African Journal of Marine Science

Book review: ‘The African marine litter outlook’

Christian TK-H Stadtländer — 2024-12-28

No abstract.

Sustainable seafood: advances in traceability, assessment, monitoring and resource management

IG Gleadalll — 2024-12-28

This review presents a synopsis of advances in some techniques and technologies that support seafood traceability while addressing some of the complexities currently challenging the integration necessary to coordinate commercial, national and international efforts in achieving seafood sustainability. These advances rely on tools such as blockchain data handling, eDNA or eRNA (together ‘eNA’) sampling, DNA metabarcoding, artificial intelligence and mobile applications. The microbiota associated with seafood organisms can also be monitored using eNA, to enable detection and management of any potential pathogenic developments in wild or aquaculture stocks. For successful and efficient traceability, it is necessary to guarantee data reliability and to support regulatory auditing. To ensure sustainability, however, also requires sampling, monitoring and assessments of the resource status as well as appropriate management. Effective traceability of seafood-related products will also help to resolve other problems, such as endangered species entering supply chains for aquaculture feed. Considering the still large proportion of seafood that is currently obtained and processed illegally, there is a pressing need for coherent local, national and international policies rooted in shared goals among stakeholders and supported by even-handed enforcement. This has been recently facilitated through a trend to shift liability from fishers to importers, and onwards throughout the value chain. In hand with these regulatory changes, the technologies described here will play a central role in achieving the vision for sustainable seafood supplies by the end of this decade.

Long-term interannual temperature variability across the KwaZulu-Natal Bight as a technique for monitoring the complex uThukela Marine Protected Area, South Africa

N Ramsarup — 2024-12-28

The uThukela Marine Protected Area (MPA), situated on the continental shelf of the KwaZulu-Natal (KZN) Bight on the northeastern coast of South Africa, has been identified as a vital ecological region. Knowledge of the oceanographic dynamics in the region is essential for understanding the functioning of the ecosystem and the effectiveness of the MPA. This study analysed ocean temperature variability at 20 sites across the KZN Bight, between 1980 and 2021, using in situ and satellite data. Significant warming of an average of 0.03 °C y⁻¹ across the period occurred at sites within and around the MPA. Coastal sea surface temperatures warmed by an average of 0.02 °C y⁻¹, during both summer and winter. However, a persistent decrease in temperatures along the length of the KZN Bight during the summer of 2017/2018 could have significant consequences for temperature-sensitive species. Significant coastal temperature variability during the period 1980–2021 was not reflected in a data subset covering 2013–2021, highlighting the importance of long-term spatially extensive monitoring when investigating climate change within MPAs. Warming biases of up to 2 °C and an underestimation of the warming rates observed in satellite-derived temperatures highlight the limitations of using remotely sensed observations to assess changes. These findings can help assess the success of MPAs and guide monitoring and research activities within the region.

Aspects of the reproductive biology of the common Octopus vulgaris from landings in the coastal trawl and artisanal fleets in the Atlantic waters of southern Morocco

B Oubahaouali — 2024-12-28

An investigation of aspects of the reproductive biology of the common octopus Octopus vulgaris caught in the Atlantic waters of southern Morocco was undertaken in 2020. The study focused on the demographic structure and sexual maturity of O. vulgaris by sampling landings of the coastal trawl and artisanal fleets active in the study area between Sidi El Ghazi and Cap Blanc. The artisanal fleet exploited mainly medium-sized individuals (on the commercial grade ‘Mitsubishi’ scale) as T5 (>1.2–1.5 kg) to T3 (>2.0–3.0 kg), whereas coastal trawlers tended to exploit smaller individuals in size classes T8 (>0.3–0.5 kg) to T6 (>0.8–0.2 kg). The sex ratio of the catches was significantly different between the coastal trawl and artisanal fleets (p = 0.043), being in favour of males in the landings of coastal trawlers (1.14:1 M:F) and in favour of females in the artisanal fleet (0.91:1 M:F). Size at first maturity of this species in the study area, denoted by dorsal length of the mantle and weight, respectively, was 14.98 cm and 370.56 g for males, and 15.75 cm and 563.08 g for females.

Socio-ecological change in bait fisheries for the common sandprawn Kraussillichirus kraussi in Durban Harbour, South Africa

D Chetty — 2024-12-28

Bait fishing for the common sandprawn Kraussillichirus kraussi in Durban Harbour, on the east coast of South Africa, has a history going back to the early 20th century and has been influenced by port development and political changes over time. Recent controversy has centred on the fishers’ rights to port access and on the interactions between two sectors that harvest sandprawns for bait. The two sectors are a recreational bait fishery and an unlicensed subsistence (or small-scale) fishery that sells its catches to anglers for an income, in contravention of fisheries regulations. To determine the spatiotemporal extent of the fisheries and the impacts of bait fishing on the sandprawn resource, data on the fishing effort, catch and size composition were collected monthly at the sandbank sites Centre Bank and Wilson’s Wharf in Durban Harbour. A generalised linear modelling framework was used to analyse fishing effort and sandprawn size composition. Small-scale fishers dominated the bait fishery (83%), and fishing effort peaked at low tides and on public holidays and weekends, when the market demand for sandprawns as bait was higher. Fishing effort differed significantly between sandbanks and was dynamic, shifting to Centre Bank when sandprawn abundance at Wilson’s Wharf decreased. Small-scale fishers mainly retained large sandprawns, and did not adhere to daily catch limits, such as those regulating the recreational bait fishery. The results are interpreted from a socio-ecological systems perspective, and within the context of accommodating otherwise excluded small-scale fisheries within South African fisheries legislation.

Strengthening the DNA barcode reference library for marine copepods in South Africa

A Rawoot — 2024-12-28

DNA barcode reference libraries that link taxonomically verified species records to standardised barcode sequences form the basis for species identification using molecular methods. We conducted an integrated morphology and molecular study of marine copepods collected from the continental shelf of eastern South Africa, western Indian Ocean, to strengthen the regional reference library for metabarcoding applications. Regional barcode records account for endemic species and geographical variation of barcode sequences. A DNA barcode gap analysis confirmed the CO1 gene region as an effective marker for distinguishing between copepod species. Intact exoskeletons after DNA extraction were retained as voucher specimens. A total of 166 new barcode records representing 24 copepod species were added to BOLD. The new barcode records included 10 species with exact matches to existing records on BOLD, four close matches (1–4% similarity gain) for regionally collected specimens, and six distant matches (4–20% similarity gain) to genetically diverged populations of the same species. Additionally, four mismatches were identified, indicating prior misidentifications or subsequent name changes. The improved reference library increased the number of species identified in metabarcoding outputs by 29% in the ‘before’ (2019) and ‘after’ (2023) treatments that matched the same amplicon sequence variants outputs to the BOLD and NCBI GenBank barcode records.

Predator avoidance by mesopredatory benthic sharks in response to potential predators in a natural environment

DBS Rooth — 2024-12-28

Some benthic elasmobranch mesopredators utilise crypsis to avoid predation by higher trophic predators. While this ability has been documented in various elasmobranchs such as rays, cryptic behaviour has been scarcely documented in catsharks (family Scyliorhinidae). Freezing behaviour by leopard catsharks Poroderma pantherinum and shysharks Haploblepharus spp. in response to sightings of a smoothhound shark Mustelus mustelus and Cape fur seals Arctocephalus pusillus pusillus was recorded during four separate baited remote underwater video (BRUV) deployments near Gansbaai, South Africa. Catsharks were seen actively swimming (foraging) most of the time (97.72%), and occasionally resting on the bottom, showing active buccal pumping. In the presence of a potential predator, they rapidly ceased all movement, including decreased gill movement, and immediately sank to the bottom. This response was initiated only when the predator swam into visual range of the catshark, and thus the freezing behaviour seems to be induced by visual cues only. The freezing behaviour is suggested to complement the colour pattern of the species in camouflage. This finding of predator avoidance behaviour in catsharks may inspire future research on predator recognition and avoidance to gain further insight into sharks’ predator–prey behaviour.

Life-history strategy and intertidal distribution in sympatric species of pulmonate limpets of the genus Siphonaria

CD McQuaid — 2024-12-28

Three species of the intertidal pulmonate limpet genus Siphonaria are sympatric on the south coast of South Africa and all lay gelatinous benthic egg masses. Siphonaria capensis and S. concinna hatch as planktonic larvae, whereas S. serrata has direct-developing larvae. Intertidal zonation of these species contradicts a model predicting direct development in species that occupy the high shore of the intertidal, and planktonic development in species that inhabit the low shore. Siphonaria concinna and S. serrata reach maximum densities on the middle to high shores, often co-existing in the same microhabitats. Siphonaria capensis is most abundant higher in the intertidal, especially in shallow pools where it lays its egg masses. Adults of both S. concinna and S. serrata are usually found on bare rock, though they deposit egg masses in other microhabitats. Whereas Siphonaria serrata uses microhabitats where desiccation is reduced, S. concinna is, in addition, able to use harsher habitats. Laboratory desiccation and field translocation experiments indicated that spawning where low-tide desiccation is reduced enhances embryonic survival. In various microhabitats, embryonic survival reflects interspecific differences in egg mass physical structure and egg capsule size that result in trade-offs between respiratory gas diffusion and desiccation. The relationship between mode of larval developmental and intertidal zonation is complex. While there may be no direct relationship between larval development and the intertidal height occupied by adults, the physical structure of egg masses and the microhabitats used for spawning are adaptive and complementary in terms of desiccation. In the absence of a capacity to migrate vertically to spawn, populations can be reproductively successful only by occupying intertidal heights with microhabitats suitable for the survival of egg masses.