Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment

Estimation of Bay of Famagusta Fish Stock Based on Recorded Catch of Trawl Fishing

Ata Atun, Deniz Ünsalan


Although the fish stocks of coastal sea areas are a subject of discussion in everyday life, there is not a wealth of quantitative information on fish stocks of coastal fishing areas. To estimate the fish stock of the Bay of Famagusta on the eastern shore of North Cyprus, the recorded daily catches of trawl fishers were used from 1989 to 1995. Fishing season spanned a period from September to May each year (270 d total, of which around 85 d are suitable for trawling). Systematic observations have indicated that 65 distinct species existed in the waters fished (Atun 1999); this indication was verified by research performed by the Dokuz Eylül University of Turkey (Cihangir et al. 2002).

A geometrical-statistical approach was used to estimate the fish stock of selected species. The sampling area was 50–100 m deep; the shallower limit is enforced by the Coast Guard and the upper limit set by the technical restrictions of the trawling gear used. The results obtained for the depth range of trawling were extended to cover the entire depth range where the species lived, assuming that the probability of a fish to be at a given depth is uniformly distributed. The fish stock was estimated on a weight basis, which can be extended to determine the number of fish in the area in question.

It should be stressed that in this research, the term fish refers to marine animal forms of commercial value, not to fishes in the biological sense. Brown shrimp Crangon vulgaris, octopus Vulgaris spp., cuttlefish Sepia officinalis, and Southern short-fin squid Illex coindeti are all referred to as “fish” in this paper.

A trawl arrangement with two doors 40 m apart (laterally) and a horizontal net entrance width of 15 m were used. The distance between the doors and the net entrance was 120 m in the trawling direction. The trawl net mouth opening was nominally 2.20 m high, providing sufficient area to catch bottom fish. The trawl net openings were 24 mm × 24 mm, also enforced by the Coast Guard. The trawling gear is illustrated in Figure 1.

The area trawled was between the isobaths of 50 m and 100 m, between the coordinates of 35°04′30″N to 35°17′24″N and 33°53′24″E to 34°00′00″E (Figure 2). The total area swept corresponded to about 8 square nautical miles (27.44 km2). For each sweep, a straight strip 15 m wide was swept on the sea bottom, between the 50- and 100m isobath lines. The fish caught represented roughly 30% of the fish population of that strip. Trawling is assumed to be performed at a nominal speed between 2.0 and 2.5 knots.

The cross section of the seabed and the isobath lines were very uniform, as illustrated in Figure 3.
The estimated fish distribution was based on the fact that swept area was the most populated area according to fishers’ past experience, but not the whole range allowed by the Coast Guard (Figure 4). Depending on the season and randomly occurring underwater currents, the fishers usually fish within 100 m of the same spot for the best catch.

The sweeping volume consisted of a cubic shape, as illustrated in Figure 5.