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The hottentot seabream Pachymetopon blochii is a small-sized (maximum 2.67 kg) sparid endemic to southern Africa. It is an important target in South Africa's Western Cape traditional linefishery, particularly in the absence of more valuable pelagic species (such as Thyrsites atun and Seriola lalandi). In 2000, South Africa's linefishery was declared to be in a state of emergency, and commercial fishing effort was consequently reduced by 70%. A subsequent increase in stock biomass and intraspecific competition, coupled with environmental changes, were hypothesised to have thereafter altered the growth rate of hottentot, from 2000 to 2010. This study aimed to revise outdated age-growth models for the hottentot by using modern techniques (sectioned otoliths), and to compare age-growth relationships before and after the declared linefish state of emergency. The maximum age observed was 19 years, with no difference in the growth rate between sexes (p = 0.39-0.43) or time-periods (p = 0.96). Although the growth rate did not change, there is evidence that the age structure of the stock changed between time-periods as a result of changes in fishing pressure between 2000 and 2010. The enhanced recent growth model for hottentot, described as Lt = 418.063 (1 - e−0.104(t - [−4.709])) (pooled sexes; n = 206), indicates a considerably slower growth rate for this species than was proposed previously using whole otoliths and has major implications for effective stock management. [ABSTRACT FROM AUTHOR]

The dusky kob ( Argyrosomus japonicus) is a large, estuarine-dependent sciaenid fish that has been severely depleted in South African waters and that, in recent years, has received considerable attention from the local fish farming industry. Discovery and application of appropriate molecular markers is necessary to improve the understanding of wild population structure, assist the effectiveness of broodstock and breeding programmes, and ensure monitoring of potential interactions between wild and farmed fish. The present study uses a recently tested approach that combines the FIASCO enrichment protocol with 454 GS-FLX Next Generation Sequencing, to identify large numbers of microsatellite-containing sequences at a low cost and high discovery rate from the dusky kob genome. Following the FIASCO enrichment (targeting specifically tetranucleotide repeats), 2,355 potential tetranucleotide microsatellites (perfect repeat motifs including eight or more repeat units flanked by regions for primer design) were identified from 1/5th of a single 454 lane. From these sequences, a test panel of 60 potential markers was selected for validation. A total of eight (13 %) markers were successfully amplified from a test sample of wild dusky kob individuals and showed high levels of polymorphism (observed heterozygosity per locus ranging between 0.375 and 0.905). Cross-species amplification of seven of these markers was also successfully carried out in another closely related and commercially important South African sciaenid species, the silver kob ( A. inodorus). The microsatellite markers developed in the present study are readily available tools suitable to address genetic variability of Argyrosomus species of southern Africa. [ABSTRACT FROM AUTHOR]

The first documented recapture of a South African-tagged juvenile blue shark Prionace glauca off Uruguay lends weight to the hypothesis of a single blue shark population in the South Atlantic. The presence of neonate blue sharks with umbilical scars and females with post-parturition scars, as well as the high frequency of small juveniles in research longline catches, confirm the existence of a parturition and nursery area off South Africa. The final positions of three tagged sharks suggest that large-scale movement patterns in the South Atlantic are a mirror image of movements in the North Atlantic, with sharks using the north-westerly Benguela Drift to migrate into the tropics and ultimately across into South American waters. The confirmed existence of a parturition and nursery area off the south coast of South Africa and the movement of sharks into both adjacent ocean basins suggest that the southern African blue sharks are part of a single stock that straddles the South Atlantic and Indian oceans, and possibly the entire Southern Hemisphere. [ABSTRACT FROM AUTHOR]

White stumpnose Rhabdosargus globiceps were sampled over 24 months in Saldanha Bay on the west coast of South Africa. The species is a rudimentary hermaphrodite, with <1% of mature fish having simultaneously developed ovaries and testes. Spawning activity extended from September to March and peaked in October and February. Mature males developed spawning colouration in spring, which can be used as an indicator of spawning activity. The amount of abdominal fat correlated with the spawning cycle in both sexes, suggesting that abdominal fat reserves are used in the development of gonads. Seasonal variation in the condition index suggests a slightly greater investment in reproduction by males than females. Females grew slightly faster than males and attained a larger size. The Saldanha Bay fish grew more rapidly and matured earlier than fish from populations on the south coast of South Africa. Age-at-50% maturity was 2+ for females and 1+ for males, and size-at-50% maturity was 222 mm (fork length) for females and 194 mm for males. It is necessary to use area-specific growth and life-history parameters for the assessment of the stock status of white stumpnose in South Africa. [ABSTRACT FROM AUTHOR]

Exploitation of temperate reef fish not only affects the target species but potentially changes the composition of reef fish assemblages. This study investigated the effect of fishing on the ichthyofaunal community at protected and exploited sites around the Goukamma Marine Protected Area (MPA) on the South African temperate south coast. Abundance and size frequency data from 273 standardised angling and 44 underwater visual census sites were analysed with generalised linear modelling and multivariate techniques to separate the effects of exploitation, habitat, time of day and season. Ichthyofaunal communities differed significantly between protected and exploited sites, which is likely a result of differential fishing pressure. Abundance and size of roman Chrysoblephus laticeps, the dominant species of the local linefishery, were significantly lower at exploited sites. Non-target species with considerable dietary overlap with roman were significantly less abundant inside the MPA, probably due to interspecific competition, whereas species whose diets differed to that of roman were more abundant at protected sites. The results show that fishing can have an influence on the composition of target and non-target species and that these effects need to be considered in fisheries management and conservation planning. [ABSTRACT FROM AUTHOR]

The effect of fishing on benthic reef communities was studied by comparing reefs within and outside the Goukamma Marine Protected Area (MPA) on the South African warm-temperate south coast. Although study sites were similar in terms of bathymetry and oceanographic conditions, benthic reef communities were significantly different with higher abundance of algae and crinoidea at fished sites. Crinoidea, the principal food source of roman Chrysoblephus laticeps, was scarce at protected sites where this species was most abundant. Low algal abundance at protected sites was negatively correlated with grazer abundance within the fish communities encountered there, suggesting a high potential for coexistence of these trophic guilds. Other fish species showed dietary overlap with roman, and their abundance was likely controlled by interspecific exploitative competition for food. The study suggests that a moderate rate of fishing can alter benthic communities through indirect effects on temperate reefs in South Africa. [ABSTRACT FROM AUTHOR]

The effect of two marine protected areas (MPAs) on roman Chrysoblephus laticeps (Sparidae), an exploited reef-fish species inhabiting the South African temperate south coast, was simulated with a spatially explicit, individual-based model based on geographically correct habitat distribution. The model domains were small compared with the dispersal range of pre-recruits, and recruitment was held constant. Adult fish movement rules were based on the results of high-resolution mark-and-recapture and telemetry studies. Fish densities, age-structure and life-history parameters were derived from comprehensive underwater surveys and biological analyses. The model included the effect of fishing on size-at-sex change. The results indicate a recovery of fish abundance-per-recruit, size frequency and sex ratio to, or close to, pre-exploitation levels within the protected areas 10 years after the implementation of both MPAs. Results suggest that, for resident species such as roman, even small MPAs (6 km2) can offer protection. The small exchange of post-recruit fish into the adjacent areas results in negligible improvement (1%) of catches. The MPAs support more and larger spawning fish, which may improve recruitment into adjacent fished areas. [ABSTRACT FROM AUTHOR]

The spatial and temporal area-use patterns of estuarinedependent juvenile dusky kob Argyrosomus japonicus in the Great Fish Estuary, South Africa, were examined using acoustic telemetry. In all, 29 individuals (307-400 mm total length) were surgically equipped with individually coded transmitters and monitored for a period of up to 195 days using an array of 11 moored data-logging acoustic receivers. Tagged dusky kob spent most time in the estuary (84%), compared with neighbouring marine (13%) and riverine (4%) environ ments. Tagged fish made extensive use of the estuary from the mouth to between 6.4 km and 10.3 km upstream, and spent approximately equal proportions of time at each of the seven receivers located between 0.5 km and 6.5 km from the mouth. A total of 18 fish undertook sea trips of a mean duration of 3.5 days, whereas three individuals made riverine excursions (mean duration = 7.3 days). A total of 12 (41%) tagged fish was captured in the estuary prior to, during or after the monitoring period. These findings highlight the importance of estuaries as critical nursery areas, and that the use of these habitats by dusky kob should be better reflected in the management arrangements for this fishery species. [ABSTRACT FROM AUTHOR]