Gary D. Grossman

Stochasticity in structural and functional characteristics of an Indiana stream fish assemblage: a test of community theory.

In general, ecological assemblages and communities appear to be regulated primarily by either deterministic or stochastic processes. It is currently important to quantify the relative frequencies of these two types of assemblages since most ecological theory is applicable only to deterministic systems. We attempted to distinguish the mechanism regulating species abundances and trophic structure in an Indiana stream fish assemblage. Samples collected over a 12-yr period were separated by season (spring, summer, and autumn) and species were then assigned to a trophic group based on published dietary data. Analyses showed a total lack of persistence for the ranks of species abundances and the ranks of trophic groups for all seasons. Consequently, we conclude that this assemblage is probably regulated by stochastic factors. This finding is concordant with many other studies which have documented the substantial effects of environmental unpredictability (i.e., floods and droughts) on other stream taxocenes.

An Energetic Model of Microhabitat Use for Rainbow Trout and Rosyside Dace

We constructed an energetic model to determine the optimal focal point current velocity (i.e., microhabitat) for rainbow trout (Oncorhynchus mykiss) and rosyside dace (Clinostomus funduloides) in Coweeta Creek, a fifth-order stream in North Carolina, USA. Energetic costs were evaluated by quantifying the metabolic expenditure associated with swimming at a given velocity. We estimated benefits by measuring potential energetic gains of feeding at a given velocity. This included estimates of the ability of the fish to capture prey at different current velocities as well as estimates of the frequency and the energy content of drifting prey at various velocities. We derived separate models for small (53-70 mm SL (standard length)) and medium (71-125 mm SL) trout, and medium (47- 52 mm SL) and large (53-70 mm SL) dace for all seasons, deriving net energy gain as a function of current velocity. We predicted fishes would occupy velocities at which net energy gain was maximized. Predicted velocities were compared with those utilized by fishes inhabiting Coweeta Creek. Optimal velocities predicted by energetic models ranged from 7.7 to 22.1 cm/s, and closely matched actual velocity use (average deviation = 2.6 cm/s). Prey capture success appeared to be the most important component in the models. Consequently, we constructed models based solely upon aspects of capture success; the average deviation from velocity use with these models was only 1.8 cm/s. Thus, the ability of dace and trout to capture prey at varying velocities appears to be the dominant factor affecting microhabitat selection in these species.

ASSEMBLAGE ORGANIZATION IN STREAM FISHES: EFFECTS OF ENVIRONMENTAL VARIATION AND INTERSPECIFIC INTERACTIONS

We assessed the relative importance of environmental variation, interspecific competition for space, and predator abundance on assemblage structure and microhabitat use in a stream fish assemblage inhabiting Coweeta Creek, North Carolina, USA. Our study encompassed a 10–yr time span (1983–1992) and included some of the highest and lowest flows in the last 58 years. We collected 16 seasonal samples which included data on: (1) habitat availability (total and microhabitat) and microhabitat diversity, (2) assemblage structure (i.e., the number and abundances of species comprising a subset of the community), and (3) microhabitat use and overlap. We classified habitat availability data on the basis of year, season, and hydrologic period. Hydrologic period (i.e., pre–drought [PR], drought [D], and post–drought [PO]) represented the temporal location of a sample with respect to a four–year drought that occurred during the study. Hydrologic period explained a greater amount of variance in habitat availability data...

FLOOD DISTURBANCE REGIMES INFLUENCE RAINBOW TROUT INVASION SUCCESS AMONG FIVE HOLARCTIC REGIONS

There is growing awareness that predicting biological invasions will require the development of conceptual models for specific taxa at appropriate scales. Salmonids are ideal taxa for testing factors that influence invasions, because large numbers have been introduced worldwide for long periods and their ecology is well known. We evaluated the hypothesis that, among regions with suitable water temperatures, environmental resistance from flood disturbances that wash away trout fry strongly influence invasion success of rainbow trout (Oncorhynchus mykiss), the most widely introduced fish species. We predicted that flow regimes in regions where rainbow trout invasions are successful would match those in their native range and would differ from those in regions where invasions are moderately successful or failed. We tested six specific predictions about how timing, predictability, frequency, duration, and annual variability of floods, as well as timing of low flows, will differ relative to timing of rainbow t...

On the use of the gonosomatic index

Abstract 1. 1. Using data collected from two teleostean fish species the assumptions of the gonosomatic index (GSI) were examined primarily by regression analysis and analysis of covariance. 2. 2. Standard length of the fish and standard length cubed can have a higher degree of correlation with ovarian weight as compared to body weight. Therefore, an ovarian weight-body weight ratio is not always the best way of expressing a gonadal index. 3. 3. When ovarian weight is regressed on some expression of body size, intercepts of the regression equations have a non-zero intercept. Furthermore, intercepts of regression equations from fish in different ovarian development stages are not always statistically homogenous. These findings are inconsistent with the GSI assumption of a zero intercept. 4. 4. The relationship of ovarian weight to body size changes with the stage of oocyte development. Thus, the GSI is an inaccurate means of comparing gonadal activity between experimental groups. 5. 5. When independent and dependent variables are subjected to log transformations, the relationship of ovarian weight to body size is less likely to vary with stage of oocyte development. Thus, expressing ovarian weight as an exponential function of some measure of body size may provide a more appropriate gonadal index. 6. 6. The analyses presented disclose that the GSI is not an accurate indicator of gonadal activity.

Do Artificial Reefs Increase Regional Fish Production? A Review of Existing Data

Abstract We reviewed the scientific literature to determine whether the construction of artificial reefs increases the regional production of marine fishes. An evaluation of this technique is warranted by its high cost and logistical difficulty. Our review indicated that reef construction may have potentially deleterious effects on reef fish populations, including (1) increasing fishing effort and catch rates, (2) boosting the potential for overexploitation of stocks by increasing access to previously unexploited stock segments, and (3) increasing the probability of overexploitation by concentrating previously exploited segments of the stock. In contrast, the literature contained few studies that unambiguously demonstrated that artificial reefs increased regional fish production rather than merely concentrated available biomass. In addition, the literature on population regulation in reef fishes did not provide convincing evidence that reef fishes were limited by insufficient quantities of hard-bottom hab...

Assemblage stability in stream fishes: a review

We quantified the stability of nine stream fish assemblages by calculating coefficients of variation of population size for assemblage members. Coefficients of variation were high and averaged over 96%; indicating that most assemblages were quite variable. Coefficient of variation (CV) estimates were not significantly affected by: (1) years of study, (2) mean abundance, (3) familial classification, or (4) mean interval between collections. We also detected minor regional differences in CVs. The high variability exhibited by many stream fish assemblages suggests that it may be difficult to detect the effects of anthropogenic disturbances using population data alone. Consequently, we urge managers to exercise caution in the evaluation of the effects of these disturbances. More long-term studies of the ecological characteristics of undisturbed stream fish assemblages are needed to provide a benchmark against which disturbed systems can be compared.We suggest that CVs are a better estimator of population/assemblage stability, than either Kendalls W or the standard deviation of the logarithms of numerical censuses. This conclusion is based on the following reasons. First, CVs scale population variation by the mean and, hence, more accurately measure population variability. Second, this scaling permits the comparison of populations with different mean abundances. Finally, the interpretation of CV values is less ambiguous than either of the aforementioned metrics.

Home range estimates for three North American stream fishes

We estimated home ranges of three fish species inhabiting a fourth order stream in the Blue Ridge Mountains of North Carolina. Individuals were uniquely marked with a subcutaneous injection of acrylic paint. Cottus bairdi, Rhinichthys cataractae and Clinostomusfunduloides moved an average of 12.9, 13.4, and 19.3 m respectively, between captures. Mean time interval between captures was 128 d; 86% of recaptures were in the stream section of previous capture. Individuals may not have moved throughout the entire section length (mean length 10.4 m); thus, these values likely overestimate actual movements.

DYNAMICS AND ORGANIZATION OF A ROCKY INTERTIDAL FISH ASSEMBLAGE: THE PERSISTENCE AND RESILIENCE OF TAXOCENE STRUCTURE

This paper examines characteristics of a rocky intertidal fish taxocene in central California. Seasonal and annual changes in taxocene structure, diversity, and recruitment were described and attempts were made to correlate these parameters with environmental variables. In addition, the persistence and resilience of taxocene structure were examined to determine whether this assemblage was regulated through deterministic or stochastic processes. A series of tidepools were defaunated 15 times over 29 mo. Sampling did not grossly affect taxocene structure in the study site and recolonization from surrounding areas was rapid. Three types of abundance patterns were observed: (1) species present year round (residents), (2) species present seasonally, and (3) species occasionally present. Productivity appeared to be the main environmental factor affecting taxocene structure because there were significant correlations between it and: (1) diversity, (2) species richness, (3) numerical abundance, and (4) recruitment to the assemblage. Wave action and temperature played a lesser role in explaining variations in taxocene parameters. The test of taxocene persistence and resilience showed that this assemblage was both persistent and resilient over the course of the study, despite repeated defaunation. These results are consistent with the predictions of the deterministic model of community organization and contradict those of the stochastic model. Consequently, this taxocene is probably successional or persistent. This result is surprising because studies of algal and invertebrate assemblages occupying this habitat indicate that these assemblages are stochastically regulated. Thus, the environmental pressures affecting the evolution of assemblage regulation have had different effects on these three taxocenes. This demonstrates that the relationship of environment to community organization is complex and dependent upon the evolutionary and ecological characteristics of the taxa examined.

Turbidity-induced changes in reactive distance of rainbow trout

Abstract We used artificial stream channels to conduct feeding trials with wild rainbow trout Oncorhynchus mykiss at three levels of suspended sediment. To examine the effects of turbidity on reactive distance and pursuit speed, we fed rainbow trout (87–185 mm standard length) pieces of mealworms Tenebrio sp. as test prey. A video camera system was used to record the pursuit speed and reactive distance of fish during foraging bouts. Turbidity had a consistent and negative effect on reactive distance (analysis of variance, P < 0.05). On average, reactive distances in the 15- and 30-NTU (nephelometric turbidity units) treatments were only 80% and 45%, respectively, of those observed at ambient turbidities (4–6 NTUs). By contrast, turbidity did not significantly affect pursuit speed. Pursuit speed varied greatly among individuals but was similar for each fish across turbidity levels. These results indicate that sediment-producing activities, such as logging and road building, could reduce foraging success wi...