Potential fishery benefits of Marine Protected Areas (MPAs) are widely acknowledged, yet seldom demonstrated, as fishery data series that straddle MPA establishment are seldom available. Here we ...postulate, based on a 15-year time series of nation-wide, spatially referenced catch and effort data, that the establishment of the Goukamma MPA (18 km alongshore; 40 km²) benefited the adjacent fishery for roman (Chrysoblephus laticeps), a South African endemic seabream. Roman-directed catch-per-unit-effort (CPUE) in the vicinity of the new MPA immediately increased, contradicting trends across this species' distribution. The increase continued after 5 years, the time lag expected for larval export, effectively doubling the pre-MPA CPUE after 10 years. We find no indication that establishing the MPA caused a systematic drop in total catch or increased travel distances for the fleet. Our results provide rare empirical evidence of rapidly increasing catch rates after MPA implementation without measurable disadvantages for fishers.
•No variation in Hg species accumulation was detected within the white muscle.•tHg and iHg had higher concentrations (p<0.001) in dark muscle than white muscle.•Positive linear correlations between ...fish weight and both tHg and MeHg were found.•Yellowfin tuna above 70kg fresh weight are likely to exceed the tHg maximum limit.
The concentrations and relationships between individual mercury species and total mercury were investigated in different muscle parts and sizes of Yellowfin tuna (Thunnus albacares). Fourteen Yellowfin tuna caught in the South Atlantic off the coast of South Africa had an average total Hg (tHg) concentration of 0.77mg/kg wet weight. No differences were detected (p>0.05) in tHg, MethylHg (MeHg) or inorganic Hg (iHg) accumulation among the four white muscle portions across the carcass, but both tHg and iHg were found in higher concentrations (p<0.001) in dark muscle than white muscle. Positive linear correlations with fish weight were found for both tHg (r=0.79, p<0.001) and MeHg (r=0.75, p<0.001) concentrations. A prediction model was formulated to calculate toxic MeHg concentrations from measured tHg concentrations and fish weight (cMeHg=0.073+1.365·tHg−0.008·w). As sampling sites and subsampling methods could affect toxicity measurements, we provide recommendations for sampling guidelines.
•ICP-MS and HPLC–ICP-MS were used to measure total metals and mercury species.•Total Hg levels in 37% of M. mustelus samples exceeded maximum allowable limits.•MeHg was the predominant Hg species ...detected and strongly correlated with total Hg.•The concentrations of 16 heavy metals (n=30) were independent of shark size.•Arsenic levels (28.31±18.79mg/kg) exceeded regulatory maximum limits.
Together with several health benefits, fish meat could introduce toxins to consumers in the form of heavy metal contaminants. High levels of mercury (Hg), especially, are frequently detected in certain predatory fish species. Mustelus mustelus fillets were analysed for 16 metals and three individual Hg species (inorganic Hg, ehtylmercury, methylmercury) with inductively coupled plasma mass spectrometry (ICP-MS) and HPLC–ICP-MS respectively. Eleven of the 30 sharks had total Hg levels above the maximum allowable limit with toxic methylmercury found as the dominant mercury species with a strong correlation (r=0.97; p<0.001) to total mercury concentrations. Limited correlations between metals and shark size parameters were observed; therefore metal accumulation in M. mustelus is mostly independent of size/age. Average values for arsenic (28.31±18.79mg/kg) exceed regulatory maximum limits and Hg (0.96±0.69mg/kg) is close to the maximum limit with all other metals well below maximum limits.
Understanding how fish associate with habitats across marine landscapes is crucial to developing effective marine spatial planning (MSP) in an expanding and diversifying ocean economy. Globally, ...anthropogenic pressures impact the barely understood temperate mesophotic ecosystems and South Africa's remote Amathole shelf is no exception. The Kei and East London region encompass three coastal marine protected areas (MPAs), two of which were recently extended to the shelf-edge. The strong Agulhas current (exceeding 3 m/s), which runs along the narrow shelf exacerbates sampling challenges. For the first time, a remotely operated vehicle (ROV) surveyed fish and their associated habitats across the shelf. Results indicated fish assemblages differed between the two principle sampling areas, and across the shelf. The number of distinct fish assemblages was higher inshore and on the shelf-edge, relative to the mid-shelf. However, the mid-shelf had the highest species richness. Unique visuals of rare Rhinobatos ocellatus (Speckled guitarfish) and shoaling Polyprion americanus (wreckfish) were collected. Visual evidence of rhodolith beds, deep-water lace corals and critically endangered endemic seabreams were ecologically important observations. The ROV enabled in situ sampling without damaging sensitive habitats or extracting fish. This study provided information that supported the Amathole MPA expansions, which extended protection from the coast to beyond the shelf-edge and will guide their management. The data gathered provides baseline information for future benthopelagic fish and habitat monitoring in these new MPAs.
Global ocean acidification is expected to chronically lower the pH to 7.3 (>2200 µatm seawater pCO
) by the year 2300. Acute hypercapnia already occurs along the South African west and south coasts ...due to upwelling- and low-oxygen events, with increasing frequency. In the present project we investigated the impact of hypercapnia on the endemic demersal shark species Haploblepharus edwardsii. Specifically, we experimentally analysed acid-base regulation during acute and chronic hypercapnia, the effects of chronic hypercapnia on growth rates and on denticle structure- and composition. While H. edwardsii are physiologically well adapted to acute and chronic hypercapnia, we observed, for the first time, denticle corrosion as a result of chronic exposure. We conclude that denticle corrosion could increase denticle turnover and compromise hydrodynamics and skin protection.
For most rare marine species, abundance trends are poorly estimated. This uncertainty often translates into disagreement on management regulations, impeding conservation efforts when they are most ...urgently required. The world’s largest sea bream, the red steenbras Petrus rupestris, has undergone a substantial and widely acknowledged decline during the 20th century. Standardised probability of encounter over the last 3 decades was used to track red steenbras abundance trajectories in 2 regions, which together represent the species’ distribution. The results predicted a reduction in abundance of 44% in the East region and 96% in the South-West region, from what was already considered to be a collapsed population at the start of the time series. The species is now largely confined to areas in the centre of its historical abundance. Content analysis of a recreational angling magazine revealed a concurrent 50% decrease in reported size between 1984 and 2012. Shore-based observer data (2009−2010) indicate that the impact of recreational fishers on this species far exceeded that of commercial fishers at the time. Regulations in the form of progressively more stringent catch and effort restrictions appear to have been largely ineffective, too lenient, implemented too late or were unsuitable to control fishing mortality for this species. This study highlights 2 fundamental challenges in management of rare marine fish species: (1) providing decision makers with a credible measure of abundance for species whose rarity limits data availability and (2) implementing effective policy changes before the specific measures become ineffective and obsolete.
A dense Ecklonia radiata (Laminariales) kelp forest extending at least 35 km has been found between 45 and 60 m depth range within the mesophotic zone inside the iSimangaliso marine-protected area ...(MPA) at the iSimangaliso Wetland park World Heritage Site on the east coast of South Africa. This is the first visual confirmation of the occurrence of E. radiata beds in subtropical South Africa, in an area situated between the tropical and subtropical bioregions, in an area that spans the Natal and Delagoa bioregions of the south-western Indian Ocean, more than 350 km north of its previously documented South African range. The kelp was found to be present across the length of the MPA, but dense beds were present only in the southern Natal bioregion, with sparse occurrences observed elsewhere on soft-coral and sponge-dominated reefs in the upper mesophotic zone. The footage was collected in November 2020, May 2021 and November 2022 during remotely operated vehicle and drop camera surveys of the mesophotic zone inside the MPA. This discovery adds to the body of knowledge on the global distribution of Laminariales populations in deep tropical and subtropical settings and the diversity of habitats within South Africa's largest coastal MPA.
► We develop a novel method of deriving relative abundance indices from multispecies catch rate data. ► The new method is easier to implement and statistically superior compared to other approaches. ...► Relative abundance indices were derived for two commercially important species exploited by the South African hand-line fishery. ► The new indices provide the first evidence of recovery of silver kob and carpenter stocks after forced effort reduction in 2000.
Abundance indices are difficult to derive from multispecies catch-per-unit-effort (CPUE) data as these critically rely on the ability to account for targeting behaviour that directs effort towards a particular target species or species-complex. We developed a novel standardization method that uses continuous principal component scores, derived from a Principal Component Analysis of the catch composition data, as non-linear predictor variables for targeted effort within a Generalized Additive Model (GAM) framework. This ‘Direct Principal Component’ method (DPC) is compared to a commonly used standardization approach, in which clusters of fishing tactics are identified from the catch composition and treated as categorical variables. We employed GAMs, which incorporate spatial, seasonal, and fishing power effects, to evaluate the statistical performance of the two alternative sets of covariates. The GAMs were applied to CPUE datasets from the South African hand-line fishery, covering three fishing regions over a period of 26 years, to provide abundance indices for two commercially important species, carpenter, Argyrozona argyrozona and silver kob, Argyrosomus inodorus. Results show that both approaches removed substantial variation from the CPUE data, but that the DPC approach was statistically superior as judged by the AIC, deviance explained and results from 10-fold bootstrap cross-validations. The DPC method represents a more direct approach, is less time-consuming and subjective and therefore considerably easier to implement. We present evidence that the DPC was able to account for substantial shifts in targeting without masking the year effect. The standardized CPUE time series showed positive responses for both species as total landings decreased due to forced effort reductions in 2000. The approach presented here has potentially unlocked useful information for stock assessment in the over two million individual catch records available for the South African hand-line fishery and similar multispecies fisheries.
The application of genome-wide cytonuclear molecular data to identify management and adaptive units at various spatio-temporal levels is particularly important for overharvested large predatory ...organisms, often characterized by smaller, localized populations. Despite being "near threatened", current understanding of habitat use and population structure of Carcharhinus galapagensis is limited to specific areas within its distribution. We evaluated population structure and connectivity across the Pacific Ocean using genome-wide single-nucleotide polymorphisms (~7200 SNPs) and mitochondrial control region sequences (945 bp) for 229 individuals. Neutral SNPs defined at least two genetically discrete geographic groups: an East Tropical Pacific (Mexico, east and west Galapagos Islands), and another central-west Pacific (Lord Howe Island, Middleton Reef, Norfolk Island, Elizabeth Reef, Kermadec, Hawaii and Southern Africa). More fine-grade population structure was suggested using outlier SNPs: west Pacific, Hawaii, Mexico, and Galapagos. Consistently, mtDNA pairwise Φ
defined three regional stocks: east, central and west Pacific. Compared to neutral SNPs (F
= 0.023-0.035), mtDNA exhibited more divergence (Φ
= 0.258-0.539) and high overall genetic diversity (h = 0.794 ± 0.014; π = 0.004 ± 0.000), consistent with the longstanding eastern Pacific barrier between the east and central-west Pacific. Hawaiian and Southern African populations group within the west Pacific cluster. Effective population sizes were moderate/high for east/west populations (738 and 3421, respectively). Insights into the biology, connectivity, genetic diversity, and population demographics informs for improved conservation of this species, by delineating three to four conservation units across their Pacific distribution. Implementing such conservation management may be challenging, but is necessary to achieve long-term population resilience at basin and regional scales.
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