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In a given fish species, disproportionate catches of one sex or the other may arise from sex change, sexually dimorphic growth combined with minimum size limits, or regional segregation of sexes. Such disproportionate catches could lead to an alteration of the overall sex ratio, which may impact the population dynamics of the stock due to (1) possible egg or sperm limitation arising from low numbers of mature individuals of a particular sex or (2) shifts in the size or age at maturity of a particular sex (or the size or age at sex change in hermaphroditic species; Huntsman and Schaaf 1994; Armsworth 2001; Alonzo and Mangel 2004, 2005; Heppell et al. 2006; Molloy et al. 2007; Alonzo et al. 2008). For example, age‐specific sex ratios are required in the stock assessment for Red Porgy Pagrus pagrus since the sex ratios vary due to protogyny (SEDAR 2012).
The sex and reproductive state of fish sampled during catch surveys are commonly assigned through the use of primary and secondary sexual characters. The most commonly used primary sexual character is the presence and developmental state of either the testes or the ovaries; however, intromittent organs, sex hormones, and sex chromosomes (in reproductive individuals) may also be used to assign sex. A number of species show a high degree of sexual dimorphism (at least when mature or actively spawning), thus allowing sex to easily be assigned based on secondary sexual characters, such as coloration, size, or other modifications of the body (e.g., nuptial tubercles in many cyprinids, coloration in most labrids and scarids, and the kype in males of many salmonids). However, a number of species, including the Greater Amberjack Seriola dumerili, do not possess obvious sexual dimorphism in secondary sexual characters but may exhibit differences in the urogenital region (e.g., shape and number of urogenital pores). Such differences have been used to successfully assign sex in a number of species (McComish 1968; Casselman 1974; Noltie 1985; Benz and Jacobs 1986; Murie 1991; St‐Pierre 1992; Vecsei et al. 2003).
The Greater Amberjack is a pelagic reef species that is found along the eastern and western Atlantic coasts, in the Mediterranean Sea, and throughout...