Application of Minimum Length Limit for Crappie Populations in Lake Alvin, SD
Explore the implementation of a 23-cm minimum length limit for crappie populations in Lake Alvin, SD based on angler opinions and pre/post-implementation data. Learn about the characteristics and metrics considered before imposing such regulations and the impact on Black and White Crappie populations.
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Presentation Transcript
Application of a Minimum Length Limit for Crappie Populations Modified from Case 9 in Murphy et al. (2010)
Lake Alvin, SD 36.4 ha impoundment Eutrophic, though little vegetation Primary LMB, BKC, WHC, BG, CC Secondary WAE, YEP, NOP, BBH 10 km from Sioux Falls High angling effort
Angler Opinions Complaints of small average size of harvested fish. 91% favor a 20-cm minimum length limit. 93% favor a 23-cm minimum length limit.
Group Think 23-cm minimum length limit implemented on 1-Jan-96. What characteristics of a fish population typically lead a manager to consider use of a minimum length limit regulation? Explain! What metrics would you want to look at before implementing a minimum length limit regulation?
Group Think What does this pre-implementation data suggest about the success of this regulation? High CPE, slow growth SD lakes exceed 100 fish/net-night Black Crappie White Crappie Mean TL Age-3 -- -- -- 207 9.0 207 9.0 Mean TL Age-3 -- -- -- 220 9.3 220 9.3 Year CPE PSD-23 CPE PSD-23 1992 1993 1994 1995 Mean 63 16 11 3 5 1 7 1 22 5 0 0 3 3 2 63 23 37 12 10 3 6 2 29 10 3 1 15 13 8 Black Crappie S-Q 110 (6) 102 (1) 96 (4) 106 (2) White Crappie S-Q Wr Year 1992 1993 1994 1995 SS Q-P 86 88 (2) 88 (2) 81 (3) P-M -- -- -- -- SS Q-P 78 (5) 81 (2) 81 (2) 71 (2) P-M 77 (7) -- 81 (2) 77 138 (8) -- 103 (6) 134 (7) 101 (11) 100 (3) -- 104 (5) 100 (7) 88 (1) 89 (3) 97 (3)
BKC and WHC Populations Relative abundance relatively lower Growth near state-wide average Size structure below balanced objectives Few fish older than age-2 Suggested overharvest of BKC and WHC
Post-Implementation Data Black Crappie White Crappie Mean TL Age-3 -- -- Mean TL Age-3 -- -- Year CPE PSD-23 CPE PSD-23 1992 1993 63 16 11 3 0 0 63 23 37 12 3 1 1994 1995 Mean 1996 1997 1998 1999 Mean 5 1 7 1 22 5 35 11 13 5 41 7 66 10 39 8 3 3 2 0 2 1 2 1 10 3 6 2 29 10 43 8 40 10 27 9 44 15 39 11 15 13 8 2 4 3 3 3 207 9.0 207 9.0 199 3.1 209 1.5 211 2.5 202 2.4 205 2.4 220 9.3 220 9.3 215 2.2 212 3.6 213 0.7 205 2.6 211 2.3
Post-Implementation Data Wr Black Crappie White Crappie Year 1992 1993 1994 1995 1996 1997 1998 1999 SS S-Q 110 (6) 102 (1) 96 (4) 106 (2) 89 (1) 116 (3) 100 (2) 107 (1) 105 (3) 101 (1) Q-P 86 88 (2) 88 (2) 81 (3) 88 (4) P-M -- -- -- -- -- -- -- -- SS S-Q 100 (3) 88 (1) 89 (3) 97 (3) 107 (1) 102 (4) 106 (2) 89 (1) Q-P 78 (5) 81 (2) 81 (2) 71 (2) 99 (2) 89 (1) 87 (3) 81 P-M 77 (7) -- 81 (2) 77 -- 82 87 (3) 83 138 (8) -- 103 (6) 134 (7) 126 (12) 129 (2) 108 (7) 107 (3) 101 (11) -- 104 (5) 100 (7) -- 112 (4) 108 -- 89 (2)
Post-Implementation Data 140 Black crappie 130 120 110 100 1992 1993 1994 1995 1996 1997 1998 1999 Relative weight 90 80 70 140 White crappie 130 120 110 100 90 80 70 SS S-Q Q-P P-M Length category
Post-Implementation Data Black Crappie White Crappie 100 100 1995 80 80 60 60 Length Increment (mm) 40 40 20 20 0 0 50 100 150 200 250 50 100 150 200 250 100 100 1999 80 80 60 60 40 40 20 20 0 0 50 100 150 200 250 50 100 150 200 250 Initial Length (mm) Initial Length (mm)
