RESOURCES

Gross, Mart R. & Charnov, Eric L. 1980. Alternative male life histories in bluegill sunfish. Proceedings of the National Academy of Sciences, 77(11): 6937-6940

Abstract: Male bluegill sunfish are shown to have two alternative mating strategies: cuckoldry or parental care. Cuckolder males first mature at age 2. They follow a developmental sequence of sneaking and then mimicking female behavior to deceptively gain access to spawnings. Males who become parentals (construct nests, attract females, provide brood care) delay maturation until age 7. The parental investment of these males is parasitized by the cuckolders. This system is an example of a truly parasitically dependent mating strategy in vertebrates. A natural selection model is developed to predict the equilibrium frequencies of the two male types. A preliminary test of the model provides qualitative agreement.

Jennings, M. J., Claussen, J. E. and Philipp, D. P. 1997. Effect of Population Size Structure on Reproductive Investment of Male Bluegill. North American Journal of Fisheries Management, 17: 516-524.

Abstract: Although a goal of fisheries management is to understand factors affecting the growth rate and size structure of exploited populations, the relation between growth rates and variation in reproductive behaviors in Lepomis species has received little attention. Allocation of energy to reproductive functions (e.g., gonadal maturation, gamete production, nesting and spawning activities, and brood defense) negatively affects growth rate and, ultimately, maximum body size. To assess how social factors influence energy allocation, we manipulated population size structure of male bluegills L. macrochirus in experimental ponds and evaluated individual reproductive behavior and testes development. We predicted that smaller parental males would invest less in reproduction in the presence of larger parental males than they would in their absence. Observations were consistent with this prediction; smaller parental males had smaller testes and nested less frequently in the presence of larger males than in their absence. Furthermore, when males of both size-groups occupied nests, larger males were more successful. Size-selective angling that removes larger males may, therefore, negatively affect the size structure of Lepomis populations by creating conditions under which smaller, and often younger fish, mature sexually and reproduce. Under those conditions, growth rates would slow at younger ages, and the maximum size attained by these fish would be reduced.

Ehlinger, T. J., Gross, M. R., and Philipp, D. P. 1997. Morphological and Growth Rate Differences between Bluegill Males of Alternative Reproductive Life Histories. North American Journal of Fisheries Management, 17: 533-542.

Abstract: We characterized the morphology of mature cuckolder and mature parental male bluegills Lepomis macrochirus from Lake Opinicon, Ontario. By rearing bluegill larvae to maturity in experimental ponds in Illinois we also examined whether morphological differences between males of the two reproductive life histories were conserved across widely varying environmental conditions. Cuckolder and parental males collected in Lake Opinicon differed in their size-adjusted body shape. They also differed in their pattern of mass allocation to testis versus somatic tissue. Cuckolder males allocated significantly more of their total body mass to testes compared to parental males. Body shape and testis:somatic ratio differences between male types reared in experimental ponds in Illinois were nearly identical to those observed in bluegills from Lake Opinicon. This divergence between male types remained consistent even when bluegills were reared over a 10-fold variation in growth rate. Average growth rate within ponds was strongly associated with the probability that a male would mature as a parental male within the first year. However, the proportion of males maturing as cuckolders was relatively constant among ponds and was not influenced by growth rate differences. These findings have important implications for management of bluegills and other Lepomis species where growth differences or reproductive divergence occur within single populations.

Rypel, Andrew L. 2015. Effects of a Reduced Daily Bag Limit on Bluegill Size Structure in Wisconsin Lakes. North American Journal of Fisheries Management, 35:2, 388-397

Abstract: This study evaluated the effect of reduced aggregate panfish bag limits (from 25 to 10) on the size structure of Bluegill Lepomis macrochirus populations in seven natural lakes in Wisconsin. For assessing the overall significance of treatments, each treatment lake was paired with a control lake in which the regulation was not implemented. Across all lakes, mean total length (TL) of sampled Bluegills was significantly greater in treatment lakes than in control lakes after the regulation was implemented: on average, mean TL increased by 20.3 mm. However, efficacy of reduced bag limits varied substantially across lakes as mean TL improvements ranged from 5.1 to 63.5 mm in individual lakes. This variation could be strongly explained (R2 = 0.81) by lake Secchi depth (lakes with reduced water clarity showed larger improvements in mean TL, R2 = 0.62) and regulation duration (size structure improved continuously with time after the reduced daily bag limit was implemented, R2 = 0.75). Reduced bag limits are a useful tool for providing improvements to Bluegill size structure in Wisconsin lakes, but would be most effective in more productive waterbodies and will require substantial time investments after implementation.

Hayward, R.S. and Wang, H.P. 2000. Inherent Growth Capacity and Social Costs of Bluegill and Hybrids of Bluegill and Green Sunfish: Which Fish Really Grows Faster? North American Journal of Aquaculture, 64: 34-46

Abstract: There is interest in knowing whether the bluegill Lepomis macrochirus or a hybrid of bluegill and green sunfish L. cyanellus (F1: male bluegill   female green sunfish; hereafter called B   G hybrids) can be grown faster to food market size (225–340 g). The predominant view is that the hybrid grows faster. In this study, the inherent growth capacities (IGCs) of age-1 bluegills and B   G hybrids were determined over four successive 25-d periods (May–August 2000) by holding them individually at 22 C and feeding them to apparent satiation three times daily. The hybrid’s IGC was greater during period 1 but fell to only 33% of the bluegill’s over the three subsequent periods; the consumption and gross growth efficiency (GGE) of the hybrid showed similar declining patterns. The growth-in-weight trajectory of bluegills crossed above that of the hybrids at about 30 g. Gonadosomatic index values suggested that hybrid growth rates declined below those of the bluegill because the former invested more energy in gonads as age-1 fish. A follow-up study, conducted under similar conditions from August 2000 to March 2001, found that individually held age-1 bluegills starting at 30 g reached more than 100 g in 200 d, gaining nearly twice the weight achieved by hybrids of similar starting weight that were reared in parallel. The costs of social interaction in terms of reduced consumption, growth, and GGE were also quantified for bluegills and hybrids by comparing individually held fish with group-held fish over periods 1–3. Social costs reduced the growth rates of grouped bluegills more than those of grouped hybrids over the 75-d period. Our findings indicate that while the IGC was higher for the hybrids as early age-1 fish, the long-term IGC (e.g., to food market weights) is higher for bluegills; however, this result may be obscured, in part, by the bluegill’s higher social costs. Reduction of bluegill social costs in certain culture settings should result in growth rates that approach their higher IGC. Also, social costs varied in response to short-term shifts in the IGCs of both fishes, indicating a previously unknown influence on social interactions in fishes.

Treml, Melissa & Claussen, Julie & Philipp, David & Pereira, Donald. 1997. A Comparison of Bluegill Reproductive Strategies and Growth among Lakes with Different Fishing Intensities. North American Journal of Fisheries Management, 17: 496-507.

Abstract: Life history theory suggests that maturation schedules of male bluegill Lepomis macrochirus and the occurrence of alternative male reproductive strategies (i.e., parental or cuckolder) may contribute to the development and duration of undesirable bluegill population size structure (few fish larger than 150 mm). To investigate this relationship, we assessed parental male maturation schedules and relative abundance of cuckolders in six lakes subject to differing levels of fishing effort. Bluegills were collected by electrofishing shortly after the onset of the spawning season. Lakes with lower fishing effort had parental males that were older and larger at maturity than parental males in lakes with high fishing effort. Also, growth of parental males in lakes with low fishing effort was faster at older ages, and growth of immature males was faster than growth of cuckolders. Unlike other lakes, two of the three low-fishing-effort lakes had very few cuckolders. Our results indicate that intense fishing effort is associated with younger ages and smaller sizes at maturity for parental male bluegills. Also, increased proportions of cuckolders may be associated with increased fishing effort.