Wild population size structure and female-specific growth of the broadnose sevengill shark, Notorynchus cepedianus, in the Southwestern Atlantic

Large sharks are globally distributed predators that contribute to the stability and functioning of marine ecosystems. Accurate estimates of their population size structure and growth dynamics are essential for effective conservation and management in the face of ongoing unsustainable fishing pressure. This is particularly critical for the broadnose sevengill shark ( Notorynchus cepedianus ) on the Southwestern Atlantic continental shelf, where this highly mobile species has experienced significant population declines. Its wide-ranging movements, combined with the broad extent of the continental shelf in the region, pose challenges for accurately characterizing its demography. In this context, long-term monitoring studies emerge as a powerful approach for generating critical biological information on the size-structure and growth of demersal migratory species such as N. cepedianus , thereby supporting robust population assessments and evidence-based management recommendations. To this end, we integrated over 15 years of tag–recapture data collected in coastal waters of the Southwestern Atlantic (∼34.6ºS to ∼49.4ºS), including records of sex and total length, and applied three non-linear growth models to estimate female growth dynamics. The results revealed distinct regional variations in size structure across the latitudinal range. Large specimens were most frequently recorded in the central region (41.2ºS – 44.0ºS), whereas the smallest individuals were predominantly captured in the north (≤ 41.2ºS). Model-based age–growth curve reconstructions suggest that females begin the migratory phase at roughly 2–7 years of age and attain maturity at about 8–15 years. These findings underscore the potential of long-term tagging programs to support effective management and regional conservation strategies and actions.