Reproduction, abundance and feeding habits of the broadnose sevengill shark Notorynchus cepedianus in north Patagonia, Argentina

Abstract

Broadnose sevengill sharks Notorynchus cepedianus caught in a recreational fishery during a 3 yr period in Anegada Bay, Argentina were examined. Monthly variations in abundance were found, with the highest mean abundance in April. Neonates and juveniles were common in the study area, indicating that Anegada Bay is a nursery area of N. cepedianus. Male and female sizes at maturity were 170 and 224 cm total length (TL), respectively, similar to other studied regions. Liver size was sexually dimorphic, with adult females having larger livers, which might allow for the maximization of oocyte size/number. Individuals <100 cm TL fed mainly on teleosts, sharks 100 to 170 cm TL consumed mainly cartilaginous fishes and less teleosts, and sharks >170 cm fed mostly on cartilaginous fishes and marine mammals. All size groups preyed on marine mammals, which may be a result of the local availability of small calves of La Plata River dolphins Pontoporia blainvillei. Possibly, the pattern of habitat use of Anegada Bay by P. blainvillei is affected by N. cepedianus. The proportion of individuals with prey within the stomach was negatively correlated with TL. As indicated by prey remains found within stomachs (most were in pieces) and by the location of the fishing hook in sharks (most were hooked in the mouth), N. cepedianus extensively handles its prey with the mouth before swallowing it, which is consistent with previous observations. Anegada Bay may be an important area for conservation of N. cepedianus in the SW Atlantic given the high abundance of juveniles and subadults. KEY WORDS: Elasmobranch · Maturity · Nursery · Predation · Marine mammalsResale or republication not permitted without written consent of the publisher

Decadal trends in shark catches and effort from the New South Wales, Australia, Shark Meshing Program 1950 - 2010

“…comm., 2010); however, it is unknown which factors would cause such largescale spatial variation in individual seasonal movements. Sevengill sharks are considered to be one of the most important apex predators in temperate coastal systems (Ebert 2002;Lucifora et al 2005) and, given the diversity of their diet, may be taking advantage of a niche vacated by other species with reduced populations. Similar niche occupation has been postulated for tiger sharks in more tropical environs (Heithaus et al 2010).…”

Maturity, reproductive cycle, and fecundity of spiny butterfly ray, Gymnura altavela (Elasmobranchii: Rajiformes: Gymnuridae), from the coast of Syria (eastern Mediterranean)

“…Conversely, the relation between the size (DW) and the liver mass (M L ) significantly differed between males and females, it was significantly higher in the former than in the latter and these significant differences between males and females suggested that liver plays a more important role in life cycle of the latter (Lucifora et al 2005). Liver size is sexually dimorphic in both oviparous and viviparous chondrichthyan species.…”

“…Moreover, cartilaginous fish store energy as lipids in the liver (Craik 1978). In viviparous females larger liver observed may be related to the increased energy expenditure during vitellogenesis, oocyte maturation, and gestation as well as females store large quantities of lipids in the liver during the reproductive cycle (Lucifora et al 2005). The highest value of HSI was recorded in juvenile male and female specimens suggested that liver constituted a reserve of nutriments for free-swimming specimens soon after parturition, this hypothesis was corroborated by decreasing of HSI values in larger juveniles.…”

Intrapopulation variations in diet and habitat use in a marine apex predator, the broadnose sevengill shark Notorynchus cepedianus

“…The most complex trees were further analysed to determine if there could be an effect of season or year of sampling for animals from these 2 coastal sites. In the analyses, females were considered mature if larger than 220 cm TL (Ebert 1989, Lucifora et al 2005. Models were run for each element separately, using the TREES package on S-PLUS 2000 ® (MathSoft).…”

“…They are seasonally abundant in shallow coastal habitats (Ebert 1989, Lucifora et al 2005, Barnett et al 2010a, where they feed mostly on other elasmobranchs, marine mammals and teleosts (Ebert 1989, 1991, Lucifora et al 2005, Braccini 2008, Barnett et al 2010b. Recently, an intensive 3-yr study on sevengill shark ecology was conducted in 2 coastal habitats of southeast Tasmania, Australia, where information on diet, population structure, habitat use and movement patterns was collected (Barnett et al 2010a(Barnett et al ,b,c, 2011.…”