Population structure of the bluemouth, Helicolenus dactylopterus (Teleostei: Sebastidae), in the Northeast Atlantic and Mediterranean using geometric morphometric techniques

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The bluemouth, Helicolenus dactylopterus (Delaroche 1809) is a marine demersal fish that is widely distributed in the Atlantic and the Mediterranean. The bluemouth is mostly considered a deep-sea species, but it has a wide bathymetric range of distribution (from 62 m to 1135 m depth). Precisely because of this distribution, it is caught in many fisheries that exploit marine organisms on the continental shelf and the deep-sea. Since the late nineties, the biology of the bluemouth has been studied in the NE and NW Atlantic, the Mediterranean and the North Sea, focusing mainly in the distribution, age, growth and reproduction of the species. However, as with other deep-sea species, there are still many gaps in what regards the biology, ecology and population dynamics of this species. As it is now widely recognized, information on a species’ population structure is of primary importance in developing an optimal strategy for its efficient management (Coyle, 1998). Thus, the overall goal of this study was to provide baseline information on the population structure of bluemouth, Helicolenus dactylopterus, around the Iberian Peninsula. Moreover, this thesis provides the first comparative study of bluemouth populations in the Northeast Atlantic and the Mediterranean. To characterize the population structure of bluemouth in terms of growth and stock components, a morphological approach was followed, because the analysis of morphological characters (i. e., meristic and morphometric characters) has proved useful for characterizing populations of a variety of marine fish (Swain et al., 2005).

To achieve this, bluemouth from 9 areas were sampled. In the NE Atlantic, specimens were caught off Galicia, the Cantabrian Sea, the Gulf of Cadiz, Portugal and the Porcupine Bank (Irish continental margin). Specimens from the Mediterranean were sampled in the Alboran Sea, off-shore Alicante (south-west of the Balearic Sea), the Catalonian coast and in Italian waters (Sicily). The samples from the Porcupine Bank and Sicily were used as reference areas in order to understand the population structure of bluemouth at a larger scale and relativize the possible differences among bluemouth populations around the Iberian Peninsula. The first specific objective of this study was to study the ontogenetic allometry of the bluemouth in the Northeast Atlantic and Mediterranean using geometric morphometrics. In this part of the study, the shape changes that occur during the growth of bluemouth were characterized to better understand its biology and ecology. The general pattern of ontogenetic changes observed in this study seemed to be related to the changing ecology of the species (i.e. ontogenetic diet and habitat adaptations) and consisted of a relative expansion of the area between the second preopercular spine and the pectoral fin, a relative deepening and shortening of the body and an upward shift of the snout as the head becomes more compact in relation to the body. However, some specific growth patterns were detected in the different areas, indicating that growth trajectories were not homogeneous among bluemouth populations. The study of allometry was also used to determine the best method to correct for allometry for the bluemouth population structure dataset. For this purpose, a pooled within-group regression yielded the best results.

The second specific objective was to identify bluemouth phenotypic stocks in the Northeast Atlantic and western Mediterranean based on geometric morphometrics and meristics. The greatest morphological differentiation was found between bluemouth from Portugal and the neighboring locations: Galicia and the Cantabrian Sea to the north and the Gulf of Cadiz to the south. This indicates that bluemouth from Portugal can be considered as a separate phenotypic stock. The overall morphological variation along the Cantabrian Sea and Galicia seemed to follow a gradient, with no clear breakpoints that could indicate the isolation between bluemouth from these regions. Thus, bluemouth from these two areas seem to constitute a single phenotypic stock. In the western Mediterranean, there was evidence that at least two bluemouth phenotypic stocks exist: one in the south-western basin (Alboran Sea) and another in the north-western basin (Balearic Sea and Catalonian coast) that extends to the transition zone in the Alicante region. A third stock in the western Mediterranean (or a subpopulation) might be present, because bluemouth from subarea A2 in the Alboran Sea presented important morphometric differences with respect to bluemouth from the neighboring areas, but his needs to be further investigated. In general, meristic variables were stable among bluemouth from the different locations, with the exception of the counts of gill rakers (GRV and GRH), where some variability was observed. Thus, the usefulness of meristic variables to identify bluemouth phenotypic stocks is questionable. It appears that in Helicolenus, the study of meristic characters may be more useful at the interspecific level rather than at the intraspecific level.

The work carried out in this thesis is a major contribution for understanding the population structure of bluemouth in European waters, providing evidence that different phenotypic stocks exist. These stocks can be used as a first approach to model population dynamics for fishery stock assessment and management. However, more work needs to be done to understand the bluemouth stock structure in the NE Atlantic and Mediterranean. A multidisciplinary study, covering both basins, is necessary to identify correctly the stock components and understand the dynamics of bluemouth populations.

The author’s work was mainly funded by a Marie Curie fellowship from the Early Stage Training site ECOSUMMER (MEST-CT-2005-020501) and a CONACyT - Mexico scholarship. This research was also supported by the project CTM2006-13964-C03-00 of the Spanish Ministry of Science and Innovation.

Peer reviewed