Abstract
The life history (age and growth and reproduction) parameters of 35 species (41 stocks) of skates and rays were analyzed using multivariate analyses. Three groups were categorized by cluster analysis (CA) based on principal component scores. Empirical equation was developed for each group to describe the relationships between the predicted a finite rate of population increase (λ′) and the life history parameters: growth coefficient (k), asymptotic length (L∞), age at maturity (Tm), annual fecundity (f/Rc), ratio between size at birth (Lb), and L∞ (Lb/L∞), and ratio between size at maturity (Lm) and L∞ (Lm/L∞). Group 1 included species with slow growth rates (k < 0.011 year–1), early maturity (Lm/L∞ < 0.62), and extended longevity (Tmax > 25 years); Group 2 included species with intermediate growth rates (0.080 year–1 < k < 0.190 year–1), intermediate longevity (17 years < Tmax < 35 years), and late maturity (Lm/L∞ > 0.60); Group 3 included species with a fast growth rate (k > 0.160 year–1), short longevity (Tmax < 23 years), and large size at birth (Lb/L∞ > 0.18). The λ′ values estimated by these empirical equations showed good agreement with those calculated using conventional demographic analysis, suggesting that this approach can be applied in the implementation of management measures for data-limited skates and rays in a precautionary manner.
Highlights
Many batoids, similar to sharks, have the life history characteristics of slow growth, late maturity, and low numbers of offspring (Ebert and Sulikowski, 2009)
The fecundity of aplacental viviparous stocks ranged from 5 for the southern fiddle ray Trygonorrhina fasciata (Marshall et al, 2007) to 17 for the Pacific electric ray (Neer and Cailliet, 2001). Among those 18 stocks where their gestation periods have been documented, 15 stocks have 1-year gestation period, the Pacific electric ray has 2.5-year gestation period (Neer and Cailliet, 2001), and the diamond stingray and round stingray have 0.5-year gestation period (Babel, 1967; Hemida et al, 2003) (Supplementary Table 1). For those species without gestation period information, gestation period or reproductive cycle (Rc) was estimated using the value from similar species or assumed to be 1 year
The empirical equations based on life history parameters of 41 skate and ray stocks were developed to estimate population increase rates in this study
Summary
Similar to sharks, have the life history characteristics of slow growth, late maturity, and low numbers of offspring (Ebert and Sulikowski, 2009). Excluding manta rays and butterfly rays, most skates and rays inhabit coastal demersal waters and play an important role in the demersal ecosystem (Ebert and Bizzarro, 2007). These skates and rays are vulnerable to anthropogenic pressure and may decline or collapse after experiencing heavy fishing pressure (Hoff and Musick, 1990; Musick, 1999). The global landings of skates and rays reported to the United Nations Food and Agriculture Organization (FAO) declined almost 20% from 2003 to 2012 (Davidson et al, 2016). With the increase in skate and ray catches, it is necessary to
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