A multiyear lattice sampling design for Maryland-wide fish abundance estimation

A latticed, multiyear, multistaged sampling design developed for the Maryland Biological Stream Survey (MBSS) enabled the Maryland Department of Natural Resources to make design-based, Maryland-wide estimates of fish abundance in wadable nontidal streams. Because budget and labor constraints prohibited completing the field work required for statewide estimates within a single year, a 3-year sampling program was designed. A sampling lattice was constructed with the 3 years of sampling (1995, 1996, 1997) as the columns and three regions within the state of Maryland (eastern, central, and western) as the rows. Each one of the three regions consisted of six river basins, and the primary sampling units (PSUs) were defined as the combinations of these basins with the 3 years for a total of 54 PSUs. Two basins from each region were sampled in each year so that all basins were sampled once. In addition, one basin within each region was sampled in a second year under a restricted randomized design to complete the first stage of sampling. This additional sample insured that all joint inclusion probabilities of primary sampling units were nonzero, In all 3 years, the second stage consisted of simple random samples of reaches proportionally selected within strata defined by Strahler order. However, the MBSS's latticed sampling design combined with estimators based on the Horvitz-Thompson method would allow the calculation of statewide totals using different sampling designs within PSUs. Two species of fish, creek chub and largemouth bass, are used to illustrate the approach.