Sex ratio, growth and recruitment of the pelagic shrimp Acetes americanus on the southeastern coast of Brazil

Abstract

We evaluated the population dynamics of Acetes americanus Ortmann, 1893 focusing on sex ratio, individual growth, longevity, and the juvenile recruitment period. Samples were collected monthly from January 2006 to June 2007 in the bay of Ubatuba, Brazil. Specimen growth was identified for each gender, and the chosen cohorts were fitted in a von Bertalanffy Growth Model (VBGM); longevity was estimated by the von Bertalanffy inverse equation, considering 99% of the asymptotic length. A total of 6881 individuals (2343 males and 4538 females) were captured. On average the body size (total length) was greater in females (14.64 ± 3.34 mm) than in males (12.27 ± 1.86 mm). The mean growth curves (obtained by grouping the cohorts for each sex), provided estimates of TL ∞ = 19.33 mm, k = 0.02 and t 0 = −0.12 days for females and TL ∞ = 15.13 mm, k = 0.03 and t 0 = −0.07 days for males, where TL ∞ is the asymptotic length, k is coefficient of growth and t 0 is the theorical age when the size is equal to 0. Longevity was estimated at 0.61 years for females and 0.50 years for males. The sex ratio tended to favor females, which corroborates with others studies of sergestids. Our finding that males of A. americanus have higher values of k and therefore achieve a smaller size relative to females has been observed in other penaeids. We concluded that this differential growth pattern between the sexes is found across Dendrobranchiata. The life cycles of penaeids have an average duration of approximately 1-2 years, but our results corroborate other studies that estimate a shorter longevity for Acetes, as species of this genus are typically smaller in size. We found continuous recruitment with two main peaks observed during the study period, corroborating previous studies of Acetes.

Population parameters and the relationships between environmental factors and abundance of the Acetes americanus shrimp (Dendrobranchiata: Sergestidae) near a coastal upwelling region of Brazil

“…JOHNSON (2003), however, has suggested that many factors (differential growth rate, differential reduction of gametes, and differential mortality between sexes) may influence the sex ratio balance. In addition, the results found in the present study support the hypothesis suggested by SIMÕES et al (2013a), which correlates the less frequent capture of males with their greater growth constant (k), thus resulting in smaller specimens that are less susceptible to being caught.…”

“…The relatively greater length of A. americanus females has been corroborated by other studies on Acetes species (Table 4), which argues for the existence of a standard of sexual dimorphism in terms of size JEONG, 2003;ARSHAD et al, 2008;AMIN et al, 2009a;AMIN et al, 2012;SIMÕES et al, 2013a). In studies on other At a depth of 15 m, the average temperature was 20.7 ± 1.8º C, with a variation from 18.0º C to 24.5º C; salinity varied from 35.0‰ to 38.0‰, with an average level of 36.9 ± 0.8‰.…”

“…The growth parameters of the different cohorts were estimated using the "Solver" tool and by varying the equation parameters (TL∞, k and t0). The criteria used to validate a cohort were the biological coherence with the life cycle of the species (the coherent estimate of longevity based on the duration of a cohort in time and growth parameter values suggested in the literature) (SIMÕES et al, 2013a). A comparison of the growth curves was performed using an F test (p = 0.05), according to CERRATO (1990).…”

“…Little is known of the biology of A. americanus, and the studies that have been performed in Brazil have focused on faunal composition, descriptions of the larvae, and geographical distribution (CALAZANS, 1992;OSHIRO;OMORI, 1996;MARTINS, 2000). SIMÕES et al (2013a;2013b) undertook two studies on the spatio-temporal distribution, juvenile recruitment period, and growth of the species along the northern coast of São Paulo state. The greatest abundance of A. americanus was observed in shallow waters less than 10 meters deep, at temperatures between 16.0 and 30.0º C, and in waters with salinity levels between 22.0% and 38.0%.…”

“…The greatest abundance of A. americanus was observed in shallow waters less than 10 meters deep, at temperatures between 16.0 and 30.0º C, and in waters with salinity levels between 22.0% and 38.0%. Species longevity was estimated to be 0.61 years for females and 0.50 years for males (SIMÕES et al, 2013a;2013b).…”