Fish populations, gill net selectivity, and artisanal fisheries in the Okavango River, Namibia

106 Pages·2010·9.46 MB·English

Fishp opulationgsi,l in ets electivity,
anda rtisanafli sheriesin
theO kavangRo iverN, amibia
Recommendationfso r a sustainablefi shery
C.J. Hay, T.F. Næsje, J. Breistein, K. Hårsaker,
J. Kolding, O.T. Sandlund, and B. v. Zyl
Y1: .
NINA(cid:127)NIKU Project Report no. 010
Directorate Resource Management Norwegian institute for Nature Research
Ministry of Fisheries and Marine Resources Tungasletta 2
Private Bag 13 355 Windhoek N-7485 Trondhelm
Namibla Norway
Fishp opulationsg, ill net selectivity,
anda rtisanafl isheriesi n
the OkavangoR iver,N amibia
Recommendationfos r a sustainablefi shery
C.J. Hay, T.F. Næsje, J. Breistein, K. Hårsaker,
J. Kolding, O.T. Sandlund, and B. v. Zyl
Ministry of Fisheries and Marine Resources, Namibia
Foundation for Nature Research and Cultural Heritage Research, Norway
nina.niku Project Report 010
Hay, C.J., Næsje, T.F., Breistein, J., Hårsaker,K ., Kolding,
Norwegian Institute for Nature Research (NINA) and
Sandlund,O .T. & van Zyl, B. 2000. Fish populations, gill net
Norwegian Institute for Cultural Heritage Research
selectivity, and artisanal fisheries in the Okavango River,
(NIKU) issue the following publications in English:
Namibia.R ecommendationsfo r a sustainablef ishery. — NINA-
NIKUP rojectR eport 010: 1-105.
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Managementf ield:
Fish,s ustainablee xploitation
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Preface
The White Paper «ResponsibleM anagement of the May, A. Mulundu, S. Beukes, the late S. Pootinu, S.
Inland Fisherieso f Namibia» was finalised in December Jonas, A. Kahuika, S. Shefeni, the late E. Shivanus, E.
1995, and forms the basisf or a new law and regulations Shikambe,E . Kahuika,t he late F. Fillipus,E . Hayango, N.
concerning fish resourcesm anagement in the different Lukas, B. May, and N. Naftali. They are all gratefully
freshwater systems in Namibia. The Okavango River is ackowlegded.
one of the most important of the perennial rivers, and
freshwater fish are a very irnportant food source for
local inhabitants. Hence,t he protection of this resource Windhoek/Trondheim,O ctober 2000
is of utmost importance to secure the future food
availability of the riparian population in this region of
Namibia. In this report management actions are recom-
mended on the basiso f eight years of biologicals tudies Clinton Hay
in the river, including survey fishing on seven different
localitiese veryy ear from 1992-99. Later reportsw ill give
recommendations for regulations of fisheries in the
other perennial riversi n Namibia. Tor F. Næsje
Our main objective has been to develop applicable
guidelines for regulations of the inland fisheries in the
Okavango River. This report will further enable the
Ministry of Fisheriesa nd Marine Resourcetso implement
the proposed law and regulations necessaryfo r sustain-
able management of the fish resourcesi n the river. The
recommended guidelines are presented in the last
chapter of the report.
In addition, a second goal of this report has been to
identify critical aspectsa nd needs for more knowledge
that should be addressed in future studies, and give
recommendations on how to obtain the necessary
information needed for future management of the
OkavangoR iver.
The project is a collaboration between FreshwaterF ish
Institute of the Ministry of Fisheries and Marine
Resources, and the Norwegian Institute for Nature
Research (NINA). The work has received economic
support from the Norwegian Agency for Development
Cooperation( NORADt)h rough the NansenP rogramme.
We would like to express our gratitude towards the
Director, ResourceM anagement, Dr. B. Oelofsen and
the Deputy Director, Resource Management, Dr. H.
Hamukuaya for their support and encouragement
during the project. We are also thankful to Prof. P.
Skelton and R. Bills from the JLB Smith Institute of
Ichthyologyi n Grahamstown,S outh Africa, who verified
the identification of the fish species, and to Prof. C.
Hocutt for fruitful deliberationsd uring the field surveys.
The Department of Water Affairs, Windhoek, provided
the water quality analysisa nd the water level data of
the OkavangoR iver.
The following staff members from the Institute were all
involved in the field surveys or data punching: J.H.
Koekemoer, the late W.A. Strauss, H. Kleynhans,T .N.
lilende, Ms. S. Hay, Ms. S. Stein, J.H. Engelbrecht,J.
3
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Contents
PREFACE 3 6 RECOMMENDEDM ANAGEMENTA CTIONS 100
6.1 Background 100
1 EXECUTIVES UMMARY 5 6.2 Management regulations 100
6.3 Biological studies 100
2 INTRODUCTION 9 6.4 Management actions 101
6.4.1 Management actions for immediate
3 STUDYA REA 11 implementation 101
3.1 General features 11 6.4.2 Management actions for future
3.2 Gill net stations 20 consideration 102
3.2.1 Matava 20 6.5 Future researchp rogrammes 103
3.2.2 Musese 21
3.2.3 Bunya 21 7 REFERENCES 104
3.2.4 Rundu 22
3.2.5 Cuito 23 APPENDIX 105
3.2.6 Mbambi 23
3.2.7 Kwetze. 24
4 LOCALF ISHERIES 26
4.1 Background 26
4.2 Surveyso n catch in local fisheries 26
4.2.1 Material and methods 26
4.2.2 Fishings easonsa nd gears in local
fisheries 26
4.2.3 Catchesi n local fisheries 26
4.3 Questionaire on fisheries 27
5 FISHS URVEY 30
5.1 Sampling design and methods 30
5.2 Data collection and treatment 31
5.2.1 Biologicald ata 31
5.2.2 Catch per unit effort 32
5.2.3 Speciesd ominance in survey
catches 32
5.2.4 Gill net selectivity 33
5.2.5 Databasesa nd software 33
5.3 Results 33
5.3.1 Speciesi n gill net catches 33
5.3.2 Speciesi n catches with other gears35
5.3.3 Surveyc atches vs. local fishery 35
5.3.4 Body length distributions in gears 37
5.3.5 Body length of mature fish 37
5.3.6 Life history and gill net selectivit
for selecteds pecies 39
5.3.7 Angling species in the Okavango
River:l ife history and gill net
selectivity 67
5.3.8 Summaryo f gill net selectivity 80
5.4 Differences among localities 84
5.4.1 Catch per unit effort at different
stations and river zones 84
5.4.2 Catch per unit effort in different giii
net mesh sizes 86
5.4.3 Variation in catch within species 93
5.4.4 Fishs izea t different stations 93
5.4.5 Fishs peciesc omposition 95
4
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River, the annual discharge nearly doubles to over
1 ExecutiveS ummary
10,000m illion rn3.
Hay,C .J.,N æsje,T .F.,B reistein,J ., HårsakerK, ., Kolding, More than 136,000p eoplel ive in the Okavangor egion.
J.,Sandlund,O .T. & van Zyl, B. 2000. Fishp opulations, An estimated9 0 % of the population live within 10 km
gill net selectivity, and artisanal fisheries in the of the river, and many of the economic and social
Okavango River, Namibia. Recommendationsfo r a activitiesi n the regiona re connectedt o the river. More
sustainablefi shery. —N INA-NIKUP rojectR eport0 10: 1- than 50 % of the human population along the river do
105. fish, both with traditional gearss uch as baskets,f unnel
traps and fencesc onstructedo f plant material,a nd with
Objective: some modern gearss uch as gill nets, seines,h ook and
The objectiveo f this report is to produceg uidelinesfo r a line, and mosquito-nets.F or more than 90 % of the
sustainable management of the fisheries in the householdsfi sh is a sourceo f subsistencea, nd saleso f
OkavangoR iver, Namibia,b ased on fish surveyd ata for fish provides omei ncomef or approximately4 5 % of the
the years 1992-1999. Data were also coHectedr e- householdsT. he highestp opulation density is at Rundu,
gardingt he subsistencefi shery in the river.T he rationale whereas no people live at Kwetze,w hich is within the
for the report is the 1995 White Paper "Responsible Mahongo Game Park. It is assumedt hat the fishing
Managemento f the Inland Fisherieso f Namibia" and pressureis correlatedt o the riparianp opulationd ensity.
the draft bill on inlandf isheries.T heseh avet he objectiv-
es of ensuring a sustainablea nd optimal utilisation of Results:
the freshwater resources,a nd to favour utilisation of Data on local fishing activitiesw ere collectedt hrough a
fish resourcesb y subsistenceh ouseholdso ver commer- surveyo f the gears( moderna nd traditional) used in the
cialisationT. he statedp olicyt akes into considerationth e subsistence fishery and interviews with fisherfolk
large differencesa mongw ater systemsin Namibiaa nd attending their gear in June 1994. This surveyr evealed
proposesa doption of separa te managementr egimesf or that the peak fishingt ime is during the receding phase
the variousr iver systems. of the flood and during low water periodsw hen the fish
are concentrated, i.e. from May onwards. There is
Material and study area: reduced fishing activity during the flood when large
Fish were collected in seven main areas (Matava, areasa long the river become inaccessiblefo r the sub-
Musese,B unya, Rundu,C uito, Mbambi, and Kwetze) sistencef ishers.A diversityo f traditional gears include,
with survey gill nets (22-150 mm stretched mesh) e.g., baited traps, corral traps, 'fish fences, scoop
and 16 other sampling methods, such as seine nets, baskets,f ish funnel, bow- and arrow, and fish spear.
mosquito nets, cast nets, angling, electrofishing Modern gears are mainly restricted to gill nets, used
apparatus, rotenone and different traditional gears. most often by men, and mosquito nets, a method used
These are later collectivelyc alled "other gears". The by women. Castsn ets were rarely used. A comparison
stations were selected to include all main habitats with earlier surveysr eveals that there is an overall
presenti n the OkavangoR iver.T he gill netsw ere mainly declinei n catchesi n subsistencefi sheriesf rom 1987 to
used in relatively deep water, whereast he other gears 1992. A socio-economics urvey in 1994 indicated that
were mainly used in shallowa nd vegetatedh abitats.A ll 56,000 people along the Namibian portion of the
seven localities were sampled at least once a year OkavangoR iverw ere fishing an averageo f 60 days per
between 1992 and 1999. A total of 47438 fishesw ere yearc atching 1,045t onnes.
sampled,1 3559 in gill nets,a nd 33879 in other gears.
In the surveyc atchesi n this investigationa total of 76
The OkavangoR ivero riginates in the central highlands fish speciesw ere recorded.G ill nets caught 47 of these
of Angola at approx. 1700 m a.s.l. and enters Namibia speciesw, hereasa ll speciesw ere recordedi n the other
at Katwitwi. The river forms the border between gears used mainly in shallow waters. These figures
Namibia and Angola before turning south towards include sevenSynodontisspeciesw hich are not easily
Botswana.A long the Namibian section of the river, separateda nd therfore have been pooled in the results.
there are large floodplainsw ith sandy substratesa nd In gill nets the ten most important speciesc onstituted
rocky outcrops, and abundant aquatic vegetation. After between 70 and 80 % of the catchesb oth by numbers
a distance of 460 km within Namibia, the river enters and weight. The three most important speciesi n gill net
Botswana where it evaporates in the swamps of the catchesa ccordingt o an index of relativei mportance( IRI)
OkavangoD elta. were silver catfish (Schilbe intermedius), bulldog
(Marcuseniusm acrolepidotus)and tigerfish(Hydrocynus
The annual flood in the Namibian portion of the vittatus).In the other gears, the ten most important
Okavango starts during December reachesi ts peak in speciesc onstituted approximately5 4 % and 37 % of
March-April and recedesd uring May. The annual dis- the total catch by numbersa nd weight, respectivelyT. he
chargeo f the Ol avangoa t Rundui s between5 ,000 and lower proportion of the dominant speciesr eflects the
6,000 million m . Belowt he confluencew ith the Cuito higher speciesd iversityi n catchesw ith other gears.T he
three most important speciesi n these gears, according
5
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to the IRI, were all cichlids; southern mouthbrooder Comparisono f fish catchesb etweent he sevens ampling
(Pseudocrenilabrupsh ilander), banded filapia (Tilapia localitiesr evealedt hat there was a correlationb etween
sparrmanii), and redbreast tilapia (T. rendalh). The humanp opulation densitya nd catches,b oth by weight
Synodontis group of speciesw as important both in gill and number of fish. The largest catchesw ere taken in
nets ando ther gears. the areas with the lowest population densities. This
correlationi s highly significantf or catchesi n kilograms.
The bodyl ength of fish caught in gill nets was generally For catches in number of fish, the trend was similar,
larger than fish caught in other gears. This is evident although not significant. The total gill net catches by
both in the combined catcheso f all speciesa nd when weight at Kwetze (3.76 kg per setting)w ere nearly five
comparing individual species.F ish caught in gill nets times as high as at Rundu, Bunya and Musese( 0.61-
were between4 and 79 cm in length, with fish between 0.68 kg per setting). Catches at Cuito, Matava and
7 and 17 cm constituting8 2.9 % of the catches.M odal Mbambiw ere intermediate,b ut considerablylo wer than
length was 9.0-9.9 cm. Fishc aught in other gearsw ere at Kwetze( 1.02-1.30k g per setting).T his indicatest hat
between 1 and 75 cm, with fish between 2 and 8 cm the fish stocks at Kwetze are relatively unexploited.
constituting8 8.0 % of the catches.M odal length in this These differences between stations were more
group was4 .0-4.9 cm. pronouncedi n the backwaterst han in the main stream
habitats. It is important to note, when evaluating the
The highest proportion of sexually mature fish was fish populationsa s a resourcef or subsistencefi sheries,
found during the periodJ anuary-March,i .e. during the that the most important factor is the biomass( weight)
peak of the rainy seasonT. his is before the main thrust of fish caught. In subsistencefi sheries,t he size of the
of the local fisheries. Most of the important species individualf ish is of less importance. In cornmercial or
(accordingto IRI)m aturea nd spawn during this period. recreationafli sheri-eso, n the other hand,t he sizeo f the
The smallests ize of sexuallym ature fish variesa mong individualf ish may be of great importance.
the different species. The overall smallest size at
maturity was found in the cichlid southern mouth- Betweent he different stations, differencesw ere larger
brooder (P.p hilander), being a mature female of 3 cm. when comparingc atchesi n the largerg ill net meshs izes
The largest size at maturity was found in sharptooth than in the smallero nes.C atchesi n smallm eshs izes( 22
catfish (C. gariepinus), with minimum sizeo f malesa nd and 28 mm) at Kwetze (1.12 kg and 56.8 fish per
femalesa t 40 and 38 cm, respectively. setting)w ere not very different from the other stations
(0.80-1.17k g and 70.6-72.8 fish perssetting)H. owever,
Basedo n their importancea ccording to number of fish the mean weight of the fish catAht in 22 and 28 mm
caught and IRI in gill nets, other gears, and local sub- mesh size at Kwetze were on average larger, 20 g
sistencef isheries,2 1 speciesw ere selectedf or a closer comparedw ith 10-13 g at the other stations. In the
description in terms of basic ecology and gill net larger meshedg ill nets (35-150 mm), differencesw ere
selectivity.I n addition, 16 speciesw ith the potential of more pronounced.K wetze had the highest catch both
being important for anglersa re also describedin these in weight and numberof fish (4.35 kg and 39.9 fish per
terms. setting),w hereas Runduh ad the lowest catch (0.57 kg
and 7.9 fish per setting).
The resultsc oncerningg ill net selectivitys how that for
most of the 21 importants pecies( in local fisheriesa nd Basedo n population densities,R undua nd Kwetze may
in the survey fishing), the highest number of fish per represent the extremes in fishing intensity in the
setting were caught in small mesh sizes( 22-45 mm, 15 OkavangoR iver,w ith closet o no fishing at Kwetze and
species)O. nly two speciesa re most efficientlyc aught in probably high exploitation rates at Rundu. These two
largerm eshs izes( 73 and 93 mm). In terms of weight of samplingl ocalitiesm ay therefore be used to exemplify
fish per setting, 11 speciesw ere most efficientlyc aught possibled ifferencesi n catchesd ue to fishing intensity.I n
in the 22-45 mm meshs izes,t wo speciesin 57 mm, and the smallest mesh sizes (22-28 mm) there were no
four speciesin 93-118 rnm.T hese resultsr eflectt hat the significant differences in catches by weight between
fish communityi n the Okavango Riveri s dominatecib y Rundua nd Kwetze( 0.8 and 1.1 kg, respectively)H. ow-
relatively small species and individuals. Among the ever, in larger mesh sizes( 35-150 mm) catches were
speciest hat are important in local fisherieso r in our severalt imes higher at Kwetze than at Rundu. In the
survey catches, only six out of 21 species have a largestm esh size( 150 mm) there was no catch at all at
minimumm ature lengtha bove 10 cm or are on average Rundu,w hereas the catch at Kwetze was 2.6 kg per
above 15 cm in the gill net catches.O nly two out of 21 setting.
speciesh ave mean lengthsa bove 20 cm in our survey
catches.M oreover,o nly seven out of the additional 16 Intensivef ishing and exploitation of fish populations
speciest hat are considereda ttractive angling species, may reduce the overall number of individualsw ithin a
have meanl engths above2 0 cm in the gill net catches. species.H owever,t he result of selectivef ishing aiming
This indicatest hat there presently is no firm basisf or a at relativelyl arge fish is often that the averages ize of
commerciafli shery for large fish in the Namibianp art of speciesa re reducedd ue to an increasingp roportion of
the OkavangoR iver. smallerf ish. For most of the relativelyl arge speciesi n
6
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the OkavangoR iver,c atchesi n weight were largest at (cid:127) Commercialisationo f the fish resources in the
Kwetze compared with the other stations. No such Okavango is not an economicallya nd ecologically
tendencyw as observedfo r the smalls peciesI.n terms of viable option. The limited fish resource should be
number of fish per setting, there was no systematic regardeds trictly as a source for a sustainables ub-
difference between Kwetze and the other stations, sistencef ishery utilised by the population along the
neitherf or large or smalls pecies.T hus,m eans izeo f fish OkavangoR iver.A ll traditional gearsm ay be allow-
is largera t Kwetzet han at the other stations. ed. Theseg earsa re an important part of the tradi-
tional life of local inhabitants.G ill nets and angling
The gill net mesh sizesu sed in this investigationw ere equipment (rods and reels) should be the only
chosent o obtain a representativec atch and size distri- moderng ear allowed.
bution of the fish populations. On average a larger (cid:127) Regulationo f the artisanal fishery by means of a
proportion of large fish were caught in gill nets at quota systemi s logisticallyim practicalA. more practi-
Kwetzet han at the other sampling localities.T his was cal systemb asedo n effort restrictionsb y means of
shown both in the total catches, and for many of the gear regulationsi s therefore recommended.R ecrea-
individual species sampled. Three examplesa re the tional and trophy fishing, however,m ay be regulated
commons peciess ilverc atfish, bulldog and tigerfish.T he through both quotasa nd gear restrictions.
largestf ish were caught at Kwetze, where mean fish (cid:127) Our results clearly show the value of sanctuaries
length in total gill net catchesw as 16.3 cm. The smallest where fishing is prohibited. Dependingo n their size
fish were caught at Rundu,w ith a mean length of 10.7 and position, sanctuaries may protect breeding
cm. Thet wo numericallyd ominant speciesin the gill net and/or feeding habitats for different species.T he
catches,s ilver catfish and bulldog, showed a similar protected areas may also serve as source areas,
pattern in length distribution among localities. Both where fish productionp rovidesa surplust hat migrat-
speciesa re largest at Kwetze and smallesta t Rundu. es out of the protected area and reinforce the
Thesed ifferencesa re reflected in the mean weight of exploited fish populations. In addition, given the
fish, which was highesta t Kwetze and lowest at Rundu appropriate regulations, sanctuaries may provide
(92 and 33 g respectively). excellent trophy fishing (e.g., catch-and-release)
attracting exclusivefi shing safarisc reating economic
Two species,s ilver catfish and bulldog, are among the activitiest o benefit local communities.
three most important species at all localities when (cid:127) No activitieso r gearss hould be allowed which may
rangingt he ten most important speciesa t each locality potentially pollute the environment. This includes
in terms of the index of relative importance( IRI)i n gill also explosives, noxious substances, poison or
net catches.S everals pecies,w hich were important or electrical devicess hould be allowed. Artificial light
commona t the unexploitedl ocality of Kwetze,w ere of during any fishinga ctivitiess hould not be allowed.
little importancea t the heavilyf ished localityo f Rundu. (cid:127) The recreational fishery should be licensed, and
Thesea re in particular African pike (Hepsetuso doe), specificr egulationsd eveloped.O rganiserso f angling
spotted squeaker (Synodontis nigromaculatus) and competitions must seek permission from the
dashtailb arb(Barbuspoechii).O ne large cichlids pecies, Ministry.
threespott ilapia(Oreocromisa ndersonii)is only found in
any significantn umbera t Kwetze. Management actions for future consideration:
Actions may dependo n further scientificr esearch,a nd
The recommendedm anagementa ctionsa re collaborationw ith local communitiesa nd neighbouring
summariseda s follows: countries.
(cid:127) The fish communityc onsistso f 76 speciese ach with (cid:127) The establishmenot f fish sanctuariesi n addition to
their specific ecology,f orming an integral part of a the Mahango Game Park should be considered.I n
complexa nd dynamice cosystemT. he exploitationo f this context, investigationsa bout the habitat use and
such a multi-speciesfi sh resources hould preferably migration patternso f riverine fish speciesa re need-
be performed non-selectively,i .e.; fish from all ed. Fishs anctuariesc ould be includedi n the already
trophic levelss houldb e caught in proportiont o their presentc ommunityc onservancies.
occurrencein the aquatice cosystemT. hisp rincipleo f (cid:127) Closed fishing seasonsc ould be implernented to
proportional exploitation forms the basis of our protect the fish population during vulnerable
managementr ecommendations. periods, for example when fish are congregated
(cid:127) The Okavango River is shared between Namibia, during spawning at low water dischargeo r during
Angola and Botswana. The present collaboration seasonaml igrations.
with neighbouringc ountries on managementi ssues (cid:127) Defineda reasf or specifica ctivities,s uch as areasf or
is limited, and the availableb iologicald ata from the fishing safaris and fishing competitions should be
sectionso f the river in Angola and Botswanai s very considered.
restricted.T he future aim should be to establisha (cid:127) The initiation of a community data collection pro-
management regime in close collaboration with gramme should be consideredt o increaset he fish
neighbouringc ountries. database.
7
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nina-nikuProject Report 010
(cid:127) Continuous international collaboration with neigh-
bouring countriess hould be given high priority.
In future researchp rogrammes,t he following is
recommended:
(cid:127) It is imperative that a modified monitoring pro-
grammeo f the river continues so that changesi n the
fish community may be identified and management
actions taken to reverse possible future adverse
effects.
(cid:127) The collection of data by the community for research
purposesh ave been done successfullye lsewhere in
Africa and should be considered in the Okavangot o
increaset he database for future stock assessment
studies.
(cid:127) The knowledge of fish behaviour, migration, and
area and habitat use, is limited. Resourcess hould be
allocated to conduct such studies. This is important
for the establishment of fish sanctuaries and to
dissolvec onflicts between the recreationala nd sub-
sistencef ishermen.
(cid:127) The socio-economicr ole of fish in the region should
be subject to ongoing studies to complement the
fisherya nd experimentald ata.
(cid:127) Namibiah as very little control over the management
of the Okavango watershed as the catchment area
falls within neighbouring countries. The Okavango
Riverm ust be managed as an entity and collabora-
tion with neighbouring countries is essential for
further improved management of the fish resources.
(cid:127) Where possible, comparable data sets from neigh-
bouring countries should be included in future
analysis.
8
© Norwegian institute for nature research (NINA) 2010 http://www.nina.no
Please contact NINA, NO-7485 TRONDHEIM, NORWAY for reproduction of tables, figures and other illustrations in this report.
nina-nikuProjectR eport0 10
2 Introduction as an essentialf ood source for the riparian human
population. Adaptive management will include moni-
toring programmes designed to ensure the local
Floodplainr ivers are among the most endangerede co- effectivenesos f the chosenm anagemenst trategies.
systems,a nd their faunasa re especiallyu nder threat of
speciese xtinction and population disturbance( Halls et In a perennial floodplain system, like the Namibian
al. 1999). Multi-speciesm ulti-gear floodplain and river portion of the OkavangoR iver,t he main river might be
fisheries have complex interactions between the regardeda s containingt he capital of the fishery,w hile
environment,t he fish communitiesa nd the fishers. the seasonal production in the floodplains and the
harvesto f fish in the main river constitutest he interest
As human populationsa nd levelso f incomer ise,s o does of that capital. Too heavy exploitation of the fish
the demandf or water for variousp urposesa, nd water is populationsi n the main river might reduce the overall
a commodity which limits development and human fish capital and thereby the interest and returns from
well-being in many parts of the world. With increasing that capital. As long as the capital of fish is good, the
demand for water for human activities,s uch as irriga- fish populations will provide a relatively stable food
tion, drinking water, power production, and flood supply.T herefore,r eliablea ssessmenatn d monitoring of
control, floodplains are increasinglyb eing modified on the status of the fish populations in the river are
both a large and smalls cale.F loodplainf ish production, necessarfyo r sustainablem anagemento f the resources
however, is dependent on the maintenance of the and a stablea nd optimal yield of fish.
natural functions of the floodplain system. Both the
"Code of Conduct for ResponsibleF isheries"a dopted Changesi n the ecosystem,in cluding destructiono f fish
by FAOC ommittee of Fisheries(1 995) and the Conven- habitats,r educedf loods, and new fishing methods,a re
tion on Biological Diversity (UNEP 1992) (ratified alteringt he fishery in the OkavangoR iver.M anagement
by more than 170 countries, including Namibia and regimes have changed from traditional and local to
Norway)a re concerneda bout the need for countriest o more centralised,a ccompaniedb y an erosion of local
manage their aquatic environment to maintain bio- checksa nd controls. Modern, more effective and de-
diversitya nd sustainablefi sheries. structive gears have been introduced, and the human
population along the river has increased.T hese ele-
The high speciesa nd habitat diversityo f floodplains is mentsa ll posea threat to the fish resources.
reflected in the complexityo f the fishery where many
different types of gearsa re used, both traditional and Previouse stimateso f maximum sustainabley ield (MSY)
modern. Often there are competitive interactions be- for the OkavangoR iver in Namibia based on different
tween different fishing gears.T he variousg earsi mpact methods have given figures between 840 and 3000
fish communities differently, and influence the distri- metric tonnes. The basis for these calculations is
bution of catches between fishers. A management dubious, as the available data and knowledge on
approachi ncluding, e.g., gear closuresa nd restrictions, complexf loodplain systemsa re not at all sufficient to
closeds easonsa, nd mesho r fish sizel imits may increase allow proper application of any MSY model (Sandlund
catchesi n some gears,a nd reduce catchesi n others. It and Tvedten 1992). Hence, neither the minimum nor
will also influence the distribution of catches and maximumf igure might be the correct one. Moreover,
incomea mong the fishersa nd in the local communities. the MSY concept itself has recently been rejecteda s a
Hence,w hen implementingm anagementr egulationsi n usefult ool in fisheriesm anagement( Hilborn & Walters
a fishery, it isimportant to identify those who have an 1992). The main reason is that MSY gives the false
interest or stake in the fishery. A descriptiono f stake- impressionth at a fixed and stable maximumo utput can
holders is essentiala s managemento f a fishery means be calculatedf or any fishery. In fact, a relativelyc orrect
managing human activities. Knowledge about stake- MSY value can only be calculated when serious
holders and relationships between different interest overfishing has already occurred (Hilborn & Walters
groups, such as subsistence,c ommercial, and sport 1992). lt, therefore, is necessaryt o develop adaptive
fishers,i s important to facilitate analysiso f the effects of managements ystems( Martin 1999) for fish stocks in
the implementedr egulations.A cceptanceo f regulations rivers and floodplains, based on monitoring data with
among stakeholdersi s essentialt o achievea successful important parameters such as community and stock
management. structures,l ife historieso f important speciesa, nd so on.
The highly variable ecologicala nd social characteristics In Namibiaf reshwater fish is a key food item for poor
of floodplain rivers often demand locally adapted people in the northern region of the country (Sandlund
managementr egimes.S uchc areful managemento f the and Tvedten 1992, Tvedten et al. 1994). As population
river systemsm ust be basedo n scientifica nd traditional growth and fishing activities increase, conflicts arise
knowledge,a nd includea n active and important role of between subsistencefi shery, commercialf isheries,a nd
local communities. It is important to maintain the recreationalf ishery. In addition, the perennial rivers of
cultural, economica nd social importanceo f riverine life Namibia,i ncludingt he OkavangoR iver,a re sharedw ith
and traditions, in addition to securings table fish yields
9
© Norwegian institute for nature research (NINA) 2010 http://www.nina.no
Please contact NINA, NO-7485 TRONDHEIM, NORWAY for reproduction of tables, figures and other illustrations in this report.