Report on black scabbard fish (Aphanopus carbo) otolith exchange 1998-1999

European Fish Ageing Network (EFAN) Report 3-99

Black scabbard fish (Aphanopus carbo Lowe, 1839) is a species inhabiting the continental shelf and slope between 180 and 1600 m depth. It is widely distributed in the northeastern Atlantic along the European continental shelf and also around isolated island groups and seamounts. Black scabbardfish is probably best described as a benthopelagic species, which make excursions into midwater. There is some evidence that these migrations occur mostly at night for feeding. There are often statements on the literature that juveniles are pelagic but evidence is lacking. The smallest specimens known, 10 to 15 cm, were taken from the stomachs of a midwater fish (Alepisaurus ferox) off Madeira (Maul, 1948).
Black scabbard fish is already commercial exploited by several countries, namely Portugal, U.K., France and Ireland. In Portugal, black scabbardfish is the target species of the longline fishery off Sesimbra (Portugal mainland) and off Madeira. In Madeira the species was caught until 1982 with the traditional drifting vertical longline (Martins & Ferreira, 1995), but it is now caught (Sena-Carvalho, pers. comm.), as in Portugal mainland, using a near-bottom drifting horizontal longline (Martins et al., 1989). While the long established Madeira's fishery (since the early 19th century) and the more recent fishery off mainland Portugal (since 1983) are longline fisheries targeting for this species, the increasing landings in northern areas result from the bycatch of deep-water trawl fisheries. This fishery, in the west of British Isles is unregulated and part of it made in international waters.
In 1998 started a DG XIV E.U. Biological Study of title: “Environment and biology of deep-water species Aphanopus carbo in NE Atlantic: basis for its management (BASBLACK)”. Its objective is to provide the basis for the development and implementation of a routine study and management of the black scabbardfish. Owing to the lack of biological and environmental information critical for the assessment and management of the species, a special effort is put into investigations of its biology, being age determination one of the main objectives.
Only a preliminary study on age and growth determination using otoliths was carried out for the species in Madeira. The results showed that black scabbard fish is a relatively fast-growing species living up to 8 years (Morales-Nin & Sena-Carvalho, 1996). Growth parameter estimates based on otolith readings and on length frequency analysis lead to similar results. However, the range of lengths used was quite narrow and adult component over represented.
As a first step on the age determination of the species in the framework of the BASBLACK Project, an Otolith Exchange was carried out with the following objectives:
1. To determine the best otolith preparation method.
2. To investigate the interpretation problems.
3. To uniformize the age determination criteria.
4. To estimate precision from the age readings of each individual age reader.
5. Finally, to provide a common methodology for all the project participants.