Marais, J.F.K.

van der Westhuizen, H.C.

English

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soo ZOOlOGICA AFRICANA VOL 12 chobiensis from Botswana by Hoogstraal & EI Kammah (1974). Table 2 shows the monthly distribution of hosts and parasites. No record was kept of the relative abundance ofthe parasites and their distribution on the bodies of hosts, but most were found under the arm, around the anus, posterior to and in the ears, on the neck and eye-lids. Ectoparasites were more abundant on adults than on juveniles, probably as a result of the extensive allogrooming of youngsters. ACKNOWLEDGEMENTS My sincere thanks are due to Dr J A ledger and his staff at the Entomology Department, South African Institute for Medical Research, Johannesburg, for identifying mites, neas and sucking lice and to Miss J Walker at Onderstepoort Veterinary Research Institute for tick identifications. I also wish to thank Prof. J D Skinner for making the study possible. REFERENCES HOOOSTRAAL, H & EL KAMMAH, K M 1974. Notes on African Haemaphysalis ticks. XII. H. (Rhipi-STOMACH CONTENT ANALYSES OF POMADASYS COMMERSONNJ FROM THE SWARTKOPS ESTUARY (PISCES: POMADASYIDAE) H C VAN DER WESTHUIZEN AND J F K MARAIS University of Port Elizabeth Accepted: April 1977 INTRODUCTION PomadDsys commeT6onni (Lace~e 1802), the spotted grunter, occurs in the warmer water of the stoma) zumpti sp.n., a parasite of small carnivores and squirrels in Southern Africa (Ixodoidea: Ixodidae). J. Parasit. 60: 188-197. LEDGER, J A 1976. The arthropod parasites of vertebrates in Africa south of the Sahara (Ethio-pian Region) Vol IV. Phthiraptera. D.Sc. thesis. PAOLA, B 1969. Description of a new species of Hirstionyssus Fonseca (Acarina: Dermanyssidae) from the Ethiopian pgrapbical region, with notes on other known species. Revue Zool. Bot. afro 80: 67-79. RAHM, U 1972. Note sur Ia ~production,l'ecologie et Ie ~gime alimentaire des Sciurid~ au Kivu (ZaIre). Revue Zool. Bot. afro 58: 321-339. THEILER, G 1962. The Ixodoidea parasites of vertebrates in Africa south of the Sahara (Etbio-pean Region). Report to the Director of Vet erin-ary Services, Onderstepoort. Pretoria. VIUOEN, S 1975. Aspects of the ecology, reproduc-tive physiology and ethology of the bush squirrel, Paraxerus cepapi cepapi (A Smith, 1863). MSc thesis, University of Pretoria. ZUMPT, F (ed.) 1966. The arthropod parasites of vertebrates in Africa south of the Sahara (Ethio-pian Region). Vol. III. (Insecta excl. Phthirap-tera). Pubis S. Afr. Inst. med. Res. 13 (52): 1-283. east Coast of South Africa with a special preference for the calm water of estuaries (Smith 19S0; Smith 1961; Wallace 1975). It is a very popular sporting fish and contributes to a large extent to recreation in the Swartkops Estuary. Records of the Swartkops Angling Club were analysed by Marais.(I976) who found that in terms of biomass, 82 per cent of the catches of anglers consisted of Pomadasys commer-sonni and in terms of numbers this species con-tributed 87 per cent. Average P. commersonni catches by angling club members from April 1972 to March 1975 in the Swartkops Estuary were 127 per month. An equal number of fish is probably caught by non-members of angling clubs. Next in abund-ance was lithog1lllthus lithog1lllthus with only 4 per month. A further indication of the relative abundance of P. commersonni in the Swartkops Estuary was obtained from a study of the catches made by Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). 1977 SHORT COMMUNICATIONS SOl anglers during the 1976 Eastern Province angling week (26 March to 3 April 1976). During this week P. commersonni made up 69 per cent of fIShes caught, followed by Argyrosomus hololepidotus (I 6 per cent). It is thus clear that P. commersonni is by far the most important angling fish in Swartkops Estuary. It was therefore decided to study the natural food preference of this species by means of stomach content analyses and to compare the results with the type of bait normally used by anglers. MATERIALS AND METHODS Pomadasys commersonni was obtained from the Swartkops River in two ways: (i) With the aid of gill-nets. (ii) From fIShermen's catches, in which case ques-tionnaires were handed to the fIShermen to determine the most popular bait used. Stomachs of92 fISh were removed and preserved ,in 10 per cent formalin for subsequent content analyses in the laboratory with a' stereo-microscope. In certain specimens, most of the contents were digested to a state where the items could not be accurately determined. In certain cases only chelae were available for identification. To overcome this problem only a numerical estimate of the food items was made and the data analysed by means of the occurrence method (Hynes 19SO; Windell 1971). In this method the number of fish, in which a certain food item was found, is expressed as a percentage of the total number of fish. RESULTS AND DISCUSSION The results, according to the occurrence method, are given in Table I. The data show that Crustacea formed the most important food component, and appeared in 94 per cent of the stomachs. Upog~bill africana appeared in 33 per cent of the fISh and Brachyura in 35 per cent. Sesarma catenata formed the largest component of the latter (14 per cent) whereas 15 per cent of the Brachyura could not be identified . Mollusca were next in importance and were found -in 28 per cent of the fISh. Mollusca consisted mainly of Assiminea spp. (10 per cent) and the bivalves PSDmmotellina capensis (9 per cent) and Solen capensis (3 per cent). The next largest component was Annelida (22 per cent). Polychaetes formed the most important class ot Annelida and were found in 14 per cent of the fISh. Plants were found in 25 per cent of the fISh, and included Zostera (4 per cent) and Graciloria verrucoso which appeared in 21 per cent of the analysed stomachs. This alga was not digested but found undamap in the intestine. It was first thought that G. verrucosa was ingested primarily to obtain the associated epifauna as was found by Fish (1951) for nlapill esculenta in Lake Victoria and Blaber (1973) for Rhabdosorgus ho/ubi in the West Kleinemond Estuary. However, further stereo-microscopic investigation showed no epifauna on freshly sampled G. verrucosa from Swartkops Estuary. Another possibility was that G. verrucosa was ingested accidentally with other material. This seems unlikely since in one case 24,8g of G. verru-coso was found in a stomach together with one specimen of Sesarma catenata weighing only 1,2g. When the individual food items were added and expressed as a percentage of the total it was found that Crustacea formed 67 per cent of the diet whereas Polychaeta and Mollusca formed 21 per cent and 12 per cent respectively. The question-naires were analysed to establish how the flShermen's bait-choice agrees with the above-determined diet. Table 2 indicates that Crustacea are being used by 79 per cent of the fishermen and Polychaeta by 14 per cent. The polychaet species most commonly used is Diopatra Mopo/itana Mopo/itana of the family Eunicidae. CONCLUSION Stomach content analyses revealed that Crustacea (in particular the mud prawn Upog~bill africana) form the most important component of the natural diet of Pomadosys commersonni in the Swartkops Estuary. As could be expected, anglers operative in the same area showed a preference for the same bait species. The fact that 25 per cent of the 92 stomachs of PomadDsys commersonni, a carnivorous fISh, con-tained plant material (mostly Graciloria verrucoso) is noteworthy. The nutritional significance of this material warrants further investigation. No difference in the diets of different size ranges of POm4t:1osys commersonni was observed during the study period. Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). S02 ZOOLOGICA AFRICANA VOL 12 TABLE I Food obtained from the stomachs of Pomadasys commersonni caught in the Swartkops Estuary (percentage of total number of fish in which found). Month F M A M J J A S 0 Tot. Period CRUSTACEA Brachyura Unidentified 25 13 33 8 33 28 15 Sesarma catenata 8 57 25 14 Rhynchoplax bovis or 8 I Hymenosoma orbiculare Cleistostoma spp. 43 17 4 5 Macrura Alpheus crassimanus 7 17 4 3 Anomura Upogebia alric-ana 13 83 71 33 24 25 38 33 Callianassa kraussi 27 33 33 12 38 14 Mysidacea Mesopodopsis slabberi 13 2 Amphipoda Unidentified 4 8 2 Melita zeylanica 8 2 Tanaidacea Apseudes cooperi 4 Isopoda Sphaeromid spp. 8 2 MOLLUSCA Gastropoda Assiminea spp. 50 7 33 17 12 8 10 Nassa kraussiana 50 7 8 5 Cephalopoda 7 I Pelecypoda Psammotellina capensis 20 17 16 9 Solen capensis 4 25 3 ANNELIDA Unidentified 25 13 67 4 7 Polychaeta 25 36 38 14 Oligochaeta 4 Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). 1977 NEMATODA Unidentified PISCES Glossogobius spp. ? Fish scales Insect larvae Broken shells ANGIOSPERMAE Zostera ALGAE Gracilaria verrucosa SHORT COMMUNICATIONS TABLE 1 (continued) Month F M A M J J A S 33 14 13 4 20 8 4 4 J3 8 14 50 20 TABLE 2 Bait preference of 30 regular anglers operating in Swartkops estuary. Bait used Percentage 0/ fIShermen Upogebia a/ricana 72 Polychaeta 14 Callianassa kraussi 7 Solen 7 S03 0 Tot. Period 1 2 5 17 4 21 Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). 504 ZOOLOOICA AFRICANA VOL 12 ACKNOWLEDGEMENTS· Grateful acknowledgement is made of tho financial assistance given by the Department of Planning and Environment. and the University of Port Elizabeth. The Department of Nature Conservation of the Cape is thanked for authorizing the use of gill nets. REfERENCES BLABER, S J M 1973. The ecology of juvenile Rhabdosargus holubi (Steindachner) (Teleostei: Sparidae). Ph.D. thesis, Rhodes University. Gra-hamstown. fISH, G R 195 I. Digestion in Ti!apill esculenta. Nature, Lond. 167: 900-901. HYNES, H B N 1950. The food of freshwater sticklebacks (Gasterosteus aculeatw and Pygos-tew pungitiw), with a review of methods used in THE HIMALAYAN TAHR ON T ABLE MOUNTAIN R BIGALKE (Sen.) 185 Alexander St., Pretorill Accepted: May 1977 It is seldom possible to state with any degree of accuracy when species of exotic animals were liberated or found their way as escapees into foreign environments. But in the case of the Himalayan tahrs on Table Mountain, the elimination of which is now being seriously tackled, it is possible to state where the animals came from. On 2 September 1935 a pair of Himalayan tahrs (Hem/tragus jem!aicw) studies of the food of fIShes. J. tJ1Iim. Ecol. 19: 36-58. MARAIS, J f K 1976. Comparative studies on the nutritional ecology of mullet in the Swartkops Estuary. Ph.D. thesis. University of Port Eliza-beth, Port Elizabeth. SMITH, J L B 1950. POmlldasys operculare and the South African seas. AM. Mag. nat. Hilt. (12) 3: 778-785. SMITH, J L B 1961. The spotted grunters of Africa. Fld. Tide, 3: 16-17. WALLACE, J H 1975. Bioiogy and ecology of the estuarine fishes of the east coast of South Africa. Ph.D. thesis, University of Natal. Pietermaritz-burg. WINDELL, J T 1971. Food analysis and rate of digestion. In Methods for assessment offllh pro-duction in fresh waters, ed. W E Ricker. IBP Handb. 3: 1-345. was sent to the Groote Schuur Zoo by me from the National Zoological Gardens in Pretoria. Either these animals, or some of their progeny, escaped from that zoo resulting in their rapid increase in Table Mountain at the cost of its flora. Although considerable dllmage has already been done to the montane vegetation, it is to be hoped that the steps now being taken to eradicate the tahrs will not be relaxed until the o\)ject has been attained. Like the klipspringer, in earlier times a common little antelope on Table Mountain, the tahr is an agile climber and jumper in rocky terrain. At Groote Schuur the animals were obviously not so securely housed that they could not escape. Their rapid increase in numbers shows that they fouJld Table Mountain at least as favourable an environment as their normal home in the Himalayan mountains. Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). 

Stomach content analyses of Pomadasys commersonni from the Swartkops Estuary (Pisces: Pomadasyidae)

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Stomach content analyses of Pomadasys commersonni from the Swartkops Estuary (Pisces: Pomadasyidae)

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