Population Dynamics of White Crappie Occurring in a Small Georgia Impoundment Stocked with Female-Only Largemouth Bass
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Population Dynamics of White Crappie Occurring in a Small Georgia Impoundment Stocked with Female-only Largemouth Bass Timothy F. Bonvechio, Georgia Department of Natural Resources, Wildlife Resources Division P.O. Box 2089, Waycross, Georgia 31502-2089 Brandon W. Baker, Georgia Department of Natural Resources, Wildlife Resources Division P.O. Box 2089, Waycross, Georgia 31502-2089 Bryant R. Bowen, Georgia Department of Natural Resources, Wildlife Resources Division P.O. Box 2089, Waycross, Georgia 31502-2089 Abstract: Crappies (Pomoxis spp.) are popular sportfish, but can be difficult to manage due to erratic recruitment and variable growth. In this study, we document the population dynamics of a white crappie (P. annularis) population in a small impoundment characterized by low predator density and abundant populations of several forage species. White crappies (n = 301) were collected by electrofishing in October 2012. Relative abundance as in- dexed by electrofishing catch per unit effort of crappie was high (103.3 fish h–1 ± 18.7 SD). A sub-sample was aged (n = 153) and growth was described by a von Bertalanffy growth curve as total length (TL) = 379.6 (1–e –0.341[age + 0.769]). Growth was considered medium to fast with crappie reaching 254 mm TL in 2.5 yrs. Mean TL of age-2 crappie was 231 mm TL, but lengths ranged from 85 to 365 mm TL. The age distribution revealed that age-2 fish comprised 93% of the population and several year-classes were completely absent from the age distribution. Aging revealed that both stunting and rapid growth were apparent in the same year-class. Crappie populations stocked in a female-only bass fishery can exhibit a high dispersion of lengths within age- classes, which can be a challenge to characterize with traditional population dynamic assessment tools. Future research and management efforts in this small impoundment should be allocated towards a creel survey that assesses angler exploitation and age demographics of the catch, as well as dietary preferences of the white crappie. Key words: crappie, growth, recruitment variability Journal of the Southeastern Associated Fish and Wildlife Agencies 2:93–100 Black crappie (Pomoxis nigromaculatus) and white crappie (P. Goodson 1966, Mitzner 1984, Boxrucker 1987). Erratic recruit- annularis) provide important recreational fisheries, comprising ment may contribute to crappies stunting because a single large 21% of total freshwater anglers in Georgia alone, ranking only be- year class can dominate the population for several years (Goodson hind black bass and catfish fisheries (USFWS and USBOC 2011). 1966). In an attempt to improve growth rate and decrease abun- However, crappie population dynamics can vary greatly compared dance of crappie in small impoundments, bottom-up (i.e., forage to other sportfish species, which creates challenges for fishery stockings) and top-down (i.e., predator stockings) approaches managers (Mitzner 1984, Hooe 1991, Boxrucker and Irwin 2002, have been used with varying degrees of success (Boxrucker and Michaletz 2013). In particular, crappie populations are known to Irwin 2002). The stocking of alternative forage entails a strong exhibit erratic or variable recruitment that can limit the effective- risk component due to potentially negative competitive effects on ness of traditional management activities (Hooe 1991, Allen and non-target species or early life stages of angler targeted species (Li Miranda 1998, Dockendorf and Allen 2005). Crappie populations et al. 1976, Ney 1990, DeVries et al. 1991). Threadfin shad (Do- often exhibit cyclic recruitment patterns, with a strong year-class rosoma petenense) stockings have increased crappie growth rates occurring every 3 to 5 years (Swingle and Swingle 1967, Guy and and population structure in some systems (McConnel and Gerdes Willis 1995). These unpredictable recruitment patterns have a 1964, Range 1972, Mosher 1984), but not others (Boxrucker 1992, great influence on population dynamics modeling (Allen and Mi- Hale 1996). Alternately, several studies have shown that predation randa 1998, Slipke and Maceina 2000). on crappie by largemouth bass (Micropterus salmoides) has been Quality crappie fisheries are often hard to achieve and maintain linked to desirable crappie populations in small impoundments in small impoundments, and this management option has been (Cichra et al. 1981, Gabelhouse 1984a, Boxrucker 1987). As a re- discouraged by managers in the past (Wright and Kraft 2012). sult of these studies, there is evidence that stocking predators in Crappie populations are known to overpopulate when introduced small impoundments decreases crappie abundance, which in turn into small impoundments, which leads to intraspecific competi- increases crappie growth rates. tion for food resulting in poor growth or stunting (Swingle 1952, Management of small impoundment fisheries can benefit from 2015 JSAFWA 93 Population Dynamics of White Crappie in a Small Georgia Impoundment Bonvechio et al. 94 new approaches to exceptional and unique fishing opportunities Table 1. Stocking history of forage, including species, years stocked, total number of stockings, that may attract and retain future anglers (Schramm and Willis number stocked, per–hectare (ha) stocking mean, mean total length (TL) stocked, minimum (Min) 2012). One such example is the stocking of all female largemouth TL stocked, and maximum (Max) TL stocked. N/A = minimum, maximum, and mean TL data for one or more of the stocking events was not taken. bass at a low density to produce trophy fishing opportunities a strategy which has been recently implemented in several private Per-ha Years Total Number stocking Mean Min Max ponds in the southern United States (Willis et al. 2010, Schramm Species stocked stockings stocked mean TL TL TL and Willis, 2012). However, the effects of this new management Bluegill 2004, 2011 3 100,223 778.7 N/A N/A N/A paradigm on a concurrent crappie population are unknown. To & 2012 Channel catfish 2005–2011 4 77,000 448.7 25 201 N/A our knowledge, there is no published study that has examined Golden shiners 2005 1 4,500 104.9 N/A N/A N/A the population dynamics of white crappie within a managed low- Goldfish 2004–2011 21 701,121 778.2 127 25 350 density predator environment. In this study we document the Lake 2008–2012 9 117,065 303.2 178 88 380 age structure, condition, growth, and relative abundance of white chubsuckers Redear 2004, 2011 3 25,035 194.5 N/A N/A N/A crappie in a small impoundment containing a low-density popula- & 2012 tion of female-only largemouth bass and several abundant forage Threadfin shad 2005 1 1,500 35 N/A N/A N/A species. White crappie 2005 1 181 4.2 N/A N/A N/A Totals 41 1, 026,625 583.7 N/A N/A N/A Methods Ocmulgee Public Fishing Area (OPFA) (3222N, 8329W) is a Table 2. Stocking history including year-class, age, number stocked, per-ha stocked, mean total 42.9-ha reservoir owned by the Georgia Department of Natural length (TL) stocked, minimum (Min) TL stocked, maximum (Max) TL stocked, and brood origin. Resources Wildlife Resources Division (GADNR) and located on N/A = Not available or not measured, or minimum, maximum, and mean TL data for this stocking event was lost. the Bleckley/Pulaski county line near Cochran, Georgia. Follow- Number Per-ha Mean Min Max ing impoundment in 2004, the reservoir was intensively managed, Year-class Age stocked stocked TL TL TL Brood origin including regular fertilization. Due to high amounts of limestone 2005 8 550 12.8 273 141 340 American Sportfish bedrock throughout the basin, the water alkalinity was naturally 2006 7 550 12.8 240 185 351 American Sportfish high (> 50 ppm; J. Miller, GADNR, personal communication), so 2008 5 53 1.3 317 227 443 Dodge County (PFA) liming was unnecessary. Mean depth was 4.0 m with the deepest (Flat Creek PFA) 2009 4 100 2.3 N/A N/A N/A Dodge County (PFA) locations exceeding 9.0 m and secchi-depth managed for a range N/A 6 455 421 480 Ocmulgee PFA between 0.5 and 1.1 m. In theory, anglers should expect lower Reproduction catch rates of largemouth bass in systems like this (Maceina and 2010 3 334 7.8 204 146 312 Dodge County (PFA) Sammons 2015). White crappies were stocked into this impound- N/A 7 441 300 528 Ocmulgee PFA Reproduction ment to develop an alternative fishery with higher catch rates for 2012 1 81 1.9 256 229 287 Ocmulgee PFA anglers. Since impoundment regulations for the largemouth bass Broods were catch and release, the white crappie were managed under the N/A 3 477 390 541 Ocmulgee PFA Reproduction statewide regulation of 30 fish per person per day, no minimum size limit. (Table 2). Male largemouth bass were found in the impoundment Forage species were stocked as OPFA initially filled in 2004 and beginning in 2009, but largemouth bass densities were likely never included bluegill (Lepomis macrochirus), redear sunfish (L. micro- > 40 fish ha–1 during the study, and mean catch-per-effort from lophus), and threadfin shad (Table 1). Channel catfishIctalurus ( 2006–2012 was 19.5 fish h–1 (SD = 13). punctatus) and white crappie (4.2 fish ha–1) were stocked in fall A unique stocking strategy was adapted at OPFA. Our goal 2005. Forage was supplemented in future years by stocking lake was to stock the maximum-sized prey that could be utilized by chubsucker (Erimyzon sucetta), golden shiner (Notemigonus cry- memorable-sized largemouth bass (i.e., > 510 mm TL; Gabelhouse soleucas), and goldfish Carassius( auratus) (Table 1). In an effort 1984b). Juvenile and adult largemouth bass typically can eat up to create a trophy largemouth bass fishery at OPFA, only female to 50% of their TL (Lawrence 1957, Johnson and Post 1996).