INCIDENCE OF ANGLING INJURIES IN SMALLMOUTH BASS (MICROPTERUS
DOLOMIEU), POOL 8, UPPER MISSISSIPPI RIVER, 1997-2000.

Eric Kramer1, J. Therese Dukerschein1, Brian Ickes2.  
1 Wisconsin Department of Natural Resources, Onalaska, WI 54650  2U.S. Geological Survey,
Upper Midwest Environmental Sciences Center, La Crosse, WI 54603.

During annual standardized fish monitoring for the Long Term Resource Monitoring Program
(LTRMP), we recorded angling injuries in the years 1997 through 2000 in smallmouth bass
(Micropterus dolomieu) collected by electrofishing within Pool 8 of the Upper Mississippi River
System.  We defined angling injuries as either healed scars or fresh tears to the maxillary,
premaxillary, mandible, or gill membranes.  Assuming that injured and non-injured fish were
both equally vulnerable to electrofishing gear, the incidence of angling injuries could be used to
estimate the fraction of surviving fish that were caught and released by anglers through that time. 
Over all years, 365 of the 2,243 smallmouth bass (180-550 mm total length) we collected showed
evidence of angling injuries.  Legal-sized fish ((350 mm [14"], n=437) over all years had over
double the injury rate (30%) of sub-legal sized fish (( 349 mm, 13%, n=1806).  This relationship
was significant (Chi-square=74.81, P((0.00) and also held when each of the four years was
analyzed independently.  The difference, however, between observed and expected injury rates in
legal verses sub-legal length classes varied somewhat year to year.  The effect was most extreme
during 2000 (Chi-square=37.12, P((0.001), followed by 1999 (Chi-square =11.54, P=0.0007);
1997 (Chi-square =8.62, P=0.0033); and 1998 (Chi square =4.89, P=0.0270).  Analysis of
marginal contributions to the overall Chi-square test result indicated that the legal sized fish were
2.88 times more likely to show evidence of angling injury than the sub-legal sized fish.  The
differences in rates of injury between larger and smaller fish could have multiple causes.  Among
the possibilities are different harvest/mortality rates, different susceptibilities to the types of lures
used by anglers, a longer time for the larger, older fish to accumulate injuries, and differences in
healing/regeneration/growth abilities.  
 
Keywords: angling injuries, smallmouth bass, Micropterus dolomieu, fishing, Mississippi River