An Efficient Sampling Survey Design to Estimate Pink Shrimp Population Abundance in Biscayne Bay, Florida

Abstract

We developed an efficient sampling design-based approach using fishery-independent surveys to estimate population abundance of pink shrimp Penaeus duorarum over time in Biscayne Bay, Florida. We initially implemented quarterly stratified random sampling (StRS) using nine habitat strata and determined that average pink shrimp density (numbers/m 2 ) was highest in late fall and lowest in spring and late summer. Coefficient of variation of the quarterly surveys, expressed as percent standard error/mean density, ranged from 5.8% to 14.3%. We found StRS to be more efficient (i.e., with lower variance) than simple random sampling (SRS) in most seasons. Statistical analyses suggested that pink shrimp densities were dependent on the biophysical habitat variables of bottom substrate, depth, and salinity. We also noted ontogenetic shifts in these relationships that were particularly pronounced at the onset of sexual maturation. Poststratification analysis was used to further evaluate several alternative habitat-based sampling schemes. Results showed that a five-strata composite design that used all three habitat variables was similar in performance, but less complex, than the original nine-strata design. In addition, the composite design outperformed both SRS and all other StRS designs indexed on single habitat variables. The new five-strata composite design was implemented in late summer 1997 and achieved a significant reduction in coefficient of variation compared with the late summer 1996 survey. This new design did not perform as well as expected in late fall 1997, which we attribute to a mismatch between our seasonal sample allocation strategy and the timing of pink shrimp recruitment into Biscayne Bay in 1997. Finally, we show how statistical sampling designs that use stratifications based on relevant habitat covariates can yield high-precision abundance estimates at low costs and provide a robust quantitative methodology for identifying habitat essential to fisheries production.

Probability sampling of stony coral populations in the Florida Keys

“…In these cases, the precision levels would enable detection of relative changes in population mean density ranging from 14% to 24% (approximately 2 SEs) in a future time period. The CVs obtained in our study are among the lowest reported for comparable surveys of marine species, e.g., American lobster Homarus americanus (CVs 4%-10%, Smith and Tremblay 2003), pink shrimp Farfantepenaeus duorarum (CVs 6%-14%, Ault et al 1999), and the sea scallop Placopecten magellanicus (CVs 6%-10%, Smith and Lundy 2006). Our survey was generally less precise for species with relatively low densities (<3 colonies/10 m 2 ).…”

“…The estimates of strata variances obtained from the Florida Keys survey will enable application of an optimal allocation strategy in a future survey. Studies have shown, however, that estimates of strata variances become more reliable over several successive surveys (Smith and Gavaris 1993;Ault et al 1999). Thus, it will likely take some time to fully realize gains in efficiency via optimal allocation.…”

“…Probabilistic survey design principles have been successfully applied for decades in a variety of disciplines including agriculture (Sen 1964), human health (Korn and Graubard 1999), and natural resources (Hughes et al 2000). In marine ecosystems, this approach has been commonly applied in surveys of exploited populations of fishes and macroinvertebrates (Smith and Gavaris 1993;Ault et al 1999;Folmer and Pennington 2000;Smith and Tremblay 2003;Smith et al 2011), and has been used in the evaluation of predator-prey interactions between marine mammals and fishes (Wright et al 2007). These statistical techniques have the advantage of generating population-level metrics, as well as optimizing sampling efficiency to obtain high precision estimates at low sample sizes.…”

Optimization of stratification scheme for a fishery-independent survey with multiple objectives

“…Stratified random sampling, commonly used in fishery-independent surveys, usually divides a target survey area into different strata and conducts simple random sampling within each stratum (Cochran, 1977). Stratification can result in an increased precision over a simple random survey design when observations are more homogenous within strata than between strata and the sampling efforts are allocated to strata in proportion to strata size or strata variance (Ault et al, 1999;Manly et al, 2002;Chen et al, 2006;Miller et al, 2007;Lohr, 2009). Thus, an appropriate stratification is important to achieve an improved precision of survey estimates (Ault et al, 1999;Smith and Lundy, 2006).…”

Effects of a marine fishery reserve and habitat characteristics in the abundance and demography of the red hind grouper,Epinephelus guttatus

“…In the Florida Keys coral reef ecosystem, delineation of fish and shellfish distribution patterns is critically important for efficient fishery-independent monitoring of reef resources (Ault et al 1999(Ault et al , 2005a(Ault et al , 2009Lindeman et al 2000). The iterative process of designing and implementing fish surveys can capitalize on analyses of fish distributional patterns as a means to inform and improve survey design characteristics (Ault et al 2005a;Smith et al 2011aSmith et al , 2011b.…”