Fish response to the annual flooding regime in the Kavango River along the Angola/Namibia border

The results of the first seasonal survey of the fish of the Kavango River floodplain along the Angola/Namibia border are reported. The river experiences peak flooding from February through June, with the 375-km long floodplain extending up to 5 km across. The floodplain was sampled five times in 1992 by seine, fish traps and rotenone. The data indicated a pronounced structural and functional response of the fish community in relation to the alternating flood and drought conditions in the river. Catch per unit effort and diversity were highest during months of peak flooding (May and June), and lowest during the month of least flow (November). The reproductive strategies of K-selected piscivorous cichlids and tigerfish were in advance of flooding. Many r-selected invertivores, especially cyprinids, were in relative synchrony with flooding and the stimulation of littoral zone plant growth, while other invertivores lagged the cyprinids. Herbivores had lowest relative abundance during peak flooding; this seemingly inverse relationship with the invertivores should not be interpreted as replacement, but rather the swamping of the system with young-of-the-year r-selected invertivores. The data support the Flood Pulse Concept, which hypothesizes that flooding is the major “driver” of productivity in lowland or floodplain rivers.Keywords: behaviour, floodplain fishery, migration, Okavango Delta, r-/K-selection, subsistence fisheryAfrican Journal of Marine Science 2001, 23: 449–46

Passive acoustic telemetry reveals highly variable home range and movement patterns among unicornfish within a marine reserve

Marine reserves are the primary management tool for Guam’s reef fish fishery. While a build-up of fish biomass has occurred inside reserve boundaries, it is unknown whether reserve size matches the scale of movement of target species. Using passive acoustic telemetry, we quantified movement patterns and home range size of two heavily exploited unicornfish Naso unicornis and Naso lituratus. Fifteen fish (N. unicornis: n = 7; N. lituratus: n = 4 male, n = 4 female) were fitted with internal acoustic tags and tracked continuously over four months within a remote acoustic receiver array located in a decade-old marine reserve. This approach provided robust estimates of unicornfish movement patterns and home range size. The mean home range of 3.2 ha for N. unicornis was almost ten times larger than that previously recorded from a three-week tracking study of the species in Hawaii. While N. lituratus were smaller in body size, their mean home range (6.8 ha) was over twice that of N. unicornis. Both species displayed strong site fidelity, particularly during nocturnal and crepuscular periods. Although there was some overlap, individual movement patterns and home range size were highly variable within species and between sexes. N. unicornis home range increased with body size, and only the three largest fish home ranges extended into the deeper outer reef slope beyond the shallow reef flat. Both Naso species favoured habitat dominated by corals. Some individuals made predictable daily crepuscular migrations between different locations or habitat types. There was no evidence of significant spillover from the marine reserve into adjacent fished areas. Strong site fidelity coupled with negligible spillover suggests that small-scale reserves, with natural habitat boundaries to emigration, are effective in protecting localized unicornfish populations