Temporal Trends in Voluntary Release of Largemouth Bass

Transcription

1 North American Journal of Fisheries Management 28: , 2008 Ó Copyright by the American Fisheries Society 2008 DOI: /M [Article] Temporal Trends in Voluntary Release of Largemouth Bass RANDALL MYERS* Texas Parks and Wildlife Department, 134 Braniff Drive, San Antonio, Texas 78216, USA JOHN TAYLOR Texas Parks and Wildlife Department, 4200 Smith School Road, Austin, Texas 78744, USA MICHEAL ALLEN Department of Fisheries and Aquatic Sciences, University of Florida, Post Office Box , Gainesville, Florida , USA TIMOTHY F. BONVECHIO Florida Fish and Wildlife Conservation Commission, 1601 Scotty s Road, Kissimmee, Florida 34744, USA Abstract. We used creel survey data collected from 1975 to 2006 to evaluate temporal changes in the voluntary release of legally harvestable largemouth bass Micropterus salmoides at four Texas reservoirs and two Florida lakes noted for providing high-quality largemouth bass fisheries. The voluntary release rate increased substantially over time at all six water bodies and reached asymptotic levels exceeding 0.90 in two Texas reservoirs in the early 2000s. Year explained from 68% to 96% of the variability in voluntary release rates. The level of voluntary release ranged from 0.53 to 0.99 among Texas reservoirs in the early 2000s. The increase in voluntary release over time was similar at the two Florida lakes, which had identical largemouth bass harvest regulations, but the levels differed. Catch and release of legally harvestable largemouth bass was more prevalent than harvest at five of the six water bodies included in this study but also varied across small spatial scales. Fishery managers should measure the level of voluntary release and be mindful of the potential effects of high voluntary release when considering the use of harvest restrictions to restructure largemouth bass populations. Voluntary release of black bass Micropterus spp. that are of legal size to harvest has increased (Quinn 1996; Noble 2002) and been implicated in sustaining or improving fishing quality (Quinn 1989). The practice of releasing legally harvestable-size black bass increased from 102 to 250% from 1986 to 1996 according to a survey of state fisheries management agencies taken by Quinn (1996). The mortality of caught-and-released black bass due to hooking is considered to be less than 15% (Pelzman 1978; Muoneke and Childress 1994; Hayes et al. 1995), and surviving released fish may subsequently be caught again by other anglers. Quinn (1989) concluded that the voluntary release of largemouth bass M. salmoides in a Massachusetts lake effectively recycled fish and improved fishing quality. At a Texas reservoir, 13% of trophy largemouth bass (3.6 kg) caught and released by anglers were later recaptured by anglers (Ryan et al. 2004). Conservation-oriented * Corresponding author: randy.myers@tpwd.state.tx.us Received November 9, 2006; accepted October 12, 2007 Published online March 13, 2008 angling has been shown to improve black bass fishing quality. Size limits have been increasingly used to lower exploitation (Radomski 2003) and remain the principal approach to black bass management (Redmond 1986; Noble 2002). However, high voluntary release may limit the effectiveness of harvest regulations for improving black bass populations. Failure to detect the effects of size and bag limits in reducing exploitation may be related to high voluntary release rates (Muoneke and Childress 1994; Wilde 1997). Henry (2003) concluded that more restrictive largemouth bass harvest regulations at Rodman Reservoir, Florida, would be ineffective at lowering exploitation because of high voluntary release (75%). Therefore, the level of voluntary release is an important factor, along with others, to consider before harvest regulations are used in an attempt to lower total fishing mortality. Published estimates of black bass voluntary release rates are rare (Quinn 1989), and the factors influencing the variation in voluntary release across water bodies have not been adequately described in the literature. The size at which fish are legal to harvest may influence angler desire to harvest fish (Clark 1983), 428

2 TRENDS IN VOLUNTARY LARGEMOUTH BASS RELEASES 429 thereby contributing to potential variation in voluntary release across water bodies. Release of largemouth bass ranged from 8 to 85% across Florida lakes before implementation of a statewide size restriction (Champeau and Thomas 1993). Anglers may also feel that it is not worthwhile to harvest fish below a protective slot limit because of their small size and be more apt to harvest fish that exceed a minimum length limit. Novinger (1990) reported that anglers released 45% of legal largemouth bass (,305 mm total length [TL]) in small Missouri impoundments managed with slotlength limits. We found no studies quantifying longterm changes in voluntary release for individual water bodies. Estimates of voluntary release are needed to accurately assess fishing mortality (Clark 1983) and understand the potential impact of catch-and-release angling on management strategies such as harvest regulations. Our objective was to evaluate the temporal trends in the voluntary release of largemouth bass in four Texas reservoirs and two Florida lakes noted for providing high quality fisheries. Methods The temporal trends in voluntary release of largemouth bass by anglers were assessed with creel survey data from Texas Parks and Wildlife Department and Florida Fish and Wildlife Conservation Commission. Water bodies for which long-term (15 years) data were available included Lake Fork ( ), Lake Monticello ( ), Sam Rayburn ( ), and Toledo Bend ( ) reservoirs in Texas, and Lakes Kissimmee ( ) and Tohopekaliga ( ) in Florida. These water bodies range from 935 to 74,869 ha and are among the most notable largemouth bass fisheries in the southeastern United States. Creel sampling was conducted throughout the year at the Texas reservoirs and in the winter and spring quarters (6 months) at Lake Kissimmee and in the fall quarter (3 months) at Lake Tohopekaliga. A stratified, two-stage, creel-sampling protocol (Malvestuto et al. 1978; Malvestuto 1996) was used in both Texas and Florida. Access-point and roving creel surveys were used for Texas reservoirs and roving creel surveys were used for Florida lakes. Creel sampling was conducted a minimum of 20 weekend days and 16 weekdays annually in Texas reservoirs and a minimum of 12 weekend days and 18 weekdays quarterly in Florida lakes. Sample days were randomly selected within each day type stratum. Temporal and spatial sampling units were chosen randomly. Either uniform or nonuniform selection probabilities were used depending on year. During sampling, angling parties were interviewed to determine the number of largemouth bass possessed for harvest and the number caught and released. Anglers were also asked to categorize caught-and-released fish as either legal size to harvest or nonlegal size. Different creel data recording protocols were used for fish possessed by tournament anglers. For the Florida lakes, Sam Rayburn Reservoir, and Toledo Bend Reservoir, legal-size fish retained by tournament anglers were recorded as caught and released because most tournaments require that fish brought in for judging be released back into the reservoir. Alternately, fish retained by Lake Fork Reservoir and Lake Monticello Reservoir tournament anglers were recorded as harvested by creel clerks. If tournament-caught fish kept in possession are treated as harvested when they actually were released, estimates of voluntary release could be biased downward, especially for lakes where tournament angling comprises a substantial portion of the largemouth bass fishery. However, tournament angling was rare on Lake Fork and Lake Monticello reservoirs because these were managed with slot-length limits and length limit waivers were not granted. Largemouth bass angling effort by tournament anglers comprised less than 5% of the total largemouth bass angling effort at Lake Fork Reservoir (Texas Parks and Wildlife Department, unpublished data). Therefore, we contend that the use of different creel data recording protocols concerning tournament anglers did not bias measures of voluntary release for these two Texas slot-length limit reservoirs. Various length and bag limit combinations were used to restrict largemouth bass harvest at the water bodies included in our study. At Toledo Bend Reservoir, Sam Rayburn Reservoir, Lake Kissimmee, and Lake Tohopekaliga, harvest was exclusively managed with minimum size limits, and at Lake Fork and Lake Monticello reservoirs, only slot-length limits were used. Daily bag limit and magnitude of size limit changed over time in all but Sam Rayburn Reservoir where the daily bag limit was five fish and the minimum length limit was 356 mm, and at Lake Fork Reservoir where the daily bag limit remained as five fish. At Toledo Bend Reservoir, the daily bag limit changed from 10 to 8 fish in 1996 and the minimum length limit changed from 305 to 356 mm in At Lake Kissimmee and Lake Tohopekaliga, the daily bag limit and size limit changed from 10 to 5 fish and from no size limit to a 356-mm minimum length limit in At Lake Fork Reservoir, the slot-length limit was mm from 1985 to 1987, mm from 1988 to 1997, mm in 1998, mm in 1999, and mm from 2000 to At Lake Monticello Reservoir, the slot-length limit was mm from 1985 to 1987, mm from 1988

3 430 MYERS ET AL. to 1997, and mm in 1998 and The daily bag limit at Lake Monticello Reservoir was five fish from 1985 to 1987, three fish from 1988 to 1997, and five fish in 1998 and For Texas reservoirs, the voluntary release rate (VRR) of largemouth bass was estimated as the total number of legally harvestable fish caught and released (LCR) divided by the sum of LCR and total number of fish harvested. Raw angler interview data from creel surveys were used in computing average yearly (June to May) VRRs for Texas reservoirs, whereas expanded creel survey estimates were used to calculate average yearly VRRs for Florida lakes because raw angler interview data were unavailable for these locations. Thus, for Florida lakes VRR was computed as the total estimated number of legally harvestable fish caught and released (LCRF) divided by the sum of LCRF and total estimated number of fish harvested. Estimates of VRR for Texas reservoirs took into account the mandatory release of legally harvestable fish due to daily bag limit restrictions. For example, if an angling party of two individuals harvested five fish and released eight additional fish of legal size to harvest from a reservoir where the daily bag limit was five fish per angler, only five of the party s total released fish were considered voluntarily released. In this case, the sum of the harvested fish and released fish (13 fish) exceeded the total bag limit for the party (10 fish), which made release of three fish mandatory. Estimates of VRR for Florida lakes were not adjusted for mandatory release because only expanded creel-survey estimates were available. Because our VRR estimates were proportions based on high sample sizes (N. 10), the annual variances for VRRs were calculated as follows (Zar 1984): Variance ¼ VRRð1 VRRÞ=ðN 1Þ; ð1þ where VRR ¼ the observed average annual voluntary release rate and N ¼ the number of angling parties interviewed. Variances were not calculated for the Florida VRR estimates because sample sizes were unavailable for all years. We inspected residual plots to evaluate whether the temporal trends in voluntary release rate should be fitted with linear or nonlinear models. For cases where a nonlinear model was appropriate, we fitted an asymptotic functional response curve, namely, VRR ¼ A½1 e bðyear YoÞ Š; ð2þ where A ¼ the asymptotic voluntary release rate, b ¼ the rate of increase in VRR to A, Year ¼ the sample year of the VRR estimate, and Y o ¼ the predicted year when VRR ¼ 0 (i.e., the x-intercept). Estimates of annual VRR were weighted by the inverse of the annual variance in the nonlinear fitting procedure. Where a linear model was appropriate, we used analysis of covariance (ANCOVA) following the methods outlined by Littell et al. (1996) to test for differences in the slope and elevation of the regression lines. We were unable to evaluate the effect of size and bag limits on release rate because regulation treatments were not adequately replicated in the data set. Results The number of largemouth bass angling parties interviewed during creel sampling ranged from 108 to 998 annually across Texas reservoirs and from 30 to 407 quarterly in Florida lakes. A total of 124 voluntary release rate estimates for legally harvestable largemouth bass were made for Texas reservoirs and Florida lakes from 1975 to At all four Texas reservoirs VRR increased over time; the range was widest at Sam Rayburn Reservoir (from 0.24 in 1986 to 0.83 in 1999) and narrowest at Toledo Bend Reservoir (from 0.16 in 1988 to 0.58 in 2001). Nonlinear models were appropriate for the Texas reservoirs because the trend in VRR was asymptotic, and year explained 82 96% of the variation in VRR (Figure 1). The magnitude of voluntary release varied among reservoirs, ranging from a low of 0.54 for Toledo Bend Reservoir to a high of 0.98 at Lake Monticello Reservoir. Because of low sample size (N ¼ 2 for each regulation type in Texas), we were unable to evaluate the effect of regulation type on voluntary release rates. At both Florida lakes, VRR increased over time, with a greater range at Lake Tohopekaliga (from 0.15 in 1975 to 0.81 in 2003) than at Lake Kissimmee (from 0.10 in 1985 to 0.64 in 2006). Linear models were appropriate for the Florida lakes as the trends were not asymptotic (Figure 2). The relationship between VRR and year by lake was best described as VRR ¼ þ (year) for Lake Tohopekaliga (r 2 ¼ 0.68, P, 0.001, N ¼ 30) and VRR ¼ þ (year) for Lake Kissimmee (r 2 ¼ 0.75, P, 0.001, N ¼ 24). An ANCOVA revealed that the slopes of release rate on year did not differ significantly between Lake Tohopekaliga and Lake Kissimmee (F ¼ 1.27, df ¼ 50, P ¼ 0.265). However, the elevation of VRR differed significantly between the two lakes (F ¼ 49.88, df ¼ 51, P, 0.001). On average, VRR was 1.4 times greater at Lake Tohopekaliga than at Lake Kissimmee. Discussion During the last two to three decades, the voluntary release of legally harvestable largemouth bass has dramatically increased in Texas reservoirs and Florida

4 TRENDS IN VOLUNTARY LARGEMOUTH BASS RELEASES 431 FIGURE 1. Relationships between the voluntary release rate of legally harvestable largemouth bass and year at four Texas reservoirs. The harvest of largemouth bass was managed with slot-length limits at Lake Fork and Lake Monticello reservoirs and with minimum length limits at Sam Rayburn and Toledo Bend reservoirs. Voluntary release rates were determined from angler interview data and estimated as the number of legally harvestable fish caught and released (LCR) by anglers divided by the sum of LCR and the number of fish harvested. The resulting nonlinear models and coefficients of determination are also shown. lakes noted for providing popular largemouth bass fisheries. Our findings were consistent with a black bass voluntary release increase of % from 1986 to 1996 reported by state agencies in a survey conducted by Quinn (1996). Voluntary release increased from 30% to 140% during the same 10-year period at our study lakes. Voluntary release has become more prevalent than harvest at five of the six water bodies included in our study. Although we found substantial increases in voluntary release, the nonlinear trend between year and release rate suggests that further increases are not imminent in Texas reservoirs. At Lake Fork and Lake Monticello reservoirs, where slot-length limits have been in effect, voluntary release has reached a functional ceiling (potential maximum level) with VRR exceeding 0.90 since the early 1990s. These reservoirs have been effectively operating as catch-andrelease fisheries despite the current size limits that allow anglers to harvest five fish larger than 36 cm daily from Lake Monticello Reservoir and five fish larger than 41 cm daily at Lake Fork Reservoir. At Texas reservoirs with minimum length limits (Sam Rayburn and Toledo Bend), voluntary release has not attained a similarly high level. However since 1998, VRR has been relatively consistent at Sam Rayburn ( ) and Toledo Bend ( ) reservoirs suggesting that further increases in voluntary release are not inevitable at these two reservoirs. Voluntary release at the two Florida lakes had not reached a functional ceiling. Recent VRR estimates for Lake Tohopekaliga (0.77 in 2005) and Lake Kissimmee (0.55 in 2005) and the linear trend between VRR and year together suggest that voluntary release could increase in these lakes. The potential for further increases in voluntary release probably varies by water body. Our results indicate that voluntary release was highly variable for Texas reservoirs. We found substantially different levels of voluntary release for the two closely located Texas reservoirs managed with minimum length limits. In 2005, the VRR for Toledo Bend Reservoir was 0.43, whereas it was 0.77 for Sam Rayburn Reservoir. Conversely, voluntary release level was similar for the reservoirs with slot-length limits, Lake Fork and Lake Monticello. Future studies should identify any effects of regulation type on voluntary release rates.

5 432 MYERS ET AL. FIGURE 2. Relationships between the voluntary release rate of legally harvestable largemouth bass and year in Lakes Kissimmee and Tohopekaliga, Florida. Voluntary release rates were determined from expanded creel survey estimates and computed as the total estimated number of legally harvestable fish caught and released (LCRF) divided by the sum of LCRF and the total estimated number of fish harvested. The solid line represents the linear regression for Lake Kissimmee and the dashed line that for Lake Tohopekaliga. The slopes of the regression lines were not significantly different (P ¼ 0.265), but the level of voluntary release was significantly greater at Lake Tohopekaliga than at Lake Kissimmee (P, 0.001). The minimum length and daily bag limits were the same for both lakes. Our VRR estimates for the two Florida lakes were for different seasons, winter and spring for Lake Kissimmee and fall for Lake Tohopekaliga, suggesting that there is a seasonal component to the levels of voluntary release that we found for those lakes. Florida is a popular destination for retired individuals during winter months, and anglers who reside there temporarily may be more harvest oriented than year-round residents, who fish during the fall. We were unable to separate the season versus lake effects for the Florida lakes, but our study provided evidence in both Texas and Florida that level of voluntary release can vary across small spatial and possibly temporal (i.e., seasonal) scales. Increased voluntary release has undoubtedly benefited many largemouth bass populations. Allen et al. (2008, this issue) evaluated temporal trends in largemouth bass fishing mortality and found that fishing mortality had declined by about half since the 1970s. Our results together, with those of Allen et al. (2008), suggest that changes in angler behavior have substantially reduced fishing mortality for largemouth bass populations. High voluntary release may limit the effectiveness of size restrictions for improving population size structure. In addition to protecting mid-size fish from harvest, slot-length limits have been predicated on thinning overabundant small largemouth bass to promote faster growth of remaining fish, thereby increasing recruitment into the protected size range (Martin 1995; Noble and Jones 1999). Wilde (1997) reviewed black bass size-limit evaluations and found that slot-length limits were largely successful at restructuring populations, whereas minimum length limits generally failed. However, most (29 of 43) of the slot-length-limit evaluation studies contained in Wilde s (1997) review were conducted during the 1980s before the widespread acceptance and practice of voluntary release. Our study indicates that voluntary release has increased substantially since the 1980s. Parks and Seidensticker (2000) reported in a study conducted after Wilde s (1997) review that the failure of a mm-TL slot-length limit to restructure largemouth bass populations in five Texas reservoirs was attributable to low exploitation of fish smaller than the slot-length limit. The current high levels of voluntary release at Lake Fork and Lake Monticello reservoirs suggest that the largemouth bass populations in these reservoirs have received only the direct benefit of protection from potential harvest, and have not benefited from reduced intra-specific competition as a result of the slot-length limits. Fishery managers obviously cannot assume that changing size limits will influence fishing mortality rates (Allen et al. 2008; this study). For the last three decades, anglers have been conditioned to release all largemouth bass through promotion of a conservation ethic by the fishing media, fishing organizations, and to some extent fisheries agencies. The Texas Parks and Wildlife Department s campaign for harvest of subslot-size fish in an effort to improve the Lake Fork Reservoir trophy largemouth bass fishery was unsuccessful and caused ire among many anglers and some fishing organizations (K. Pratas, Texas Parks and Wildlife Department, personal communication). The utility of harvest regulations for restructuring largemouth bass populations in the future may be largely dependent on angler willingness to harvest fish. Studies identifying angler attitude and motivation towards largemouth bass harvest may be useful in helping identify strategies to encourage harvest where appropriate. Acknowledgments We thank B. Betsill, J. Estes, and B. Farquhar for reviewing a previous draft of this manuscript and providing helpful comments that improved this work. T. Coughlin, M. Hulon, and M. Mann coordinated the creel surveys in Florida. Funding for this project was partially provided by the Federal Aid in Sport Fish Restoration Act, Project F-30-R.

6 TRENDS IN VOLUNTARY LARGEMOUTH BASS RELEASES 433 References Allen, M. S., C. J. Walters, and R. M. Myers Temporal trends in largemouth bass mortality, with fisheries implications. North American Journal of Fisheries Management 28: Champeau, T. R., and P. W. Thomas Voluntary release of largemouth bass by Florida anglers. Proceedings of the Annual Conference Southeastern Association of Fish and Wildlife Agencies 45(1991): Clark, R. D., Jr Potential effects of voluntary catch and release of fish on recreational fisheries. North American Journal of Fisheries Management 3: Hayes, D. B., W. W. Taylor, and H. L. Schramm, Jr Predicting the biological impact of competitive fishing. North American Journal of Fisheries Management 15: Henry, K. R Evaluation of largemouth bass exploitation and potential harvest restrictions at Rodman Reservoir, Florida. Master s thesis. University of Florida, Gainesville. Littell, R. C., G. A. Milliken, W. W. Stroup, and R. D. Wolfinger SAS system for mixed models. SAS Institute, Cary, North Carolina. Malvestuto, S. P Sampling the recreational creel. Pages in B. R. Murphy and D. W. Willis, editors. Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland. Malvestuto, S. P., W. D. Davies, and W. L. Shelton An evaluation of the roving creel survey with nonuniform probability sampling. Transactions of the American Fisheries Society 107: Martin, C. C Evaluation of slot length limits for largemouth bass in two Delaware ponds. North American Journal of Fisheries Management 15: Muoneke, M. I., and W. M. Childress Hooking mortality: a review for recreational fisheries. Reviews in Fisheries Science 2: Noble, R. L Reflections on 25 years of progress in black bass management. Pages in D. P. Phillip and M. S. Ridgeway, editors. Black bass: ecology, conservation, and management. American Fisheries Society, Symposium 31, Bethesda, Maryland. Noble, R. L., and T. W. Jones Managing fisheries with regulations. Pages in C. C. Kohler and W. A. Hubert, editors. Inland fisheries management in North America, 2nd edition. American Fisheries Society, Bethesda, Maryland. Novinger, G. D Slot length limits for largemouth bass in small private impoundments. North American Journal of Fisheries Management 10: Parks, J. O., and E. P. Seidensticker Evaluation of a mm slot length limit for largemouth bass in five Texas reservoirs. Proceedings of the Annual Conference Southeastern Association of Fish and Wildlife Agencies 52(1998): Pelzman, R. J Hooking mortality of juvenile largemouth bass, Micropterus salmoides. California Fish and Game 64: Quinn, S Trends in regulatory and voluntary catch-andrelease fishing. Pages in L. E. Miranda and D. R. DeVries, editors. Multidimensional approaches to reservoir fisheries management. American Fisheries Society, Symposium 16, Bethesda, Maryland. Quinn, S. P Recapture rates of voluntarily released largemouth bass. North American Journal of Fisheries Management 9: Radomski, P Initial attempts to actively manage recreational fishery harvest in Minnesota. North American Journal of Fisheries Management 23: Redmond, L. C The history and development of warmwater fish harvest regulations. Pages in G. E. Hall and M. J. Van Den Avyle, editors. Reservoir fisheries management: strategies for the 80s. American Fisheries Society, Special Publication 15, Bethesda, Maryland. Ryan, M. J., M. W. Brice, and L. Fries Use of an angler incentive program for data collection and management of a trophy fishery. Proceedings of the Annual Conference Southeastern Association of Fish and Wildlife Agencies 56(2002): Wilde, G. R Largemouth bass fishery response to length limits. Fisheries 22(6): Zar, J. H Biostatistical analysis, 2nd edition. Prentice- Hall, Englewood Cliffs, New Jersey.