Diving Depths of Four Alcids

-Incidental catches of 12,243 Common Murres (Uria aalge), 875 Atlantic Puffins (Fratercula arctica), 36 Black Guillemots (Cepphus grylle), and 9 Razorbills (Alca torda) were recorded off Newfoundland during the summers of 1980-1982 (26,445 net-days of fishing effort). Most catch occurred in stationary gill nets set on the sea floor at depths of up to 180 m and revealed that murres, Razorbills, puffins, and guillemots can dive to depths of at least 180, 120, 60, and 50 m, respectively. Diving ability appeared to be directly correlated with body size. Received 5 March 1984, accepted 2 June 1984. LITTLE is known about the depths to which alcids and other aquatic birds are capable of diving (Kooyman 1975). Using depth recorders, Kooyman (1975) and Kooyman et al. (1982) established that Emperor (Aptenodytes forsteri) and King (A. patagonica) penguins can dive to depths in excess of 240 m. Although penguins are probably the best underwater swimmers among the ten families of diving birds, Kooyman (1975) suggested that "If most other birds can descend and ascend at similar rates (e.g. 2 m/s) then a 180 m 'bounce' dive is probably within the range of most diving birds . " properly adapted for the extreme conditions found at those depths. As Northern Hemisphere ecological counterparts to penguins, alcids are morphologically similar. They exploit similar prey, such as euphausiids, squid, and small schooling fishes (Bedard 1969, Kooyman 1975). All pursue prey underwater using partly folded wings to propel themselves (Bedard 1969), and numerous adaptations for underwater "flight" and feeding have evolved in the Alcidae (Storer 1952, Stettenheim 1959, Bedard 1969, Spring 1971). Studies of diets (Tuck and Squires 1955, Belopol'skii 1957) and a few records of catches in fishing gear (Tuck 1961) imply that alcids sometimes forage near the ocean bottom at considerable depths, but there are no detailed accounts of diving ability or estimates of maximum diving depths. In Newfoundland, thousands of alcids, particularly Common Murres (Uria aalge) and Atlantic Puffins (Fratercula arctica), drown each year in surface-set salmon (Salmo salar) and bottom-set cod (Gadus morhua) gill nets as they forage for capelin (Mallotus villosus) in waters intensively fished by man (Piatt et al. 1984). Net-mortality is acute during the one-month period that capelin form large, dense spawning schools inshore. We have accumulated detailed data on 912 incidents involving 13,163 alcids caught in gill nets. These data suggest that the diving abilities of different alcid species differ markedly and that the maximum diving depths attainable by alcids have been considerably underestimated (e.g. Stettenheim 1959, Pearson 1968, Kooyman 1975). STUDY AREA AND METHODS During the summers of 1980-1982, 39 inshore fishermen from communities adjacent to 7 major seabird colonies in Newfoundland (Wadham, Penguin, Cabot, Funk, and Baccalieu islands, Witless Bay, and Cape St. Mary's) recorded daily seabird catches with details on the depths and locations of net entrapment (Piatt et al. 1984). Cod gill nets were positioned on the sea floor at varying depths up to 180 m. The bulk of inshore fishing effort occurs at depths of less than 60 m, and only 5% of fishing effort observed in our study occurred at greater depths. On about 30 occasions John F. Piatt accompanied fishermen at sea and observed fishing techniques and removal of seabirds caught in nets retrieved from depths of up to 180 m. In addition, several thousand net-drowned alcids brought in to fishing wharves were examined, and over one thousand were autopsied to determine sex, age, and stomach contents.