The Cape horse mackerel stock off Namibia is assessed using a fleet-disaggregated age-structured production model including historical International Commission for the Southeast Atlantic Fisheries (ICSEAF) and current data. Data from acoustic biomass surveys, on commercial catch per unit effort and on commercial catch-at-age, were used to estimate current stock status over a range of model specifications. A management tool, the so-called management monitor graph, was introduced in order to track past management relative to stock status. Target, limit and precautionary reference points, decision rules and harvesting strategies, according to which the stock should be managed, are described and tested. The target reference point was set at maximum sustainable yield (MSY), the precautionary reference point at 80% of MSY and the limit reference point at 30% of MSY. Owing to some inconsistencies in the dataseries, evaluation of the current state of the resource is challenging, but estimates are that the resource is around the MSY level, somewhere between 250 000 and 300 000 t.
Using a web-based survey conducted among 2,481 Namibian, aged 18 years or older, the factors and motivations driving individuals' decisions on marine fish consumption, spatial fish consumption, and possible strategies to promote domestic marine fish consumption were explored. Most participants (97.9%) were aware of the importance of fish in the human diet, with many preferring hake (Merluccius capensis and M. paradoxus) (31.5%) and Cape horse mackerel (Trachurus capensis) (21.7%). Most respondents (64.1%) were poor fish consumers, consuming fish once a week or once a month. Participants claimed that they mostly purchased marine fish from retail fish shops (50.7%), wholesale fish companies (18.8%), and the Namibian Fish Consumption Promotion Trust (17.4%). Factors affecting marine fish affordability in Namibia were explained with a Logit Model, with age, education, gender, monthly income, and region of residence as the explanatory variables. Responses regarding fish affordability were principally driven by age, education, and monthly income (p < 0.05). The Khomas region purchased the most marine fish (60,764.8 weighted kg) in 2019. There was a consensus across all participants that regular fish consumption is beneficial to human health; however, participants listed affordability and accessibility of marine fish as critical constraints. Results indicate that Namibian marine fish consumption is poor and needs to be promoted. Results suggest ways to stimulate marine fish consumption locally and elsewhere to meet the UN Sustainable Development Goal 2 to end hunger and alleviate malnutrition.
The validity of abundance estimates from hydroacoustic surveys relies, inter alia, on the ability of the fishing gear on the research vessel to sample non-selectively. This study compares the length frequencies of Cape horse mackerel Trachurus trachurus capensis taken in Namibian waters by the R.V. Welwitchia and commercial midwater trawlers. Results indicate that the length distributions of catches taken by the Welwitchia were significantly different from those from commercial trawlers, with a greater proportion of fish >25 cm being sampled by the latter. Also, the biomass estimated per length-class from hydroacoustic surveys over the period 1994-2000 was compared with those from annual landings of the commercial fishery. The length distribution of horse mackerel in purseseine catches compares favourably with those from the research vessel. However, comparisons with the midwater trawl catches indicated that the length frequencies obtained from research vessels during the years 1994-1997 underestimated the number of large fish in the population and biased the biomass in those years. From 1998 to 2000 the bias was negligible. The magnitude of the error varied between years, but it remained fairly low. To compensate for this bias, length distribution data from midwater trawlers should be integrated into the acoustic biomass calculation procedure.
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