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Hay, CJ, Næsje, TF, Jacobs, FJ, Simasiku, EK, Tweddle, D. 2020. Results and lessons learned after eight years of monitoring gillnet catches in the Zambezi and Chobe Rivers. NINA Report 1791. Norwegian Institute for Nature Research. Freshwater fish play an important role in the livelihood of millions of people around Africa. Despite Namibia being classified as semi-arid with very little open water sources compared to other parts of the continent, freshwater fish are vital for communities living along the Kavango, Zambezi, Chobe and Kwando Rivers in North-eastern Namibia. Recent studies have shown a decline in high-value fish species and the commercialisation of the resource that is contrary to the Inland Fisheries Policy of Namibia that states that inland fish should be for subsistence and for the benefit of the local communities. The aim of the project was to record the fishing patterns and catch rates from the fishery through the use of local fishers from the area, to provide the necessary information to manage the fish resource sustainably for the benefit of the local communities for present and future generations. The data set was analysed by dividing the data into two groups. Data were grouped into those collected between 2010 and 2013 (the period where the fisheries reserves had probably not yet had an impact on the resource) and those collected between 2015 and 2018 the period where the protected areas may have had any impact on the resource. The fishery targets certain fish species, mainly from the family Cichlidae, driven by local and regional markets. This commercialisation resulted in increased fishing effort over the years causing a decline in these targeted fish species. Selective fishing by the fishers was emphasised when comparing the catches from that fishery with those from the survey fishing by the Ministry that are considered to be representative of the fish population in these rivers due to the wide range of mesh size gillnets used. Three species, Oreochromis andersonii, O. macrochir and Coptodon rendalli dominated the gillnet catches from the fishery contrib-uting 65.3% of the total Index of Relative Importance (IRI). There has been a decline in the collection of data by the fish monitors towards the later stages of the study. The timely follow-up and validation of data received from the fish monitors are recommended to ensure high quality data. The catch per unit effort both in number and in weight declined from the first to the second sampling period, except for Kalimbeza where the catch rate in weight remained the same, perhaps indicating that the establishment of a fishery reserve in the Kalimbeza area had had some beneficial impact in stemming the decline seen in the other areas. The maximum length of selected fish species (of the more important species recorded in the catches) also declined during the study period. It is recommended that the monitoring by the fish monitors continue, but that the quality of the data be regularly evaluated.

Fifteen adult nembwe Serranochromis robustus (Günther, 1864) were tagged with radio transmitters in the Zambezi River, Namibia, from 4–15 November 2000 to record behaviour and outline the implications for fisheries management. The fish were tracked on average every 3.7 days until 18 May 2001. They stayed within relatively small home ranges, with a 95% probability of localization within an average area of 184 563m2. The fish utilized a mean river stretch of 1330 m (range = 24– 3787). Nembwe were recorded in a variety of habitats, and the individual variation in movements and habitat use was substantial. All the fish were recorded in the mainstream of the river, but 62% of the fish were recorded in one or more additional main habitat types. During rising and high water, 67% and 71% of the fish, respectively, were recorded in adjacent temporary flooded areas during some or all tracking surveys, but did not undertake long-distance migrations onto the floodplains. It is concluded that although staying within relatively small home ranges, nembwe appears as a species with a variable and flexible habitat utilization.Keywords: fish, radio-tagging, telemetry, home range, behaviour, fisheries management

In the Upper Zambezi and Okavango ecoregions, Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius and Serranochromis macrocephalus are important in subsistence fisheries, while S. intermedius and S. macrocephalus are often caught in commercial catches. Despite their importance, there is little information on their age and growth and age validation. Growth zone deposition rate in otoliths of B. lateralis, H. cuvieri, S. intermedius and S. macrocephalus was validated as annual using edge analysis in this study. Annual deposition of growth zones was corroborated by a fluorochrome marking experiment. Both methods demonstrated that one growth zone was deposited annually. Edge analysis demonstrated that the highest proportion of opaque zones was detected between August and December, most likely as a result of slow growth during lower temperature water during the preceding winter. With growth zone deposition validated as annual, future research should focus on determining the growth, maturity and mortality rates of these species, parameters which are important for their management.Keywords: Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius, Serranochromis macrocephalus

Hay, C.J., Næsje, T.F. & Thorstad, E.B. 2008. Fish populations, gill net catches and gill net selectivity in the Kunene River, Namibia. - NINA Report 325. 98 pp. The Kunene River The Kunene River originates near Huambo in Angola, from where it flows in a southerly direction towards Namibia. The catchment area is 107000 km2. In Angola, the upper reaches are relatively steep, while the middle sections form floodplain habitats. Once the river reaches Ruacana in Namibia, it turns west towards the sea, forming the border between Angola and Namibia for a distance of approximately 340 km. Floodplains are absent along the Namibian section. Objective The objective of this report is to provide baseline information about the fish resources in the Kunene River to form the biological foundation for recommendations for a sustainable management. Based on fish survey data from the period 1994-2004, the fish resources are described through studies of species diversity, relative importance of the different species, life history parameters, catch per unit effort and gill net selectivity. Methods Fish were collected at 18 locations with gill nets and seven other sampling methods (collectively called “other gears”), such as seine nets, cast nets, electrofishing apparatus and rotenone. The gill nets (22-150 mm mesh size) were used to survey open, deep-water habitats in the main stream near the shore and in deep backwater areas. Other gears targeted mainly small species and juveniles in shallow, vegetated and rocky habitats. Ten surveys were carried out in the period 1994-2004. A total of 16959 fish were caught, of which 6862 with multi-filament gill nets and 10097 with other gears. The most important species were identified by using an index of relative importance (IRI), which is a measure of the relative abundance or commonness of the species based on number and mass of individuals in the catches, as well as their frequency of occurrence. Results A total of 50 fish species were identified, of which four were marine species. In addition, Synodontis spp., an unknown freshwater species, an unknown marine species and Gobii-dae spp. were recorded. The families represented with the highest number of species were the Cyprinidae and Cichlidae, with 14 and 12 species, respectively. Southern Africa, Namibia, Kunene River fish populations, life history, CPUE, gill net selectivity, fish surveys, management of fisheries, fish diversity

Thorstad, E.B., Hay, C.J., Økland, F., Nickanor, N. & Næsje, T.F. 2007. Spatial behaviour and management of greenhead tilapia (Oreochromis macrochir) in the Zambezi River, Namibia. - NINA Report 287. 26 pp. The large cichlids in the Upper Zambezi River are valuable species in commercial and subsistence fisheries, and are popular among recreational anglers. However, reports of reduced catches are a major concern for the management authorities. To be able to develop local and regional management strategies, information on fish movements and habitat use is fundamental. The aim of this study was, therefore, to provide information on behaviour and habitat use of one of the most important cichlids, the greenhead tilapia (Oreochromis macrochir). Twenty-two greenhead tilapia (body length 25-44 cm) were captured and radio tagged 27- 60 km downstream from Katima Mulilo, Namibia, during 18-25 November 2003. They were subsequently tracked on average every 3.3 day (a total of 74 tracking surveys) during a period of rising water level (1 December - 28 March), high water level (29 March - 2 May) and decreasing water level (3 May - 5 August). Five transmitters were returned from local fishermen, giving a minimum exploitation rate of 23% during the study. Total distance moved by individuals during the study was on average 4,076 m (range 334- 19,666 m). Mean distance moved between tracking surveys was 100 m (range 14-518 m), and did not differ among periods. Home ranges were relatively small, with a 50% probability of localisation within an average area of 0.5 km2 and a 95% probability of localisation within an average area of 3.1 km2. Home range size did not differ among periods. The length of the river stretch used was on average 2,554 m (range 171-13,697 m). The fish utilised permanently water covered areas only (42% of the fish), alternated between permanently and temporarily water covered areas (50% of the fish), or utilised only temporarily water covered areas (8% of the fish). During rising water, 42% of the fish utilised temporarily flooded areas, during high water 40% and during decreasing water 50%. The proportion of fixes in temporarily flooded areas did not differ among periods. During the study, 67% of the fish were recorded in the main channel of the river, 63% in side channels, 63% in backwaters, 63% in swamps, 25% on the floodplain and 8% in the mouth of backwaters. (Note that percentages add up to more than hundred because some fish are recorded in more than one habitat type.) The fish were recorded in different positions related to vegetation; 83% of the fish were recorded at no vegetation (> 5 m away from vegetation), 75% near vegetation (≤ 5 m away from vegetation) and 83% inside/under vegetation. Only one fish was never recorded near or inside/under vegetation. Water depth where the fish were recorded varied between 0.3 and 12.7 m, and was on average 4.2 m. The fish were mainly associated with sandy substratum; 92% of the fish were recorded on sandy substratum, 58% on clay and 50% on muddy, soft bottom. Total width of the river where the fish were positioned varied between 30 and 2,000 m, and was on average 322 m. Distance to nearest shore varied between 1 and 1000 m, and was on average 51 m. Southern Africa, Namibia, Caprivi, Upper Zambezi River, Cichlidae, greenhead tilapia, Oreochromis macrochir, telemetry, radio tagging, tracking, movements, home range, habitat use, exploitation, flood plain, behaviour, management, fishery, catch-and-release angling, NINA Rapport

Næsje, T. F., Hay, C. J., Nickanor, N., Koekemoer, J., Strand, R. and Thorstad, E. B. 2007. Fish populations, gill net catches and gill net selectivity in the Lower Orange River, Namibia, from 1995 to 2001. - NINA Report 231. 81 pp. The White Paper “Responsible Management of the Inland Fisheries of Namibia” was finalised in December 1995, and forms the basis for the new Inland Fisheries Resources Act and Regulations concerning fish resources management in the different freshwater systems. All perennial rivers in Namibia are shared with neighbouring countries and also form large sections of the international borders between these countries. The effects on the resources of the subsistence, commercial and recreational fisheries in neighbouring countries must also be taken into consideration. Hence, successful management of the fish resources must be regionally orientated. When implementing fisheries regulations for such complex systems, information on the fish resources and their exploitation in the different water bodies is needed. Based on a series of studies of the fish resources in the perennial rivers in Namibia, recommendations are given for management regulations of the fisheries in the different rivers. These management regulations are aimed at involving local, national and international authorities and stakeholders. It is a priority to secure a sustainable utilisation of the fish resources for the benefit of local communities and future generations. Important aspects of fisheries management have been studied to form the basis for new management strategies. Studies involve descriptions of the fish resources (Hay et al. 2000, 2002, Næsje et al. 2004, this report) and the exploitation of fish resources, including the socioeconomic infrastructure of local societies (Purvis 2001a, b, Næsje et al. 2002, Hay et al. in prep.), fishing competitions (Næsje et al. 2001), catch and release fisheries (Thorstad et al. 2004), and movement, migrations and habitat utilisation of important fish species (Økland et al. 2000, 2002, 2005, Thorstad et al. 2001, 2002, 2003a, b, 2005). The studies of fish migrations conclude that certain fish species may migrate between countries, both laterally and longitudinally in these river systems, which emphasise the importance of joint local and regional co-management of the fish resources both on a national and international scale. Other species, however, are more stationary and, hence, more vulnerable to local exploitation. The biological and sociological aspects of the subsistence, semi-commercial and recreational fisheries have documented that in the absence of a strong formal system of fisheries management, the informal (or traditional) management component has remained in Namibia. However, there are strong calls from all levels for an improved and effective system for national and multinational fisheries management. In the present report, the fish populations in the Orange River are described on the basis of five surveys performed in the period 1995 - 2001. The project is a collaboration between the Freshwater Fish Institute of the Ministry of Fisheries and Marine Resources (MFMR), Namibia, and the Norwegian Institute for Nature Research (NINA). The study has received financial support from the Norwegian Agency for Development Cooperation (NORAD), the Ministry of Fisheries and Marine Resources in Namibia and the Norwegian Institute for Nature Research. Lower Orange River, Namibia, fish populations, management of fisheries, Ramsar site

Hay, C.J., Næsje, T.F., Kapirika, S. Koekemoer, J.H., Strand, R., Thorstad, E.B. & Hårsaker, K. 2002. Fish populations, gill net catches and gill net selectivity in the Zambezi and Chobe Rivers, Namibia, from 1997 to 2000. NINA Project Report 017: 1-88. Objective The objective of this report is to provide baseline information about the fish resources in the Zambezi and Chobe Rivers to form the biological foundation for recommendations for a sustainable management of the fisheries. Based on fish survey data from the period 1997-2000, the fish resources are described through studies of species diversity, relative importance of the different species, life history parameters, catch per unit effort and selectivity of gill nets. Methods Fish were collected in five areas (Katima Mulilo, Kalimbeza, Lake Lisikili, Impalila and Kabula Bula) with survey gill nets (multi-filament, 22–150 mm stretched mesh size) and ten other sampling methods, such as seine nets, cast nets, electrofishing apparatus and rotenone. These are collectively called ”other gears” in this report. The gill nets were used to survey open, deep water habitats (> 1 m) in the main stream near the shore and deep backwater areas with some aquatic vegetation. The other gears targeted mainly small species and juveniles of long-lived species in shallow, vegetated and rocky habitats. Nordic multi mesh sized mono-filament gill nets were included during the survey in 2000 to improve sampling in the deep-water habitats and of the smaller species. Furthermore, fish caught during a fishing competition were sampled in 2000 to include biological data from larger specimens. Data from sampling with Nordic nets and the fishing competition were only included in the life history analyses of selected species, and not in other analyses. The restrictive use of these data ensures comparable data sets with previously reported Okavango River surveys, where these methods were not used (Hay et al. 2000) Surveys were carried out three years in the spring during 1997-2000 and three years in the autumn during 1997-1999. A total of 66875 fish were sampled, 39852 in gill nets, 7005 in Nordic nets, 562 during the fishing competition and 19456 with other gears. The most important species in the survey catches were identified by using an index of relative importance (IRI), which is a measure of the relative abundance or commonness of the species based on number and weight of individuals in catches, as well as their frequency of occurrence. Seventeen of the most important species collected were selected for a more detailed analysis of life history and gill net selectivity. Results A total of 69 fish species were recorded during the surveys, in addition to unidentified Synodontis species. Due to difficulties with the taxonomic classification in the Synodontis spp. group, these species have been pooled, except the easily recognised Synodontis nigromaculatus. Seven Synodontis species have previously been listed for the Zambezi River, thus there may be up to six Synodontis species in the pooled Synodontis spp. group. The fish families represented with the highest number of species were the Cyprinidae and the Cichlidae, with 20 and 17 species, respectively. Six species were considered to be habitat specialists, which means their life history activities are confined to specific habitats, and that they required particular effort and equipment for collection. The habitat specialists recorded were Barbus codringtonii, Nannocharax macropterus, Leptoglanis cf dorae, Clariallabes platyprosopos, Chiloglanis fasciatus and Chiloglanis neumanni. Four of the species were difficult to find, whereas C. platyprosopos was common in its habitat. Low numbers of Barbus kerstenii and Clarias stappersii were caught. These species are, therefore, also considered rare in the Namibian part of the Zambezi/Chobe Rivers. Fourty species were caught in the gill nets (excluding Synodontis spp.). The ten most important species constituted 96 % of the total IRI. The two most important species (Brycinus lateralis and Schilbe intermedius) contributed to 73 % of the total IRI. The Characidae was the most important family in the gill net catches according to IRI (56 %), whereas the Cichlidae family constituted only a small part (2 %). Sixty-seven species were caught with the other gears (excluding Synodontis spp.). The ten most important species constituted 74 % of the total IRI. The two most important species (Tilapia sparmanni and Pharyngochromis acuticeps) contributed to 30 % of the total IRI. In contrast to the gill net catches, the Cichlidae was the most important family in catches with other gears, according to IRI (58 %). The species diversity was higher for the catches with other gears than with gill nets, which is attributed to the flexibility of the other gears, and that a much wider range of habitats was sampled. Thirty-six species were caught with gill nets at Kalimbeza, 33 species at both Kabula-Bula and Lake Lisikili, 28 species at Katima Mulilo and 24 species at Impalila (excluding Synodontis spp). Generally, ranking of the ten most important species in the gill net catches were corresponding at the different stations. When listing the ten most important species according to IRI at the five stations, only 15 species were represented in total. According to IRI, B. lateralis and S. intermedius dominated the gill net catches at all stations, with the exception of the Lake Lisikili, where Petrocephalus catostoma contributed more in number and weight than S. intermedius. Species diversity in the gill net catches measured as the Shannon diversity index differed among stations, with the highest diversity in the Lake Lisikili and the lowest at Katima Mulilo. The year round presence of vegetation and lenthic conditions may have contributed to the high species diversity in the Lake Lisikili. All the other stations included main stream habitats that usually yielded a lower catch and less variability in species. Hydrocynus vittatus was absent at Kabula-Bula in the Chobe River, both in gill net catches and in catches with other gears. The backwater habitat at Kabula-Bula is considered less favourable for H. vittatus. Among the ten most important species according to IRI, nine species were on the list both during high and low water. B. lateralis dominated the gill net catches during both periods. Water level had little effect on the species diversity in the gill net catches. However, three species had a marked decrease in the IRI from the high to the low water period, whereas six species had a marked increase. The body length of the fish caught was up to 92 cm. The modal length of fish caught in gill nets was 8.0-8.9 cm, whereas for fish caught with the other gears 3.0-3.9 cm. Thus, larger fish were caught with gill nets than with other gears, and this was true both for the species combined and for individual species. Twenty of the species caught had a maximum body length of 6 cm or smaller. Of the selected species, twelve species had a minimum length at maturity smaller than 10 cm, two species between 11 and 20 cm and two species larger than 20 cm. The minimum length at maturity was larger than or similar to the smallest fish caught with gill nets in all the selected species, except for both sexes of M. acutidens and males of P. catostoma. The length at 50 % maturity was larger than the minimum length of fish caught with gill nets for all the species of which 50 % maturity could be determined. The 17 species selected for a more detailed data analysis, contributed to 93 % of the biomass of fish caught with gill nets and 56 % of the biomass of fish caught with other gears (one of the selected species was never caught in gill nets). These species represented a large variation in biology, distribution and sizes. Measured as numbers of fish caught per setting, the smaller gill net mesh sizes were the most effective in catching these species. For nine of the species, catch per unit effort in numbers was highest for the 22 or 28 mm mesh size, and for three of the species the 35 mm mesh size. Only two species were most effectively caught in the larger mesh sizes (57 and 73 mm). Measured as weight per setting, larger mesh sizes were nina Project Report 017 more effective; six species were most effectively caught in the 22-28 mm mesh size, five species in the 35-45 mm mesh size and five species in the 57-150 mm mesh size. For all species combined, the 28 mm mesh size was the most effective measured both as numbers of fish caught and weight per setting. The Lake Lisikili station showed the highest catch per unit effort, both in terms of number of fish caught and weight. The lake resembles a large backwater habitat, especially during flood, which may increase the productivity of the area. The lowest catch per unit effort in both number and weight was at Katima Mulilo, where the main stream habitat dominates. Main stream habitats are usually less productive than backwater and floodplain habitats. The results did not show an unambiguous relationship between the catch per unit effort, habitat (mainstream versus backwater) and water level (low water versus high water). Statistical analyses were carried out in all cases where comparable data for all mesh sizes existed, separating the effects of station, habitat and water level. Furthermore, comparisons were made for small mesh sizes (22 to 35 mm) and large mesh sizes (45 to 73 mm) separately, and for catch per unit effort measured in numbers and weight separately. Backwaters had in all cases a significantly higher catch per unit effort than the mainstream - or no differences between backwaters and the mainstream were found. Regarding high and low water, no particular pattern could be seen. Conclusions The results from the surveys in the Zambezi/Chobe Rivers were compared with previous studies in the Okavango River (Hay et al. 2000). Generally, the fish fauna in the Zambezi/Chobe and Okavango Rivers showed great similarities, and there is a considerable overlap in the distribution of species between the rivers. The complex and diverse nature of the fish fauna in the Namibian part of the Upper Zambezi has been revealed through the present surveys. However, detailed knowledge on the biology and behaviour of most of the species are still lacking. Basic information on life history, reproduction, movements, habitat preferences and habitat utilisation of target species is needed to regulate the fishery among the different countries and exploitation methods, and to evaluate the possible benefits of nature reserves and sanctuaries. The Upper Zambezi is presently still relatively undisturbed by human impacts. For that reason alone, this system should be better studied to provide a baseline for future manipulations.