Population structure and reproduction of the deep-water shrimp Plesionika martia (Decapoda: Pandalidae) from the eastern Ionian Sea

The population dynamics, growth, and reproduction of the deep-water pandalid shrimp Plesionika martia were studied in the eastern Mediterranean Sea. Samples were collected monthly (July 1999-June 2000) at a depth range of 440-600 m between Zakynthos Island and Peloponnissos (eastern Ionian Sea, Greece). Additional samples were taken in April and May 2001. Size-frequency distribution revealed that mean female size consistently exceeded that of males throughout the year (CL range: 8-23.5 mm and 9.3-29.1 mm for males and females, respectively). Smaller individuals of both sexes occurred only at depths less than 500 m. Mean size of both sexes increased linearly with depth, whereas a less prominent trend of sex ratio in favor of females by depth was observed. The overall yearly and the monthly sex ratio were in favor of females except during winter, when the two sexes were equally represented. Carapace length-wet weight relationships showed negative allometry, for both males and females. Ovigerous females occurred year around, although the main reproductive season extended from April to October. The smallest ovigerous female was 11.8 mm CL, whereas the size at 50% sexual maturity (CLm50) was estimated as 16.16 mm. Fecundity and reproductive output were found loosely related to shrimp size. The von Bertalanffy growth curve parameters were estimated as: L? = 30.6 mm, k = 0.31 year-1 in females and L? = 28.2 mm, k = 0.53 year-1 in males. Regarding the major life history traits, P. martia from the eastern Ionian seemed to conform to those in other Mediterranean areas. Nevertheless, some population differences exist, which can be related to the oligotrophic conditions and the lack of fishing pressure in the studied area.