9 research outputs found
Seasonal and Long-Term Changes in Relative Abundance of Bull Sharks from a Tourist Shark Feeding Site in Fiji
Shark tourism has become increasingly popular, but remains controversial because
of major concerns originating from the need of tour operators to use bait or
chum to reliably attract sharks. We used direct underwater sampling to document
changes in bull shark Carcharhinus leucas relative abundance at
the Shark Reef Marine Reserve, a shark feeding site in Fiji, and the
reproductive cycle of the species in Fijian waters. Between 2003 and 2009, the
total number of C. leucas counted on each day ranged from 0 to
40. Whereas the number of C. leucas counted at the feeding site
increased over the years, shark numbers decreased over the course of a calendar
year with fewest animals counted in November. Externally visible reproductive
status information indicates that the species' seasonal departure from the
feeding site may be related to reproductive activity
Reproductive biology of the cockfish, Callorhinchus callorynchus (Chondrichthyes: Callorhinchidae), in coastal waters of the northern Argentinean Sea
Feeding together: a global diet analysis of twenty-three species of chondrichthyes on a feeding ground area
Seasonal Reproductive Biology of the Bignose Fanskate Sympterygia acuta (Chondrichthyes, Rajidae)
Most skates are adapted to shelf and slope environments experiencing less seasonal variation than coastal ecosystems. Here, we analyze the reproductive ecology of Sympterygia acuta. We hypothesize that, like its congener Sympterygia bonapartii, S. acuta has a seasonal reproductive cycle. To test this hypothesis, we examined multiple lines of evidence: (1) time of appearance of females carrying egg cases and wild neonates; (2) seasonal variation in gonadosomatic index and follicle diameter, as indicators of reproductive activity; and (3) egg-laying season, incubation time, and fecundity in captive individuals. A total of 351 specimens were examined. Size at 50 % maturity was 475 and 478 mm total length for males and females, respectively. A marked seasonal reproductive cycle was observed. Both gonadosomatic index and follicle diameter of wild adult females increased from winter to spring and reached their lowest value during summer. Fecundity was, on average, 52 eggs per female per laying season. Egg laying of captive females peaked between August and December; eggs hatched after 119–131 days. This schedule predicts the appearance of neonates in the wild by January through April. Accordingly, wild neonates and young-of-the-year were observed between January and May. Unlike most other skates, southwest Atlantic Sympterygia species are adapted to life in shallow, coastal waters, matching the seasonality of the coastal environment with egg-laying activity in spring and hatching in summer. These shallow coastal waters, which are important in the life cycle of Sympterygia spp., are threatened by human impacts.Fil: Mabragaña, Ezequiel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Nordeste. Instituto de BiologĂa Subtropical. Instituto de BiologĂa Subtropical - Nodo Puerto IguazĂş | Universidad Nacional de Misiones. Instituto de BiologĂa Subtropical. Instituto de BiologĂa Subtropical - Nodo Puerto IguazĂş; ArgentinaFil: Corbo, Maria de Lourdes. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina. Provincia de Buenos Aires. GobernaciĂłn. ComisiĂłn de Investigaciones CientĂficas; ArgentinaFil: DĂaz de Astarloa, Juan MartĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin
Contrasting life history and reproductive traits in two populations of Scyliorhinus canicula
The role of natural and sexual selection in generating variability in biological traits between populations represents an intriguing issue in evolutionary biology. Considering their occurrence in different environments and the
extensive incidence of post-copulatory sexual selection, elasmobranchs represent an interesting, yet still poorly investigated group. In this study, the life history and reproductive traits of two populations of Scyliorhinus canicula
from the northern Adriatic Sea and the Strait of Sicily were compared. Differences in maximum size and size at sexual maturity were observed. The two populations also displayed differences in male and female genitalia. Males in
the northern Adriatic Sea presented heavier testes, longer epididymis, seminal vesicles and claspers compared with those in the Strait of Sicily, suggesting the occurrence of stronger sperm competition at the former site. Similarly,
females in the northern Adriatic Sea showed heavier oviducal glands and longer reproductive tracts compared with those in the Strait of Sicily. The coevolution between male and female genitalia suggests the occurrence of stronger sexual conflict and/or cryptic female choice in the population from the northern Adriatic Sea. Therefore, natural selection, represented by the different selective pressures occurring at different latitudes, and sexual selection, represented by potentially differing strengths of post-copulatory sexual selection and sexual conflict, may act individually in driving divergence in life history and reproductive traits in these two populations of S. canicula