Reproductive biology, size and age compositions and growth of the batoid Urolophus paucimaculatus, including comparisons with other species of the Urolophidae

Abstract

The biology of Urolophus paucimaculatus in south-western Australian waters has been examined and compared with that of the co-occurring Urolophus lobatus, Trygonoptera personata and Trygonoptera mucosa. These four species represent the only two genera of the Urolophidae. Urolophus paucimaculatus conceives in early/mid-summer and gives birth in late spring/early summer, closely paralleling the situation with U. lobatus. Although Trygonoptera species likewise have a 10–12-month gestation period, they conceive and give birth in late autumn to mid-winter. The marked intergeneric differences in birth time help account for pronounced intergeneric differences in the diets of their newly born young. By birth, Urolophus paucimaculatus attains ~50% of its asymptotic size. The relatively large mean disc width of the four urolophids at birth, i.e. 105–128 mm, accounts for the small litters of these species (1–2 young per litter). Size at maturity and maximal size and age of each species are greater for females than males and are greater for Trygonoptera than Urolophus species. The growth of U. paucimaculatus and the other urolophids throughout pre- and postnatal life can be described by a single smooth growth curve. The maintenance of a constant pattern of growth from conception is remarkable because the diet and behaviour of these elasmobranchs changes radically at parturition.