The availability of updated biological information is essential to any successful fisheries management plan. An example could be to analyze the main size conversion factors, commonly used to estimate values from one or more known body measurements and particularly helpful when a specimen is damaged and may also serve as a tool for species identification. In the Mediterranean Sea, limited morphometric information on skates (Rajidae) has been reported, mainly in association with reproduction and growth studies. The goal of this paper is to estimate relationships between different body measurements to increase the information relative to the most common skate species in Sardinian seas (Central-Western Mediterranean): Dipturus oxyrinchus, Leucoraja circularis, Raja asterias, R. brachyura, R. clavata, R. miraletus and R. polystigma. For each species, total length (TL), disc width (DW), disc length (DL) and length up to the first dorsal fin (D1L), all in millimeters, and total weight (TW), in grams, were taken. An exploratory analysis of morphometric ratios (DW:TL, DL:TL, DL:DW, D1L:TL) was performed and the least-squares method was used to estimate the parameters of the linear expressions TL=aDW+b, TL=aDL+b, TL=aD1L+b and DW=aDL+b. The relationship between TW and TL was fitted and the function was log-transformed. All species showed an allometric growth (b>3). Differences in the morphometric ratios were observed within species. L. circularis and D. oxyrinchus showed the most distinctive shapes, relative to the other species: the former showed a narrower disc in relation to TL, the latter had the disc longer in relation to TL. Both skates had the disc longer than wide. The results indicated that the conversion factors were useful to determinate catch size, explore life history change. Moreover, these factors could made morphological comparisons between different species from different geographical areas and should be considered an useful tool to discriminate skate species.
Conversion factors for skates (Rajidae) in Sardinian seas (Central-Western Mediterranean Sea)
BELLODI, ANDREA;MOCCIA, DAVIDE;Marongiu M. F.
2014-01-01
Abstract
The availability of updated biological information is essential to any successful fisheries management plan. An example could be to analyze the main size conversion factors, commonly used to estimate values from one or more known body measurements and particularly helpful when a specimen is damaged and may also serve as a tool for species identification. In the Mediterranean Sea, limited morphometric information on skates (Rajidae) has been reported, mainly in association with reproduction and growth studies. The goal of this paper is to estimate relationships between different body measurements to increase the information relative to the most common skate species in Sardinian seas (Central-Western Mediterranean): Dipturus oxyrinchus, Leucoraja circularis, Raja asterias, R. brachyura, R. clavata, R. miraletus and R. polystigma. For each species, total length (TL), disc width (DW), disc length (DL) and length up to the first dorsal fin (D1L), all in millimeters, and total weight (TW), in grams, were taken. An exploratory analysis of morphometric ratios (DW:TL, DL:TL, DL:DW, D1L:TL) was performed and the least-squares method was used to estimate the parameters of the linear expressions TL=aDW+b, TL=aDL+b, TL=aD1L+b and DW=aDL+b. The relationship between TW and TL was fitted and the function was log-transformed. All species showed an allometric growth (b>3). Differences in the morphometric ratios were observed within species. L. circularis and D. oxyrinchus showed the most distinctive shapes, relative to the other species: the former showed a narrower disc in relation to TL, the latter had the disc longer in relation to TL. Both skates had the disc longer than wide. The results indicated that the conversion factors were useful to determinate catch size, explore life history change. Moreover, these factors could made morphological comparisons between different species from different geographical areas and should be considered an useful tool to discriminate skate species.
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