Field assessments of heart rate dynamics during spawning migration of wild and hatchery-reared Chinook salmon.

During spawning, adult Pacific salmonids ( spp) complete challenging upriver migrations during which energy and oxygen delivery must be partitioned into activities such as locomotion, maturation and spawning behaviours under the constraints of an individual's cardiac capacity. To advance our understanding of cardiac function in free-swimming fishes, we implanted migrating adult Chinook salmon () collected near the mouth of the Sydenham River, Ontario, with heart rate () biologgers that recorded every 3 min until these semelparous fish expired on spawning grounds several days later. Fundamental aspects of cardiac function were quantified, including resting, routine and maximum , as well as scope for (maximum-resting ).