Untitled - CNR

Fishery and Sea Resourcesspecies more fishing by principal Sicilianfleet (Mazara del Vallo and Sciacca) intolast years [1].These resources undergo wide interannualbiomass fluctuation mainly due to environmentalvariability effects on the recruitment.In recent decades, the refinementof knowledge on growth and developmentof fish oocytes [2] and reproductive biology[3] permitted more precise definitionsof fish fecundity. The Daily Egg ProductionMethod (DEPM) was developed in thelate 1970s by the Coastal Division of theSouthwest Fisheries Center, La Jolla, CA,USA [4] as a response to the growing needto devise a suitable direct method for theassessment of northern anchovy (Engraulismordax), an indeterminate spawner withpelagic eggs [3]. The DEPM is based onthe number of oocytes released per fishin each spawning event (batch fecundity)and the proportion of females reproducingdaily (spawning fraction). Estimationof spawning fraction for anchovy is possiblebecause of the identification of Post-Ovulatory Follicles (POFs).The POFs represent cellular residuals inovary reabsorbing after deposition [3] andthe resorption time is species specific andchanges accordingly to the residence temperature.In literature most studies whichreport anchovy POF duration vs. temperaturewere performed within different temperatureranges but under 22°C [5, 6, 7]. InMediterranean Sea, especially during summerseason when anchovy spawning takesplace, the SST reaches 28°C and the watercolumn temperature 24°C.The official methodology foresee to calculatethe spawning fraction by means ofPOFs 24 hours old (POF 0), but these aregenerally overrepresented in the samples,so Piquelle and Stauffer [8] suggest to replacePOF 0 with an average of POF1 +POF2. So far, the POFs aging and S estimatemethods used in Mediterranean wasthe same produced for lower temperature,but recent studies show a most rapid resorptionat Sicilian temperatures than inAtlantic water [9]. In the Strait of Sicilyboth POF 0 and POF 1 are in one day.An overestimation of the POFs durationleads to an underestimation of S and consequentlyan overestimation of B. It wasdeemed appropriate to reconsider previousestimates of biomass and spawning fraction,because only the POFs of first day(24h) after spawning should be used to estimatethe spawning fraction. The evaluations,obtained by old and new method ofPOFs aging, were compared and they wereshowed significant differences. These resultscannot be neglected to the stock sustainablemanagement.2 Materials and methods.Anchovy adults specimens were caughtduring the peak spawning season (June andAugust) in the Strait of Sicily (Figure 1),from 1998 to 2006 (in a non-continuous),aboard a research vessel equipped toDEPM surveys. During the catches, thewater temperature was measured by a CTDprobe. In 2005, the sampling was increasedby specimens from commercial vessels.The ovaries were preserved in buffer formalinat 4% and analysed by traditionalhistological techniques and Haematoxylinand Eosin Method for colouring. Sexualmaturity stages (ICES 2004, modified byauthors) and presence and age (POF 0, 1and 2; Figure 2) of post-ovulatory follicleswere estimated for each ovaries. For 2005and 2006, the histological sections wereobserved twice: according to new findingsabout the POFs duration in the Mediter-2116