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Cryptic species in Iphisa elegans Gray, 1851 (Squamata: Gymnophthalmidae) revealed by hemipenial morphology and molecular data
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From Amazonia to the Atlantic forest:molecular phylogeny of Phyzelaphryninae frogs reveals unexpected diversity and a striking biogeographic pattern emphasizing conservation challenges
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Low genetic diversity in tepui summit vertebrates
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Reptiles of Venezuela: an updated and commented checklist
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Fruits and seeds from the Tienen Formation at Dormaal, Palaeocene–Eocene transition in eastern Belgium
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Fish otoliths and their relevance to archaeology: an analysis of medieval, post-medieval and recent material of plaice, cod and haddock from the North Sea
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The growth increments were investigated of late medieval, post-medieval and modern otoliths of plaice, cod and haddock from the North Sea. Thin-sectioned otoliths were used to age all the analysed individuals and to reconstruct their growth patterns. In addition, fish lengths of the archaeological specimens were calculated after the relation between otolith width and fish length was established using modern material. The age and fish length distribution, and the growth patterns obtained on the archaeological material allow inferences about fish trade, market strategies and consumption behaviour on producer sites (coastal sites) and consumer sites. Differences in growth patterns were observed between the archaeological and recent populations of the three demersal species analysed which may be related to a change in fishing pressure through time. However, diachronic changes in species distribution, temperature, food availability and selection of catch in function of market strategies may have played a role as well. Age and body size data allow some inferences about the exploited fishing grounds, but the growth patterns are of limited use in this respect.
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An identification key for dermal denticles of Rajidae from the North Sea
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As a result of more systematic fine sieving on archaeological sites, dermal denticles and isolated teeth of rays are now more frequently recovered than before. A detailed description of the teeth is available in the literature, but no comparative study of the morphology of the dermal denticles exists that allows the identification of such elements issued from archaeological sites. A key and illustrations are provided for the identification of the dermal denticles of 10 ray species from the North Sea. In addition, the ray denticles have been analysed from seven medieval and postmedieval sites showing their potential for the interpretation of ichthyo-archaeological assemblages.
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The ancient fish fauna from Asa Koma (Djibouti) and modern osteometric data on 3 Tilapiini and 2 Clarias catfish species
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The fi sh fauna is presented from Asa Koma; a prehistoric site dated around 1800 cal BC and located in Djibouti near Lake Abhé. The site comprises numerous hearths from which the fi sh bones that form the majority of the faunal remains were recovered. Only two fi sh species occur, namely Oreochromis niloticus and Clarias gariepinus, which are also the two major taxa occurring in the saline lake today. The skeletal element distribution and the frequency of charred remains were analysed and, in addition, detailed size reconstructions were carried out. On the basis of modern skeletons from 47 tilapia and 39 Clarias, the metrical relationship between fi sh length and individual bone measurements (32 measuring distances for tilapia and 40 for Clarias) was established with the aid of the “least squares method”. The equations are all listed for future use by other researchers. The fi sh and other fauna do not allow a precise environmental reconstruction, but the large size of the Clarias possibly indicates less saline conditions than today. Using the reconstructed sizes of the fi sh from Asa Koma, modern data on the behaviour of the species, ethnographic and archaeological parallels, and palaeohydrological data, attempts are made to establish the most likely season of fi shing, the possible location of the fi shing grounds, and the fi shing methods that may have been used. Finally, the possible fi sh preparation and fi sh processing methods are discussed.
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Growth changes in plaice, cod, haddock and saithe in the North Sea: a comparison of (post-)medieval and present-day growth rates based on otolith measurements
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Fishing effort has strongly increased in the North Sea since the mid-19th century, causing a substantial reduction in the population size of exploited fish stocks. As fisheries research has developed simultaneously with the industrialisation of the fisheries, our knowledge of population dynamics at low levels of exploitations is limited. Otoliths retrieved from archaeological excavations offer a unique opportunity to study growth rates in the past. This study compares historical and present-day growth rates for four commercially important demersal fish species. A total of 2532 modern otoliths (AD 1984–1999) and 1286 historical otoliths (AD 1200–1925) obtained from archaeological excavations in Belgium and Scotland were analysed. Comparison of the growth patterns between eras revealed a major increase in growth rate of haddock, whereas growth changes were not observed in saithe and only in the smaller size classes of plaice and cod. Comparison of our results with literature data indicates that the observed growth rate changes in plaice and cod occurred within the 20th century. Apparently the onset of industrialised fisheries has not greatly affected the growth of plaice, cod and saithe populations in the North Sea. This result contradicts the expectation of density-dependent limitation of growth during the era of pre-industrialised fishing, but is in agreement with the concentration hypothesis of Beverton (Neth. J. Sea Res. 34 (1995) 1) stating that species which concentrate spatially into nursery grounds during their early life-history may ‘saturate’ the carrying capacity of the juvenile habitat even though the adult part of the population is not limited by the adult habitat.
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Seasonality only works in certain parts of the year: The reconstruction of fishing seasons through otolith analysis
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Seasonality estimations using incremental data usually suffer from small sample sizes and from the lack of comparison with sufficiently large modern samples. The present contribution reports on incremental studies carried out on large assemblages of plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus) from a late medieval fishing village (Raversijde, Belgium) on the North Sea coast. In an attempt to refine previous seasonality estimates made for this site, and to expand conclusions concerning general methodology, extensive monthly samples of modern otoliths of these species, caught within the North Sea, have also been investigated. The modern material shows that the timing of the seasonal changes in the edge type (hyaline or opaque) of the otoliths is extremely variable and that it is dependent on the fishing ground, the year considered, and the age of the fish. It also appears that the increase of the marginal increment thickness is highly variable, to such an extent that the thickness of the last increment of a single otolith is mostly useless for seasonality estimation. Where large archaeological otolith assemblages can be studied, preferably from single depositional events, seasonality determination becomes possible on the condition, however, that the archaeological assemblage corresponds to fish that were captured during their period of fast growth. The growth ring study on the otoliths from Raversijde shows that plaice fishing took place in spring and that it was preceded by a haddock fishing season, probably in late winter/early spring.
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