Studies on the Psammolittoral Meiofauna of Algoa Bay

The meiofauna communities at three tide levels on a sheltered and an exposed beach have been analysed and compared. Twenty-nine nematode, eight harpacticoid and two mystacocarid species and species groups have been used. A similarity analysis indicated three distinct communities, one occurring in sand that dries out during low tide, one occurring in fine sand that remains saturated during low tide and one occurring in coarser sand that remains saturated during low tide. Diversities decreased from high to low tide levels on both beaches regardless of meiofauna numbers. The distribution of nematode feeding types is discussed.     

Aspects of the reproductive biology of the southern mullet,Liza richardsoni,from Algoa Bay,South Africa

The reproductive biology of the southern mullet from Algoa Bay was studied between June 1978 and October 1980. Gonadosomatic indices and macroscopic and microscopic examinations of the gonads were used to establish the breeding cycle. The period of greatest sexual development extends from September to March and spawning occurred throughout that period. Spawning probably occurs close in shore. Liza richardsoni exhibited the phenomenon of group synchronism, two distinct oocyte groups being present within a pre-spawning ovary. The proportion of yolkless oocytes exceeded that of vitellogenic oocytes in ripe fish. However, it was not apparent whether all the vitellogenic oocytes would reach maturity. This highlights the need for quantitative histological studies to accompany fecundity estimates. Histological investigations were useful in the clarification of breeding cycle determinations based on gonadosomatic indices and visual macroscopic assessments.     

Plant selection and grazing activity of the invasive snail Theba pisana in coastal Algoa Bay,South Africa

The land snail Theba pisana is a coastal species native to the Mediterranean but has been introduced to regions all over the world, including South Africa and Australia, where it is considered a pest. This study examines the diet of T. pisana and its preference for certain dune plants in the Cape Recife Nature Reserve of Algoa Bay in the Eastern Cape, South Africa. Field observations identified plants being fed on by T. pisana, accounting for almost half of the dune plant species present in the study area. Five plant species, on which snails were found frequently and in high abundance, were selected for feeding preference experiments. Laboratory experiments and field observations indicate that T. pisana feed preferentially on Tetragonia decumbens over Osteospermum moniliferum, Osyris compressa and Cynanchum obtusifolium. It is clear that while T. pisana is reported to have a generalist diet, consuming a range of plant species commonly found in South African dune vegetation, it also exhibits a definite preference for T. decumbens. The reasons for this preference need to be investigated further.     

Species diversity and size ranges of cephalopods in the diet of jackass penguins from Algoa Bay,South Africa

An analysis of cephalopod remains collected from jackass penguin Spheniscus demersus regurgitations and stomachs at St Croix Island, Algoa Bay, in 1976 and 1977 revealed the presence of three cephalopod species. Most common was Loligo reynaudi, with Heterotuthus sp. and Argonauta argo constituting trace items. Beak measurements were used to estimate dorsal mantle lengths and wet masses of cephalopods taken by penguins. The dominant cephalopod taken by penguins was the same species as that harvested by commercial fisheries. Despite an overlap in the size range of squid taken by penguins and trawlers, penguins tended to take smaller squid and did not take the larger squid landed by trawlers. The seasonal occurrence of squid in the penguin diet in 1976 and 1977 was the opposite of the abundance of squid in the area as reflected by trawler landings. This is explained in terms of the abundance and preference for other prey items. It is suggested that penguins take fish in preference to squid because of the relatively higher energy content and food value of fish.     

Shallow-Water Trawling Off the Swartkops Estuary,Algoa Bay

Juvenile fish occurring in Algoa Bay off the mouth of the Swartkops estuary were collected using a 3-m beam trawl. Pomadasys ollvaceum, Engraulis capensis, Caffrogoblus agulhensls, Argyrosomus hololepidotus and Galeichthys feliceps were the most abundant species in the trawl catches. Despite the proximity of the Swartkops estuary the trawls failed to capture species which are abundant as Juveniles in the estuary and it is concluded that the estuary has little influence on the juvenile fish fauna outside the mouth.     

Diet composition and breeding cycle of blacktail,Diplodus sargus capensis (Pisces: Sparidae), caught off St Croix Island,Algoa Bay,South Africa

The contents of the alimentary tracts of D. sargus capensis were analysed to establish diet composition. The importance of analysing stomach, intestine and total alimentary tract, separately, is emphasized. D. sargus capensis is an omnivore preying on lower intertidal and shallow subtidal benthic species. Cirripedia and algae were the most important groups and constitute ca. 60% of the total dietary composition. Ulva sp., Perna perna and Balanu, spp. were prefered species. A new index for ranking prey items, which combines the modified points method and the frequency of occurrence method, is suggested. It is especially useful for omnivorous fish where prey items sucl as seaweed and colonial organisms are difficult to enumerate. Ambosexual individuals differentiate into functional males or functional females. Active spermatogenesis in the ovo-testis suggests a special type of protandric development. D. sargus capensis has an extended breeding cycle with a peak spawning period from October to December.     

White shark (Carcharodon carcharias)-inflicted bite wounds observed on Cape fur seals (Arctocephalus pusillus pusillus) at Black Rocks,Algoa Bay,South Africa

This paper presents the first quantitative study on the seasonal occurrence and body location of white shark (Carcharodon carcharias)-inflicted injuries on Cape fur seals (Arctocephalus pusillus pusillus) at Black Rocks, in Algoa Bay. Between January 2010 and October 2011, 22 boat trips were made to Black Rocks to chum for white sharks. On 19 of the trips a series of overlapping photographs were taken of the northern side of Black Rocks and the percentage of seals, which exhibited fresh white shark bite wounds recorded. A total of 53 sharks and 28 fresh shark-inflicted injuries were recorded on seals over the course of the study period. The maximum number of sharks sighted per hour (1.2) was in July and the highest percentage of shark bitten seals in November (0.6%). There was no significant relationship between the monthly sighting rate of sharks and the percentage of shark bitten seals (P = 0.40). The percentage of shark-inflicted injuries observed on seals increased with seal size. Most injuries were observed in the forebody (37.5%) and lower body regions (37.5%). Very few injuries (6.3%) were observed in the head and neck region. The low number of bite-inflicted injuries observed suggests that white sharks attack seals infrequently at Black Rocks.     

A Leopard Seal from Hout Bay,South Africa

The catch per unit effort of Oreochromis mossambicus, Clarias gariepinus and Cyprinus carpio at different localities at Hartbeespoort Dam was investigated. Catches of the three species were between three and ten times higher on the southern shore of the lake than on the northern shore. The gradient of each locality was found to be the most important variable determining catch. Gill-net catches of O. mossambicus from littoral and limnetic stations indicated equal abundance of the species in these two habitats. The implications of the results for improved predictions of fish yield from lakes, and for management are discussed.     

The reproductive biology of the moony,Monodactylus falciformis,in Algoa Bay

Gonadosomatic indices, macroscopic and microscopic examinations of gonads were used to establish the breeding cycle of Monodactylus falciformis. Spawning took place between October and February and evidence for serial spawning is presented.     

Composition and seasonal variability of the suprabenthic reef-fish assemblage in False Bay,South Africa

The composition and seasonal variability of a False Bay suprabenthic reef-fish assemblage was investigated monthly at a protected reef site (to a depth of 25 m) for 14 months. In total, 25 484 fish from 28 species (26 demersal) were counted. Sparids dominated the assemblage (50 % of species and 87.3 % of individuals), followed by cheilodactylids (15.4 % of species and 7.5 % of individuals). Pachymetopon blochii (30.6 %), Sarpa salpa (17.7 %), Boopsoidea inornata (16.1 %), Chrysoblephus laticeps (10.4 %) and Spondyliosoma emarginatum (9.2 %) were the five most abundant species, while the ten most abundant species made up over 93 % of censused individuals. Composition was relatively stable year round, irrespective of water temperature variations, with 16 of the 26 reef-fish species censused encountered during more than 10 monthly censuses. Triakus megalopterus and large Chrysoblephus gibbiceps were the only species whose abundance appeared to vary seasonally.     

Subtidal distribution of Callianassa kraussi and C. gilchristi in Algoa Bay

Four subtidal transects were sampled in Algoa Bay. Callianassa kraussi and C. gilchristi were recorded from the sheltered south-western shores of the bay. The contribution of these two species to total macrofaunal and crustacean biomass is given for the King’s Beach transect. The factors affecting the distribution of these species in Algoa Bay are discussed.     

Growth and production of Donax Sordidus Hanley on an Open Sandy Beach in Algoa Bay

A population of Donax sordidus (Mollusca, Pelecypoda) has been studied for two years on an open sandy beach. There were summer and winter settlements each year with the former being larger. Growth was rapid, the animals reaching 20 mm length within one year. Few live longer than 17 months. Production averaged 168,7 mg dry matter m^-2y^-1 and the steady state $$\overline{P}/\overline{B}$$ was 1,30y^-1. Energy values averaged 17,84 kJg^-1dry tissue and had a seasonal cycle with maximum values before spawning.     

Reproduction and larval distribution of the penaeid prawn Macropetasma africanus (Balss) in Algoa Bay

Breeding adults and larvae of Macropetasma africanus were sampled over a two-year period in Algoa Bay, South Africa. Gonadal macro-and microscopic examination enabled classification of breeding females into four stages of development. Breeding females were present throughout the study with a summer peak of late maturing and mature females. Larvae were present in the plankton throughout the study with peak abundance in summer. Protozoea, mysis and post-larval stages were recorded with the mysis stage most abundant. Significantly higher numbers of the mysis and post-larval stages were taken at shallow stations (5 m) off sandy beaches than at the deeper stations (18 m). The presence of breeding females in the mature stage of ovarian development and the increase in larval abundance In summer indicates spawning throughout the year with peak intensity in summer.     

The ichthyoplankton assemblage of the Algoa Bay nearshore region in relation to coastal zone utilization by juvenile fish

The nearshore ichthyoplankton of Algoa Bay was sampled at six stations over a two-year period between 1980 and 1982. Larvae of 26 families of teleosts were identified with Gobiidae constituting 48,0%, Engraulidae 26,7% and Clupeidae 12,1% of all larvae sampled. Caffrogobius spp., Engraulis capensis and Etmmeus teres were the dominant species. Representatives of families such as Sparidae and Mugilidae which numerically dominate juvenile nursery areas in Algoa Bay were not abundant in the nearshore ichthyoplankton. The various taxa occurring in the ichthyoplankton are discussed in terms of distribution of adults and juveniles, breeding biology and available information on early life history. The paucity of larvae of coastal species with pelagic eggs is highlighted and, with reference to the findings of other workers and local oceanographic conditions, a possible spawning strategy is suggested.     

Mysidacea of the Mtentu River Estuary,Transkei, South Africa

The Mtentu River has a straight open tidal estuary flowing between steep grassy or indigenous forest-covered slopes. Total high-water surface area is about 0,3 km.^a The zooplankton was studied by periodic sampling over a period of thirteen months. Some physical characteristics of the estuary are presented. The seasonal and spacial distribution and relative importance of four species of mysid, is discussed. The most common mysid in the estuary was Mesopodopsis africana, although Rhopalophthalmus terrcmatalis, in view of its larger size, contributed more to the overall mass of mysids in the samples.     

Age,growth and food of Cheimerius nufar (Ehrenberg, 1820) (Sparidae), collected off St Croix Island,Algoa Bay

Age and growth of the santer, Cheimerius nufar, were determined from otoliths. One hyaline and one opaque ring are laid down yearly. The von Bertalanffy growth function yielded the equation L_t = 953,56 [1-e^-654(t ^{+ 2,6177})]. The length-mass relationship W = 0,00005 L^2,7831 was used to determine growth in mass: W_t = 9790,24 [1-e^{-0,0654(t+2,6177)}]^2,7831. Stomach and intestine content analyses were done, using a modification of the points method, as well as the frequency of occurrence method. C. nufar is primarily a piscivore, but also preys on cephalopods and crustaceans.     

Aspects of the ecology of feral cats on Dassen Island,South Africa

Numbers of feral cats on Dassen Island (33°25'S/18°06'E) increased from 20–25 in May 1979 to 37–50 in June 1980. Kittens were born in eight months of the year with birth peaks in October-November and in January. Mean litter size was 2,7 and 80% of kittens born between August 1979 and January 1980 survived until June 1980. Kittens died from starvation and disease. In June 1980 51–56% of the cats were <1 year old. The number of cats is recovering rapidly from heavy culling. Depredation by cats is a potential threat to sea-bird colonies. The diet and feeding behaviour of the cats were studied in order to assess the importance of this threat. An ‘average’ cat's annual diet, assessed from scats, included: 134 European rabbits (Oryctolagus cuniculus), 37 jackass penguins (Spheniscus demersus), 25 Cape cormorants \Phalacrocorax capensis), 31 other birds and 24 house mice (Mus musculus). Each cat killed 105 rabbits and 13 birds each year, the balance of its diet being made up by carrion. Adverse effects of the presence of cats, compared to other factors, were not yet so serious as to necessitate artificial control of cat numbers.