Sonic tracking of wild cod, Gadus morhua, in an inshore region of the Bay of Fundy: a contribution to understanding the impact of cod farming for wild cod and endangered salmon populations

Abstract

Abstract Sea cage trials of Atlantic cod farming have begun in the Bay of Fundy region. We fitted inshore wild cod (n = 10) captured in the Quoddy region with sonic tags during the late summer of 2004 to provide data on their temporal and spatial residency and habitat usage, with a view to understanding the potential for impact between escaped farmed cod and wild cod and other fish species, particularly Atlantic salmon. Most of the tagged cod remained within a restricted corridor in the inshore zone, occupied deep water (75–130 m) within several kilometres of the release point, and undertook local movements. Three cod undertook more extensive movements; one fish emigrated offshore immediately, and two fish moved as far as 14 km from the release point before returning, 52–54 h later, to the area in which the other cod were located. The mean residence time in the inshore zone was 55 days. In the late autumn, there was a staggered pattern of departure from the coastal zone, although one fish over-wintered in Passamaquoddy Bay. Three of the nine cod that migrated offshore in autumn 2004 returned within a three-week period in May 2005, after a mean absence of 172 days, and reoccupied the inshore region inhabited the previous year. These cod left the region again after a mean residence of 120 days during the spring and summer. The presence of some of the tagged cod in the principal migration corridor for wild salmon smolts during the period of their migration suggests that escapes from cod farms could result in increased predation on salmon smolts from endangered populations.