12th Panhellenic Symposium of Oceanography & Fisheries, Corfu, Greece 2018 POPULATION DYNAMICS OF THE STRIPED SOLDIER SHRIMP PLESIONIKA EDWARDSII (DECAPODA, PANDALIDAE) IN THE S.E. AEGEAN SEA. Pantazi V1,2, Megalofonou P2, Kalogirou S1, Kapiris K1 1Institute 2 Faculty of Marine Biological Resources and Inland Waters, HCMR, Greece, skalogirou@hcmr.gr, kkapir@hcmr.gr of Biology, Department of Zoology-Marine Biology, University of Athens, Greece, vyropan@gmail.com, pmegalo@biol.uoa.gr Key words: growth, mortality, population structure, Plesionika edwardsii, Aegean Sea Introduction/Aim: Plesionika edwardsii (Brandt, 1851) (striped soldier shrimp) is a cosmopolitan, nektobenthic crustacean with wide geographic distribution presenting local commercial interest. In the eastern Mediterranean Sea, P. edwardsii occurs sporadically in the catch of trawlers on the continental slope concurrently with other commercial crustaceans. There is a great information gap on the biology of this decapod related to scarce and sporadic studies. This is the first work contributing to the study of the population dynamics of this decapod in this area. The aim of this work is to describe growth, age structure, and mortality rate of P. edwardsii in the southeastern (SE) Aegean Sea providing additional information for this species in the literature. Methods: Data on the population biology (age, growth, mortality) were monthly collected during November 2014 to October 2015 with baited shrimp traps (mesh size of 12 mm, knot to knot) in the SE Aegean Sea. The specimens were caught from a depth range of 60 to 280 m depth. In total, 1907 specimens were analyzed (1507 females, 400 males). Bhattacharya’s method (FiSAT package), was used to identify the modes in its polymodal length-frequency distributions. The estimation of the von Bertalanffy growth parameters were estimated for each sex using FISAT program. The growth performance index (φ’) per sex was also estimated. The total instantaneous mortality (Z) and the natural mortality (M) per sex were calculated using various methods (Hoening, Djabali, Gunderson & Digert). More year classes were estimated for females than for males. The implementation of FiSAT determined 1-3 modal groups for females with satisfactory separation indices (S.I.) and with mean length ranging from 12,36 mm (March) to 24,58 mm (May). The estimated modal lengths of males ranged from 13,01 to 23,16 mm presenting also satisfactory S.I. values. The growth performance index φ’ of P. edwardsii in the study area was 2,677 for females and 2,639 for males. Estimated asymptotic carapace length (CL∞) and growth coefficient (K) showed higher values in females (CL∞=32,50 mm, K=0,45 year-1) comparatively to males (CL∞=29,50 mm, K=0,50 year-1), resulting in better overall growth performance in females. The maximum life span (tmax) was estimated at 6,66 years for females and 6 years for males. Natural mortality (M) values were 0,497 for females and 0,539 for males. This size difference between the two sexes is evident in all the modes, corroborating the view that the males are characterised by a lower growth rate. This slower growth pattern of males is also proved from the growth estimated parameters (lower L∞, higher K, and smaller φ’). Fishing mortality (F) was 0,153 for females and 0,181 for males. Total instantaneous mortality (Z) (M+F=Z) was 0,72 for females and 0,65 for males Main Conclusions: The growth parameters are similar to other studies and the mortality values are similar between sexes. Size difference was evident between the two sexes in all the modal groups, accompanied by a lower growth performance φ’for males. -41-