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Marine Ecology Progress Series

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MEPS 610:163-173 (2019)  -  DOI: https://doi.org/10.3354/meps12853

Tracking the decline of the world’s largest seabream against policy adjustments

Sven E. Kerwath1,2,*, Denham Parker1, Henning Winker1,3, Warren Potts4, Bruce Mann5, Christopher Wilke1, Colin Attwood2

1Department of Agriculture, Forestry and Fisheries, Vlaeberg 8018, Cape Town, South Africa
2Biological Sciences, University of Cape Town, Rondebosch 7700, South Africa
3Centre for Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, University of Cape Town, Rondebosch 7700, South Africa
4Department of Ichthyology and Fisheries Science, Rhodes University, Grahamstown 6140, South Africa
5Oceanographic Research Institute, PO Box 10712, Marine Parade 4056, Durban, South Africa
*Corresponding author:

ABSTRACT: For most rare marine species, abundance trends are poorly estimated. This uncertainty often translates into disagreement on management regulations, impeding conservation efforts when they are most urgently required. The world’s largest sea bream, the red steenbras Petrus rupestris, has undergone a substantial and widely acknowledged decline during the 20th century. Standardised probability of encounter over the last 3 decades was used to track red steenbras abundance trajectories in 2 regions, which together represent the species’ distribution. The results predicted a reduction in abundance of 44% in the East region and 96% in the South-West region, from what was already considered to be a collapsed population at the start of the time series. The species is now largely confined to areas in the centre of its historical abundance. Content analysis of a recreational angling magazine revealed a concurrent 50% decrease in reported size between 1984 and 2012. Shore-based observer data (2009-2010) indicate that the impact of recreational fishers on this species far exceeded that of commercial fishers at the time. Regulations in the form of progressively more stringent catch and effort restrictions appear to have been largely ineffective, too lenient, implemented too late or were unsuitable to control fishing mortality for this species. This study highlights 2 fundamental challenges in management of rare marine fish species: (1) providing decision makers with a credible measure of abundance for species whose rarity limits data availability and (2) implementing effective policy changes before the specific measures become ineffective and obsolete.


KEY WORDS: Rare fishes · Content analysis · Probability of encounter · Fisheries regulations · Recreational fishing impact · Management failure · Red steenbras · Petrus rupestris


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Cite this article as: Kerwath SE, Parker D, Winker H, Potts W, Mann B, Wilke C, Attwood C (2019) Tracking the decline of the world’s largest seabream against policy adjustments. Mar Ecol Prog Ser 610:163-173. https://doi.org/10.3354/meps12853

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