|Scientific Name:||Lithognathus lithognathus|
|Species Authority:||(Cuvier, 1829)|
Lithognathus capensis Swainson, 1839
Pagellus lithognathus (Cuvier, 1829)
Pagrus lithognathus Cuvier, 1829
|Red List Category & Criteria:||Endangered A2bcd; B2ab(ii,v) ver 3.1|
|Assessor(s):||Mann, B.Q., Buxton, C.D., Pollard, D., Carpenter, K.E. & Iwatsuki, Y.|
|Reviewer(s):||Bennett, R., Russell, B. & Lindeman, K.|
|Contributor(s):||Gorman, C. & Comeros-Raynal, M.|
The White Steenbras (Lithognathus lithognathus) is a slow-growing, long-lived, late maturing, and estuarine-dependent species endemic to South Africa. This species undertakes annual migrations where is it subject to targeted fishing effort at spawning aggregation sites. Estuaries are critical nursery habitats for L. lithognathus and juveniles are obligatory inhabitants of estuaries for up to three years. Lithognathus lithognathus is susceptible to fragmentation due to intrinsic characteristics such as strong site fidelity and a small home range. Furthermore, its estuarine habitat is extremely vulnerable to habitat degradation due to anthropogenic activities including infrastructural development, boating activities, freshwater abstraction and overfishing. These pose major threats to the shallow water and estuarine habitats that this species depends on and have profound impacts on recruitment, population size and structure. Spawning may be restricted to inshore areas off a few estuaries along the Transkei coast. While L. lithognathus is afforded some protection in several no-take MPAs throughout its range, the stock is regarded as collapsed and drastic management measures have been implemented in order to rebuild the stock. Despite the decommercialization of L. lithognathus, illegal fishing and non-compliance of minimum landing sizes still pose threats to this species. There are also continual efforts to lift the commercial ban that would almost certainly result in the complete collapse of the stock. CPUE trends and significant changes in relative contribution of this species to overall catch composition infer very substantial reductions in abundance across its distributional range. The current status of the stock is <25% of the pristine biomass and is considered to be collapsed with spawner biomass per recruit of L. lithognathus estimated at 6% of the pristine stock. Numbers have decreased an average of 55% estimated over a 36 year period (1951-1968, 1977-1987, 1983-1991) and landings have declined at a faster rate by an average of 83% over 36 years (1960-1991, 1991-1996) in the Southwestern Cape shore fishery. Moreover, current trajectories of exploitation and deleterious impacts to its estuarine habitat may indicate further population declines of this species. The estuaries inhabited by L. lithognathus juveniles range from the Berg Estuary on the Western Cape to Mbhanyana on the Eastern Cape coast which comprises c. 146 km2 of estuary surface area. This species is therefore listed as Endangered under A2bcd; B2ab(ii,v) based on population declines in excess of 55% extrapolated over three generations (=39 years), an AOO of 146 km2, the continuing decline of mature individuals and area of occupancy, and under five threat based locations.
Recommended conservation measures include: additional marine/estuarine protected areas, a closed fishing season, MPA angling closures, improvement in law enforcement and compliance, and reduction in illegal fishing in spawning grounds. A network of estuarine protected areas and the establishment of no-take areas in the sandy lower reaches of estuaries is recommended to aid the protection of juveniles. We further recommend continued monitoring of the status of its population and estuarine habitat. Importantly, the population of this species needs to be closely monitored as further population declines may warrant listing in a higher extinction risk threshold in the next five years.
Lithognathus lithognathus is a South African endemic found from the mouth of the Orange River to KwaZulu-Natal (Smith and Smith 1986, Lamberth and Mann 2000) to a depth of 25 m (Bennett 2012). The core distribution of this species ranges just from north of Cape Columbine in the west to the Mbashe Estuary in the east (Lamberth and Mann 2000). The estuaries inhabited by L. lithognathus juveniles range from the Berg Estuary on the Western Cape to Mbhanyana on the Eastern Cape coast which comprises c. 146 km2 of estuary surface area (Bennett et al. 2012, Bennett and Lamberth 2012).
There is some evidence of the presence of L. lithognathus off the Namibian coast but this has yet to be confirmed (Bianchi et al. 1999, Bennet and Lamberth 2012). A juvenile recorded from the Cunene River Estuary also needs to be confirmed (Bennett and Lamberth 2012). Although occasionally found as far north as Durban in KwaZulu-Natal (van der Elst 1988), occurrence is rare north of Coffee Bay along the Wild Coast (Mann et al. 2003).
|FAO Marine Fishing Areas:||
Atlantic – southeast; Indian Ocean – western
|Range Map:||Click here to open the map viewer and explore range.|
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).
|Habitat and Ecology:||
Lithognathus lithognathus has specific and restricted distributional ranges for each its life stages (i.e. estuarine juvenile, post-estuarine sub-adults and adult). Adults of this species inhabit inshore marine environments to 25 m depth (Bennett 2012), usually over sandy or mixed sand and rock shorelines (Smith and Smith 1986; Bennett 1991, 1993; P.D. Cowley, South African Institute for Aquatic Biodiversity, unpublished data). Juveniles have an obligatory estuarine-dependent nursery phase (Wallace et al. 1984) where they inhabit estuaries for up to two to three years (Bennett et al. 2011, Bennett 2012) with high site fidelity (Bennett et al. 2012). Late juveniles up to 40 cm FL inhabit the surf zone (Cowley 1999, Bennett 2012) while late juveniles/sub-adults (40 cm to 50 cm FL) are semi-resident in the surf zone and exhibit some nomadic movement up to 400 km (Bennett 1993, 2012). Some individuals >50cm begin to under take large scale migrations while the majority remain resident (Bennett 2012). Some adolescents from one to five years of age and 65 cm, will extend their range into deeper water to <25 m depth (Bennett 1993). Based on a study using acoustic telemetry, the mean home range for early juveniles in the Great Fish Estuary, Eastern Cape was small relative to the size of the estuary (Bennett et al. 2011) with similar results from the East Kleinmonde Estuary, Eastern Cape (Bennett et al. 2012) and from the Kariega Estuary (R. Bennett and P. Cowley unpublished data). The adult diet of this species primarily consists of polychaetes, crustaceans, molluscs, mysids, and echinoderms (Bennett 1993). Estuarine juveniles feed on annelids, algae (Mehl 1973), copepods, ostracods (Wooldridge and Bailey 1982), and brachyura (Whitfield 1985) while surf zone juveniles feed on amphipods, mysids, macrurans, polychaets and bivalves (Bennett 1993).
Lithognathus lithognathus can live from 25 to 30 years of age (Bennett 1993) and has a maximum length and weight of 137.6 cm and 26.3 kg, respectively (Bennett 1993, South African Shore Anglers Association 2012). Juveniles <5 cm recruit into estuaries along the Eastern and Southern Cape coasts from September to November (Bennett 1993). These recruitment periods are short and depend greatly on periods of high rainfall to open the estuaries which would otherwise not be accessible otherwise (Bennett et al. 2011). Lithognathus lithgnathus is not able to recruit during overwash events in the East Klienmonde Estuary, during periods of extended drought when the mouth of the estuary was closed, no recruitment of L. lithognathus was observed (James et al. 2007).
Lithognathus lithognathus is a rudimentary hermaphrodite, functional gonochorist (Mehl 1973, Bennett 1993). The length at 50% maturity for both sexes is 65 cm and the age at 50% maturity is about six years TL (Bennett, 1993). This species has a single spawning period (Beckley 1984, Bennett 1989, Whitfield and Kok 1992) which occurs in late winter from July to August (Bennett 1993). On the eastern part of the Eastern Cape off the Transkei coast, spawning takes place inshore near the mouths of estuaries over fluvial mud deposits (Bennett 1993). Spawning may be restricted to inshore areas off a few estuaries along the Transkei coast (Mbashe, Mtata, Mzimvubu and Great Kei) (van Niekerk and Turpie 2011). There is evidence that some adult L. lithognathus undergo an annual, spawning migration along the shore that commences in autumn (Bennett 1993; S. Lamberth, Department of Agriculture, Fisheries and Forestry pers. comm.; Bennett 2012). Catch data indicate that adults aggregate in False Bay, Western Cape and move northwards and eastwards to the northern parts of the Eastern Cape coast in time for late winter spawning, aggregating again near the Mbashe Estuary by late winter (Bennett 1993). Eggs and larvae drift southwards after being spawned close inshore along the Eastern Cape coast (especially from the Mbashe River mouth area). After metamorphosis they enter estuaries along the Southeastern Cape, Southern Cape, and Southwestern Cape coasts (Bennett 1993). Post flexion larvae enter estuaries from 1.8 cm to 5.0 cm TL (Beckley 1984, Bennett 1989, Whitfield and Kok 1992).
Generation length for L. lithognathus is estimated to be 13 years, using the following equation for a gonochoristic fish species: Generation length = Σxlxmx/Σlxmx
|Use and Trade:||Lithognathus lithognathus is targeted by recreational fishers and is primarily caught by shore anglers in the Western and Eastern Cape (Brouwer et al. 1997). This species is also taken by beach seine and was previously taken by purse seine and was targeted commercially until both were banned (Lamberth and Jourbert 1999, Bennett 1993). This species is not a significant component of the spearfish fishery (Mann et al. 1997) and are considered negligible when compared to the recreational shore and commercial beach seine fisheries (Bennett and Lamberth 2012). This species has been successfully reared in captivity but it is likely to be too slow growing to result in commercial production (Bennett et al. 2011).|
Lithognathus lithognathus is threatened by over-fishing, climate change and habitat loss and degradation (Bennett 1993, Whitfield 1997, Bennett et al. 2011). Adults undertake a predictable annual spawning migration, aggregating at certain points where they are targeted heavily by recreational shore anglers. The very narrow spawning habitats of L. lithognathus are only provided by the fluvial fans off the Mbashe and five, at most, other estuaries on the South African coastline. Considering that this species aggregates to spawn in a small area, illegal harvesting in this area (particularly over the spawning season) is a major threat. The Dwesa-Cwebe MPA encompasses the area believed to represent the species’ main spawning grounds, and there is anecdotal evidence of considerable illegal harvesting of this species (mainly large breeding adults) in this MPA, particularly in the spawning season by both recreational and subsistence anglers (R. Bennett pers. comm. 2014). Lithognathus lithognathus possesses life history characteristics that make this species vulnerable to extrinsic impacts during all three life phases. As juveniles, this species inhabits estuaries, especially the lower reaches of estuaries, which provide critical nursery habitats where they will reside for a year or more (Bennett et al. 2011, R. Bennett and P. Cowley unpublished data). The total area of South African estuaries is approximately 600 km2. Sub-adults and adults reside in the surf zone and in shallow inshore waters where they exhibit high site fidelity while adults undertake an annual spawning migration and form predictable spawning aggregations. Habitat degradation due to infrastructural development, boating activities, freshwater abstraction and overfishing are majors threats to the shallow water and estuarine habitats and have profound impacts on recruitment, as well as population size and structure of species (Whitefield and Cowley 2010). In addition, the site fidelity and small home ranges exhibited by this species (Bennett et al. 2011) makes L. lithognathus vulnerable to fragmentation which may exacerbate the issue.
Lithognathus lithognathus has a short recruitment period as it depends greatly on periods of high rainfall which result in the opening/closing of estuaries on the Southern Cape and can result in highly variable estuarine recruitment. The recruitment to estuaries represents a potential bottleneck to the successful maintenance of the population. Lithognathus lithognathus is not able to recruit into estuaries during overwash events nor during extended periods of drought, which has serious implications in terms of climate change. As the effects of climate change are likely to worsen, prolonged periods of drought and shifts in rainfall seasonality may pose serious threats to the recruitment of this species in the future (Bennett et al. 2011). Additionally, water temperature changes may impose constraints on the timing of spawning, with consequent impacts on successful recruitment (Sheaves 2006). Despite a commercial fishing ban prohibiting the sale of this species and recreational fishing regulations, illegal fishing practices still pose a threat to L. lithognathus. Illegal gill-netting occurs along the south coast and other areas (Hutchings and Lamberth 2002). Stricter recreational regulations were imposed in 2005 but compliance with these regulations is poor. A few examples include Keurbooms Estuary (King et al. unpublished manuscript) and Sundays Estuary (Cowley et al. 2009) where 100% of L. lithognathus taken are smaller than the legal size limit. The lack of regulation compliance and increasing annual participation in the recreational shore fishery pose an increasing threat to L. lithognathus (Bennett et al. 2011).
Marine Protected Areas (MPAs) are considered to play a major role in the conservation of L. lithognathus (Bennett and Lamberth 2012). The De Hoop MPA had an increase in CPUE after its closure and currently has the second highest CPUE recorded for this species anywhere along the coastline (Bennett and Attwood 1991, 1993; Bennett 2012). The De Hoop, Tsitsikamma, and Sardinia Bay no-take MPAs afford some refuge to one to five year old <65 cm L. lithognathus individuals which exhibit a fair degree of residency (Bennett and Attwood 1991, 1993). In addition, the Dwesa-Cwebe no-take MPA affords protection to adult spawning aggregations of this species (Bennett 1993; S. Lamberth, MCM pers. comm.). In 2001, a commercial ban was established for L. lithgnathus prohibiting the sale of this species and the by catch of this species (Hutchings and Lamberth 2002). For recreational and subsistence fishers L. lithognathus has a minimum size limit of 60 cm TL and a daily bag limit of one fish per person per day. This also applies to seine and gill net fishermen in False Bay and along the West Cape coast where no L. lithognathus may be kept or sold. Subsistence anglers are permitted to sell their catch of L. lithognathus locally (Department of Agriculture and Fisheries 2012).
Compliance with fishing regulations for this species is poor as illegal gill-netting occurs along the south and west coast (Lamberth et al. 1997). Also a large proportion of L. lithognathus taken by recreational and subsistence shore and estuarine fishers are smaller than the legal size limit (Cowley et al. 2004, Bennett et al. 2011). The legal bag limit for this species does not play a major role in the protection of this species as two or more legal-sized L. lithognathus individuals are caught in less than 2% of shore angler outings (Brouwer et al. 1997). The implementation and enforcement of fishing regulations for L. lithognathus requires revision (Bennett et al. 2011). Continual efforts are made to lift the ban on commercial fishing of L. lithognathus (i.e. to allow sale) which would almost certainly result in the total collapse of the stock. The economic value of the recreational fishery needs to be determined and recognized in local fisheries management procedures (Bennett et al. 2011).
A variety of additional conservation efforts have been proposed including more marine/estuarine protected areas, a closed fishing season (Bennett 1993, 2012), the closure of Amathole and Goukamma MPAs to shore angling (Bennett 2012), improvement in law enforcement and compliance, and reduction in illegal fishing in spawning grounds (Bennett and Lamberth 2012, Venter and Mann 2012). A network of estuarine protected areas and the establishment of no-take areas in the sandy lower reaches of estuaries is recommended to aid the protection of juvenile L. lithognthus (Bennett et al. 2011). A closed fishing season from July to September during which time adults aggregate to spawn would aid in the protection of this species (Bennett 1993).
|Citation:||Mann, B.Q., Buxton, C.D., Pollard, D., Carpenter, K.E. & Iwatsuki, Y. 2014. Lithognathus lithognathus. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 20 December 2014.|
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