Models of fish school size in relation to environmental productivity

A simple energy-balance model, relating energetic requirements of fish schools to food production, was used to predict shoal sizes. Lower limits to school size are unlikely to be set by food but rather by predation. Upper limits depend on both food and school behavior, being greater for schools that break up to feed than for schools that remain continuously cohesive. Faced with a decreasing food supply, a school could either break into smaller schools or change behavior, increasing the area available for foraging. The models suggest that environmental productivity needs to be considered when examining fishery statistics such as (catch per unit effort), where maximum catch may be limited by maximum school size.     

Density affects female and male mate searching in the fiddler crab, <Emphasis Type="Italic">Uca beebei</Emphasis>

In most species, only one sex searches for mates while the other waits. Models of sex-specific mate-searching behavior predict single-sex searching, but the factors that determine which sex searches are not understood. In this study, we examine the effects of density and predation risk on mate-searching behavior in the fiddler crab Uca beebei. U. beebei is one of the few fiddler-crab species in which both sexes search for mates. In a field experiment conducted in Panama, we manipulated crab density and perceived predation risk in replicate plots. Females searched more and males searched less at high densities. At high levels of perceived predation risk, both sexes similarly reduced their search rates. Observations of plots that naturally varied in crab density show that females were more likely to search for mates in areas of higher density, where there were more males. Females may preferentially search for mates in high-density areas because the abundance of nearby burrows, into which they can run to escape predators, decreases their costs of searching and because the abundance of males and male burrows facilitates comparisons and thus may increase their benefits from searching. Males at high densities decrease their mate-searching rate perhaps in response to the increase in female searching and to the corresponding increase in the intensity of their competitors' mate-attraction signals.     

Acid mine drainage from inactive eastern coal operations

The most widely used technique for abatement of acid drainage from inactive surface mines and refuse disposal areas is revegetation of a soil cover applied to the waste material. Nonetheless, acid production often persists and in some cases, limits establishment of vegetation. This paper reports on several field studies intended to determine the location of pyrite oxidation zones and migration pathways of oxidation products at inactive spoil and refuse sites. Oxygen required for pyrite oxidation is believed to he provided in the gaseous state from the atmosphere. Therefore, the oxygen concentration in unsaturated mine waste should provide an estimate of the weathering tendency in the local environment. We are currently monitoring gas composition in refuse and spoil at six sites. Barren refuse appeared to be oxygenated (>2% 0₂) in a shallow zone extending less than 1 metre below the surface during most of the year. Preliminary data from coal spoil showed that oxygen can be available throughout the unsaturated thickness, even at a revegetated site. Gas composition varied vertically and laterally at a single site and also appeared to show seasonal dependence. Hydrologic factors are also important in acid production and transport. Discharge monitoring alone does not adequately describe the mass transport of acid products through the spoil. For example, at one reclaimed mine the mean sulfate content in six monitoring wells ranged from 24% to 240% of the mean concentration at the discharge point. Sources of recharge and relative flow rates determine the contribution of a particular zone to overall discharge quality. These basic studies of acid production and transport indicate some shortcomings of standard reclamation practices at certain sites. This information will he used to develop alternative abatement technology designed to mitigate acid production at the source.     

Temporal constraints and female preference for burrow width in the fiddler crab, <Emphasis Type="Italic">Uca mjoebergi</Emphasis>

We studied sampling behaviour and mate choice in the fiddler crab Uca mjoebergi. Once a female selects a mate, she copulates in his burrow and remains there until releasing her aquatic larvae. U. mjoebergi occurs in habitats that are inundated only by the highest amplitude spring tides. Females can only release their larvae during these tides, and release before or after will result in complete failure of reproductive effort. Matings occur over a 5-day period near the end of neap tides. Our results suggest that within the mating period, females adjust their larval developmental rates by selecting specific burrows in which to incubate their clutches. We found that at the start of the mating period, females chose larger males as mates. Since male size was positively correlated to burrow width, females were selecting wide burrows and effectively incubating at lower temperatures. This would slow down the developmental rates of larvae. In contrast, females that mated late in the mating period selectively chose small males. By incubating in narrower, warmer burrows, these females may increase the developmental rates of larvae. We propose that females are selecting burrows to influence incubation rate and ensure timely release of their larvae. Female U. mjoebergi appear to adjust their preference for the direct benefits of mate choice to increase their reproductive success.     

Larval abundance and recruitment of the sand dollar Dendraster excentricus in Monterey Bay,California, USA

Seasonal abundance of planktonic larvae of the sand dollar Dendraster excentricus was determined in Monterey Bay, California, USA. Larvae were counted from two offshore stations and also over a coastal sand dollar bed, and these data were compared with settlement in the sand dollar bed, with adult population structure and with adult reproductive condition. These measurements were made during the period July 1978 to October 1980 and in October 1981. Sand dollar larvae were most abundant in the plankton during the summer, a period when phytoplankton productivity tended to be high and currents were relatively slow and variable. In some years, small-scale current variations appeared to prevent many larvae in the open bay from reaching the nearshore sand dollar beds; however, in other years, massive shoreward transport of the larvae evidently did occur, since the adult population in the sand dollar bed exhibited a mode in size, indicating a large settlement. A comparison of settled individuals in 1980 and the adult size-frequency distribution in 1981 gives an estimated mortality rate of 88% yr^-1 for early juveniles of D. excentricus.     

Sex, intimidation and severed limbs: the effect of simulated predator attack and limb autotomy on calling and emergence behaviour in the field cricket Gryllus bimaculatus

Crickets can autotomize a limb in order to evade predation; however, this autotomy compromises their escape speed and, therefore, their ability to avoid subsequent predation events. We recorded two measures of predator-avoidance behaviour in field crickets (Gryllus bimaculatus) exposed to varying levels of predation threat, with the most extreme level leading to autotomy of a limb. Our first measure of caution was time to emergence from cover, which was affected by perceived predation treatment, with both autotomized males and females being significantly more cautious than intact individuals. For males (but not females), the presence of a calling conspecific encouraged earlier emergence. Our second measure of caution was alteration of male calling behaviour. Autotomized males remained silent for significantly longer time after disturbance than intact males, but there was no difference in call rate once they had resumed calling, suggesting that behavioural changes were not merely a result of injury response but a controlled modification of behaviour as a result of autotomy. These data suggest that autotomy in field crickets results in altered calling behaviour, which was not significantly altered with different acoustic environments.     

Microbial source tracking of Escherichia coli in a constructed wetland.

Little information has been gathered on the effect of avian species on the microbial water quality in constructed wetlands. To address this concern, fecal pollution from nonpoint and point sources was evaluated in a constructed wetland in Tolleson, Arizona. Antibiotic resistance profiling and biochemical fingerprinting were performed on 325 Escherichia coli isolates, collected from key points in the wetlands. Multivariate statistical analysis was used to interpret the data for samples collected on October 3 and December 12, 2000, and January 16, 2001. It was found that the passerine population was the major source of the Escherichia coli in the water samples collected in the wetlands on October 3 and December 12, 2000, whereas the regrowth in the treated municipal wastewater was the main source on January 16, 2001. This information is useful in providing data for operators in the monitoring of wetlands created for wastewater treatment and wildlife habitat.     

Biosorption of cadmium and copper contaminated water by Scenedesmus abundans

Experiments were conducted comparing the individual removals of cadmium and copper from water via biosorption using Scenedesmus abundans, a common green algae, to removal in a multi-component system to determine competitive effects, if any, between the metals. The goal was to characterize the biological treatment of water contaminated with heavy metals using live aquatic species. In addition, experiments were performed to measure cell viability as a function of metal concentration and also to compare metal removal using living species to that using nonliving ones. It was shown that, while both living and nonliving S. abundans removed cadmium and copper from water, living algae significantly outperformed nonliving algae. Further, in characterizing biosorption by three concentrations of live S. abundans, capacity curves were created comparing the metal biosorbed per mass algae to the initial metal concentration in solution. The algae concentration was not a factor in the biosorption of either metal individually, such that the capacity of the algae for the metal increased with decreasing algae concentration. At the lowest algae concentration considered, competitive effects were observed at copper and cadmium concentrations above 4 mg/l each. At the highest algae concentration considered, no competitive effects were observed in the range of cadmium and copper concentrations studied (1-7 mg/l). It was concluded that biological treatment of heavy metal contaminated water is possible and that at adequately high algae concentrations, multi-component metal systems can be remediated to the same level as individual metals.     

Improved recovery of repeat intoxicated drivers using fingernails and blood spots to monitor alcohol and other substance abuse

Objectives: This study reports the results of a pilot program in Kenosha County that used a combination of direct biomarkers extracted from blood spots and nails to monitor repeat intoxicated drivers for their use of alcohol and drugs with a detection window spanning from 3 weeks to several months. The objectives were to test whether the direct biomarkers phosphatidylethanol (PEth), ethylglucuronide (EtG), and 5 drug metabolites would (1) help assessors obtain a more objective evaluation of repeat offenders during the assessment interview, (2) allow for timely identification of relapses and improve classification of drivers into risk categories, and (3) predict recidivism by identifying offenders most likely to obtain a subsequent operating while intoxicated (OWI) offense within 4 years of enrollment in the program.

Methods: All (N = 261) repeat offenders were tested using PEth obtained from blood spots and EtG obtained from fingernails; 159 participants were also tested for a 5 drugs of abuse nail panel. Drivers were tested immediately after the assessment interview (baseline) and at 3, 6, 9, and 12 months after baseline. Based on biomarker results and self-reports of abstinence, offenders were classified into different risk categories and required to follow specific testing timelines based on the program's decision tree.

Results: The baseline analysis shows that 60% of drivers tested positive for alcohol biomarkers (EtG, PEth, or both) at the assessment interview, with lower detection rates (0–11%) for the 5 drug metabolites. The comparison of biomarkers results to self-reports of abstinence identified 28% of all offenders as high risk and assigned them to more frequent testing and more intense monitoring. The longitudinal analysis shows that 56% (completers) of participants completed the program successfully and the remaining 44% (noncompliant) terminated prematurely. Two thirds (68%) of the completers were able to reduce or control their drinking and one third relapsed at least one time during their mandated monitoring periods. After a brief intervention by the assessors, 79% of relapsers tested negative for biomarkers in their repeat tests. The rearrest analysis showed that offenders classified in the noncompliant and relapsers groups were 7 times more likely to receive a new OWI 4 years after enrollment compared to drivers classified as abstainers or controllers. Refractory drivers were monitored the longest and reported no subsequent rearrests.

Conclusion: These findings demonstrate the benefits of more individualized interventions with repeat OWI offenders and calls for further development of multimodal approaches in traffic medicine including those that use direct alcohol biomarkers as evidence-based practices to reduce recidivism.