Red List of South African Species

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Vulnerable (VU)
Assessors: Bruce Mann Colin Buxton David Pollard Kent Carpenter
Facilitators: Claire Gorman Mia Comeros-Raynal
Reviewers: Nikki James Barry Russell Ken Lindeman

Rationale

Acanthopagrus vagus is endemic to southern Africa from Knysna, Western Cape, South Africa to southern Mozambique. Acanthopagrus vagus adults are almost entirely restricted to estuaries but this species has a marine egg and larval phase, requiring connection to the sea. Estuarine degradation in South Africa has greatly reduced the availability of suitable habitat for this species. Furthermore, this species has been subjected to localized overfishing in certain estuarine systems including Kosi Bay. Catches of A. vagus in the Kosi Bay estuary system have declined substantially due to an increase in artisanal fishing effort; an estimated 60% decline in CPUE from the artisanal trap fishery was recorded from 1986 to 1999, and ~30% decline in CPUE in the recreational fishery from 1995 to 1999. These population declines are exacerbated by persistent drought conditions over the past eight years (2002–2010) in northern KwaZulu-Natal which have substantially contracted available habitat in large coastal estuarine systems particularly Lake St Lucia. However, good rainfall has been recorded in St Lucia since 2011 and although the mouth is still closed, a small channel has been constructed linking the system to the Umfolozi mouth allowing some connection to the sea. The estimated area of occupancy (AOO) of its estuarine habitat in South Africa is 532 km2; the estuarine habitat in its entire range is extrapolated to be 1,213 km2 qualifying for Vulnerable under B2ab. In addition, this species is severely fragmented due to the impacts of climate shifting on estuarine environments, limiting suitable habitat and altering connectivity to the sea; given the habitat specificity this species exhibits during certain life stages, this poses a serious threat, meeting the criteria B2a. The limited habitat availability coupled with significant population reductions in excess of 30% over three generation lengths (24 years), places this species at an elevated extinction risk. In addition, the species has a complex population structure as a protandrous hermaphrodite in a degraded and specialized ecosystem. There are fishery regulations in place for this species, however, these are difficult to enforce. An increase in the number of estuarine protected areas (EPAs) is likely to be one of the most effective management interventions. We recommend designation of additional no-take EPAs in KwaZulu-Natal and prevention of illegal fishing. Furthermore, an updated stock assessment for this species is highly recommended. This species is listed as Vulnerable under criterion A2bcd; B2ab(ii,iii,v).


Distribution

Acanthopagrus vagus is endemic to southern Africa, ranging from Knysna, Western Cape, South Africa to southern Mozambique (Iwatsuki and Heemstra 2010). Acanthopagrus vagus is common in the Eastern Cape, KwaZulu-Natal and northwards to at least central Mozambique (Heemstra and Heemstra 2004, Iwatsuki and Heemstra 2010). This species has not been confirmed in Madagascar but is likely to occur in that area (Iwatsuki and Heemstra 2010). The estimated area of occupancy (AOO) of the estuarine habitat of this species in South Africa is estimated at 505 km2 including some 194 estuaries (van Niekerk and Turpie 2011). The AOO is estimated at 1,213 km2 when calculated including estuarine floodplains (N. James pers. comm. 2014).

Population trend

Trend

As A. vagus is largely restricted to the estuarine environment (except during the egg and larval phase when it is found in the marine environment), the stock has been greatly reduced as a result of estuarine degradation and overexploitation and is considered to be collapsed in Kosi Bay, with spawning biomass per recruit (SBPR) estimated at <25% (James et al. 2008). Estimates suggest that there were between 45,000 and 56,000 individuals of A. vagus >22 cm TL in the Kosi Bay system from 1984 to 1985 based on a tag-recapture study (Kyle and Robertson 1997). Stock assessments of A. vagus in Kosi Bay in northern KwaZulu-Natal indicate that this species is likely to have been reduced to around 24% of its pristine level of spawner biomass per recruit at current levels of fishing mortality (James et al. 2008). The recent severe drought in Lake St Lucia, which comprises 80% of the estuarine area in KwaZulu-Natal, has also had a substantial impact on the A. vagus population in that system (Cyrus and Vivier 2006). Acanthopagrus vagus is the only sparid in southern Africa that has been regularly recorded in rivers and associated freshwater pans (Skelton 1993).

CPUE decreased significantly from 0.017 fish/angler/hour in 1986 to 0.007 fish/angler/hour in 1999 (~58%) in Kosi Bay recreational catches (James et al. 2001). CPUE also had a downward trend in St Lucia between 1956 and 1977 based on NCAU competition data (van der Elst 1978). Trend in catch composition of A. vagus by mass remained relatively constant in the Kosi recreational fishery from 1987 to 1995 and subsequently declined from 4.1% in 1994 to 0.6% in 1999 (James et al. 2001). The number of fish traps and number of baskets per trap has increased exponentially in recent years and has resulted in the reduction of A. vagus in the Kosi system (Kyle 2013). The St Lucia recreational fishery CPUE had an overall increasing trend from 1989 to 1999 (Mann et al. 2002); however, the subsequent drought and extended closure of the St Lucia system since 2002 has resulted in an extremely low catch of A. vagus as revealed by a seine and gill net survey conducted between 2006 and 2008 (Vivier et al. 2010). 

Contribution of A. vagus by number in the St. Lucia recreational fishery peaked at 37% in 1994 and remained relatively high thereafter (Mann et al. 2002). Acanthopagrus vagus only comprised 0.2% of the catch in a seine and gill-net survey conducted from 2006 to 2008, after almost five years of estuary closure (Vivier et al. 2010). The mean size of fish captured in Kosi Bay from 1985 to 1998 was 31.4 cm TL while fish caught in 2001 were smaller with a mean size of 26.9 cm TL (James et al. 2001). A sex ratio of 8.8:1 (M:F) was recorded during a spawning aggregation at the mouth of Kosi (Garratt 1993).

Threats

Currently, A. vagus is heavily overexploited in the Kosi system and the stock is considered to have collapsed (James et al. 2008). Minimum size and bag limit regulations appear to be ineffective as there is inadequate compliance with regulations in the trap and gillnet fisheries as they are poorly managed. The recent rapid and uncontrolled escalation of fishing effort by the trap-fishery is cause for concern as it could lead to a rapid deterioration in stock status (James et al. 2008, Kyle 2013). In addition to increased fishing pressure on estuaries, degradation of estuarine habitats in KwaZulu-Natal, including reduced freshwater inflows have most likely had a serious effect on populations of this estuarine-dependent species (Mann et al. 2000). Drought conditions over the past eight years (2002–2010) in northern KwaZulu-Natal have substantially contracted available habitat in large coastal estuarine systems particularly Lake St Lucia. However, good rainfall has been recorded in St Lucia since 2011 and although the mouth is still closed, a small channel has been constructed linking the system to the Umfolozi mouth allowing some connection to the sea (B. Mann pers. comm.). It is suggested as a useful indicator species of environmental quality in subtropical South African estuaries (Whitfield 1997).

Estuaries are often subjected to multiple stressors as a result of coastal anthropogenic actives as well as habitat shifting and degradation from climate change (Thrush et al. 2008). These impacts can result in the loss of connectivity, potentially isolating populations and communities and limiting them to suboptimal habitats (Tilman et al. 1994, Fahrig 2003, Holyoak et al. 2005, Crooks and Sanjayan 2006). The cumulative impacts pose a major threat to A. vagus due to its habitat specificity during certain life stages.

Uses and trade

Acanthopagrus vagus is an important component of the catch taken by the various fishing sectors in the Kosi estuarine system, northern KwaZulu-Natal, South Africa where it is currently considered to be overexploited (James et al. 2008). This species is an important component of estuarine sport anglers catches in KwaZulu-Natal. Acanthopagrus vagus is caught by subsistence and artisanal fishers in St Lucia, Kosi Bay and in other estuarine systems in KwaZulu-Natal and southern Mozambique using lines, fish traps and gill-nets (Kyle 1986, Mann 1995, Kyle 1999, Kyle 2013).

Acanthopagrus vagus is taken by recreational boat, shore anglers, and by subsistence fishers using lines, fish traps, and gillnets (James and Mann 2013). In the three large estuaries of northern KwaZulu-Natal (Kosi Bay, St Lucia and Richards Bay), A. vagus is of particular importance to the recreational and subsistence catches (James 2001, James et al. 2001, Mann et al. 2002, Beckley et al. 2008) as well as in the Durban Harbour (Pradervand et al. 2003). Fishing mortality in the Kosi system was calculated to be 1.88 per year, 87% of which was attributed to trap-fishing, 6% to gill-net and 7% to recreational fishing (James et al. 2008).

Conservation

Acanthopagrus vagus is a prohibited species for commercial fisheries in South Africa (i.e. no sale allowed). For recreational fishers, there is a daily bag limit of five fish per person per day and a minimum size limit of 25 cm TL in place (Department of Agriculture, Forestry and Fisheries 2012). However, minimum size and daily bag limitations seem to be ineffective as conservation tools for this species as there is a high amount of non-compliance of these regulations, especially in the trap and gill-net fisheries (Kyle 1999) and the overall management of A. vagus is poor in the region (James et al. 2008). 

Some protection is afforded to A. vagus in the St Lucia Wilderness Area, Lake Amanzimnyama (fourth lake in Kosi Bay), the mouth area of the Kosi estuary, the Mhlatuze estuary and in the Mtentu, and Msikaba estuaries within the Pondoland MPA, as these areas are closed to fishing (B. Mann, ORI, personal observation). However, all of these no-take EPAs are exposed to illegal gill-netting (Mann et al. 1998) . 

Establishment of additional no-take EPAs in KwaZulu-Natal and the Eastern Cape and the prevention of illegal fishing would be beneficial for A. vagus. Illegal seine and gill-net fisheries in the Mhlatuze Estuary needs to be addressed especially because of the poor status of this species in Kosi Bay and St Lucia. In Kosi Bay the number of fish traps and baskets needs to be drastically reduced, channels between lakes should be kept open and fish traps should not be permitted to extend into those channels. A channel should be kept open between fish kraals on either side within the lakes and upper estuary (James and Mann 2013, Kyle 2013).

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