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Browsing by Author "Mann, Bruce Quintin."

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    An assessment of the shore-based and offshore boat-based linefisheries of KwaZulu-Natal, South Africa.
    (2011) Dunlop, Stuart William.; Mann, Bruce Quintin.; Van der Elst, Rudy P.
    The purpose of this study was to evaluate the current management effectiveness of the KwaZulu-Natal linefishery (i.e. the shore linefishery and the offshore boat-based linefishery). Methods used included a stratified-random creel sampling technique and an associated questionnaire survey for the shore-based linefishery and a random access-point technique and associated questionnaire survey for the offshore boat-based linefishery. Additional catch and effort data for the offshore boat-based linefishery was also obtained from Marine and Coastal Management’s (MCM) Linefish Observer Programme. The study was undertaken between February 2009 and April 2010. Total participation within the two linefisheries ranged between 41283-68200 shore-anglers and 21220-28857 boat-fishers (2001-4445 boats). Excluding the increase in the number of boat-fishers that fish off charter vessels (i.e. charter clients), it seems that there have been relatively few new entrants into the marine linefishery of KZN since 1994-96. In contrast, total angler effort in both the shore (779382-1287548 angler-days.annum-1) and offshore (39664 boat outings annum-1) linefisheries has decreased substantially in the past 12 years. Overall catch per unit effort (CPUE) for the KZN shore linefishery amounted to 0.18 ±0.3 fish.angler-1.hour-1 or 0.07 ±0.13 kg.angler-1.hour-1. Eighty-four fish species, belonging to 39 families were recorded in catches of shore-anglers during the study period. Only five species accounted for 75% of the catch recorded along the coast (Sarpa salpa 34.8%, Pomatomus saltatrix 14.7%, Diplodus capensis 14.5%, Pomadasys olivaceum 6.5% and Rhabdosargus holubi 4.9%). The total annual catch for the KZN shore linefishery was estimated between 249.2 and 276.7 metric tonnes (mt).annum-1 (636589 - 706995 fish.annum-1). Overall CPUE was significantly different between the various sectors of the KZN offshore boatbased linefishery. The commercial boat sector had the highest CPUE both numerically (p < 0.05; 307.4 fish.outing-1) and by weight (p < 0.05; 235.6 kg.outing-1). Contrastingly, the recreational boat sector had the lowest CPUE both numerically (p < 0.05, 8.6 fish.outing-1) and by weight (p < 0.05, 15.0 kg.outing-1). The charter boat sector (p < 0.05, 26.6 fish.outing-1 or 41.6 kg.outing-1), although far lower than commercials, had a CPUE slightly higher than the recreational boat sector. In total, 86 fish species, belonging to 27 families were recorded in catches of boat-fishers (all sectors) during the study period. The top five species that comprised the bulk of the commercial catch numerically included Chrysoblephus puniceus (66.0%), Cheimerius nufar (22.4%), Lethrinus nebulosus (4.6%), Pachymetopon aeneum (1.9%) and Chrysoblephus anglicus (0.9%). Similarly, recreational catch composition was dominated by C. iii puniceus (33. 9%), L. nebulosus (9.0%), Thunnus albacares (7.4%), Scomber japonicus (5.3%) and C. anglicus (4.4%). The top five species in charter boat-fishers’ catches comprised C. puniceus (34.4%), L. nebulosus (16.7%), T. albacares (13.1%), C. anglicus (8.1%) and P. aeneum (4.6%). The socio-economic characteristics of the KZN shore and offshore linefisheries have changed very little since the last national linefish assessment conducted during 1994-96. Recreational (both shore and boat-based) and charter anglers generally agree with most of the linefishery regulations, with exception of the beach vehicle ban. However, knowledge and compliance with the current fishery regulations by recreational and charter anglers was limited. Commercial fishers had good knowledge of all the fishery regulations, but did not agree with the minimum legal size and daily bag limits that are in place on certain fish species. Subsequently, the majority of commercial skippers interviewed stated that they disobeyed these two regulations frequently. General policing of the KZN linefishery by EKZNW seems to be more focused on permit requirements rather than enforcing species-specific linefish regulations. Comparison of the catch and effort results of this study with the long-term monitoring data stored on the NMLS showed that while the NMLS data is limited by a number of biases, it still provides a valuable system for monitoring long-term trends in the KZN linefishery. Analysis of overall CPUE, catch composition and total catch in both the shore and offshore linefisheries of KZN suggested that both fisheries are currently in a relatively stable condition and that little change has occurred in the past 12 years. However, comparisons of speciesspecific CPUE values from this study with recent literature suggest that some species (i.e. Argyrosomus thorpei and Scomberomorus commerson) are severely overexploited. Furthermore, in relation to the catches recorded throughout most of the 20th century, current catch trends suggest that linefish resources have been fished to very low levels which are only ‘superficially’ sustainable at current levels of fishing effort.
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    The biology of and fishery for king mackerel, Scomberomorus commerson (Scombridae), along the southern Mozambique and KwaZulu-Natal coast.
    (2013) Lee, Brendon.; Mann, Bruce Quintin.; Van der Elst, Rudy P.
    The king mackerel, Scomberomorus commerson, is an epipelagic, schooling predator supporting significant commercial, artisanal and recreational fisheries throughout the coastal waters of its Indo-Pacific distribution. Despite the importance of the species within the South West Indian Ocean, little research has been undertaken on its biology and fisheries on a regional basis over the past 20 years. The aim of this study was to evaluate the fishery and biology of S. commerson in the South West Indian Ocean and identify gaps in information required to ensure its effective management. Catch and effort data for the KwaZulu-Natal recreational S. commerson linefishery were extracted from the National Marine Linefish System in order to assess spatial and temporal trends in abundance. Generalized linear models utilizing the delta method were used to quantify the effect of year, month, region, rainfall and sea surface temperature on CPUE. Biological samples of S. commerson were collected monthly from within KwaZulu-Natal and southern Mozambique. Samples were analysed using standard biological techniques. A per-recruit analysis was conducted using the biological parameters from KwaZulu-Natal and southern Mozambique in order to assess the status of the S. commerson stock and provide management recommendations based on the findings. Long-term trends in CPUE were cyclic in nature with peaks and troughs appearing to be independent of fishing pressure. Seasonal abundance reflects the south-north migration into KwaZulu-Natal waters with short term environmental factors such as sea surface temperature significantly affecting spatial and temporal extent of the migration among regions. S. commerson spawn in southern Mozambique waters from September to January (spring-summer) with males maturing at a smaller size (65.2cm FL) compared to females (82.3cm FL). The overall sex ratio (M: F) was 1:1.36 possibly as a result of linefishing selecting for faster growing, larger females. S. commerson in KwaZulu- Natal and southern Mozambique display rapid growth over the first two years before slowing down considerably after maturity is reached. Females grow faster and live longer compared to males dominating the older and larger size classes, and attaining a maximum observed age of 14 years, although fish probably live up to 20 years. Natural mortality rate was estimated at 0.27 yearˉ¹. Fishing mortality for the combined region was 0.21 yearˉ¹. The per-recruit analyses for the KwaZulu-Natal and southern Mozambique indicated that the fishery is being optimally exploited with a current spawner biomass per recruit at 49% of its theoretical pristine level. Uncertainty with regards to the fishing pressure in southern Mozambique as a result of illegal fishing and fishing sectors targeting smaller S. commerson is a cause for concern. The current recreational daily bag limit of 10 fish.person.dayˉ¹ is considered excessive by many stakeholders. Given the similarity of the recreational ski-boat fishery in southern Mozambique, a reduction in the DBL of S. commerson to five fish pppd in both KwaZulu-Natal and southern Mozambique waters would benefit recreational fishers by more equitable sharing of the catch and potentially by reducing fishing mortality at times when the fish are aggregated and vulnerable to high catch rates. A reduced DBL limit would also reduce the incentive of individual anglers to make large catches and to sell their fish illegally.
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    Movement, growth and stock assessment of the coastal fish Lichia amia (Teleostei: Carangidae) off the South African coast.
    (2008) Smith, Daniel.; Mann, Bruce Quintin.; Van der Elst, Rudy P.
    The limited range of garrick/leervis Lichia amia, its popularity as a gamefish to all sectors of the marine recreational linefishery and the degradation of many estuaries which function as nurseries for this species, has aroused concern about the stock status of this species. In addition, other than a preliminary investigation conducted by ORI in 1992, relatively little research has been undertaken on this important recreational species. Considering the recreational value of L. amia and the need to provide a scientific basis for its management, a comprehensive stock assessment was required. This study therefore investigated the biology and stock status of L. amia off the South African coast. Through ad hoc biological sampling undertaken from 1978-2007 and validation of growth by means of OTC marking, the growth of the L. amia population was best described as: Lt=1206mmfl(1-e-20[t+1.10 years]). Growth was also determined using tag-recapture and length frequency data. The tag-recapture data was further utilized in illustrating the movement behaviour of L. amia. Trends in catches were determined from the analysis of catch and effort data from the National Marine Linefish System (NMLS) and Boat Launch Site Monitoring System (BLSMS) databases. This showed a decreasing trend in the CPUE of L. amia along the KZN coast over time for all sectors of the KZN marine recreational linefishery investigated. The growth parameter estimates from the length-at-age data were used in undertaking a per-recruit assessment of L. amia. The results of the spawner-biomass-per-recruit (SBPR) model indicate that L. amia is at 14% of its unfished level. According to the South Africa.s Linefish Management Protocol (LMP), the L. amia stock has thus collapsed and appropriate management options to rebuild the stock are discussed.
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    The status of the riverbream Acanthopagrus berda (Sparidae) in estuarine systems of northern KwaZulu-Natal, South Africa.
    (2001) James, Nicola Caroline.; Beckley, Lynnath E.; Mann, Bruce Quintin.
    Acanthopagrus berda is an estuarine-dependent fish species which is widespread in the tropical Indo-Pacific. In South Africa, it is particularly abundant in the three large northern KwaZulu-Natal estuarine systems, namely Kosi Bay, St Lucia and Richards Bay. In these systems, A. berda is harvested by a variety of methods, including traditional fish traps, gillnets and hook and line. The importance of A. berda to the different fisheries was evaluated by analysing all the available monitoring data specific to catches in these three systems. A. berda was found to be one of the five most important species taken in both the gill net and recreational fisheries at Kosi Bay and St Lucia. It was less important in the marine-dominated Richards Bay system. Catches were generally seasonal, with trends in catch per unit effort (cpue) for A. berda related to annual spawning migrations. The long-term trend in cpue for this species in the Kosi recreational fishery showed a disturbing downward trend. Ages of A. berda specimens caught in northern KwaZulu-Natal estuaries were determined by examining whole otoliths. Age estimates were validated by marginal zone analysis and oxytetracycline labelling, which indicated that opaque deposition occurs primarily from September to November each year. The reproducibility of age estimates was described by a coefficient of variation of 10%. The special von Bertalanffy growth curve was found to best describe the growth of A. berda. The parameters of the von Bertalanffy growth curve indicated that A. berda in northern KwaZulu-Natal is slow growing, attaining at least 16 years of age. The age and growth parameters and mortality estimates from catch curves were used to complete a per-recruit stock assessment of the species. The results of the spawning biomass per-recruit model using different ages of first capture indicate that A. berda is at 47% to 55% of its unfished level. Although these results may indicate that A. berda in northern KwaZulu-Natal is not at present overexploited, longevity coupled with late maturation, sex change, estuarine dependency, increasing catches of A. berda and poor monitoring give cause for concern for the continued sustainable use of this species in northern KwaZulu-Natal.