Biological basis of water quality assessment : the Kavango River, Namibia

Charles H. HOCUTT (l), Peter N. JOHNSON(l), Clinton HAY (2), Ben J. VAN ZYL (2)

ABSTRACT

The Kavango River rises in the central highlands of Angola, flows south to form a 415 km border befween Angola and Namibia, and then continues in a southerly direction another 65 km as the primary source of the Okavango Delta, Botswana. The central secfion of the river along the Namibialilngola border is a characteristic low-gradient floodplain system; annual floods approach 6 m above normal stage, with fhe floodplain sometimes exlending up 10 5 km across. The river is criticalto the daily living requirements of the Kavango people, most (85 %) of whom live within 10 km of the river at a subsistence levez. Given the prospects of population increase, water development] diversion projectst land reallocation programmes, alteration of land use pafterns and chronic drought, the Ministry of Fisheries and Marine Resources is developing baseline procedures 10 manage the system for the sustainable utilizaiion of its resources, upon which the indigenous people are either dirèctly or indirecfly dependent. In fhis regard, a concerted effort is being made 10 establish a water quality monitoring protocol for Namibian waters based on biological criteria. Instream biological criteria are a routine eomponent of water quality moniforing programs in developed coun- tries, but have been seldom utilized in less developed couniries. One method which has received favorable use over the pas1 10 years in North America and Europe is the Index of Biotic Integrity (IBI). The IBI relies on the structural and funcfional components of the fish communily as a repection of overall aquatic system “health”. A fish commu- nily assemblage data base obiained in 199.2 is ufilized 10 formulate the conceptual basis for an IBI for ihe Namibian portion of bhe Kavango cafchment. Limitations of the procedure are recognized, and recommendations are given for the establishment of a similar protocol in other sub-Saharan counfries. KEYWORDS: Rivers - Tropical - Quality index - Africa - Angola - Namibia.

RÉSUMÉ

CRITÈRESBIOLOGIQUES DE LA QUALITÉDE L'EAU : LE FLEUVEKAVANGO EN NAMIBIE Le fleuve Kavango prend sa source dans les hauts plateaux d’Angola,, se dirige vers le sud fornzant la fronfière Angola-Namibie sur 415 km de direction Ouest-Est, et coule ensuite vers le sud pendant 65 km avant de former le delta de 1’0kavango au Botswana. La portion moyenne de la rivière le long de la frontière es1 caractéristique des fleuves de faible pente des plaines d’inondation. Les crues sont d’environ 6 m au-dessus du niveau normal, avec un lit majeur de

(1) Coastal Ecology Research Laboratory Uniuersify of Maryland Easfern Shore Princess Anne, MD 21853, USA. (2) Freshwafer Fisheries Insfifufe Minisfry of Fisheries and Marine Resources Marienfal, Narnibia.

R~U.Hydrobiol. trop, 27 (4) : t361-.3S4(1994). 362 C. H. HOCUTT,P. N. JOHNSON,C. HAY, B. J. VAN ZYL

5 km de large. Le fleuve est vital pour les populations locales dont 85 % vive& à moins de 10 km du fleuve. Compte tenu des prévisions d’accroissemenf de la population, des besoins en eau, des programmes de redistribution des terres, de l’évolution des pratiques agricoles ef d’une sécheresse chronique, le ministère des Pêches et des Ressources marines prépare les bases d’une gestion durable des ressources dont les populations locales sont directement dépendantes. Clest dans ce cadre q’une recherche a été mise en place pour définir un protocole de suivi de la qualifè des eaux en Namibie, protocole basé sur des critères biologiques. L’utilisation de critères biologiques pour suivre la qualité des cours des rivières dans les pays tempér& est commune. C’est moins le cas pour les pays tropicaus. L’indice d’inlègrité biologique (IBI) est utilisé depuis plus de 10 ans en Europe et en Amérique du Nord. Il permet une esfimation de la santé d’une rivière par l’analyse de son peuplement de poissons. Des données sur le peuplement de la portion namibienne du Kavango, obtenues en 1992, sont ulilisées ici pour base #un indice approprié. Les limites de l’approche sont analysées ef des recommandaiions pour son extension à d’autres pays au sud du Sahara sont présentées.

MOTSCLÉS : Fleuves - Milieu tropical - Indice de qualit. - Afrique - Angola - Namibie.

INTRODUCTION tection Agency (USEPA). The FWPCA provided specific recommendations t,o protect the integrity of The World Conservation Strategy (IUCN, 19SO) the Nation’s waters, primarily through the develop- recognized that (a) conservation of resources and ment. of physico-chemical criteria or standards for development are not incompatible, but indeed they the discharge of industrial effluents. are mutually dependent, and (b) unless development Through the mid-1980s, the USEPA relied heavily is guided by ecological, as well as by social, cultural on physic.o-chemical guidelines to regulate indust,rial and et.hical considerations, it will continue to fail to discharges and minimize impact in aquatic (receiv- meet or sustain its desired economic objectives. It is ing) systems. However, there was an increasing clear that development. within emerging nations awareness that such guidelines, although valuable, must not be at the sake of sustaining natural heri- often did not adequately reflect impact in situ. For tage (HOCUTTet al., 1992). Particularly for less devel- instance; the USEPA recognized that biological oped countries, environmental policies that attempt impairment and loss of biotic integrity cari result to ant.icipate or predict Sign&ant economic, social from sub-let,haI or synergistic effects of pollutants and ecological impacts rather than react t.o them, are not measurable by chemical and physical analyses becoming increasingly necessary for the arhievement alone (USEPA, 1990). For this latter and very of certain important goals : the satisfac.tion of basic important reason, the Water Quality A&, of 1957 needs, such as foods, clot.hing, sanitation and shel- amendment to the FWPCA of 1972/1977 specifically ter ; the development of a high quality environment ; authorized the USEPA t,o require a11 U.S. states to the opt,imum use of available resources; and the adopt narrat.ive biological criteria as a part of their cont.rol of pollution and other forms of environmen- water quality standards. This signified a shift in t,al degradation. Such anticipatory environmental environmental assessment and regulation philoso- policies involve actions to ensure that conservation phy, i.e., a move from “ discharge pipe criteria ” to and other environmental considerations are t,aken receiving-system impact. fully into account. at the earliest possible stage of HOCUTTet al. (1992) summarized that virtually a11 any decision that is likely to affect the environment water resource development projects on the African (IUCN, 1980). continent have either failed to meet their stated The review by HOCUTTei ~1. (1992) drew parallels objectives, and/or had socio-cultural and ecological between the development of environmental assess- impacts that were not predicted beforehand. Many ment protocols for emerging nations with the evolve- African cult.ures live at subsistence levels and are ment of the process in the USA, whose st,andards highly dependent upon the quality and quantity of have been adapted worldwide. Notably, t,he Nation- adjacent aquatic resources as a means of survival, al Environmental Policy Act (NEPA) of 1970 and yet the continent, is experiencing accelerated altera- the Federal Water Pollution Control Act (FWPCA) t,ions in land use and water quality impacts. of 1972 as amended in 1977 and 1987 represents t,he Common impacts have included destruction of bio- key federal mandate for the maintenance and pro- diversity, forests and traditional farms; social dis- tection of water quality in the USA. NEPA estab- ruption, including separation of traditional family or lished the environmental assessment process, and ethnie groups, resettlement int.o unacceptabIe areas, simultaneously created the U.S.’ Environmental Pro- land reallocation, and inundation of culturally-

R~U.Hydrobiol. trop. 27 (4) : 361-384(1994). i

WATER QUALITY A§SESSMENTIN THE KAVANGO RIVER 363

important. sites ; destruction of traditional fisheries ; Kavango River desertification ; salinization ; alterations in water quality and quantit.y, inc.luding downstream The Kavango River rises in the southern high- impacts ; ac.cumulation of agro-cliemicals ; and lands of central Angola as the Cubango River, flows health and disease (see GOLDSMITH and HILDYARD, in a southeasterly direction along the Namibial 1984 ; TIMBERLAKE, 1985). Knowledge of pre-devel- Angola border for ca. 415 km, and continues another opmental aquatic system conditions is crucial if 65 km as the primary source of the Okavango Delta, long-term resource uiilization is an objective (BREEN Bot,swana (fig. 1). The Delta is considered one of the et al., 1984). true natural wonders of the world, however this does It is a premise of our presentat.ion that the est,ab- not preclude various regional plans in Angola, Bot- lishment of biological monitoring protocols is an swana and Namibia to utilize the river’s vast water extension of, and complement.ary to, biodiversity resources, averaging 10,500 x 10Gm3 per year at the surveys whic.h are often aimed toward natural heri- Botswana border (BALDWIN, 1991). Such plans have tage programs. We present the conceptual basis for included Botswana’s Southern Okavango Integrated the development of an Index of Biotic Integrity Water Development Project (SOIWDP) and Nami- (IBI) for the Kavango River, following the mode1 of bia’s Eastern National Water Carrier (ENWC) sys- ~

Y f- \ ZAMBIA

IY H WI 1 D I H Grootfontein 0

Lak - - T S.p\A/ A

FIG. 1. - Drainage map of the Kavango River basin (from SKELTON ef al., 1985). Le bassin du /leme Kavango (d’après SKELTON et al., 1985).

R~U.Hydrobiol. trop. 27 (&) : 361-383(lS.94). 364 C. H. HOCUTT, P. N. JOHNSON, C. HAY, B. J.VAN ZYL

Equator KENYA

‘\

TANZANIA

‘OP0/- . -- c-i a \ % Q, \ I 0 1 0 7 .-h-J r+ :‘r c 4 .I a 0 - / *\

0 Ci 8 - - - International boundaries q/l m 0Kalahari sands i!BsA22i’es 0 600 km

FIG. 2. - The Kalahari Desert. biome in sout.hern hfrica (from ROSS1987). Le biome du désert du Kalahari en Afrique australe.

The Kavango River remains a rather unspoiled the quality and quantity of ihe catchment’s wat.er catchment in a west,ern world context, with minor resources. human impact in Namibia other than through Put. in terms of the indigenous human population, organic enrichment and riparian zone mismanage- the region is a focus for drought relief aid, being ment. Watershed development has thus far been within the Kalahari Desert biome (fig. 2) with an retarded ; however, with political normalization of average annual rainfall of <20 cm. Over 85 O$-,of the t,he region, various wat,er and terrestrial resource 150,000 Kavango people are considered subsistence utilization schemes are likely to be considered for the wage earners, and live within 10 km of the river catchment. Presumably, the cumulative effect of (SANDLUND and TVEDTEN, 1992); the population is developmental projects Will significantly impact the expected to double over the next decade. The seasonally fluctuating flood-driven processes of the Kavango people are dependent upon the river as a Kavango River, with subsequent adverse effect,s on protein source (the fishery), for potable water sup-

Res. Hycirobiol. trop. 27 (4) : 361-384 (1994). WATER QUALITY ASSESSMENT IN THE KAVANGO RIVER 365

plies, bathing and 1ivestoc.k watering. Thus, develop- dat,a requirement. Given (a) the likelihood of imple- ment activities which are likely to alter the mentation of various water diversion/utilization product,ivity of the system by upset.ting t.he balance schemes proposed for the future in the drainage, between floodplain submergencel exposure will have (b) increasing population, (c) t,he prospects of land a profound impac.t on the local populace. This reform policy in Namibia (ADAMS et al. 1990), whiçh dependence upon t,he river is furt.her compounded by Will alter land use patterns and potentially lead to the Angolan war to the north, result.ing in an increa- increased overgrazing and desertification ; and sing number of refugees seeking shelter and relief (d) cont,inued chronic regional drought, it is similarly along the border area and in Namibia. prudent t,o commence the conceptual development Knowledge of the seasonal structure and function- of a methodology to assess their probable long-term ing of the floodplain fishery is largely anecdotal. synergistic impact. However, given the shifting sand substrate of t.he river bed, annual productivity is linked to the flood- ing cycle and its effects on the littoral zone. The Current aquatic resource concerns in southern Africa river experiences peak flooding February through April, filling extensive floodplains along the Nami- GAIGHER el al. (1980) listed four major threats to bian/Angolan border, where the gradient is minimal threatened fishes in South Africa’s Cape Province : (fig. 3). Flooding in the lower Okavango Delta lags (1) farming and short-sighted land use practices, river flooding by up to 6 mont.hs. The floodplain in (2) introdu&ion of exot.ic fish species, (3) human set- Namibia is up to 5 km ac.ross as annual floods wax tlement, mining and industrial development and and wain. It is t.he temporary littoral zone which is (4) dam and weir construction. SKELTON (1983) identified by high macrophyte growth and secondary emphasized that the destruction of habitat is clearly productivity. The lit.toral zone vegetation serves as the most, significant threat to southern African aqua- ne&ng areas, feeding zones and refugia for most fish tic environments and their respective organisms by species. The vegetation itself acts as a minera1 and stating that... “ It is not only realistic but true to say nutrient sink, with Kavango water having minimal that habitat destruction is becoming more and more levels of condu&ivity (e.g., ~40 umhos) and evident in southern Africa as the human population nutrients during flooding condit.ions. grows “. Ten years have passed since that statement, As the Namibian Ministry of Fisheries and Marine and conditions have not improved. Resources (NMFMR) seeks solutions to manage t,he Pr!sently, the Kavango River is relatively free of fishery in light, of increasing demand, knowledge of perturbations related to development projects and the status of the flshery resource and its seasonal modern industrialization. The current state of the variability is an exceptionally important baseline Kavango may be deemed fairly pristine (via qualita-

Platorand $ 1400 g a Y\ 1200

kgadigadi 800 1485 Distance from source (km)

FIG. 3. - Longitudinal gradient profile of the Kavango River basin (from SANDLUND and TVEDTEN, 1992). Profil longifudinal du bassin du jleuoe Kaclango (d’après SANDLUND cf TVEDTEN, 1992).

R~U. Hydrobiol. trop. 27 (4) : 361-331 (1994) 366 C. H. HOCUTT,P. N. JOHNSON,C. HAY, B. J. VAN ZYL tive observations) in areas of sparse human popula- ~~~~;LAURENSONand HOCUTT,1986 ;O'KEEFE and tion (e.g. upstream where the river initially forms DE MOOR, 1988). the Angolan/Namibian border near Kat.witwi ; down- Chemical pollution, although currently not a stream near the Botswana border in the region of t.he major threat to the aquatic fauna of the Kavango Mahongo Game Reserve) and modestly degraded in River, cari be considered a prominent factor in the areas near the river’s population cent,ers (e.g. Rundu, destruction of southern African aquatic habitats and Bagani). Factors directly contributing to aquatic the consequential deleterious effects on fish commu- habitat degradation in the Kavango River include nities (SKELTON,1983). The decimation of entire fish the effects of livestock grazing (erosion, increased populations have been attributed to chemical pollu- turbidity, demolished aquatic and terrestrial vegeta- tants, e.g., cattle dip in the Hluhluwe River drainage tion beds), organic enrichment from human and ani- of South Africa (BROOKSand GARDINER,1980) and mal inputs, flow modifications and agro-chemical the adverse effects of endosulfan insecticide applica- disturbances. tion has been reported for both fish and birds in the Especially in highly populat.ed areas, herds of Okavango Delta (DOUTHWAITE,1982; MATTHIESSEN livest.ock along the river’s edge cari be observed graz- and ROBERT~,1982). ing the banks and floodplain habitats, and tromping The introduct,ion of non-native species is another through backwater pools (VAN DER WAAL, 1991). major threat to the indigenous freshwater of fishes of Increased suspended particulate loads would be sout,hern Africa. SKELTON(1983) stated that endemic expected in these areas of overgrazing, resulting in species with restricted distributions are especially turbid conditions that &ay disrupt photosynthesis vulnerable to predation by recreational species such and destroy benthic habitats. The destruction of as trout (Saho spp.) and blackbass (Micropterus riparian vegetation from both cattle grazing and the spp.), which have been introduced throughout South artisanal method of trampling weed beds for fish har- Africa. Presently, there are no known exotic species vesting certainly contribute largely to the visibly in the Kavango River proper, but HOCUTT and unstable river banks. Not only do these practices JOHNSON(in press) reported two established species impinge upon the river’s primary source of in a spring of the intermittent Omatako sub- productivity, they also negate t.he riparian vegeta- drainage. tive zones’ ability to stabilize river bank struc.ture. VAN DERWAAL (1991) suggested that large-scale soi1 Biological monitoring erosion in densely populated areas may cause deeper oxbows and side channels to fil1 with sediment, thus Ecologists have used ayuatic biota to monitor water minimizing the available refugia for fishes. qua1it.y since th& pioneering efforts of KOLKWITZ Present flow modification schemes such as small- and MARSSON(1908, 1909) and FORBES(1928). Sinc.e scale irrigation syst.ems and construction of canais t.hat early work, the concept of biological monitoring for livestock watering pose no real problems cur- has been greatly refined with a general trend away rently due to their minimal nature. However, in the from the indicat,or species concept towards an in- event of larger-scale implementation of water diver- tegrated, community-based approach (PATRICK, sion projects or impoundment construction suc.h as 1949; CAIRNS,1974; HOCUTT, 1975). One such inte- the Eastern National Water Carrier system in Nami- grated methodology currently in vogue in Nort,h bia, t.he effects of such practices ‘Cari be considered America to quantify the empiric.al relationships beti far-reaching as downstream users are indirectly ween land use and stream health via fish communi- impacted, the physical stability of t.he watercourse is ties is the Index of Biotic Integrity (IBI), fîrst for- altered and the biota is disrupted (APPLETONet al., mulated by ~Fish River in S0ut.h defined and reproducible over space and time; and Africa, modified flow regimes result.ed in the altera- (6) the variability of the unit of measurement, must tion of invertebrat,e community structure and the be low. ~

Rev. Hydrobiol. hop. 27 (4) : 361-384 (1994). WATERQUALITY ASSESS&fENT IN THE KAVANGORIVER 367 to the last criterion, noted that variation may either government agencies responsible for the sustainable be a consequence of sampling bias, a natural phe- utilization of the aquatic resources of the (particular) nomenon or anthropogenic affect. As they quote catc.hment. Al1 of these reasons have particular rele- HERRICKSand SCHAEFFER(1985), “ The concern is vance in a developing country conte& where other not that a measure be variable, but that the nature aquatic communities (e.g., macroinvertebrates) are, of the variability be well unde&ood “. poorly documented and where persons living at the Various t,axonomic groups of organisms have subsistence level are dependent upon the local water proven useful in monitoring water resource qua1it.y. resources to meet their daily living needs, including For instance, SIEGFRIED(1988) analyzed lake acidifi- the fishery as a protein resource. cation problems in relation to planktonic community KARR'S (1981) original Index of Biotic Integrity structures. Aquatic macrophytes assisted in classi- (IBI) was constructed for Midwestern USA streams, fying and determining trophic status in lakes and integrated 12 attributes of fish assemblages to (CANFIELD et al., 1984). An amphibian diversity determine biotic integrity or “ health ” of the system component aided in assessing coastal streams in (tabl. 1). Categories of attributes (metrics) included northern California (MOYLEet al., 1986). hlacroinver- species richness and composition, t,rophic structure, tebrate community groups are commonly used as and fish abundanae and health. Each metric reflect- cursory indicators of lotit system quality (HOWRIILLER ed the quality of a different port.ion of the fish and SCOTT,1977; SCHAEFFERet al., 1985). PLAFKIN community that responds in a different manner to et al. (1989) presented the conceptual basis for a the functioning of an aquatic ecosystem (FAUSCH rapid bioassessment. protocol (RBP) that stresses et aZ., 1984). The combination of metrics was subse- bent.hic community composition and function. The quently refined to reflect insights from individual, RBP approach is championed by many authorities population, community, ecosystem, and zoogeo- despite t,he reservations of CU~~MINS(1991). graphie perspectives (MILLER et al., 1988). The pri- The use of fis11 communities to biologically assess mary underlying assumptions of the IBI concept are stream condition and health, i.e., biotic integrity, is presented in Table II. now in common practice in North America and The conceptual basis of the IBI has been con- Europe (e.g., HOCUTT, 1985, 1988; HOCUTT and stantly revised since its introduction (e.g., KARR et STAUFFER,1980; KARR ef al., 1986; ANGER~IEIER al., 1986; MILLER et al., 1988; FAUSCHet al., 1990), and SCHLOSSER,1987 ;STEEDMAN,1988 ;FAUSCH~~al., and now is a standard for the Nat,ional instream 1984, 1990; OBERDORFFand HUGHES,1992).A sub- water quality monitoring program of the USA Envi- stantial literature base exists for various anthrop’oge- ronmental Protection Agency (USEPA, 1990). The nie effects, including aquatic resource degradation application of the principles of the IBI have also through stormwater runoff, stream burial, channel- been introduced to Canada (STEEDILIAN,1988) and ization, thermal pollution, land use practices, mining Europe (OBERDORFFand HUGHES, 1992). The IBI activities, siltation, organic and inorganic pollution. concept is not without its limitations (HOCUTT1981, Guild-based approaches have allowed for insight into 1988; KARR et al., 1986; FAUSCHet al., 1990). How- struct.ural and functional community-level fluct,ua- ever, the beauty of the IBI concept is that it inc.or- tions as well as indications of the extent of degrada- porates the principles of community structure and tion in aquat,ic systems (KARR, 1987). function into an index measurement of st,ream The rationale for use of fish communities in biolog- hea1t.h. Additionally, the tenets of the IBI cari be ical monitoring programs is strongly stated, includ- modified to meet individual catchment or regional ing : (1) The taxonomy, ecological requirements and needs. An appealing aspect of the IBI is that, one life history aspects of fishes are generally better does not loose information in its calculation, i.e., the known t.han for other phyletic. groups; (2) Through constituent metrics are available for furthe.r analy- their ontogenetic development, fish occupy a variety sis. of trophic levels and habitats; (3) Different compo- With the expected technological and ec,onomic nents of the fish community, and their life stages, are constraint‘s of developing countries, freshwater sensitive to a number of different sources of environ- resource monitoring and assessment strategies in ment,al degradation, including both the direct and Africa are not highly prioritized and in most cases indirect effects of st.ress; (4) In general, fish are at are nonexistent. In South Africa, however, there the top of the aquat.ic foodchain, and thus are inte- have been studies regarding aquatic resource moni- graters of temporal and spatial alterations in toring, dating back to HARRISON(1958, 1961), OLIFF ambient environmental conditions ; and (5) Import- (1960) and ALLANSON(1961). CHUTTER(1972) used ant,ly, the fish community has both economic and bent.hic macroinvertebrate faunal diversity to for- aesthet.ic values which cari be assigned to it, thus it mulate a biotic index for assessing the degree of commands attention from both t,he public and organic pollutlion in South African rivers; this sys-

Reo. Hydrobiol. trop. 27 (4) : 361-384 (1994). 368 C. H. HOCUTT, P. N. JOHNSON, 'C. HAY, B. J. VAN ZYL

TABLE 1

The original Index of Biot,ic Int.egrity (IBI) mekics proposed by KARR (1981) Les unifés de l’indice d’lnfégrifé Biofique proposées inifiafemenf par KARR (1981)

Category Metric

Species richness 1. Total number of fish species and composition 2. Number and identity of darter species 3. Number and identity of sunfish species 4. Number and identity of sucker species 5. Number and identity of intolerant species 6. Proportion of individuals as green sunfish

Trophic composition 7. Proportion of individuals as omnivores 8. Proportion of individuals as insectivorous cyprinids 9. Proportion of individuals as piscivores (top carnivores)

Fish abundance 10. Number of individuals in a sample and condition Il. Proportion of individuals as hybrids 12. Proportion of individuals with disease or other anomalies

tem has been updated recently and is known as t.he list,ed a11 the long-term data sets regarding aquatic South Afriçan Sc.oring System No. 2 (SASSZ) resources of southern African water-bodies to date, (KLEYNHANS ef al.). T. D. Harrison and his co-work- remarking that very few have been synthesized or ers (pers. commun) have modified RAMM'S (1988, analyzed for long-term t,rends related to either nat,u- 1990) community degradation index into a multi-dis- ral climatic fluctuations or anthropogenic effects. ciplinary, environmental-based health index for over More recently, DAVIES ef al. (1993) summarized some 50 South African estuaries. CAMBRAY et al. (1988) not.able case histories for South african c.atchments.

TABLE II

Underlying assumptions of the Index of Biot.ic Integrity (IBI) concerning how Lst.ream flsh communit.ies change wit.h environmental degradat.ion (after FAUSCH ef a/., 1990) L’Évolufion attendue de l’lndiçe d’lnfégrifé Biofique lors d’une dégradation de l’environnement (d’après F,~WCH et. al., 1990)

(1) The number of all native species and those in specific taxa or habitat guilds declines

(2) The number of intolerant species declines

(3) The proportion of individuals that are members of tolerant species increases

(4) The proportion of trophic specialists such as insectivores and top carnivores declines

(5) The proportion of trophic generalists, especially omnivores, increases

(6) Fish abundance generally declines

(7) The proportion of individuals in reproductive guilds requiring silt-free coarse spawning substrate declines

(8) The incidence of externally-evident disease, parasites and morphological anomalies increases

(9) The proportion of individuals that are members of introduced species increases

(10) The incidence of hybrids may increase

Reu. H9drobinl. frop. 27 (z!) : 301-384 (199J). WATER QUALITY ASSESSMENT IN THE KAVANGO RIVER 369

1 1 19’E 200E 2hE Katwitwi

ANGOLA

I

.----___--- N A M I B I A “\

0, , , , ,50Fm

FIG. 4. - The Kavango River area of st.udy, with zona1 divisions and sampling locations in 1992. La division zonale du peuve Kavango, avec les stations échantillonnées en 1992.

MATERIAL AND METHODS established reed and papyrus beds that are perma- nently inundated and considered as the uppertioet ” panhandle ” portion of the Okavango Delta proper Study area (VAN DER WAAL, 1987). For t.he purposes of com- paring spatial and seasonal fish assemblage variabi- From the northern border within Namibia, the lity as it is reflected with the proposed biological cri- Kavango River cari be divided into four zones based teria, the focus is concerned wit.h Zones 1, 2 and 3. on the occurrence of extended floodplain and asso- ciated habitats (VAN DER WAAL, 1991 ; VAN ZYL, 1992), subst.rate and charaçteristic riparian vegeta- Methodology tion (SMITH, 1976; BETHUNE, 1990) (fig. 4). Zone 1, from Katwitwi to Kasivi, is characterized by very Fish community samples were taken from 80 little floodplain development. and mostly shallow- localities during five collecting periods along the water environments with sand and/or rock sub- Kavango River in 1992. A high but increasing flood strates. Small rapids are scat.tered throughout, with stage was observed in February which peaked before prevalent, submergent vegetat,ion and aquatic weed May and receded until December, 1992 when the beds in a rather well def’med river bed. In Zone 2, river began rising again. Sampling localities were ini- from Kasivi to Mbambi, t,he floodplain bec.ornes well tially chosen based on accessibility, with emphasis developed, extending at times to over 5 km in given to re-sampling the sites withm each collecting breadth (SANDLUND and TVEDTEN, 1992). The main period (see figure 4 for a distribut.ion map of sam- river is wider here, seasonally broadening into innu- pling localities). However, this proved at times to be merable inferior channels, back bays and oxbow impossible given that the character of the river and ponds (fig. 5). The substrate in the main river is pre- its floodplain varied throughout the year, thus for dominantly sand with the occasional occurrence of the purpose of screening river sections t.o create a rock outcroppings. The back bays and oxbow ponds monitoring protocol, locations that were in close occur as a rule over submerged pasture-land. Zone 3, proximity (f 1.5 km) to one another in each zone from Mbambi t.o Popa Falls, finds the floodplain were sometimes lumped as a single location. Exact diminished, with wooded islands encircled by nar- locations of longitude and latitude were triangulated rower channels. Bedrock, large boulder and grave1 with a Magellan lOOO-Plus Global Positioning Satel- substrates associated with rapids are common in this lite (GPS) hand-held unit. area. Zone 4 below Popa Falls, including the Sampling was conducted on a seasonal basis with Mahango Game Reserve, is charact,erized by well 5 sampling periods throughout 1992. A total pf

Rev. Hydrobiol. trop. 27 (4) : 361-384 (1994). 370 C. H. HOCUTT, P. N. JOHNSON, C. HAY, B. J.VAN ZYL

FIG. 5. - SchemaGc diagram of floodplain river (from FORRESTER ef cd., 1989). Diagramme schématique d’une plaine d’inondation (d’après FORESTERet al., 1989).

TABLE III

Percent (70) occurrence and percent, (%) of total catch for each species collected from the Kavango River, 1992. *Sec below for occurrence ranking Pourcentage d’occurrence et pourcentage de la prise iotale de chaque espèce capturée dans le fleuve Kavango en 1992 % % Occurrence “%? Occurrence Ci%’

Hippopotomyrus ansorgii 10.00% 0.14% C/arias gariepinus 10.75% 0.18% Hippopotomyrus discorh nchus 11.25% 0.18% C/arias ngamensis 25.OU% 0.25% Marcusenius macrolepr d otus 27.50% 0.63% C/arias theodome 12.5G% 0.13% Mormyrus lacerda 11.25% 0.12% Petrcxephalus catostoma 33.75% 1.41% Chiloganis fasciatus 12.50% 0.2e% Potlimyrus castehaul 38.75% 0.92% Synodontis spp. 63.75% 2.12% Bfycinus lateralis 35.W~ 1 A556 Schilbe intermedius 41.25% 2.03% Hydrocynus vittatus 16.75% 0.63% Apiocheiiichthys hutereaui 25.00% 0.65% Micralestes acutidens 43.75% 6.29% Aplocheilichthys johnstoni 82.5U% 6.21% Rhabdalestes maunensis 3.75% OSKi% Aplccheilichthys katangae 7.5Wo 0.18% Hepsetus odoe 5.00% 0.05% Hemichromis elongatus 11.2536 0.15% Oreochromis andersonii 43.75% Hemigrammocharax machadoi 10.03% 0.18% Oreochromis macrochir 5.00% %E- Hemigrammocharau multifasciatus 33.75% 1.37% Pharyngochromis acuticeps 75.000/ 5.04; Nannocharax macropterus 1.25% 0.01% ^eudoc[eniia@s ph@der 06.25% Barbus afrovemayi 17.5u?? 0.52% serranccnrom~s angusucqs 15.00% Barbus annectens 3.75% 0.030/ Serranochromis carlottae 1.25% Barbus bamardi 0.91% Serranochromis coddngtonii 12.50% Barbus barotseensis 0.25% Serranochromis giardi 3.75% Barbus bifrenatus 2.38% Serranochromis macrocephalus 51.25% Batius eufaenia 1.74% Serranochromis robustus jallae 60.00% 1.05% Barbus fasciolatus O.ES% Tilapia rendalli 80.00% 10.82% Barbus haasianus 0.16% Tilapia ruweti 18.75% 2.49% Barbus linecmaculatus 0.35% Ti/apia sparrmanii 80.00% 8.11% Barbus multilineatus 0.08% Ctenopoma multispinis 7.50% 0.24% Barbus paludinosus 37çm"-.. -.- Barbus poechii 6.11% Aethiomastacembelus frenatus 5.00% 0.03% Barbus tadiatus 3.10% Aethiomastacembelus vandenraali 10.00% 0.11% Barbus thamalakanensis 2.78% Barbus unitaeniatus 0.53% * Commonness ranking in text based on the following ctfterfa: Coptostomabarbus wittei 0.01% Aank Labeo cyindricus Range 1.98% verv common > 75.0% Labeo lunatus 0.03% corhmon Opsaridium zambezense 40-74.9% 2.21% fairlv common 25-39.9% Amphilius uranoscopus 6.25% 0.11% unc&nmon 1 O-24.9% Leptoglanis dorae scarce 5- 9.9% 3.76% rare < 5.0% Leptoglanis rotundiceps 1.25% %Y?00 Parauchenoglanis ngamensis 8.75% 0:13%

R~U. Hydrobiol. trop. 27 (4) : XL384 (1994). WATERQUALITY ASSESSMENTIN THE KAVANGORIVER 371

TABLE IV Percent (%) of total catch for each family or group of fishes per Kavango River zone Importance de chaque famille ou grvupe d’espèces (en 7; de la prise totale) dans chaque zone du fleuve Kavango

Fish Family or Group Zone 1 Zone 2 Zone 3 Zone 4 Total Cichlids 44.5 53.3 30.0 15.6 46.2 Cyprinids 19.0 28.7 42.3 30.2 27.8 Characins 16.4 4.8 4.8 6.4 8.4 Cyprinidonts 8.1 6.2 3.7 35.9 7.0 Çiluriforms 7.0 4.3 8.8 1.7 5.2 Mormyrids 3.5 2.0 8.1 3.5 3.4 Citharines 0.9 1.7 2.1 3.5 1.6 Anabantids 0.0 0.3 0.2 3.5 0.2 Mastacembelids 0.4 0.04 0.1 0 0.1 Hepsetids 0.1 0.03 0.1 0 0.1

14 families, 33 genera and 63 species were collected was then broadcast.ed into the habit.ats, and aft,er a (t.he taxonomically difflcult catfish of the genus few moments the stunned ilsh would be net,ted after Synodontis are t.reated here as a single species). The they began to surface. During minimal flow condi- relative occurrence (% occurrence) and relat.ive tions and if deamed appropriate, a Seine net would abundance (94 tot,al catch) of each spec.ies is indica- sometimes be placed at a defined point to collect any ted in Table III. The percent of total catch per zone flshes drifting wit,h the current. (Upper, floodplain, lower) for each family or group of In shallow-wat.er flowing habitats, espec.ially with flshes is indicated in Table IV. The following dis- grave1 and sand substrates, a 3 x 1.5 m Seine net cussion is st,ructured such that. each family of tlshes with 5-mm mesh was t,he collecting gear of choice. (or group) is addressed in descending order of total The seine would be dragged along the substrat,e, relative abundance. vigorously poked into weed beds, or plunged and Biological criteria based on fish community assem- swept over flsh visible through the clear water. In blages were developed for assessing the Kavango t,he case of shallow flowing wat.ers with grave1 and River. Regional ichthyological literat,ure (JUBB, submerged aquatic veget.ation, the “ cast and kick ” 1967; POLL, 1967; VAN DER WAAL and SKELTON, seining method was used. Dubbed the ‘(Yankee- 1984; BELL-CROSSand IIIINSHULL, 1988) and per- doodle dance ” by an amused spectator, P. H. Skelton, sonal observation, were the cornerstone for develop- this technique calls for casting the net in a down- ing the biological criteria for a Kavango River IBI. stream direction, anchoring it in the substrate, and Diet, habitat preferences and ecological require- thoroughly disturbing the grave1 and plant material ments for a11species known from t.he Kavango River by kicking and çhurning up the bot,tom. Often times were charact,erized (HOCUTT and JOHNSON, 1992). if called for, seining was done to supplement. a rot,e- There was no trophic discrimination bet,ween the dif- none collect.ion, and vice versa. ferent life stages of the individual taxa (STAUFFERet Attempis were made to use a Coffelt 12-v gas- al., 1978; ~(ARRet al., 1986). powered backpack, a Smith-Root. mode1 VII 24-v Fish sample collections were obtained using a battery-charged backpack, and a Coffelt 700~watt variet,y of gears, dependent upon water levels and boat/shore-mounted electrofishing units to sample habitats encount.ered. The primary objec.tive was to flshes. Al1 these unils were found to be ineffective obtain a representative sample (HOCUTT, 1978) of the due to the low conductivity encount.ered, with fish communities within t.he localized habitats, with exceptions being in higher flow, rocky habitats. The each collection terminating only aft.er no new species normal protocol with the backpac.k unit was t,o shoek were found with continued use of gear(s) employed. in an upstream direc.tion probing t*he subst,rate and In backwater areas, wit.h slow to st.agnant slow aquatic vegetation with the meshed end of the anode conditions and dense aquatic vegetation, the ich- pale, with t,he dip netter following close behind col- thyocide rotenone was the primary collect,ing tool. lecting stunted fish. The technique normally involved mixing powdered Other flsh collecting methods also were used occa- rotenone with water and a small amount of dish soap sionally such as wire-mesh minnow traps employed to enhance the solubility of t.he powder. The mixture at camp site collecting localities. In the evening, four

Heu. Hydrobiol. trop. 27 (g) : 36L38d (1994). 372 C. H. HOCUTT, P. N. JOHNSON, C. HAY, B. J. VAN ZYL

t.raps would be baited with bread, t,ethered to shore- TABLE V line vegetation, casted out and retrieved the follow- List of proposedbiological criteria metrics used to characterize ing morning. An experimental $1 net with four dif- and assesstropical floodplain river syst.ems ferent mesh sizes was used sparingly to collect larger Lisie des variables proposhes pour caracfériser ei analyser les sys- rheophilic. fish ; it was set either overnight or for tèmes fleuve-plaine d’inondation tropicaux several hours before retrieval. A 30 x 1.5 m bag Seine with 70-mm mesh was occasionally used in tur- bid backwaters. Some collections were supplemented Species Richness and Composition by using a large beach Seine (5 x 25’ with 5 x 5’ bag (1) Total number of native fish species of .25” mesh), while simple dip netting was employed (2) Total number of benthic specialist species (3) Total number of cichlid species under other occ’asions. Angling, the remaining sam- (4) Total number of pelagic-rheophilic species pling method used, was selective for the more preda- cious species, such as tigerfish (Hydrocynus vittutus). Trouhic Composition Light to medium weight spin-casting rigs or fresh- (5) Proportion of individuals as principal herbivores and detritivores tut bait were used either from boat or shore. (6) Proportion of individuais as principal invertivores Fishes were preserved in 10 O,& formaldehyde (7) Proportion of individuals as opportunistic scavengers immediately after collecting and st,ored at least. ten (8) Proportion of individuals as piscivores days for proper hardening. The samples were then Fish Abundance and Condition rinsed with freshwater for several days before t.rans- (9) Total number of individuals in a sample fer to 70 o/. ethyl alcohol. Al1 specimens were do- (10) Total number of exotic and introduced species nated to the State Museum of Windhoek for cata- (11) Proportion of individuals with visible anomalies loguing and permanent storage. Seasonal data interpretations presented below are based exc.lusively on relative abundance, i.e., num- bers of each taxa collected. Data< are presented in an annotated fashion, with parallel discussion of rele- vant literature emphasizing the works of BELL- Metric 1 : Total number of native fish species. - CROSSand MINSHULL (1988)and VANDERWAAL and This was included as a general indication of relative SKELTON (1984). Species are ranked on the basis of biodiversity, with the rationale being that species their relative abundance; however it is underst.ood richness Will decrease with increased environmental that flsh collecting is a qualitative and gear-selective degradation. KARR 6.1981) proposed t.his metric for procedure that might mask the conclusions pre- midwestern U.S. stream fish assemblages ; others sented. retained it (see MILLER ef al., 1988) in various re- gional North Americ.an applications, and OBER- DORFF and HUGHES (1992) included it in their cha- racterization of the Seine River basin in France. RESULTS While this metric has shown wide applicability in temperate waterways, there is no reason why its basic premise would not hold true in tropical sys- Fish communit,y samples (tabl. 3-4) from the tems. Kavango River were used to formulate the prelimi- nary measurements (or metrics) based on faunal Metric, 2. : Total number of benthic specialist spe- att.ributes regarding species richness and composi- cies. - This replaces the number of darter species tion, trophic struct.ure, abundance and condit.ion. metric of KARR (1951) while retaining its original The metrics proposed to characterize the status of intent of assessing benthic habitat conditions. Such the Kavango River fish assemblage are listed in subst.rat.e habitats are known t.o be degraded by the Table V, and with t.he variation of each metric sum- effects of siltation (KARR ef al., 1986), which is a marized by river zone and season in Tables VI and major concern regarding southern African lotit VII, respectively. water resources (GA~GNER et al., 1980; SKELTON, 1983). The fish to be included in this metric are de- fined as those with speçific biological requirements Proposed metrics for IBI adapted for benthic habitats. When assessing south- ern African fauna, the following groups should be SPECIES RICHNESS AND COMPOSITION included in this metric.; Labeo spp. (small, benthic Faunal composition and species richness were dwelling species of this cyprinid genus), Amphiliidae assessed using four metrics designed to monitor over- (mountain catfish), Bagridae (grunter catfish), Chilo- a11biodiversity and habitat-specific fish assemblages. ylnnis spp. (members of this Mochokidae catfish

HEU.H@Aiol. trop. 27 (4) : .%l-384 (1991). WATERQUALITY ASSESSMENTIN THE KAVANGORIVER 373

TABLE VI Summary values for each proposedmetric on a zona1scale Valeurs proposées des variables pour l’étude zonale

Metric Minimum Average Maximum

Zone 1 2 3 1 2 3 1 2 3

Number of native fish species 8 2 10 17 14 18 30 30 24

Number of benthic specialist 0 0 0 1 o+ 1 5 4 1 species

Number of pelagic rheophilic 0 0 0 2 1 1 4 4 4 species

Number of cichlid species 2 0 2 6 5 6 9 9 8

Proportion (%) of individuals as principal herbivores/detritivores 2.2 0.0 3.7 25.0 30.5 25.1 59.4 90.6 88.8

Proportion (%) of individuals as principal invertivores 27.8 0.0 7.8 67.9 59.5 63.7 95.3 87.2 92.0

Proportion (%) of individuals as opportunistic scavengers 0.0 0.0 0.0 5.2 3.8 9.0 41.1 25.0 36.0

Proportion (%) of individuals as 0.0 0.0 0.0 2.0 6.1 2.2 5.5 67.0 8.4 piscivores

Number of individuals in sample 47 8 61 192 214 160 555 769 266

Proportion (%) of individuals as introduced or invasive species 010 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ci.0

Proportion (%) of individuals with visible disease or anomalies 0.0 0.0 0.0 0.0 0.0 0.0 0.0 o.o+ 0.0

genus specifically adapted for roc.ky habitats) and Metric 4 : Total number of pelagic rheophilic spe- Mastacembelidae (spiny eels). Benthic specialists of cies. - This new metric is designed to assess open- the Kavango River included in the calculation of wat.er flowing areas by monitoring the number of this met.ric are the following species : Labeo cylindri- species inhabiting such habitats. Degradation of rus, dmphilius uranoscopus, Leptoglanis dorae, open-water flowing habitats should be reflected by a L. rotundiceps, Parauchenoglanis ngamensis, Chilo- decrease in pelagic rheophiles. Species to be exam- glanis fasciatus, Aeihiomastacembelus frenatus, and ined in calculation of this metric include the majo- A. vandermaali. rity of the characins (Brycinus lateralis, Hydrocynus Metric 3 : Total number of cichlid species. - This vitiatus, and Micralesfes acutidens) and the cyprinid metric replaces the number of sunflsh species metric Opsaridium zambezense. of KARR (1981) keeping its int.ent of measuring the degree of degradation of submerged vegetation, TROPHICSTRUCTURE which members of the cichlid family generally inha- bit. There are 17 cichlid species known from the Alterations in habitat and water quality due to Kavango River in Namibia, a11 of which should be land use practices often result in food resource fluc- included when tallying t.his metric ; 14 were collected tuations in aquatic systems, which are reflected in in this survey (tabl. IV). the structural changes in trophic composition (KARR

Rev. Hydrobiol. frop. 27 (4) : 361-383 (1994). 374 C. H. HOCUTT,P. N. JOHNSON,C. HAY, B. J.VAN ZYL

Summary values for each proposed metric on a seasonal scale Valeurs proposées des variables pour l’étude saisonnière

Minimum Average Maximum Metric Season Feb May June Sep Nov Feb May June Sep Nov Feb May June Sep Nov Number of native 5 2 5 11 7 13 15 20 18 15 23 26 30 26 24 fish species

Number of benthic specialist species 0 0 0 0 0 o+ o+ 1 2 1 1 2 5 4 4 Number of pelagic rheophilic species 0 0 0 0 0 2 11 124 3 3 23

Number of cichlid 2 0 2 2 65 65 67 8 9 79 species

% herbivores/ 3.9 0.0 0.0 12.6 1.1 37.0 24.1 17.0 24.0 32.7 90.6 85.5 59.4 32.7 81.0 detritivores

% invertivores 0.0 14.5 37.1 24.4 7.8 58.3 70.4 72.0 64.9 51.7 91.4 95.3 91.8 79.5 81.5 % opportunistic 0.0 0.0 1.2 0.7 0.0 1.3 3.6 8.7 8.6 6.5 5.5 22.3 35.6 34.5 41.1 scavengers % piscivores 0.0 0.0 0.0 0.0 0.0 3.4 1.9 2.3 2.5 9.1 9.4 9.4 4.2 8.4 67.0 Total individuals 37 53 a 61 43 174 260 221 149 158 561 758 769 285 299 % introducedj 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 invasive species % with disease 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 or anomalies

et al., 1986). Four metrics were developed to monitor preferences having mouth and lip morphology sug- these fluctuations in tropical floodplain rivers. gesting invert.ebrate diets were included in this Metric 5 : Proportion of individuals as principal group. Invertivorous cyprinids dominate the herbivores/ detritivores. - This new metric is used Kavango River fish bi0diversit.y. to assess the quality of the aquatic system food base Metric 7 : Proportion of individuals as opport,unis- at the primary level. Fishes to be mcluded in this tic scavengers. - This is similar to KARR'S (1981) group are defined as those with diets known to percent omnivore metric in that the proport.ion of c.omprise primarily plant, material, plankton, det,ri- opportunist,s is thought to inc.rease as degradation tus and algae. Members of this dietary assemblage disrupts the food web by limiting or decreasing found in the Kavango River include : Labeo cylindri- available food base components. Members of this ~US, L. lunalus, Oreochromis andersonii, 0. macrochir, group are fishes known to show catholic feeding Tilapia rendalli, T. ruweti, and T. sparrmanii. behavior or feeding plasticity. The following Metric 6 : Proportion of individuals as principal Kavango River species are designated as opport.un- invertivores. - Designed to assess the secondary or istic scavengers : Clariallabes pla$prosopos, Clarias invertebrate food base, this is similar to those modi- dumerilii, C. gariepinus, C. ngamensis, C. stappersii, fied from KARR'S(1981) original metric proport,ion of Paruuchenoglanis ngamensis, Schilbe intermedius and insectivorous c.yprinids (see MILLER el al., 1988). Synodontis spp. Princ.ipal invertlvores are defined as those fish with Metric 8 : Proportion of indivicluals as pisciv- diets primarily consisting of aquatic larvae, insects, ores. - This original metric of KARR'S (1981) is crustaceans and mollusks. With the absence of stom- retained to assess trophic diversit.y at t,he top of the ach analgsis dat.a for most of the tropical fish fauna food chain. Fishes are deemed piscivores if as adults in southern Africa, spec,ies wit.h gnknown feeding their diet, is comprised primarily of fish, while as

RE~. Hytirobiol. trop. 27 ($) : 361-384 (1991) WATERQUALITY ASSESSMENT IN THE KAVANGORIVER 375

juveniles invertebrates may be their food items of zones 1 and 2, respectively. The least diverse collec- choice. The following list includes a11 fishes of the tion was obtained during May in zone 2, harboring Kavango River used in the calculat.ion of this only two species. metric : Hydrocynus vittatus, Hepsetus odoe, Serrano- Metric 2 : Total number of benthic specialist spe- chromis altis, S. angusticeps, S. macrocephalus, cies. - As to be expected, these species occurred S. robustus and S. thumbergi. most frequently in the non-floodplain zones, wit.h zone 3 showing the highest frequency of appearance ABUNDANCEAND CONDITION (over half of a11 samples). Benthic specialists were Relative abundance and fish health of populat,ions rarely found in zone 2, as over 75 o/. of a11collections are evaluated using the following three metrics, a11of within that zone were absent of these species. which are based on those proposed by KARR (1981). Almost 50 oh of the Zone 1 samples contained mem- Metric 9 : Number of individuals in a sample. - bers of this group. The Sept,ember collecting period This metric evaluates sample abundance as it relates found the highest incidence of occurrence of these ’ to catch per unit of sampling effort. The logic behind species, with 70 oh of a11samples having benthic spe- this is that with similar sampling methods and cialists. The most species of this group (5) collected effort, degraded sit,es are expected to harbor fewer at any one site occurred in Zone 1 during June. individuals than sites with higher quality conditions Metric 3 : Total number of pelagic rheophilic spe- (KARR et al., 1986). cies. - Zone 1 found the highest relative species Metric 10 : Proportion of individuals as intro- occurrence of t.his group, with 2 species collec,ted per duced or invasive species. - This is similar to site on the average and over 80 yo of a11 samples metrics modified to replace K~RR'S (1981) original containing at least one pelagic rheophile. Zone 2 had percent h$-brids (MILLER et al., 1988), but. is unique the lowest relative frequency of occurrence, wit.11just. in that it mcludes native invasive species. The ratio- over 50 y/o of a11collections having a member of t.his nale behind this is that since t.he Kavango River pro- group. The pelagic rheophilic group peaked in rela- per is absent of bot,11exot.ic and regionally invasive tive frequency during t,he February and November species (SKELTONef al., 1985; VAN DERWAAL, 1991), sampling periods, with 2 species obtained per collec- t.he initial effects of exotics on the native fish assem- tion on the average. The May sampling effort yielded blage structure cari be monitored and documented, the lowest relative incidence regarding t.his group, e.g., if indeed Trichogaster trichopterus and Astyanax with over half the collections absent of any pelagic orthodus are successful in colonizing the river proper rheophiles. The maximum possible number of pe- from the Omatako sub-drainage (HOCUTTand JOHN- lagic rheophilic species (4) was obtained in a11three SON,in press). The obvious assumpt.ion here is that zones exclusively during the February sampling the integrity of native fish communit.ies is compro- period. mised when foreign species have invaded or are Metric 4 : Total number of cichlid’species. - On a introduced. longitudinal basis, this metric showed no trends as Metric 11 : Proportion of individuals with visible relative occurrence of cichlid species was quite simi- anomalies. - This metric is a direct evaluation of lar from zone to zone on the average. Basically, t,he fish health, and is retained from KARR (1981). Any same cari be said regarding seasonal comparisons, as individuals observed to have disease, deformities, averages and medians barely fluct.uate from period lesions and tumors are included in t.he calc.ulat.ion of to period. The May sampling effort., however, indi- this metric. cates a slight decrease in t,he median value. A single collection was absent of any cichlids, obtained Seasonal and spatial t-rends during May in zone 2. The maximum number of cichlids collected in any one sample (9) was taken SPECIESRICHNESS AND Con~POsITIoN from zone 1 (twice in June) and zone 2 (once in both Metrir 1 : Total number of native fish species. - June and November). On a longitudinal basis, this metric yielded higher values in the non-floodplain zones, with the greatest TROPHICCOMPOSITION median and average relative species richness in zone Metric 5 : Proportion of individuals as principal 3. Seasonally, species richness was found to be lowest herbivores and detritivores. - The medians and in the February, May and November sampling peri- averages for this trophic group are roughly c.on- ods, while on the average t,he June effort yielded the strained within the 20 to 30 oh range for .the three most. species per collecting site. It was during t.his zones, with zone 3 showing slightly higher relative period when the most diverse collections were ob- values than the other two. Temporally, herbivore tained, with two samples of 30 species each, from and detritivore proportions show tw6 distinct, modal

R~U. Hydmbiol. trop. 27 (4) : 361-384 (1993). 376 C. H. HOCUTT,P. N. JOHNSON,C. HAY, B. J. VAN ZYL groupings : (1) February, September and November, where this dietary assemblage comprised over 95 yo and (2) May and June. The former sampling periods of a single collection. portray a consistency in their medians, which are Metric 7 : Proportion of individuals as opportunis- confined t.o the 25 to 30 94 range, while the latter are tic sc.avengers. - Based on bot.h medians and aver- markedly lower, approximating the 15 percentile ages, t,he proportion of this group peaked in zone 3, Furthermore, these latter sampling periods each while zones 1 and 2 were fairly similar and slightly contain a single sample completely lacking any lower. Throughout the year, on average the propor- members of t.his dietary assemblage, both of which tion of this group per sample ranged from a low in occurred within zone 2. The maximum relative pro- February (1.3 Oh) to highs in June and September portion of herbivore/detritivore feeders was found in (over 8 %). Collections lacking opportunistic scav- zone 2 during the February effort, comprising over engers were obtained most frequently in February, 90 yo of the entire sample. while a11samples in June and September contained Metric 6 : Proportion of individuals as principal some members of this group. The highest proportion invertivores. - The median and average range over of this feeding group from a single collec.tion was a11three zones for this trophic group is roughly be- found in a November sample from zone 1, where this tween 60 and 75 %, with Zones 1 and 3 slightly opport.unist. assemblage comprised over 40 o/. of a11 higher relative t,o Zone 2. A seasonal trend is reveal- individuals. ed when comparing the proport,ion of invert,ivores to Metric. 8 : Proportion of individuals as pisci- the proportion of herbivores/detritivores (fig. 6). The vores. - Zone 2 was found to harbor the highest May and June efforts, which harbored t.he lowest relative proportions of piscivorous fishes based on proportion of the latter, yield the highest, proportion both median (3.0 %) and average (6.1 y;), while the of the former relative to the other sampling periods. other zones ranged between 1.5 to 2 7; for these The invertivore assemblage during May and June parameters. Seasonally, fish eaters were most prev- ranged between 70 and 78 o/. based on medians and alent. during the November sampling period where averages, while the remaining periods ranged from two collections yielded piscivore proportions over roughly 50 to 67 %, with the November effort yield- 20 O,$,and one sample was comprised of 67 o/. ; these ing the lowest relative proportion for this group. three samples were a11obtained within zone 2. Each February of zone 2 harbored the only collection zone and eac.h sampling period found collections absent of principal invertivores, while the maximum absent of this group, with zone 2 and May sampling proportion obtained was during May within zone 1 efforts having higher relative incidence of this result.

~UNDANCE AND CONDITION Metric 9 : Number of individuals in sample. - Invertivores a “’ The range of average values along the Kavango River for this metric spanned from 160 in zone 3 to Herbivores - Detritivores A 214 in zone 2. On a seasonal basis, the average num- ber of individuals peaked during the May effort and Feb. lP@i bottomed out during the September sampling period. The smallest and largest number of individ- 1 . May ’ n r\ uals collected from any single site (S and 769 spec.i- I ” I mens, respectively) were both obt.ained from zone 2 June yB 1 in June. The results of this metric are simply general indicat.ions of relative abundance and nothing more, k--B--l Sept. as they are not calculated as a function of catch per I A unit. of sampling effort. Nov. 1 - - & 1 Metric 10 : Proportion of individuals as intro- 1 I I I I I I 1 1 , duced or invasive species. - No introduced species 0 10 20 30 40 50 60 70 80 90 100 are known from t.he Kavango River proper at the Relative abundance (%) present time. Metric Il : Proportion of individuals with visible FIG. 6. - Seasonaltrophic composit,ion in relative abundance for principal invertivore and herbivore-detritivore feeding anomalies. - After examining over 14,000 individ- groups. uals, only a single specimen (juvenile Oreochrotnis Variations saisonnière de la composition trophique pour les prin- andersonii) collected in November within zone 2 was cipaux groupes herbivores-détrifivores el invecfivores. found wit,h a visible anomaly (ect,oparasite).

Rev. Hydrobiol. frop. 27 (4) : 361-384 (1994). WATERQUALITY ASSESSMENTIN THE KAVANGORIVER 377

DISCUSSION 30 y0 of the total), and lowest in May and June (-r 15 Y,). (6) Th e number of invertivores varied inversely with the herbivores and detritivores Inherent within fluc.tuating syst.ems such as sea- (fig. 6), with the highest relative numbers (70-78 %) sonal rain driven, tropical floodplain rivers, there are in May and June. They were reasonably well distrib- difflculties regarding assessment and characteriza- uted across a11three zones (60-75 %). (7) The oppor- tion. As opposed to lot,ic systems in temperate cli- tunistic sc.avengers peaked in Zone 3. They were mates with characteristic steadfast. processes, rela- present in lowest numbers in February, and highest tively speaking (see VANNOTEet nl., 1980), tropical in June and September (8 %). (8) Piscivores, espe- floodplain rivers are much less stable and unpredict- cially tigerfsh, were probably under-sampled, but able (LOWE-MCCONNELL,1987; DAVIES et al., 1993), seemingly occurred in highest percentages in Zone 2, perhapç tending t,owards community stat.es without. and in November ; and (c) of the abundance and condi- structure (O'KEEFE, 1986). tion metrics, (9) numbers of specimens, peaked in CAMBRAY et al., (1988) perceived t.hat aquatic May, but were distributed evenly longitudinally. organisms adapted to very constant and predictable Metrics (10) numbers of introduced and invasive conditions may become recognizably different within individuals and (11) t.hose fish with anomalies, each a year or two of a minor change, while those of a were considered representative of a near-Perfect highly fluctuating system might. not react percept,i- state with only one specimen of flsh observed with bly over many generations. As data sets regarding an anomaly. fluctuations in natural tropical systems (i.e. water The variability in the metrics noted for the Kavango quality) are either nonexistent or un-synthesized above contrasts considerably to STEEDMAN'S (CAnrnRAY ei al., I988), monitoring the impacts of (1988) excellent study of Ontario streams; the low natural variability and catastrophic events is impos- variation he observed for sampling stations within sible since knowledge of baseline conditions has net and bet,ween years is a desirable asset of IBI scoring, been achieved. CAMBRAY et al. (1988) theorized that while high variability cari imply low resolution of the t.he effects of anthropogenic interference on t.he long- index. We interpret t.he variability as nat,ural, term cycles of inland aquatic biota on t.he continent. which, ideally, Will influence the sampling protocol are often obscured by non-foreseen natural processes in future studies, e.g., st.andardizing sampling gear, (e.g., unpredictable and inequitable distribution of stations and time of year. rainfall). This emphasizes the point, t.hat. natural dis- These data indicat.e a pronounced structural re- turbances and those of anthropogenic origin must be sponse of the fish c0mmunit.y in relation to the alter- discernible to properly u.nderstand cause and effect. nating flood and drought conditions in the river relationships relating to degradation and biotic re- (e.g., fig. 3), with lowest diversity and fewest num- sponse (DAVIES ei al., 1993). It has been generalized bers of specimens occurring during the low flow that in the case of southern African systems, changes months, October to December. It also appears that due to anthropogenic disturbances exceed those due the reproductive strategies of some Kavango flshes to normal annual events, while natural abnormal are in advance of flooding (e.g., cichlids) while other catastrophic events cari alt,er the aquatic environ- species (e.g., many c.yprinids) are in sync wit.h flood- ment. to a similar degree (&vfrmA~ et cd., 1988). ing and the stimulation of littoral zone plant growth. The proposed IBI metrics derived to characterize These observations concur with the synt.hesis of the Kavango River flsh fauna (t.abl. V) were highly LOWE-MCCONNELL(1987) that could be used to pre- variable, both spatially and temporally (tabl. VI and dict that many Kavango floodplain fishes will exhi- VII). TO summarize : (a) of the four species richness bit (a) greatly fluctuating populations, (b) short. life nietries, (1) the average number of species was high- cycles with early maturation and rapid growth, and est in Zone 3, and highest in June. (2) The number of (c) seasonal reproductive cycles, wit,h predominate benthic species peaked in September, 70 y0 of a11 r-type selection. samples, with highest numbers generally occurring Given the shifting sand substrate of the river bed, in Zone 3. These species were absent in 75 a/( of t,he it cari be assumed that productivity is driven by the Zone 2 collections. (3) The pelagic species numbered annual flooding of the littorallriparian zone and the highest in Zone 1, lowest in Zone 2, and seasonally consequent promotion of growth of higher vegeta- were found in greatest numbers in February and tion (i~mcomm, 1979). Phytoplankton product.iv- lowest in May. (4) The number of cichlid species showed ity is considered negligible in the Kavango, but the the same basic trends seasonally and longitudinally ; truc significance requires assessment. The high (b) amongsi the trophic metrics, (5) t,he percentage of macrophyte growth in the littoral zone serves as herbivores and detritivores was generally the highest nesting areas, feeding zones and refugia for most fish in February, September and November samples (20- species with few having a true aftînity for the more

Rtw Hydrobiol. frop. &Y (4) : 361-383 (199$). 378 C. H. HOCUTT,P. N. JOHNSON,C. HAY, B. J. VAN ZYL open structureless mid-channel. The CO-PIS have (3) how these parameters are affected by natural defined the floodplain zone of the Kavango as longi- variability (longitudinally and seasonally) within the tudinally encompassing approximat.ely 375 km of syst.em ; and (4) the often expansive catchments, the river. encompassing two or more countries with different The River Continuum Concept of VANNOTEet al. management priorities and agenda. Another limita- (1980) serves as the current general mode1 of longitu- tion is (5) the shear number of indigenous species in dinal structure and functioning of lotit. systems. many African catc.hments, numbering > 700 species However, .JUNKet al. (1989) provided insight to the in the Zaire River system (SKELTON,1993). functioning of floodplain rivers through their manu- From the perspeciive of systematics and biogeog- script outlining the Flood Pulse Concept, which raphy, the taxonomy of many species in sub-Saha- recognized t.hat flooding is the major “ driver” of ran Africa is under review, and often difficult lowland or floodplain rivers. The conc.ept implies (GREENWOOD,1983). Additionally, many species t,hat the frequency, magnitude, and rates of rise and have discont.inuous or disjunc.t distributions result- fa11 of flooding will he reflect.ed in t.he ecological cha- ing from either physical (CRASS,1962), ecological racter of the associated biot-a (DAVIEB et al., 1993). (JACKSON,1962) or behavioral (BELL-CROSS,1965) JUNK et al. (1989) defined the floodplain as an Aqua- barriers. GAIGHERand POTT (1973) listed other pos- tic-Terrestrial Transition Zone (ATTZ), that. sible causes of discontinuity such as range constric- excludes permanent lotit and lentic habit,ats within tion due to competition, extermination by predation the zone of inundation, thus emphasizing the flood- and catast,rophic. destruction of fish-life in interme- plain as an area of alternation of wetting and drying diate areas. Historic climate change yielding adverse phases (DAVIES et al., 1993). conditions (low temperatures, and aridity) has re- The variability in t.he Kavango is c.ompounded by sult.ed in distribution gaps and isolation of African three distinct zones of different physiographic fea- fishes species (SXELTON, 1980). These factors in addi- tures of the stream bed, the channel, substrate and tion to those above Will hinder the construction of an littoral zone formation, a11influencing fish structure IBI. and function as well as sampling bias. Thus, it is It is highly desirable to estsablish routine moni- premature to finalize criteria for the Kavango based toring and assessment procedures for Africa’s inland on a single year’s effort; however, this data base is waters (e.g., see KLEYNHANSet cd., 1993). However, extremely useful for serving as a baseline and re- techniques such as the calculation and use of the fining a monitoring protocol after continued sam- rather sophisticated IBI may be restricted, as noted pling. by our data base and the other limitations list.ed HOCUTT(1981) first drew att.ention to the limita- above. For this rea’gon, certain African count.ries tions of the IBI concept, and rec.ommended that the lacking taxonomically trained personnel or adequate inherent difficulties of obt.aining a representative resources, may want to devise a simplistic appr0ac.h sample should not be minimized, especially in a for use in t.heir regional waters. J. Cairns and his developing country context. Factors which influence co-workers (CAIRNSef al., 1968; CAIRNSand DICKSON, this concern are (a) the qualitative nature of sam- 1971) demonstrated several years ago in the pling, (b) gear selectivity, and (c) experience, t.raining construction of a Sequential Comparison Index (SCI) and motivat,ion of the personnel involved. Addition- t,hat the consistency of taxonomie ident.ification is ally, it should be recognized that biota,,are seasonally more important than systematic preciseness when abundant or scarce dependent upon ecological and constructing community-based indices of stream life hist,ory requirements, inc.luding (a) migratory health. The SC1 was developed as a simple rapid pro- habits, (b) reproductive strategies, (c) habitat. prefe- cedure for analyzing aquatic communit,y data based rentes, (d) behavior, e.g., some species might be noc- on t.he visual slmi1arit.y of a specimen being c,om- turnal, (e) longitudinal zonation, and (f) zoogeogra- pared to anot,her. It was found that even persons phic considerations. Importantly, most species pass without training in biology could recognize different through different. t,rophic levels during t.heir onto- taxonomie groupings of organisms based on gross geny (WINEMILLER, 1991), and this must. be a anatomical features, and this information could be long-term consideration in refining an IBI mode1 adapted to calculate a “ diversity ” index for the (STAUFFERet al., 1978; KARR ebal., 1986). sample being examined. Added to these general limitat,ions are others It is apparent for floodplain rivers such as the which apply io most Afric.an countries : (1) a Iimit,ed Kavango that sampling efforts need to be coupled or modest data base on the life history of regional wit.h certain slow characteristics or flood stage over a fishes not target,ed for commercial enterprize (the period of many years to ascertain the status and latter always receive priority); (‘2) a void of informa- condition of faunal assemblages, and whet.her a tion on fish community structure and function, and somewhat fixed community st.ructure exists WATERQUALITY AS§ESSMENT IN THE KAVANGORIVER 379

(O’KEEFE, 1986). Emphasis should also be given to This does not preclude the fact, however, that sampling in coincidence with biot.ic processes such as other procedures which were historically used in the growth stage and reproductive intervals (CAMBRAYet Northern Hemisphere, but recently discarded in al., 1988), SOas to track environmental condit,ions as favor of the IBI approach, should be re-evaluated related to fish community life histories. Further- for their utility in African states and other develop- more, the development of standardized sampling ing countries, e.g., the Jaccard coefficient (HOCUTTet methodology will give more meaning to faunal al., 1974), species richness indices (PIELOU, 1975) or comparisons on both intra- and inter-drainage scales. Sequential Comparison Index (CAIRNSand DICKSON, As KLEYNHANSet al. (1993) noted for the Trans- 1971). This is especially SO given the various limita- vaal, RSA, many sub-Saharan catchments have been tions of the IBI procedure noted above, whic,h are sufficiently impacted that it is difflcult t.o re- compounded in Africa due to limited skilled man- c.onstruct what represents a pristine condition, or to power, variable environmental conditions influenc- establish control stations. Additionally, it is difllcult. to ing monitoring procedures, and general anecdotal judge which species are sensitive or tolerant to various stat,e of knowledge on aquatic, community structure categories of ecosystem disturbance. KLEYNHANS and functioning. The objective should be to evaluate et al. (1993) att.empted to overcome these problems established models, and to adapt them to the natio- by evaluating paramet,ers such as known distribu- nal or regional need to establish a relatively simple tion patterns, habitat and flow requirement,s, and rapid procedure for screening and monitoring water relative commonness, in relation to the historical quality. dat,a bases. Their philosophy is based largely on the recommendations by the LJSEPA (PLAFKIN el al., 1989) for implement,ing rapid bioassessment proto- cols to screen for “ troubled waters “. SUMMARY CAIRNS(1981) observed that biological assessment and monitoring of inland waters cari be expected to The establishment of aquatic resource monitoring pass through four developmental phases : (1) aware- protocols in -4frican st,ates should not be viewed as ness,‘(2) observat.ional, (3) predictive and (4) manage- an academic exercise. Al1 continental rivers either rial. He noted that developed countries are at the have modilîed slow regimes or land use-associated predictive stage, but conceded that present pract,ices impacts. Given the likelihood of increased wat,er had proven inadequate for the prediction of effects resource utilization, stream alterations, development or the validation of t.he predictions. KARR (1957, activities, population expansion, riparian zone modi- 1991, 1994), however, considered that aquatic ecolo- fications, global warming and SO fort,h, it is prudent. gists were at the threshold of predictive capability, t,o consider long-term water quality surveil1anc.e pro- and defended the science by drawing analogies to the grams for a11catchmenfs. As st,ated in the introduc- US. Bureau of Economies 80 y0 failure rate to pre- tory remarks, such programs should be considered dict even the sign of change of the nation’s gross complementary to, and an expansion of, biodiversity national product,, despite having a massive data base surveys aimed toward the doc.umentation of natural and powerful economic models. WELCOMME(1979a) heritage. As summarized by the World Conservation implied that a k 25 o/Oprecision should be an objec- Strategy (IUCN, 1980), sustainable development and tive of predicting the effects of environmental t.he mamtenance of natural systems are mut,ually change on flsheries. dependent processes. The biological criteria for aquatic resource assess- Some of the first steps to establish a biomonitoring ment proposed in this investigat.ion for the Kavango protocol are as follows : (1) Reference stations are River is regarded by no means as definitive, and by mandatory, thus the initial screening of prospective a11means preliminary. As the llrst attempt. to char- “ cont.rol ” sites is required ; (2) Effort, gear, method- acterize a floodplain river system by the struct.ure, ologies and personnel should be standardized; function and condition of its resident flsh commu- (3) Basic research on life history strategies of llshes, nity assemblages, this work is considered as a base and their structural and functional attributes in rela- line mode1 to build on in the face of continuing envi- tion to the ambient environment is a critical need. If ronmental degradat,ion and resource disparagement. possible, seasonal sampling efforts should be conduc- As biologists become more familiar with ecological ted during flooding, peak flooding, post flooding and requirements and t.olerance responses, those species low flow conditions to establish natural variability ; which prove to be indicative of particular distur- (4) Various biotic indices need to be evaluated on a bances Will be revealed, and the IBI bioçriteria case-by-case basis, and rellned to meet specific mode1 cari be shaped and evolved into a more effec- needs. No single index is universally free from bias tive monitoring tool. (USEPA, 1990); (5) Biotic information should be

R~U. Htptrobiol. trop. 27 (4) : 361-384 (1994). 380 C. H. HOCUTT,P. N. JOHNSON,C. HAY, B. J. VAN ZYL supplemented by physico-chemical data where pos- continued development, of water resource assessment and bio- sible ; and (6) Importantly, inter-basin management monitoring protocols amongst hfrican st,ates ! plans should be established by respective countries for a11 catchments since most bisect international ACKNOWLEDGMENTS boundaries, and there is a genuine need to avoid a “ tragedy of the commons " (HARDIN, 1968). The authors are indebted to t.he organizers and sponsors of PARADI for their generous support. of the presentation of this manuscript at, the International Symposium on Biological ADDENDUM Diversity in African Fresh and Brackish Water Fishes (PARADI) in Dakar, Senegal, November 1993. Particularly, This manuscript was presented as part of the Proceedings of we recognize the unt,iring ent.husiasm and cooperation of the Int.ernational Symposium on Biological Diversity in Afri- PARADI Secretary J. F. Guégan! cari Fresh and Brackish wat.er Fishes (PARADI), Dakar, Sene- The research effort was carried out through (a) the Histori- gai, 15-20 November 1993. cally Black Colleges and Universities (HBCU) sub-program of The senior author noted during his presentation that the t.he U.S. Agency for International Development, Contract. symposium was significant in t.hat it would serve as a bench DAN-5053-G-00-1048-00, awarded to the UniversitJi of XIary- mark of aquatic resource monitoring activities in Africa. For land Eastern Shore (UMES), and (b) a Senior Fulbright instance, three additional presentations considered the modifi- Research Fellowship to t.he senior aut.hor in affiliation with the cation of the Index of Biotic Integrity (IBI) for regional appli- Multi-Disciplinary Research Centre (MRC) of the University of cation : G. P. Ganda (Sierra Leone), A. Kamdem Toham et al. Namibia (UNAM). (Cameroon), and T. Oberdorff (general overview). Several ot,her This research represent.s a collaborative effort between per- presentations also considered fish community impacts from sonnel of UMES, UNAM’s MRC, and the Namibian Ministry anthropogenic sources : W. 0. Alegbeleye and P. E. Anyanwu of Fisheries and Marine Resources (NMFMR). UNhM faculty (Nigeria), F. W. B. Bugenyi (Uganda), 4. Cohen et al. (Lake or advisers who facilit,ated our efforts include Vice Chancellor Tanganyika), P. de Rham (Madagascar), 1. Doadrio and Peter Katjavivi, Prof. K. Mshigeni, Prof. A. Mafeje and A. Machordom (North Africa), T. D. Harrison ef al. (South Dr. 0. Hübschle. The senior aut.hor part,icularly recognizes Africa), E. F. B. Katunzi (Tanzania), J. W. Lewis et a/. UMES President William Hytche and Vice President. Edward (ea: situ monitoring), G. S. Merron (Okavango Delta), and Ellis for their persona1 commitment to the Namibia linkage. M. L. J. Stiassny (Madagascar), among others. Added to t.his Drs. G. J. Kleynhans and J. A. Cambray provided intuitive were various reviews which highlighted the impacts of exotics insight. to biolo&al monitoring in southern African waters. and fish transfers : S. A. 0. Dache (Lake Victoria), P. de Rham Special recognition is extended t.o Liz and Pete Kibble of and M. L. J. Stiassny (Madagascar), M. Gophen et al. (Lake Rundu for their unselfish support, home, garage services and Victoria), R. Lowe-McConnell et al. (t,he Great. Lakes), R. Ogutu- companionship in the Kavango province, a11 of which made Ohwayo and M. Bruton (general overview), J. P. Olowo and t.his study more personally rewarding ! R. Ogutu-Ohwayo (Uganda), and B. C. W. van der Waal (Nami- bia). It is apparent that the door has been opened for the Manuscrif accepfé par le Comité de rédaciion le 28 janvier 1996

Rev. Hydrobiol. hop. 27 (&) : 361-384(1994). WATER QUALITY ASSESSMENT IN THE KAVANGO RIVER 381

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