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The diversity and distribution patterns of intertidal fish in the Agulhas bioregionRoux, Maryanne January 2013 (has links)
This study aimed to expand the existing knowledge on the diversity and distribution patterns of intertidal fishes in the Sardinia Bay MPA and adjacent open access areas. It focussed particularly on in intertidal fish communities along the Agulhas Bioregion coast which has been understudied, especially in recent years. Typical resident species belonging to the family Clinidae were the most abundant, conforming to previous studies. Species from the family Gobiidae were the second most abundant in this study but this family was not previously recorded as being abundant. Transient species were unimportant in the current study which is in contrast to previous studies in the region and suggests a change in species composition. Certain transient species utilised intertidal rockpools as part of their nursery areas in the Eastern Cape, as has previously been found around Algoa Bay. A decrease in species richness from east to west was recorded in this study which has been noted by previous authors and the diversity and distribution patterns of the intertidal fish in the current study conformed to patterns found previously. The position of the biogeographic boundary between the Agulhas and Natal Bioregions could not be confirmed but Wavecrest (along the Transkei coastline) appeared to be part of a transition zone rather than a fixed break. More sampling around this area is recommended to determine the location and understand the dynamic nature of this boundary. The fish species were found to be vertically distributed across the shore with most of the resident species being more abundant across the low shore while the transient species were more abundant in the middle to low shore pools. This vertical distribution has been found at many sites around the world. The volume of the pools proved to be the primary controlling factor while the effect of temperature on vertical distribution could not be demonstrated. The benefits of the Sardinia Bay Marine Protected Area on this unexploited community of fishes could not be demonstrated but the long term benefit of protection has yet to be shown. Results from this study suggest that despite the correspondence with general biogeographic trends, the intertidal fish community has changed in composition (at least in terms of transient species) during the last 30 years and the cause for these changes may in part be reduced recruitment from exploited linefish.
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Extractives from six species of South African Marine Opisthobranch MolluscsMcPhail, Kerry Lee January 2001 (has links)
The natural product chemistry of six species of South African opisthobranch molluscs and some of their dietary marine invertebrates was investigated. Nineteen previously undescribed secondary metabolites and twelve known compounds were isolated and their structures determined by a combination of spectroscopic and chemical methods. The circumtropical sea hares Aplysia parvula and A. dactylomela were found to contain halogenated red algal metabolites. 3Z-bromofucin (120), the Z analogue of a known Laurencia CIS acetogenin, was isolated from A. parvula. A. dactylomela yielded a series of novel non-aromatic cuparanes, the algoanes (121-123), the novel tricyclic Iaurane ether ibhayinol (124) and three known chamigrane sesquiterpenes, prepacifenol epoxide (101), pacif-7-enediol (104) and nidificene (125). A variety of new octocoral sesquiterpenes were isolated from the endemic South African arminacean nudibranch Leminda millecra including algoafuran (150), cubebenone (151), 8-hydroxycalamenene (152) and a series of seven triprenylated toluquinones and toluquinols (153-159). L. millecra also yielded the known sesquiterpenes millecrones A (142) and B (143) and isofuranodiene (149). Twenty eight voucher specimens and eighteen crude extracts of South African octocorals collected by the Coral Reef Research Foundation were screened by GC and GC-MS and 142 was found in Alcyonium fauri, while 143, 151 and possibly 149 were present in Leptogorgia palma. An investigation of southern African chromodorids yielded the known macrocyc1e latrunculin B (220) and two new spongiane diterpenes (221) and (222) from Chromodoris hamiltoni, while the known spongiane diterpene (210) was isolated from the endemic nudibranch Glossodoris sp. 4. The endemic nudibranch Hypselodoris capensis contained the known furanosesquiterpenes nakafuran-8 (223) and -9 (224) and the known furanosesterterpenes variabilin (195), 22-deoxyvariabilin (225) and furospinosulin (227) together with the new variant 22-deoxy-23-hydroxymethylvariabilin (226). Compounds 223 and 224 were also found in a Dysidea sponge, while the furanosesterterpenes 195, and 225-227 were present in a Fasciospongia sponge upon which H capensis specimens were found. The Dysidea dietary sponge of H capensis also yielded a new aromatic sesquiterpene, tsitsikarnmafuran (266), whose structure was confirmed by the synthesis of two possible regioisomers.
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Regional differentiation of three goatfishes (Parupeneus Spp.) within the Western Indian OceanSpringbok–Njokweni, Nosiphiwo January 2015 (has links)
Goatfishes inhabit inshore reefs and corals and are commercially important across their distribution in the Western Indian Ocean (WIO). The biogeography of these species in the WIO has not been explored with regards to their levels of diversity and relationships among regions. The genetic connectivity and differentiation of three goatfishes of the genus Parupeneus (P. barberinus, P. macronemus and P. rubescens) was studied using two mitochondrial genes (ND2 and 16S rRNA) and one nuclear gene (RAG1) using specimens from East and southern Africa, islands around the Mascarene plateau, Oman, Maldives and the Red Sea. Haplotype diversities, networks and AMOVA were used to measure genetic variance among localities and defined regional groups. There were high haplotype (HD > 0.9) and low nucleotide diversities (< 0.006) among all species for all gene regions, suggesting high levels of genetic differentiation among different areas, except for the mtDNA 16S data for P. macronemus and P. rubescens. For all three species, the FST population pairwise values revealed significant differentiation in all datasets for most population pairwise comparisons with the Maldives and genetic connectivity with haplotypes being shared among other localities. The 16S and RAG1, AMOVA for P. barberinus revealed a significant (P < 0.05) strong genetic structure among groups, for example P = 0.00 was estimated in the 16S data for four groups (the Maldives, WIO islands, Kenya and eastern mainland). This study found evidence for regional differentiation within the WIO for these three species supporting the presence of genetic breaks among areas. This differentiation could be either due to the historical isolation among areas or due to geographic and oceanic barriers such as the Mascarene Plateau and the Agulhas Current eddies in the Mozambique Channel. The effects of oceanographic features and physical barriers in the species distribution range and the dispersal potential based on the life history features of the species can have an influence on the genetic structuring of a population. It is also important to note that the length of the pelagic larval phase is just one factor affecting dispersal in marine organisms that can also explain the difference in genetic population structure. Unfortunately there is no specific information on the larval dispersal of these three goatfish. Therefore, studies are needed to be conducted on the specific biology and life history strategies of each Parupeneus species. These results suggest the importance of other factors, such as currents, and larval retention that may cause strong differentiation. These factors should also be considered when observing larval dispersal and its effect on population genetic structure. This study support the hypotheses that physical factors, processes (geographic barriers and oceanographic characteristics) and life history parameters need to be studied to understand the genetic differentiation of these Parupeneus reef fishes.
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Movement patterns and genetic stock delineation of an endemic South African sparid, the Poenskop, Cymatoceps nasutus (Castelnau, 1861) / Movement patterns and genetic stock delineation of an endemic South African sparid, the Poenskop, Cymatoceps nastus (Castelnau, 1861)Murray, Taryn Sara January 2013 (has links)
Poenskop Cymatoceps nasutus (Pisces: Sparidae), an endemic South African sparid, is an important angling species being predominantly targeted by the recreational shore and skiboat sector. This species is slow-growing, long-lived, late-maturing and sex-changing, making poenskop acutely sensitive to over-exploitation. Despite interventions, such as the imposition of size and bag limits (currently 50 cm TL and one per licensed fisher per day) by authorities, catch-per-unit-effort trends reflect a severe and consistent stock decline over the last two decades. Poenskop has been identified as a priority species for research and conservation. Although the biology and population dynamics of this species have been well-documented, little is known about the movement behaviour of poenskop. Furthermore, there is a complete lack of information on its genetic stock structure. This thesis aimed to address the current knowledge gaps concerning movement behaviour and genetic stock structure of poenskop, making use of a range of methods and drawing on available information, including available fishery records as well as published and unpublished survey and research data, and data from long-term monitoring programmes. Analysis of available catch data (published and unpublished) revealed a decline in the number of poenskop caught as well as size of fish taken over the last two decades, ultimately reflecting the collapse of the stock (estimated to be at 20% of their pristine level). Improved catch-per-unit-effort data from the Tsitsikamma National Park Marine Protected Area (MPA), and larger poenskop being caught in the no-take areas than adjacent exploited areas of the Pondoland MPA confirmed that MPAs can be effective for the protection and management of poenskop. The current MPA network in South Africa is already wellestablished, and encompasses considerable reef areas, being preferable for poenskop habitation. Conventional dart tagging and recapture information from three ongoing, long-term fishtagging projects, conducted throughout the poenskop’s distribution, indicated high levels of residency at all life-history stages. Coastal region, seasonality and time at recapture did not appear to have a significant effect on the level of movement or distance moved. However, on examining the relationship among coastal movements and fish size and ages, larger and older fish (adults) moved greater distances, with juveniles and sub-adults showing high degrees of residency. An estimation of home-range size indicated smaller poenskop to hold smaller home-ranges, while larger poenskop hold larger home-ranges. Large easterly displacements of a number of adult poenskop is in accordance with previous findings that this species may undertake a unidirectional migration up the coastline of South Africa where they possibly settle in Transkei waters for the remainder of their lives. This high level of residency makes poenskop vulnerable to localised depletion, although they can be effectively protected by suitable MPAs. Despite considerable tagging effort along the South African coastline (2 704 poenskop tagged with 189 recaptures, between 1984 and 2010), there remains limited information on the connectivity of different regions along the South African coastline. This was addressed using mitochondrial DNA sequencing. The mitochondrial DNA control region was used due to its high substitution rate, haploid nature, maternal inheritance and absence of recombination. The mtDNA sequencing showed no evidence of major geographic barriers to gene flow in this species. Samples collected throughout the core distribution of poenskop showed high genetic diversity (h = 0.88, π = 0.01), low genetic differentiation among regions, no spatial structure (ɸST = 0.012, p = 0.208) and no evidence of isolation by distance. The collapsed stock status of poenskop as well as the fact that it is being actively targeted by recreational and commercial fishers suggests that this species requires improved management, with consideration given to its life-history style, residency and poor conservation status. Management recommendations for poenskop, combined with increasing South Africa’s existing MPA network, include the possibility of setting up a closed season (during known spawning periods) as well as the decommercialisation of this species. The techniques used and developed in this study can also be adopted for other overexploited linefish species.
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A preliminary examination of selected biological links between four Eastern Cape estuaries and the inshore marine environmentVorwerk, Paul D January 2007 (has links)
The coastal transition zone (CTZ), which links the terrestrial and marine environments, has been identified as a region of high biological diversity and elevated production. Results of studies conducted in the northern hemisphere indicate that the links between estuaries and the adjacent marine environment is critical to ecological functioning within the CTZ. This study assessed the influence of selected estuaries with different hydrodynamic characteristics on the adjacent marine environment along the south-eastern coastline of southern Africa. Four estuaries were examined, including two permanently open systems, the fresh water deprived Kariega and fresh water dominated Great Fish, and two temporarily open/closed estuaries (TOCE), the Kasouga and East Kleinemonde. Results of the study indicated that outflow of estuarine water from the Great Fish Estuary contributed to a plume of less saline water being evident within the adjacent marine environment. The plume of water was associated with increased zooplankton biomass and particulate organic matter (POM) and chlorophyll-a concentrations. Adjacent to the Kariega Estuary, no evidence of fresh water outflow into the marine environment was observed. However, in the sea directly opposite the mouth of the estuary an increase in zooplankton abundance and biomass was evident. Results of numerical analyses indicated that the increase in zooplankton abundance observed adjacent to the mouth of both permanently open estuaries could not be attributed to the export of zooplankton from the estuary, but rather the accumulation of marine species within the region. The mechanisms responsible for this accumulation were not determined, but it was thought to be associated with increased food availability in the estuarine frontal zone. A similar, but less dramatic biological response was also observed in the marine environment adjacent to the two TOCEs. It is suggested that the increase in biological activity within these regions could be ascribed to seepage of estuarine or ground water through the sand bar that separates these estuaries from the sea. Results of stable carbon isotope analyses indicated that both the Great Fish and Kariega estuaries exported carbon to the nearshore marine environment. The area influenced by estuarine derived carbon was dependent on the volume of estuarine outflow to the marine environment. Adjacent to the fresh water dominated Great Fish Estuary, estuarine derived carbon was recorded up to 12km from the mouth, while adjacent to the fresh water deprived Kariega, estuarine derived carbon was only evident directly opposite the mouth. The recruitment of macrozooplankton (> 2cm) into the fresh water deprived Kariega Estuary was in the range recorded for other permanently open southern African estuaries with higher fresh water flow rates. This indicates that the mechanisms which allow estuarine dependent larvae to locate and enter estuaries are not related to fresh water inflow. In conclusion, this study has demonstrated that despite their small size relative to European and North American systems, South African permanently open and temporarily open/closed estuaries also influence biological activity within the adjacent nearshore marine environment.
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Trends in fish community structure and recruitment in a temporarily open/closed South African estuaryJames, Nicola Caroline January 2007 (has links)
Long-term interannual changes in richness, abundance, diversity and structure of the fish community in the temporarily open/closed East Kleinemonde Estuary, Eastern Cape, are described and the recruitment success of two estuary-dependent marine species assessed. In addition, laboratory experiments were conducted to assess the possible role of olfaction in the recruitment process of an estuary-dependent marine fish species. Multivariate analyses of the annual marine fish communites identified two distinct groups with more species recorded during years that succeeded spring (September to November) mouth opening events than in years following no mouth opening events in spring. Interannual community stability (IMD) and seriation (IMS) also increased from the ‘other’ to the ‘spring’ years. These results highlight the importance of the timing of mouth opening to the marine fish community in a temporarily open/closed estuary. This study also made use of long-term records of daily mouth state and linked them to the recruitment of distinct year-class cohorts in two spardis with contrasting lifehistory characteristics. Lithognathus lithognathus only recruited into the estuary in years when the mouth opened between late August and January. This was linked to the limited spawning season of this species and its inability to enter closed estuaries via wave overwash events. In contrast, recruitment by Rhabdosargus holubi juveniles appeared to be uninterrupted and was not determined by the seasonality of mouth opening. This species dominates the marine-spawning component of the East Kleinemonde Estuary and its success is attributed to an extended spawning season and its ability to recruit into estuaries during both overwash and open mouth conditions. Attraction of postflexion Rhabdosargus holubi larvae to estuary, surf zone and river water was also measured using a rectangular choice chamber. In two sets of experiments, conducted during peak recruitment periods, larvae from both the surf zone and estuary mouth region selected estuary water with a significantly higher frequency than sea water. Larvae collected in the mouth region showed a stronger preference for river water than those collected in the surf zone, thus suggesting that these fish are more attracted to freshwater influenced nursery areas once they have entered the estuary than those in the surf zone. Larvae collected in the marine environment also selected surf zone water with significantly higher frequencies than estuary water or offshore sea water, thus confirming the importance of the surf zone as an interim nursery area for postflexion R. holubi.
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Assessment of the effect of Goukamma Marine Protected Area on community structure and fishery dynamicsGötz, Albrecht January 2006 (has links)
This study presents a detailed investigation into size, density and community structure of temperate marine reef fish in the medium-sized Goukamma Marine Protected Area (Goukamma MPA) and adjacent fishing grounds on the south coast of South Africa. The oceanographic conditions, the spatial distribution of the benthic community and the prevailing fishing effort are also described. Life history traits and per-recruit (PR) models for the principle target species, roman (Crysoblephus laticeps) are compared between the protected and exploited area. From the study results, various strategies are proposed for the use of MPAs in the conservation and management of linefish species along South Africa’s south coast. The distribution and topography of reefs in the protected and exploited sections of the study area were found to be comparable. Atmospheric pressure ranged from 992 to 1,032 mb, being significantly lower in summer. Wind speeds ranged from 0.7 to 71.3 km/h. Water temperatures ranged between 9.0 and 22.2 ºC and turbidity between 0.3 and 45.8 NTU. Water temperature and clarity were uniformly low in winter. In summer the water was generally warm, clear and stratified, with a thermocline at around 20 m, although intermittent upwelling events caused water temperature to decrease and clarity to deteriorate. Current speeds ranged between 0.11 and 2.59 km/h and were significantly higher in spring and autumn. Easterly currents prevailed in spring, summer and autumn and westerly and southerly currents in winter. Hake (Merluccius capensis), various resident reef fish and kob (Argyrosomus japonicus) were most frequently targeted by the local linefishery. A significant amount of illegal fishing was found to occur in the protected area. Fishing effort was found to be highest around the border of the MPA (2.7 boats/km²) and lowest in the core of the MPA (0.2 boats/km²). If law enforcement remains poor it may be necessary to adapt the management strategy to extend the reserve, thereby mitigating against illegal fishing and ensuring a core area of no exploitation. Various other alternatives were investigated and it was demonstrated that the amount of fish caught of legal size could be increased by about 23% and post-release mortality of undersized fish reduced by 50% through the introduction of a suit of restrictive measures. Randomly stratified underwater visual census (UVC) and controlled fishing were used to investigate the ichthyofauna and benthic community at protected and exploited sites in the study area. Resulting density and size data from 273 fishing sites and 177 point counts were analyzed using generalized linear models (GLMs). Fish communities were found to vary significantly, depending on the level of exploitation. Roman, the principle reef fish species targeted by the fishery had significantly higher densities within the protected parts of the study area (CPUE: 4.3 fish/anglerhour; UVC: 2.2 fish/point-count) as compared to the exploited part (CPUE: 3.4 fish/anglerhour; UVC: 1.8 fish/point-count), correlating strongly with the observed fishing effort. Also mean sizes were significantly higher in the protected area (299 mm from fishing survey and 233 mm from diving estimates) as compared to the exploited section (283 mm from fishing survey and 198 mm from diving estimates). Although other fish species also had significantly higher mean sizes at protected sites in most cases their densities were significantly lower. This suggests a top-down control of the fish community by the dominant predator (roman). The results of the UVC showed the diversity of the ichthyofauna to be significantly higher inside the protected area. Interestingly this did not apply to the results of the controlled fishing experiment where the diversity of fish in the catch was lower in the protected area - a result that may be explained by the selectivity of fishing for the most aggressive species – and a reminder of the limitations of controlled fishing experiments. Possibly the most important finding of the study revolved around the benthic community. These were significantly different at exploited and protected sites, with algae and crinoids more abundant at exploited sites. Crinoids are the principle food of roman and were low in abundance where roman abundances were high, suggesting that the dominant top predator reduced crinoids. Furthermore, it substantiates the correlation of roman abundance with fishing effort, since habitat preferences can be ruled out by the observed causal predator-prey distribution pattern. Low algae abundances at protected sites correlated with high strepie (Sarpa salpa) frequencies within the fish communities encountered there. Strepie, a shoaling and abundant benthic grazer, does not compete for food with roman, suggesting a high potential for coexistence of the two species. As expected, and found by other studies, life history traits of roman differed between protected and exploited sample-sites. With a significantly lower age-at-maturity and age-atsex- change, the exploited population showed a typical response to fishing effort. The sex ratio of this protogynous hermaphrodite was found to be sustained at healthy levels by phenotypic plasticity. However, one important additional factor was highlighted by the study; the average condition factor of the protected population was significantly lower (0.0283 g/cm³) compared to the exploited population (0.0295 g/cm³). This was probably due to the higher intra-specific competition for lower food abundance in the protected area. Interestingly the diving and fishing survey methods yielded similar mortality results for roman. Total mortality rate estimates derived from length frequency analysis from the diving and fishing survey were not different (0.32 and 0.29 y⁻¹, respectively) as were natural mortality rate estimates (0.24 and 0.19 y⁻¹, respectively). Natural mortality rate (M) estimates indicated by Pauly’s and Hoenig’s relationship were similar (0.25 and 0.23 y⁻¹, respectively). Detailed yield-per-recruit (Y/R) and spawner biomass-per-recruit (SB/R) analyses were presented for different levels of M, varying age-at-recruitment (tR) and fishing mortality (F). Current tR (7.60 y) and F (0.16 and 0.25 y⁻¹, from the diving and fishing dataset, respectively) suggests an optimal exploitation of the population in the exploited part of the study area. However, a separate SB/R analysis of the male part of the population showed their vulnerability to over-exploitation, even at reduced age-at-sex-change from fishing. There therefore remains a high risk of recruitment failure for the roman population. Of course MPAs can be used to measure stock status directly if the influence of factors such as cachability, habitat and sampling method on CPUE assessments can be limited or reduced. The experimental design in this study allowed for contemporary CPUE comparisons across the border of the Goukamma MPA. Results were similar to those obtained by the SB/R analyses. CPUE extrapolations therefore, using small MPAs, can provide reliable and consistent estimates, and offer a practical alternative to conventional assessment strategies. This study has highlighted the importance of ensuring a well structured and comprehensive survey design when undertaking a comparison of protected and exploited marine areas. The results provide a comprehensive framework for future management of the Goukamma MPA and other protected areas along the temperate coastline of South Africa.
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The ichthyofauna in a small temporarily open/closed Eastern Cape estuary, South AfricaLukey, James Robert January 2006 (has links)
The ichthyofaunal community structure, population dynamics and movement patterns in the small temporarily open/closed (TOCE) Grant’s Valley estuary, situated along the Eastern Cape coastline, were investigated over the period May 2004 to April 2005. Community structure in the littoral zone was assessed, while growth of selected ichthyofaunal species was investigated using the MULTIFAN model. Population size was assessed using mark recapture models and movement within the estuary using the Hilborn (1990) model. Total ichthyofaunal densities and biomass within the littoral zone ranged between 0.31 to 21.45 fish m⁻² and 0.20 to 4.67 g wwt m⁻², with the highest values typically recorded during the summer. Results of the study indicated that the ichthyofaunal community structure within the estuary was closely linked to the mouth phase and the establishment of a link to the marine environment via overtopping events. In the absence of any link to the sea, the ichthyofaunal community was numerically dominated by estuarine resident species, mainly Gilchristella aestuaria and to a lesser extent, by the river goby, Glossogobius callidus which collectively comprised ca. 88% of all fish sampled. The establishment of the link to the marine environment contributed to an increased contribution of marine breeding species (e.g. Rhabdosargus holubi, Myxus capensis and Atherina breviceps) to the total ichthyofaunal abundances. In contrast, total ichthyofaunal biomass was almost always dominated by marine breeding species by virtue of their larger sizes. Results of hierarchical cluster analyses did not identify any spatial patterns in the ichthyofaunal community within the littoral zone. Results of MULTIFAN analysis indicated estuarine resident fish species bred over an extended period with peaks occurring in the summer months. Conversely, marine breeding fish were shown to recruit into the estuary following overtopping and breaching events. Results of the mark-recapture experiment indicated a population of ca. 12 000 (11 219 – 13 311) individuals greater than 50mm SL. Marine-breeding species (R. holubi, Monodactylus falciformis, and two mullet species) numerically dominated the ichthyofauna, possibly as a result of their effective use of overtopping events. The two mullet species, M. capensis and Liza richardsonii, and the Cape stumpnose, R. holubi moved extensively throughout the estuary, while the remaining species exhibited restricted movement patterns possibly due to the preference for refuge and foraging areas associated with reed beds. The observed movement patterns of individual fish species appeared to be associated with both foraging behaviour and habitat selection.
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A retrospective assessment of the Port Alfred linefishery with respect to the changes in the South African fisheries management environmentDonovan, Bruce 18 July 2013 (has links)
Since the study on the Port Alfred/Kenton-on-Sea/Boknes linefishery by Hecht and Tilney (1989) there have been substantive changes to the linefish management environment in South Africa. Using the Port Alfred linefishery as a model, the aim of this study was to evaluate the effectiveness of the linefish management regulations that were implemented by Marine and Coastal Management (MCM) since 1992, and to assess the behaviour and 'status' of the fishery in response to these changes. Changes to both the licensing structure and catch regulations have had a significant effect on the functioning of many aspects of the Port Alfred linefishery (fishing effort, catch composition, cpue) as well as on the structure of the fishery and its socio-economic profile. Overall commercial cpue decreased from 1985 to 1998. Since 1998 there has been a significant increase in cpue (from 2.3 Kg.fisher⁻¹ hour⁻¹ to a peak of 4.8 Kg.fisher⁻¹.hour⁻¹ in 2005. This was attributed to good catches of geelbek, particularly in 2005, 2007 and 2008 (during these years geelbek contributed an average of 35% to the total landings in comparison to a mean contribution of II % between 1985 and 2004). However, size spectra analysis suggests that the increase in overall cpue since 1998 misrepresents the actual status of the fishery. If geelbek is excluded from the analysis on the grounds that it is the only species in the fishery that is highly migratory, susceptible to recruitment fluctuations and it does not contribute to the catches on a year round basis, then the results suggest that the fishery is still in a declining phase despite the 80% reduction in commercial effort and numerous stricter catch regulations (e.g. size/bag limits). Furthermore, the cpue of silver kob, which has been the "mainstay" species of the fishery, has consistently declined over the last 23 year period (from 1.69 Kg.fisher⁻1 .hour1 in 1986 to 0.86 Kg.fisher⁻1.hour⁻1in 2007). The substantial reduction in commercial effort in the fishery from 33 vessels in 2001 to 13 in 2002 resulted in a shift from commercial to recreational fishing. The number of active commercial vessels in Port Alfred alone decreased from 29 in 1989 (Hecht 1993) to four in 2008. During the same timeframe, the number of regularly active recreational vessels had almost doubled (16 in 1989 to 26 in 2008). Despite the greater number of recreational boats in the fishery they only landed approximately half the average yearly tonnage of the commercial vessels (21,5 and 44,7 tonnes,annum-I , respectively) between 2006 and 2008, This was ascribed to the differences in catch regulations for the two sectors, Furthermore, it was speculated that increasing operating costs and narrowing profit margins have contributed to lower levels of compliance in both the commercial and recreational sectors since 2006, For example, 16% of silver kob landed during 2006-08 were under the minimum size, Despite the changes made to the regulations since 1998 and the 60,6% reduction In legislated commercial effort in the fishery between 2001 and 2002 it was concluded that the fishery has continued to decline, Except for the good recruitment of geelbek (which may be due to regulatory changes made in 1992) the changes in the management environment have had no measurable positive effect on this fishery, It is recommended that commercial effort should not be allowed to increase beyond the current number of active boats, that there should be an area restriction on all commerciallinefish vessels, that the current recreational bag limit for silver kob should be re-assessed, there should also be a concerted and nationally funded effort to educate recreational anglers about the merits of catch and release, and the frequency of catch inspections of both sectors should be increased, / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in
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