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Breeding success of 5 Cory’s shearwater Calonectris diomedea sub-colonies of Lavezzu Island (Lavezzi Archipelago, Corsica) was checked annually for 25 consecutive years from 1979 to 2004. Between 1989 and 1994, 4 ship rat Rattus rattus controls were performed in several subcolonies. In November 2000, rats were eradicated from Lavezzu Island and its 16 peripheral islets (85 ha) using traps then toxic baits. We compare cost (number of person-hours required in the field) and benefit (Cory’s shearwater breeding success) of control and eradication. The average breeding success doubled when rats were controlled or eradicated (0.82) compared to the situation without rat management (0.45). Moreover, the average breeding success after eradication (0.86) was significantly (11%) higher than after rat controls (0.75). Furthermore, the great variation in breeding success recorded among sub-colonies both with and without rat control declined dramatically after eradication, suggesting that rats had a major impact on breeding success. The estimated effort needed to perform eradication and checking of the permanent bait-station system during the year following eradication was 1360 person-hours. In contrast, rat control was estimated to require 240 or 1440 person-hours per year when implemented by trained and untrained staff, respectively. Within 6 yr, eradication cost is lower than control cost performed by untrained staff and confers several ecological advantages on more ecosystem components than Cory’s shearwater alone. Improved eradication tools such as hand or aerial broadcasting of toxic baits instead of the fairly labour-intensive eradication strategy we used would dramatically increase the economic advantage of eradication vs. control. Therefore, when feasible, we recommend eradication rather than control of non-native rat populations. Nevertheless, control remains a useful management tool when eradication is not practicable.

Flourescein dye was used to trace water movements and to determine flow velocities and volume transports on two Guam fringing reef flats. Wave-driven water crossed most portions of the reef margin in a direction roughly perpendicular to the shoreline. As it moved across the reef flat it gradually changed direction until it was flowing as a longshore current in a deepened moat zone adjacent to the shoreline. After flowing in this longshore current for distances up to 1500 m, the water gradually moved seaward in a more dispersed pattern and exited the reef flat through major cuts in the reef margin. Smaller, more restricted portions of both reef flats had very sluggish water movements with less distinct patterns. Of the total water volume crossing transects which extended perpendicularly from the shoreline, 10-100% flowed in the moat zone within 80 m of the shore. Flow velocities ranged up to 0.6 m sec1. Mean volume transport across entire transects was up to 61.6 m3 sec1. and in the moat zone alone was up to 23.5 m3 sec-1. There was a significant correlation between surf and flow velocity, as well as between surf and volume transport in the moat, at all transects and tidal states tested in one bay; but the correlations were less conclusive in the other bay. Velocity was more strongly correlated with surf than was volume transport in the moat for most of the correlation analyses.