Mike S. Allen

Evaluating the potential efficacy of invasive lionfish (Pterois volitans) removals.

The lionfish, Pterois volitans (Linnaeus) and Pterois miles (Bennett), invasion of the Western Atlantic Ocean, Caribbean Sea and Gulf of Mexico has the potential to alter aquatic communities and represents a legitimate ecological concern. Several local removal programs have been initiated to control this invasion, but it is not known whether removal efforts can substantially reduce lionfish numbers to ameliorate these concerns. We used an age-structured population model to evaluate the potential efficacy of lionfish removal programs and identified critical data gaps for future studies. We used high and low estimates for uncertain parameters including: length at 50% vulnerability to harvest (Lvul), instantaneous natural mortality (M), and the Goodyear compensation ratio (CR). The model predicted an annual exploitation rate between 35 and 65% would be required to cause recruitment overfishing on lionfish populations for our baseline parameter estimates for M and CR (0.5 and 15). Lionfish quickly recovered from high removal rates, reaching 90% of unfished biomass six years after a 50-year simulated removal program. Quantifying lionfish natural mortality and the size-selective vulnerability to harvest are the most important knowledge gaps for future research. We suggest complete eradication of lionfish through fishing is unlikely, and substantial reduction of adult abundance will require a long-term commitment and may be feasible only in small, localized areas where annual exploitation can be intense over multiple consecutive years.

Population Viability of the Gulf of Mexico Sturgeon: Inferences from Capture–Recapture and Age-Structured Models

Abstract The Suwannee River, Florida, population of the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi, a subspecies of Atlantic sturgeon A. oxyrinchus oxyrinchus, was evaluated using a capture–recapture approach and an age-structured model to examine population trends from 1986 through 1995. The capture–recapture analysis revealed a positive rate of change (λ) in the adult population, indicating that it was slowly increasing from the mid-1980s through the mid-1990s. The age-structured model revealed that the population was highly sensitive to changes in egg-to-age-1 mortality, the percentage of females that spawn annually, and adult mortality. The model predicted that even slight increases in annual adult mortality (from 16% to 20%) would result in a decline in the Suwannee River Gulf sturgeon population. Population trends were consistent for both modeling procedures and were similar to those in published reports. Although this population is currently expanding, care should be taken to protect adul...

Habitat and diet partitioning between shoal bass and largemouth bass in the Chipola River, Florida

Abstract We investigated the macrohabitat use, microhabitat use, and food habits of shoal bass Micropterus cataractae and largemouth bass M. salmoides in the upper Chipola River, Florida. We electrofished two macrohabitats (pools and shoals) during the summer (May–August) and fall (September–December) of 1999 and 2000. The ratio of shoal bass to largemouth bass differed among macrohabitats, being highest in the shoals and lowest in the pools. Age-0 and adult (age-1 and older) shoal bass were collected in areas of higher-than-average percentages of rocky substrate in both shoals and pools. Age-0 and adult largemouth bass were associated with areas of reduced current velocity and those with higher-than-average amounts of woody debris. Though the diets of age-0 and adult shoal bass and largemouth bass were similar, a few differences were apparent. Age-0 largemouth bass diets contained grass shrimp Palaemonetes spp., whereas age-0 shoal bass diets contained mostly mayflies (order Ephemeroptera: families Baeti...

Largemouth Bass Abundance and Angler Catch Rates following a Habitat Enhancement Project at Lake Kissimmee, Florida

Abstract A habitat enhancement project was conducted at Lake Kissimmee, Florida, during 1995-1996 to improve fish habitat and remove dense inshore vegetation caused by stabilized water levels. We evaluated abundance of age-1 (<250 mm total length (TL)) and adult (fish at least 356 mm TL and all sizes of fish caught by anglers) largemouth bass Micropterus salmoides before and after the habitat enhancement. Mean electrofishing catch per hour (CPH) of age-1 largemouth bass increased significantly after the 1995-1996 habitat enhancement, suggesting strong year-classes for 2 years after the habitat enhancement (i.e., 1997-1998 year-classes). Growth of age-1 largemouth bass also increased following habitat enhancement; mean total length of age-1 fish averaged 143 mm before enhancement and 186 mm after enhancement. Catch curves conducted in 2001 and 2002 corroborated historical electrofishing data indicating that the 1997 and 1998 year-classes were abundant as adults compared with other year-classes in the age f...

Relation of Age-0 Largemouth Bass Abundance to Hydrilla Coverage and Water Level at Lochloosa and Orange Lakes, Florida

Abstract Changes in electrofishing catch per hour (CPH) of age-0 largemouth bass Micropterus salmoides were examined in relation to aquatic macrophytes and seasonal water elevation at Lochloosa and Orange lakes, Florida, during the 1990s. At Lochloosa Lake, stepwise multiple regression revealed a significant positive relationship between the mean CPH of age-0 largemouth bass and the percentage of areal coverage by hydrilla Hydrilla verticallata. At Orange Lake, mean CPH was directly associated with the percentage of areal coverage by hydrilla and inversely related to summer water levels. Thus, the influence of vegetation on age-0 largemouth bass abundance was similar at both lakes, but the effects of water levels were not. Further investigations into the effects of fluctuations in water levels on age-0 largemouth bass in natural lakes are needed.

Biphasic effects of intraaccumbens μ-opioid peptide agonist DAMGO on locomotor activities

The effects of bilateral microinjections of mu-opioid receptor agonist DAMGO (0.00, 0.01, 0.1, or 1.0 microgram/side) were tested in rats for 120 min in activity monitors. The horizontal movement, rearing, and stereotypy times in seconds were measured during 12 consecutive 10-min time blocks. DAMGO (0.01, 0.1, and 1.0 microgram) resulted in biphasic effects, inhibition followed by activation for each of the three measures. These data replicate the behavioral effects of ICV DAMGO except that the duration of the behavioral effects were longer with Acb injections.

Comparison of Electrofishing and Rotenone for Sampling Largemouth Bass in Vegetated Areas of Two Florida Lakes

Abstract We compared the sampling precision and efficiency of electrofishing and rotenone for assessing populations of largemouth bass Micropterus salmoides in vegetated portions of two Florida lakes. Sampling was conducted at Lochloosa and Orange lakes in north-central Florida from 1990 to 1999. Significant differences in length frequencies were determined between the two methods in 5 of 9 years for each lake. In years where differences existed, electrofishing collected larger fish than did rotenone. The maximum deviation between cumulative relative length frequencies for the two methods was not related to total vegetation, native emergent vegetation, or hydrilla Hydrilla verticallata coverage at either lake. Sampling precision was greater for electrofishing than for rotenone; electrofishing also required less sampling effort to detect changes in the abundance of juvenile and adult largemouth bass. Electrofishing was a more precise and cost-effective method than rotenone for estimating largemouth bass ab...

Temporal Water Chemistry Trends (1967–1997) for a Sample (127) of Florida Waterbodies

ABSTRACT Total phosphorus, total nitrogen, total chlorophyll and Secchi visibility data from 127 Florida lakes across three time periods, Early (1967–1972), Middle (1979–1981), and Present (1996–1997) were compared using paired t tests and repeated measures analyses of variances. Although the population of Florida has increased 116% over the last 27 years, expected increases in lake concentrations of nutrients were not found. For this sample of lakes, total phosphorus concentrations decreased over a 30-year time period and total nitrogen concentrations showed no significant change. Secchi visibility, one of the simplest parameters to measure and easily understood by lake-users, also showed no significant change over time. The sample of lakes showed a significant but small increase in total chlorophyll concentrations. The increase was unexpected because total phosphorus concentrations decreased and total nitrogen concentrations stayed the same, suggesting that other factors were impacting total chlorophyll concentrations in this group of lakes. It is speculated that changes in color, fluctuating water levels, and increases in the amount of aquatic plant control over time may help explain some of the increases in total chlorophyll. Independent estimates of normal month-to-month and year-to-year temporal variance for Florida lakes were calculated using long-term Florida LAKEWATCH data (71 lakes, with greater than 4 years of monthly data) and compared to the variance among the Early, Middle, and Present time periods. Most of the differences detected among the time periods using statistical analyses were within calculated normal monthly temporal variance. Thus, increased nutrient concentrations or decreased water clarity, that is often speculated to occur with population growth and watershed development, have not been documented in this sample of Florida lakes.

Hurricane Impacts to Lake Okeechobee: Altered Hydrology Creates Difficult Management Trade Offs

Abstract Human modifications to ecosystems can excerbate effects of natural disturbances, but interactions between disturbance and altered hydrology are rarely assessed. Lake Okeechobee, Florida, was impacted by four large hurricanes in 2004–2005 that caused large lake-wide reductions in the coverage and biomass of aquatic macrophytes. We quantified dramatic changes in the aquatic plant and littoral fish assemblage after hurricanes, including decreased fish richness, diversity, and biomass, and large reductions in the species that support important fisheries. Human-induced hydrologic changes prevented the lake from expanding to the historically connected floodplain during and following hurricanes, which likely exacerbated impacts to aquatic plant and fish communities. Altered hydrology has complicated management scenarios for returning the lake to pre-hurricane conditions because policy options that will initiate recovery at Lake Okeechobee (i.e., lower water levels) will exert negative impacts on east an...

Evaluating mark–recapture sampling designs for fish in an open riverine system

Sampling designs for effective monitoring programs are often specific to individual systems and management needs. Failure to carefully evaluate sampling designs of monitoring programs can lead to data that are ineffective for informing management objectives. We demonstrated the use of an individual-based model to evaluate closed-population mark–recapture sampling designs for monitoring fish abundance in open systems, using Murray cod (Maccullochella peelii (Mitchell, 1838)) in the Murray–Darling River basin, Australia, as an example. The model used home-range, capture-probability and abundance estimates to evaluate the influence of the size of the sampling area and the number of sampling events on bias and precision of mark–recapture abundance estimates. Simulation results indicated a trade-off between the number of sampling events and the size of the sampling reach such that investigators could employ large sampling areas with relatively few sampling events, or smaller sampling areas with more sampling events to produce acceptably accurate and precise abundance estimates. The current paper presents a framework for evaluating parameter bias resulting from migration when applying closed-population mark–recapture models to open populations and demonstrates the use of simulation approaches for informing efficient and effective monitoring-program design.