Search results for "Chondrichthye"
showing 10 items of 28 documents
Long-term dynamics of pelagic fish density and vendace (Coregonus albula (L.)) stocks in four zones of a lake differing in trawling intensity
2001
– An 11-year time series of hydroacoustic fish density estimates and fisheries statistics of vendace (Coregonus albula (L.)) from four zones of a lake differing in trawling intensity was analyzed in order to test the hypothesis that intensive trawling has detrimental effects on pelagic fish stocks, especially vendace recruitment. The standardized fish density estimate in trawled zones showed no decrease in comparison to the non-trawled zone. No signs of recruitment failure associable with trawling intensity were found. The growth of vendace at the end of the study period was slower than that at the beginning, indicating a higher density, most clearly so in the zone with highest trawling int…
Late Devonian (Famennian) chondrichthyes from Mexico
2019
The Paleozoic vertebrate fossil record from Mexico is very scarce and strongly biased by rock exposure, composed mainly of upper Paleozoic (Carboniferous and Permian) outcrops (e.g., Sánchez-Zavala et al., 1999; Poole et al., 2005; González- Rodríguez et al., 2013). In particular, the Mexican Paleozoic fish fossil record comprises a few isolated chondrichthyan scales and some semiarticulated symphysial tooth whorls belonging to the iconic shark Helicoprion, with ages ranging from the Late Carboniferous to the early Permian. The first reported Paleozoic fish from Mexico belongs to a semiarticulated symphysial tooth whorl of Helicoprion mexicanus from the Permian of Coahuila, near Las Delicia…
The determination of maturity stages in male elasmobranchs (Chondrichthyes) using a segmented regression of clasper length on total length
2013
A novel statistical method for estimating the stages of maturity in male sharks and skates based on a segmented regression (SRM) is proposed. We hypothesize that this method is able to find the transition points in the three-phase relationship between total length (TL) and clasper length (CL). We applied an SRM to TL–CL data of nine species, from large pelagic sharks (e.g., Carcharhinus falciformis) to small coastal skates (e.g., Rioraja agassizi), captured in the southwestern Atlantic and northeastern Pacific. As expected, SRM detected two breakpoints, defining three maturity stages (immature, maturing, and mature), in six out of nine species. For three species, it was not possible to fin…
Regional endothermy as a trigger for gigantism in some extinct macropredatory sharks
2017
Otodontids include some of the largest macropredatory sharks that ever lived, the most extreme case being Otodus (Megaselachus) megalodon. The reasons underlying their gigantism, distribution patterns and extinction have been classically linked with climatic factors and the evolution, radiation and migrations of cetaceans during the Paleogene. However, most of these previous proposals are based on the idea of otodontids as ectothermic sharks regardless of the ecological, energetic and body size constraints that this implies. Interestingly, a few recent studies have suggested the possible existence of endothermy in these sharks thus opening the door to a series of new interpretations. Accord…
MEDLEM database, a data collection on large Elasmobranchs in the Mediterranean and Black seas
2020
The Mediterranean Large Elasmobranchs Monitoring (MEDLEM) database contains more than 3,000 records (with more than 4,000 individuals) of large elasmobranch species from 21 different countries around the Mediterranean and Black seas, observed from 1666 to 2017. The principal species included in the archive are the devil ray (1,868 individuals), the basking shark (935 individuals), the blue shark (622 individuals), and the great white shark (342 individuals). In the last decades, other species such as the thresher shark (187 individuals), the shortfin mako (180 individuals), and the spiny butterfly ray (138) were reported with increasing frequency. This was possibly due to increased public a…
Lonchidion derenzii, sp. nov., a new lonchidiid shark (Chondrichthyes, Hybodontiforms) from the Upper Triassic of Spain, with remarks on lonchidiid e…
2016
Lonchidiidae Herman, 1977, represents one of the most diverse and controversial families of Hybodontiformes, the sister group of Neoselachii (i.e., modern sharks, skates, and rays). It was initially erected as a monogeneric family including only Lonchidion Estes, 1964, a genus of small euryhaline hybodonts from the Mesozoic. Recently, Cappetta (2012) recognized up to eight genera within the family: Baharyodon, Diplolonchidion, Vectiselachos, Hylaeobatis, Isanodus, Parvodus,Lissodus, andLonchidion, although the content of the family is still under discussion (see, e.g., Rees, 2008; Khamha et al., 2016). Major discrepancies concern the phylogenetic relationships between Lonchidion and Lissodu…
First historical records of Carcharhinus brachyurus (Chondrichthyes, Carcharhiniformes) in the Mediterranean Sea
2009
The dried jaws of two specimens of Carcharhinus brachyurus were found in the collections of the Zoological Museum of the University of Palermo. Both pieces belong to the great Doderlein collection of fishes from Sicily assembled during the end of the nineteenth century (1862-1892) and are labelled as Carcarias (Prionodon) lamia and Carcharias lamia, respectively. These findings represent the first historical evidence of the presence of C. brachyurus in the Mediterranean Sea and add the southern Tyrrhenian to the species distribution within the Mediterranean. Moreover, sexual dimorphism in tooth morphology is documented for the first time in Mediterranean specimens. Some meristic and morphol…
Species diversity of the deep-water gulper sharks (Squaliformes: Centrophoridae:Centrophorus) in North Atlantic waters - current status and taxonomic…
2014
The gulper sharks (genus Centrophorus) are a group of deep-water benthopelagic sharks with a worldwide dis- tribution. The alpha taxonomy of the group has historically been problematic and the number of species included in the genus has varied considerably over the years and is still under debate. Gulper sharks are routinely caught in mid- and deep-water fisheries worldwide and some have shown a considerable decline in abundance in the last few decades. Clear and consistent species discrimination of Centrophorus is essential for an efficient and sustain- able management of these fisheries resources. Our study used molecular cytochrome oxidase subunit I (COI) and 16S ribosomal RNA gene seque…
Squamation and ecology of thelodonts
2017
Thelodonts are an enigmatic group of Paleozoic jawless vertebrates that have been well studied from taxonomical, biostratigraphic and paleogeographic points of view, although our knowledge of their ecology and mode of life is still scant. Their bodies were covered by micrometric scales whose morphology, histology and the developmental process are extremely similar to those of extant sharks. Based on these similarities and on the well-recognized relationship between squamation and ecology in sharks, here we explore the ecological diversity and lifestyles of thelodonts. For this we use classic morphometrics and discriminant analysis to characterize the squamation patterns of a significant num…
By-catch of cetaceans and other species of conservation concern during pair trawl fishing operations in the Adriatic Sea (Italy)
2010
By-catch is one of the main sources of anthropogenic mortality in marine species of conservation concern worldwide. Between 2006 and 2008, the Consorzio Nazionale Interuniversitario per le Scienze del Mare (CoNISMa) coordinated a monitoring programme of cetacean by-catch in Italian pelagic trawlers, funded in compliance with European Regulation 812/2004. Sixteen independent observers monitored a total of 3141 hauls. The observation coverage ranged between 0.9 and 6.3% of the regional fishing effort. Almost all by-catch events were recorded in the northern Adriatic Sea. By-catch rates of bottlenose dolphins (Tursiops truncatus) and loggerhead turtles (Caretta caretta) were 0.0006 and 0.0255 …