic surveys (spring 2014; autumns 2016, 2017) in Tierra del Fuego (TDF) and the Marine Protected Area Namuncura-Burdwood Bank (MPAN-BB), the first Argentinian open-sea marine protected area. Daily growths (DG) of larvae and post-larvae were estimated by individually modeling size and otolith radius relationships through back-calculation procedures using potential and linear functions respectively. Increment widths (IW) and DG values and trajectories were assessed for older sprats (i.e. survivors) sampled in the autumn surveys considering the habitat, year sampled and sprats’ hatching seasons, and were additionally evaluated in relation to sea-surface temperature (SST). IW and DG trajectories differed primarily according to the habitat sampled and sprats’ hatching seasons. Overall, strong coupling was detected between IW and DG trajectories with SST in both habitats. However, statistical assessment on particular comparisons showed that this general trend is not strictly invariant. Even though several results pinpointed a positive correlation between IW and DG with SST, the highest DG were estimated for summer- and autumn-born sprats sampled in 2016 in the MPAN-BB, period and habitat with the lowest SST values. These results unveil a complex relationship between spatial and temporal variability during early growth of Fuegian sprats, supplying relevant information that could be used in the creation of adequate ecosystem based management strategies in the SWAO.
Highlights
The Fuegian sprat Sprattus fuegensis (i.e., Austral sprat, Patagonian sprat, Malvinas (Falkland) sprat) is a small clupeid that inhabits the coasts and shelves of southern South America (Cousseau, 1982; Aranis et al, 2007) and is usually referred to as the most important pelagic resource in the Southwest Atlantic Ocean (SWAO) south of 47◦S (Bellisio et al, 1979)
A total of 217 individuals were analyzed in this study, with 134 specimens sampled in the Marine Protected Area Namuncurá-Burdwood Bank (MPAN-BB) and 83 in Tierra del Fuego (TDF)
A wider range was observed both between and within habitats in 2016 and 2017 compared to 2014, with a range of more than 90 days of age among larvae from the MPANBB in 2016. This variability was replicated by the estimated hatching seasons, registering larval hatching during summerautumn (2016) and spring-summer (2017) in the MPAN-BB but exclusively in summer in TDF
Summary
The Fuegian sprat Sprattus fuegensis (i.e., Austral sprat, Patagonian sprat, Malvinas (Falkland) sprat) is a small clupeid that inhabits the coasts and shelves of southern South America (Cousseau, 1982; Aranis et al, 2007) and is usually referred to as the most important pelagic resource in the Southwest Atlantic Ocean (SWAO) south of 47◦S (Bellisio et al, 1979). As many other small pelagic fishes, this zooplanktivorous sprat exerts an essential trophic role as an intermediary link between lower trophic levels and top predators of ecological and economical relevance (e.g., Ramírez, 1976; Bezzi, 1984; Schiavini et al, 1997; Ciancio et al, 2008; Belleggia et al, 2014; Scioscia et al, 2014) Due to their high biomass schools and trophic position, S. fuegensis possibly controls the energy flux at the wasp-waist level (Cury et al, 2000; Bakun, 2006; Fauchald et al, 2011; Ricciardelli and Boy, unpublished data). Combined with the high susceptibility of small pelagic fishes to ocean-atmosphere variations (Alheit and Hagen, 2001; Peck et al, 2013), this background pinpoint the importance of understanding Fuegian sprat early stages’ growth and the potential influence of environmental change over them, features poorly understood to the date
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