Catching methods for capture-based aquaculture

Young greater amberjack (25-100 g) are captured from the end of August to the beginning of October-December in the Mediterranean (Andaloro, Potoschi and Porrello 1992; Lazzari and Barbera 1989a,b; Potoschi et al. 1999) by using fish aggregating devices (FADs) made from leaves and branches called “ramos” or “catces”, to which they are attracted (Grau 1992; Greco et al.

1991). Flotsam and FADs are used by fishermen to improve pelagic and demersal fish catches, mainly in the central and western Mediterranean basin (Massuti and Morales-Nin 1991, 1995). Oceanic and coastal FADs minimize both searching time and operating costs for fishing vessels. While the traditional FADs in Mediterranean have undergone little modification, both their design and durability has been improved in the United States (Raymond, Itano and Buckley 1989).
In Sicily, traditional FADs are built with vegetal material and their use is linked exclusively to the availability of economically important species, e.g. greater amberjack (Potoschi and Sturiale 1996). Before reaching the FAD area, juveniles aggregate under floating objects such as flotsam and vegetal matter. These objects have been seen to play an important role in the diffusion and transport of young fish towards coastal areas (Druce and Kingsford 1995). A typical example of the capture of greater amberjack juveniles is seen in the Castellammare Gulf (Sicily region, Italy): from July to December, several hundred FADs, built with palm leaves (covering approximately

2 m2), or with green canes (covering 4-5 m2) (Mazzola et al. 1993; D’Anna, Badalamenti and Raggio 1999; Piscitelli et al. 2001). These are positioned to float in the Gulf, and are anchored with a rope to a ballast weighing 30-40 kg. They are set along transects extending perpendicularly to the coast for several kilometres. The transects extend from shallow (<15 m) coastal waters offshore to depths of about 500 m. The same method is used in several other areas of Sicily for catching wild juveniles for rearing in open sea cages (Badalamenti et al. 1998). Near these FADs, named “cannizzu” (pronounced “ca-nni-tzu”), fishermen use simple purse seines for catching greater amberjack juveniles. When these hover underneath FADs, they gain a number of advantages. For example, they are able to save energy because the floating structures are anchored to the sea bottom and there is thus no need for the fish to swim, but only to hover, in order to catch prey. Furthermore, staying in the shade means that predators cannot see the juveniles while the juveniles themselves can spot their prey more easily. Their twilight feeding activity also facilitates prey location (Badalamenti et al. 1995, 1998).
Juveniles are captured in the Aeolian Islands under drifting flotsam and, to improve catch rates, artificial wreckage made up of twisted cane mats, moored to the bottom are used; small manual purse seines (20 mm mesh) are made specifically for catching greater amberjack by these FADs (Porrello et al. 1993). Wild juveniles (30-50 g or 80-100 g) are caught with a purse seine net set around FADs in Spain, during August to October. These are then reared in floating cages, reaching about 1 kg by the following June (Crespo et al. 1994; Nash 1995). However, production of farmed greater amberjack at a commercial level in Spain stopped in 1999, but it is still cultured on a limited scale in seabass/seabream farms there, to test its feasibility and market potential.
Greater amberjack are also an important fish in aquaculture in Taiwan Province of China. There, juveniles again aggregate under FADs and are caught by a small seine net for environmental survey purposes (Liu 1985, 2001).
The techniques used for capturing Japanese amberjack (S. quinqueradiata) are similar to those employed for S. dumerili and S. lalandi. “Mojako” of 2-10 g are caught under drifting Sargasso seaweed with a circular net from fishing boats, round haul-nets or hand-nets from April to June, and then transported to collection sites. The total catch is higher along the Pacific coast than in the Sea of Japan. The smallest size of fish associating with FADs in Japanese amberjack is 12 mm TL; at this length, they show mutual attraction and soon form shoals around flotsam or other floating objects (Hong Seong et al. 1997; Masuda and Tsukamoto 1999).
¦ Transfer of juveniles from fishing to on-growing facilities
The practice in Italy is to catch greater amberjack juveniles and to transfer them within PVC tanks placed on board fishing vessels with open water re-circulation and oxygenation systems, and sometimes with temperature regulators (Greco et al. 1991, 1992; Caridi et al. 1992). The optimum density for juvenile transport has been calculated to be 2 kg/m3 (Caridi et al. 1992). In some cases mortality from handling stress has been reported, ranging from 1.5% to 2% (Greco et al. 1991; Porrello et al. 1993) and 5-6% (Lazzari and Barbera 1989a). The capture and transportation of S. dumerili juveniles to cages in general (Mazzola, Mirto and Danovaro 2000) caused negligible mortalities, proof of the species “hardiness”.
In Japan, wild juveniles are weaned onto prepared feed after capture, and weak individuals are removed. They are then sold to producers who put them into net cages. Small juvenile Japanese amberjack and related species are sensitive to feed deprivation. If a fishing boat catches “mojako” far away from port the fish will become cannibalistic in the holding tanks. Yellowtail fry (25-40 mm in length) are kept in onboard storage tanks until return to port. If the fish do not receive feed for more than three days, the “mojako” fail to adapt to the prepared feed. It has been shown that a prolonged fasting period, before first feeding in net pens, will significantly affect growth rates later in the culture period. If a good quality prepared feed is accepted while the fish are on the collecting boat, the problem can be overcome (Nakada 2000).