Dusky kob

1. What is it?

Dusky kob (Argyromus japonicas) are migratory, spawning fish. Juveniles are restricted to estuaries and spawning adults are often found on reefs and wrecks making them an easy target for commercial and recreational fishers. In addition, juveniles and sub-adults are vulnerable to increased estuarine pollution and degradation. Throughout the years, the South African spawning stocks have been severely depleted to levels of around 1.0-4.5% of their unexploited populations. Stock levels are currently rated as over-fished.

2. How was it caught or farmed?

Dusky kobs are farmed on land in special tanks known as RAS tanks (Recirculating Aquaculture Systems). This system is a recirculating system which means it is either fully or semi-closed to the ocean. Juveniles are hatchery based but do rely on wild brood stock which is regulated through permit conditions. Kob farmed in this manner rely on a moderate amount of feed, both protein and terrestrial based. The terrestrial component is fully traceable and certified as sustainable. The risk of disease outbreaks and fish escaping is considered to be minimal.

Kob are farmed in semi-closed ponds, cages and fenced-off pieces of river, usually in areas previously used for other agriculture. Juveniles are hatchery based but do rely on wild brood stock which is regulated through permit conditions. Kob farmed in ponds require low amounts of feed, both protein and terrestrial based. The terrestrial component is fully traceable and certified as sustainable. The risk of disease outbreaks and fish escaping is considered to be minimal.

Dusky kobs are mainly caught using traditional linefishing methods. The linefishery operates from small ski- and deck boats using a rod and reel or handlines, making them a popular target for recreational linefishers. Linefishing is a relatively selective fishing method with few impacts on the marine environment and little accidental bycatch.

Dusky kob are caught as bycatch in inshore trawl fishery for hake (MSC certified) and sole using trawl nets. In the inshore zone, trawl nets are dragged along the sea bed at depths in the area from the coast to the 110m isobath or to 20 nautical miles from the coast, whichever is the greater distance. The offshore zone is defined as offshore of this inshore zone; inshore trawl sector vessels are also permitted to fish in the offshore zone although they are limited in actuality by vessel size/power. Demersal trawling is known to damage the seabed; the extent and impact of this damage remains unknown. This methodology is not selective, however, and a number of other benthic species are often caught in the nets as well. Seabird bycatch was highlighted as an issue and the subsequent introduction of tori lines (lines covered in coloured streamers making attachment lines more visible to birds) has led to a decrease in bird mortalities.

3. Where is it from?

Dusky kobs are found all along the inshore coastal zone of South Africa. Management of this kob farming industry is largely effective with strict environmental assessments and special permits. At present there is no third party audit for this industry. Consumers should note that the size of farmed kob may often be smaller than that of the legal minimum size for wild capture kob. If in doubt about the origin of kob on sale it is advisable to ask your seafood vendor for further information.

Dusky kobs are found along the inshore zone along most of the South African coastline. Management for the sector is considered partly effective. In South Africa this sector is principally managed through a total allowable effort (TAE) limitation and there are additional restrictions to protect overfished species such as bag (1 pp/pd) and minimum size limits (> 60 cm) for recreational fishers. There is some concern over the impact of the small-scale fishery rights allocation beyond the recommended TAE and the continuously growing recreational sector.

Dusky are caught between Cape Agulhas and the Great Kei River at depth shallower that 110 m. Management is considered to be partly effective. Management is mainly directed at the target species hake (MSC certified) and sole in the form of Total Allowable Catch (TAC) and permit limitations. Some ecosystem-based management measures have been implemented, such as the use of tori lines to minimize seabird interactions and limited fishing areas. There is a fishery conservation project (FCP) presently underway seeking to test a co-management approach that would bring under management 10 non-target species in the sector. Additional ecological concerns are little information on impacts to sensitive shark, skates and ray populations as well as impacts to the seabed. Efforts are underway to improve the scientific observer coverage at sea for this sector to better understand ecosystem impacts.