Living on the edge: latitudinal variations in the reproductive biology of two coastal species of sharks

Abstract

Differences in the reproductive biology of both the Australian weasel shark Hemigaleus australiensis and the Australian sharpnose shark Rhizoprionodon taylori were apparent between individuals from the southern-most extent of their range in eastern Australia (Moreton Bay) and those from northern Australia. For H. australiensis from Moreton Bay the total length (L ) at which 50% of individuals were mature (L ) was 759 mm for females and 756 mm for males, values that were respectively 17-26% larger than reported for the species in northern Australia. The relatively low percentage (63%) of pregnant mature females and presence of small, similar-sized, embryos in utero in both May and November suggested a semi-synchronous, annual reproductive cycle in Moreton Bay, whereas a synchronous, biannual reproductive cycle occurred in northern Australia. It is likely that H. australiensis has a resting phase between gestation cycles at the southern-most extent of its range. For R. taylori from Moreton Bay the L s were 588 and 579 mm for females and males, respectively, values 2-3% larger than for individuals from the mid-Queensland coast and 31-35% larger than for individuals from northern Australia. The length at which 50% of the females were maternal (611 mm L ) in Moreton Bay was greater than the L , indicating that not all sharks mate immediately after maturing. Rhizoprionodon taylori in the south had an annual reproductive cycle incorporating a 7-8 month embryonic diapause, with pups probably born in February. A mean fecundity of 7·5 was almost double that reported from northern Australia. Regional variations in the reproductive characteristics of H. australiensis and R. taylori may influence their resilience to fishing and other anthropogenic pressures. The substantial differences reported here highlight the importance of region-specific life-history parameters to successful management and conservation.

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

“…Length-at-maturity estimates for the GOP showed that males also matured at smaller sizes then females. The length at which both 50% of males and females in the GOP reached maturity resembled data from north and western Australia recorded by [ 15 ] which were smaller than that observed by [ 8 ] and [ 9 ]. These findings highlight latitudinal variation for this species suggesting length-at-maturity increases with higher latitudes.…”

“…The Australian sharpnose shark Rhizoprionodon taylori is a small carcharhinid species known to have one of the fastest growth rates of all shark species [ 7 , 8 ]. Initial studies suggested it grows rapidly in the first year of life, on average increasing to 140% of its length-at-birth, and attains a maximum length of only 67 and 97 cm TL respectively in different locations in Australia [ 8 , 9 ]. Maturity is reached after only one year with a litter of 1–10 pups produced every year following maturity [ 8 , 10 ].…”

“…These limited movements mean that there may be differences in the life history of this species between the GOP and other regions. These differences need to be investigated since variations in size at birth and length-at-maturity could affect fisheries risk assessments, and have already been documented between different locations in Australia [ 9 , 10 , 15 ].…”

Temporal and latitudinal comparisons of reproductive parameters in a heavily exploited shark, the bonnethead, Sphyrna tiburo (L. 1758), in the southern Gulf of Mexico

“…Latitudinal variation in life-history parameters is well documented in teleost fish (Blanck & Lamouroux, 2007;Heibo et al, 2005;Lappalainen et al, 2008) and spatial variation has recently been examined in elasmobranchs; however, this variation cannot always be attributed to latitude. In addition to the bonnethead shark (Lombardi-Carlson et al, 2003;Parsons, 1993b), latitudinal variation was observed for the starspotted dogfish, Mustelus manazo (Yamaguchi et al, 2000), the angular angel shark, Squatina guggenheim (Colonello et al, 2007), the little skate, Leucoraja erinacea (Frisk & Miller, 2009), the kite skate, Dipturus chilensis (Licandeo & Cerna, 2007), the roughtail skate, Bathyraja trachura (Winton et al, 2014), the Australian weasel shark, Hemigaleus australiensis, and the Australian sharpnose shark, Rhizoprionodon taylori (Taylor et al, 2016). Neer & Thompson, 2005), the smoothhound shark, Mustelus mustelus (Saidi et al, 2008), and the blacknose shark, Carcharhinus acronotus (Sulikowski et al, 2007).…”

Skate-ing on thin ice: molecular ecology of longnose skates in the Southeast Pacific Ocean

“…In the case of Valdivia and Punta Arenas, differences in morphology between both stocks may be driven by the smaller body size of the specimens from Valdivia. Overall, the body size of specimens from Punta Arenas was the largest across sampling localities, which is consistent with the latitudinal increase of body size, as described for elasmobranch fishes (Taylor et al, 2016), but may be related to the lower level of fisheries exploitation of the resident stock in localities southward of Puerto Montt .…”