true

ISRA FACTSHEETS

WESTERN INDIAN OCEAN REGION

ISRA FACTSHEETS

WESTERN INDIAN OCEAN REGION

uThukela ISRA

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uThukela ISRA

uThukela

Summary

uThukela lies within the Natal Bight off the KwaZulu-Natal coast in South Africa. The area is known for its mosaic of habitats, including reefs, gravel fields, muddy seafloors, and extensive estuarine environments. This area overlaps with the uThukela Marine Protected Area and incorporates Critical Biodiversity Areas offshore and inshore in the south. uThukela also overlaps with the Natal Bight Ecologically and Biologically Significant Marine Area. Within this area there are: threatened species (e.g., Dusky Shark Carcharhinus obscurus); range-restricted species (e.g., Twineye Skate Raja ocellifera); reproductive areas (e.g., Spinner Shark Carcharhinus brevipinna); and undefined aggregations (e.g., Milk Shark Rhizoprionodon acutus).

uThukela

uThukela

DESCRIPTION OF HABITAT

uThukela lies off the KwaZulu-Natal (KZN) coast in South Africa. It is located between Richards Bay and Umhloti, incorporating ~130 km of coastline and extending from the highwater mark to ~50 km offshore. This area is known for its mosaic of habitats, including reefs, unusual gravel fields, rich muddy seafloors, and extensive estuarine environments (Green et al. 2022). uThukela is in the Natal Bight, which is the widest shelf region of the subtropical east coast of South Africa. The area is a highly significant and unique biodiversity area, which is aptly reflected in its Zulu-derived name uThukela meaning ‘surprise’. The inshore area hosts 14 estuaries (Richards Bay, uMhlathuze, uMlalazi, aMatigulu, iNyoni, uThukela, iZinkwazi, iNonoti, uMdlotane, uMvoti, uMhlali, uThongati, iSetheni, iSiyaya) that result in large freshwater and sediment input into the coastal waters of the area, leading to more turbid waters than adjacent regions (Fennessy 1994). The area receives most rainfall between September–April, leading to a seasonal peak in freshwater and sediment discharge in the austral summer (Middleton & Oliff 1961). These estuaries also support mangroves, reed marshes, and seagrass meadows. The strong reliance on benthic productivity is a marked feature of the area (Fennessy et al. 2016), in contrast with systems which rely on upwelled nutrients.

The area overlaps with the uThukela Marine Protected Area (MPA) and incorporates Critical Biodiversity Areas (CBAs) offshore and to the north and south. CBAs are biodiversity priority areas that currently fall outside of protected areas but are important for the persistence of a viable representative sample of all ecosystem types and species as well as the long-term ecological functioning of the landscape as a whole (SANBI 2017). The area also overlaps with the Natal Bight Ecologically and Biologically Significant Marine Area (EBSA; CBD 2023).

This Important Shark and Ray Area is benthopelagic and is delineated from inshore and surface waters (0 m) to 250 m based on the distribution of Qualifying Species and the bathymetry of the area.

CRITERION A

VULNERABILITY

Six Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened SpeciesTM regularly occur in the area. Threatened sharks comprise one Critically Endangered species, one Endangered species, and three Vulnerable species; threatened rays comprise one Endangered species (IUCN 2023).

CRITERION B

RANGE RESTRICTED

This area holds the regular presence of the Diamond Ray and Twineye Skate as resident range-restricted species. Historical and contemporary benthic trawl data (Fennessy 1994; S Fennessy unpubl. data 2023), long-term (40-year) catch data from the National Marine Linefish System (NMLS; Oceanographic Research Institute [ORI] 2023), and regular Baited Remote Underwater Video (BRUV) surveys (SAIAB 2023) support their regular occurrence in uThukela. The Diamond Ray is a southern African endemic species (southern Mozambique to central Namibia; Daly et al. 2022) and was the second-most captured shark and ray species in trawls in the area between 1989–1992 with a 66% frequency (Fennessy 1994). Catches have also been recorded in more recent research trawls in the area (S Fennessy unpubl. data 2023). The Twineye Skate is a South African endemic species and uThukela is the only area in KZN where the species has been regularly and predictably captured (Ebert et al. 2021; Fennessy 1994; S Fennessy unpubl. data 2023).

Diamond Rays and Twineye Skates occur in the Agulhas Current Large Marine Ecosystem (LME) and the Benguela Current LME.

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

uThukela is an important reproductive area for three shark species.

Pregnant Spinner Sharks are regularly caught in the area with historical shark net catches of pregnant females (n = 290) in KZN. Near-term females, which made up 69% (n = 200) of the total catch of pregnant females, were taken mainly at Richards Bay and Zinkwazi, indicating a pupping ground inshore of the uThukela Banks (Bass et al. 1973; Allen & Cliff 2000). Pupping takes place between March and August with a peak in April and May (Bass et al. 1973; Allen & Cliff 2000). Shark net catches in this area between 2020–2022 confirm that uThukela is still an important reproductive area for Spinner Sharks. Catches included relatively high numbers of Spinner Sharks, comprising adults in mating condition and pregnant females with term pups (KwaZulu Natal Sharks Board [KZNSB] unpubl. data 2023). This species was also caught in the KZN inshore prawn trawl fishery on the uThukela Banks, with a size range of 60–160 cm TL (Fennessy 1994). Size-at-birth of the Spinner Shark is 65–75 cm TL (Bass et al. 1973) and therefore catches included neonates, which is additional evidence that the area may be a nursery ground (Fennessy 1994).

Pregnant and neonate Dusky Sharks are regularly caught in the area. Historical shark net catches of pregnant females in KZN were highest in the area, at Zinkwazi and Richards Bay (Dudley et al. 2005). Most embryos were at or near full term, indicating the presence of a pupping ground in this area. The size-at-birth for the species is 100 cm total length (TL) (converted from fork length; Natanson & Kohler 1996). A recent study of neonates (defined by an open umbilical scar) at Zinkwazi confirmed that they exhibit periods of residency in the area before dispersing (R Daly unpubl. data 2023). Although neonate Dusky Sharks can move large distances along the coast after pupping, coastal sites such as those in the area appear to be particularly important for them (Hussey et al. 2009). Long-term competitive angling catch data between 1977–2017 (40 years) confirms that the area, particularly north and south of the uThukela River, including Zinkwazi, is frequented by high numbers of neonates, with catches of >100 individuals by a team of eight anglers in eight hours not uncommon during late winter/spring (ORI unpubl. data 2023).

Pregnant Scalloped Hammerheads are regularly caught in the area. Term pregnant females with embryos ranging 40–55 cm TL were encountered in historical KZN shark net catches between October and March 1978–1998 (de Bruyn et al. 2005). They also had large ovarian follicles (±30 cm), suggesting that they mate soon after pupping. Size-at-birth of the species is 45–55 cm TL (Bass et al. 1975). Adults in mating condition, including many pregnant females, were caught in November and December, mostly in the shark nets of Richards Bay and Zinkwazi in the area. This was indicative of a pupping ground and possibly a mating ground in the area (de Bruyn et al. 2005).  Catches of sexually active adults in these nets continues (KZNSB unpubl. data 2023). This species was caught in large numbers in the KZN inshore prawn trawl industry on the uThukela Banks (Fennessy 1994) and was the most frequently captured species (71%) in trawls between 2003–2005 (n = 181; S Fennessy unpubl. data 2023). Catches spanned a wide size range from 40–150 cm TL, but with a mean of 60 cm TL, indicating that a majority of neonates and young-of-the-year individuals were caught (Fennessy 1994).

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

uThukela is an important area for undefined aggregations of two shark and one ray species. Further information is required to define the nature and function of these aggregations.

A study of 34 White Sharks fitted with SPOT satellite tags showed that individuals spent more time in uThukela than any other MPA in South Africa, despite the fact that this area is >1,100 km away from the tagging site. At present, it is unclear why they had this activity hotspot in the area. Six of the tagged individuals showed resident behaviour in the area for several weeks (Kock et al. 2022). Recent data from the KZN shark nets shows that catches of this species are far higher in the area in nets at Richards Bay and Zinkwazi than anywhere else on the KZN coast, which highlights the importance of this area as an aggregation site for the species (KZNSB unpubl. data 2023).

The uThukela River mouth in the area is an important aggregation site for Milk Sharks. Competitive recreational angling data (1977–2017) from the National Marine Linefish System (NMLS) database shows peaks in catches of 51–80 sharks made in six hours by teams of eight anglers operating within a maximum of a few hundred metres of each other. These catches are confined to the summer months when rainfall is high, and the uThukela River creates a turbid nearshore environment (ORI unpubl. data 2023).

Diamond Rays aggregate close to shore in the area during summer. Competitive recreational angling data from the National Marine Linefish System and tag-and-release data from the ORI cooperative tagging project both show peaks in catches in summer in this area, with >100 individuals caught in an eight-hour period within a small area (usually ~50 m) by a team of eight anglers on several occasions (Daly et al. 2022). As the majority of these individuals are adults, it is suspected that such aggregations are driven by reproductive needs.

uThukela

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