Cape horse mackerel
|Cape horse mackerel|
Cape horse mackerel (Trachurus capensis) is a pelagic species, usually found to a depth of 300 m. They are mostly found over the continental shelf, often over sandy bottoms. The shoals rise to feed in surface waters at night, but can be found close to the bottom during the day. Horse mackerel are very abundant in South African and Namibian waters, though much of the catch is exported. Their stock status is uncertain, but expert opinion is that the stock is most likely underfished.
Cape horse mackerel is a bycatch species in the offshore demersal trawl, which operates mainly off the waters of the Western Cape at depths of 110m and deeper. The offshore demersal trawl fishery operates using trawl nets which are dragged behind the boat along the ocean floor at depths from 110 – 800 m. Cape horse mackerel caught in the midwater trawl fishery are considered to be more sustainable than those caught in the offshore trawl fishery (see Cape horse mackerel assessment for midwater trawl). This fishery primarily targets deepwater hake (Merluccius paradoxus) on soft, sandy bottoms, as well as commercially valuable bycatch species such as kingklip (Genypterus capensis) and monkfish (Lophius vomerinus). Although trawling is a highly unselective fishing method, offshore fishing grounds are not generally very biodiverse (i.e. they are only inhabited by a few species) and the discard rate for this fishery is estimated to be 10% of the total catch. However, this fishing method is likely to have significant impacts on bottom habitats and concerns are expressed around the number of seabird mortalities caused during trawling (estimated at 8000 per year). The hake component of the offshore demersal trawl fishery has been certified by the Marine Stewardship Council since 2004, and the current management system for this fishery employs a number of ecosystem-based management measures which address issues such as bycatch, closed areas and benthic habitat impacts. The Cape horse mackerel is managed in terms of a maximum precautionary catch Limit (MPCL). The MPCL has been maintained at 44 000 tonnes in recent years and accommodates both mid-water-directed and bycatch in the hake-directed demersal trawl sector. Juvenile horse mackerel are occasionally targeted on the West Coast where a 5 000 tonnes precautionary catch limit is enforced (the whole small pelagic sector is closed if the limit is exceeded). Despite the absence of direct evidence of ecosystem change, a potential for ecosystem impact exists, as this is an important small pelagic species, and fills a similar ecosystem niche to other small pelagic species such as sardine and anchovy.