The current status of the stock is <25% of its pristine biomass and is considered to be collapsed with spawner biomass per recruit of
L. lithognathus estimated at 6% of the pristine state (Bennett 1993, Lamberth and Joubert 1999). Stocks <25% of the pristine status are indicative of stock depletion in long lived species and yield a high risk of collapse (Clark 1991, Mace and Sissenwine 1993, Thompson 1993, Mace 1994). Reductions in CPUE of >90% coincide with spawner biomass ratios of <10% and are indicative of severe stock depletion (Griffiths 2000). There is an urgent need for reassessment as considerable changes have taken place regarding the exploitation and protection of
L. lithognathus and it is possible that the population of this species has declined further
(Bennett and Lamberth 2012, Bennett
et al. 2011).
Lithognathus lithognathus exists in a single, well-mixed population (Bennett 2012) with the main portion of the stock located inshore and in estuaries along the east and west coasts (Brouwer
et al. 1997, Lamberth and Mann 2000, Brouwer and Buxton 2002). The distributional range of this species does not have any major geographical barriers to impede gene flow resulting in a well-mixed population with no subpopulation structure (Bennett
et al. 2011). The core range of
L. lithognathus may have contracted as this species did not feature in shore-angler catches along the west coast of South Africa and no individuals of
L. lithognathus were collected in gillnet catches from Cape Point to the Olifants River Mouth from 1997 to 1999 (Lamberth
et al. 1997, Hutchings and Lamberth 1999).
Lithognathus lithognathus was reported the most common angling species in the Swartkops Estuary on the Eastern Cape in the early 1900s but its contribution declined significantly by the 1970s (Marias and Baird 1980) and was absent from gillnet catches in the same estuary in 1992 (Baird
et al. 1996).
Lithognathus lithognathus is primarily caught by shore anglers in the Western and Eastern Cape (Brouwer et al. 1997) with catches from the 1930s to the 1990s being responsible for ~50% of the total annual catch by mass of L. lithognathus and ~75% by number (Bennett 1993). By the 1980s, shore angling catches were estimated at 28,000 individuals of L. lithognathus (Bennett 1993) and 39,000 (86 tonnes) by 1996 (Lamberth 1996). The beach seine fishery contributed to the majority of L. lithognathus mortality prior to 1960 (Bennett 1993). The beach seine fishery was responsible for 25% by number and 50% by mass of the total catch (Lamberth et al. 1994). Total annual catch from 1985 to 1990 was approximately 30,000 to 35,000 fish about 70% of which was taken by recreational anglers and 30% by commercial fisherman with the catch divided equally between the two fisheries in terms of mass (Bennett 1993). Annual catches of L. lithognathus were estimated to be ~20 tonnes on average but peaking at 100 tonnes in some years and catches were initially widespread in the Northern, Western, and Eastern Cape but largely reduced to False Bay in 1982 (Penney 1991). Lithognathus lithognathus taken in the purse seine fishery in False Bay before 1980 was responsible for approximately 300 tonnes annually but reached a peak of 1,000 tonnes from 1980 to 1982. Public outcry resulted in a ban on purse seining of L. lithognathus in 1983 (Bennett 1993). The catch in the purse-seine fishery was almost entirely made up of mature fish and likely to have accelerated the stock collapse that occurred about that time (Bennett 1993, Penney 1991). Following the ban, the commercial beach-seine fishery averaged 20 tonnes annually while the recreational shore fishery exceeded 80 tonnes of L. lithognathus catches annually (Bennett 1993). A commercial ban (no sale allowed) was implemented in 2001 in response to fear of a continued decline in catches; however, the ban was not executed in a timely manner as the L. lithognathus stock had already collapsed (Lamberth and Joubert 1999). This species is caught by normal beach-seine and sinking “Russman” seine along the Western and Southwestern Cape while the legal fishery was confined to False Bay where up to 20 tonnes or 4,700 fish were landed annually (Lamberth et al. 1994). Lithhgnathus lithognathus is the sixth most frequently reported by-catch species caught in the Western Cape gill-net fishery but comprises less than 1% of monitored catches by mass and by number (Hutchings and Lamberth 1999).
CPUE for the shore angling fishery declined from 2.3 fish/100 angler hours from 1971 to 1984 to 0.9 fish./100 angler hours in the 1990s, 1996. representing a 61% decrease over a ten year period (Bennett 1993, Bennett et al. 1994, Lamberth 1996, Brouwer et al. 1997, Bennett et al. 2011). CPUE from both recreational and commercial fisheries has declined considerably over the past 40–50 years (Bennett 1993, Lamberth et al. 1994, Brouwer et al. 1997, Lamberth 2000, Pradervand and Baird 2002). This species contributed ~30% to annual angler catches by mass in the 1960s in the Southwestern Cape shore fishery but declined to 8% in 1990 to 1991, and to 0.6% in 1994 to 1996 (Lamberth 1996). A similar decline in catch composition of shore angler catches and seine net catches in the Western Cape has also been recorded (Bennett 1993, Lamberth 1996). Catch frequencies have declined by almost an order of 2.3magnitude over the last decade. Between 1971 and 1984, 90% of angler outings yielded zero, and 5.2% one fish as opposed to 97% and 2.3% for 1994 to 1996 (Bennett et al. 1994, Lamberth 1996). An 85% decline in mean annual reported catches of L. lithognathus was observed in the beach seine fishery from 23,061 fish/year between 1897 and 1906 to 3,147 fish/year between 1983 and 1991 (Bennett 1993); however, this decline could be a result of the net catches of “linefish” being outlawed in all areas except False Bay during 1983 to 1991 (Bennett 1993, Lamberth et al. 1994). After the closure to fishing at Koppie Alleen, CPUE increased in the De Hoop MPA from 0.42 fish/100 angler hours between 1984 and 1985 to 2.63 fish/100 angler hours by 1990 (Bennett and Attwood 1991), and to 4.68 fish/100 angler hours at Koppie Alleen and Lekkerwater by 1992 (Bennett and Attwood 1993). Long-term seine-net monitoring programs conducted in the Berg Estuary indicated increases in CPUE since the commercial closure in 2001 (K. Hutchings, University of Cape Town unpublished data) as well as an increase in CPUE along the Algoa Bay shoreline over the past seven years since the ban on beach driving in 2002 (P.D. Cowley,South African Institute for Aquatic Biodiversity unpublished data).
Although L. lithognathus is not a significant component of the spear fishery, anecdotal evidence notes that relatively high numbers of large L. lithognathus adults are taken by spearfishers (Mann et al. 1997) but catches are considered negligible when compared to the recreational shore fishery and to commercial beach-seine fisheries (Bennett and Lamberth 2012). Catch data for subsistence fisheries in the surf zone are limited (Mann et al. 2003); however there is evidence that suggests large catches of undersized individuals by estuarine subsistence and recreational fisheries (P. Cowley, South African Institute for Aquatic Biodiversity pers. comm., Bennett and Lamberth 2012). Recreational boat catches from estuaries are very low relative to other angling species and individuals that are landed are usually undersized. Lithognathus lithognathus was historically a major component in recreational and competition catches in some estuaries (Marias and Baird 1980). Boat-based catches are negligible and formed a small component of commercial lineboat catches from 1897 to 1906 in Walker Bay but absent from 1985 to 1996 (Attwood and Farquhar 1999). This species was a small component in commercial lineboat bycatch in False Bay until the 1990s (Lamberth and Bennett 1993). Total bycatch is estimated at under one tonne annually for recreational and commercial lineboats (Lamberth and Mann 2000). Bycatch recorded for monitored gillnet catches along the Western Cape was negligible in the 1990s (Hutchings and Lamberth 2002); however, under-reporting in the fishery is high, leaving the contribution of this fishery to total catch higher than it is reported to be (Lamberth et al. 1997). Lithognathus lithognathus has been successfully cultured in the marine aquaculture industry but is still in the preliminary stages. A number of biological, social, and economic concerns are to be addressed before full production commences (Bennett et al. 2011).
Cowley and Whitfield (2001) quantified population size estimates in the East Kleinemonde Estuary, Eastern Cape over a three year period. Population estimates for L. lithognathus ranged from 300 to 3,500 individuals while an increasing trend in annual recruitment was observed from 2002 to 2006 (Cowley and Whitfield 2001, James et al. 2007). Occurrence of this species on the west coast between Cape Point and the Orange River is now rare and juvenile populations in the estuaries in this region have declined by 80% to 91% of pristine reference conditions (Lamberth et al. 2008). The hypothetical, historical west coast spawning population of L. lithognathus is functionally extinct due to beach-seine and gillnet fishery over-exploitation (S.J. Lamberth, Department of Agriculture, Fisheries and Forestry pers. obs.; Bennett and Lamberth 2012). In recent years, L. lithognthus was ranked as the second most common teleost in shore angler catches based on a survey north of Sundays River in Algoa Bay from 2006 to 2009 (Chalmers 2011) and is now ranked as the first most common teleost in research angling (P.D. Cowley, South African Institute for Aquatic Biodiversity, unpublished data). Although there is no apparent trend in mean size, recent improved CPUE along the shoreline in Algoa Bay primarily consists of sub-adults and late juveniles which suggests that the mean size has probably decreased (Bennett and Lamberth 2012).