Abstract
AbstractDrastic increases or decreases in biomass often result in density‐dependent changes in life history characteristics within a fish population. Acknowledging this phenomenon and in light of the recent biomass increase in Barndoor Skate Dipturus laevis, the current study re‐evaluated the growth rate and sexual maturity of 244 specimens collected from 2009–2011within closed areas I and II on Georges Bank, USA. Ages were estimated using vertebral band counts from skate that ranged from 21 to 129 cm TL. The von Bertalanffy growth function was applied to pooled age‐at‐length data. Parameter estimates from the current study of L∞ = 155 cm TL and k = 0.10 represent a significant decrease from previously reported parameters of L∞ = 167 cm TL and k = 0.14. In addition to changes in growth parameters, age at 50% maturity for both males (based on clasper length, testes mass, and percent mature spermatocytes) and females (based on data from shell gland mass, ovary mass, and follicle diameter) increased by 3 years and 4 years, respectively. Based on our results and the 10‐ to 12‐year gap in the collection of samples, it is likely that Barndoor Skate within this region have exhibited pliability in life history parameters.Received January 21, 2013; accepted July 9, 2013
Highlights
Batoids within the family Rajidae are thought to comprise at least 22% of the fishes within the subclass Elasmobranchii (Ebert and Compagno 2007)
In the United States portion of the northwest Atlantic Ocean, the Northeast Skate Complex (NESC) consists of seven species, five of which occur in the Gulf of Maine (GOM) and southern New England: the Winter Skate Leucoraja ocellata, Barndoor Skate D. laevis, Thorny Skate Amblyraja radiata, Smooth Skate Malacoraja senta, and the Little Skate L. erinacea (McEachran 2002; NEFMC 2007)
Many factors may have contributed to the decline of the Barndoor Skate population, it has been hypothesized that both direct and indirect fishing pressure played a significant role reducing the biomass of this species (Casey and Myers 1998; Gedamke et al 2005; NEFMC 2007)
Summary
Batoids within the family Rajidae are thought to comprise at least 22% of the fishes within the subclass Elasmobranchii (Ebert and Compagno 2007) Like their cartilaginous relatives (sharks and rays), skate exhibit an equilibrium life history strategy (i.e., late sexual maturation, low fecundity), which makes them vulnerable to direct and indirect fishing pressure (e.g., Hoenig and Gruber 1990; Winemiller and Rose 1992; Sulikowski et al 2003, 2007). An increasing population with an elevated density can respond with a reduced growth rate and increasing age and size at maturity (Rose et al 2001) Such density-dependent changes have been widely documented in teleost fishes, they have been observed in only a few exploited shark species and never documented in a batoid (Sminkey and Music 1995; Carlson and Baremore 2003; Sosebee 2005). The objectives of the current study were to re-evaluate age, growth, and maturity of the Barndoor Skate and determine whether compensatory changes in these life history parameters have occurred within the sampled population
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