Reproductive isolation and the nest sites of Lake Malawi chambo, Oveochvomis (Nyasalapia) spp.

The nest sites of chambo, Oreochromis (Nyusalupia) spp. were surveyed in the vicinity of Cape Maclear, Lake Malawi. O. karongae (Trewavas) nested at depths of 0.5 to 28 m, while O. lidole bred at depths greater than 17 m. Nesting areas overlapped between these two species. O. lidole (Trewavas) nests were generally larger than those of O. karongae . Both species bred from September to March. Contrary to previous suggestions, the two chambo species were not reproductively isolated by breeding depth, season, or beach type.     

The feeding habits of Alestes baremose and Hydrocynus forskali (Pisces) in Lake Albert, East Africa

The stomach contents of 1922 Alestes baremose Joannis and 1184 Hydrocynus forskali Cuvier caught in Lake Albert, East Africa were examined. The fish were caught in gill nets in three main different types of habitat; in lagoons, inshore in the main body of the lake and offshore. Zooplankton, ephemeropteran imagines and higher plant species constituted almost the whole diet of A, baremose , although the relative importance of these three items varied with habitat. In the lagoons and inshore Hydrocynus forskali was mainly piscivorous, but offshore where the largest specimens occur it was feeding mainly on Caridina nilotica. The role of Hydrocynus species as predators in Lake Albert is discussed and it is shown that in this lake predation intensity bythis genus must be considered entirely in terms of H.forskali .     

How can the feeding habits of the sand tiger shark influence the success of conservation programs?

The feeding habits of the sand tiger shark Carcharias taurus , one of the most threatened sharks of the world, are poorly known. Sand tiger sharks are critically endangered in the South-west Atlantic. Since 2007, the law requires that all individuals caught in recreational fisheries off Argentina must be released. Using data from a north Patagonian recreational fishery ( n =164 stomachs with contents), we analyzed the diet of sand tiger sharks in relation with size, sex, maturity stage and season; assessed prey consumption patterns and hooking location; and estimated diet overlap with fishery landings. Sand tiger sharks consumed mainly teleosts (55.4% of the total prey number, N ) and elasmobranchs (41.84% N ), and ate more benthic elasmobranchs (batoids and angel sharks) as they become larger. Sharks swallowed prey mostly in one piece (93.7%) and were hooked mainly in internal organs (87.4%, n =175), causing occlusion and perforation of the esophagus and stomach, and lacerations to the pericardium, heart and liver. Sand tiger sharks fed on the most heavily landed species, overlapping almost completely (>90%) with fishery landings. Conservation plans should take into account that releasing hooked sharks could be insufficient to minimize fishing mortality and that competition for food with fisheries is likely to occur.     

Distribution of sawfishes (Pristidae) in the Queensland Gulf of Carpentaria,Australia, with notes on sawfish ecology

Synopsis Pristis microdon, P. zijsron, P. clavata and Anoxypristis cuspidata are distributed throughout the Queensland section of the Gulf of Carpentaria, Australia. In a survey of the four species, Anoxypristis cuspidata was the most abundant and was recorded in both the inshore and offshore set net fisheries. The size distribution and catch locations of A. cuspidata suggest that the inshore area to a depth of 10 m may be the preferred habitat for juveniles of this species, while adults primarily occur offshore. Pristis microdon, P. zijsron and P. clavata were recorded only in the inshore fishery with catches dominated by immature animals. Pristis microdon was caught in the inshore fishery late in the monsoonal wet season (February to April) and inhabited both freshwater and estuarine environments. Pristis zijsron occurred only on the sand and mud flats outside river mouths whilst P. clavata inhabited both the sand and mud flats and upstream estuarine habitats. Observations on reproductive staging and the capture of neonate specimens suggest that in all four pristids, pupping occurred through the wet season until the beginning of the dry season in May. A seasonal set net closure for the barramundi, Lates calcarifer and shark fisheries, which has been in place since 1980 in Queensland Gulf waters, therefore offers a measure of protection to breeding female sawfish and their offspring.     

Identification of the Lake Malawi Oreochromis (Nyasalapia) spp. using multivariate morphometric techniques

With the aim of reliably distinguishing these commercially important species on the basis of external characteristics alone, morphometric techniques were employed on a sample of the four species of Oreochromis ( Nyasalapia ) described from Lake Malawi: O. karongae, O. lidole, O. saka and O. squamipinnis . Univariate analysis of variance on the ratios of 23 variables to standard length indicated many differences among all species, but there was considerable individual variation, and consequent overlap. Residuals from a regression of each variable on length were employed for multivariate analysis. Cluster analysis on the means of the residuals was used to construct a phenogram which formed the basis for denning a series of dichotomous discriminant analyses. In each discriminant analysis, variables were successively eliminated in the reverse order of the magnitude of their correlation with the discriminant function. The combination of variables producing 95% accuracy of classification was selected, and the discriminant function equations for each step calculated. Some further variables were eliminated by checking for redundancy through analysis of correlations. The resulting equations enable O. karongae to be separated using eight measurements, O. lidole using 10, and O. saka and O. squamipinnis to be distinguished by a combination of 13 measurements.     

An experimental study of phytoplankton feeding in three tilapiine cichlids

Three species of tilapia ( Oreochromis lidole, O. karongae and O. niloticus ) were fed on four planktonic algal diets in the laboratory. The algal concentrations were measured over a 24-h period and the ingestion rates calculated. In monocultures of large algae (average filament length=477 μm) O. niloticus had the highest ingestion rate, but on small algae (particle size <8 μm) O. lidole was the fastest, while O. karongae enhanced nanoplankton production. With algae of mixed sizes, O. niloticus was able to remove small algae quicker than the other fish species. Thus, the presence of larger algae can influence the impact of a planktivorous species on nanoplankton. O. lidole is likely to have the greatest impact on plankton communities heavily dominated by smaller algae.     

Evolutionary relationships of the Lake Malawi Oreochromis species: evidence from allozymes

Three tilapiine species belonging to the endemic Lake Malawi species flock known as' chambo' Oreochromis ( Nyasalapia ) karongae , O. (N.) lidole and O. (N.) squamipinnis and the species Oreochromis (Oreochromis) shiranus were collected from the wild. These four species were analysed at 43 enzyme loci using starch gel electrophoresis. No significant deviations from Hardy-Weinberg equilibrium were observed after correcting for multiple simultaneous testing. The expected heterozygosity ( H _e) was lowest in O. (O.) shiranus ( H _e=0.082). The three chambo species had higher levels: H _e=0.103 to H _e=0.116. The three chambo species as a whole were polymorphic (99%) at 16 different loci sharing 10 of these in common. No fixed differences between the three chambo species were observed but highly significant allele frequency differences existed between all the chambo species. The F _ST calculated for the three chambo species was 0051, closer to intra-specific than to inter-specific levels. O. (O.) shiranus could be clearly separated from all chambo species at five fixed loci. Comparison of the allozyme data from these species with five species from the same sub genera support the hypothesis that the chambo form a monophyletic group and that O. (N.) macrochir or a related species represents the sister taxon.     

The food and feeding ecology of Mugilidae in the St. Lucia lake system

The diet and feeding interrelationships of ten species of Mugilidae were studied over a two-year period in the St. Lucia lake system of South Africa. Qualitative stomach analyses were performed on over 1000 fish of more than 5 cm (standard length). All are soft bottom substrate feeders ingesting inorganic particles mixed with food items. The food of most species is the same and consists of Assiminea bifasciata , foraminifera, the large centric diatom Aptinoptychus splendens , small centric and pennate diatoms, and filamentous algae. Individual species of mullet however, differ, in the size of inorganic particles ingested and exhibit marked sand grain size preferences. The consumption of the various food items may depend upon their occurrence on substrates of the preferred particle size. There is no apparent change in diet and particle size preference according to age in any of the species and no seasonal variation was recorded in the diet. It is suggested that interspecific competition for food is reduced by substrate particle size selection and perhaps by differences in feeding periodicity. Where there is an apparent overlap in diet, as in the case of Assiminea bifasciata , on substrates of the same size then there is a superabundance of the food organism which serves to minimize competitive interactions.     

The predation of mysids by fish of the Rockall Trough,northeastern Atlantic Ocean

The stomach contents of representatives of approximately 100 species of pelagic and demersal fish caught in the Rockall Trough, northeastern Atlantic ocean, have been examined for the occurrence of mysids. More than 40 species of fish included mysids in their diets. The majority of the 21 species of mysids identified in the stomachs live in close association with the sediment and are rarely caught in pelagic nets. Mysids contributed significantly to the diets of many demersal fish but were not apparently important constituents of the food of pelagic fish.     

Appendicularians: an important food supply for the Argentine anchovy Engraulis anchoita in coastal waters

The stomach contents of 532 adult specimens of the Argentine anchovy, Engraulis anchoita, caught in coastal waters of the Argentine Sea from 1994 to 1996, were analyzed. Larger amounts of food were found in the stomachs of anchovies collected in the northern surveys (35–40°S), with the highest values attained in 1994. Main diet items were copepods, appendicularians, cladocerans, fish eggs, and pteropods. Anchovies caught in the southern surveys (40–45°S) ingested less food, whereby the main items were copepods and appendicularians. Plankton samples collected simultaneously with the fishing trawls were also analyzed. Except for Fritillaria borealis, which occurred only in plankton samples, the same appendicularian species (Oikopleura dioica and O. fusiformis) were found in both stomach contents and in plankton samples. The Ivlev selectivity index calculated for O. dioica and O. fusiformis and for the different maturity stages of both species were in all cases ～0, supporting the hypothesis of a non‐selective feeding.     

The fishery of the Comoros,with comments on its possible impact on coelacanth survival

Synopsis The traditional methods of deepsea handline fishing in the Comoros are described. The main target species is the oilfish Ruvettus pretiosus, and the coelacanth Latimeria chalumnae is caught as a bycatch. In recent years motorised dugout canoes as well as outboard- and inboard-powered boats have been introduced into the fishery, and more efficient fishing tackle has become available. The more modern gear is intended for use on pelagic fishes and has added a new dimension to the fishery. Traditional handline fishermen are not considered to be a threat to the coelacanth, but the fishermen equipped with motorised boats and modern tackle would constitute a real threat if they direct their efforts on inshore reefs.     

The food and feeding habits of greenback grey mullet, Liza subviridis (Valenciennes), from different habitats and at various stages of growth

An analysis of the stomach contents of Liza subviridis at various stages of growth and from different habitat types is given. Transitions in diet with respect to size were observed. Postlarval stages of less than 12 mm standard length fed only on zooplankton. The transition to bottom feeding occurred in specimens 16–20 mm, with food items consisting of zooplankton, diatoms, detrital material and inorganic sediment. The transition was complete on attaining a length of 24 mm whereby food items comprised diatoms, detrital material, filamentous algae and inorganic sediment. The relevance of this information in aquaculture is discussed. The stomach contents of adult Liza subviridis taken from different habitat types were consistent, comprising diatoms, detrital material and inorganic sediment. Filamentous algae was also consumed where available.     

Locomotor patterns, territory, and tunnel utilization in the mole-rat Spalax ehrenbergi

The northern bottlenose whale has been caught in the Faroe Islands for centuries, with written catch records going back to 1584 and unbroken from 1709. A total of 811 whales has been reported in the period 1584-1993. The Faroese bottlenose whaling is an opportunistic drive fishery of pods sighted very close to shore. Natural strandings also occur. Most of the fishery has taken place in two close southern villages of the Faroese archipelago (72% of the catch). The high season is 20 August-20 September. The pod contains 1-7 whales with an average of 2.1 whales. Most of them are immature males or mature females with juveniles, but as many males as females have been caught overall. Females and males at every stage of development have been caught in the Faroes, although it appears that the bottlenose whales approaching the Faroese coast and then driven ashore have not included as large and as small individuals as those shot offshore. A body weight (W in kg) and length (L in cm) relationship has been calculated for both sexes combined: W = 0.0000131 x L^3.07. Females and immature males have a grey and bulbous forehead. As the males mature their forehead becomes flatter and lighter, and only large mature males have a white and flat forehead. The stomach contents of nine whales contained in total at least 13 squid species. A comparison with pilot whaling shows that bottlenose whales arrive 2-4 weeks later than the pilot whales and that the geographical distribution of the catch is very different for both species, suggesting a different pattern of migration through the archipelago.     

Diet and Habitat use by Bluefish, Pomatomus Saltatrix, in a Chesapeake Bay Estuary

Bluefish, Pomatomus saltatrix, are recreationally valuable finfish along the Atlantic seaboard and in the Chesapeake Bay. Diet and habitat use patterns for bluefish life history intervals in Chesapeake Bay estuaries are poorly described although it is widely acknowledged that this apex piscivorous species relies on estuarine habitat for feeding and nursery grounds after oceanic spawning and inshore migration of larvae. Bluefish diet, distribution, and abundance patterns were examined in relation to oyster reef, oyster bar, and sand bottom habitat in the Piankatank River, Virginia. Bluefish from all sites were predominantly piscivorous and were more abundant at reef sites than non-reef sites. Bluefish caught in association with the oyster reef consumed a wider diversity of prey items than fish from other sites; diet diversity may contribute to bluefish success during periods when small pelagic food fish abundance is reduced. Bluefish estuarine habitat use is positively correlated with the presence of oyster shell habitat and the complex trophic communities centering on oyster reefs.     

Genetic isolation between coastal and fishery‐impacted,offshore bottlenose dolphin (Tursiops spp.) populations

The identification of species and population boundaries is important in both evolutionary and conservation biology. In recent years, new population genetic and computational methods for estimating population parameters and testing hypotheses in a quantitative manner have emerged. Using a Bayesian framework and a quantitative model‐testing approach, we evaluated the species status and genetic connectedness of bottlenose dolphin (Tursiops spp.) populations off remote northwestern Australia, with a focus on pelagic ‘offshore’ dolphins subject to incidental capture in a trawl fishery. We analysed 71 dolphin samples from three sites beyond the 50 m depth contour (the inshore boundary of the fishery) and up to 170 km offshore, including incidentally caught and free‐ranging individuals associating with trawl vessels, and 273 dolphins sampled at 12 coastal sites inshore of the 50 m depth contour and within 10 km of the coast. Results from 19 nuclear microsatellite markers showed significant population structure between dolphins from within the fishery and coastal sites, but also among dolphins from coastal sites, identifying three coastal populations. Moreover, we found no current or historic gene flow into the offshore population in the region of the fishery, indicating a complete lack of recruitment from coastal sites. Mitochondrial DNA corroborated our findings of genetic isolation between dolphins from the offshore population and coastal sites. Most offshore individuals formed a monophyletic clade with common bottlenose dolphins (T. truncatus), while all 273 individuals sampled coastally formed a well‐supported clade of Indo‐Pacific bottlenose dolphins (T. aduncus). By including a quantitative modelling approach, our study explicitly took evolutionary processes into account for informing the conservation and management of protected species. As such, it may serve as a template for other, similarly inaccessible study populations.     

Convergence and divergence in prey of sympatric canids and felids: opportunism or phylogenetic constraint?

Since the canids and felids diverged in the mid‐Eocene or earlier, each family has developed a suite of morphological and behavioural adaptations for obtaining and consuming prey. We here distinguish between prey taxa captured and eaten as a result of these phylogenetic adaptations, and those because they are fortuitously encountered, and argue that such supplementary prey, often opportunistically caught, create a buffer between sympatric, and potentially competitive, canids and felids and thus enhance coexistence. We base our analysis on dietary data derived from the stomach contents of four sympatric canid and felid species in the Free State Province, South Africa (canids: Cape fox Vulpes chama and black‐backed jackal Canis mesomelas; felids: African wild cat Felis silvestris lybica and caracal Caracal caracal), and from results of studies on these species elsewhere in southern Africa. The two canid species preyed heavily on invertebrates, and thus opportunistically, while the felids (especially the caracal) concentrated on mammals, prey they are phylogenetically adapted to capture. Only three species of mammalian prey are shared by the four species. The ratio of opportunistically‐to‐phylogenetically mediated prey taxa used (the O/P ratio) differ between the species, with the black‐backed jackal having the most opportunistically caught taxa in its diet, and the caracal the least. As predicted, a comparison of this data with those from dietary studies of the same species carried out elsewhere indicates that the number of opportunistically obtained prey taxa varies more than those resulting from phylogenetic adaptations. The largest canid had the widest food spectrum (35 prey taxa) while the smallest felid had the most restricted one (11 prey taxa). We argue that using the O/P distinction allows a better understanding of changes in food niche breadth of particular species, especially in xeric areas, and gives a better indication of possible exploitative competition for food by sympatric carnivores than when regarding all prey taxa as actively pursued. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 527–538.     

Food and feeding of three Citharinus species in Lake Kainji, Nigeria

This paper provides information on the food and feeding habits of three Citharinus species in Lake Kainji. A total number of 2357 specimens made up of 1628 Citharinus citharus , 705 C. distichodoides and 24 C, latus were examined. The majority of the fish caught by gill-netting had empty stomachs unlike those caught by cast-netting and electrofishing. The main food items were planktonic and epipelic blue-green and green algae. All the three species had similar feeding habits and also fed on the same items; their food varied with the seasons. Citharinus spp. have high gut length/standard length ratios which are adaptations to the microphagous and planktivorous feeding habits.     

Fish abundance and trophic structure from the commercial catch in Lake Patzcuaro, Mexico

The composition, abundance and trophic structure of the fish community in Lake Patzcuaro is analyzed, using data from eight samples taken from the commercial fishery acquired between August 1990 and April 1991. A total of 65 767 individuals, caught with gillnets selective to all fish and size, were analyzed. Eleven species (8 native and 3 exotic) were recorded during the study. Zooplanktivorous were the most representative species, amounting to 91% of the total number. Also, they were the most characteristic species (36.4%) when feeding habits were considered, followed by carnivore and omnivore (27.3% each), and herbivore (9.1%). Three species groups and three time-associated groups were detected by means of classification methods. Lake Patzcuaro's ichthyofauna is to be considered as a transitional community that has not reached equilibrium, particularly after the introduction of exotic species and local extinction of native species. However, Lake Patzcuaro has the greatest fishery production of all tropical lakes in the Central Plain of Mexico and it is mainly sustained by native species. The differential use of feeding resources by the fish species and the diversity in their habits must be taken into account to design strategies to maintain the fish structure (avoiding new introduction of exotic species) and the fish production in Lake Patzcuaro.     

Analysis of the Inshore Macrozoobenthic Community in Lake Naini Tal,U. P., India

Certain parameters of the zoobenthos community structure, viz., population density, species richness, diversity, dominance and similarity indices in the inshore area (0–1 m stratum) of Lake Naini Tal were examined during 1978–1979. Significant changes in community structure were found both in space and time. A classification applied on similarity index values of the data from different sampling occasions showed two clusters of species–winter and summer clusters. Similar analysis of the sample data from different sites suggested three clusters of species for polluted water, clean water and intermediate sites. It is suggested that variation in the benthos community structure over the season is primarily related to temperature, availability of food and life cycle pattern, while its variation in space is related to sediment texture and degree of pollution.     

Stomach pH,feeding rhythm and ingestion rate in Oreochromis niloticus L. (Pisces: Cichlidae) in Lake Awasa,Ethiopia

Fish were caught in February and October, 1985 with gill and trawl nets at different time intervals. The length and weight of the fish, the stomach pH and the weight of the stomach contents were determined. The feeding pattern of O. niloticus was observed to have a diel rhythm. The stomach became more acidic towards the afternoon and most of the evening. The pH of the stomach had a significant regression on stomach fullness. The feeding rate of O. niloticus in Lake Awasa was estimated from daily feeding periodicity and rate of gastric evacuation. The fish ingests 11.5% of their wet body weight daily at an average water temperature of 21.5 °C. It is believed that the fish ingests and assimilates adequate supply of energy (9.1 KJ/day) for growth, maintenance and other energy requiring activities of the fish.