Population structure, recruitment, and mortality of the freshwater crabDilocarcinus pageiStimpson, 1861 (Brachyura, Trichodactylidae) in Southeastern Brazil

Abstract

Freshwater crabs of the family Trichodactylidae are widely distributed in major river basins of the South American continent. The population structure of one species, Dilocarcinus pagei, was analyzed in an artificial reservoir in Southeastern Brazil, recording data on the sex ratio, recruitment, and mortality. A total of 1339 crabs were collected and included 804 males and 535 females (3 ovigerous and 4 with hatchlings); the sex ratio was 1:0.61 (males: females). Two modes of male and female carapace width (CW) were recorded, with means of 14.4 mm (n = 407) and 38.9 mm (n = 394) for males and 17.9 mm CW (n = 269) and 39.2 mm (n = 267) for females. The mean size of males (CW = 26.6 ± 13.8 mm) was significantly larger than that of females (CW = 28.5 ± 12.8 mm). The data indicated that recruitment occurs in summer (January-March), with the reproductive period in spring (October-December), periods with the highest rainfall and temperature values in the region. Reproduction leads to the death of the parents, influencing the sex ratio, which oscillates mainly during the reproductive period.

Population structure, mortality, and recruitment of Macrobrachium amazonicum (Heller, 1862) (Caridea: Palaemonidae) in the eastern Amazon region, Brazil

“…The reproductive period was characterized by the breakdown of the monthly frequency modes of ovigerous females (Davanso et al, 2013;Taddei et al, 2015;Pescinelli et al, 2016) using FISAT II (Gayanilo et al, 2005), which determined the magnitude of reproductive pulses, which were then compared to the periods of recruitment. The sex ratio was calculated using the chi-square test (χ 2 ) with a significance level of 5% (Sokal & Rolph, 1995), which measured deviation from the expected 1.0 male:1.0 female for the total number of individuals in each size class and each month.…”

“…The absence of previous studies on mortality in palaemonids and other groups of freshwater shrimps makes it difficult to speculate on the subject. Compared with the freshwater crab Dilocarcinus pagei Stimpson, 1861(Taddei et al, 2015, M. amazonicum exhibited Figure 6. Histograms of the monthly size-class distribution (carapace length) of females of Macrobrachium amazonicum captured from March 2013 to February 2014; without eggs in white, and ovigerous females in gray.…”

“…Downloaded from https://academic.oup.com/jcb/article-abstract/37/2/131/3089767 by Universidade Estadual Paulista J�lio de Mesquita Filho user on 24 June 2019 higher values for M (1.41/year) and Z (1.133/year), even considering that parental crabs die after the annual reproductive cycle of that species (Taddei et al, 2015). The high mortality rate of M. amazonicum may be related to the greater abundance and density of the shrimp relative to the crab, which increases competition among individuals and leads to higher mortality values.…”

“…Much information is still needed for a better understanding of the biology of freshwater decapods. Notable topics for future studies include identifying characteristics that differentiate among populations in various environments (Nóbrega et al, 2014), determining whether reproduction is continuous or restricted to a time of year; genetic characteristics (Vergamini et al, 2011), maximum size for each sex, sex ratio, the size at which reproduction begins (Castilho et al, 2015), and recruitment and mortality patterns (Taddei et al, 2015). The data obtained in these studies serve as a basis for determining the minimum landing size, known as the size in the closed season, as well as making it possible to evaluate the somatic growth of individuals, all of which is essential information for cultivation and population management projects (Reis et al, 2015).…”

Length/weight relationship and condition factor of Macrobrachium jelskii (Miers, 1877) and M. brasiliense (Heller, 1862) (Decapoda, Palaemonidae) in two locations in the state of São Paulo

“…Analyses of crustacean growth (Davanso et al, 2013;Taddei et al, 2015) showed that individuals with the highest growth rate reach the smaller maximum size, as evidenced by the equation that estimates these variables (see Bertalanffy, 1938).…”