Growth estimates of young-of-the-year broadnose sevengill shark

Growth estimates of young-of-the-year broadnose sevengill shark, Notorynchus cepedianus, a top predator with poorly calcified vertebrae

Andrés J. Jaureguizar, Federico Cortés, J. Matias Braccini, Rodrigo Wiff, Andrés C. Milessi

ABSTRACT:

The broadnose sevengill shark, Notorynchus cepedianus (Péron, 1807), is a large marine top predator in temperate coastal ecosystems. Some aspects of its life history have been determined but its growth pattern is yet to be fully understood. We used a multi-modeling approach and a sensitivity test to estimate growth parameters from young-of-year (YOY) length data collected off San Antonio Cape (SAC), Argentina, a critical habitat in the Southwest Atlantic Coastal Zone (SACZ). The best selected model, a sex-combined logistic growth model, estimated an asymptotic length (L_∞) of 92.58 cm TL (95% CI: 86.48 – 105.89 cm), a growth coefficient (K) of 0.006818 days ^-1 (95% CI: 0.004948 – 0.008777), and a size at birth (L₀) of 40.73 cm. The predicted annual growth (i.e. L_{1 –} L₀) was 43.2 cm TL. Males had smaller L_o, higher K, and achieved larger sizes after one year. The YOY in SAC attained a larger L₁ and grew faster than their Australian and South African wild counterparts. The consistent year-round presence of YOY in the SAC highlights the importance of this area as a pupping ground and potential nursery for N. cepedianus; this has direct implications for the allocation of research and management effort for the conservation of this species in the Southwest Atlantic.

Journal of Fish Biology, DOI: 10.1111/jfb.14976

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