Abstract
Pontinus kuhlii is a Scorpaenidae which forms part of the bottom longline by-catch in the Canary Islands fisheries within setting operations from 200 to 400 metres depth. Information on their biology and on the age determination and growth of the species is very scarce. The main objective of the study was to look at this biological aspect based on 421 specimens caught in the Canarian Archipelago during the period July 1996 and August 1997, 286 of which were male, 130 female and 5 indeterminate. Age was determined through the interpretation of annual growth rings of otoliths and scales, and the results fitted the von Bertalanffy growth function. Otolith sectionings were discarded due to annuli losses caused by the edge structure. The structures used in age interpretation showed numerous false rings that made the process difficult, causing 17% of the cases to be rejected. However, the age interpretations from scales showed less variability in relation to the whole otolith. The ages of the specimens ranged from 6 to 18 years for males and from 6 to 14 years for females. The growth parameters for males were: K= 0.132, L? = 46.7 and to= 1.74; for females: K= 0.094, L?= 46.3 and to= 0.05; and for the total: K= 0.095, L?= 52.2 and to= 1.01.
Highlights
The Scorpaenidae Pontinus kuhlii (Bowdich, 1825), commonly called offshore rockfish, is a demersal species that inhabits the rocky substratum of slope at depths that range from 100 to 460 metres (Nunes, 1974; Eschmeyer and Dempster, 1990; Franquet and Brito, 1995; Menezes, 1996)
The difficulties found in the current work in relation to the age interpretation of P. kuhlii were shown by Isidro (1996) working with otoliths of this species caught in the Azores, establishing that 36%
The tendency to underestimate age from otoliths could be due to a systematic error in the interpretaedge ramifications and growth rings in minor axis are difficult to identify at the outer margin
Summary
The Scorpaenidae Pontinus kuhlii (Bowdich, 1825), commonly called offshore rockfish, is a demersal species that inhabits the rocky substratum of slope at depths that range from 100 to 460 metres (Nunes, 1974; Eschmeyer and Dempster, 1990; Franquet and Brito, 1995; Menezes, 1996). Their geographical distribution extends from the Azores. Archipelago, P. kuhlii inhabits the shallower waters. Isidro (1990, 1996) has contributed with data on growth and reproduction, as well as a preliminary study on management of the stock in the waters of the Azores
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