Sensitive skates or resilient rays? Spatial and temporal shifts in ray species composition in the central and north-western North Sea between 1930 and the present day

Walker, Paddy; Hislop, J. R. G.

doi:10.1006/jmsc.1997.0325

Cited by 220 publications

(251 citation statements)

References 17 publications

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“…In the present study, the PCL 50 occurred once C. callorhynchus female reached 74% of the maximum observed PCL, maturing at a smaller proportion than C. capensis females in South Africa (88% of the maximum size) (Nibam, 2011). The delayed size at maturity in holocephalans, a general pattern in chondrichthyans, indicates that they are particularly sensitive to fishing pressure (Walker, Hislop, 1998;Stevens et al, 2000).…”

Section: Discussionmentioning

confidence: 99%

Reproductive biology of the cockfish, Callorhinchus callorynchus (Chondrichthyes: Callorhinchidae), in coastal waters of the northern Argentinean Sea

et al. 2017

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The cockfish, Callorhinchus callorynchus, is a widely distributed holocephalan in the south-western Atlantic and an important resource for Argentinean fisheries. The reproductive characteristics of this species were studied in northern Argentinean coastal waters, where specimens arrive seasonally (winter-spring). Sexual dimorphism in maximum precaudal length (PCL) and total body mass (TM) was found, being females (PCL=630 mm; TM=3330 g; n=167) larger and heavier than males (PCL=482 mm; TM=1630 g; n=19). Maturity size for females was 466.22 mm PCL, representing 74% PCL of the largest female sampled. The mean number of ovarian follicles was 8.37 (± 4.84). The highest values of ovarian follicles diameter, gonadosomatic and oviducalsomatic indices were found in spring. A high proportion of mature females (44%) had atretic ovarian follicles, suggesting that they were in the resting stage of their reproductive cycle. The low number of mature males recorded and the absence of mature females with spermatophore masses or egg cases indicate that the study area would not be a reproductive zone. The seasonal presence of C. callorynchus in this region could be related to trophic movements. These results, obtained in an area with high fishing pressure on chondrichthyans, will be useful for implementing conservation and management measures.Keywords: Holocephalans, Maturity, Ovarian fecundity, Seasonality, South-western Atlantic.El pez gallo, Callorhinchus callorynchus, es un holocéfalo con amplia distribución en el Atlántico Sudoccidental y un recurso importante para las pesquerías en Argentina. Las características reproductivas de esta especie fueron estudiadas en aguas costeras al norte del Mar Argentino, adonde se acercan estacionalmente (invierno-primavera). Se observó dimorfismo sexual en los valores máximos de longitud precaudal (LPC) y masa corporal total (MT), siendo las hembras (LPC=630 mm; MT=3330 g; n=167) más grandes y pesadas que los machos (LPC=482 mm; MT=1630 g; n=19). La talla de maduración para las hembras fue de 466,22 mm LPC, representando el 74% de la LPC máxima observada. El número promedio de folículos ováricos fue 8,37 (± 4,84). Los valores más altos del diámetro de los folículos ováricos, índice de la glándula oviductal e índice gonadosomático fueron hallados durante primavera. Una gran proporción de hembras maduras (44%) presentaron folículos ováricos atrésicos, sugiriendo que se encontraban en la etapa de reposo de su ciclo reproductivo. El bajo número de machos maduros registrados y la ausencia de hembras maduras con espermatóforos o cápsulas de huevos indican que las aguas costeras del norte de Argentina no serían una zona reproductiva. La presencia de C. callorynchus en el área de estudio podría estar relacionada con movimientos tróficos. Los resultados, obtenidos en un área con una gran presión pesquera sobre los condrictios, serán útiles para implementar adecuados planes de manejo y conservación de esta especie.

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Section: Discussionmentioning

confidence: 99%

Reproductive biology of the cockfish, Callorhinchus callorynchus (Chondrichthyes: Callorhinchidae), in coastal waters of the northern Argentinean Sea

et al. 2017

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“…Skates are particularly challenging to identify and a lack of species composition monitoring has masked severe population declines (Brander 1981;Walker and Hislop 1998;Iglésias et al 2010). They are slow growing, late maturing fishes with a relatively low fecundity; a set of life history traits which renders them highly susceptible to over-exploitation (Dulvy and Reynolds 2002).…”

Section: Distinctiveness Of Raja Maderensismentioning

confidence: 99%

Resolving taxonomic uncertainty in vulnerable elasmobranchs: are the Madeira skate (Raja maderensis) and the thornback ray (Raja clavata) distinct species?

et al. 2016

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Skates and rays constitute the most speciose group of chondrichthyan fishes, yet are characterised by remarkable levels of morphological and ecological conservatism. They can be challenging to identify, which makes monitoring species compositions for fisheries management purposes problematic. Owing to their slow growth and low fecundity, skates are vulnerable to exploitation and species exhibiting endemism or limited ranges are considered to be the most at risk. The Madeira skate Raja maderensis is endemic and classified as 'Data Deficient' by the IUCN, yet its taxonomic distinctiveness from the morphologically similar and more wide-ranging thornback ray Raja clavata is unresolved. This study evaluated the sequence divergence of both the variable control region and cytochrome oxidase I 'DNA barcode' gene of the mitochondrial genome to elucidate the genetic differentiation of specimens identified as R. maderensis and R.clavata collected across much of their geographic ranges. Genetic evidence was insufficient to support the different species designations. However regardless of putative species identification, individuals occupying waters around the Azores and North African Seamounts represent an evolutionarily significant unit worthy of special consideration for conservation management.

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“…While this difference may not be biologically significant, the distinct parameters can be incorporated into the demographic models for the regional management plans. High levels of fishing mortality have been implicated in dramatic changes in the abundance, distribution and size composition of several skate species in other marine regions and can be perceptible in less than a decade of fishing (Walker and Hislop 1998;Agnew et al 2000). Although B. interrupta is currently not a targeted skate species, it is caught as bycatch and occasionally retained (Stevenson and Lewis 2010).…”

Section: Discussionmentioning

confidence: 99%

“…The tendency of elasmobranchs to mature relatively later and larger than teleosts is often used to explain why they may be more vulnerable to overfishing (Walker and Hislop 1998; Dulvy et al 2000;Dulvy and Reynolds 2002). While most teleosts begin to mature between 40 and 80% of their maximum size (Beverton and Holt 1959), elasmobranchs mature towards the higher end of this spectrum (Holden 1974), with skates maturing between 75 and 90% of their maximum TL (Ebert 2005;Gedamke et al 2005).…”

Section: Late Maturationmentioning

confidence: 99%

“…Owing to their prevalence as by-catch in groundfish fisheries and in directed fisheries, skates have become a taxon of concern. They are especially vulnerable to groundfish fisheries because of their generally large size and demersal life style (Walker and Hislop 1998;Ebert et al 2008aEbert et al , 2008b. The decline of some skate populations in recent decades, especially in the North Atlantic, has been attributed to fishing pressures (Walker and Hislop 1998;Frisk et al 2005).…”

Section: Introductionmentioning

confidence: 99%

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A comparison of reproductive parameters of the Bering skate, Bathyraja interrupta, from two Alaskan large marine ecosystems

Ainsley

Ebert

Cailliet

2011

Mar. Freshwater Res.

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Abstract. Estimates of size at maturity are crucial to fisheries stock assessments and may change spatially and temporally. This study directly compares life-history characteristics of a skate species in two large marine ecosystems in a region where there is both a directed fishery and considerable skate by-catch in other fisheries. The Bering skate, Bathyraja interrupta, is one of the most common skate species in Alaskan waters, occurring in two large marine ecosystems, the eastern Bering Sea (EBS) and the Gulf of Alaska (GOA), but little is known about its life history. Skates were sampled from both regions between 2004 and 2007. In the GOA, the size at maturity was estimated to be 69 cm total length (TL) for males and 71 cm TL for females, while in the EBS size at maturity was estimated as 70 cm and 72 cm TL for males and females, respectively. Median size at maturity differed by sex but not by region. Our results indicate that B. interrupta shows late maturity, typical of most skate species, suggesting that more detailed monitoring of skate populations and precautionary management is warranted as skate fisheries expand.

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Sensitive skates or resilient rays? Spatial and temporal shifts in ray species composition in the central and north-western North Sea between 1930 and the present day

Cited by 220 publications

References 17 publications

Reproductive biology of the cockfish, Callorhinchus callorynchus (Chondrichthyes: Callorhinchidae), in coastal waters of the northern Argentinean Sea

Reproductive biology of the cockfish, Callorhinchus callorynchus (Chondrichthyes: Callorhinchidae), in coastal waters of the northern Argentinean Sea

Resolving taxonomic uncertainty in vulnerable elasmobranchs: are the Madeira skate (Raja maderensis) and the thornback ray (Raja clavata) distinct species?

A comparison of reproductive parameters of the Bering skate, Bathyraja interrupta, from two Alaskan large marine ecosystems

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