Vulnerability assessment of Lake Malawi’s ornamental fish resources to export ornamental trade
Introduction
The global ornamental fish trade, including ancillary products, has an estimated value of US$ 15–30 billion per year (Raghavan et al., 2013; Evers et al., 2019), and a > 10 % average annual growth (Dey, 2016). Despite their economic importance, management of ornamental fisheries is challenged by a paucity of information on the status of the exploited fish stocks (Dee et al., 2014). In addition, conventional stock assessment methods and management measures are most suitable for single species management unlike ornamental fisheries which are multispecies (Fujita et al., 2013; Militz et al., 2018). Furthermore, these fisheries are usually not considered a priority for management in many countries worldwide (Dee et al., 2014).
The ornamental fish export trade in Malawi is mostly based on the colourful rock dwelling cichlid fishes from Lake Malawi with an average of 28,000 live fish being exported annually and valued at US$218,000 at 2020 prices (Msukwa, 2020). This multispecies fishery started operating in the early 1970s and the number of licensed exporters has varied annually between one and four (Malawi Government, 2016a; Msukwa, 2020). The number of fish exported varies amongst the species of fish with a few species being dominant (Msukwa, 2020). The exporters employ SCUBA diving teams to catch the ornamental fish in rocky shores of the Malawian side of Lake Malawi by chasing the fish into small nets (Msukwa, 2020). Each SCUBA diving team comprises of four people using a small boat. According to interviews with the ornamental fish exporters in Malawi, the number of SCUBA diving teams per exporter in 2018 ranged between one and four and in total there were seven teams located in different parts of Lake Malawi. The frequency of fishing and the number of ornamental fish caught per fishing trip were dependent on the importing clients’ orders. The fish are exported throughout the year with the peak export volumes in November and December and the lowest volumes in July and August when south easterly winds predominate on the lake. Since this fishery started operating, there has been no assessment of the status of targeted fish stocks besides the baseline study of Ribbink et al. (1983). Additionally, the Malawi Fisheries and Aquaculture Policy (Malawi Government, 2016a) and its implementation, monitoring and evaluation strategy (Malawi Government, 2016b) focus on the food fishery and provide no information about the ornamental fishery of Lake Malawi.
One option for managing fisheries with limited data is the ecosystem-based fisheries management approach, which considers fishing as one of many possible factors that affect ecosystem functions (Hobday et al., 2007, 2011a; Micheli et al., 2014). This is pertinent in fisheries that are impacted by numerous externalities. A tool developed for implementation of ecosystem-based fisheries management is ecological risk assessment for effects of fishing - ERAEF (Smith et al., 2007; Hobday et al., 2007, 2011a; Fujita et al., 2013). The ERAEF framework defines a hierarchical approach for assessing risk including scoping, qualitative assessment, semi quantitative assessment (Productivity Sustainability Analysis - PSA) and quantitative assessment (Smith et al., 2007; Hobday et al., 2011a). The ERAEF approach is a flexible tool that is applicable to all types of fisheries (Hobday et al., 2011a).
The PSA was initially developed to assess the sustainability of the bycatch in the Australian prawn fishery but it has been commonly used for assessment of species vulnerability in many fisheries with some modifications to cater for more attributes of the ecosystem vulnerability (Patrick et al., 2009; Brown et al., 2015; Clarke et al., 2018; Hordyk and Carruthers, 2018). The assumption of the PSA approach is that vulnerability to exploitation of a fish population is dependent on two components – the susceptibility of the fish population to fishing activities and the productivity of the population, which determines the rate at which the population will recover after potential depletion by fishing (Hobday et al., 2007, 2011a; Micheli et al., 2014). PSA was initially based on seven productivity attributes and six susceptibility attributes (Hobday et al., 2007), but subsequent studies have defined more attributes for different fish stocks (Patrick et al., 2009; Hobday et al., 2011a). In addition, different studies have used different sets of productivity and susceptibility attributes depending on relevance and availability of trait information (McCully et al., 2013). PSA attributes are scored at three risk categories - 1 (low), 2 (medium) or 3 (high). The-cut-off points for scoring different vulnerability categories are adaptable and can be tailored to suit specific fish stocks based on life history characteristics (Salini et al., 2007; Patrick et al., 2009; Hobday et al., 2011a; Dransfeld et al., 2013).
This study uses the PSA approach to assess vulnerability to overexploitation of targeted ornamental fish species of Lake Malawi. The study also compares the PSA vulnerability scores with IUCN assessment of the fish species in order to assess the correlation between the two approaches for assessing species vulnerability to overexploitation. The results of the analysis are useful for evaluating the application of PSA as an alternative for assessment of undescribed ornamental fish species which are difficult to assess using other risk assessment approaches.
Section snippets
Background on the study
This study was based on the ornamental fishery of Lake Malawi in the southern part of Africa which exploits more than 700 fish taxa of which only 300 are described and the rest undescribed (Msukwa, 2020). One hundred and three of the exploited taxa were selected for this study (Table S1) based on their prevalence in export records from Malawi between 1998 and 2019 (Msukwa, 2020). Eighty-four of the selected species are described and 19 are undescribed. The targeted ornamental fish species of
Ranking of fish species based on vulnerability scores
The overall productivity scores of fish species ranged from 1.4 to 2.5 with a mean value of 1.87 ± 0.33, while the overall susceptibility scores ranged from 1.08 to a maximum value of 3.00 with a mean value of 1.59 ± 0.42 (Table 2, Table S3). The vulnerability scores ranged from 1.78 to 3.84 with a mean of 2.49 ± 0.37 (Table 2, Table S3).
The PSA classified seven species in the high-vulnerability category. Aulonocara sp ‘walteri’ is on the first rank with a vulnerability score of 3.84, followed
Discussion
This study employed the PSA approach to assess and rank the vulnerability of commonly exported ornamental fish species of Lake Malawi to exploitation for the export trade. The majority (71) of the 103 ornamental fish species assessed had low vulnerability to overexploitation while twenty-five species had medium vulnerability. Seven species had high vulnerability to overexploitation because of their high susceptibility scores and medium to high productivity scores. According to IUCN (2020), four
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
We are indebted to all the people who contributed to the success of this research. The Director of the Department of Fisheries in Malawi allowed us to access ornamental fish export file records. The staff at Salima District Fisheries Office and Senga Bay Fisheries Research Unit were quite helpful in organising ornamental fish export data files for our access. The comments and suggestions made by anonymous reviewers and editors were quite useful for improvement of this paper. This study was part
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