Icthyofauna of Oramiriukwa River in Imo State, Nigeria

Oramiriukwa one of the rivers in the Imo River drainage basin runs approximately a 14.0km course from its headwaters in Abba Isu (Nwangele LGA) and discharge into Otamiri River. Based on the fish catches of local fishermen using a variety of fishing gear in a sampling station in Emekuku (Owerri LGA), a total of 17 families of fish consisting of 27 species were identified in the river. In the January sample the most numerically abundant species were Tilapia zilli (12.5%). Calamoichthys calabaricus (8.7%) and T. guineensis (8.6%). In the July samples the most numerically abundant species were Mastacemblus loenbergii (9.2%). T. zilli (7.2%) and Hemichromis fasciatus (6.6%). The Shannon Weiner Diversity index for Oranmiriukwa River was high (1.305) implying a relatively diversified and equilibrated fish community

Factors influencing the emigration of juvenile Bonga from the Cross River estuary

Studies were conducted to identify and quantify the proximate factors responsible for the emigration of juvenile bonga Ethmalosa fimbriata (Bowdich, 1825) from the Cross River estuary. A time series of bonga cpue, salinity, turbidity and plankton abundance was undertaken, juvenile bonga was abundant in the estuary when salinities ranged between 1 and 9ppt. at salinities outside this range, they were absent. We conclude that salinity is the proximate factor that initiates the emigration of juvenile bonga from the estuary

Recruitment pattern and fish production within the Andoni River system in the Niger Delta of Nigeria

Biweekly samples of fish species obtained from five randomly selected Andoni artisanal fisheries within the Andoni River system, Niger Delta of Nigeria were collected between January and December 1999 and their length frequencies analyzed using FISAT (FAO-ICLARM STOCK ASSESSMENT TOOL). The peak recruitment period for Chrysichthys nigrodigitatus, Ethmalosa fimbriata, Eucinostomus melanopterus, Galeodes decadactylus, Pomadasys jubelini and Sarotherodon melanotheron constituting 54.55% was between June and October while Liza grandisquamis and Lutjanus goreensis, Ilisha Africana. Tilapia guinensis and Pseudotolithus elongate constituting 27.27% had two peak recruitment periods including March-May and May- October. In view of this result it is advisable for fishers to intensify fishing effort between May and October for most commercially important fish species for bountiful harvest

Seasonal variation of some trace metal concentrations in some fish species on stretch of River Kubanni, Zaria

In a semi-urbanized stretch of river Kubanni, Zaria, seasonal variations of some tree metals (copper, zinc and lead) in fish species (Clarias sp., Tilapia sp and Alestes sp) were investigated over a period of eight months. Water and fish were sampled monthly, pooled separately and seasonal analysis of each trace determined using atomic absorption method. The concentration of each of the elements in water higher in the dry season than during the rainy season. The dry and rainy season concentrations of copper, zinc and lead were 6.85~c10.66 mu gg super(-1)&1.45~c1.10 mu gg super(-1); 2.13~c1.68 mu gg super(-1)&0.1 5~c0.05 mu gg super(-1); and 0.52~c0.50 mu gg super(-1) & 0.31~c0.14 mu gg super(-1) respectively. Similarly, all the three accumulated more zinc and lead in the dry season than during the rainy season. Tilapia species and to some extent, Alestes species being pelagic had a higher concentration of trace metals than Clarias species which is a bottom dwelling fish Tilapia species may therefore be a better indicator species than Clarias species for monitoring trace metals in water bodies. Reasons for the observed variations in the trace metals were discussed

Influence of number of valves on catch composition of a fishing pot trap (Lege) in River Rima, north western Nigeria

Three types of prototype (Lege) traps with different numbers of entrance valves were evaluated in River Rima, north western Nigeria. The traps contained 4,6 and 8 valves, tagged 4-V, 6-V and 8-V respectively. The experiment was carried out in a randomized complete block design with one factor each replicated three times. Data collected on fish diversity, number, biomass and sizes were subjected to descriptive statistics and analysis of variance. The results of the catch composition showed close diversity index of 0.86 for 6-V, 0.80 for 8-V and 0.60 for 4-V Lege traps. However, the number (41%) and biomass (48%) of fish caught in the 6-V Lege trap were significantly (P<0.05) higher than those caught in the other traps. There was no definite trend in the sizes (length and girth) of fish caught in the traps. On the basis of species diversity, and the number and biomass of fish caught, the 6-V Lege showed preference for adoption than the other two traps. However, further studies are recommended on the appropriate mesh size net for the trap in line with the provisions of fisheries edicts

Report on the physical, bacteriological and biochemical analyses of seawater samples collected off existing sewage outfalls in the Sierra Leone River Estuary

The studies reported were undertaken as part of a wide environmental feasibility study for the establishment of a modern sewage system in Freetown. The aim of this part of the study was to determine whether the hydrological regime of the Sierra Leone River Estuary would permit the large-scale introduction of sewage into the estuary without damaging the environment. The important factors were whether: 1) there would be sufficient dilution of the sewage; 2) fleatable particles or other substances would create significant adverse effects in the estuarine ecosystem. The outfall sites are described together with the sampling stations, methods and analyses. Results include: 1) T/S profiles; 2) chemical analysis of the water. A review of literature on the Sierra Leone River Estuary is included which provides information on the plankton, benthos and fisheries. Results suggest that at certain points where local circulations occur it would be inadvisable to locate untreated sewage outfalls. Such points are frequently observed in small embayments. These studies have been of short duration but the data can serve as baseline for more extended investigations which would give a more complete picture of the seasonal patterns in the estuary.

Design of a Recreational Fishing Survey and Mark-Recapture Study for the Blue Crab, Callinectes sapidus, in Chesapeake Bay

The development of bay wide estimates of recreational harvest has been identified as a high priority by the Chesapeake Bay Scientific Advisory Committee (CBSAC) and by the Chesapeake Bay Program as reflected in the Chesapeake Bay Blue Crab Fishery Management Plan (Chesapeake Bay Program 1996). In addition, the BiState Blue Crab Commission (BBCAC), formed in 1996 by mandate from the legislatures of Maryland and Virginia to advise on crab management, has also recognized the importance of estimating the levels and trends in catches in the recreational fishery. Recently, the BBCAC has adopted limit and target biological reference points. These analyses have been predicated on assumptions regarding the relative magnitude of the recreational and commercial catch. The reference points depend on determination of the total number of crabs removed from the population. In essence, the number removed by the various fishery sectors, represents a minimum estimate of the population size. If a major fishery sector is not represented, the total population will be accordingly underestimated. If the relative contribution of the unrepresented sector is constant over time and harvests the same components of the population as the other sectors, it may be argued that the population estimate derived from the other sectors is biased but still adequately represents trends in population size over time. If either of the two constraints mentioned above is not met, the validity of relative trends over time is suspect. With the recent increases in the human population in the Chesapeake Bay watershed, there is reason to be concerned that the recreational catch may not have been a constant proportion of the total harvest over time. It is important to assess the catch characteristics and the magnitude of the recreational fishery to evaluate this potential bias. (PDF contains 70 pages)

Toxic blue-green algae: The "problem" in perspective

The incidence of blue-green algal blooms and surface scum-formation are certainly not new phenomena. Many British and European authors have been faithfully describing the unmistakable symptoms of blue-green algal scums for over 800 years. There is no disputing that blue-green algal toxins are extremely harmful. Three quite separate categories of compound have been separated: neurotoxins; hepatotoxins and lipopolysaccharides. There is a popular association between blue-green algae and eutrophication. Certainly the main nuisance species - of Microcystis, Anabaena and Aphanizomenon are rare in oligotrophic lakes and reservoirs. Several approaches have been proposed for the control of blue-green algae. Distinction is made between methods for discharging algae already present (eg algicides; straw bales; viruses; parasitic fungi and herbivorous ciliates), and methods for averting an anticipated abundance in the future (phosphorous control, artificial circulation etc).

Ecosystem study Altenwoerth: impacts of a hydroelectric power-station on the River Danube in Austria

The aim of this article is to briefly describe the effects of the Altenwoerth Barrage, on the River Danube, on some physical variables and their consequent effects on water chemistry and the biota of the river. The methods used for biological sampling are summarised, especially those used in the limnological part of the study, and the macroinvertebrate and fish fauna listed. Comparisons are then made between the impounded section of river immediately above the dam and two unimpounded free-flowing sections of the river. Further developments on the Danube are considered.

The first reported occurrence of the mayfly parasite Spirinella adipophila (Sporozoa) in a British river

During a 2-year survey on the distribution and ecology of mayflies in the upper reaches of the River Wey (a tributary of the River Thames) in Surrey, Spirinella was found in large numbers in the larvae of Ephemera Danica, and in low numbers in larvae of E. ignita and H. lateralis. Samples of E. danica taken from seven other tributaries of the Thames showed that Spirinella is present in most of them and often in high numbers.

Chrysosphaerella and the phytoplankton of the Little Sea, Dorset

The Little Sea is an 80-acre, shallow freshwater lake formed about a hundred years ago by sand-dunes cutting off a sea-inlet at Studland Bay, near Swanage. This work presents a general survey of the phytoplankton in the lake from October 1990 to December 1993. Many species were present throughout the year; others showed seasonal variations. Numerically, the diatoms, Monoraphidium and sometimes Rhodomonas, were the main constituents of the phytoplankton. One species of alga in the lake of particular interest is Chrysosphaerella longispina Lauterb. which, up to 1991, had only been recorded from five localities in Britain.

Burrowing behaviour of signal crayfish, Pacifastacus leniusculus (Dana), in the River Great Ouse, England

Observations were made on crayfish burrows in five locations on the Great Ouse River. The burrow densities and the relative abundance of crayfish were observed. Also, laboratory experiments were carried out in order to study the characteristics and mechanisms of burrowing.

The macroinvertebrate fauna of pools in the floodplain (fadama) of the Anambra River, Nigeria

The Anambra River is the largest tributary of the lower Niger River below Lukoja. Between the months of May and November the river is subject to seasonal flooding from heavy precipitation and land runoff into the drainage system. During the flood phase, pools form on the floodplains (known as the fadama) and these pools receive materials and biota from the main river channel. The biota often includes representatives of freshwater vertebrates (including fishes) and invertebrates. On this brief note, the authors report on the macroinvertebrates found during preliminary studies on four fadama pools during the non-flood season between December 1994 and April 1995. 523 specimens were collected, of which 86% were arthropods, 9% were annelids (mostly Tubifex and Nais) and a few leeches (Hirudo), and 5% were gastropod molluscs of the arthropods, 75% were insects particularly Hemiptera and Diptera.

Limnological aspects of three man-made lakes in Sri Lanka

An investigation was undertaken to study the physicochemical characteristics, phytoplankton and fish fauna of three major deep lakes on the River Mahaweli: Kotmale, Victoria and Randenigala. These lakes were created mainly for hydroelectric purposes during the period 1984 to 1986. In all three lakes, thermoclines were present during most months of the year, but did not appear to be very stable. They tended to disappear during January - February but were well established in August - November. Fifteen species of blue-green algae were identified as well as 27 desmid species and 25 non-desmid green algae. Melosira granulata and M. undulata were the dominant diatom species. The family Cyprinidae dominated the fish fauna by number of species, but by biomass the exotic cichlids (tilapias) were dominant.

The River Endrick - then and now, monitoring by photography

A major survey of the River Endrick was carried out in 1959-60. This survey was repeated three decades later in 1989-90 and comparisons were made of the fauna at the two times of sampling. During both surveys, photographs were taken of all the sampling sites and the objective of the present paper is to compare some of these photographs and discuss the value of photography in studies of river ecology. The sites used for photographic comparison were not chosen originally for that purpose but as appropriate places on the river from source to mouth to study its ecology. The pairs of photos now available have proved of interest and value and some lessons have been learned in relation to the selection of sites for any future photographic studies. Ideally photos should be taken in more than one season of the year as much of the river can be obscured by riparian trees and shrubs during the vegetative season. The exact position from which each photograph is taken is also a major factor to be considered.