Wounding of Pacific Salmon by Predators in Gillnet Catches in the Russian Economic Zone in 2004

摘要

We describe data on wounds, scars, and marks on Pacific salmon caught during a gillnet survey by the R/V Ecopacific in the northwest North Pacific Ocean and southwest Bering Sea in summer-fall 2004. A classification scheme to systematize visual observations of various types of wounds caused by two major predator groups (piscivorous fish and seals) is suggested. Three general trends in the results apply to all species of salmon caught in gillnets during their prespawning migrations. First, wounding by fish and seals does not depend on salmon body size at either the intra- or inter-specific level. Second, the highest percentage of wounds were caused by seals and two piscivorous species, longnose lancetfish and North Pacific daggertooth (25-47% of wounds in North Pacific waters adjacent to Kamchatka). The percentage of wounds caused by lampreys was relatively low. Third, the percentage of healed wounds (scars) in mature salmon increased at the end of the prespawning migration, indicating that the energy expended to regenerate injured tissues may delay maturation. It was difficult to distinguish between natural wounds, which occurred before salmon were caught, and artificial wounds, which occurred after salmon were caught, particularly because of the length of fishing operations (-10 hr) and the ready availability of gillnet-caught salmon to predators. The results, however, can be used an indicator of general background conditions that influence natural predation of salmon during their prespawning migrations in the open ocean.