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Extracted from:
Fish Farms at Sea: The Ground Truth from Google Earth
Pablo Trujillo*, Chiara Piroddi, Jennifer Jacquet
Fisheries Centre, University of British Columbia, Vancouver, British Columbia, Canada 

In the face of global overfishing of wild-caught seafood, ocean fish farming has augmented the supply of fresh fish to western markets and become one of the fastest growing global industries.   

Due to extensive and expanding overfishing of wild-caught seafood [3,4], ocean fish farming has grown to augment the supply of fresh fish to western markets. Indeed, it is one of the fastest growing global industries [5]. The accuracy of available data for farmed fish is important to gauge the magnitude and growth of this industry, its role in feeding global seafood demand, and also for determining the industry’s impact on small pelagic fish because farmed fish currently require large quantities of wild fish for fishmeal and oil [6].

Ocean fish farming began in the Mediterranean in the early 1980s and is now widespread. Stationary cages speckle the coasts of 16 Mediterranean countries and are visible from satellite imagery available through Google Earth (Figure 1) which we used to estimate the farmed fish production in the Mediterranean Sea, which we compare to data on farmed fish production provided by each Mediterranean country provided to the FAO, the organization mandated to collect data for capture fisheries and farmed fish production, in 2006.

Figure 1: Mediterranean coast with assigned place mark to each aggregation of fish cages (sub-sample of original study). View in a larger map


Of the entire Mediterranean coast, Google Earth satellite images were available for 91% of the Mediterranean shores.  We identified and counted 248 tuna cages (circular cages > 40 m diameter [11] and 20,976 other fish cages (Figure 1) within 10 km offshore, the majority of which were off Greece (49%) and Turkey (31%).  Around 80% of cages are located within 1 km of shore (Table 1).

Table 1: Number of cages, closest and furthest cage to shore, average area per cage, and the various assumptions used to estimate finfish production for each Mediterranean country.  We provide three different estimates of finfish production based on different assumptions about the percentage of cages (50, 75, 100) that are fully operational.  The final column provides the reported finfish production to FAO in 2006 by country.

Table 1

[Download the full paper here]

(numbering follows the original paper)

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