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Marine Turtle Newsletter 53:14-16, © 1991

Turtles Caught Incidental to Demersal Finfish Fishery in Oman

Steven R. Hare
School of Fisheries (WH-10), University of Washington, Seattle, Washington 98195 USA

The coastline and offshore waters of Oman serve as major nesting and foraging locations for several species of sea turtles, including green turtles (Chelonia mydas), hawksbills (Eretmochelys imbricata), loggerheads (Caretta caretta), and olive ridleys (Lepidochelys olivacea) (Ross and Barwani 1979). As such, the incidental catch of sea turtles is an issue of great concern in Oman. In January 1989, the Oman Marine Science and Fisheries Center's "On Board Data Collection Program" (DC Program) was established for the purpose of providing detailed temporal and spatial analyses of demersal trawler catches in Oman's Exclusive Economic Zone. This Program also provided important data on the extent to which sea turtles are incidentally captured by trawlers operating in Omani waters.

The DC Program was patterned largely after the U. S. National Marine Fisheries Service's Foreign and Domestic Fisheries Observer Programs operated in the northeast Pacific Ocean. A corps of 10 Omani biologists underwent three months of training in sampling techniques aboard factory trawlers, before beginning placement aboard the trawlers in May 1989. Per sampling schedule, a team of two Data Collectors boarded a vessel prior to departure for fishing grounds and remained on board for the duration of the cruise (typically one month). During the program, the fleet expanded from two to eight trawlers; seven of the eight were South Korean. The vessels were sampled in relatively equal frequency. Four major sampling objectives were followed:

1. time, area, depth, and catch size were recorded for all hauls while on board,
2. as many of the hauls as possible were sampled for catch composition, with particular regard to determining retained and discard quantities,
3. biological data on the most important commercial species were collected, and
4. the accuracy of factory production figures were determined.

Estimated total turtle catch, based on DC Program sampling, in the 1989 demersal trawl catch was 586 individuals. Turtle catch for the first four months was estimated using the average turtle catch for the last eight months of the year. The actual count for months 1-8 was 201 turtles; the extrapolation was based on area/month combinations, reflecting sampling coverage. Sampling coverage varied from month to month, ranging from 0% (months 1-4) to 100% (month 7) and averaging 34.2%. It is possible, therefore, that actual turtle catch may have been higher or lower than the estimated 586. It is most likely, however, that the estimate of captured turtles is low. This is due primarily to sampling interference; in plain terms, the crew often knew that turtles had been caught and actively prevented Data Collectors from obtaining this information. The turtles were mostly unidentified to species or sex, as the utmost concern was to return them rapidly to the sea.

The Data Collectors estimate that 50% of the turtles were either dead or had no chance for survival upon return to the sea. I saw one haul with six turtles that died, likely from suffocation. Turtles died either as the result of being dragged underwater for 1-2 hours or being dumped in a bin with 10 tons of fish, from which they are not uncovered for another hour. As the trawlers must, by law, return the turtles to the sea, they are faced with the problem of getting them out of the bin. This involved putting a lasso around one limb and lifting the turtle out of the bin via crane-this occurring on a vessel that is constantly shifting to and fro. During one event, the crane operators misjudged and the turtle's shell caught on an overhang; the crane kept pulling and the limb was ripped from the body before the turtle plummeted a dozen feet back into the bin. The average weight of the captured turtles was estimated to be 80+ kg.

Turtle catch was highly variable, though a major peak in turtle incidence occurred in October in the area off Ras Madrakah. Incidence rates, in number of turtles per MT [metric tonne] retained catch, for areas with turtle catch are given in Table 1. In October, an average of 0.242 turtles per MT retained catch were taken in Area 762 (Figure 1). This increased to 0.348 individuals in November. The highest incidence rate was found in Area 768 (south of Masirah Island); however, the total retained catch was small during this period. The high turtle incidence rate off Ras Madrakah coincides with the post-monsoon cuttlefish season. Shallow water trawling resulted in a higher turtle catch than might otherwise have been the case. In blatant violation of regulations, the trawlers operated in waters shallower than 50 m. Two things happened as a result of this: a high catch of undersize fish (a great contributor to the overall 40% discard rate of catch) and turtle catch.

Table 1. Turtle incidence rate (individuals per MT retained catch) in the 1989 demersal trawl catch in Omani waters. Data are not available for January-April (from Hare 1990).

In summary, Oman is an important breeding area for sea turtles and the trawler concession zone parallels the major nesting beaches. Current estimates are that half the turtles trawled up do not survive upon return to the sea. For much of the year, incidental catch of turtles is fairly low. Data for 1989 showed that the majority of the turtles were caught in two small regions in October and November, and that incidental catch may be exacerbated by shallow water trawling. Not coincidentally, the areas and times in question match the Ras Madrakah cuttlefish fishery. The turtle catch can be greatly reduced by shutting the Ras Madrakah region, or other regions, when incidence rates rise too high.

Hare, S. R. 1990. Demersal Finfish Final Report. USAID/Omani-American Joint Commission, Project no. 272-0101.1-1.

Ross, J. P. and M. A. Barwani. 1979. Review of sea turtles in the Arabian Area, p.373-383. In: Biology and Conservation of Sea Turtles (K. A. Bjorndal, ed.). Smithsonian Inst. Press, Washington D.C.