No abstract

There is recent evidence of widespread declines of shovelnose ray populations (Order Rhinopristiformes) in heavily fished regions. These declines, which are likely driven by high demand for their fins in Asian markets, raises concern about their risk of over-exploitation and extinction. Using life-history theory and incorporating uncertainty into a modified Euler-Lotka model, the maximum intrinsic rates of population increase (rmax) were estimated for nine species from four families of Rhinopristiformes, using four different natural mortality estimators. Estimates of mean rmax, across the different natural mortality methods, varied from 0.03 to 0.59 year-1 among the nine species, but generally increased with increasing maximum size. Comparing these estimates to rmax values for other species of chondrichthyans, the species Rhynchobatus australiae, Glaucostegus typus, and Glaucostegus cemiculus were relatively productive, while most species from Rhinobatidae and Trygonorrhinidae had relatively low rmax values. If the demand for their high-value products can be addressed then population recovery for some species is likely possible, but will vary depending on the species.

Shark‐like rays (Order Rhinopristiformes) are among the most threatened families of marine fish, yet little is known about their populations. These rays are normally taken as opportunistic catch in fisheries targeting other species and are thus poorly reported. One exception is the Indonesian tangle net fishery, which targets shark‐like rays. Market surveys of Muara Angke landing site in Jakarta, north‐western Java were conducted between 2001 and 2005, and the landed catch from the tangle net fishery was recorded (the Muara Angke landing site includes landings from more than one fishery). In total, 1,559 elasmobranchs (sharks and rays) were recorded, comprising 24 species of rays and nine species of sharks. The most abundant species landed were the pink whipray Pateobatis fai and the bottlenose wedgefish Rhynchobatus australiae, the latter being the main target species. Catch composition varied based on differences in species catchability and may also be indicative of localized declines. The fishery was highly selective for larger sized individuals, while smaller size classes of many ray species, including the target species, were also caught in other Indonesian fisheries, resulting in fishing pressure across all age classes. The decline of tangle net vessels in the fishery and the potential shift in catch composition in the Indonesian tangle net fishery increase concerns about the status of shark‐like rays and stingrays in Indonesia.

Oceanic whitetip sharks (Carcharhinus longimanus) in the Western Central Pacific have been overfished and require improved assessment and management to enable planning of recovery actions. Samples from 103 individuals (70 males and 33 females; 76.0–240- and 128–235-cm total length (TL) respectively) were used to estimate age, growth and maturity parameters from sharks retained by longline fisheries in Papua New Guinea. Back-calculation was used because of the low number of juveniles and a multimodel framework with Akaike’s information criterion corrected for small sample size (AICc) estimated growth parameters. The von Bertalanffy growth model provided the best fitting growth model for both sexes. Parameter estimates for males were: asymptotic length (L∞)=315.6cm TL; growth coefficient (k)=0.059 year–1; and length at birth (L0)=75.1cm TL. For females, the parameter estimates were: L∞=316.7cm TL; k=0.057 year–1; and L0=74.7cm TL. Maximum age was estimated to be 18 years for males and 17 years for females, with a calculated longevity of 24.6 and 24.9 years respectively. Males matured at 10.0 years and 193cm TL, whereas females matured at 15.8 years and 224cm TL. C. longimanus is a slow-growing, late-maturity species, with regional variation in life history parameters, highlighting increased vulnerability to fishing pressure in this region.