Marine Life of Southern Africa
Author: Prof Rudy can der Elst ~ Oceanographic Research Institute, Durban
( Article Type: Overview )
South Africa is endowed with an exceptionally rich marine environment. Besides the huge diversity of ecosystems, at least 11 130 species of marine animals and numerous species of marine plants and seaweeds have been identified. These many species represent an enormously valuable resource to South Africa. Aside from the great industrial value of several species, there are additional less obvious benefits attributable to many of the other organisms. While traditionally much attention is devoted to the management of harvesting resources, it is equally important to protect the overall biodiversity of the South African marine environment. These two activities need not be divergent.
It is known that there are some 2 200 species of fish in our seas, equivalent to about 15% of the total number of marine fish species worldwide. There are 270 families of fishes represented in South Africa, equivalent to 83% of all marine fish families known. Strikingly, up to 13% are endemic, ranking amongst the highest anywhere. There are several families considered to be typically South African. These are the klipfishes (38 species), the gobies (28 species), the seabreams (25 species), the catsharks (11 species) and the toadfishes (7 species). Even more impressive are the invertebrates with an estimated 36% considered endemic. Notable families are the sea cucumbers (122 species), squids (195 species), jellyfishes (469 species) and pelagic copepods (354 species).
This marine species richness is largely attributable to the diversity of habitat and the fact that South Africa is located at the confluence of three great oceans: the Indian, Atlantic and Southern Oceans. However, the distribution of these species is not uniform along the 2881-km coastline, clearly an implication for their conservation. Accordingly, several attempts have been made to group all these species into zoo-geographic provinces.
One of these defines three or four regions as follows:
Cool temperate southwest coast: ~ From Luderitz to Cape Point
Warm temperate south coast: ~ From Cape Point to East London
Subtropical east coast (south) ~ From East London to Durban
Subtropical east coast (north) ~ From Durban to Maputo
In a more detailed analysis, the coast was divided into 52 sections of 50 km each. Using distributional fish records, it was shown that there were huge differences along the coast. Analysis of the data reveals a progressive increase in diversity from west to east and, significantly, the proportion of endemic species was highest along the south coast region. Protecting these different species is clearly a challenge, but the analysis revealed that protecting 25% (650km) of the coastline would secure the conservation of all inshore fish species. In order to conserve only the 227 species of coastal endemics, 21% (550km) of coastline required protection.
Conservation status of marine fishes
The conservation status of marine resources can be determined in different ways, for example:
- Quantitative stock assessment including the regenerative capacity of fish stocks.
- The Red Listing of species according to IUCN categories.
Both methods are of inherent value, the former especially for the benefit of fisheries development and the latter for protection of biodiversity. Indeed, the two methods are inextricably linked and should be viewed simultaneously if any real progress towards conservation of marine resources is to be achieved.
Global status of marine fisheries
Each year the Food and Agricultural Organisation of the UN (FAO) collects the catch and effort statistics from fishing nations around the world. For statistical purposes, these data are allocated to 16 oceanic regions, before being processed on an individual species and family basis. The results of this process are summarised into a global assessment of the status of marine (and freshwater) fishes. Obviously, only the exploited species are given consideration. However, as fishing represents one of the main pressures on the survival of fish species, this represents an important indicator of species conservation status.
The first global assessment was made in 1971 and since then there have been regular updates. Several general conclusions can be drawn from these results.
- Despite substantial increases in effort and technology, the historic annual growth in total catch has ceased and the world’s harvest of marine fish has reached a plateau.
- Considering individual species-area complexes, 200 of the world’s top fish species have been classified into one of four categories: undeveloped, developing, mature and senescent stocks. These results show that more than 35% of these top species are in serious decline with a further 25% having reached maximum exploitation levels. In other words, 60% of the world’s top marine fish species are at – or even beyond – their levels of maximum sustainable yield and hence their regenerative capacity.
- Considering the above information on a regional basis, 9 out of the 16 regions are overfished. South Africa falls in two of the regions, one of which (the SE Atlantic) is considered overfished, while the other (SW Indian Ocean) is still indicating an annual growth in landings.
- One of the more significant deductions from the global fishery analysis is the progressive change in species composition of landings. In the 1950s, the bulk of the global catch was made up of some 50 species of fish. This progressively changed with more species being added as historically important species became depleted – referred to as serial overfishing. At present, more than 600 species constitute the world’s catch – and so the number of potential new species will eventually run out and only depleted species will remain.
- The level of wasted by-catch in the world’s fisheries is quite staggering. A total of 27 million tons of marine life is dumped each year, equivalent to almost a third of all fish harvested.
South African fish and fisheries
The big industrial marine fisheries of South Africa have endured large-scale fluctuations over the years. Much of this is attributable to environmental variability and interactions between species. However, in the 1960s and 1970s, the landings of several species were allowed to escalate beyond levels of sustainability, posing a threat to the biodiversity of the region. Fortunately, this situation has since stabilised, largely due to improved assessment and management strategies implemented by Marine and Coastal Management (MCM). This is especially true for the pelagic and demersal fisheries, but less so for some inshore resources such as abalone. Indeed, several serious issues remain, despite growth in landings. Serial over-fishing is not only a global issue and South African fisheries have also shown a progressive increase in the number of species harvested over the years. In 1964 only 17 species of marine fish were reported in national landings. Today at least 51 species are involved, with additions such as swordfish, orangeroughy and toothfish. The concern over by-catch is also a local problem. For every ton of prawns caught on the Tugela Banks, up to four tons of fish are dumped, including endemic and rare species.
The situation is even less optimistic with demersal linefish species. Comprised predominantly of endemic species of the seabream family (Sparidae), these fishes have been severely depleted. Most famous amongst these are the seventyfour, red steenbras, red stumpnose and similar species.
Following concerted efforts by South African linefish researchers, the various species were assessed and allocated to different levels of conservation status. This was a quantitative assessment based on the species’ regenerative capacity termed the ‘spawner biomass per recruit’ (SB/R). Based on extensive data from many species and studies, it was deduced that if SB/R fell below 25% of virgin stock levels, its regenerative capacity would be severely damaged. The only conclusion that can be drawn is that demersal, and especially endemic, linefish species are seriously depleted, many to levels below regenerative capacity. It can be argued that these depletions, some of more than 90%, ranks amongst the most serious impacts on biodiversity and species richness in the region.
While human pressures through fishing have impacted severely on many species, the decline in the quality and extent of suitable habitat also plays a part. Degraded estuaries and increased silt loads all contribute to increasing pressure on some fish species.
South Africa red data of fishes
The original approach to redlisting involved the allocation of species to four categories: threatened, endangered, vulnerable and rare. This was later expanded to include data deficient and recovered species. While the system proved useful for the protection of terrestrial plants and animals, it was rather simplistic and quite inadequate for marine organisms, especially fishes. In fact, only 4.2% of the global redlisted species are marine species. This shortcoming was realised by WWF and IUCN, who arranged a joint expert workshop in 1996 in London to identify specific shortcomings in redlisting criteria for marine fishes and thence to develop guidelines for improving the classification. The first attempt at classification of fishes in red data categories was done by Skelton in 1977, when he recorded 28 species of fishes, four (14%) of them marine linked. A decade later, Skelton listed 50 species, 14 (27%) of them marine related – all estuarine. Now, 14 years later, IUCN and the Department of Environmental Affairs and Tourism has released a new South African red data list for marine animals as part of a CITES species management plan. This time the list has 53 marine fish species, a 13-fold increase since 1997, and with 33 species exclusively marine. How does this list compare to international trends? Data are available for the global listing of marine fishes as well as for Australia. This comparison in numbers listed is reflected in the table on the previous page. The table of Red Data Categories indicates that southern Africa and Australia have reasonably similar levels of redlisting, while the proportion allocated to ‘data deficient’ in Australia is much higher than that in southern Africa. In contrast, South Africa has listed a greater proportion in the critical and low risk categories.
South Africa cannot protect its marine resources in isolation. Many of our species are shared with other nations and many others migrate across national boundaries. This calls for concerted regional collaboration in resource management and conservation. Approximately 30% of the world’s population live in countries surrounding the Indian Ocean, but this ocean generates only 5% of the global fish catch. It is estimated that there are more than half a million people in this region who are engaged in a daily routine of harvesting marine resources. These range from subsistence harvesting along intertidal shorelines to small scale fishing ventures at the individual or community level, ranging to the nation’s territorial limits. However, the capacity to manage these resources, as well as the data required to monitor stocks is often inadequate. For this reason a number of regional research and management programmes have been introduced. South Africa actively participates in several of these.
There is no doubt that the challenges facing marine conservation in the southern African region are enormous. Added to this has been a steady decline in scientific expertise, as many scientists have been lured overseas. But this also provides new opportunities that need to be grasped and developed. Notwithstanding several serious conservation problems, South Africa has an excellent marine conservation record. Technical knowledge remains good, but this must also be matched with political will to implement conservation strategies based on good science.