Temporal and spatial migration of Atlantic cod (Gadus morhua) inside and outside a marine protected area and evidence for the role of prior experience in homing

Abstract

Despite efforts to protect the resident Atlantic cod (Gadus morhua) population in Gilbert Bay, Labrador, its abundance has decreased since the area was designated a Marine Protected Area (MPA). As part of an effort to understand the reasons for the decline, tracking of cod tagged with surgically implanted ultrasonic transmitters was conducted to determine the migratory behavior of cod in relation to MPA boundaries. Acoustic tracking used a network of data-logging receivers deployed in Gilbert Bay and contiguous marine waters, permitting year-round monitoring of fish movements over several years. Acoustic tracking indicated that 93% of mature migratory cod >55 cm total length homed to the overwintering area where they were initially tagged. During summer months some individuals moved to the mouth of the bay and marine waters outside the MPA. Collectively, the home range of the Gilbert Bay cod encompassed an area within about 40 km of their overwintering and spawning site, but included a large area (∼270 km2) outside the MPA. Eleven percent of tagged cod released outside their home range returned to the capture site within 1 year after tagging. In contrast, fish transplanted 15 or 25 km from the capture site, but still within their home range, exhibited 100% success in homing, suggesting the importance of prior experience with the migration route for successful homing. This study documents the importance of knowledge concerning the migratory and homing behavior of resident fish populations for their conservation and management.