Using biological variables and reproductive strategy of the undulate ray Raja undulata to evaluate productivity and susceptibility to exploitation

Abstract

The present work provides a detailed analysis of the reproductive strategy of the undulate ray Raja undulata in Portuguese mainland waters. The species was found mostly between 30 and 40 m deep on sandy bottoms. Egg-laying sites were observed in the north, centre and south-west regions, mainly at depths below 30 m. The peak of the reproductive season occurred from December to May. Asynchrony between reproductively active females and males appeared to occur, although most adult males were capable of reproducing throughout the year. The estimated length at 50% maturity was 86·2 cm (8·7 years) and 76·8 cm (7·6 years) total length for females and males, respectively. The maximum potential fecundity was estimated to be 69·8 follicles per female per reproductive season, which are released in 4·7 batches of 15 follicles. The life-history and demographic parameters of R. undulata are similar to those of other skate species, while the potential rate of population increase (0·49) is above the published values for other elasmobranch species. With these new findings, this study makes an important contribution to the understanding of the life history of R. undulata, and provides a first evaluation of the productivity and susceptibility of the species to exploitation.

Reproductive biology of the Alaska skate Bathyraja parmifera, with comments on an intersexual individual

“…The nature of the relationship between maternal size and the number or size of vitellogenic oocytes in oviparous elasmobranchs appears to be species specific. Some studies have reported no significant effect of maternal size on reproductive output (Perez-Brazen et al, 2014;Serra-Pereira et al, 2015), while others have reported trends similar to those observed in B. parmifera (Ainsley et al, 2011;Haas, 2011). While these relationships tend to be weak and highly variable, they may be still be useful information for fisheries managers, potentially with extra protection afforded to larger, more productive females.…”

“…The nature of the relationship between maternal size and the number or size of vitellogenic oocytes in oviparous elasmobranchs appears to be species specific. Some studies have reported no significant effect of maternal size on reproductive output (Perez‐Brazen et al , ; Serra‐Pereira et al , ), while others have reported trends similar to those observed in B . parmifera (Ainsley et al , ; Haas, ).…”

“…Examination of Fig. (a) also suggests that misclassification of resting females as maturing did not occur, as shell glands would be expected to regress in size during the resting phase (Serra‐Pereira et al , ).…”

Distribution and life history trait models indicate vulnerability of skates

“…Ellis et al, 2012Ellis et al, , 2004Serra-Pereira et al, 2014;Walker et al, 1997). Reproduction of R. undulata is supposed to occur between winter and spring, with egg-laying occurring shortly after (Moura et al, 2007;Serra-Pereira et al, 2015). Whereas, the reproductive strategy for R. clavata and R. montagui is supposed to peak in summer (Koop, 2005;Serra-Pereira et al, 2011).…”

“…The three skates were additionally divided according to two size classes: juveniles (<=25 cm; equation 7), and mature (>=80 cm for R. undulata, >=75 cm for R. clavata and >=65 cm for R. montagui; equations 8 to 10), to investigate potential essential skate habitat. The size classes were based upon density frequency plots and existing literature(Coelho and Erzini, 2006;Ellis et al, 2012;Koop, 2005;McCully et al, 2012;Serra-Pereira et al, 2015. Presence absence models by sex were also explored (equations 11 to 16).…”