SANBI

Rationale

The seventy-four seabream (Polysteganus undulosus) is endemic to southern Africa, inhabits deep offshore reefs, and exhibits slow growth and late maturation. This species was once heavily exploited throughout its range, and particularly where it formed spawning aggregations, leading to the contraction of its distribution and the collapse of the stock in the 1960s. Individuals of this species have not been recently reported north of Sodwana Bay and south of Cape Agulhas. Although the stock had collapsed by the 1960s, strict fishery regulations were not implemented until 1985, and were subsequently revised in 1992 with no evidence of stock recovery. This led to the implementation of a ten year catch moratorium for P. undulosus in 1998. In 2007, an assessment was conducted on P. undulosus which showed limited recovery of the adult stock but increasing numbers of juveniles in their traditional nursery areas in the Eastern Cape. This work led to the moratorium being extended for a further five years. In addition to the moratorium, several no-take MPAs are likely to aid in the recovery of this stock, particularly the Pondoland Marine Protected Area (MPA) established in 2004. Despite this species' occurrence in no-take MPAs and the moratorium, P. undulosus is still subject to illegal fishing, as a result of high prices on the black market, which poses a major threat to the recovery of this species. Catches declined substantially from over 1,000 tonnes in the early 1900s to less than 400 tonnes in the 1920s and 1930s and by the 1980s only 5.4 tonnes were reported. CPUE for P. undulosus thus declined by ~99% and SBPR is currently estimated at <5%. The moratorium was extended to 2013 and the status of the stock needs to be re-evaluated. Based on population declines of >90% extrapolated over three generation lengths (=39 years) this species is listed as Critically Endangered under A2bcd. However, juveniles of this species have become increasingly abundant in the Border area of the Eastern Cape (Kei Mouth to East London) to the extent that fishermen are reporting not being able to catch other reef fish species due to the prevalence of P. undulosus. This suggests that the moratorium and MPAs are working and at least that population is recovering.

Distribution

Polysteganus undulosus is endemic to the southeastern coast of southern Africa from Cape Point, Western Cape to the mouth of the Limpopo River in southern Mozambique (Ahrens 1964, Smith and Heemstra 1991, van der Elst 1988, Heemstra and Heemstra 2004, Garratt 1996). The depth range for this species is 40 m to 160 m (Mann and Fennessy 2013). The overexploitation of P. undulosus has resulted in a range contraction from its historical distribution with no specimens recently reported north of Sodwana Bay and south of Cape Agulhas (Mann 2007). The centre of the adult distribution is currently deep offshore reefs between Durban and East London (Mann 2007).

Habitat View more ecological information

Population trend

Trend

The historic distributional range of P. undulosus has decreased in size with no fish recently reported north of Sodwana Bay and south of Cape Agulhas (Mann 2007). Prior to the closure of the fishery in 1998 the spawning biomass per recruit (SBPR) was believed to have been <5% of its pristine level (A. Govender pers. comm. in Chale-Matsau 1996). Polysteganus undulosus has thus been considered commercially extinct since before the fishery closed in 1998 (Chale-Matsau et al. 2001, Moloney et al. 2013). During the 20th century, catches and catch per unit effort (CPUE) of adult P. undulosus declined off KwaZulu-Natal by more than 90% (Garratt 1996, Penney et al. 1999) while catches in the Western and Eastern Cape provinces also declined by more than 90% (Griffiths 2000). Stocks <25% of the pristine status are indicative of stock depletion in long-lived species and are at 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).

Polysteganus undulosus is currently closed to commercial and recreational fisheries due to the overexploited status of the stock (Department of Agriculture, Forestry and Fisheries, South Africa 2012). This species was heavily targeted by commercial and recreational fisheries throughout the 20th century. Catch per unit effort (CPUE) was revealed to be <1% than that of historical values based on commercial and fishery-independent survey data, while more recent stock assessments show a decline in CPUE of 99% (Griffiths 2000). Polysteganus undulosus was initially targeted by harbour-based lineboats and then later by smaller, shore-launched skiboats, especially on their spawning grounds in KwaZulu-Natal, south of Durban. Initially, large adult fish comprised the bulk of the catch taken by this fishery but by the late 1960s catches in KwaZulu-Natal had collapsed and only small quantities of this species continued to be caught in the Eastern Cape (van der Elst and Garratt 1984, Penney et al. 1999, Mann 2007). Line catches from the Southeastern and Southern Cape also declined considerably during the 20th century (Griffiths 2000). A retrospective stock assessment conducted in 1996 (based on data collected during 1962–1963 by Ahrens (1964)) revealed that the stock had collapsed in the 1960s (Griffiths 2000, Chale-Matsau et al. 2001). The decline of CPUE by more than 90% throughout its distribution triggered the implementation of a moratorium in 1998 to allow the stock to recover (Mann and Fennessy 2013).

In 1910, P. undulosus comprised 70% of the KwaZulu-Natal commercial linefish catch with 1,550 tonnes landed and from 1921 to 1933 catch composition of this species ranged from 30% to 50% with 337 tonnes caught. By the late 1950s the annual catch of P. undulosus had halved despite a dramatic increase in fishing effort (van der Elst and Garratt 1984, Penney et al. 1999). By 1985, only 5.4 tonnes were reported by the commercial line fishery, comprising < 1% of the total commercial linefish catch in KwaZulu-Natal (Penny et al. 1989, Birnie et al. 1994, Chale-Matsau 1996, Penney et al. 1999). By 1997, the last year that the fishery for P. undulosus was still open, the total reported catch of P. undulosus by the commercial line fishery throughout South Africa was only 2.6 tonnes with a mere 1.4 tonnes reported from KwaZulu-Natal, representing a dramatic collapse (NMLS, unpublished data; Mann 2007). A similar collapse in P. undulosus catches was reported for Cape waters (Griffiths 2000). For example, the average catch per boat year dropped to 0.09% in the Southwestern Cape, 0.01% in the Southern Cape and 0.22% in the Southeastern Cape of historical values (Griffiths 2000). Average catch per boat year was: 40 kg (1897-1906), 28 kg (1927-1931), and 0.04 kg (1986-1998) in the Southwestern Cape; 580 kg (1897-1906), 200 kg (1927-1931), and 0.07 kg (1986-1998) in the Southern Cape; and 5,944 kg (1897-1906), 339 kg (1927-1931), and 13 kg (1986-1998) in the Southeastern Cape (Griffiths 2000).

Since the implementation of the moratorium on catching P. undulosus in 1998, poaching still occurs driven by high prices on the black market (Mann 2007). A reassessment of P. undulosus conducted in 2007 showed a slight increase in the mean size of adult fish but little evidence of recovery of the adult spawning population in southern KwaZulu-Natal. However, juveniles of this species have become increasingly abundant in the Border area of the Eastern Cape (Kei Mouth to East London) to the extent that fishermen are reporting not being able to catch other reef fish species due to the prevalence of P. undulosus. This suggests that the moratorium and the MPAs proclaimed in the area are working and that the population is now showing signs of recovery (B. Mann pers. comm.)

Threats

Polysteganus undulosus was overexploited and fished down to very low levels throughout the 20th century (Penney et al. 1999, Griffiths 2000). During the peak spawning season (August to October), P. undulosus historically formed predictable spawning aggregations in areas such as the Illovo Banks south of Durban which were heavily targeted by line fishermen (Penney et al. 1999). This resulted in recruitment overfishing and severe depletion of the stock. The range of P. undulosus has contracted and at the time of last assessment (2007) limited evidence of recovery of the adult stock was available (Mann 2007, Mann and Fennessy 2013). In addition to forming a predictable spawning aggregations, P. undulosus exhibits intrinsic characteristics including slow growth and late maturation (Chale-Matsua et al. 2001, Mann 2007) that slow stock recovery and make this species more vulnerable to additional exploitation by illegal fishing practices and incidental catches (Mann and Fennessy 2013). Polysteganus undulosus does not reach sexual maturity until about eight years of age and long-lived, late maturing species are generally more susceptible to overexploitation, even at low levels of fishing (Acosta and Appeldoorn 1992). Polysteganus undulosus is an iconic species and a popular food fish and despite the moratorium, illegal and unreported harvesting of this species for human food has continued (B. Mann and C. Buxton pers. comm. 2009) which could impede the recovery of the stock.

The removal of large sparid fish can change the community structure, reduce both primary and secondary production in a temperate-reef ecosystem (Babcock et al. 1999) and can reduce the links of reef ecosystems with the pelagic food web. Virtually all South African warm/temperate, bottom-dwelling, subtidal linefish species have been overexploited which can result in the loss of productivity, commensurate socio-economic impact and a high risk of commercial extinction with harmful impacts to trophic flow and biodiversity likely (Griffiths 2000).

Uses and trade

Polysteganus undulosus is currently closed to commercial and recreational fishing due to the severely overexploited status of the stock (Department of Agriculture, Forestry and Fisheries, South Africa 2012). This species was heavily targeted by commercial and recreational line-fisheries throughout the 20th Century (Penney et al. 1999, Griffiths 2000).

Conservation

Polysteganus undulosus is currently closed to commercial and recreational fishing due to the severely overexploited status of the stock (Department of Agriculture, Forestry and Fisheries 2012).

The first conservation actions for P. undulosus were implemented in South African legislation in 1984 and included a minimum size limit of 25 cm TL, a bag limit of five fish per person per day (pppd) and a closed season during the spawning season from the 1st of September to the 30th of November (Garratt 1988, regulations in terms of the Sea Fisheries Act No. 58 of 1973). Amendments were made to this legislation in 1992 including an increased minimum size limit to 40 cm TL and a reduced daily bag limit to two fish pppd (Chale-Matsau et al. 2001, regulations in terms of the Sea Fisheries Act No. 12 of 1988). Following research conducted by Chale-Matsua et al. (2001) in 1996 and no further improvement in catches, a 10-year moratorium was implemented for P. undulosus in South Africa in 1998 (Department of Agriculture, Forestry and Fisheries 2012). From 2006 to 2007 a reassessment of the P. undulosus stock was conducted on the KwaZulu-Natal coast (Mann 2007). Little evidence was found of increased catch per unit effort off the KwaZulu-Natal coast although there was some evidence of increased abundance of juvenile fish in the Eastern Cape. Based on this research, the then responsible South African government department (Department of Environmental Affairs and Tourism) extended the moratorium until 2013 where after, the stock status should be re-evaluated. In addition to traditional fisheries management, a number of large no-take MPAs have been established along the South African coast. One of the most recent MPAs to be established was the Pondoland MPA between Port Edward and Port St Johns and extending out to the 1,000 m depth contour (Mann et al. 2006). It is likely that the Dwesa-Cwebe, Amathole and Bird Island MPAs currently play an important role in providing protection for juvenile P. undulosus which appear to be fairly resident (B. Mann, ORI pers. obs.), while the Pondoland MPA may play a role in protection of adults (Mann et al. 2006). There has been little evidence of P. undulosus receiving protection in MPAs further south (i.e. Tsitsikamma, Goukamma, Stilbaai and De Hoop) (Mann and Fennessy 2013).

The slow recovery of the P. undulosus stock is not surprising given its slow growth and late age at maturity. It may be that its niche has been filled by other reef fishes, although this has not been investigated. Due to its rarity and high price on the black market, poaching of P. undulosus has continued despite the implementation of the moratorium (Mann 2007). Mann (2007) recommended that the moratorium should remain in place for a further 10 years, until end of 2017, before consideration is given to reopening the fishery. Consideration should also be given to extending the Aliwal Shoal MPA northwards to include some of the historical spawning grounds on the Illovo Banks and focus on protecting the deep reefs in this area, particularly between August and November (Mann 2007). Monitoring the status of a fish species which has been closed to fishing is difficult as all fishery-dependent data are excluded. Fishery-independent and non-invasive methods, such as underwater videography, should be used to monitor P. undulosus populations. There is also a need for additional information about the movement patterns and the distribution of eggs and larvae (Mann and Fennessy 2013). Fishing mortality is also incurred when P. undulosus are accidentally hooked and brought to the surface in the process of which severe barotrauma occurs (Mann and Fennessy 2013). Nevertheless, it is believed that overall fishing mortality has been greatly reduced for this species since the implementation of the moratorium and the increased public awareness about the critical status of this stock. The abundance of juvenile P. undulosus in the Border area of the Eastern Cape bodes well for the eventual recovery of this population and careful consideration will need to be given to how this species is managed in future should the moratorium be lifted.

References

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,]

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