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Rationale

The West Coast Steenbras (Lithognathus aureti) is a Namibian endemic that only occurs to 10 m depth. The northern subpopulation of this species is an important component of the recreational shore fishery while the southern subpopulation is occasionally targeted by commercial line-boats. Lithognathus aureti is believed to be optimally exploited, but the fishery should be monitored and controlled effectively for both the northern and southern subpopulations. However, this species can live to 50 years of age and exhibits protandrous hermaphroditism, both of which predispose L. aureti to overexploitation and a heightened risk of extinction. In addition, the estimated area of occupancy (AOO) for this species is 3,086 km²and, given the limited inshore distribution of this species, we infer that this AOO is almost reaching the thresholds of Vulnerable under criterion B2. There are continuing declines in the AOO and number of mature individuals. Therefore, it is listed as Near Threatened.

Distribution

Lithognathus aureti is endemic to Southern Africa, from Rio Longa, Angola; to Cape Town, South Africa, but it is rare outside of Namibian marine waters (Holtzhausen 2000, Heemstra and Heemstra 2004). This species occurs to depths of about 10 m (Holtzhausen 2000). The AOO for this species is 3,086 km².

Habitat View more ecological information

Population trend

Trend

Two distinct subpopulations of Lithognathus aureti are found in Namibian waters, including a closed and separate subpopulation in the southern region at Meob Bay and a second stock occurring in the central and northern regions (van der Bank and Holtzhausen 1998/1999). The northern subpopulation of L. aureti is considered to be optimally exploited as spawning biomass per recruit is estimated at between 40% and 50% of its pristine level (Beyer et al. 1999, Holtzhausen 2000, Holtzhausen and Kirchner 2001a). Lithognathus aureti made up 12% of the total annual recreational catch of rock-and-surf anglers in the area of its northern subpopulation during the 1996-1997 season in Namibia (Kirchner 1999). The northern subpopulation is exploited recreationally and commercially and current depletion is 42% of spawning biomass per recruit (Holtzhausen and Kirchner 2001a).

Threats

Lithognathus aureti is an important species in both commercial and recreational sectors in Namibia (Holtzhausen et al. 2001) and exhibits life history characteristics such as slow growth and longevity that make this species extremely susceptible to over-fishing. It also has a restricted distribution and its habitat is largely limited to the surf zone out to 10 m depth (Holtzhausen and Kirchner 2001b, B. Mann pers. comm. 2014).

Uses and trade

Lithognathus aureti is an important species in the recreational fishery in Namibia (Kirchner et al. 2000), with the northern stock primarily exploited by recreational shore anglers in the West Coast Recreational area (260 km) and in Torra Bay and Terrace Bay in the Skeleton Coast Park (65 km), together constituting one fifth of Namibia’s 1,500 km-long coastline. The southern stock is occasionally targeted by commercial line-boats when kob (Argyrosomus inodorus) is scarce (Holtzhausen and Mann 2000, Mann and Potts 2013). It is estimated that the Namibian recreational line-fishery contributes $35 million per annum to the GDP of the country, of which approximately $4.5 million could be attributed to the L. aureti resource (Holtzhausen and Mann 2000). Lithognathus aureti is only taken as an incidental catch by recreational ski-boat anglers (Mann and Potts 2013). This species is commonly fished between October and March (Bianchi et al. 1999).

The SSB for the northern subpopulation was estimated at 772 tonnes (range 538–1,121) and MSY at 134 tonnes (range 109–173) which was equalled in the 1995/1996 season and was almost double the amount harvested in the 1998/1999 season. Commercial line-boat catches of both stocks of L. aureti have been recorded since 1973 (35 tonnes landed) and reached a peak in 1980 (407 tonnes landed), followed by a downward trend with a zero catch in 1993. The use of set nets was banned in 1992 to protect the species (Holtzhausen 2000). After not harvesting the southern subpopulation for 11 years, 67 tonnes and 97 tonnes were harvested in 1997 and 1999, respectively, with 82% of these catches consisting of females of ten years and older (Holtzhausen and Mann 2000).

Conservation

In South Africa, Lithognathus aureti is prohibited in the commercial line-fishery (a "no sale" species), and there is a daily bag limit of one fish per person per day for recreational and subsistence fishers as well as a minimum landing size of 60 cm TL (Department of Agriculture, Forestry, and Fisheries 2012). In Namibia, each angler may only have ten teleost fish, including kob, west coast steenbras, blacktail, and galjoen and no more than two individual fish longer than 65 cm TL may be kept. Each person may transport three times the daily bag limit but is limited to not more than ten of each species, and all fish must be whole. Of the ten L. aureti allowed, six may be over 65 cm TL . The minimum landing size in Namibia is 40 cm TL but only two fish above 65 cm TL may be kept per person per day (Mann and Potts 2013).

Although there is no closed season specifically for L. aureti, there is a closed season for all angling species from 25 January to 15 April applicable to the Sandwich Bay area only. Sandwich Bay area and the recently proclaimed MPA in southern Namibia provide some protection for this species. Although four-fifths of the coastline is closed to recreational angling (i.e., diamond mining areas), line-boats may operate along the entire 1,500 km of coastline. In Namibia, for all angling species, there is a limit of one rod per angler with a maximum of two hooks, the use of polychaete worms as bait is prohibited, a recreational angler may not sell his catch, and there is a ban on the use of set-nets by line-boats. No new rights of exploitation for line-boats have been granted since 1992 (Holtzhausen and Mann 2000).

The northern L. aureti resource in Namibia is small, with an estimated MSY of c. 134 tonnes per year (Holtzhausen and Kirchner 2001a), and thus should be managed wisely. The recreational shore fishery should be carefully monitored to ensure that the MSY is not exceeded. Exploitation of the southern subpopulation by line-boats should also be carefully monitored and controlled (Mann and Potts 2013).

References

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