Age, growth, and demography of the sandbar shark, Carcharhinus plumbeus, over temporal and spatial scales
Numbers of sandbar sharks, Carcharhinus plumbeus, in the Northwest Atlantic have experienced drastic declines since the early 1980's reaching their minima during the early 1990's. Catch rates in the early 1990's were a mere 25% of those during the 1980's. Such drastic reductions...
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| Format: | Text |
| Language: | English |
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W&M ScholarWorks
2008
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| Online Access: | https://scholarworks.wm.edu/etd/1539616830 https://doi.org/10.25773/v5-dcpf-mn33 https://scholarworks.wm.edu/context/etd/article/2397/viewcontent/3308114.pdf |
| Summary: | Numbers of sandbar sharks, Carcharhinus plumbeus, in the Northwest Atlantic have experienced drastic declines since the early 1980's reaching their minima during the early 1990's. Catch rates in the early 1990's were a mere 25% of those during the 1980's. Such drastic reductions in other fish stocks have often caused compensatory responses, most notably the cod stocks in the Northwest Atlantic. Compensatory responses in depressed populations may include decreased natural mortality, increased fecundity, or increased growth rates. Compensation for population fluctuations below carrying capacities have been recognized for many terrestrial and oceanic r-selected organisms, but few instances have been noted for K-selected species. Due to slow-growth and late maturity, compensatory responses in K-selected species such as the sandbar shark probably require generation-scale time periods to become evident. A previous age and growth study discovered slight increases in juvenile sandbar shark growth rates when vertebral centra samples obtained in 1980-81 and 1990-1992 were compared. The Virginia Institute of Marine Science shark long-line survey reported the lowest abundance of sandbar sharks in 1992. Animals pupped during this time may display greater differences in growth rates due to drastically reduced population size. Samples obtained over the 2001-2004 time period were compared to the aforementioned time periods to investigate potential compensatory responses in the sandbar shark population in the Northwest Atlantic. Growth estimates for the sandbar shark, Carcharhinus plumbeus, in the Northwestern Atlantic were estimated using a reparameterized von Bertalanffy growth model. Sharks were tagged in Virginia waters with roto-tags and double return nylon dart tags from 1992 to 2006 by the shark longline survey of the Virginia Institute of Marine Science. Captured sharks were measured, tagged, and released by VIMS scientists. Age and growth estimates were determined for the sandbar shark, Carcharhinus plumbeus, from Oahu, ... |
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