Academic journal article Estonian Journal of Ecology

Spirogyra Africana (Fritsch) Czurda Bloom and Associated Fishing Impairment in a Tropical Freshwater lagoon/Spirogyra Africana (Fritsch) Czurda Oitseng Ja Sellega Seotud Kalandusprobleemid Troopilises Mageveelises Laguunis

Academic journal article Estonian Journal of Ecology

Spirogyra Africana (Fritsch) Czurda Bloom and Associated Fishing Impairment in a Tropical Freshwater lagoon/Spirogyra Africana (Fritsch) Czurda Oitseng Ja Sellega Seotud Kalandusprobleemid Troopilises Mageveelises Laguunis

Article excerpt

INTRODUCTION

Literature on algal blooms in Nigeria is scanty although in the last two decades the number of papers dealing with blooms in the fresh, brackish, and marine zones has been increasing (Nwankwo, 1993; Nwankwo et al., 2003, 2004; Onyema & Nwankwo, 2006, in press). Nwankwo et al. (2003) surveyed harmful and/or toxic algal species in coastal waters of south-western Nigeria. Recently, a report by Onyema & Nwankwo (in press) documented an incidence of substratum discolouration of parts of the Lagos Lagoon. According to the report the discolouration was caused by the cyanobacterium Oscillatoria tenuis. Blooms of other cyanobacteria (Microcystis, Anabaena, Trichodesmium) as well as of diatoms (Coscinodiscus, Bellerochea, Chaetocerus, Cerautolina) and dinoflagellates (Ceratium, Noctiluca) have also been reported in waters of south-western Nigeria (Nwankwo, 1993; Nwankwo et al., 2003, 2004; Onyema & Nwankwo, 2006).

The lagoons of south-western Nigeria are a meandering net of nine lagoons with innumerable creeks (Webb, 1958; Nwankwo, 2004; Emmanuel & Kusemiju, 2005; Onyema & Nwankwo, 2006). Fishing in these lagoons is an important livelihood for folks in the region. Fishing in this regard is largely artisinal with an array of gear types used, especially nets (Emmanuel, in press). Cast nets and gill nets, are according to workers, the most widely used artisanal fishing gears in Nigerian waters (Reed et al., 1967; FAO, 1969; Udolisa & Solarin, 1979; Emmanuel & Kusemiju, 2005). According to Fagade (1969) and Kusemiju (1973), the cast net is the commonest fishing gear in the Lagos and Lekki lagoons. In the Lekki Lagoon most fish species are caught with boat seine, a community-based fishing operation, which requires between 15 and 30 individuals of high strength. Reports from the Lekki Lagoon in 2006 and particularly in the dry season, implicated a web of greenish slime in water, which clogged up the net meshes as it was hauled hence impairing fishing operations. Algal blooms are usually a reflection of the nutrient levels of an aquatic system and these in turn affect the fish assemblages and fisheries components.

Previous works on the Lekki Lagoon include those of Ikusemiju (1973, 1975) and Ikusemiju & Olaniyan (1977), which deal with the diverse fishes of the lagoon and present biological information on the catfish species endemic to the lagoon. We report here an investigation into the greenish and slimy materials observed to smear and attach to fishing nets impairing fishing operations and diminishing catches for the fishermen in parts of the Lekki Lagoon.

MATERIALS AND METHODS

Description of the study site

The Lekki Lagoon is a large expanse of shallow fresh water located in both Lagos and Ogun states of Nigeria. The lagoon covers an area of nearly 247 [km.sup.2] (Kusemiju, 1973) (Fig. 1). A greater part of the lagoon is shallow and less than 3.0 cm deep, while there are areas of up to 6.4 km in depth (Kusemiju, 1973). The lagoon is located between longitudes 4[degrees]00? E and 4[degrees]12? E and latitudes 6[degrees]25? N and 6[degrees]37? N. The lagoon is fed by the Oni River in the north-eastern part, while the Oshun and Saga rivers flow into its north-western part. The lagoon supports a major fishery with as many as 30 fishing villages/settlements located on the edge of the lagoon including Origbe, Dopemu, Lupaye, Imoba, and Emina. There are well over 2000 fishing canoes operating in the lagoon and at least 10 000 active fishermen in the region. The fish species common to the area are freshwater endemic species.

Collection of water and algal samples

Water samples for the analysis of water chemistry characteristics were collected between 12 and 2 h on each occasion with a 1.50 cl plastic container with a screw cap. Samples were collected from five stations of the area where these green smears appeared on fishing nets during and after fishing to provide data for the wet and dry season conditions. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.