Skates in the demersal trawl fishery of San Matías Gulf: species composition, relative abundance and maturity stages

Abstract

-Argentina is one of the countries with the largest overall landings of skates and rays (24 000 t/year). As a consequence of high levels of exploitation and deficient management tools, many of these species are threatened with extinction. In the bottom trawl fishery of San Matías Gulf, northern Patagonia, skates and rays are caught as bycatch and all have historically been recorded in the fishery logbook under the category "rays". Therefore, species composition and their characteristics were unknown. The aim of this study was to characterize the commercial exploitation of batoid species in this fishery. Our results indicate that commercial landings include nine species of skate, six of which are common. Among these, Atlantoraja platana, Sympterygia bonapartii and Dipturus chilensis were considered the main species of this fishery. Their combined relative abundance and weight made up about 90% of the batoid catch throughout the year. Sexual segregation was detected in four species in which individuals of one sex dominated commercial landings. The commercial fraction was composed of individuals with a wide range of sizes. Immature individuals could represent 90% of the individuals landed for some species. At present, lack of data prevents us from quantifying the impact that this fishery is having on these species, but our findings highlight the importance of conducting research surveys to assess the abundance and geographic extent of these populations. The information presented here provided the basis for the proposal of a new logbook format incorporating species-level identification. The new logbook was implemented on 1 January 2010.

Reproductive biology of the eyespot skate Atlantoraja cyclophora (Elasmobranchii: Arhynchobatidae) an endemic species of the Southwestern Atlantic Ocean (34ºS - 42ºS)

“…F, females; M, males; N, number of individuals sampled; TL, total length. Other data references: (a) Oddone et al (2008), (b) (2005), (c) Estalles et al (2011 According to the results registered here, the lack of seasonal variation of LFOD and OGW and the occurrence of females with eggs in the uterus throughout the year, A. cyclophora might undergo an annual reproductive cycle. In addition, the higher values in the female GSI observed in December, might be explained by a peak of reproductive activity in spring season, as was proposed by Oddone et al (2008) Mabragaña et al, 2002); A. castelnaui (according to Collonelo et al, 2012); Rioraja agassizi (Müller & Henle, 1841) (according to Colonello et al, 2007a;], where temperatures and photoperiod may affect egg laying rate (Colonello, 2009).…”

“…Atlantoraja cyclophora is distributed from Cabo Frio, Brazil (22ºS) to San Jorge Gulf in Argentina (47ºS) and inhabits from the coast out to maximum depths of 300 m in Brazil and up to the 130 m isobath in Argentina Cousseau et al, 2007). This vulnerable species (Massa et al, 2006) is taken as by-catch along all its distribution area by commercial bottom trawl fisheries (Paesch, Domingo, 2003;Oddone, Vooren, 2005;Tamini et al, 2006;Góngora et al, 2009;Estalles et al, 2011;Massa, Hozbor, 2011;Orlando et al, 2011). The coastal 2 e170098 [2] ecosystem of the Southwest Atlantic Ocean, between 34ºS and 42ºS and <50 m deep, constitutes the region where the greatest landings of cartilaginous fish are recorded (Massa et al, 2004;Massa, Hozbor, 2011).…”

“…Oddone, Vooren (2005) studied the reproductive biology of A. cyclophora in southern Brazil between 100 and 300 m depths, and later, Oddone et al (2008) complemented the reproductive studies of this species in southeastern Brazil, up to 146 m depth. In Argentina, Estalles et al (2011) reported estimates of size at maturity for males and females of A. cyclophora in the San Matías Gulf (41°S-42°S), but there is no information on reproductive variables in the area between 34°and 42° S. Also, like other elsamobranchs (Chiaramonte, Pettovello, 2000;Mabragaña, Cousseau, 2004;Colonello et al, 2007b), a latitudinal gradient in the maximum TL and size at maturity has been noted for A. cyclophora (Oddone, Vooren, 2005;Oddone et al, 2008;Estalles et al, 2011).…”

Reproductive biology of Sympterygia bonapartii (Chondrichthyes: Rajiformes: Arhynchobatidae) in San Matías Gulf, Patagonia, Argentina

“…As a result, different sizes of fish may be selected, modifying the size frequency distributions obtained in each work. The differences between the present study and the one of Estalles et al (2011) are included in this category since in 2011 only the commercial fraction was analysed. The differences may be due to a bias in the size frequency distributions of the skates as a result of the selection of the largest sizes carried out by fishermen on board.…”

“…This skate is one of the most abundant and fished along the Argentine coast. It is caught and landed by bottom trawlers in mixed-species fisheries and in fisheries targeting the common hake Merluccius hubbsi Marini, 1933, where it is part of the bycatch (Massa et al, 2004;Tamini et al, 2006;Estalles et al, 2011). It is also caught and discarded in the fishery of the Patagonian red shrimp Pleoticus muelleri (Bate, 1888), where its discards are thought to represent an important fraction of its stock (Cedrola et al, 2005).…”