BINDURA UNIVERSITY OF SCIENCE EDUCATION
DEPARTMENT OF ENVIRONMENTAL SCIENCE
AN ASSESSEMENT OF FISH CATCH RATES AND CATCH COMPOSITION OF THE SANYATI BASIN OF LAKE KARIBA
STUDENT NAME: MAVURU ALLEN
(REGISTRATION NUMBER): B1128943
A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS OF THE BACHELOR OF ENVIRONMENTAL SCIENCE HONOURS DEGREE IN WILDLUFE AND RANGELAND MANAGEMENT
Date of submission 30/04/2015
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DEDICATION I dedicate this thesis to my mum .
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ACKNOWLEDGMENTS Special thanks to my academic supervisor Mr W Mhlanga who worked tirelessly during this research project. I would also like to acknowledge my field supervisor Mr Tendaupenyu I.T who is also the Officer in Charge at Lake Kariba Fisheries Research Institute (LKFRI) for his assistance and support during my study.
Thanks to Mr Makumbe P and Mr Ngorima P who assisted in data analysis and all the advice.
I also wish to thank the following people: Ranger Maziva, Ranger Machengo, Ranger Vhareta, Ranger Goza, Coxswain Chavuta, Senior Ranger Mr Chaita and the rest of the LKFRI staff for their assistance and support during my primary data collection.
I would also like to acknowledge the support and cooperation by the Chairmen of Nyaodza fishing village (Mr Moforo S), the rest of the committee members and all fishermen at Nyaodza fishing camp, the Chairmen of Fothergill fishing village (Mr Anderson P), the rest of the committee members and all the fishermen during primary data collection.
To friends and family thank you for your support.
To my mum thank you for your love.
The success of the thesis was made possible by the Zimbabwe Parks and Wildlife Management Authority and the LKFRI who provided all the necessary resources.
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ABSTRACT A study was conducted in the Sanyati basin to determine changes in catch, effort, catch per unit effort (CPUE) and the overall catch composition at Lakeside station from the year 2002 to 2012 and also to determine CPUE in the artisanal fishery. The study used both secondary and primary data. Secondary data was obtained from the Experimental fishing programme at Lakeside and primary data was collected from Nyaodza and Fothergill fishing villages. An Analysis of Variance was conducted on catch, effort and CPUE data. The results revealed that there was a significant difference in both catch and effort among the years (p<0.05). However, no significant difference was observed in CPUE among the years 2002 to 2012 (p>0.05). Synodontis zambezensis appeared as the most dominant species at Lake side station with an Index of Relative Importance (IRI) of just over 36% IRI followed by Hydrocynus vittatus having just over 29% IRI while the third dominant species was S agochromis codringtonii with an IRI of 24%. Catch, effort and catch composition for Nyaodza and Fothergill fishing villages were also determined and CPUE for the two fishing villages were compared to determine if there was a significant difference. A t test was conducted to determine if there was a significant difference between the two fishing villages among the sampled months and results revealed that there was no significant difference in mean CPUE between the two fishing villages in May and June ( p>0.05). However, a significant difference was noted between the two fishing villages for the month of July ( p<0.05). The exotic Oreochromis niloticus appeared as the most dominant species in the artisanal fishery contributing 50.03% of the catch at Nyaodza in terms of numbers and 57.51% at Fothergill fishing village.It was concluded that the experimental fishing at Lakeside station is not a true representative of the inshore fishery in Lake Kariba since the area is closed to commercial fishing. The dominance of S. zambezensis was attributed to the use of smaller mesh sizes in the experimental fishing. It was also concluded Oreochromis mortimeri is still one of the most important fish species in the artisanal fishery although its contribution has declined and has been replaced by the exotic Oreochromis niloticus .
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TABLE OF CONTENTS DEDICATION ...... ii ACKNOWLEDGMENTS ...... iii ABSTRACT ...... iv TABLE OF CONTENTS ...... v LIST OF TABLES ...... vii LIST OF FIGURES ...... viii LIST OF ABBREVIATIONS ...... ix CHAPTER ONE ...... 1 1.0 BACKGROUND TO THE STUDY ...... 1 1.2 PROBLEM STATEMENT ...... 3 1.3 AIM OF THE STUDY ...... 3 1.4 OBJECTIVES OF THE STUDY ...... 3 1.5 RESEARCH QUESTIONS...... 3 1.6 JUSTIFICATION ...... 4 CHAPTER TWO ...... 5 2.0 LITERATURE REVIEW ...... 5 2.1 IMPORTANCE OF FISHERIES ...... 5 2.2 HISTORY OF FISHERIES IN LAKE KARIBA ...... 5 2.3 EXPERIMENTAL FISHING ...... 6 2.4 ARTISANAL FISHERY ...... 8 CHAPTER THREE ...... 11 3.0 METHODOLOGY ...... 11 3.1 STUDY AREA ...... 11 3.2 DATA COLLECTION ...... 11 3.2 DATA ANALYSIS ...... 12 CHAPTER FOUR ...... 14 RESULTS ...... 14 4.1 SPECIES RECORDED...... 14 4.2.1 CATCH IN EXPERIMENTAL FISHING ...... 15 4.2.3 EFFORT ...... 15 4.2.4 CATCH PER UNIT EFFORT ...... 16 4.2.5 SPECIES COMPOSITION ...... 17 4.3 ARTISANAL FISHERY ...... 18 CHAPTER FIVE ...... 20
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DISCUSSION ...... 20 5.1 EXPERIMENTAL FISHING ...... 20 5.1.1 CATCH ...... 20 5.1.2 EFFORT ...... 20 5.2 CATCH PER UNIT EFFORT (CPUE) ...... 21 5.3 SPECIES ABUNDANCE ...... 22 5.2 ARTISANAL FISHERY ...... 23 5.2.1 CPUE ...... 23 5.2.2 SPECIES COMPOSITION ...... 24 CHAPTER SIX ...... 26 6.1 CONCLUSIONS ...... 26 6.2 RECOMMENDATIONS ...... 26 REFERENCES ...... 27
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LIST OF TABLES
TABLE PAGE
Table 4.1: Species recorded during the study period 14
Table 4.2: Species abundance at Lakeside station 17
Table 4.3: CPUE in the artisanal fishery during the study period 18
Table 4.4: Species abundance in the artisanal fishery 19
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LIST OF FIGURES
FIG PAGE
Fig 3.1: Map of the study area showing basin 5 11
Fig 4.1: Trends in catch in the experimental fishing from 2002 to 2012 15
Fig 4.2: Trends in effort in the experimental fishing form 2002 to 2012 16
Fig 4. 3: Trends in CPUE in the experimental fishing form the period 2002 to 2012 16
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LIST OF ABBREVIATIONS
BUSE Bindura University of Science Education
CPUE Catch per Unit Effort
ES Environmental Science
FAO Food and Agriculture Organisation
IRI Index of Relative Importance
LKFRI Lake Kariba Fisheries Research Institute
SOFIA State of the World Fisheries and Aquaculture
SPSS Statistical Package for Social Sciences
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CHAPTER ONE 1.0 BACKGROUND TO THE STUDY Lake Kariba is one of the largest man made Lakes in the world. Karenge and Kolding, (1995) concluded that Lake Kariba is a fresh water ecosystem with its production being largely controlled by the fluctuating Lake level and nutrient input into the Lake. Fluctuations in Lake levels are through the inputs and outputs with inputs largely being direct precipitation and inflow from rivers while outputs are through evaporation, release through the turbines and release through the sluice gates. Begg, (1970) described Lake Kariba as a monomictic, mesotrophic Lake with each basin exhibiting its own individuality. Basins 3, 4 and 5 are truly lacustrine with temperature induced turnover in July while basin 1 and 2 are riverine, flushed out in May by the Zambezi river floods (Begg, 1970).
Lake Kariba fishery can be classified into the capture fishery and aquaculture fishery, (Mhlanga and Mhlanga, 2014). The capture fishery exploits fish from the wild while the aquaculture fishery involves culturing or rearing fish in the cages. There are also sub sectors under the capture fishery and these are; the capital intensive pelagic fishery, the sport fishery which mainly targets the Tiger fish ( Hydrocynus vittatus ) and the artisanal fishery which mainly targets the indigenous large species and the introduced Oreochromis niloticus using gillnets.
The experimental fishing is a programme which is conducted / carried out by the Lake Kariba Fisheries Research Institute (LKFRI) mainly for research purposes. It is done at Lakeside station which is in the Basin 5 commonly known as the Sanyati basin. Commercial fishing is not allowed at Lakeside station as it is a closed area to fishing as the area has been set aside for tourists to enjoy their time without disturbances from fishing activities. Kolding et al , (2003) has noted that experimental fishing has been conducted since 1960 in Lake Kariba. The experimental fishing is conducted almost on a weekly basis and sampling has remained the same (Kolding et al , 2012). Although experimental fishing has been said not to be a true representation of the fishery due to the fishing pattern (Kolding et al , 2003) it is however important as it can be used to monitor fish population changes especially changes in terms of species composition and species abundance.
Karenge and Kolding, (1995) observed that changes in terms of species composition have taken place in Lake Kariba especially in the Sanyati Basin. In the initial stages of the Lake, the cyprinids Labeo congoro , Labeo altivelis , characins Distichodus schenga , and Distichodus
1 mossambicus were abundant in the Lake but declined a few years later with the cichlids gradually becoming important especially in the Sanyati Basin which is more lacustrine (Kolding et al , 2003). The cichlid Serannochromis codringtonii which was not common during the initial stages of the Lake gradually replaced the native Oreochromis mortimeri as the dominant species among the cichlids while Synodontis zambezensis and Serannochromis macrocephalus also gradually increased in abundance (Kolding et al. 2003). Presently about 45 fish species have been recorded in Lake Kariba, five of which are introduced (Marshall, 2006 in Zengeya and Marshall 2007). Kenmuir, (1984) highlighted that two of the introduced fish species, Tilapia rendalli and Serannochromis robustus may have invaded the Lake naturally and this is probably because these two species were not recorded in the pre impoundment surveys conducted along the Zambezi River and also because there is no record of the introduction of these two fish species in Lake Kariba. The other three introduced fish species ( Oreochromis macrochir , Limnothrisa miodon and Oreochromis niloticus ) are truly exotic fish species as the introduction of these species has been documented. Using experimental gill netting data (Chifamba, 2006) predicted a major change in the composition of inshore fish species of Lake Kariba due to the displacement of the native species by the introduced fish species.
The artisanal fishery is a labour intensive fishery with minimum capital invested. It is conducted from fishing villages scattered along the Lakeshore and is restricted to areas of less than 10metres (Sanyanga, 1997). The fishery began in 1962 on the Zimbabwean side of the Lake (Karenge and Kolding, 1995). Only multifilament gillnets of not less than 120mm [4ʺ(inch)] are allowed and entry into the fishery is regulated by the Zimbabwe Parks and Wildlife Management Authority (ZPWMA). The regulation of fisheries in Zimbabwe is done through the Parks and Wildlife Act of 1996. Entry into the fishery is regulated through the issuing of permits and use of certain mesh sizes. However, how often fishers go out to fish is largely determined by weather pattern, alternative sources of livelihoods, profitability of the fishing business at any given time, condition of the fishing gear and volume of the catch at any given time (Lake Kariba Catch Survey, 2011).
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1.2 PROBLEM STATEMENT A lot of studies on fish population changes in Lake Kariba have been carried out (for example, Kenmuir, 1984; Karenge and Kolding, 1995, Songore, 2002) but the information needs to be updated as many changes have taken place in Lake from fishing effort, drought, and even the introduction of inshore fish species such as Oreochromis niloticus . There is no up to date information on the changes that have taken place in terms of catch composition, effort, catch and the catch per unit of effort in the Sanyati basin of Lake Kariba. Since there is need to update data and use it for management purposes it is therefore important that the database is updated.
1.3 AIM OF THE STUDY To assess the catch, effort, Catch per Unit Effort (CPUE) and the catch composition of the Sanyati basin inshore fishery.
1.4 OBJECTIVES OF THE STUDY To determine changes in the catch, effort, and CPUE in the experimental fishing of the Sanyati basin for the period 2002 to 2012. To determine Sanyati basin catch composition in the experimental fishing for the period 2002 to 2012 using Index of Relative Importance (IRI %) and species abundance To compare the CPUE for Nyaodza and Fothergill fishing villages To determine catch composition and abundance in the artisanal fishery for Nyaodza and Fothergill fishing villages using Species abundance.
1.5 RESEARCH QUESTIONS How have effort, catch and CPUE in the experimental fishing at Lakeside station changed over the years from 2002 to 2012? What is the overall species composition in the experimental fishing from the year 2002 to 2012 using IRI % and Species abundance? Is there any significant difference in the CPUE between Nyaodza and Fothergill fishing villages? What is the current species composition in the Sanyati basin inshore fishery using data from Nyaodza and Fothergill fishing villages?
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1.6 JUSTIFICATION Both qualitative and quantitative studies on Lake Kariba have shown that catch, effort and CPUE have been declining since the 90s on the Zimbabwean side of the Lake. It is interesting to determine the current catch, effort, CPUE and the species composition in both the experimental fishing and artisanal fishery in the Sanyati basin of Lake Kariba following the economic hardships which Zimbabwe has been experiencing which could have caused an increase in the effort especially in the artisanal fishery. Due to limited financial and human resources, only Nyaodza and Fothergill fishing villages were sampled in the artisanal fishery. The study will help to update the information on catch, effort, CPUE and the catch composition in the inshore fishery of the Sanyati basin of Lake Kariba and this information can be used by the Lake Kariba fisheries managers for the conservation purposes of the Sanyati basin inshore fishery.
It has been noted that catches in the artisanal fishery have continued to decline and also species of economic importance have changed (Lake Kariba Frame survey, 2011). The study seeks to determine how the catch, effort CPUE and catch composition have changed over the years.
The project is also a baseline against which future research projects can be compared as it is now foundation information useful in the future.
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CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 IMPORTANCE OF FISHERIES Fisheries are important as a source of employment and in supplementing protein and other essential nutrients. In the whole world fish remains the most traded food commodity (FAO, 2014). Global fish production has also increased over recent years with food fish supply increasing at an average annual rate of 3.2% and also the world per capita fish consumption has increased from an average of 9.9kg in the 1960s to 19.2kgs in 2012 (FAO, 2014). In addition, the FAO, (2014) has also noted that the fishing industry employs tens of millions of the global population and supports the lives of hundreds of millions of the population in the world as a whole.
In Africa, the contribution of fisheries vary from creation of employment, supplementation of nutrition, contributing to the Gross Domestic Product (GDP), foreign currency generation, boosting government funding through taxes and licences (permits) and employment in the provision of ancillary services. Employment in the fishery sector in the whole of Africa is about 12.3 million people (as full time or part time fishers and processors) which is about 2.1% of Africa’s population of the ages between 15 and 64 years (FAO, 2014).
In Zimbabwe, Lake Kariba is one of the suppliers of fish through the capture fishery (Kapenta and artisanal fishery) and the aquaculture fishery conducted by the Lake Harvest Company which breeds the exotic Nile Tilapia ( Oreochromis niloticus ).
2.2 HISTORY OF FISHERIES IN LAKE KARIBA Begg, (1970) in Karenge and Kolding, (1995) using Lake Kariba as an example described three typical changes in biological development which new impoundments seem to undergo and these are: (a) the filling phase characterised by eutrophy and high productivity but low diversity, (b) the decreased production but increased diversity phase and (c) the stabilisation phase. He argued that the third phase in Lake Kariba began around 1968 (10 years after the construction of the dam) and lasted up to 1972. However, the FAO (2003) concluded that Lake Kariba’s fish population cannot be considered stable and further changes could still take place and this could be due to fish introductions, commercial exploitation and subsequent environmental changes or as part of natural Lake maturation process.
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2.3 EXPERIMENTAL FISHING The LKFRI has conducted the experimental fishing since 1960. The experimental gill netting programme is done at Lakeside station which is in the Sanyati basin. The programme uses a fleet of 12 panel multi filament gill nets ranging from 38mm to 178mm stretched mesh sizes with 12.5mm increments. The nets are set overnight perpendicular to the shore with smallest sizes inshore. In total the fleet makes 550metres in length. Each individual fish caught is identified to species, and the mesh size, weight, length, sex and maturity stage are recorded. Kolding et al , (2012) has concluded that the sampling design in the experimental fishing has remained the same.
Karenge and Kolding, (1995) have noted that the data from the experimental fishing probably form one of the most reliable data from Lake Kariba. They concluded that the Lakeside data is important in showing the relative changes in species composition and population structures over time and could be used in population dynamics and community ecology. However, other scholars have argued that experimental gill nets are not a true representation of the fishery and this is mostly because of the different methods used in setting nets and the species selectivity of gill nets (Musando, 1996). According to Kenmuir, (1984) species such as Tilapia rendalli , Synodontis zambezensis , Clarias gariepinus and Malapterurus electricus are known to evade gillnets. M. electricus has a low catchability due to its body form (Karenge and Kolding, 1995). In their study they concluded that the relative abundance of these species which are known to evade gillnets are probably underestimated in the gill net catches.
CPUE in the experimental fishing is expressed as catch (kg wet weight) per standard setting and the standard unit setting is 45m mesh panel (Karenge and Kolding, 1995). The FAO, (2003) observed an increasing trend in the catch rates in the experimental fishing at Lakeside station on the Zimbabwean side of the Lake compared to the Zambian experimental fishing which showed a decreasing trend. Although the mean weight in the experimental catch rates also increased at Lakeside station compared to the Zambian experimental fishing which had a decreasing trend, the actual values were higher on the Zambian side compared to the Lake side station and this has been attributed to the higher dominance of the Tiger fish ( Hydrocynus vittatus ) and the Distichodids in the Zambian experimental fishing compared to the Lakeside station which had a higher proportion of the cichlids (FAO, 2003; Musando, 1996). On the contrary, Songore, (2002) observed a fluctuating but declining trend in CPUE at Lakeside. However, from 1994 a decrease in the Zambian mean weight was also observed and the predominance of the squeaker ( Synodontis zambezensis ) in the Zongwe estuary was
6 highlighted as the probable reason (FAO, 2003). Using Lakeside data in their study Karenge and Kolding, (1995) observed a fluctuating CPUE during their period of investigation, with two peaks in 1974 and 1986 and they recorded an overall mean CPUE of around 4.5kg/45.7m (SD 1.8kg). They concluded that on a weight basis four fish species ( H.vittatus , O. mortimeri , S. codringtonii and M. longirostris ) contributed most of the fluctuations. However, changes in species composition could also trigger changes in the experimental fishing catch rates (CPUE) as has been observed by the FAO, (2003) on the Zambian side in the experimental fishing during the 1994 to 2000 period.
Using experimental Lakeside data in their 1969 to 1992 study, (Karenge and Kolding, 1995) concluded that the fish families which were abundant in the early filling phase of the Lake such as the Cyprinids and the Distichodids had declined significantly and were now of minor importance. They concluded that the cichlids were now the dominant fish family in the Lake. The dominance of the cichlids in the Lake confirmed predictions by Kenmuir, (1984) who highlighted that the cichlids would increase in abundance while the riverine fish species would decline as a result of the lacustrine environment created by the damming of the Zambezi River. This is largely because the lacustrine waters are a prime habitat of the cichlids (Kenmuir, 1984). However, in the Zambian waters Characidae, Cichlidae and Mochokidae are the most dominant fish families while the Cichlids dominate the Zimbabwean waters (Musando, 1996). At species level, (Kenmuir, 1984; Karenge and Kolding, 1995; Donnelly, 1971) concluded that H. vittatus is the dominant inshore fish species using experimental gill netting data. This is probably due to the abundance of Kapenta which constitutes over 50% of its food items (Sanyanga, 1997) and also it lacks a predator which controls its population except only fishing. However, Sanyanga, (1996) argued that the Mochokid S. zambezensis has taken over as the dominant inshore fish species in Lake Kariba, pointing out that S. zambezensis was uncommon during the early filling phase but started appearing in the experimental catches around 1969 and it has continued to increase and has now taken over as the most abundant inshore fish species. Sanyanga, (1996) attributed the dominance of S. zambezensis to the fact that it is not captured in the commercial fishery and also that it is not extremely predated on due to its spikes which it uses for defence. In addition, S. zambezensis does not have a strict food regime which gives it a better chance of becoming more abundant and widely distributed (Sanyanga, 1997). According to Songore, (2002) S. zambezensis is now commonly caught in the experimental gillnetting programme at Lakeside and it is has continued to increase significantly since it started appearing in in the experimental gill netting in 1962.
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According to Mhlanga, (2000) and Chifamba, (1998) the exotic O. niloticus and the native O. mortimeri share the same diet and yet the exotic O. niloticus has a higher growth rate (Chifamba, 2003). In addition, Mhlanga, (2000) and Zengeya and Marshall, (2008) have noted that the O niloticus is now wide spread in Lake Kariba and is expected to increase in abundance. It has also been observed by Chifamba, (2006) that during the period 1994 to 2004 the catches of O. mortimeri at Lakeside station increased to peak in 1995 followed by a steady decline until the catches were reduced to zero and within the same period the catches of O. niloticus increased with a sudden rise in the catches in 1998. According to Songore, (2002) O. niloticus has a negative relationship with O. mortimeri .
There is need to determine the changes that have occurred in the catches, effort, CPUE and species composition in the experimental fishing as a result of fish introductions and the Lake maturation processes that have taken place.
2.4 ARTISANAL FISHERY The artisanal fishery is characterised by minimal technology, labour intensive and low funding (Ibrahim et al . 2007). This type of fishery makes up the most important sector which accounts for the major fish supply in the developing world and according to the FAO, (1991) in Ibrahim et al . (2007), out of 1.9million people engaged in either fulltime, part time and seasonal fishing about 98% are in the artisanal fishery.
According to the Lake Kariba 2011 frame survey, the inshore fishery in Lake Kariba on the Zimbabwean side is conducted from fishing villages scattered along the Lake shore. There are seven fishing areas (C1 C7). Areas C1 and C3 are under the Zimbabwe Parks and Wildlife Management Authority (ZPWMA). Area C2, C4 and part of C5 are under the jurisdiction of Nyaminyami Rural District council while a part of C5 to C7 is under Binga District Council. Area C1 is the one which constitutes fishing villages in the Sanyati basin and these include Gache Gache, Nyaodza and Fothergill. The number of fishing villages has remained the same comparing with the 2000 survey (Lake Kariba Frame Survey report, 2011).
Artisanal fishing in Zimbabwe began in 1962 and only one type of gear (gill nets) is used. When the fishery began, the catches were very high and this was attributed to the eutrophic state of the Lake from the fresh inundation and the rapid colonisation of opportunistic riverine detritus feeding species such as mudfish (Labeos) and distichodontids (FAO, 2003). The artisanal fishery is dominated by the cichlids (Donnelly, 1971 unpublished).
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Mean annual fishing effort has been operating below the maximum legal limit of 2 530 nets on the Zimbabwean side (FAO, 2003). However, fishing effort has significantly affected the inshore fish stock (Marshall, 2012). The 1994 Lake Kariba Statistical report noted that effort in the artisanal fishery has been declining but the peak effort of 28 000 000m was recorded in 1998. On the contrary, the Lake Kariba 2011 Frame Survey showed that the number of gill nets in the artisanal fishery has been increasing 1 487nets recorded in 1990, 3 914 nets in 1998, 3 198 nets in 2000 and 4 501 nets recorded in 2011. In addition, the same survey established that the number of fishers has decreased from 1 272 in year 2000 to 1 154 in 2011. The FAO, (2003) has established that the Zimbabwean artisanal fishery is much more regulated and enforced resulting in a fishing pressure and fishing pattern which has not changed much over time and the fish stocks are only moderately exploited. Effort in the artisanal fishery also fluctuates during the year.
The average catch rates in the artisanal fishery are generally only one third of the experimental catch rates and the difference has been attributed to fishing (FAO, 2003). CPUE for Nyaodza and Fothergill fishing villages have fluctuated over the years but with an increasing trend. Peak CPUE for Nyaodza was recorded in 1991 (7.93kg/100m), (LKFRI 1991 Statistical Report) while peak CPUE for Fothergill fishing village was recorded in 1989 (7.07kg/100m)
According to the 1993 LKFRI statistical report, the artisanal fishery has been dominated by breams mainly comprising of O. mortimeri , S. codringtonii and T. rendalli . At species level O. mortimeri has dominated the catches followed by H. vittatus while S. codringtonii has been the third dominant inshore fish species. Mhlanga, (2000) also concluded that O. mortimeri is important for artisanal gill net fishery in Lake Kariba highlighting that in a number of fishing areas it constitutes more than 18% by weight of total annual landings. However, the 2011 Lake Kariba Frame Survey noted that the exotic O. niloticus has taken over as the dominant inshore fish species in the artisanal fishery in Lake Kariba. This has confirmed the predictions by Chifamba, (2006) who argued that the exotic O. niloticus would out compete the native O. mortimeri and take over as the most dominant fish species in the artisanal fishery. Zengeya and Marshall, (2008) also confirmed that the exotic Nile Tilapia has established itself in most parts of the Lake. However, studies by Chifamba, (2006) and Zengeya and Marshall, (2007) were not carried out in the artisanal fishing area. Zengeya and Marshall, (2007) carried out their study in riverine ecosystems. It is not confirmed if the change in catch composition in the artisanal fishery has taken place or if the O. mortimeri has disappeared in the artisanal fishery as predicted by Chifamba, (2006).
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CHAPTER THREE
3.0 METHODOLOGY
3.1 STUDY AREA Lake Kariba is located on the Zambezi River in Mashonaland West province of Zimbabwe, between latitudes 16˚ 28ʹ to 18˚ 04ʹS and longitudes 26˚ 42ʹ to 29˚ 03ʹE (Kolding et al . 2003). According to Marshall, (1997) its catchment area extends over parts of Angola, Zambia, Namibia, Botswana and Zimbabwe. The Lake is divided into five basins and the current study was carried out in the Sanyati basin commonly known as basin 5 (FIG 3.1).
Fig 3.1 : Map of Lake Kariba showing the study area (Basin 5)
3.2 DATA COLLECTION Secondary data used in the research were from the Lakeside station which is an unfished area in the Sanyati basin. Experimental fishing data were for the period 2002 to 2012. Primary data were collected from two fishing villages in the Sanyati basin namely Nyaodza fishing village and Fothergill fishing village. Fishing effort has evolved differently between these two fishing
11 villages Due to limited resources the artisanal data were collected for 3 months during the winter period from May to July 2014.
Secondary data were from the experimental gill net sampling programme at Lakeside station for the period 2002 to 2012 inclusive. The fleet was set overnight from around 1700hrs to 0700hrs perpendicular to the shore with the smaller meshes inshore. In total the fleet has a total length of 550m. The data was stored in the Microsoft excel data base at LKFRI. The catch was grouped according to mesh size and for each specimen the following information was recorded; the species name, standard length (in centimetres), weight (in grams), sex and maturity stage.
Primary data were collected from two fishing camps/villages in the inshore artisanal fishery, namely Nyaodza and Fothergill. Both fishing camps are in the Sanyati Basin. The data from the fishing camps were collected for 6 consecutive days each month during the 2014 winter period from May to July using Catch return forms. These catch return forms provided for the recording of the following information; date, mesh size, number of nets used, fish species, number of fish caught and weight of each species caught. Data recording was done every morning from around 0600hours to 1000hours at the landing sites and weighing of fish was done using a spring balance weighing scale and a digital weighing scale.
3.2 DATA ANALYSIS To determine the commonness or contribution of each species in the experimental fishing, the index of relative importance (%IRI) was used. %IRI was calculated using the following formula:
IRI= (%weight+%number)*%frequency (Kolding and Karenge, 1995)
Catch for the experimental fishing was calculated by summing up the landings for each year while catch in the artisanal fishery was determined by adding up landings for the sampling period.
Fishing effort in the experimental fishing was determined by counting the number of nets set per each year multiplied by 45m (standard length of nets used in the experimental gill netting programme in Lake Kariba) and for the artisanal fishery it was also calculated by counting the number of gill nets used multiplied by 100m (each net in the artisanal fishery has a maximum length of 100m).
CPUE was determined by dividing total catch by total effort.
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A Shapiro Wilk test was used to test data for normality and data were normally distributed. An analysis of variance (ANOVA) was then conducted to test for significant difference in catch, effort and CPUE in the experimental fishing. Means for catch and effort were compared using a Tukey posthoc. In comparing the catch rates (CPUE) for Nyaodza and Fothergill fishing villages a parametric ( t test ) was used. All comparisons were conducted at a 95% level of significance. All analyses were done in the Statistical Package for Social Sciences (SPSS) version 21.
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CHAPTER FOUR
RESULTS
4.1 SPECIES RECORDED Table 4.1 : Species recorded during the study period. Those with an asterisk indicate species recorded in the artisanal fishery while the rest of the species were recorded at both Lake Side station and in the artisanal fishery. [Source Lake Kariba Fisheries Research Institute (LKFRI) data base]
Family Scientific name Common name Characidae Brycinus imberi Imberi Hydrocynus vittatus Tiger Fish * Clariidae Clarias gariepinus Sharp tooth catfish * Heterobronchus longifilis Vundu * Cyprinidae Labeo altivelis Hunyani Salmon (Mudsucker) Labeo cylindricus Red eye Labeobarbus marequensis Lowveld large scale yellow fish Cichlidae Oreochromis mortimeri Kariba bream * Sagochromis codringtonii Copper Bream * Oreochromis macrochir Green Bream Tilapia rendali Red breasted bream * Serranochromis Purple Bream macrocephalus Oreochromis niloticus Nile Tilapia * Mochokidae Synodontis zambezensis Squeaker * Synodontis nebulosus Spotted Squeaker Schilbeidae Schilbe intermedius Silver Barbel Mormyridae Mormyrops anguilloides Cornish Jack * Mormyrus longirostris Bottle Fish * Marcusenius macrolepidotus Bull Dog Cyphomyrus dischorhynchus Parrot Fish Distichodontidae Distichodus schenga Chessa
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The results show that 22 fish species were recorded in the experimental fishing while 10 species were recorded in the artisanal fishery.
4.2.1 CATCH IN EXPERIMENTAL FISHING There was a significant difference in catch from 2002 to 2012 (F=4.261, df=10, p=0.002). Catch in the experimental fishing fluctuated throughout the study period. There was a sharp increase from mean catch of 135.53kg in 2002 to a mean catch of 854.94kg in 2003 followed by a general decline up to a mean catch of 122.41kg in 2012.
CATCH IN THE EXPERIMENTAL FISHING
1000 bc abc
800
600 abc 400 ab CATCH abc
CATCH(kg) ac a a ac a 200 a
0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 200 YEAR
FIG 4. 1: Trends in catch (kg/year) in the experimental fishing from 2002 to 2012. Significant differences are indicated by different letters (p<0.05, Tukey posthoc). Data are means with SE. 4.2.3 EFFORT Effort fluctuated during the study. However, an increase was observed from a mean effort of 2 800m in 2002 to 4 500m in 2012. Peak effort of 19 733m was recorded in 2003. This is shown in FIG 4.2.
15
EFFORT IN EXPERIMENTAL FISHING 25000 bc 20000 bc
15000
abc 10000 ac a ac
EFFORT (m) a a a 5000 ac a
0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
5000 YEAR
FIG 4. 2: Trends in effort in the experimental fishing at Lake Side station from 2002 to 2012. Significant differences are shown by different letters (p<0.05, Tukey posthoc) 4.2.4 CATCH PER UNIT EFFORT
CPUE IN EXPERIMENTAL FISHING 8 7 6 5 4 3
CPUE(kg/100m) 2 1 0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 YEAR
FIG 4. 3: Trends in CPUE in the experimental fishing from the period 2002 to 2012 The CPUE for the experimental fishery fluctuated throughout the study period with an increasing trend from 2002 to 2004 and 2007 to 2009 while decreasing trends were observed
16 from 2004 to 2007 and 2009 to 2012. There was no significant difference among the years (p=0.086)
4.2.5 SPECIES COMPOSITION Table 4.2: Species abundance in the Experimental fishing for the period 2002 to 2012. [Source LKFRI data base]
Family Scientific Name Number %IRI Characidae Brycinus imberi 269 0.07 Hydrocynus vittatus 9019 29.82 Clariidae Clarias gariepinus 404 1.34 Heterobronchus longifilis 12 0.00 Cyprinidae Labeo altivelis 49 0.01 Labeo cylindricus 8 0.00 Labeobarbus marequensis 2 0.00 Cichlidae Oreochromis mortimeri 20 0.00 Sagochromis codringtonii 4442 24.47 Oreochromis macrochir 3 0.00 Tilapia rendali 258 0.19 Serranochromis macrocephalus 557 0.64 Pseudocrenilabrus philander 1 0.00 Oreochromis niloticus 576 1.47 Mochokidae Synodontis zambezensis 9973 36.34 Synodontis nebulosus 26 0.00 Schilbeidae Schilbe intermedius 802 0.69 Mormyridae Mormyrops anguilloides 149 0.33 Mormyrus longirostris 295 0.87 Marcusenius macrolepidotus 2759 3.56 Cyphomyrus dischorhynchus 386 0.18 Distichodontidae Distichodus schenga 16 0.00
17
The table reveals that S. zambezensis is the dominant species at Lake Side station followed by H. vittatus while S. codringtonii is the 3 rd dominant species.
4.3 ARTISANAL FISHERY Table4.3 : Comparison of CPUE for Nyaodza and Fothergill fishing villages
FISH MEAN CPUE ±SE t p MONTH VILAGE (kg/100m)
May Fothergill 6.887 0.248 1.573 0.76
Nyaodza 8.4348 1.005
June Fothergill 5.1596 0.6260 1.279 0.257
Nyaodza 7.3184 1.3982
July Fothergill 2.8026 0.420397 4.462 0.007
Nyaodza 7.2142 0.63134
There was no significant difference in CPUE between Fothergill and Nyaodza fishing both in May and June (P˃0.05). However, there was a significant difference in CPUE between the two fishing villages in July (P˂0.05).
Table 4. 4 shows the exotic O. niloticus as the dominant fish species in the artisanal fishery having 50.03% at Nyaodza and just over 56 % in terms of number at Fothergill fishing village. T. rendali is the second dominant species at both sites contributing 31.79% at Nyaodza fishing village while it contributed 20.66% at Fothergill fishing village. The native O. mortimeri and S. codringtonii appeared as the 3 rd and 4 th dominant fish species at both sites respectively.
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Table 4.4 : Species contribution between Nyaodza and Fothergill fishing villages
NYAODZA FISHING FOTHERGILL FISHING VILLAGE VILLAGE SPECIES NUMBER % NUMBER NUMBER % NUMBER D. schenga 0 0 1 0.03 C. gariepinus 479 3.63 18 0.47 H. longifilis 1 0.01 3 0.08 M. longirostris 57 0.43 3 0.08 M. anguilloides 36 0.27 5 0.13 H. vittatus 355 2.69 43 1.12 S. zambezensis 248 1.88 104 2.71 O. mortimeri 545 4.13 256 6.66 T. rendalli 4198 31.79 794 20.66 S. codringtonii 457 3.46 221 5.75 O. niloticus 6606 50.03 2210 57.51 Other Bream 151 1.14 174 4.53 Other Fish 71 0.54 11 0.29
In Table 4.4 above, other bream refer to those cichlids which had their names not included in the catch return forms but were observed during the study period. Other fish refer to fish species other than cichlids which didn’t have their names on the catch return forms
19
CHAPTER FIVE
DISCUSSION
5.1 EXPERIMENTAL FISHING
5.1.1 CATCH Catch fluctuated during the study period. Initially the catch was very low followed by a sudden sharp increase in 2003. From 2003 catch followed a general decline up to 2008 and then it fluctuated until 2012 (Fig 4.1). The observed trends in catch are almost similar to those followed by effort during the study period. Since the Lakeside is not open to commercial fishing, it is likely that fishing effort will influence catch in the experimental gill netting programme. Significant differences were observed in mean catch among the years from 2002 to 2012. These changes can be attributed to changes in fishing effort in experimental fishing. According to Ndebele Murisa et al . (2011) catches in Lake Kariba seem to be affected by climate and fluctuations in the Lake levels. They concluded that the increase in water temperature and the increase in evaporation rates and the experienced droughts around Lake Kariba area are the causes of the observed decline in catches. However, Marshall, (2012) has refuted these claims arguing that there is little evidence to suggest that climate change has negatively impacted inshore fishery of Lake Kariba. Rather he noted that there is strong evidence to suggest that fishing has a negative impact on the inshore fish stock. This is unlikely so since the Lakeside is not open to commercial fishery and hence fishing pressure is not likely to affect or cause a decline in the catches at Lakeside station as it has also been noted by the FAO, (2003) that the Zimbabwean experimental fishing programme is not affected by fishing pressure. The observed fluctuations and the decline in catches are probably as a result of decline and fluctuations in fishing effort in the experimental fishing.
5.1.2 EFFORT Effort also fluctuated during the study period. A significant difference as indicated by different letters in (Fig 4.2) was observed among the years (p<0.05). The differences among the years and the decline in effort are likely to be as a result of the availability of resources for carrying out the experimental gill netting programme. Sometimes nets may get torn by crocodiles as they feed on fish caught in the gill nets and replacing these may take time due to lack of money to purchase new ones and this may result in decline in effort. Lack of fuel and also transport to go and set the nets may also cause a decline in effort in experimental gill netting programme.
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5.2 CATCH PER UNIT EFFORT (CPUE) Although CPUE fluctuated during the study period (Fig 4.3) unlike catch and effort, there was no significant difference observed among the years (p>0.05). Generally, fluctuations in CPUE in all fisheries are expected just as fluctuations in catch and effort as highlighted by the FAO, (2003). Fluctuations in cpue have also been observed in the experimental fishing by Musando, (1996) and the FAO, (2003). Although fluctuations were observed in these studies, a declining trend was observed in the Zambian waters while an increasing trend was observed at Lakeside in the Zimbabwean waters. In this study, fluctuations were observed but with a declining trend with initial CPUE of 3.2kg/100m in 2002 and a CPUE of 2.67kg/100m (Fig 4.3). According to Musando, (1996) the decline in CPUE in the Zambian waters was due to fishing pressure since the experimental gill netting programme of Zambia is carried out in areas open to commercial fishing.
In the studies by Musando, (1996); Songore, (2002), FAO, (2003) and Karenge and Kolding, (1995) the experimental gill netting catches on the Zimbabwean side were dominated by lager species ( H. vittatus , and the Cichlids) which could have contributed to a higher CPUE compared to the Zambian side CPUE which is generally lower than the Zimbabwean CPUE. They attributed the increasing trend in CPUE to the dominance of H. vittatus and little fishing pressure on the Zimbabwean side. The decrease in CPUE as observed in this study maybe as a result of the decrease in the abundance of the H. vittatus (Table 4.2) which is a large species and the increase in S. zambezensis which is a smaller species and is very light in weight. However, the decrease in CPUE at Lakeside was also observed by Songore, (2002) from 1960 to 2001 and yet H. vittatus was still the most dominant fish species at Lakeside.
According to Karenge and Kolding, (1995) production in Lake Kariba is influenced by hydrological regimes (fluctuations in Lake Levels). Fluctuations in CPUE are probably a result of fluctuations in Lake Levels. Fluctuating fishing effort is unlikely to have caused fluctuations in CPUE as fishing pressure does not seem to affect inshore fish stock at Lake Side station since no commercial fishing is done at Lake Side station. According to Ndebele Murisa et al , (2011) the continued increase in temperature and climate change have a negative impact on catch rates in Lake Kariba. However, climate change is not probably the cause of fluctuations in CPUE at Lake Side station because in their study Ndebele Murisa et al , (2011) pointed out that temperatures have continued to rise and so the catch rates are expected to decline or continue to decline. This is not the case with the CPUE at Lake Side station as it did not show
21 a significant (Fig 4.3) decline but rather it keeps fluctuating which is likely to be as a result of fluctuations in Lake Levels.
5.3 SPECIES ABUNDANCE The catches were dominated by the Mochokidae family having just a percentage Index of Relative Importance (IRI) of 36% largely represented by S. zambezensis (Table 4.2) followed by Characidae family with just less than 30%IRI mainly composed of H. vittatus and the third dominant family being the Cichlidae having just less than 27% IRI largely composed of S. codringtonii and O. nitloticus . The contribution of species by family is similar to the findings by Musando, (1996) who observed the Mochokidae (29%IRI) as the dominant family followed by Characidae (28%IRI) and the third dominant fish family being the Cichlidae (23% IRI)
At species level the most dominant species was Synodontis zambezensis followed by Hydrocynus vittatus while the 3rd dominant species was S codringtonii (Table 4.2). The dominance of S. zambezensis in this study taking over from H. vittatus is similar to observations by Musando, (1996) who concluded that that S. zambezensis was now the dominant inshore fish species in the experimental gill netting programme in the Zambian waters.
In addition, Sanyanga, (1995) also established that S. zambezensis was the dominant inshore fish species on the Zimbabwean side of the Lake. She attributed this to the fact that this species lacks a predator due to its defensive mechanism (having some spikes which deter carnivores such as the H vittatus (Sanyanga, 1997). In addition, she adds that S zambezensis is not commercially important and so is not affected by fishing pressure and also the species does not have a strict diet and this helps it to establish it population in the Lake (Sanyanga, 1997). H vittatus which has always been the dominant species (Karenge and Kolding, 1995; Kenmuir, 1984) has declined in abundance and this is likely to be as a result of fishing pressure especially in breeding areas such as river mouths by artisanal fishermen as they try to raise their catches. It has also been observed that the population of H vittatus commonly known as tiger fish is influenced by the abundance of Limnothrisa miodon (L miodon ) commonly known as kapenta. This is because L miodon constitutes over 50% of the food consumed by the tiger fish. The decline in kapenta catches as highlighted by Ndebele Murisa et al., (2011) could be the cause of the decline in the abundance of H vittatus. The dominance of S. zambezensis taking over from H. vittatus could simply be as a result of the natural succession process of Lake Kariba. This is likely so because Musando, (1996) established that S. zambezensis was the dominant species in the Zambian experimental gillnetting programme which is carried out in areas open
22 to commercial fishing and on the Zimbabwean side it is now the dominant species and yet the Lakeside is not open to commercial fishing.
Among the Cichlids, S. codringtonii appeared as the dominant species contributing 24.47%IRI of the total species recorded. Using Lakeside data Songore, (2002) also highlighted that S. codringtonii continued to increase in abundance taking over from O. mortimeri as the dominant species. He attributed this to the fact that S. codringtonii is a mouth brooder and so it protects its young ones from predation and harsh conditions which enhances its population.
The rest of the species contributed % IRI of less than 2. However, it of interest to note that the native Oreochromis mortimeri (O mortimeri ) which used to be the dominant cichlid in the Lake (Kenmuir, 1984) has declined contributing a 0.00%IRI while the introduced Oreochromis niloticus (O niloticus ) has increased in abundance contributing just below 2%IRI in the catches at Lake side station. The decline in the contribution of the O mortimeri has confirmed predictions by Chifamba, (1998) who argued that O mortimeri and the introduced O niloticus share the same niche and yet O niloticus has a fast growth rate (Mhlanga, 2000; Chifamba, 1998) and this gives it competitive advantage and this leads to the displacement of the native O mortimeri by O niloticus . It has also been noted by Songore, (2002) that O. niloticus has a negative relationship with O. mortimeri and this could cause a decline in abundance of O. mortimeri while O. niloticus increases.
5.2 ARTISANAL FISHERY
5.2.1 CPUE The results obtained in the artisanal fishery showed that there was no significant difference in the CPUE between the two fishing villages during the May June period. This is probably due to similarity in the gear used in the fishery and some similarity in gear setting. This is likely so because the 2011 Lake Kariba Frame survey concluded that the artisanal fishery in Lake Kariba is conducted by well experienced fishermen who have been in the fishing industry for many years and uses experience gained to target certain species of commercial importance. This also serves to explain the similarity in the catch composition. However, for July there was a significant difference in the CPUE between the two fishing villages. The significant difference in CPUE during the month of July is probably as a result of pre landing sales by fishermen as buyers also patrol the fothergill fishing grounds very often compared to Nyaodza fishing ground, (Mavuru A, as per observation). This is likely so because the CPUE has a declining trend from May and July happens to have the lowest mean CPUE and for this reason pre
23 landing sales would have increased as buyers may have tried to evade competition at the landing sites.
It is also interesting to note that according to the Lake Kariba Fisheries Research Institute statistical report of 1997, CPUE for Nyaodza fluctuated during the period 1987 to 1997 but with an increase observed. The peak CPUE was 7.93kg/100m in 1991 while the last recorded CPUE in 1997 was at 6.06kg/100m. Comparing with the obtained CPUE for Nyaodza fishing village there hasn’t been much change (Table 4.3). For Nyaodza fishing village, the LKFRI statistical report for 1991 showed an increasing trend in terms of CPUE with CPUE of 6.2lg/100m recorded in 1988 and a CPUE of 6.53kg/100m recorded in 1991. Peak CPUE of 7.07kg/100m for Fothergill fishing village was recorded in 1989. The catch per unit effort obtained for Fothergill fishing village varied between 6.88kg/100m in May to 2.8kg/100m in July (Table 4.3). Although it shows a declining trend during the study period but it hasn’t changed much comparing with the figures given above obtained from the LKFRI statistical reports. The CPUE has not changed much probably because effort has not continued to increase but rather it has decreased as noted by the Lake Kariba Frame Survey, (2011).
5.2.2 SPECIES COMPOSITION 9 fish species were recorded at Nyaodza while 10 fish species were recorded at Fothergill fishing village. The bream (cichlid) family dominated the catches at both sites largely constituting of the introduced O. niloticus , T. rendali , the indigenous O. mortimeri and S. codringtonii . The dominance by the cichlids in the artisanal fishery might be as a result of target fishing by the fishermen. This is because the fishermen target certain species which are of commercial importance and these happen to be the bream family (Donnelly, 1971; Kolding et al. 2003). The characids were represented by H. vittatus while S. zambezensis represented the mochokids family. Under the Mormyridae M. longirostris and M. anguilloides were recorded. At species level, the exotic Nile Tilapia appeared as the dominant fish species. Previous studies have noted the indigenous Kariba Bream as the dominant and most important fish species in the artisanal fishery of the Sanyati basin of Lake Kariba (Songore et al . 1998). This study observed O. niloticus as the dominant and most important fish species in the artisanal fishery while the catches of the Local Kariba Bream have declined. This dominance of the exotic O. niloticus was predicted by Chifamba (2006) who proposed that O. niloticus would displace the Kariba Bream where these two coexist. The dominance of O. niloticus over O. mortimeri is probably because the two species share the same niche and yet the exotic O. niloticus is said to have a high growth rate and other competitive advantage over the native O.
24 mortimeri (Chifamba, 2006). These two compete for both food and habitat and yet exotic species generally are physically adapted to their environment and this makes O. niloticus a better competitor than the native Kariba Bream.
25
CHAPTER SIX
6.1 CONCLUSIONS Catch in the experimental fishing fluctuated but with a declining trend. The changes in catch are likely to be as a result of changes in effort since Lakeside is closed to commercial fishing. Effort also followed a similar trend with catch. Fluctuations in effort are probably as a result of the availability of resources and man power in the setting of gill nets in the experimental fishing programme. Catch per unit effort (CPUE) also fluctuated during the study period but there was no significant difference observed among the years from 2002 to 2012. However, CPUE showed a slight decline during the study period. A declining CPUE was also noted by Musando, (1996) on the Zambian side and Songore, (2002) in the experimental gill netting programme on the Zimbabwean side. The decline in CPUE is probably as a result of the dominance of the smaller species S. zambezensis .
The Mochokid S. zambezensis appeared as the dominant inshore fish species at Lakeside contributing 36%IRI. Its dominance is likely to be as a result of the natural succession of the Lake.
There was no significant difference in CPUE found between Nyaodza and Fothergill fishing villages for May and June but this is probably due to the fact that most of the fishermen for both fishing villages are experienced and so they use their experience to target certain fishes of economic importance especially the Cichlids. This is likely so as catches of both fishing villages were dominated by the exotic O. niloticus . However, a significant difference was observed between the two fishing villages in July and this might be as a result of difference in fishing intensity between the two fishing villages.
6.2 RECOMMENDATIONS As has been noted by other scholars (for example, Songore, 2002; Karenge and Kolding 1995) the Lakeside is not a true representative of Lake Kariba since it is closed to commercial fishing. This can also be confirmed by the difference in the Species composition obtained although sampling intensity might affect. I recommend that the experimental gill netting be conducted both in the areas open to fishing and areas closed to fishing so that true trends can be observed. There is also need to encourage or allow the use of small mesh sizes in artisanal fishery so as to avoid selective fishing since other small fish types such as Synodontis zambezensis are avoided in larger mesh sizes.
26
REFERENCES Begg.W.G, (1970) Limnological observations on Lake Kariba during 1967 with emphasis on some special features . Rhodesia: DNPWM
Chifamba P. C. (1998) Status of Oreochromis niloticus in Lake Kariba, Zimbabwe following its escape from fish farms. In: Stocking and introduction of fish . (ed Cowx I G) pp. 267 273. Fishing News Books.
Chifamba, P.C. (2006) Spatial and historical changes of indigenous O. mortimeri following introduction of exotic O. niloticus in Lake Kariba Proceedings of the 11th World Lakes Conference, Nairobi, Kenya, 31 October to 4th November 2005. Proceedings volume 2
Donnelly B. G, (1971) The Fish Population Changes in Lake Kariba Between 1960 and 1968. Part 2. Characidae and Cithrinidae. Lake Kariba Fish. Inst. PROJ. Report
FAO (1991): FAO year book fisheries statistic catches and landing 1989, fisheries series 36 and FAO Statistic Series 68. Rome: FAO.
FAO (2003) Management, co-management or no management? Major dilemmas in southern African freshwater fisheries . Rome: FAO
FAO, (2014) The State of the World Fisheries and Aquaculture opportunities and challenges. Rome:FAO
Ibrahim B.U, Auta J, Balogun J.K, (2009) A Survey of the Artisanal Fisheries of Kontagora Reservoir, Niger State, Nigeria. Bayero Journal of Pure and Applied Sciences , 2(1 ): 47 51
Karenge L. P and Kolding J (1995) Inshore fish population changes in Lake Kariba, Zimbabwe. In: Pitcher TJ and Hart PJB (eds) Impact of Species Changes in African lakes . London: Chapman and Hall. pp. 245–275
Karenge L, M. Mugwagwa M and Muchabaiwa L.D, (1995) 1994 Fisheries Statistic Lake Kariba Zimbabwe Shore. PROJECT REPORT NO. 82: ZPWMA
Kenmuir, D.H.S. (1984) Fish population changes in the Sanyati basin, Lake Kariba, Zimbabwe, S. Afr. J. Zool ., 19 , 3:194 209.
Kolding S, Musando. B,and Songore. N (2003) Inshore fisheries and fish population changes in Lake Kariba .Rome: FAO
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Kolding. J; Songore. N; Nagelkerke. L.K; Zwieten P. A (2012) Diversity, disturbance and succession in the fish community of Lake Kariba, Zimbabwe, from 1960 to 2001. Presentation at LKFRI; 17 November 2012
Lake Kariba Frame Survey, (2011) Zimbabwe Lake Kariba Fisheries Frame Survey Report. (Unpublished)
Marshall B.E, (2012) Does climate change really explain changes in the fisheries productivity of Lake Kariba (Zambia Zimbabwe)?, Transactions of the Royal Society of South Africa , 67:1, 45 51
Mbewe M, Mweemba J, Habulembe I, (2011) Catch Assessment Survey for Kariba, Kafue and Itezhi Tezhi. Zambia: Department of Fisheries.
Mhlanga, W (2000) An assessment of the fish population of the lower reaches of the Sanyati River, Zimbabwe. African Journal of Aquatic Science , 25 : 84–88
Mhlanga, W and Mhlanga, L. (2014) Cross-commons interactions of fish resources in Lake Kariba . In Mhlanga, L; Nyikahadzoi, K; Haller, T. (Eds). Fragmentation of natural resources management: Experiences from Lake Kariba. PLAAS & Lit Verlag. Zurich and Berlin (ISBN 978 3 643 90400 3). www.lit verlag.ch. Pages 65 – 89.
Musando B, (1996) Inshore Fish Population Changes in the Zambian Waters of Lake Kariba form 1980 to 1995. MPhil Thesis. Department of Fisheries and Marine Biology. Norway: University of Bergen
Ndebele Murisa M. R, Mashonjowa E and Hill T, (2011) The implications of a changing climate on the Kapenta fish stocks of Lake Kariba, Zimbabwe, Transactions of the Royal Society of South Africa . 66(2 ), 00–100
Sanyanga, R. A (1996) Variations in abundance of Synodontis (Pisces: Mochokidae) Peters 1852 in the inshore fishery of Lake Kariba. Elservier- Fisheries Research 26 , issue 1 2 pp 171 186
Sanyanga, R. A (1997) Food composition and selectivity of Synodontis zambezensis (Pisces: Mochokidae) in Lake Kariba and the ecological implications. Hydrobiologia. 361, issue 1 3 pp 89 99
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Songore N, (2002) The Fish Population Changes in Lake Kariba between 1960 and 2001. MPhil Thesis. Department of Fisheries and Marine Biology. Norway: University of Bergen.
Songore, N. and Kolding, J. (2003) Diversity, disturbance, and ecological succession of the inshore fish populations in Lake Kariba, Zimbabwe from 1960 to 2000. Paper presented for The Linnean Society of London Symposium on the use of long term databases for the prediction of ecological change.
Songore, N ; Moyo A and Mugwagwa M.(1998) 1998 Fisheries Statistics Lake Kariba Zimbabwean shore. PROJECT REPORT No. 95: ZPWMA
Zengeya T. A & Marshall B. E, (2008) The inshore fish community of Lake Kariba half a century after its creation: what happened to the Upper Zambezi species invasion?, African Journal of Aquatic Science , 33 :1, 99 102
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