Biology and stock structure of the forkbeard, Phycis phycis (Linnaeus, 1766), in the southern Northeast Atlantic

Tese de doutoramento, Ciências do Mar, Universidade de Lisboa, Faculdade de Ciências, 2015The biology and ecology of many commercially important species are not subject to study before these species begin to be exploited. The knowledge of stock structure and degree of mixing among populations is important for the rational management of marine resources, especially when dealing with commercially important marine fish species. The forkbeard, Phycis phycis, is a benthopelagic fish with a wide distribution in the southern Northeast Atlantic and is one of the most important gadiform species commercially exploited in Portuguese waters. However, no information on the species biology for Portuguese coast exists, the stock structure along its distribution area is unknown and its exploration unregulated. Thus, this thesis aims to gather new and important biological information on the species and elucidate the stock structure of forkbeard in the southern Northeast Atlantic. In relation to biology, the age and growth study described in this thesis suggests that forkbeard is a relatively slow growing, long-lived species, that does not show sexual dimorphism in growth. Fishing mortality estimates for this species is representative of a low/moderate exploitation pattern. The reproductive strategy study indicates that forkbeard is a group-synchronous, batch spawner species with a determinate fecundity. In Portuguese waters, spawning season occurs from September to early January and the length at first maturity was estimated as 35.9 cm and 28.5 cm TL for females and males, respectively. Stock structure of forkbeard along its distribution area was investigated using otolith shape analysis, body geometric morphometrics and genetic analysis. The morphological techniques suggest the existence of at least three phenotypic stocks in the southern Northeast Atlantic (mainland Portugal, Azores and Madeira), and the genetic analysis suggests the existence of two genotypic stocks, between the southern Northeast Atlantic and the Mediterranean.Fundação para a Ciência e a Tecnologia (FCT), projeto PROMAR 31-03-05-FEP-