Biology, stock assessment and management of the panga Pterogymnus laniarius on the Agulhas Bank, South Africa

The panga, Pterogymnus laniarius (Cuvier, 1830), is a South African endemic sparid fish species. On the Agulhas Bank, South Africa it is a commercially important species, caught as bycatch in the hake directed trawlfisheries and targeted by offshore hook-and-linefishers. Recently there has been considerable interest shown in directing further fishing effort on this species. The lack of a suitable management procedure for teleost bycatch in South Africa was the principal reason for undertaking this study. This thesis investigates aspects the panga's life history, particularly those aspects that have management implications. A full knowledge of this species' distribution and abundance was necessary as this could highlight the existence of any nursery areas, ontogenetic migratory patterns and areas of high spawner biomass. The derived parameter estimates were then included as inputs into stock assessment models to determine the status and productivity of the resource. Growth studies based on sectioned sagittal otoliths revealed that the panga was a relatively slow growing fish with ages of 16 years being recorded. Growth was best described by the von Bertalanffy growth model as Lt=379.4(1-e⁻°·¹³⁽t ⁺ ¹·⁷⁸⁾). Total, natural and fishing mortalities were estimated at 0.36 year⁻¹, 0.28 year⁻¹ and 0.08 year ⁻¹, respectively. Detailed histological examination of the gonads revealed that panga is a late gonochorist, males and females maturing after a non-functional intersexual stage. Females mature at approximately 200 mm fork length or 4 years of age. Reproduction occurs throughout the year although there is a slight peak in winter. Gametogenesis was found to be similar to that of other sparid fishes and marine teleosts in general. The panga feeds predominantly on crustaceans with a distinct ontogenetic shift in feeding habits. Juvenile fish feed predominantly in the water column on mysids after which they move to the benthos. Subadult fish feed principally on ophiuroids and amphipods. Adult fish remain on or near the benthos, feeding predominantly on crabs, and on polychaetes, ophiuroids and fishes to a lesser extent. Several aspects of the panga's biology contribute to its ability to sustain a higher fishing pressure than other sympatric sparid species. These include its late gonochoristic reproductive style, protracted spawning season, maturation before recruitment and preference for soft substratum prey that enables it to utilise large areas of the Agulhas Bank. The panga's longevity, slow growth and low natural mortality rate, however, mitigated against these factors and were considered in the stock assessments. A heterogeneous Geographical Information System (GIS) was developed to analyse the distribution and abundance patterns of the panga. The GIS developed in this thesis makes a significant contribution towards the development of a South African Fisheries Information System to analyse and manage fish resources in general and bycatch resources in particular. The GIS developed in this study combines statistical Generalized Additive Modelling and standard GIS methods. Analysis of fourteen biannual fishery independent biomass surveys, disaggregated by life history stage, revealed that a nursery area for immature fish (<23 cm TL or < 4 years of age) exists on the Central Agulhas Bank. After sexual maturation, approximately 40% of the biomass migrated eastwards, colonising large areas of the Eastern Agulhas Bank.ilie location of the nursery area appears to be a result of the pelagic eggs and larvae being advected towards the coast in an anti-cyclonic gyre, stemming off the Agulhas current and later deposited over the Central Agulhas Bank. The weak bottom currents on the Central Agulhas Bank prevented juvenile loss to the Benguela system. The eurytopy of adult fish to various physical variables such as temperature, dissolved oxygen and stronger currents enabled it to reduce conspecific competition and migrate eastwards with distribution primarily determined by depth. Relative biomass estimates revealed a gradual increase in biomass of 5.5% per annum between 1988 and 1995. Predictions from yield-per-recruit, biomass-per-recruit and spawner biomass-per-recruit analyses showed that there was scope for further exploitation. A FSB₅₀ fishing strategy was considered to be the most appropriate fishing strategy as it did not reduce the spawner biomass-per-recruit to less than 50% of unexploited levels. Effort control was considered the most effective management tool as the age-at-50%-selectivity occurred after age-at-sexual maturity and releasing undersized fish was undesirable due to heavy mortalities resulting from severe barotrauma. The panga resource was also assessed using an age-structured production model. The values for the free parameters of the model were estimated using biomass indices derived from fishery-independent trawl surveys. Although the data were fairly uninformative about the productivity of the resource, the results indicated robustly, that the population has recovered from low levels in the mid-1970's and could sustain higher levels of fishing intensity. Risk analysis calculations were used to assess the sustainability of different catch scenarios. The level of sustainable catch was found to be sensitive to the selectivity pattern of the gear utilised. Both stock assessment methods used in this study to investigate the status of the panga resource showed that the resource could theoretically sustain higher catches. It was found that although the stock could be harvested using available fishing methods, the sympatry of this species with other commercial species was of concern as the latter would form a significant bycatch in a panga directed fishery. The failure of current harvesting methods to address the bycatch problem highlights the management problem in South Africa and stresses the need for creativity by both scientists and fishers in designing new and improved methods for selectively harvesting bycatch fish resources. Considering that no suitable method is currently available to fish the panga stock in a directed fishery the fishery should be managed as status quo until some suitable and efficient gear is developed

Spatio-temporal patterns in maturation of the chokka squid (Loligo vulgaris reynaudii) off the coast of South Africa

Knowledge of the temporal and spatial characteristics of chokka squid (Loligo vulgaris reynaudii) biology in South African waters is limited, so the possibility of there being a geographically fragmented stock was examined by investigating the distribution of maturity patterns for the species, covering all known spawning areas and using both historical and recent data. Gonadosomatic indices (GSI) varied between year-round consistency and apparent seasonal peaks in both summer and winter; there was no clear spatial pattern. Monthly percentage maturity provided further evidence for two peak reproductive periods each year, although mature squid were present throughout. Sex ratios demonstrated great variability between different areas and life history stages. Male-biased sex ratios were only apparent on the inshore spawning grounds and ranged between 1.118:1 and 4.267:1. Size at sexual maturity was also seasonal, squid maturing smaller in winter/spring than in summer/autumn. Also, squid in the east matured smaller than squid in the west. Although the results from the present study do not provide conclusive evidence of distinct geographic populations, squid likely spawn over a significantly larger area of the Agulhas Bank than previously estimated, and squid on the west coast of South Africa may return to spawn on the western portion of the Agulhas Bank. It remains likely, however, that the east and west coast populations are a single stock and that migration of juveniles to the west coast and their subsequent return as sub-adults is an integral but non-essential and variable part of the life history

Evolution of Labeo victorianus predates the Pleistocene desiccation of Lake Victoria: evidence from mitochondrial DNA sequence variation

Geological data show that Lake Victoria dried out some 15 000 years ago. These data suggest that the entire faunal diversity within the lake has evolved since this time. However, mitochondrial DNA sequence diversity in the endemic cyprinid fish, Labeo victorianus, was high (24 haplotypes in 38 individuals; percentage sequence divergence of 0.74%), suggesting that the evolution of this species predates this Late Pleistocene climatological event. This finding is consistent with what has been reported earlier for cichlid fishes in the lake

Population structure and growth of polydorid polychaetes that infest cultured abalone Haliotis midae

Polydorid polychaetes can infest cultured abalone thereby reducing productivity. In order to effectively control these pests, their reproductive biology must be understood. The population dynamics and reproduction of polydorids infesting abalone Haliotis midae from two farms in South Africa is described using a length-based, age-structured model. Shells were infested mainly by introduced Boccardia proboscidea. Polydora hoplura and Dipolydora capensis were also present but in numbers too few to identify factors influencing infestation. At both farms, B. proboscidea lived for a minimum of 12 months. Growth rate, size at maturity, maximum size, infestation intensity, recruitment, percentage of the population brooding and mortality appear to be affected by abalone feeding regime and water temperature, and these factors need to be considered in controlling infestation. Brooders and recruits were present throughout the year, but increased significantly during mid- to late winter/early spring when water temperature and day length increased. Treatment measures should therefore be implemented throughout the year but with increased effort when water temperature increases

Spatial aspects of the reproductive and feeding biology of the striped robber, Brycinus lateralis (Pisces: Characidae), in the Okavango Delta, Botswana

The Okavango Delta is a vast inland wetland system situated in northern Botswana. High rainfall is received in early summer in the southern Angolan highlands and throughout the Delta with the flood waters reaching the upper riverine floodplain between March and May where it percolates through to the lower drainage rivers between July and September. Aspects of the reproductive and feeding biology of two allopatric populations of the striped robber, Brycinus lateralis, a small characin species inhabiting the northern riverine floodplain and southern drainage rivers, were investigated. Both populations were similar in the biological aspects studied, with the flood cycle having little influence on the timing of reproduction, sexual maturity and dietary composition. Female fish from both populations matured sexually at 57mmSL, breeding over a protracted period during the warm, summer months. In both populations, the sex ratio was female-dominated at 4.8:1 (riverine floodplain) and 2.2:1 (drainage rivers). The striped robber is an opportunistic micro-carnivore with immature fish feeding predominantly on Daphnia spp. and adults being largely insectivorous

Spatial and seasonal distribution patterns of the ragged-tooth shark Carcharias taurus along the coast of South Africa

Off South Africa, the ragged-tooth shark Carcharias Taurus has been occasionally reported from the West Coast, but it is more commonly found along the East and South coasts from Cape Town to northern KwaZulu-Natal (KZN) (Bass et al. 1975, Smale 2002). Mating is thought to occur off the south coast of KZN from October to late November (G Cliff, Natal Sharks Board, unpublished data). Pregnant females then move northward to spend the early part of their gestation in the warmer waters of northern KZN and possibly southern Moçambique. During July and August, the near-term pregnant females begin to move southwards towards the cooler waters of the Eastern Cape (Wallett 1973, Bass et al. 1975, G Cliff, unpublished data), where they give birth from September to November (Smale 2002). After parturition, many of the females migrate back to KZN. The whereabouts of mature males outside of the mating season is unclear. These broadscale distribution and migratory habits for C. taurus have been inferred from limited catch records obtained for only parts of its range along the South African coast

Shark fishing effort and catch of the ragged-tooth shark Carcharias taurus in the South African competitive shore-angling fishery

In South Africa, Carcharias taurus is commonly known as the ragged-tooth shark or raggie. The species is also referred to as the sand-tiger shark in North America and as the grey-nurse shark in Australia. It is a long-lived species with an estimated longevity of up to 40 years (Goldman 2002). Female sharks reach sexual maturity at approximately 10 years (Goldman 2002), and they exhibit a biennial reproductive cycle (Branstetter and Musick 1994, Lucifora et al. 2002, G Cliff, Natal Sharks Board, unpublished data). Intra-uterine cannibalisation results in a maximum fecundity of two pups per litter after a gestation period of approximately 9–12 months (Bass et al. 1975, Gilmore et al. 1983). These life-history characteristics make this species particularly susceptible to overexploitation

Circadian preference and physical and cognitive performance in adolescence:A scoping review

Adolescence is a crucial period of development which coincides with changes in circadian rhythmicity. This may augment the impact of circadian preference on performance in this group. We aimed to scope the literature available on chronotypes and their effect on physical and mental aspects of performance in adolescents. Methods: Studies were identified by systematically searching bibliographical databases and grey literature. Results: The Morningness-Eveningness Questionnaire was the most frequently reported tool for circadian preference assessment. Academic achievement was the most prevailing outcome, with evidence suggesting that morning type adolescents tend to outperform evening types, yet the results vary depending on multiple factors. Performance in tests of intelligence and executive functions was generally better at optimal times of the day (synchrony effect). Physical performance was examined in 8 studies, with very heterogeneous outcomes. Conclusions: Although the associations between circadian preference and performance in adolescents are evident in some areas, there are many factors that may be involved in the relationship and require further investigation. This review highlights the assessment of physical performance in relation to chronotypes, the multidimensional assessment of circadian preference, and the need for longitudinal studies as priorities for further research

Evaluation of Criteria to Detect Masked Hypertension

The prevalence of masked hypertension, out-of-clinic daytime systolic/diastolic blood pressure (SBP/DBP)≥135/85 mmHg on ambulatory blood pressure monitoring (ABPM) among adults with clinic SBP/DBP<140/90 mmHg, is high. It is unclear who should be screened for masked hypertension. We derived a clinic blood pressure (CBP) index to identify populations for masked hypertension screening. Index cut-points corresponding to 75% to 99% sensitivity and prehypertension were evaluated as ABPM testing criterion. In a derivation cohort (n=695), the index was clinic SBP+1.3*clinic DBP. In an external validation cohort (n=675), the sensitivity for masked hypertension using an index ≥190 mmHg and ≥217 mmHg and prehypertension status was 98.5%, 71.5% and 82.5%, respectively. Using NHANES data (n=11,778), we estimated that these thresholds would refer 118.6, 44.4 and 59.3 million US adults, respectively, to ABPM screening for masked hypertension. In conclusion, the CBP index provides a useful approach to identify candidates for masked hypertension screening using ABPM

Spatial description of hake-directed fishing activity off the west coast of South Africa

Historically, the two species of Cape hakes Merluccius capensis and M. paradoxus off South Africa were commercially exploited exclusively by demersal trawling. In 1994, hake-directed demersal longline was introduced on an experimental basis, and in 1998 was initiated as a commercial fishing sector. The effect of a combined fleet composed of both trawlers and longliners on the Cape hake resource is not fully understood. Analysis of fishing intensity and catch-rate data revealed that the highest catch rates were found around the 400m and 500m isobaths for the trawl and longline fisheries respectively. Catch rates from both fishing sectors were also noted to be higher over sediments with a sand component. Differences between areas of the highest fishing intensity and highest catch rates were noted. In addition to other factors, it is suggested that a ‘friction of distance’ effect applies — vessels will trade-off higher catch rates with the increased costs associated with fishing in deeper waters