Population structure and aspects of the reproductive biology of the blackmouth catshark, Galeus melastomus Rafinesque, 1810 (Chondrichthyes: Scyliorhinidae) caught accidentally off the Greek coasts

Abstract

The population composition and aspects of the reproductive biology of 452 blackmouth catsharks, Galeus melastomus were investigated. The sharks were incidentally caught off the North-Western Aegean, the Eastern Corinthian and Northern Euboean Gulfs by commercial bottom trawlers and longlines at depths between 200 and 500 m. The overall sex ratio (1:1.1 females:males) was not different from the theoretical unit (1:1). No differences in the sex ratios were detected among seasons, areas or depth strata. Significant differences in the population structure regarding different maturity stage proportions at different seasons, fishing areas and depths, were observed. The sampled population mainly consisted of immature catsharks (77%), predominantly trawled off the NW Aegean and Corinthian Gulf during winter and autumn. Fifteen per cent of the samples, mainly captured in spring and summer off the N Euboean Gulf, were mature. Eight per cent of the specimens was found to be maturing. Higher frequencies of heavier female individuals were observed. Based on the maturation ogives and the total lengths (TL) for each sex, using logistic regression which presented sex-related differences, male Galeus melastomus achieved maturity at 433.6 mm while females at 483.5 mm. The number of egg capsules in the oviducts spanned from 1–12 per female with sizes varying from 38 × 14 mm to 55 × 20 mm. This is the first study investigating the demography and aspects of Galeus melastomus reproduction in the Eastern Mediterranean.

Deep-Water Cartilaginous Fishes in the Central Mediterranean Sea: Comparison between Geographic Areas with Two Low Impact Tools for Sampling

“…Female of the latter species has low fecundity with only one embryo and a reproductive cycle that could last two years, making this species particularly vulnerable to human impact [77,78]. The highest resilience shown by G. melastomus could be explained not only by its wide distribution, but also by its reproductive traits (i.e., egg deposition occurring throughout the year and deposition of multiple egg case) and its feeding strategy [16,75,79,80]. G. melastomus, in fact, is an opportunistic meso-predator and scavenger or generalist feeder with a broad spectrum of pray; it is capable of adapting its diet to seasonal fluctuations of pray and taking advantage of discarded material from fishing activities [16,76,80].…”

Shedding light on the deep: The case of the velvet belly lanternshark in the North Aegean Sea

“…Sexual dimorphism in terms of body size is commonly observed among shark species (Irvine et al, 2006;Jakobsdottir, 2001;Kousteni, 2015;Kousteni & Megalofonou, 2011Metochis et al, 2018) and is already recorded for E. spinax in the Tyrrhenian Sea (Cecchi et al, 2004), Sardinian waters (Porcu et al, 2014), the Alboran Sea , off southern Portugal Coelho & Erzini, 2008a, 2008c and off the Azores Islands (Aranha et al, 2009), with females growing significantly larger than males. The species is also known to display bioluminescent sexual dimorphism to increase reproductive success, with males presenting sex-dependent hormonal responsive luminous claspers (Claes & Mallefet, 2009).…”

“…The correlation of clasper length with body size is a strong indicator of the length where the onset of maturity happens in several shark species given the rapid increase in clasper size during maturation progress (Ellis & Shackley, 1997; Ivory et al ., 2004; Kousteni et al ., 2010; Kousteni & Megalofonou, 2011, 2015, 2019; Metochis et al ., 2018). This pattern was observed in male E. spinax from the North Aegean Sea with clasper length increasing in a profound way from one stage of maturity to the other.…”

“…In the Ligurian Sea, five to 14 embryos were recorded per litter (Vacchi & Relini Orsi, 1979). Low uterine fecundity has also been recorded in the eastern Atlantic, with Hickling (1963) The correlation of clasper length with body size is a strong indicator of the length where the onset of maturity happens in several shark species given the rapid increase in clasper size during maturation progress (Ellis & Shackley, 1997;Ivory et al, 2004;Kousteni et al, 2010;Kousteni & Megalofonou, 2011, 2015Metochis et al, 2018). Liver plays an important role in the buoyancy and movement of sharks (Phleger, 1998).…”

Growth Modeling of the Giant Electric Ray Narcine entemedor in the Southern Gulf of California: Analyzing the Uncertainty of Three Data Sets

“…A Kruskal–Wallis test was used to examine for differences among months, followed by a nonparametric multiple comparison test to find the months among these differences were presented [ 30 ]. In addition, a Kolmogorov–Smirnov distribution test was used to examine for differences in age structures between sexes [ 39 ].…”