SANBI

Rationale

This taxon has an extremely narrow distribution range and is endemic to the Tradouw catchment where it has an approximate extent of occurrence (EOO) of 40.96 km² (based on minimum convex polygon) and an area of occupancy (AOO) of 20 km² (based on a 2x2 km² grid). The population also represents a single location as all threats are impacting on the entire population. There is continuous decline in the EOO, AOO, habitat quality and number of mature individuals as a result of surface water abstraction, water pollution from agrichemicals and residential impacts and invasion of the river by alien fish species such as Largemouth Bass (Micropterus salmoides), Banded Tilapia (Tilapia sparrmanii) and Bluegill Sunfish (Lepomis macrochirus). Surveys conducted between 2012 and 2015 indicate that there are extreme fluctuations in the number of mature individuals, number of subpopulations and AOO, as a result of the impacts of threats. This taxon therefore qualifies as Critically Endangered under B1ab(i,ii,iii,v)c(ii,iii,iv).

Distribution

Based on currently known distribution data, the Barrydale Redfin (Pseudobarbus burchelli sensu stricto) is confined to the Tradouw catchment of the Breede River water management area. The Tradouw River and its major tributary, the Huis River, comprise the current known distribution of the Barrydale Redfin, indicating the extremely limited natural distribution range of this lineage (Chakona et al. 2013). Within this system, it has been shown that the taxon has a discontinuous distribution range and is absent from areas that are dominated by non-native fish species (Jordaan et al. unpublished data).

Habitat View more ecological information

Population trend

Trend

The Huis River historically used to have perennial flow, but complete water abstraction above the Huis Waterfall has converted it into an intermittent river that recedes into a series of isolated pools during the dry season. Surveys have indicated that the pools that form within the stretch of river from a small causeway in the upper Huis to the confluence of the Huis and the Tradouw River are highly unstable as they may persist throughout the dry season in some of the years, but also dry up completely in other years depending on the intensity of the dry season. These conditions cause extreme fluctuation in available habitat resulting in extreme population fluctuations. The distribution of this taxon can therefore be split into two subpopulations which persist throughout the dry season, one occurring in deep pools above the causeway in the upper Huis River and the other occurring in the lower Tradouw River in the Tradouw's Pass. A third small subpopulation has been recorded in the upper Tradouw River but this subpopulation is unlikely to be viable as it consists of few adult individuals and is highly threatened by non-native fish and impacts associated with commercial agriculture (deciduous fruit production). These subpopulations become connected during the rainy season when flow resumes, but the Tradouw catchment has been heavily invaded by alien fishes and is severely impacted by pollution from the town of Barrydale. Results from ongoing monitoring indicate that there has been a progressive increase in the abundance of alien species and Barrydale Redfins have not been recorded in river sections with high numbers of alien fishes. Monitoring has also revealed a decline in the number of mature individuals and contraction of historical range of the Barrydale Redfin due to localised extinction in areas invaded by alien species (Jordaan et al. unpublished data).

Threats

This taxon is threatened by loss of habitat and the impacts of alien invasive fishes. The main causes of habitat loss are complete surface water abstraction, inadequate management of alien invasive vegetation in riparian zones and damage to instream river structure as a result of poor land-use practices (instream bulldozing and poor management of bank erosion). There is extensive bulldozing of the Huis River upstream of the town of Barrydale up to the causeway. The area above the causeway is unimpacted by bulldozing and has been identified as an ideal sanctuary that needs to be protected to secure the Barrydale Redfin from imminent extinction. However, the town's water extraction point is above the upper limit of this taxon's current distribution. Complete water abstraction has left much of the upper Huis completely dry, with the exception of a few isolated pools below the waterfall. The deep pools in the Tradouw’s Pass provide more stable habitat for this taxon.

The lower Tradouw River below Barrydale has however been severely affected by nutrient enrichment through sewage effluent discharge from the town and potential agrichemical pollution from the upper Tradouw River. This is exacerbated by extensive water abstraction for agricultural purposes in the upper Tradouw River. The impact of pollution on the Barrydale Redfin has however not yet been studied or documented. The pools in the gorge have also been heavily invaded by three alien fish species; Largemouth Bass (Micropterus salmoides), Banded Tilapia (Tilapia sparrmanii) and Bluegill Sunfish (Lepomis macrochirus) which have become established in the Tradouw catchment. Preliminary results from ongoing surveys indicate that Barrydale Redfins have been locally extirpated in pools that have been invaded by Largemouth Bass and Bluegill Sunfish (Jordaan et al. unpublished data). Banded Tilapia is likely to impact the Barrydale Redfins through competition, but this needs to be established through dedicated studies that compare the trophic ecology and habitat use of the two species. Other threats include invasion of the Tradouw catchment by alien vegetation, mainly Black Wattle (Acacia mearnsii) and pines (Pinus spp.).

Uses and trade

All indigenous fish species of the Western Cape Province are listed as Endangered Wild Animals under Schedule 1 of the Provincial Nature Conservation Ordinance for the Western Cape, thereby preventing the collection and trade of the species without a permit. Translocations of indigenous freshwater fish species are controlled by Cape Nature’s Indigenous Fish Utilisation policy (Jordaan et al. 2016a).

Conservation

A Biodiversity Management Plan for Species (BMPS) is in the process of being developed based on national Norms and Standards for conservation plans. The plan aims to improve the conservation status of the Barrydale Redfin and increase the taxon’s area of occupancy through securing of critical habitats and mitigation of anthropogenic impacts. The objectives of the plan include to: (1) initiate research and monitoring to inform conservation action, (2) to prevent further habitat loss and degradation and rehabilitate habitat in key sanctuary areas, (3) to establish and maintain effective communication and awareness between and among stakeholders and (4) to mitigate the impacts of alien fish (Jordaan et al. 2016b). Specific actions relating to these objectives, and how to facilitate successful implementation, is in the process of being defined through a consultative stakeholder process. There is need for strategies that will ensure management of alien fishes as well as implementation of measures to control both point and diffuse sources of pollution. There is also need for studies to determine ecological flow requirements to ensure recovery of the Barrydale Redfin.

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