Figure 1. Modern bass fishing tournaments minimize the impacts of handling, but fish are not released at their original sites of capture.

Size matters: A comparison of weight measurements and length-weight estimates for fishing tournaments

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Ali J. Ahmed and Paul Shipman, Ph.D.

Rochester Institute of Technology, Rochester, New York 14623

This article is based upon the results of an undergraduate-level research project performed during Summer 2010. We acquired available Smallmouth Bass (Micropterus dolomieu) and Largemouth Bass (Micropterus salmoides) weight and length data from state fish and game agencies in order to run simulated fishing tournaments and compare the results of winners using two methods of measurement.  The first method used combined weight of five fish per angler to determine winners of fishing tournaments.  The second method used weight estimates from measured lengths to determine the winners.  Catch, photograph, and release methods are becoming increasingly popular among competitive angling, particularly within the rapidly growing sport of kayak fishing.  We found similar tournament outcomes were achieved using both methods of evaluation.


Current catch, weigh, and release (CWR) scoring methods for sport fishing tournaments (particularly bass fishing tournaments) are aimed at conserving and improving sport fisheries compared with catch and kill methods used many years ago.  However, numerous studies have shown significant fish mortality are associated with the CWR method that varies with temperature, handling time and conditions, and severity of injuries associated with the initial catch (White, et al., 2007; Nelson. 1998). In addition to the continued problem of some mortality, most tournament venues release all fish at a point location (usually near the tournament weigh-in site or boat launch) and studies have shown that fish tend to remain in that area after release and seldom return to their original area of capture which indicates that life cycles of the fish are significantly impacted.

Figure 1. Modern bass fishing tournaments minimize the impacts of handling, but fish are not released at their original sites of capture.

Recently, some tournament venues have been exploring the feasibility of catch, photograph, and release (CPR) scoring methods (in particular, walleye and kayak fishing tournaments).  The CPR method is thought to reduce both the mortality and life cycle impacts because the handling time is greatly reduced and the fish are released at the sites where they are caught, allowing them to resume their normal
activities.  However, CPR scoring methods have been criticized because  of errors associated with photographing fish against a measuring board, the potential for cheating, measuring length is not the same as weighing (a longer fish does not always indicate a heavier fish, which is considered to be the standard for tournaments), and the decreased excitement of not being able to allow participants and spectators to see the large fish caught during the tournament.

Materials and Methods

We compared weight measurements with length-weight estimates to determine whether the both methods of scoring for fishing tournaments would yield similar results. We requested largemouth bass (Micropterus salmoides) and smallmouth bass (M. dolomieu) measurement data (weights and body lengths) from multiple state fish and wildlife agencies, which included New York, Pennsylvania, Oklahoma, Kansas, Texas, and Georgia.

Figure 2. Bass body lengths are easily determined from photographs, allowing fish to be released soon after and at their original sites of capture.

We entered the data into an Excel spreadsheet and culled the data set to include only fish longer than 12 inches in length as would be done during a standard fishing tournament due to New York State fishing regulation size limits.  We then set up formulas to estimate weights based upon commonly used length-weight estimates for these bass species:

Length x Length x Length


We chose a subset of smallmouth bass data and ran 100 randomized simulations of fishing tournaments with ten contestants using a common tournament format whereby the anglers are scored based upon the combined weights of five fish, with the winner having the heaviest total.  We compared the winners of each tournament using each method of measurement, and counted the number of times the first place winner was the same for both methods of measurement.  Because fish might vary more the older and large they get, we ran an additional 100 simulations and counted the number of times the 10th place winner was predicted by both methods.  We also examined the relationship of both measures using linear regression and compared the means to determine whether the length-weight estimate was biased in either over-estimating or under-estimated bass weights.

Figure 3. The results of our linear regression of measured weights with estimated weights of smallmouth bass.

Results and Discussion

Of the states with which we corresponded, only the State of New York Department of Conservation (NYDEC) provided us with the data that we requested. We acquired 72,831 total records dating from 1977 to 2009.  We suspect that much data exists for these other states, but that the other agencies were not prepared or willing to meet our requests.  Of the records from (NYDEC) that included weights and lengths, 35,757 were largemouth bass, and 37,074 were smallmouth bass.  We ran our simulations on a subset of 2233 smallmouth bass larger than 12 inches caught and measured between 1988 and 2009.

During our first 100 random simulations, we found that both methods of measurement predicted the same winners 75% of the time.  During our second 100 random simulations, we found that the same winners were predicted by both methods 77% of the time,

We found that the length-weight estimate significantly over-estimated the weights of smallmouth bass used for our simulation (t-test, p = 0.01, N = 2233), having a mean estimate of 2.83 lbs. vs. the measured mean weight of 2.63.  The measured weights and estimated weights were significantly correlated (r = 0.93, p = 0.001) and indicated as we predicted, that there was more variability in weights of larger fish.

One reason that kayak angling tournaments use CPR methods for determining winners, is due to the fact that most fishing kayaks lack adequate live wells for sustaining fish between the time they would be caught and weighed using CWR. Bass tournaments using motor boats, on the other hand, commonly require live wells.  In personal communications with hundreds of tournament bass anglers who compete using CWR, there is a common perception that length measurements are inferior for determining the outcomes of tournaments.  Part of the excitement and popularity of CWR tournaments is also achieved by top anglers getting to show off large live fish at the weigh-ins.

Figure 4. The recent popularity of kayak fishing tournaments has increased the need to study catch, photograph, and release methods as ways to minimize impacts on fish.

We conclude that CPR methods used for evaluating fishing tournaments might yield surprisingly similar scores as those determined using CWR methods if methods for reliably measuring fish lengths on the water by anglers could be done in a manner that minimized potential cheating.  If CPR were to be adopted and developed, we believe that it would benefit the fisheries in which the tournaments are held.  The stigma associated with using CPR methods are most likely due to cultural reasons and because CWR methods allow judges to directly observe the fish being submitted for scoring.

We found no reasons to argue that length measurements are inferior to weight measurements with respect to determining which fish were the “biggest” fish, which is really what tournament participants are seeking to assess.  We could however, predict that length measurements are less likely to change in the span of a tournament event compared with weight measurements that might change from the time a fish is caught during a tournament and when it finally is weighed on scales.  It is a common occurrence that bass will regurgitate the contents of their stomachs while being held in live wells, never mind the fact that a fish having recently consumed a large amount of prey, would weigh more than it would with an empty stomach.

Currently used methods of weight estimation could also and should be improved to provide better species and region-specific estimates of weight estimates based upon length measurements.  More accurate weight estimates using body dimensions are available, however, most of these require both length and girth data.  We were not able to find any girth measurements among state agency data that we acquired.

Literature cited

Nelson, K.L. 1998. Catch-and-release mortality of striped bass in the Roanoke River, NorthCarolina. North American Journal of Fisheries   Management 18: 25-30.

White, A.J., J.F. Schreer, S.J. Cooke. 2007. Behavioral   and physiological responses of the congeneric Largemouth (Micropterus salmoides)   and Smallmouth bass (M. dolomieu) to various   exercise and air exposure durations. Fisheries   Research 89: 9–16.


We would like to extend our gratitude and thanks to Mr. Eulas Boyd.  We would also like to extend a special thanks to Ms. Casey Festa, Mr. William Culligan, and the rest of the staff at the NY Department for Environmental Conservation, for all their help and hard work. This material is based upon work supported by the National Science Foundation under Award No. HRD-0703452.