Effects of release parameters on recovery rates of tagged groundfish species

A compilation of groundfish mark-recapture studies conducted in the Northwest Atlantic from 1953 to 1985 was examined by analysis of deviance to determine the effects of release parameters on subsequent recoveries of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius virens), and American plaice (Hippoglossoides platessoides). Fish length was a major determinant of recoveries for all four species, with recovery rates generally increasing with increasing fish length. Depth of capture was a significant determinant of recoveries for cod and haddock, with recovery rates decreasing as depth increased. Year of release was a significant determinant for all four species, with recovery rates declining in recent years. Declines in recovery rates of cod, haddock, and pollock occurred during certain months or seasons. Recovery rates decreased where fish were tagged in areas most distant from inhabited coastal regions, but the interpretation of this effect is complicated by changes in the fisheries over time between areas. Recovery rates also decreased with increasing catch size and varied between different tag types and capture methods. The results should prove useful in the design of tagging protocols and analysis of recovery data.