- Title
- The biology of the sand shark Rhinobatos Annulatus, in Algoa Bay with notes on other elasmobranchs
- Creator
- Rossouw, Gideon Johannes
- Subject
- Sand sharks
- Subject
- Guitarfishes
- Date Issued
- 1983
- Date
- 1983
- Type
- Doctoral theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/52802
- Identifier
- vital:44061
- Description
- The biology of the lesser sand shark, Rhinobatos annulatus, was studied off sandy beaches in Algoa Bay over a period of two years. Tagging studies, due to low numbers tagged, did not reveal major movements. However, comparison of numbers of sand sharks caught off the beach and deep water during summer and winter months suggested that migration occurred during these seasons with the animals being inshore in summer. Annual rings on the vertebral centra were used to determine age. Both sexes can reach a maximum age of seven years. Conventional growth curves could not be fitted and empirical curves were used to illustrate growth. The reproductive cycle was investigated and indicated that both sexes matured after three years of age. The breeding season was during late summer when the shallow water was utilized as a nursery area. The sand shark is an aplacental viviparous species with a gestation period of 10 months. Breeding occurred every year and fecundity increased with total body length to a maximum litter size of 10 young. The most important prey items taken inshore were the mysid Gastrosaccus psammodytes, the prawn Macropetasma africanum, the crab Ovalipes punctatus and the sand mussels Donax spp. Differential predation by different length classes of sand shark resulted from a dynamic zonation of these different size classes in the surf zone. Smallest individuals fed closest inshore. Seasonal variation recorded in the hepatosomatic index was primarily due to the accumulation of hepatic lipids. This variation showed significant correlations with the breeding cycle in adult sand sharks. The contribution of liver lipids to the formation of egg yolk was estimated and found to be secondary to lipid reserves for maintenance. Liver colour varied depended on the amount of liver lipids. Ancillary observations were made of other elasmobranchs in the surf zone.
- Description
- Thesis (DPhil) -- Faculty of Science, 1983
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (188 pages)
- Format
- Publisher
- University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- rights holder
- Rights
- All Rights Reserved
- Rights
- Open Access
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Ross.pdf | 32 MB | Adobe Acrobat PDF | View Details Download |