The Diets of Littoral Fish from the Cape Peninsula
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The diets of littoral fish from the Cape Peninsula B. Bennett, C.L. Griffiths and Mary-Louise Penrith Zoology Department, University of Cape Town, and South African Museum, Cape Town Intertidal fish communities in the south·western Cape have a high Little information on the feeding ecology of South African density and biomass, implying that the fish are important con· littoral fish has been published. In 1945 Smith made the obser sumers in the intertidal zone. Stomach content analyses of 20 vation that clinids, the most abundant group, were carnivorous. species were undertaken to ascertain which food resources are most heavily exploited and the extent to which the co-existing Since then, data on the diets of eight species sampled from fish compete for the same food resources. Three prey types, the intertidal zone have been published, all by people working arnphipods, isopods and polychaetes, occur in the diets of almost in the eastern Cape. Christensen examined the dietes of Clinus all the species examined and together comprise more than half cottoides (1978a), Pavoclinus graminis and P.laurentii (I 978 b), the total volume consumed by 14 of the species. Despite the and three sparid species (1978c). Stobbs (1980) provided in overlap in food types consumed, there was considerable subdivi· fonnation on the feeding of Chorisochismus dentex and Butler sion of the resource, much of which may be explained in terms of horizontal and vertical distribution patterns of the various fish (1982) attempted to relate the feeding of Caffrogobius coffer species, their habitat preferences, mouth sizes and changes in with the tidal cycle and time of day. diet during growth. The standing stock of food in the pools is Despite the paucity of published works, a considerable body thought to be too low to support the resident fish populations, of unpublished infonnation is available on the feeding ecology suggesting that some food, at least, is obtained outside the pools . of intertidal fishes, particularly in the south-western Cape. ) while the tide is in. For this reason, the fish are considered to be 0 Penrith's (1965) doctoral thesis includes a detailed analysis of 1 concentrated in the pools at low tide, indicating that the 0 the diets of six common clinid species and notes on several 2 availability of suitable pool habitats may be important in con· d trolling the denSities of intertidal fish communities. others; Pitt-Kennedy (1964), in an honours project, examined e t S. Afr. J. Zool. 1983, 18: 343 - 352 the diets of the two most abundant gobiid species; Jackson a d (1950) in his unpublished M.Sc. thesis, provides brief notes ( r Visbevolkings van die getysones van die suidwestelike Kaap het on the diets of six clinid species, a goby and Chorisochismus e hoe digthede en biomassas, wat aandui dat die visse belangrike h s dentex; Hutchings (1968) described the diet of the sparid Sar i roofdiere van die sone is. Maaginhoudanalises van 20 spesies is l and Branch (unpublished) has accu~ulated a con b ondemeem om vas te stel watter voedselbronne die meeste benut po sa/pa; u word en die mate van kompetisie tussen simpatriese vissoorte vir siderable amount of fish feeding data during his extensive P e dieselfde voedselsoorte. Drie prooi-kategori'*l, nl. Amphipoda, studies of intertidal communities. h t Isopod a en Polychaeta kom voor in al die spesies wat ondersoek Further information has recently been collected by Bennett y is en vorm saam meer as die helfte van die totale volume wat b & Griffiths (unpubl.) in the course of an analysis of distribu deur 14 spesies gaoot is. Ten spyte van die oorvleueling van d tion patterns of littoral fish on the Cape Peninsula. For the e t voedselkategoriee, was daar heelwat verdeling van die bron, wat n grotendeels verklaar kan word deur die horisontale en vertikale purposes of the present analysis data from these sources have a r verspreidlngspatrone van die onderskeie visspesies se habitat· been pooled to give an overall sample of I 938 stomachs from g e voorkeure, mondgroottes en verandering van dieet gedurende twenty different species representing six genera. The data of c groei. Die gedagte bestaan dat die biomassa van die voedsel te n Hutchings (1968) are not included as Sarpa salpo is not usually e laag is om die plaaslike visbevolking te onderhou, wat daarop dui c resident in the intertidal zone and those of Jackson (1950) were i l dat ten minste 'n gedeelte van die voedsel ver buite die poele r presented in insufficient detail to be included in the analysis. e gedurende hooggety verkry word. Daar word dus aangeneem dat d die visse gedurende laaggety in die poele gekonsentreer is, wat It is hoped that this comparative information_ will help to n indicate which food items are most heavily exploited by lit u aandui dat die beskikbaarheid van geskikte poelhabitatte y belangrik kan wees ten opsigte van die beheer van die digtheid toral fish communities as a whole and show to what extent a van die visbevolkings van die getysones. w co-existing species may compete for the same food resources. e t S.·Afr. Tydskr. Dierlc. 1983, 18: 343 - 352 a G Material and Methods t e n A list of fish species treated in this study, and of the sources i b B. Bennett· and C.L. Griffiths of all material referred to, is given in Table I. The fish were a S Zoology Department, University of Cape Town, Rondebosch, 7700 collected at low tide from intertidal rock pools and gulleys, y Republic of South Africa b mainly by poisoning with rotenone dissolved in acetone, but Mary·Louise Penrith d hand nets and baited hooks were also used on occasion. All e Present address: Transvaal Museum, Pretoria c fish were killed by placing in formalin or alcohol, after which u ·To whom correspondence should be addressed d they were transferred to formalin for storage. o r p Received 26 November 1982; accepted 22 February 1983 Only the stomach contents were analysed, food elsewhere e R 344 S.-Afr. Tydskr. Dierk. 1983, 18(4) Table 1 Sources of the data on which this study to permit a meaningful analysis of stomach contents. The most is based abundant group were the Clinidae (klipfishes) with sixteen species (12 Clinus, 3 Pavoclinus and I Blennioclinus), which Number of guts examined together made up over 70070 of the fish caught. The remain ing fish consisted of Gobiidae (gobies) with two species, of ~ -5:i which one (Caffrogobius caffer) was very common, one species °C ::s c Co of sucker fish Chorisochismus dentex (family Gobiesocidae) ... C C. ::l and the eel-like Halidesmus scapularis (Congrogadidae). .,... '" -l -0 The numbers of each species of fish examined, their size so Species ~; f- ranges and the composition of the stomach contents, by volwne Clinidae and percentage occurrence, are given in Table 2. The percen Clinus acuminatus 30 32 3 65 tage occurrence ofindividual prey species in the stomachs of C. agilis 106 3 109 each fish is shown in Table 3. The feeding habits and diets C. anguillaris 2 15 17 of each species of fish analysed are discussed individually C. berrisfordi 7 7 below. C. brevicristatus 7 7 (I) Clinus acuminatus was recorded almost exclusively near C. capensis 8 5 14 27 the top of the shore in barren rocky pools. It occurs on C. cottoides 169 178 19 366 both the west and south-west coasts but is more abundant C. dorsalis 25 18 12 55 west of Cape Point. This species seldom attains more than C. heterodon 9 50 59 120 mm (Penrith 1965). C. superciliosus 312 313 20 645 Sixty-five specimens between 34 mm and 127 mm were C. taurus 3 3 found to have food in their stomachs. Decapods (32%), C. venustris 18 18 molluscs (19%) and goose barnacles (15%) were the most Pavoclinus gram in is 9 9 important food items by volwne, although all three P. mus 109 109 categories occurred infrequently. The most frequently oc P. pavo 7 2 9 curring food categories were amphipods (62%), isopods Blennioclinus (53%) and polychaetes (16%). brachycephalus 47 4 51 Clinus acuminatus changes its diet with increasing size. Gobiidae Caffrogobius caffer 162 96 258 Fish less than 50 mm rely almost exclusively on amphi nudiceps pods, isopods and polychaetes, while for individuals . C. 5 41 9 55 ) longer than 80 mm decapods and molluscs are of primary 0 Gobiesocidae 1 importance, although the other taxa continue to be taken. 0 Chorisochismus den/ex 50 50 2 Congrogadidae No prey species had a particularly high frequency of d e occurrence in the sample examined (Table 3). Eight species t Halidesmus scapularis 19 19 a occurred in more than 5% of the fish examined, the am d ( phipods Paramoera capensis (12%) and Hya/e spp. (II %) r e h occurring most often. The occurrence of goose barnacles s i l in the digestive tract was usually in an advanced stage of diges in the stomachs indicates that C. acuminatus will feed b u tion and its inclusion in analyses would have prejudiced results opportunistically on any suitable food that becomes P in favour of less digestible food items. Sample sizes for each available. e h species (Tables I and 2) reflect only the nwnber of stomachs (2) Clinus agilis is abundant on the west coast, but becomes t y examined that actually contained food. Unless otherwise stated, considerably less common east of Cape Point. This species b all fish length measurements are standard length (SL). inhabits weedy pools in the middle and lower areas of d e t The stomachs were opened into water in a watch glass or the intertidal wne.