Longevity of Atlantic Sharpnose Sharks Rhizoprionodon terraenovae and Blacknose Sharks Carcharhinus acronotus in the western North Atlantic Ocean based on tag-recapture data and direct age estimates

Abstract

Longevity of Rhizoprionodon terraenovae and Carcharhinus acronotus in the western North Atlantic Ocean was examined using direct age estimates from vertebral sections and tag-recapture data. Time-at-liberty ranged from 7.7-14.0 years (mean =10.1) for R. terraenovae and 10.9-12.8 years (mean =11.9) for C. acronotus. Maximum estimated longevity was determined to be 19.8 years through tag-recapture data and 18.5 years from direct age estimates for R. terraenovae and 22.8 years through tag-recapture data and 20.5 years through direct age estimates for C. acronotus. These longevity estimates represent a large increase over previous estimates and may have significant effects on analyses that depend on longevity including lifetime fecundity, mortality rates, demographic analyses and stock assessments.

Distributions and Movements of Atlantic Shark Species: A 52-Year Retrospective Atlas of Mark and Recapture Data

“…Such information, particularly over large spatial and temporal scales, is essential for the development of appropriate management strategies (Ferreira et al, 2015) and in determining the usefulness of conservation measures (Sims, 2010). The wealth of data garnered from the CSTP highlights the importance of continuing these longterm tagging programs (Frazier et al, 2015). Given the fact that shark species are slow growing, long-lived, and highly mobile, with relatively low return rates for tagged sharks-continued tagging efforts are essential to provide this critical life history and population dynamics information.…”

“…Longevity can be estimated using the oldest aged specimen in a traditional hardpart ageing study (minimum estimate), calculations from von Bertalanffy growth function parameter estimates (e.g., L ∞ ), or using radiocar-bon dating in combination with band pair counts (Natanson et al, 2002;Andrews et al, 2011). Maximum time at liberty records from M/R data serve as direct evidence of longevity, particularly if size (age) at tagging is taken into account (Casey and Natanson 1992;Frazier et al, 2015). Times at liberty verify calculated data for certain species (e.g., shortfin mako, blue shark, sandbar shark), or serve as a proxy for minimum lifespan estimates for species with no published age data.…”

Growth rates of bonnetheads (Sphyrna tiburo) estimated from tag-recapture data

“…Validation of age estimates is recommended for all age and growth studies; however, validation of all age classes is difficult and rarely achieved (Cailliet et al, 2006). Although validation of ages has been completed for several species of elasmobranchs Ardizzone et al, 2006;Kneebone et al, 2008), there is a growing body of evidence that indicates that age underestimation commonly occurs for long-lived species, such as sharks (e.g., Francis et al, 2007;Passerotti et al, 2014;Harry, 2018;Natanson et al, 2018b), as well as recent evidence that age underestimation may also occur in sharks with intermediate longevities (Frazier et al, 2014). For these reasons, modeling of growth with tag-recapture data and newer methods of modeling that combine tag-recapture data with age estimates have been recommended (Eveson et al, 2007;Aires-da-Silva et al, 2015;Francis et al, 2016;Natanson and Deacy, 2019).…”

“…The bonnethead (Sphyrna tiburo) is a relatively small shark species, with individuals reaching a maximum size of 150 cm total length, that is commonly found in the coastal and estuarine waters of the western North Atlantic Ocean from North Carolina to southern Brazil, including the Gulf of Mexico (GOM) and the Caribbean Sea (Compagno, 1984). Significant differences in life history characteristics exist between bonnetheads captured off the Atlantic coast of the southeastern United States (hereafter referred to as the Atlantic region) and those caught in the eastern GOM (Frazier et al, 2014). Regional variation in life history between populations in the Atlantic region and in the GOM has been found for other coastal shark species, including the Atlantic sharpnose shark (Rhizoprionodon terraenovae) (Carlson and Loefer 1 ), blacknose shark (Carcharhinus acronotus) , and finetooth shark (C. isodon) (Drymon et al, 2006;Vinyard et al, 2019).…”

Genetic structure and congeneric range overlap among sharpnose sharks (genusRhizoprionodon) in the Northwest Atlantic Ocean

“…Due to heavy prevalence of R. terraenovae in northwestern Atlantic ecosystems and artisanal fisheries, several studies have examined its life history characteristics, such as reproductive biology (Parsons 1983;Loefer and Sedberry 2002), age and growth (Parsons 1985;Branstetter 1987;Loefer and Sedberry 2002;Frazier et al 2015), and temporal changes in distribution and abundance (Marquez-Farías and Castillo-Geniz 1998;Parsons and Hoffmayer 2005). Parsons and Hoffmayer (2005) assessed populations in the northern Gulf of Mexico from March to October from 1998 to 2000, noting that the ratio of mature males to mature females caught within the Mississippi Sound was immensely skewed (80:1), indicating that mature females may predominantly remain nearshore or offshore.…”