Michael A. Nannini

The influence of selection for vulnerability to angling on foraging ecology in largemouth bass Micropterus salmoides

Several traits related to foraging behaviour were assessed in young-of-the-year produced from largemouth bass Micropterus salmoides that had been exposed to four generations of artificial selection for vulnerability to angling. As recreational angling may target foraging ability, this study tested the hypothesis that selection for vulnerability to angling would affect behaviours associated with foraging ecology and prey capture success. Fish selected for low vulnerability to angling captured more prey and attempted more captures than high vulnerability fish. The higher capture attempts, however, ultimately resulted in a lower capture success for low vulnerability fish. Low vulnerability fish also had higher prey rejection rates, marginally shorter reactive distance and were more efficient at converting prey consumed into growth than their high vulnerability counterparts. Selection due to recreational fishing has the potential to affect many aspects of the foraging ecology of the targeted population and highlights the importance of understanding evolutionary effects and how these need to be considered when managing populations.

Largemouth Bass Selected for Differential Vulnerability to Angling Exhibit Similar Routine Locomotory Activity in Experimental Ponds

Abstract A growing body of work is focused on attempting to understand the biological mechanism(s) by which some fish are highly vulnerable to angling while others are not. We used electromyogram telemetry to monitor routine locomotory activity of artificially selected largemouth bass Micropterus salmoides in experimental ponds to test two potential explanatory hypotheses: (1) that the difference in angling vulnerability between high-vulnerability (HV) bass and low-vulnerability (LV) bass is related to a difference in routine activity level between the two groups, and (2) that the difference in vulnerability between HV and LV bass is related to a difference in the diel activity pattern displayed by each group (e.g., LV fish are more active at night, a time where there is typically little bass fishing effort). Neither hypothesis was supported by our results. Differences in vulnerability to angling in artificially selected lines of largemouth bass were not related to inherent differences in routine locomoto...

Do Behavioral Syndromes Affect Foraging Strategy and Risk‐Taking in a Juvenile Fish Predator?

Abstract Behavioral syndromes often have individuals varying along a continuum of personality traits. Some individuals exhibit bold or aggressive behaviors and are willing to explore novel stimuli, whereas others are shy and tend to avoid novel stimuli. Species that undergo an ontogenetic diet shift may experience a particularly important benefit if the shift to more-profitable prey is linked to this willingness to explore novel stimuli. However, actively selecting more-evasive prey can make these predators more vulnerable to predation themselves. We used largemouth bass Micropterus salmoides as a model to examine the role of behavioral syndromes in structuring predator strategies for dealing with these conflicting environmental pressures. Exploration behavior was first determined by testing willingness to explore a novel environment. Behaviors were then measured in two other contexts where exploration and boldness could potentially have fitness consequences: (1) the likelihood of consuming a novel prey i...

Sex-specific consequences of experimental cortisol elevation in pre-reproductive wild largemouth bass.

Experimental implants were used to investigate the effect of elevated cortisol (the primary stress hormone in teleost fish) on energetic and physiological condition prior to reproduction in male and female largemouth bass (Micropterus salmoides). Fish were wild-caught from lakes in Illinois, and held in experimental ponds for the duration of the study. Between 9 and 13 days after cortisol treatment, and immediately prior to the start of the reproductive period, treated and control animals were sampled. Females exhibited lower muscle lipid content, lower liver glycogen content, and higher hepatosomatic indices than males, regardless of treatment. Also, cortisol-treated females had higher hepatosomatic indices and lower final mass than control females, whereas males showed no differences between treatment groups. Finally, cortisol-treated females had higher gonadal cortisol concentrations than control females. In general, we found evidence of reduced energetic stores in female fish relative to male fish, likely due to timing differences in the allocation of resources during reproduction between males and females. Perhaps driven by the difference in energetic reserves, our data further suggest that females are more sensitive than males to elevated cortisol during the period immediately prior to reproduction.

The effect of vegetation density on juvenile bluegill diet and growth

Experimental ponds (0.4 ha) were used to evaluate the effects of vegetation density on bluegill (Lepomis macrochirus) diet and growth in the absence of pelagic predation risk. Fish (30–50 mm, total length) were stocked at a rate of 15 kg per pond. By the end of the 3-month experiment, bluegill in the low vegetation treatment (109 g m−2 ± 21.0 SE, n = 4) had grown 20% longer than the fish in the high vegetation treatment (712 g m−2 ± 54.3 SE, n = 4) despite having similar mean stomach fullness. Bluegill in the high vegetation treatment ingested more gastropods and odonates and less benthic prey (chironomids) than did the fish in the low vegetation treatment. Very little pelagic zooplankton were eaten by fish in either treatment despite the lack of predation risk in the open water habitat. These results suggest that bluegill chose to forage in a vegetated habitat even in the absence of predation risk, resulting in reduced growth.

Effect of Predators on Growth and Reproductive Investment in Bluegills: Comparison of Populations with Differing Size and Age of Maturation

Abstract Growth rate and age of maturation are two important factors that control adult body size. Predators can also exert an influence on the size and age of maturation of their prey. We compared the growth, timing of maturation, and investment in gonad development of bluegills Lepomis macrochirus in ponds with and without largemouth bass Micropterus salmoides predators. In addition, we compared the response between bluegills from stunted (small size and early age of maturation) and nonstunted (larger size and later age of maturation) populations to determine whether predation could explain the occurrence of stunted body size in bluegills. For both males and females, we found that bluegills grew faster but matured at the same rate in the presence of predators. The investment in gonad development (measured by the gonadosomatic index) did not differ between individuals raised with predators and those raised without. Regardless of predator treatment, fish from the nonstunted population grew more than those...

The release and regulation of rotifers: examining the predatory effects of invasive juvenile common and bighead carp

Ecosystem level effects of common (Cyprinus carpio) and bighead carp (Hypophthalmichthys nobilis) have generally focused on adult life stages. The objective of our mesocosm study was to investigate and contrast the roles of juvenile common and bighead carp in structuring planktonic invertebrate assemblages, with focus on rotifers. We examined whether predation by juvenile carp was indiscriminate or size-selective with respect to prey size. Furthermore, we examined how changes to large and small prey influenced the potential for compensatory increases of some taxa within prey assemblages. Both species of juvenile carp reduced large zooplankton taxa. However, rotifer responses were variable depending on the taxon and predator combination. Juvenile common carp enhanced abundance for Polyartha and Squatinella, but most taxa were unaffected. Juvenile bighead carp had a more varied effect on rotifer abundance, having no effect on most, reducing Keratella and enhancing Anuraeopsis. We also estimated net filtration volume of the zooplankton community for each of the treatments and found partial compensation in net filtration because of the increased abundance of a few rotifer taxa, but this reduction did not match the depletion of macrozooplankton. Rotifers that benefitted from the presence of fish predators likely responded positively because of reduced predation by mesopredators, because of their short generation times, and/or from reduced competition.

Effects of maternal cortisol treatment on offspring size, responses to stress, and anxiety-related behavior in wild largemouth bass (Micropterus salmoides)

Cortisol, the main glucocorticoid stress hormone in teleost fish, is of interest as a mediator of maternal stress on offspring characteristics because it plays an organizational role during early development. The present study tested the hypothesis that maternal exposure to cortisol treatment prior to spawn affects offspring phenotype using wild largemouth bass (Micropterus salmoides). Baseline and stress-induced cortisol concentrations, body size (i.e. length and mass), and behavior (i.e. anxiety, exploration, boldness, and aggression) were assessed at different offspring life-stages and compared between offspring of control and cortisol-treated females. Cortisol administration did not affect spawning success or timing, nor were whole-body cortisol concentrations different between embryos from cortisol-treated and control females. However, maternal cortisol treatment had significant effects on offspring stress responsiveness, mass, and behavior. Compared to offspring of control females, offspring of cortisol-treated females exhibited larger mass right after hatch, and young-of-the-year mounted an attenuated cortisol response to an acute stressor, and exhibited less thigmotaxic anxiety, exploratory behavior, boldness and aggression. Thus, offspring phenotype was affected by elevated maternal cortisol levels despite the absence of a significant increase in embryo cortisol concentrations, suggesting that a mechanism other than the direct deposition of cortisol into eggs mediates effects on offspring. The results of the present raise questions about the mechanisms through which maternal stress influences offspring behavior and physiology, as well as the impacts of such phenotypic changes on offspring fitness.

Size‐Dependent Consequences of Exogenous Cortisol Manipulation on Overwinter Survival and Condition of Largemouth Bass

Little is known about the size-dependent consequences of stressors on wild animals, which is particularly relevant during winter where size-specific trends in survival are common. Here, exogenous cortisol manipulation was used to investigate the effect of a physiological challenge on overwinter mortality and spring condition of largemouth bass (Micropterus salmoides) across a range of body sizes. Fish were wild-caught in the fall, assigned into either control or cortisol manipulated treatments, and held in replicated experimental ponds. For bass that survived the winter, length, mass, and health metrics (e.g., gonadosomatic index [GSI], hepatosomatic index [HSI], and water content) were determined in the spring. Winter survival was marginally lower for cortisol treated bass; however, there was no influence of initial length, mass, or condition on overwinter survival. When bass were grouped by size, survival was significantly higher for bass 300-350 mm in length compared to those <200 mm. The treatment did not strongly influence spring health metrics, suggesting that largemouth bass that survived the winter were able to recover from the effects of the cortisol elevation. Initial size and sex were linked to some spring health metrics, with large females having the highest GSI and HSI scores. Overall, results from this study do not support the notion that there are size-dependent responses to cortisol manipulation in a teleost fish. Rather, this type of physiological challenge may modulate the natural rates of winter mortality that are primarily driven by starvation and predation, independent of body size, in subadult and adult largemouth bass.

Does prey community composition affect the way different behavioral types interact with their environment

We examined how different exploratory behavioral types of largemouth bass responded to differing prey communities by determining effects on growth, survival and diet in experimental ponds. We found evidence that non-explorer largemouth bass target young-of-year bluegill early on in life, but bluegill were not an important diet item by late summer. The presence of young-of-year bluegill as prey does appear to affect the foraging strategy of the two exploring types differently. In the absence of small bluegill, both behavioral types feed primarily on benthic invertebrates and zooplankton. When small bluegill were present, we saw a shift away from zooplankton as prey for largemouth bass. However, that shift was toward more benthic invertebrates for non-exploring behavioral types and toward terrestrial insects for exploring behavioral types. Thus, it appears that prey community composition can have important effects on the way in which different behavioral types interact with their environment.