Demographic Variation between Colour Patterns in a Temperate Protogynous Hermaphrodite, the Ballan Wrasse Labrus bergylta

David Villegas-Ríos,Rafael Bañón,Alexandre Alonso-Fernández,Mariña Fabeiro,Fran Saborido-Rey

doi:10.1371/journal.pone.0071591

David Villegas-Ríos, Rafael Bañón + Show 3 more

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https://doi.org/10.1371/journal.pone.0071591

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Abstract

Fish populations are often treated as homogeneous units in typical fishery management, thereby tacitly ignoring potential intraspecific variation which can lead to imprecise management rules. However, intraspecific variation in life-history traits is widespread and related to a variety of factors. We investigated the comparative age-based demography of the two main colour patterns of Labrus bergylta (plain and spotted, which coexist in sympatry), a commercially valuable resource in the NE Atlantic. Individuals were aged based on otolith readings after validating the annual periodicity of annuli deposition. The relationships between the otolith weight and fish age and between otolith length and fish length were strong but differed between colour patterns. The fit of the growth models to the age and length data resulted in divergent growth curves between colour morphotypes and between sexes. Males and spotted individuals attained larger mean asymptotic sizes (Linf) than females and plain individuals, respectively, but converged to them more slowly (smaller k). Estimates of mortality based on catch curves from two independent datasets provided a global total mortality (Z) of 0.35 yr–1, although Z was larger in plain and female individuals. Overall, the results of this research have direct implications for management of L. bergylta and, as a precautionary measure, we recommend considering both colour patterns as two different management units.

Highlights

Age-based demographic studies of marine fishes are one of the foundations of population biology and provide essential information for ecosystem and fisheries management [1]
Validation of ageing criteria A significant positive linear relationship was observed between fish age and otolith weight (r2 = 0.79, F = 453.2, p,0.001, n = 498) but it differed significantly between plain and spotted individuals and between sexes (Figure 2a and Table 2)
A positive significant relationship was obtained between fish total length (TL) and otolith length (r2 = 0.75, F = 243.8, p,0.001, n = 243) with significant differences between colour patterns (Figure 2b and Table 2)

Summary

Introduction

Age-based demographic studies of marine fishes are one of the foundations of population biology and provide essential information for ecosystem and fisheries management [1]. Demographic parameters have been found to differ between populations of the same species geographically separated by tens to thousands of kilometres [3,4,5], highlighting the need to investigate local populations rather than apply models based on parameters from other regions for management purposes [6]. Some species have developed into reproductively isolated sympatric morphotypes which can eventually promote population evolutionary divergence and speciation [10] Failing to consider this level of intraspecific variation in the demographic parameters can result in inadvertent undesirable outcomes and can have important implications for the sustainability and productivity of fisheries [9,11]

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