Dipturus Trachyderma Research Articles

Towards sustainable fishery management for skates in South America: The genetic population structure of Zearaja chilensis and Dipturus trachyderma (Chondrichthyes, Rajiformes) in the south-east Pacific Ocean.

The longnose skates (Zearaja chilensis and Dipturus trachyderma) are the main component of the elasmobranch fisheries in the south-east Pacific Ocean. Both species are considered to be a single stock by the fishery management in Chile however, little is known about the level of demographic connectivity within the fishery. In this study, we used a genetic variation (560 bp of the control region of the mitochondrial genome and ten microsatellite loci) to explore population connectivity at five locations along the Chilean coast. Analysis of Z. chilensis populations revealed significant genetic structure among off-shore locations (San Antonio, Valdivia), two locations in the Chiloé Interior Sea (Puerto Montt and Aysén) and Punta Arenas in southern Chile. For example, mtDNA haplotype diversity was similar across off-shore locations and Punta Arenas (h = 0.46–0.50), it was significantly different to those in the Chiloé Interior Sea (h = 0.08). These results raise concerns about the long-term survival of the species within the interior sea, as population resilience will rely almost exclusively on self-recruitment. In contrast, little evidence of genetic structure was found for D. trachyderma. Our results provide evidence for three management units for Z. chilensis, and we recommend that separate management arrangements are required for each of these units. However, there is no evidence to discriminate the extant population of Dipturus trachyderma as separate management units. The lack of genetic population subdivision for D. trachyderma appears to correspond with their higher dispersal ability and more offshore habitat preference.

Vulnerabilidade de espécies capturadas pela pesca de emalhe-de-fundo no Sudeste-Sul do Brasil: produtividade-suscetibilidade (PSA)

Durante a última década, a pescaria de emalhe dirigida ao peixe-sapo (Lophiusgas trophysus) desenvolveu-se sobre o talude do sudeste-sul do Brasil, provocando capturas incidentais bento-pelágicas, principalmente de peixes. Com o intuito de avaliar o impacto causado pela pesca foi utilizada a Análise de Produtividade-Suscetibilidade-PSA com as informações obtidas durante as operações de pesca em 2001. De acordo com as espécies de peixe nas capturas, foi estabelecido um conjunto de atributos qualitativos ou semiquantitativos relacionados í­Â "produtividade” das mesmas e sua "suscetibilidade” í­Â pesca de emalhe profundo. Estes atributos foram ranqueados em três categorias, "alto” (3),"médio” (2) e "baixo” (1). Os escores médios obtidos pelos indicadores de produtividade para elasmobrí­¢nquios (1,32) foram inferiores í­Â queles obtidos para teleósteos (1,88). Em termos de suscetibilidade, ambos os grupos de peixes apresentaram í­­ndices próximos, com valores médios de 2,00(elasmobrí­¢nquios)e 1,96 (teleósteos). Dentre as mais vulneráveis ao emalhe-de-fundo estão os elasmobrí­¢nquios: Dipturus trachyderma, Echinorhinus brucus, Squalus megalops, Squatina argentina, Atlantoraja castelnaui e Torpedo puelcha. Algumas espécies, valiosas como Urophycis mystacea,Merluccius hubbsie o próprio peixe-sapo estiveram capturados de maior vulnerabilidade. A abordagem da PSA proporciona uma base empí­­rica qualitativa na avaliação dos impactos ecossistêmicos das pescarias, priorizando espécies que necessitam de ações de manejo, incluindo aquelas que seus dados populacionais são escassos ou inexistem.

A review of longnose skates Zearaja chilensis and Dipturus trachyderma

Longnose skates may have a high intrinsic vulnerability among fishes due to their large body size, slow growth rates and relatively low fecundity, and their exploitation as fisheries target species places their populations under considerable pressure. They are found circumglobally in subtropical and temperate coastal waters. Although longnose skates have been recorded for over 150 years in South America, the ability to assess the status of these species is still compromised by critical knowledge gaps. Based on a review of 185 publications, a comparative synthesis of the biology and ecology was conducted on two of the most commercially important elasmobranchs in South American waters, the yellownose skate <em>Zearaja chilensis</em> and the roughskin skate <em>Dipturus trachyderma</em>; in order to examine and compare their taxonomy, distribution, fisheries, feeding habitats, reproduction, growth and longevity. There has been a marked increase in the number of published studies for both species since 2000, and especially after 2005, although some research topics remain poorly understood. Considering the external morphological similarities of longnose skates, especially when juvenile, and the potential niche overlap in both depth and latitude occupied, it is recommended that reproductive seasonality, population structure and connectivity be assessed to ensure their long-term sustainability.

The phylogenetic position of the roughskin skate Dipturus trachyderma (Krefft & Stehmann, 1975) (Rajiformes, Rajidae) inferred from the mitochondrial genome

The complete mitochondrial genome of the roughskin skate Dipturus trachyderma is described from 1 455 724 sequences obtained using Illumina NGS technology. Total length of the mitogenome was 16 909 base pairs, comprising 2 rRNAs, 13 protein-coding genes, 22 tRNAs and 2 non-coding regions. Phylogenetic analysis based on mtDNA revealed low genetic divergence among longnose skates, in particular, those dwelling the continental shelf and slope off the coasts of Chile and Argentina.

Biogeographic patterns in the cartilaginous fauna (Pisces: Elasmobranchii and Holocephali) in the southeast Pacific Ocean.

The abundance and species richness of the cartilaginous fish community of the continental shelf and slope off central Chile is described, based on fishery-independent trawl tows made in 2006 and 2007. A total of 194,705 specimens comprising 20 species (9 sharks, 10 skates, 1 chimaera) were caught at depths of 100–500 m along a 1,000 km transect between 29.5°S and 39°S. Sample site locations were grouped to represent eight geographical zones within this latitudinal range. Species richness fluctuated from 1 to 6 species per zone. There was no significant latitudinal trend for sharks, but skates showed an increased species richness with latitude. Standardised catch per unit effort (CPUE) increased with increasing depth for sharks, but not for skates, but the observed trend for increasing CPUE with latitude was not significant for either sharks or skates. A change in community composition occurred along the depth gradient with the skates, Psammobatis rudis, Zearaja chilensis and Dipturus trachyderma dominating communities between 100 and 300 m, but small-sized, deep-water dogfishes, such as Centroscyllium spp. dominated the catch between 300 and 500 m. Cluster and ordination analysis identified one widespread assemblage, grouping 58% of sites, and three shallow-water assemblages. Assemblages with low diversity (coldspots) coincided with highly productive fishing grounds for demersal crustaceans and bony fishes. The community distribution suggested that the differences between assemblages may be due to compensatory changes in mesopredator species abundance, as a consequence of continuous and unselective species removal. Distribution patterns and the quantitative assessment of sharks, skates and chimaeras presented here complement extant biogeographic knowledge and further the understanding of deep-water ecosystem dynamics in relation to fishing activity in the south-east Pacific Ocean.

Egg capsules of the yellownose skate Zearaja chilensis (Guichenot 1848) and the roughskin skate Dipturus trachyderma (Krefft and Stehmann 1974) (Rajiformes: Rajidae) from the south-eastern Pacific Ocean

Egg capsules of Zearaja chilensis were obtained from individuals kept in captivity and from dead specimens captured in Valparaiso Bay, central Chile. One female under laboratory conditions deposited three pairs of egg capsules in 6 days. The egg capsules of Dipturus trachyderma were obtained from a female captured in Valdivia, south Chile. Fresh egg capsules of both species were golden-brown and thick walled. Size of egg capsules of Z. chilensis ranged from 94 to 144 mm in capsule length and 64 to 76 mm in capsule width. Those of D. trachyderma ranged between 197 and 199 mm in capsule length and 110.0 and 129.0 mm in capsule width. Range and mean values of capsule length and width of egg capsules described in this study were smaller than those reported for the same species in the south-western Atlantic Ocean. This is the first report on egg-laying rate of Z. chilensis and the first description of egg capsules of Z. chilensis and D. trachyderma from the south-eastern Pacific Ocean.

Morphological description of Dipturus mennii (Chondrichthyes: Elasmobranchii: Rajidae) and its differentiation from Dipturus trachyderma

Squamation patterns and skeletal anatomy (neurocranium, visceral arches, synarcual cartilage, scapulocoracoid, puboischiadic bar, and mixopterigium) of Dipturus mennii Gomes & Paragó, 2001 are described as a contribution to our limited knowledge of the anatomy of species of Dipturus Rafinesque, 1810. The hyoid and branchial arches, as well as the synarcual cartilage, are described for the first time in this species. We provide morphological comparisons of this species with Dipturus trachyderma (Krefft & Stehmann, 1975), a species that may be confused with D. mennii; we further corroborate, through anatomical features, that these species warrant separate taxonomic recognition. The main differences between D. mennii and D. trachyderma were found in squamation of the nuchal and middisc region, neurocranium, pectoral girdle, and principally the clasper skeleton. The morphology of the pelvic girdle is similar in both species. Dipturus is characterized by having the ventral terminal cartilage J-shaped (as opposed to the Z-shaped ventral terminal cartilage in Zearaja, whose species were, until recently, placed in Dipturus). Additional characters that may be derived for Dipturus include the anterior rostral groove and elevated rostral proportions

Incorporating uncertainty into estimation of natural mortality for two species of Rajidae fished in Chile

Methods to estimate annual mortality rate ( M ) are usually based on life history traits and their application provide a deterministic estimate for M . However, there are two sources of uncertainty coming from equations that describe these methods: (i) error in the life history traits estimates (hereafter ‘trait-error’) and (ii) variability of the equations coefficients (hereafter ‘coefficient-error’). Thus, we use these two sources of uncertainty to incorporate error on M estimates for yellownose skate ( Dipturus chilensis) and roughskin skate ( Dipturus trachyderma) off the Chilean coast. Based on the quality of the life history parameters available for these species, five methods to estimate M were selected which required the analysis of lifespan a max , age at maturity a 50 % , and von Bertalanfy growth parameters ( l ∞ , t 0 , and k). For Pauly’s methods, the error on the habitat temperature was also assessed. Incorporating only uncertainty from trait errors produced estimates of median M for D. chilensis ranging from 0.12 to 0.15 year −1 for females and 0.14 to 0.18 year −1 for males. For D. trachyderma, this same estimate was 0.09–0.15 year −1 for both sexes combined. Incorporating all sources of uncertainty (trait and coefficient-error) increased the coefficients of variation (CV) of M nine-fold for D. chilensis (females) and seven-fold for D. trachyderma and increased estimates of M by up to 35% in comparison with median values. We think Pauly’s method is the most appropriate for both analysed species in terms of trade-off between parameter needed and CV of M estimates incorporating all sources of uncertainty. Most of the empirical methods used herein were proposed, in principle, for teleost fishes within a deterministic framework. We discuss the applicability of these methods to elasmobranchs and how the incorporation of uncertainty may improve population modelling for these species.

Age, growth, and reproduction of the roughskin skate, Dipturus trachyderma, from the southeastern Pacific

AbstractLicandeo, R., Cerna, F., and Céspedes, R. 2007. Age, growth, and reproduction of the roughskin skate, Dipturus trachyderma, from the southeastern Pacific. ICES Journal of Marine Science, 64: 141–148. Age, growth, and reproductive parameters of the roughskin skate, Dipturus trachyderma, in the southeastern Pacific are reported. Age was estimated by counting the growth rings of thin sections of vertebral centra from 201 fish (61–253 cm total length, LT). No systematic ageing bias was observed, and the precision of growth ring counts indicated a high level of reproducibility. Marginal increment analysis supported the hypothesis of annual deposition of growth rings, which form during winter. The oldest female and male were 26 and 25 y, respectively. Von Bertalanffy parameters for combined sexes based on length-at-age data were L∞=257.7 cm LT, K=0.081 y−1 and t0=–1.363 y. Skates from the southernmost areas attained a larger mean size than those from more northern areas, and females reached a larger adult size than males. Males began the maturation process at ∼186 cm LT, indicated by the abrupt enlargement of the claspers. Developed oviducal glands, uteri, and ovaries indicated that females began to mature at 200 cm LT. The length and age at which 50% of the population matured were 215 cm LT and 17 y for females and 195 cm LT and 15 y for males. The youngest mature female and male D. trachyderma were 15 and 13 y, respectively. The ovarian fecundity ranged from 28 to 68 follicles. Females carrying egg cases were found in March and July. Dipturus trachyderma is slow-growing, long-lived, attains large size, matures late, and has low fecundity, life history characteristics that make it highly susceptible to exploitation.