Polypteridae, Teleostei) in the Pendjari River (Benin

Bulletin of Fish Biology Volume 16 Nos. 1/2 31.12.2016 83-86

Short note/Kurze Mitteilung

Fishery impact on bichirs (Polypteridae, Teleostei) in the Pendjari River (Benin)

Auswirkungen der Fischerei auf Flösselhechte (Polypteridae, Teleostei) im Pendjari (Benin)

Timo Moritz

Deutsches Meeresmuseum, Katharinenberg 14-20, 18437 Stralsund, & Zoologisches Institut mit Phyletischem Museum, Universität Jena, Erbertstr. 1, 07743 Jena, [email protected]

Zusammenfassung: Reusenfänge von Polypterus endlicherii Heckel, 1847 und Polypterus senegalus Cuvier, 1829 aus dem Pendjari in Benin wurden untersucht. Beim Vergleich von Gebieten mit Fischerei und ohne Fischerei zeigte sich, dass beide Arten in den ungestörten Gebieten häufi ger sind und in Gebieten mit Fi- scherei im Durschnitt eine geringere Standardlänge aufweisen. Letzteres ist bei P. endlicherii besonders stark ausgeprägt; es scheint, dass diese Art (und möglicherweise auch andere große Polypterus-Arten) besonders empfi ndlich auf Fischereiaktivitäten reagieren. Um dies zu belegen, wären weitere vergleichende Untersu- chungen hierzu nötig, jedoch sind völlig ungestörten Flussabschnitte in der westafrikanischen Savanne so gut wie nicht mehr zu fi nden..

The family Polypteridae is endemic to and Pendjari River, also within the national park widely distributed in African freshwaters. Some (MORITZ & LALÉYÉ subm.). species show a wide distribution, e.g. Polypterus Sampling took place in the Pendjari National endlicherii and Polypterus senegalus, occurring from Park, Northern Benin, between November the Nile basin to all over West Africa, the lat- 2004 and Mai 2005. Three locations on which ter species even in the Katanga area of the repeatedly sampling took place are included Southern Congo basin (GOSSE 1984). During here: the “Mare Diwouni”, a lake close to the ichthyologic fi eldwork in the Pendjari National border of Burkina Faso, “Pendjari-Hotel”, Park in Benin there was a unique possibility a river section affected by fi shery, where the to study an undisturbed river stretch of the Pendjari forms the boundary between Burkina Pendjari River. Fish sizes and densities remark- Faso and Benin, and “Pendjari-Bondiagou”, an ably differed to catches from other sampling undisturbed river section in the south-western points of the Pendjari River. This especially part of the Pendjari National Park. Although holds true for two Polypterus species of the area. there are several lakes along the river close to Thus, in this note three sample locations within the border of Burkina Faso, we unfortunately the Pendjari National Park were compared: a did not fi nd a lake without traces of fi shery, i.e. lake and a river section, which are exploited nets, net-holding sticks, hook-lines, fi shermen by fi shermen, and a river section in an almost or boats. undisturbed area. The Pendjari National Park Three-chambered double fykes (= hoop is limited in its western and northern direction traps), 11 mm mesh size in the last chamber, by the Pedjari river, which is the eastern most with 5 m leader net with 18 mm mesh size were tributary of the Volta basin. At the same time applied; leading net and fyke opening were the Pendjari river forms along its northern 40 cm. The double fykes were installed in water shore the frontier to Burkina Faso. Fishery depths of 0.5 to 1 meter. Whenever possible, is conducted from both countries along the fykes were installed in a way that the last chambers

Bull. Fish Biol. 16 (1/2) 83 of a trap allowed access to surface in order not were present only as remnants, e.g. fi ns, heads, to drown obligate air breathers (e.g. crocodiles, bones, in the fykes. snakes, turtles, lungfi sh, and bichirs). Caught fi sh Results are summarized in table 1; statistics were measured by standard length (SL) and total are performed with the programm PAST 2.17 length, and weighted. After that procedure, they (HAMMER et al. 2001): Both Polypterus species were released on the collection point, with the seem to be more common in the undisturbed exception of very few voucher specimens. area, by comparing the average number of Both river sections showed similar shore specimens per trap and day. In Bondiagou P. vegetation, gallery forests, but at Bondiagou the senegalus was present in two out of three traps; treetops of both sides get in contact, which is P. endlicherii was represented by more than two not the case at “Pendjari-Hotel”. Thus, Bon- specimens per trap. Sizes were smaller in areas diagou is almost impossible to reach by boat with fi shery, which is most accented in P. endli- and thus fi shery seems excluded, as fi shermen cherii: the average standard length in areas with enter the Pendjari upstream by boats (MORITZ fi shery was only two-thirds of the length found & LALÉYÉ subm.). Additionally, ichthyological in undisturbed areas (fi g. 1). Furthermore, the investigations are very diffi cult due to a risky total ratio between specimens of P. endlicherii combination of dense vegetation and high and P. senegalus differed from 1:2.71 in the Mare abundance of hippos (Hippopotamus amphibius). Diwouni over 1:1.25 in the Pendjari river at The high fish abundance can be seen even “Hotel” to 1:0.30 at Bondiagou. distant from the water: big Brycinus macrolepidotus The results show not only differences be- (Alestiidae) are swimming often close to the tween the disturbed and undisturbed areas, but surface and air-breathing fi shes often gulp air also differences between the two species. The on the surface. This investigation concentrates smaller P. senegalus was more common in the on Polypterus, as the traps of the undisturbed lake than in the river; it is often found also in area were mainly stuffed with big predators, wide distances from the main river (pers. obs.) i.e. Polypterus spp., Clarias spp., Auchenoglanis and often the only bichir managing to migrate occidentalis, Malapterurus electricus. Non-predatory into small reservoirs (pers. obs.). In P. endlicherii fi shes like alestids, mormyrids and mochokids, there is no abundance difference in the investi- except of some big Hemisynodontis membranaceus, gated lake and the neighbouring river.

Tab. 1: Sampling sites and respective catches; SL – standard length. Tab. 1: Untersuchungsstellen und zugehörige Fangdaten; SL – Standardlänge.

84 Fig. 1: Standard length of Polypterus species from Pendjar River at Bondiagou (B), the Hotel (H) and the lake Mare Diwouni (D); areas with ﬁ sheries (dark grey) and undisturbed area (light grey). Letters indicate statistical differences (Kruskal-Wallis-test, p<0.05). Abb. 1: Standardlänge der Polypterus-Arten vom Pendjari bei Bondiagou (B), Hotel (H) und im Mare Diwouni (D); Gebiete mit Fischerei (dunkelgrau) und ungestörtes Gebiet (hellgrau). Buchstaben geben statistische Unterschiede an (Kruskal-Wallis-test, p<0,05).

Fishery may have a high impact to certain for these trends: high sensitivity to fi shery at species, even if the actual fi shery activity seems all, heavy overexploitation, habitat alteration or low. This became evident during the last decades pollution are only some possible reasons. especially for some deep-sea species expressing The comparison of only three localities in the a rather slow life mode with slow growth, high herein presented study can only be a snapshot and longevity, late sexual maturity and probably does not allow any statistically confi rmed state- also low numbers of offspring, e.g. Hoplosthetus ments. But it should be regarded as an alarming atlanticus (BOYER et al. 2001, BRACH 2001, CLARK signal. A study which would aim to investigate 2009) and Dissostichus eleginoides (COLLINS et the primary fi shery impact on freshwater fi sh al. 2010). Examples from freshwaters may be communities in West Africa will likely be doo- sturgeons, for which however additional treats med to fail, due to the virtual absence of totally like blocking of migration routes further affect undisturbed water bodies. The Bondiagou river their decline (BIRSTEIN et al. 1997). For tropical stretch of the Pendjari gave an impression how freshwaters such informations are limited and undisturbed West African savannah rivers may often restricted to vague comparisons of single have looked like: during dry season the remaining reports of former times and today. NEUMANN water body is stuffed with fi sh – many of them et al. (2016) for example discussed possible predators. The fi shes of the savannah regions are changes in the fi sh community of the Main un doubtedly adapted to severe conditions, e.g. Nile, but also for this important water body time high temperatures, fl uctuating food availability, series from fi shermen catches or ichthyological risk of desiccation, and many are adapted to monitoring programs are not available and con- this environmental stress among other things clusions have to be estimated based on single by producing high numbers of offspring and by reports of former decades. Even if a heavy quick growing during good conditions. These are decline seems to be substantiated, it seems optimal conditions for high productive fi shery – almost impossible to reconstruct the reasons but the systems will work only as long as there are

Bull. Fish Biol. 16 (1/2) 85 enough big adults producing the high offspring help with research permissions. Additional thanks numbers. Should these conclusions be correct it is to all persons helping in fi eld work, especially absolutely inevitable to establish totally protected Vivica VON VIETINGHOFF, Kevin CONWAY and Ger- zones, from which fi shes can recolonize areas hard VON DER EMDE, and to Matthias MERTZEN for of intense fi shery (MORITZ & LINSENMAIR 2004), proofreading. This investigation was funded by the not only to protect the big species itself, but also BIOTA subproject W07 of the German Federal to guarantee sustainable and profi table fi shery. Ministry of Education and Research. A further necessity for sustainable biodiversity protection is profound and detailed information Literature on the life history of each species. We are for example not aware if large Polypterus species un- BIRSTEIN, J., J.R. WALDMAN, & W.E. BEMIS. 1997. dertake spawning migrations. There are reports Sturgeon biodiversity and conservation. Kluver that they perform lateral migrations, i.e. from the Academic Publisher, New York. BOYER, D.C., C.H. KIRCHNER, M.K. MCALLISTER, A. main river bed to fl ood plains (DAGET 1954), but STABY, A., & B.I. STAALESEN. 2001. The Orange migrations inside river systems are not yet known. Roughy fi shery of Namibia: lessons to be learned During a fi eld trip to Sudan in 2016, a fi sherman about managing a developing fishery. South very reliably reported that large Polypterus species African Journal of Marine Science 23, 205-221. occur only during certain times of the year at BRACH, T.A. 2001. A review of Orange Roughy Ho- the White Nile of Kosti (Mohammaed Abakar plostethus atlanticus fi sheries, estimation methods, Abdallah, Fisheries Reserach Institute Khartoum, biology and stock structure. South African Journal Apr. 2016). Thus, it seems that our knowledge on of Marine Science 23, 181-203. the life history of bichirs is still only fragmentary. CLARK, M.R. 2009. Deep sea seamount fi sheries: a The herein reported observations may indica- review of global status and future prospects. Latin American Journal of Aquatic Research 37, 501-512. te that P. endlicherii is highly sensitive to fi shery COLLINS, M.A., P. BRICKLE, J. BROWN, & M. BELCHIER. impact immediately responding with alteration 2010. The Patagonian Toothfi sh: biology, ecology in size-spectrum. This could be due to several and fi sheries, pp. 227-300. In: Advances in Marine reasons. One possible reason could be a high Biology. Volume 58 (LESSER, M., ed.). Academic sensitivity for fi ll nets: bichirs are mainly noc- Press, New York. turnal predators, which may be unable to detect DAGET, J. 1954. Les poissons du Niger superior. Mémoi- gillnets visually. With their armoured, only slightly res de l’Insitute Francais d’Afrique Noire 36, 1-391. compressible body they usually push obstacles GOSSE, J.-P. 1984. Polypteridae, pp. 18-29. In: Check- aside, instead of obviating them (pers. obs. in cap- list of the freshwater fi shes of Africa. Volume 1 (DAGET, J., J.-P. GOSSE, & D.F.E. THYS VAN DEN tivity). They are forceful, but not very persistent. AUDENAERDE, eds). Orstom, Paris. Therefore, the bichirs are predestined to entrap HAMMER, Ø, D.A.T. HARPER, & P.D. RYAN. 2001. themselves in gill nets and as they are obligate air PAST: Paleontological Statistics software package breathers they soon will drown. As gill nets are for education and data analysis. Palaeontologica size depending fi shing gears, species with bigger Electronica 4, 1-9. minimum maturation size will be more affected. MORITZ T., & K.E. LINSENMAIR. 2004. West African fi sh The minor decrease in size and abundance of P. diversity – distribution patterns and possible con- senegalus in the present study is in conformity with clusions for conservation strategies, pp. 187-195. In: the hypothesis that fi shery highly affects large African Biodiversity (HUBER, B.A., B.J. SINCLAIR, & K.-H. LAMPE, eds). Springer, New York. bichir species like P. endlicherii. NEUMANN, D., H. OBERMAIER, & T. MORITZ. 2016. An- notated checklist for fi shes of the Main Nile Basin Acknowledgements in the Sudan and Egypt based on recent specimen records (2006-2015). Cybium 40, 287-317. I thank D. A. TIOMOKO, director of the Parc Na- tional de la Pendjari, Benin, and P. LALÉYÉ and B. Received: 12.12.2016 SINSIN, Univeristé Abomey-Calavi, Benin, for their Accepted: 17.12.2016