Studies on Migratory Movements of the Prawn Penaeus kerathurus (Forskal, 1775) at Amvrakikos Gulf, Western Greece

Abstract

The prawn Penueus kerafhurus completes its life cycle in Amvrakikos Gulf. The reasons for not entering the open sea depend on the status of biotic and abiotic factors of the gulf. The migratory movements of the species in the gulf are described by a simple square model, in each corner of which, the wintering, spawning, nursery, and recruitment area exist. The wintering area is located below the 25m isobath and wintering period lasts from late December to late March. Spermatophores on females are observed throughout the year but the highest percentages between April and August. The spawning season begins late in spring and continues through the summer. The spawning area is located below the 10m isobath, mainly around 25m. The nursery area of Penaeus keruthurus is in shallow waters near river estuaries, and the temporal limits were determined to be between mid-summer and mid-autumn. Finally, the recruitment area is located near the nursery area, with recruitment taking place in autumn, while the major stock renewal is restricted to winter. ProblemThe term migration in the biological sense refers to the periodic movements of animals away from a region and their subsequent return to the same region.The ethology of migration can be determined by a combination of interspecific and environmental factors. These causative factors include a greater distributional range, a more constant food supply, and a suitable reproductive environment.More specifically, since the migration of prawns is a seasonal phenomenon (JENSEN, 1958;LINDER & ANDERSON, 1956;CAMPILLO, 1979), changes in the environmentwhich are associated with the different seasonscan be assumed to play an important role. These changes can involve length of day, temperature, salinity, food availability, and even lunar periodicity. U. S.

Reproductive biology of the prawn Melicertus kerathurus (Decapoda: Penaeidae) in Thermaikos Gulf (N. Aegean Sea)

“…Courtney et al (1995) proposed that the simplest and most logical alternative to using an index in reproductive studies would be to use a measure of mean ovary weight for speciWc size classes of females. In Thermaikos, high percentages of advanced (vitellogenic/ mature) ovaries (83-91 %) were recorded from May to July, in accordance with the results from Amvrakikos Gulf (June, 85 % in Klaoudatos et al 1992, or May, 80 % in Conides et al 2008, the Adriatic (June, 90 %) (Lumare et al 2011), Smyrni Bay (Türkmen and Yilmazyerli 2006) and Gulluk Bay (July, 80 %) (Türkmen et al 2007). In a recent study from Amvrakikos, mature females comprised 59-73 % of the female population in the period May-August, with a (Conides et al 2008).…”

“…Similar high percentages (60-100 %) of inseminated females appeared for shorter or longer periods in other areas: in Adriatic for 2 months (June-July) (Lumare et al 2011), in Cádiz for 3-4 months (June-July-September) (Rodríguez 1985), and in Cabès for 5 months (May-September) (Ben Meriem 1993). In contrast, in Amvrakikos Gulf, maximum insemination frequency seems to be signiWcantly lower (56 % in June) (Klaoudatos et al 1992) than in Thermaikos. High percentages of spermatophore insemination are recorded throughout the year for other closed thelycum species: Melicertus longistylus, elicertus latisulcatus (Courtney and Dredge 1988), Penaeus esculentus (Crocos 1987b), arsupenaeus japonicus (Minagawa et al 2000).…”

“…This may be due to the signiWcant diVerence in size frequency distribution, with signiWcantly smaller-sized individuals sampled in the second compared with the Wrst period (Kevrekidis and Thessalou-Legaki 2006). Klaoudatos et al (1992) and Ben Meriem (1999) reported that inseminated females are observed throughout the year.…”

“…In the light of the present Wndings, both medium-and large-sized spawners are Wshed by trawlers (open Wshing period: October to May) at the beginning and the end of the reproductive period. Catches are most proWtable in October at a depth < 50 m (Kevrekidis and Thessalou-Legaki 2006) and comprise new recruits and 1 + old females (Kevrekidis and Thessalou-Legaki 2011) close to CL 50 (present study), Heldt (1938) Gulf of Tunis (Mediterranean Sea) June-July to October-November Ben Mustafa (1967) Gulf of Gabès (Mediterranean Sea) June-July to early October Ben Meriem (1993) Gulf of Cádiz (Atlantic Ocean) May-September Rodríguez (1985) South Adriatic Sea Late May to mid August (June, July) Lumare et al (2011) Southeastern Mediterranean Sea April-October (May, August, September) Abdel Razek (1985) Smyrni Bay (Central Aegean Sea) April-September (May-July) Türkmen and Yilmazyerli (2006) Gulluk Bay (Southeastern Aegean Sea) May-October (May-July) Türkmen et al (2007) mvrakikos Gulf (Ionian Sea) May-August (May, August) Klaoudatos et al (1992) mvrakikos Gulf (Ionian Sea) Late April to late September (August) Conides et al (2008) Thermaikos Gulf (North Aegean Sea) Late April to mid-October (June, July) Present study while they are minimal in May due to reproductive migration inshore. Thus, an issue arises concerning the advent of each trawling season (October) and/or the allowable trawling depth/distance from the shore, in the same month, as it has been shown that the period of high catch rates is signiWcantly related to depth (Kevrekidis and Thessalou-Legaki 2006).…”

“…In Greece, information is only available from Amvrakikos Gulf (Ionian Sea) (Klaoudatos et al 1992;Conides et al 2008).…”