Leandro E. Miranda

Winter Survival of Age-0 Largemouth Bass Relative to Size, Predators, and Shelter

Abstract Winter mortality of age-0 largemouth bass Micropterus salmoides is sometimes size dependent, with smaller fish experiencing higher mortality. We conducted this study to determine if the presence of predators influenced winter mortality of young largemouth bass, if predators influenced all sizes of young equally, and if increased shelter availability moderated a possible relation between predator-induced mortality and fish size, We stocked 0.06-ha experimental ponds with largemouth bass (30 fish/pond) of five length groups (55–100, 101–125, 126–150, 151–175, and 176–200 mm total length), with and without predators (three largemouth bass 250–350 mm long), and four levels of shelter (0, 10, 16, and 26% brush coverage of surface area of ponds). In ponds without shelter, survival ranged from 10 to 97% in the presence of predators and from 77 to 93% in the absence of predators. Fish less than 126 mm long had gradually lower survival in the presence of predators, but near 80% survival in the absence of ...

Immobilization Thresholds of Electrofishing Relative to Fish Size

Abstract Fish size and electrical waveforms have frequently been associated with variation in electrofishing effectiveness. Under controlled laboratory conditions, we measured the electrical power required by five electrical waveforms to immobilize eight fish species of diverse sizes and shapes. Fish size was indexed by total body length, surface area, volume, and weight; shape was indexed by the ratio of body length to body depth. Our objectives were to identify immobilization thresholds, elucidate the descriptors of fish size that were best associated with those immobilization thresholds, and determine whether the vulnerability of a species relative to other species remained constant across electrical treatments. The results confirmed that fish size is a key variable controlling the immobilization threshold and further suggested that the size descriptor best related to immobilization is fish volume. The peak power needed to immobilize fish decreased rapidly with increasing fish volume in small fish but ...

An Evaluation of the Value of Harvest Restrictions in Managing Crappie Fisheries

Abstract We used an equilibrium yield model to simulate the effect of reducing exploitation on yield and average weight of white crappies Pomoxis annularis, based on empirical growth data and various levels of conditional natural mortality. Modeling indicated that reducing exploitation would likely increase yield as fish growth increased and natural mortality decreased; however, reducing exploitation would not substantially affect yield when conditional natural mortality exceeded 30–40%, regardless of growth. For instance, a 250-mm minimum length limit provided higher yield than a 200-mm minimum length limit only if growth was above average and conditional natural mortality was less than 30–40%. Average weight of crappies harvested increased with growth and length at recruitment to the fishery but decreased with exploitation and conditional natural mortality. Our results suggest that a length limit could improve both yield and average weight for crappie fisheries only if growth is rapid and natural mortal...

Fish Assemblages in Oxbow Lakes Relative to Connectivity with the Mississippi River

Abstract The alluvial valley of the lower Mississippi River contains hundreds of fluvial lakes that are periodically connected to the river during high water, although the frequency, duration, and timing of the connections vary. To help design plans to restore and preserve fish assemblages in these alluvial lakes, this investigation tested whether predictable patterns in lake fish assemblages were linked to the level of connectivity with the river. Results suggested that connectivity played an important role in structuring fish assemblages and that it was correlated with variables such as lake size, depth, distance from the river, and age, which exhibit a continuum of predictable features as the river migrates away from abandoned channels. Annual floods homogenize the floodplain and promote connectivity to various degrees, allowing for fish exchanges between river and floodplain that directly affect fish assemblages. The major physical changes linked to reduced connectivity are loss of depth and area, whi...

Relationship between Vegetation Coverage and Abundance, Size, and Diet of Juvenile Largemouth Bass during Winter

Abstract Juvenile largemouth bass Micropterus salmoides were collected by electrofishing during October through March 1992–1994 from coves (≤25 ha) covered with aquatic macrophytes over 1–65% of their area. Mean total length of juvenile largemouth bass was highest in coves with the least vegetated cover, but increase in mean length between October and March was highest in coves having near 20% vegetation coverage. Catch per unit effort decreased between October and March; decreases were least at vegetation coverages near 10–20%, highest at coverages of 5% or less, and intermediate at coverages of 30–65%. By March, these disparate decreases contributed to the formation of a dome-like relationship between vegetation coverage and catch per unit effort. Consumption of fish foods was highest when vegetation coverage was low, but decreased asymptotically as coverage increased; consumption of invertebrate foods increased at low coverage, peaked near 20–30% coverage, and decreased at higher coverage. We suggest t...

Uncertainty of Exploitation Estimates Made from Tag Returns

Abstract Over 6,000 crappies Pomoxis spp. were tagged in five water bodies to estimate exploitation rates by anglers. Exploitation rates were computed as the percentage of tags returned after adjustment for three sources of uncertainty: postrelease mortality due to the tagging process, tag loss, and the reporting rate of tagged fish. Confidence intervals around exploitation rates were estimated by resampling from the probability distributions of tagging mortality, tag loss, and reporting rate. Estimates of exploitation rates ranged from 17% to 54% among the five study systems. Uncertainty around estimates of tagging mortality, tag loss, and reporting resulted in 90% confidence intervals around the median exploitation rate as narrow as 15 percentage points and as broad as 46 percentage points. The greatest source of estimation error was uncertainty about tag reporting. Because the large investments required by tagging and reward operations produce imprecise estimates of the exploitation rate, it may be wor...

Riverine characteristics dictate composition of fish assemblages and limit fisheries in reservoirs of the upper Paraná River basin

A qualitative comparative approach has been used to review whether fish assemblage characteristics, such as paucity of lacustrine-adapted fish species, long food chains, and disproportionate number of piscivorous species, limit fishery yields in reservoirs of the Upper Parana River basin. The paucity of lacustrine-adapted species appears to limit fishery yields, but attempts to introduce lacustrine species have been generally unsuccessful. The food chains of species targeted by the fisheries are relatively long, but short food chains seem to be an adaptation of lacustrine species. Because reservoirs with many piscivorous species sustain high fishery yields elsewhere in the world, the hypothesis that an excessive number of piscivores limits yields is not supported. Instead, inadequacies of fish assemblages in reservoirs of the Upper Parana River basin appear to be symptomatic of an unsuitable environment for lacustrine fish species. The physical characteristics of reservoirs in the Upper Parana River basin, exacerbated by climatic patterns, may preclude the emergence of successful reservoir species from within the extant pool of riverine species. The resulting assemblages have characteristics that are neither riverine nor lacustrine, and are maladapted to support fisheries in the reservoirs. The introduction of lacustrine species is destined to failure because environmental characteristics are not lacustrine, except in reservoirs positioned high in the watershed, where increased retention times allow lacustrine conditions. Published in 2001 by John Wiley & Sons, Ltd.

Injury and Mortality of Warmwater Fishes Immobilized by Electrofishing

Abstract Most studies of injury associated with electrofishing have focused on salmonids; few have given attention to warmwater fishes. Under controlled laboratory conditions, we treated bluegill Lepomis macrochirus, channel catfish Ictalurus punctatus, and largemouth bass Micropterus salmoides of various sizes to duty cycles ranging from 1.5% to 100%. This range of duty cycles represented continuous DC and pulsed-DC frequencies ranging from 15 to 110 Hz and pulse durations of 1 to 6 ms. At each duty cycle, fish were exposed to power densities in excess of those required to immobilize them within 3 s, and we subsequently determined the incidence of hemorrhage, spinal injury, and mortality. Incidence of hemorrhage averaged 3% (range, 0–25%), differed among species, and was not related to duty cycle or fish size. Incidence of spinal injury averaged 3% (range, 0–22%) and mortality averaged 10% (range, 0–75%); both differed among species and were related to duty cycle, fish size, and interactions among these ...

Size Selectivity of Crappie Angling

Abstract Over 6,000 black crappies Pomoxis nigromaculatus and white crappies P. annularis were tagged in five lakes and reservoirs to quantify size selectivity of angling. Total length of fish tagged ranged from 20.0 to 39.8 cm; fish caught by anglers ranged from 20.0 to 38.8 cm. Return rates were low at lengths near 20 cm, increased gradually to a peak between 26 and 32 cm, and decreased for longer fish. This pattern was consistent among the five lakes and reservoirs and did not differ between species. Observed size-selective exploitation resulted in the lopsided removal of intermediate age-classes, thereby simulating a reversed slot length limit. Crappie population dynamics and fisheries can be severely affected if angling selectivity and exploitation are high. Management of crappies to favor desirable population characteristics may need to focus on enhancing or weakening the effect of size selectivity.

Fish assemblage dynamics in a Neotropical floodplain relative to aquatic macrophytes and the homogenizing effect of a flood pulse

The presence of aquatic macrophytes is a key factor in the selection of habitats by fish in floodplain lakes because these plants enhance the physical and biological complexities of aquatic habitats. The seasonal flood pulse may influence this interaction, but there is no information in the literature about the effects that flood events may have on macrophytes assemblages and its associated effects on fish assemblages. Thus, this article aimed to investigate whether species richness, evenness and similarities in fish assemblage composition differed between littoral areas vegetated with macrophytes and unvegetated areas, before and after a flood. We sampled three lakes in the floodplain of the upper Paraná River basin. Sampling was conducted before (December 2004 and January 2005) and after (early March, late March and May 2005) a flood event. Overall, species richness and evenness were higher in macrophytes-covered areas. Before the flood, the composition of fish assemblages was distinct when comparing vegetated and unvegetated areas. After the flood, the similarity in fish assemblage composition was higher, indicating a homogenization effect of floods for fish inhabiting littoral areas of floodplain lakes. After the flood, opportunistic species dominated the fish assemblages in aquatic macrophytes, apparently restructuring assemblages in the littoral, restarting a succession process. Thus, the observed homogenization effect of the flood could minimize biological interactions and could induce fish assemblages to begin a new process of structurization.