A review of longnose skates Zearaja chilensis and Dipturus trachyderma

Abstract

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. These skates 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 commercially important elasmobranchs in South American waters, the yellownose skate Zearaja chilensis and the roughskin skate Dipturus trachyderma; 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 it is recommended that reproductive seasonality, connectivity and population structure be assessed to ensure their long-term sustainability.

Skate-ing on thin ice: molecular ecology of longnose skates in the Southeast Pacific Ocean

“…In these cases, the amplified fragments from cox1 gene did not provided enough information to establish phylogenetic relationships in the species studied; mainly due to the use of technologies now considered obsolete, their inability to develop species-specific primers, and the inherent evolutionary close-proximity of longnose skates (Díaz de Astarloa et al, 2008;Naylor et al 2012a, b;Vargas-Caro et al, 2015, 2017. Sequences of all mitochondrial loci amplified in the present study showed over 98% identity and a low number of -82-based on morphology Moura et al, 2008;Toffoli et al, 2008;Ward et al, 2005Ward et al, , 2007Ward et al, , 2008Ward et al, , 2009Wong et al, 2009;Zemlak et al, 2009).…”

“…There are few species of cartilaginous fishes considered target species in coastal and oceanic fisheries in the southeast Pacific Ocean (Bustamante et al, 2014b), although the longnose skates Zearaja chilensis and Dipturus trachyderma are of considerable commercial importance in Chilean waters (Lamilla et al, 2010;Vargas-Caro et al, 2015;SERNAP, 2015). Several authors have carried out taxonomic revisions and produced identification guides which include aspects of the morphology and biology of both species (see Vargas-Caro et al, 2015); however, the identities of Z. chilensis and D. trachyderma are still confused in landing records due to similarities in body shape and colour (Vargas-Caro et al, 2015).…”

“…Several authors have carried out taxonomic revisions and produced identification guides which include aspects of the morphology and biology of both species (see Vargas-Caro et al, 2015); however, the identities of Z. chilensis and D. trachyderma are still confused in landing records due to similarities in body shape and colour (Vargas-Caro et al, 2015). Juveniles of both species are caught indiscriminately and in high proportions by fisheries , and the recorded identity of the species landed usually relies on the expertise of the fishers.…”

“…Juveniles of both species are caught indiscriminately and in high proportions by fisheries , and the recorded identity of the species landed usually relies on the expertise of the fishers. Immature longnose skates may lack (or may have lost) the morphological characters required for accurate species identification, such as the presence of a single nuchal thorn, or the number of thorns on the tail (Vargas-Caro et al, 2015). The general lack of rigor in ensuring that landing records are correct can be a major issue for fishery management and quota allocation, and may undermine any conservation measures enacted for these species.…”

“…However, such data are generally insufficient to allow different stocks to be distinguished, as is required for sound fisheries management practices (Vargas-Caro et al, 2015). Molecular analysis has become an important tool in the study of exploited fish populations (Dudgeon et al, 2012), and is frequently applied to examine stock structure and connectivity, and to identify species from body parts, such as fins and carcasses (Lavery & Shaklee, 1991;Shivji et al, 2002;Heist 2004Heist , 2005, Griffiths et al, 2010Portnoy, 2010), each of which can aid fisheries management and conservation efforts (Ovenden et al, , 2010Portnoy, 2010).…”