Andrew B. Barbour

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.

Apparent survival estimation from continuous mark–recapture/resighting data

Summary The recent expansion of continuous-resighting telemetry methods (e.g. acoustic receivers, PIT tag antennae) has created a class of ecological data not well suited for traditional mark–recapture statistics. Estimating survival when continuous recapture data is available ensues a practical problem, because classical capture–recapture models were derived under a discrete sampling scheme that assumes sampling events are instantaneous with respect to the interval between events. To investigate the use of continuous data in survival analysis, we conducted a model structure adequacy simulation that tested the Cormack–Jolly–Seber (CJS) and Barker joint data survival estimation models, which mainly differ through the Barkers inclusion of secondary period information. We simulated a population in which survival and detection occurred as a near continuous (daily) process and collapsed detection information into monthly sampling bins for survival estimation. While both models performed well when survival was time-independent, the CJS was substantially biased for low survival values and time-dependent conditions. Additionally, unlike the CJS, the Barker model consistently performed well over multiple sample sizes (number of marked individuals). However, the high number of parameters in the Barker model led to convergence difficulties, resulting in a need for an alternative optimization method (simulated annealing). We recommend the use of the Barker model when using continuous data for survival analysis, because it outperformed the CJS over a biologically reasonable range of potential parameter values. However, the practical difficulty of implementing the Barker model combined with its shortcomings during two simulations leaves room for the specification of novel statistical methods tailored specifically for continuous mark–resighting data.

Combining Samples from Multiple Gears Helps to Avoid Fishy Growth Curves

AbstractSize-at-age information is critical in estimating growth parameters (e.g., the von Bertalanffy growth function [VBGF]) that are used to assess fish populations. Due to gear selectivity, single sampling methods rarely sample all ages or all sizes equally well. Most growth estimates rely on samples from a single gear or a haphazard combination of gears, potentially leading to biased and imprecise growth parameter estimates. We evaluated the efficacy of combining samples from two gears with different size selectivity to estimate VBGF parameters; we then applied that approach to a case study on the Lochloosa Lake (Florida) population of Black Crappies Pomoxis nigromaculatus. Simulated age- and size-structured populations were randomly sampled with two gears characterized by different size-selectivity curves (one gear was selective for smaller fish; the other was selective for larger fish). Maximum likelihood VBGF estimates obtained for each gear separately were compared with estimates from a combined ...