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Research surveys are important to evaluate fishery resources' spatial distribution and abundance. Although the underlying sampling is usually conceived with a focus on specific species, efficient designs can also collect data on secondary species. We present a framework to explore and evaluate the adequacy of alternative sampling designs for fishery research surveys aiming to maximize accuracy estimates of the secondary species abundance while maintaining the quality of the abundance estimates of primary species. A geostatistical model-based approach was developed considering the semi-continuous nature of the data and the excess of zero values commonly observed for secondary species. New sampling designs were defined according to optimization weights and evaluated based on the resulting prediction exactness. The framework was applied to the bottom trawl survey conducted along the Portuguese continental coast with European hake, Merluccius merluccius , as the primary species and thornback ray, Raja clavata , as the secondary species. The sampling design URSI provided the best balance between the accuracy for both primary and secondary species. The methodology can be replicated for other bottom trawl research surveys and an extended set of species. We recommend that a decision on which sampling design to adopt in future surveys should consider a cost-efficiency analysis. [ABSTRACT FROM AUTHOR]

The present study is the first to provide data on the reproductive biology of cuckoo ray Leucoraja naevus in Portuguese continental waters. No difference in size at maturity was detected between sexes, which was estimated as 56 cm total length. Spawning occurs all year round, but maximum activity was during winter months. Maximum fecundity is c. 63 eggs female−1 year−1. Encapsulated eggs are released in batches, nine in total with a mean number of seven extruded eggs in each batch. [ABSTRACT FROM AUTHOR]

The article presents a description of the ribbonfish Trachipterus trachypterus. Trachipterus is a genus of the family Trachipteridae that comprises rare fish with no commercial value. The major external morphological characteristics of the fish are elongated and compressed body, protrusible mouth and silvery colour with some darker blotches along the body.

Elasmobranchs represent important components of marine ecosystems, but they can be vulnerable to overexploitation. This has driven investigations into the population genetic structure of large-bodied pelagic sharks, but relatively little is known of population structure in smaller demersal taxa, which are perhaps more representative of the biodiversity of the group. This study explores spatial population genetic structure of the small-spotted catshark (Scyliorhinus canicula), across European seas. The results show significant genetic differences among most of the Mediterranean sample collections, but no significant structure among Atlantic shelf areas. The data suggest the Mediterranean populations are likely to have persisted in a stable and structured environment during Pleistocene sea-level changes. Conversely, the Northeast Atlantic populations would have experienced major changes in habitat availability during glacial cycles, driving patterns of population reduction and expansion. The data also provide evidence of male-biased dispersal and female philopatry over large spatial scales, implying complex sex-determined differences in the behaviour of elasmobranchs. On the basis of this evidence, we suggest that patterns of connectivity are determined by trends of past habitat stability that provides opportunity for local adaptation in species exhibiting philopatric behaviour, implying that resilience of populations to fisheries and other stressors may differ across the range of species.

Understanding of spatio-temporal patterns of sensitive fish species such as skates (Rajidae) is essential for implementation of conservation measures. With insufficient survey data available for these species in Portuguese Continental waters, this study shows that fishery-dependent data associated with fishers' knowledge can be used to identify potential Essential Fish Habitats (EFH) for seven skate species. Sites with similar geomorphology were associated with the occurrence of juveniles and/or adults of the same group of species. For example, sites deeper than 100 m with soft sediment include predominantly adults of Raja clavata, and are the habitat for egg deposition of this species. Raja undulata and R. microocellata are the more coastal species, preferring sand or gravel habitats, while coastal areas with rocks and sand seabed are potential nursery areas for R. brachyura, R. montagui and R. clavata. The main output of this study is the identification of preferential fishing sites enclosing potential EFH for some species, associated with egg-laying and nursery grounds. The location of these areas will be considered for future seasonal closures, and studies will be conducted to evaluate the biological and socio-economic impacts of such measures. As in the past, fishermen will collaborate in the process of evaluating those impacts, since they have practical and applied knowledge that is extremely valuable for evaluating the advantages and disadvantages of such closures. In conclusion, this study is a first contribution to the understanding and identification of EFH for skate species, associated with nursery and egg deposition sites, with direct application to management.

Many sharks and skates are particularly vulnerable to overfishing because of their large size, slow growth, late maturity and low fecundity. In Europe dramatic population declines have taken place in common skate (Dipturus batis L.), one of the largest demersal fish in regional shelf seas, leading to extirpations from substantial parts of its former range. Here we report the discovery of cryptic species in common skate collected from the northeast Atlantic continental shelf. Data from nuclear microsatellite markers indicated two clearly distinct clades and phylogenetic analysis of mitochondrial DNA sequences demonstrated monophyly of each one of them. Capture locations showed evidence of strong spatial segregation, with one taxon occurring mainly in waters off the southern British Isles and around Rockall, while the other was restricted to more northerly shelf waters. These apparently cryptic species showed overlapping substrate and depth preferences, but distributional limits were closely related to temperature gradients, potentially indicating thermal limits to their distributions. This discovery of hidden diversity within a large, critically endangered marine vertebrate demonstrates how marine biodiversity can be underestimated, even in such a relatively well-studied and heavily exploited region.