Predictable fish aggregations of commercially valuable species are particularly susceptible to overexploitation. Giant trevally Caranx ignobilis are ecologically important top predatory fish targeted ...in both recreational and commercial fisheries; however, little is known about their aggregation dynamics or susceptibility to overexploitation. This study employed acoustic telemetry to investigate the temporal and spatial characteristics of one of the largest known aggregations of this species over a 3 yr period in a marine protected area in Mozambique, West Indian Ocean. Tagged fish were monitored for between 386 and 1176 d, during which they exhibited distinct aggregative periods in austral spring and summer. The detection frequency of fish at the aggregation site was significantly associated with rising mean sea temperatures and the full moon period. Whilst at the aggregation site, fish exhibited clear patterns of diel periodicity, with maximum hourly detections recorded during midday. All fish exhibited periods of absence from the aggregation site between summer seasons, in which time many of them ranged across an international border for distances of between 11 and 633 km before returning to aggregate at the same site in the following season. These results confirm that the studied giant trevally aggregation is temporally and spatially predictable, and consistent with a transient site-specific fish spawning aggregation. The spatiotemporal predictability of the aggregation highlights the need for the effective management of this transboundary population of giant trevally, for which this study has provided conservation management recommendations.
Wedgefishes (Rhinidae) are threatened by unsustainable fishing globally, and especially in the Southwest Indian Ocean (SWIO), due to their high-value fins in the shark trade. The whitespotted ...wedgefish
Rhynchobatus djiddensis
and the bottlenose wedgefish
R. australiae
are both classified as Critically Endangered on the IUCN Red List of Threatened Species, yet a lack of species-specific knowledge and taxonomic uncertainty still exists within this genus. Genetic approaches aid in taxonomic classification and identifying distinct populations for targeted conservation. Morphological specimen identification of samples (n = 189) collected across the SWIO was confirmed based on the cytochrome oxidase c subunit I (
COI
) and/or nicotinamide adenine dehydrogenase subunit 2 (
ND2
) gene regions. The genetic diversity and population structure within and between species and sampling locations were investigated using a dual marker approach: (1) 2 concatenated mitochondrial gene regions, namely
COI
and the control region (n = 117), and (2) 9 nuclear microsatellite markers (n = 146). The overall genetic diversity was moderate, with an indication that different evolutionary forces are at play on a mitochondrial versus nuclear level. The 2 species were delineated based on both marker types, and for
R. djiddensis
, the sampling locations of South Africa and Mozambique were genetically homogeneous. For
R. australiae
, significant differentiation was found between sampling locations, with Madagascar and Tanzania being genetically the most similar. This information provides critical insights into the distribution range and population structure of the whitespotted wedgefish species complex that can support the sustainable management of wedgefishes.
This review examines the changing status of 10 estuary-dependent marine fish species in 10 South African estuarine systems, ranging from the Kosi Estuary in the northeast to the Berg Estuary in the ...southwest. In all of these systems, the selected fish species were found to be in population decline, but the causes of the declines varied from one system to another. Recreational and small-scale/subsistence fishing was a common pressure on fish stocks in most of the reviewed estuaries, but environmental degradation and pollution were the prime drivers for major population declines in the St Lucia and uMhlanga estuaries, respectively. Of six primary linefish species that have been well studied, two species are categorised as having an overexploited stock status and four species have reached a collapsed level where the spawner biomass per recruit (SBR) is now <25% of the original unimpacted level. Furthermore, two of those species (dusky kob Argyrosomus japonicus and white steenbras Lithognathus lithognathus) are in the 4‒6% SBR range and have been officially categorised as Endangered on the IUCN Red List. Unless definite steps are taken to reduce fishing pressure on the species discussed in this review, and successful policies put in place to promote healthy estuarine environments around the coast, estuarydependent fish stocks will continue to decline-to the detriment of the fish populations and the people who depend on fish for food, recreation and/or employment.
•Development of a coupled reaction-diffusion model for a two-component mobility structure seen in several fish species.•Exact non-trivial steady states of nonlinear models for mobility structured ...populations with external harvesting.•Critical conditions for annular MPA explain why gilthead bream are more at risk than white bream in Medes fishery.
Mobility stratification, identifiable from k-means clustering on an appropriate displacement data set, is a common feature of many fish species wherein distinct low-mobility ‘station-keeper’ and high-mobility ‘ranger’ types are recognized. From recapture records of speckled snapper Lutjanus rivulatus, we develop a Gaussian mixture model of the probability density function for random displacements by the two types. This leads to a system of two coupled reaction-diffusion equations. We consider a single no-take area (NTA) in one and two dimensions containing a mobility-structured species. The minimum size of this NTA that leads to species survival is derived and then generalised to a population with n mobility types. Exact non-uniform 1-D steady states are constructed for the full nonlinear mobility-structured model with lethal (zero density boundary condition) harvesting outside of the NTA. This model is then extended to include an array of evenly spaced NTAs with a bounded harvesting rate allowed between them. The minimum size of linear, circular and annular NTAs and the maximum sizes of the surrounding fractionally harvested zones that ensure species survival and connectivity are calculated.
Understanding the spatiotemporal characteristics of effort is a critical component of managing fisheries. Recreational shore-angling is the largest sector of the linefishery and one of the primary ...recreational activities undertaken along the coast of KwaZulu-Natal (KZN), South Africa. The aim of this study was to make a reliable estimate of current total shore-based angling effort in KZN and to examine the spatial and temporal distribution of the effort. To do this, randomised monthly flights to count shore-anglers in an 'instantaneous' manner were conducted along the entire KZN coastline between January and December 2018, and then compared with similar aerial surveys conducted in 1994/95 and 2007/08. A total of 44 flights were undertaken, with 21 and 23 flights conducted along the north and south coasts, respectively. Ground-truthing revealed that the aerial counts of shore-anglers were 89% accurate. Angler effort was significantly higher over weekends and during good-weather days. Seasonality of shore-based angling effort showed that greatest effort occurred during the winter months (June to September), coinciding with the seasonal availability of popular angling species. More-developed stretches of the KZN coast with higher population densities and easier beach-access had the highest angling effort. Total annual angler effort was calculated to be 785 538 angler-days y-1, which represents a 22.9% decline from the estimate made in 1994/95 and a 6.9% decline from the estimate made in 2007/08. Spatial distribution of shore-based fishing effort was very similar in 2007/08 and 2018, with the major differences being a decrease in fishing effort at St Lucia and Maphelane, and a slight increase in effort on the 'upper' (northern) south coast during 2018. Based on the results of this study, recommendations for improved management of the KZN shore fishery include: (i) follow-up using an independent roving-creel survey; (ii) improvement of coastal law enforcement; (iii) implementation of a linefish observer programme; and (iv) a repeat of the aerial survey every 10 years.
Research on the socio-economic aspects of marine protected areas (MPAs) in South Africa is reviewed to guide evaluation and integration. After a brief international review, we used declaration ...notices and management plans to determine the extent to which social and economic objectives have been included in the purpose statements of MPAs. We then reviewed the current state of knowledge about the social and economic effects of South African MPAs. While many MPAs have purposes and objectives that include some social and economic objectives, these are limited in scope. Most of the MPAs that were declared before 2019 did not include objectives directly related to people or their needs. Social or economic research has been undertaken in fewer than half of the 23 coastal MPAs. Literature is largely limited to: (i) studies on negative impacts of MPAs on adjacent rural communities; (ii) selected aspects of tourism; and (iii) various aspects related to resource use. A wide range of other tangible and intangible effects, including those experienced by a broader set of stakeholders and over differing scales of time and space, have seldom been addressed. A case study on the Tsitsikamma MPA exemplifies challenges associated with understanding the full scope of social and economic aspects of MPAs. We conclude with recommendations to address the challenges of building a better understanding of the social and economic effects of MPAs, ensuring that these are addressed in establishing or revising objectives for each MPA, and assessing the extent to which the objectives meet both human and environmental needs.
A tag-recapture study was undertaken on the Natal seacatfish Galeichthys troworum in the Pondoland Marine Protected Area (PMPA) on the east coast of South Africa. A total of 473 fish were tagged over ...a period of 8 years, and 136 individuals (28.8%) were recaptured over a period of 16 years, some of them on multiple occasions. Most recaptures (82%) were caught within 200 m of their release site, with movements ranging between 0 and 617 m, and time-at-liberty ranging between 0 and 3 407 days (9.3 years). Data analysis showed that all recaptured fish remained in relatively small home ranges (of ∼360 m linear distance) and none of them abandoned their home range and moved out of the 2-km
2
sampling blocks. While the no-take area of the PMPA provided effective protection for these fish, their relative abundance was similar in an adjacent exploited area. This is likely because G. troworum is not a desired linefish species, with most individuals caught being released, coupled with high post-release survival.
We reviewed 140 papers to assess the ecological effectiveness of South Africa's marine protected areas (MPAs). Evidence was assessed for coverage and representivity, protection of important ...biodiversity areas, other recognised elements of effectiveness, connectivity, and ecological effects-from the scale of individual MPAs to the MPA network scale. We conducted complementary novel analyses to supplement the review and to objectively determine where and how the MPA network can be improved. Evidence shows that South Africa's MPAs now provide some protection to all ecoregions and 87% of ecosystem types but to less than 50% of assessed species groups. MPAs are generally well-sited, but gaps were revealed on the west coast and in estuaries, the deep sea, and two ecologically and biologically significant areas. Enforcement emerged as a key concern, and many MPAs could be improved through expansion or by increasing no-take areas. The majority of relevant papers recorded beneficial ecological effects, detectable as increases in parameters such as the abundance, biomass, sizes or reproductive output of species. Few papers examined whether ecological benefits translate into adjacent fisheries benefits, but all those that did recorded positive effects. Full protection was more effective than partial protection, with effectiveness most clearly demonstrated for vulnerable target taxa. Further research and monitoring to achieve evaluations of effectiveness are recommended, with greater focus on neglected MPAs and species. Understanding the ecological connectivity between MPAs, an important dimension for climate-change adaptation and hence for the persistence and resilience of South Africa's marine biodiversity, is identified as a key area for future research and inclusion in MPA planning.
Scientific output has proven the value of the Oceanographic Research Institute's Cooperative Fish Tagging Project (ORI-CFTP) to biological and fisheries research, with more than 95 published ...manuscripts based on data from the ORI-CFTP. This study reviews the project from the perspective of participating anglers. A total of 267 members of the ORI-CFTP responded to an online survey designed to gather data on the profile of tagging members, their preferred methods of communication, attitudes towards fish tagging and fish conservation in general, changes in angling behaviour since becoming a member of the project, and support for the continuation of the ORI-CFTP. The results reveal that the ORI-CFTP has indeed made a considerable contribution towards improving the conservation ethics and behaviour of marine recreational anglers in South Africa. Improved communication with anglers- both taggers and non-taggers-through the ORI-CFTP has the potential to amplify much-needed conservation information to the broader angling community and thereby enhance environmental awareness. Recommendations on how to improve the ORI-CFTP and other angling-related citizen science projects are provided.
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