48 DECEMBER 2012 • WORLD AQUACULTURE • WWW.WAS.ORG At present we have achieved a good production of eggs, fry and juveniles, with an increasing number of broodstock (Table 1). Study of Reproductive Sites Spawning areas of carpione are characterized by the presence of gravel and cobbles free of mud, mainly located in proximity to river estuaries or recent landslides from mountains. Historical maps show the distribution of spawning areas, mainly located in the northwestern part of the lake for the winter reproductive period and in the southern part for the summer one (Fig. 4). The functionality and conservation status of reproductive sites was assessed during spring 2010 by direct and indirect measurements. Transects of the lake coast (24.5 km) were made with an underwater robotic camera operated at depths between 50 and 250 m. Sonar sensor measurements were conducted to investigate the geologic and stratigraphic profile of the lake floor. Gravel stratification was connected with weak streams, which might indicate functional reproductive sites. Indirect measurements were able to distinguish two morphological classes of spawning areas: submerged alluvial fans and coastal cliffs (Fig. 5) (Lunelli 2010). Reintroduction Techniques Stocking of high numbers of alevins in past decades did not lead to an effective increase in commercial harvest of carpione. In deep reproductive areas, reintroduction will be conducted by positioning Vibert boxes containing eyed eggs. Thereby, eggs also will be protected from predation by burbot Lota lota, a species introduced to Lake Garda around 1858. The species is a voracious predator on eggs and can reach great depths in the lake, as observed during underwater surveys. The Future of Carpione The production of elevated quantities of eggs, fry and juveniles indicate the promise of future ex situ multiplication and reintroduction of carpione. This represents an encouraging result, considering this is the first attempt to rear carpione. We are aware, however, that a viable hatchery strain of S. carpio should be reinforced repeatedly by wild spawners. This will be a major challenge in the future, given the scarcity of wild carpione. We observed good reproductive sites in our study and lake monitoring surveys showed a trophic condition ranging from oligotrophy to mesotrophy (Salmaso et al. 2009). Accordingly, these data allow us to hypothesize that the most severe threat factors, which led to the drastic decline of the carpione, are not related to environmental degradation but primarily to overfishing during spawning periods and competition of the carpione with introduced exotic fish species. Furthermore, the occurrence of wild fish prone to reproduction outside the fishing prohibition period highlights the inefficiency of fishing period restrictions. Finally the available information regarding the biology of S. carpio are based on only a few studies, in which few individuals were analyzed. As a consequence, many aspects have not yet been investigated. Traditional and innovative methodologies should be combined, such as radio tracking to study migration behavior, stomach content analysis to investigate food competition between the carpione and exotic fishes, and histological analysis of gonads to reveal details of reproductive biology. Unfortunately the small number of individuals caught in recent years has constrained new research endeavors. Hopefully our research efforts are not too late! FIGURE 4. A map from 1725 of reproductive sites in Lake Garda, Italy. TABLE 1. Available carpione at present. Stage Number of individuals Eggs/Fry 2012 100,000 Juveniles 2011 15,000 Broodstock 2008-2010 400
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