Out of the pot and into the fire: Explaining the vulnerability of an endangered small headwater stream fish to black-bass Micropterus spp. invasion.

Introduced predatory fishes have had consistently severe consequences for native fishes in stream environments around the world, although the drivers of these effects are often unclear. In the Swartkops River headwaters in South Africa, native Eastern Cape redfin Pseudobarbus afer were always absent from sites occupied by non-native black basses Micropterus salmoides and Micropterus dolomieu, but generally co-occurred with the native predators Anguilla marmorata and Anguilla mossambica. A natural experiment provided by flood-mediated recolonization of black-bass occupied sites by P. afer demonstrated depletion in black-bass invaded sites. Field behavioural observations of P. afer indicated that they foraged among benthic cover during the day, but suspended in open water at night. As the nocturnal A. marmorata and A. mossambica foraged actively within structural cover at night and M. dolomieu and M. salmoides are diurnal or crepuscular predators, P .afer is thus optimized to avoid predation by native anguillid predators and not the functionally unique predatory black basses. The integration of distributional, temporal population dynamics and behavioural data suggests that the severe effects of Micropterus spp. are probably a consequence of prey naïveté and behaviour evolved to evade native predators.

A review of Clarias gariepinus invasions in Brazil and South Africa.

African sharptooth catfish Clarias gariepinus is native to most of Africa and small parts of Asia, but has been introduced to 37 countries mainly for aquaculture. This review of introductions, establishment, spread and impact of C. gariepinus in Brazil and outside of its native range in South Africa provides evidence that the species has been able to overcome all barriers to invasion in both countries. Following initial introductions across geographical barriers, containment seems to have been impossible and escape from aquaculture facilities and spread by illegal introductions is an invasion pathway in both countries. There is evidence of individuals dispersing rapidly following escape, and surviving and reproducing at multiple sites in a wide spectrum of habitats in both countries. There is a severe paucity of research on impacts, many of which are inferred from field and laboratory observations, but have not been demonstrated at population or community level. Such impact studies are urgently required to better understand the consequences of these invasions and to develop appropriate strategies to mitigate impacts and spread.

Managing conflicts arising from fisheries enhancements based on non-native fishes in southern Africa.

Southern Africa has a long history of non-native fish introductions for the enhancement of recreational and commercial fisheries, due to a perceived lack of suitable native species. This has resulted in some important inland fisheries being based on non-native fishes. Regionally, these introductions are predominantly not benign, and non-native fishes are considered one of the main threats to aquatic biodiversity because they affect native biota through predation, competition, habitat alteration, disease transfer and hybridization. To achieve national policy objectives of economic development, food security and poverty eradication, countries are increasingly looking towards inland fisheries as vehicles for development. As a result, conflicts have developed between economic and conservation objectives. In South Africa, as is the case for other invasive biota, the control and management of non-native fishes is included in the National Environmental Management: Biodiversity Act. Implementation measures include import and movement controls and, more recently, non-native fish eradication in conservation priority areas. Management actions are, however, complicated because many non-native fishes are important components in recreational and subsistence fisheries that contribute towards regional economies and food security. In other southern African countries, little attention has focussed on issues and management of non-native fishes, and this is cause for concern. This paper provides an overview of introductions, impacts and fisheries in southern Africa with emphasis on existing and evolving legislation, conflicts, implementation strategies and the sometimes innovative approaches that have been used to prioritize conservation areas and manage non-native fishes.

Age and growth and maturity of southern Africa's largest cyprinid fish, the largemouth yellowfish Labeobarbus kimberleyensis.

The aim of this study was to use specimens of the largemouth yellowfish Labeobarbus kimberleyensis, southern Africa's largest cyprinid [IUCN red-listed as Near Threatened (NT)], obtained from gillnet by-catch to describe aspects of its biology in order to assist future conservation and management decisions. Ninety three L. kimberleyensis were collected between March 2007 and May 2008 from Lake Gariep, South Africa. Labeobarbus kimberleyensis was present in 38% of all gillnet catches, but in low numbers (2% of the catch) and it contributed 8% to the catch by mass. Age was estimated using astericus otoliths. Growth increment formation on these otoliths was validated as annual using edge analysis and the mark-recapture of chemically tagged captive fish. Resultant analysis showed that the species is slow growing and the oldest aged fish was a 17 year, 690 mm fork length (L(F)) male. The smallest ripe female fish measured 394 mm L(F) and was 7+ years old and the smallest mature male was 337 mm L(F) and 5+ years old. Slow growth and late maturity make this species vulnerable to exploitation emphasizing the need for continued high conservation priority.

Regional variation in otolith Sr:Ca ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes.

Otolith Sr:Ca ratios of the African longfinned eel Anguilla mossambica and giant mottled eel Anguilla marmorata from nine freshwater sites in four rivers of South Africa were analysed to reconstruct their migratory life histories between freshwater and saltwater habitats. For A. mossambica, the Sr:Ca ratios in the otolith edge differed significantly among rivers and had large effect sizes, but did not differ among sites within a river. Otolith Sr:Ca ratios did not differ among rivers for A. marmorata. When rivers were pooled, the edge Sr:Ca ratios of A. mossambica were not significantly different from those of A. marmorata. According to the river-specific critical Sr:Ca ratio distinguishing freshwater from saltwater residence, most A. mossambica and A. marmorata had saltwater habitat experience after settlement in fresh water. This was primarily during their elver stage or early in the yellow eel stage. During the middle and late yellow eel stage, freshwater residency was preferred and only sporadic visits were made to saltwater habitats. The data also suggest that regional variations in otolith Sr:Ca ratios affect the critical Sr:Ca value and are a challenge for the reconstruction of migratory life histories that should be explicitly considered to avoid bias and uncertainty.

Validating and corroborating the deposition of two annual growth zones in asteriscus otoliths of common carp Cyprinus carpio from South Africa's largest impoundment.

A total of 816 common carp Cyprinus carpio asteriscus otolith pairs were collected from Lake Gariep, South Africa. Otoliths were interpreted whole, submerged in methyl salicylate and viewed under transmitted light. The precision of growth zone counts of the primary reader was estimated at 5·54 and 7·03% using the average per cent error method and the coefficient of variation, respectively. Age-bias plots indicated no systematic bias between the primary reader and the three secondary readers for up to nine growth zones (95% of the sample). Growth zone deposition rate was validated using a mark-recapture experiment of chemically tagged C. carpio (n = 21) conducted in a large earthen pond under ambient conditions in the vicinity of Lake Gariep. The validation results were corroborated for the wild population by edge analysis and a length-based age-structured model. All three methods suggest that growth zone formation occurred biannually, exemplifying the importance of age validation as a prerequisite for understanding the life history of C. carpio.