Reproductive biology of the greeneye spurdog Squalus chloroculus (Squaliformes, Squalidae)

Abstract

The reproduction of the greeneye spurdog Squalus chloroculus was studied based on animals caught in the multispecies and multi-gear southern and eastern scalefish and shark fishery on the upper continental slope off southern Australia. One hundred and ninety-nine females (502-990 mm, total length, L ) and 189 males (515-810 mm L ) were examined. The female reproductive cycle, based on 41 breeding animals, is continuous and triennial, with the pregnancy period estimated to be 31-34 months, seasonal and synchronous with the ovarian cycle; a third of the breeding female population is estimated to give birth between September and December each year. The estimated L at which 50% of females are mature is 799 mm (95% c.i.: 794, 804), whereas the L at which 50% are maternal is 825 mm (95% c.i.: 817-833), but these estimates are probably biased by the phenomenon of apparent change of L at maternity and L at maturity following severe length-selective fishing mortality. Litters ranged from four to 15 embryos with a 1:1 sex ratio, and litter size increased with maternal length. The breeding cycle of males is neither seasonal nor synchronous with the female cycle. The estimated L of males where 50% are mature was 629 mm (95% c.i.: 603, 645).

Geographical variability in life‐history traits of a midslope dogfish: the brier shark Deania calcea

“…This would bias the length–frequency distribution of each age class remaining in the population towards larger animals; and has the effect of straightening the estimated von Bertalanffy growth curve, an effect of the Rosa Lee phenomenon (Lee, ) as has been demonstrated for gillnet fishing on gummy shark Mustelus antarcticus Günther 1870 (Moulton et al , ; Walker et al , ). It also has the effect of displacing maturity ogives towards an increased size at maturity, referred to as ‘phenomenon of apparent change of length‐at‐maturity’, as seen for S. chloroculus (Rochowski et al, ) and M. antarcticus (Walker, ).…”

“…Although testing of the M T and L T relationship did not detect differences due to the pregnancy condition of some females, the small number of pregnant females, the restricted size range of these females and a high probability of incorrect classing of reproductive condition caused by some of them spontaneously aborting upon capture might have masked the effect that pregnancy has on the M T and L T relationships. The small number of large females (more likely to be pregnant) may very well be due to selectivity of the trawls, as the larger females may be best able to escape the nets, as indicated for the greeneye spurdog Squalus chloroculus Last, White & Motomura 2007 (Rochowski et al , ).…”

“…Non-continuous cycles are thought to favour shorter (c. 1 year) pregnancy periods (Hamlett, 1999;Pethybridge et al, 2011). Animals can allocate energy exclusively to embryo growth, as compared with continuous breeders such as Squalus acanthias L. 1758 (Hanchet, 1988), the shortnosed or piked spurdog Squalus megalops (Macleay 1881) (Braccini et al, 2006) and S. chloroculus (Rochowski et al, 2015), which simultaneously grow ovarian follicles and embryos, and theoretically have longer pregnancy periods. For this reason, a c. 1 year pregnancy cycle may be expected for D. calcea.…”

Notes on the reproductive biology of the Brazilian electric ray Narcine brasiliensis (Elasmobranchii: Narcinidae)

“…These observations may be because females in this study aborted when caught. Abortion under stress is well documented for elasmobranchs, as well as within lecithotrophic viviparous species (Baremore, ; Irvine et al ., ; Akhilesh et al ., ; Rochowski et al ., ), hence values of uterine fecundity may be underestimated. An alternative hypothesis could be that Bigelow & Schroeder () based their information on individuals from another population of the same species and even mixed species collectively named N .…”

The first reproductive parameters and evidence of multiple paternity in one new spiny dogfish species, Squalus albicaudus (Squaliformes, Squalidae)

“…The low fecundity observed here is in agreement with the literature for species belonging to the Squalus genus [ i.e ., three to six pups per litter in S. megalops , three to four in S. blainvillei (Ebert et al ., 2013), one to five pups in Squasimodo quasimodo (Tagliafico et al ., 2018)]. A continuous reproductive cycle has already been reported for species of the Squalus genus (Braccini et al ., 2006; Natanson et al ., 2017; Rochowski et al ., 2015). No correlations were observed between total female length and number of embryos per litter, which is in line with findings for Squalus cubensis and S. quasimodo (Tagliafico et al ., 2018).…”