SANBI

Rationale

Diplodus capensis is abundant along the southeastern seaboard of South Africa. This species is a major component of recreational and subsistence shore-based fisheries in the region and is prohibited in the commercial fishery (a "no sale" species). Diplodus capensis appears to have been able to sustain increasing fishing pressure with the aid of no-take MPAs in the area and species specific fishery regulations. Diplodus capensis exhibits early age and small size at maturity and an adaptable mode of reproduction which are likely to have facilitated the effective conservation efforts. However, D. capensis also exhibits life history traits that could render it susceptible to overexploitation including hermaphroditism, slow growth and long life span. The protandry exhibited by D. capensis makes females vulnerable to increased fishing pressure which in turn skews the sex ratio of the population, ultimately leading to a decline in overall population productivity by the reduction of fecundity and possibly recruitment. Since the females are larger in size they are also the limiting factor in regards to fecundity, thus reducing the number of large, fecund females can largely impede the fertility of a population. The spawning aggregations formed by D. capensis adults take place near the surface of the water and contribute to the vulnerability of this species as their spawning locations are predictable and easily targeted. Although a decline in population has not yet been observed, D. capensis should be closely monitored as this species is extremely important to recreational and subsistence fisheries. Improved regulation enforcement is recommended for this fishery as widespread non-compliance of minimum landing size may pose a threat to D. capensis. In addition to improved regulation enforcement, larger MPAs and a fisher awareness program are also recommended to aid in the conservation of D. capensis. Given that it is widespread and the populations appear to be stable, currently it is not at a high risk of extinction in the near future and is therefore listed as Least Concern.

Distribution

Diplodus capensis is known from Southern Angola and Namibia (Richardson et al. 2011) and from Cape Point in South Africa to southern Mozambique, and possibly also southern Madagascar, to 40 m depth (Fischer and Bianchi 1984, Smith and Heemstra 1986, Mann and Attwood 2000, Mann and Dunlop 2012). The similarity between Madagascan and southern African populations remains to be clarified (B. Mann pers. obs.) This species is most commonly observed <10 m depth (Mann 1992).

Habitat View more ecological information

Population trend

Trend

Catch composition of Diplodus capensis in KwaZulu-Natal decreased from 1956–1960 and 1978–1982 (van der Elst and De Freitas 1988, van der Elst 1989). Little change occurred between surveys conducted during 1975–1977 (9.2%) and 1994–1996 (8.7%) in KwaZulu-Natal but then increased to 14.5% during a survey conducted from 2009–2010 (Joubert 1981, Mann et al. 1997, Dunlop and Mann 2012). A decrease was observed between surveys conducted during 1985–1986 (18.4%) and 1994–1996 (7.6%) in the Port Elizabeth area (Clarke and Buxton 1989, Brouwer 1997). An increase in catch composition by competitive shore anglers was observed between 1950–1959 and 1976–1985 in False Bay, Western Cape due to a change in targeting (Bennett 1991). The mean size of D. capensis in KwaZulu-Natal has remained constant between three discreet sampling periods (1975–1977, 1994–1996, and 2009–2010) at around 22.5 cm FL (Joubert 1981, Mann et al. 1997, Dunlop and Mann 2012). No consistent trend in mean size was observed in the Southwestern Cape (Bennett et al. 1994). Fishing and total mortality rates are unknown for D. capensis; however, a range of natural morality values (0.12/yr to 0.63/yr) were calculated for D. capensis in the Tsitsikamma National Park using variety of methods (Götz et al. 2008).

Although no formal stock assessments have been conducted for Diplodus capensis, angler surveys conducted along the KwaZulu-Natal coast showed an increase in CPUE between three surveys conducted during 1975–1977 (0.1 fish/angler/day), 1994–1996 (0.103 fish/angler/day), and 2009–2010 (0.143 fish/angler/day)(Joubert 1981, Mann et al. 1997, Dunlop and Mann 2012). Long-term monitoring of shore angler catches from 1985 to 2008 in KwaZulu-Natal from the National Marine Linefish System (NMLS) also showed an overall increase in CPUE by number from 0.03 to 0.055 fish/angler (National Marine Linefish System, unpublished data). A decrease in CPUE was observed in the Port Elizabeth area from 19.4 g/person/hour (1985–1986) to 11 g/person/hour (1994–1996) (Clarke and Buxton 1989, Brouwer 1997). In the Southwestern Cape, an increase in CPUE was observed between 1938 and 1992 primarily due to a change in targeting by competitive shore anglers but this may also have been partly due to regulations being implemented in 1985 (Bennett 1991, Bennett et al. 1994). Trends in CPUE and mean size from the Tsitsikamma National Park fluctuated regularly from 1998–2005 (Götz et al. 2008).

Threats

Diplodus capensis exhibits a number of life history attributes that make this species potentially vulnerable to overexploitation including: longevity, hermaphroditism, and residency. In addition, this species is heavily targeted by recreational and subsistence shore fishers (Brouwer et al. 1997, Mann and Dunlop 2012). The hook and line fishery targets larger individuals of D. capensis, which puts fishing pressure on larger females and can skew the sex ratio of the population. Sequential hermaphroditic species are subject to dramatic life history and demographic changes as a result of exploitation. However, some species are able to avoid skewed sex ratios by shifting their size/age at sex-change in areas of low to moderate exploitation.

Uses and trade

Diplodus capensis is caught in the recreational and subsistence, hook and line shore fishery along the entire eastern seaboard of southern Africa where it is the third most important shore angling species by number (Joubert 1981, Brouwer et al. 1997, Mann et al. 2003, Dunlop and Mann 2012). It is occasionally taken by spearfishers (Mann et al. 1997) but is generally considered to be too small. This species is a no-sale recreational only species and may not be caught and sold in commercial fisheries (Department of Agriculture, Forestry and Fisheries 2012).

Conservation

In South Africa, Diplodus capensis is currently managed in terms of a daily bag limit of five fish per person per day and a minimum size limit of 20 cm TL for recreational and subsistence fishers and has been decommercialized (Department of Agriculture, Forestry and Fisheries 2012). In addition to traditional management regulations D. capensis is protected within a number of no-take MPAs in southern Africa, inter alia De Hoop (Bennett and Attwood 1993), Still Bay, Tsitsikamma (Cowley et al. 2002), Bird Island, Dwesa-Cwebe (Venter and Mann 2012), Pondoland (Mann et al. 2006), Aliwal Shoal, St Lucia and Maputaland MPAs (World Database of Protected Areas, accessed March 2014). All of the no-take MPAs on the southeastern seaboard with suitable inshore habitat will afford this species refuge due to its high degree of residency (Bennett and Attwood 1991, Mann 1992, Bennett and Attwood 1993, Attwood and Bennett 1995, Cowley et al. 2002, Götz et al. 2008, Mann 2012, Venter and Mann 2012).

The implementation of fishery regulations and establishment of no-take MPAs along the coast of South Africa have likely played a major role in sustaining the population of D. capensis (Attwood and Bennett 1995). However, this species exhibits life history characteristics such as early age and small size at maturity, an adaptable mode of reproduction, high fecundity and generalist lifestyle which contributed to its survival even in areas of relatively high fishing pressure.

Due to the importance of this species in recreational and subsistence fisheries, regular monitoring of catch and effort in South Africa should be undertaken and improved in many areas (Mann and Dunlop 2012). In a survey conducted between Kei Mouth and Port Edward from 1997–1998, of the D. capensis caught, 35% were below the minimum size limit. This suggests that better enforcement of regulations is needed, particularly in the Eastern and Western Cape. Additional recommendations include better enforced no-take marine protected areas and the establishment of a fisher awareness program (Mann et al. 2003).

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,]

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