Net-mortality of Common Murres and Atlantic Puffins in Newfoundland, 1951-81

Abstract

Band recoveries ( N = 315) over 26 years (1951-77) and three surveys of seabird bycatch in inshore fishing nets (1972, 1980-81) indicate that there has been a substantial net-mortality of Atlantic Puffins ( Fratercula arctica ) and Common Murres ( Uria aalge ) in Newfoundland coastal waters for the past 2 decades. Offshore (e.g. Grand Banks) gill-netting is limited, but some data suggest that murre net-mortality also occurs offshore at murre wintering areas. The vast majority of inshore net-mortality incidents occur over a 2-week period during the annual inshore spawning migration of capelin ( Mallotus villosus ), the major prey item for alcids in eastern Canada. Most murres (83%) were drowned in bottom-set (30-185 m) cod ( Gadus morhua ) gill nets, whereas more puffins were drowned in surface-set salmon ( Salmo salar ) gill nets or cod traps (55%) than in cod gillnets (45%). Murre band recoveries, colony censuses, and fishing-effort data suggest that at the second largest Common Murre colony in Newfoundland (Witless Bay Seabird Sanctuary, 77,000 breeding pairs) net-mortality was relatively low in the 1950s and early 1960s, but increased during the 1960s as the murre population grew in size and gill-net fishing effort increased in the colony area. By 1971, net-mortality accounted for 70% of murre band recoveries and calculations show that almost 30,000 breeding adults, or about 20% of the local breeding population, were drowned in that year. More reliable estimates of alcid bycatch in the Witless Bay area have been made on the basis of actual bycatch surveys. In 1972 about 20,000 adult murres, or 13% of the breeding stock, were killed in gill-nets. Net-mortality of murres apparently diminished through the 1970s as capelin stocks declined and fewer birds foraged in heavily netted inshore areas. Bycatch surveys in the Witless Bay area in 1980-81 revealed that, relative to previous years, murre net-mortality was greatly reduced and resulted in the loss of only 3-4% of the breeding stock. Even these low mortality rates, however, are cause for concern as adult murre mortality from all sources (including hunting, oil, and natural mortality) should not exceed 6-12% per annum to maintain a stable breeding population. Little is known about the magnitude of net-mortality at other major Newfoundland murre colonies though it is known to be a problem in all colony areas. The bycatch of adult Atlantic Puffins in the Witless Bay area was low compared to murre bycatch and in 3 years of study never exceeded 1.6% of the breeding population. During the 1970s, fishing effort increased five-fold in colony areas and we predict that if capelin spawning stocks return to early 1970s size, then net-mortality of puffins and murres in Newfoundland coastal regions will increase dramatically. Indeed, preliminary examination of 1982 capelin spawning and seabird bycatch data suggests that capelin were much more abundant inshore and murre bycatch increased two- to three-fold over 1981.