An estuarine system as a possible nursery habitat for the broadnose sevengill shark: San Antonio cape-Southwest Atlantic

The nursery habitats of the broadnose sevengill shark Notorynchus cepedianus (Peron, 1807) remain largely unknown. The identification of these critical habitats is important for the conservation of these top-down regulator species and general coastal ecosystem dynamics. We investigated the role of the San Antonio cape (Argentina) as a nursery habitat for N. cepedianus and tested the hypothesis that physical conditions (turbidity, sea surface temperature) are more important than prey abundance in the habitat use by young-of-the-year (YOY). We used the presence, relative abundance, and size structure of YOY from a small-scale gillnet fishery (2008-2014) to assess the intra- and inter-annual persistence in habitat use. The results indicated intra- and inter-annual persistence in estuarine habitat use, and comparisons with previous studies suggested that YOYs were more commonly encountered in San Antonio cape than in other suitable areas. Finally, the YOYs' use of the area may be explained by a combination of the spatial-temporal variation in turbidity conditions and food abundance. These results suggested San Antonio cape as a nursery habitat for N. cepedianus YOYs and highlighted the importance of understanding key biophysical effects that regulate the use, movement, and residency of N. cepedianus in their nursery habitats.