Age, growth and maturity of the Australian sharpnose shark Rhizoprionodon taylori from the Gulf of Papua

Abstract

Coastal sharks with small body sizes may be among the most productive species of chondrichthyans. The Australian sharpnose shark (Rhizoprionodon taylori) is one of the most productive members of this group based on work in northern and eastern Australia. However, life history information throughout the remainder of its range is lacking. To address this knowledge gap, the age, growth and maturity of R. taylori caught in the Gulf of Papua prawn trawl fishery in Papua New Guinea, were studied. One hundred and eighty six individuals, comprising 131 females (31–66 cm TL) and 55 males (31–53 cm TL) were aged using vertebral analysis and growth was modelled using a multi-model approach. The lack of small individuals close to the size at birth made fitting of growth curves more difficult, two methods (fixed length at birth and additional zero aged individuals) accounting for this were trialled. The von Bertalanffy growth model provided the best fit to the data when used with a fixed length-at-birth (L0 = 26 cm TL). Males (L∞ = 46 cm TL, k = 3.69 yr-1, L50 = 41.7 cm TL and A50 = 0.5 years) grew at a faster rate and matured at smaller sizes and younger ages than females (L∞ = 58 cm TL, k = 1.98 yr-1, L5o = 47.0 cm TL and A50 = 0.93 years). However, none of the methods to account for the lack of small individuals fully accounted for this phenomenon, and hence the results remain uncertain. Despite this, the results reaffirm the rapid growth of this species and suggest that the Gulf of Papua population may grow at a faster rate than Australian populations. Rhizoprionodon taylori is possibly well placed to withstand current fishing pressure despite being a common bycatch species in the Gulf of Papua prawn trawl fishery. However, further research needs to be undertaken to estimate other key life history parameters to fully assess the population status of this exploited shark species and its vulnerability to fishing in the Gulf of Papua.

Life‐history, exploitation and extinction risk of the data‐poor Baraka's whipray (Maculabatis ambigua) in small‐scale tropical fisheries

“…LOAs are presented alongside standard precision metrics (Table 1). Variability in age band counts was not considered to be unusually high when compared to other studies (Baje et al ., 2018; Gutteridge et al ., 2013; Jacobsen & Bennett, 2010). Consensus was reached between readers for all specimens with initial disparities >1 year, suggesting that the significant bias identified by the Bland–Altman approach was likely to have been overcome.…”

Small fins, large trade: a snapshot of the species composition of low‐value shark fins in the Hong Kong markets

“…We found four of the seven species of the genus Rhizoprionodon , a group of small, coastal sharks characterized by high productivity and frequent occurrence in coastal fisheries landings throughout the tropics and subtropics (Simpfendorfer & Burgess, ; Harry et al ., ; Ba et al ., ; Baje et al ., ). Rhizoprionodon species represented 27.6% of our samples, with the milk shark R. acutus being the most common (25.3%; Table ).…”

“…The milk shark is the most widely distributed species within the genus (Compagno, 1984), and one of the most common species found in the Hong Kong retail markets (Fields et al, 2017;Cardeñosa et al, 2018a). The life-history traits of milk sharks, and other Rhizoprionodon species, allows them to withstand higher fishing pressures than most elasmobranch species (Harry et al, 2010;Baje et al, 2018). However, these species are caught together with other less productive and threatened elasmobranch species in juvenile or adult stages, including several found in our survey (e.g.…”

Dietary overlap of carcharhinid sharks in the Gulf of Papua

“…Since the cumulative prey curves show that the sample size was not sufficient to fully describe diets further sampling and proper identification of prey will be required to adequately characterise diets and investigate the extent of these preliminary observed differences. Both R. taylori and C. coatesi are morphologically similar but appear to be reproductively different, R. taylori breeds annually and has a rapid growth rate reaching maturity in less than 1 year (Baje et al 2018) compared to aseasonal reproduction in C. coatesi, which reaches maturity at 5 years of age (Baje et al 2019) these factors may also influence feeding behaviour at various life stages such as the broad diet of R. taylori is needed to support rapid growth in the first year of life to reach maturity.…”

“…The Australian blackspot shark (Carcharhinus coatesi), the milk shark (Rhizoprionodon acutus) and the Australian sharpnose shark (Rhizoprionodon taylori) are all smallbodied coastal sharks that are commonly caught as bycatch in the Gulf of Papua Prawn Fishery (GoPPF) in Papua New Guinea, making up 9, 7 and 29% respectively of the total elasmobranch by-catch sampled by number (White et al 2019). The life histories of C. coatesi and R. taylori indicate that the populations of each species may be affected differently by the fishery based on growth and biological productivity (Baje et al 2018;Baje et al 2019). However, the ecology of these sympatric sharks has not been investigated in the Gulf of Papua, and their ecological roles are not well understood.…”