Estimating abundance from gillnet samples with application to red drum (Sciaenops ocellatus) in Texas bays

Abstract

A model of gillnet selection is developed to accommodate the possibility that some catch observations will be known more precisely than others and allow for nonlinear relationships between the selection parameters and mesh size. The model is used to show that gillnet selection for red drum (Sciaenops ocellatus) in Texas bays may be explained as a unimodal process approximating a skewed Laplace distribution, where the optimal length varies in proportion to mesh size and the variance in proportion to the optimal length. It is also suggested that the number of encounters with the net ought to depend on swimming speed of the quarry, which in turn varies predictably with length. This information, along with the estimates of selection, is used to develop indices of abundance for each length-class. The results indicate that the recruitment of year-old red drum to Texas bays has fluctuated markedly since 1975, but without any persistent trends. However, the survival of these and older fish has increased dramatically owing to various regulations promulgated since 1981.

Abiotic and biotic correlates of yellow perch recruitment to age‐2 in southern Lake Michigan, 1984–2007

“…Annual gillnet catch-per-unit-effort (GNCPUE, fish net )1 night )1 ) of adult (sexually mature) yellow perch was used as an index of stock size. Gillnet catch rate has been shown to be linearly related to yellow perch abundance in Lake Michigan (Porch et al 2002;Irwin et al 2008;Olin et al 2009). GNCPUE was computed for 10-mm length classes (range 50-400 mm) separately for males and females.…”

“…Annual gillnet catch‐per‐unit‐effort (GNCPUE, fish net −1 night −1 ) of adult (sexually mature) yellow perch was used as an index of stock size. Gillnet catch rate has been shown to be linearly related to yellow perch abundance in Lake Michigan (Porch et al. 2002; Irwin et al.…”

Overestimation of percid fishes (Percidae) in gillnet sampling

“…In a situation when the fish change direction frequently or have a limited home range, Anderson (1998) recommended application of a random walk or diffusion model to describe encounter rates as a function of swimming speed and turning frequency. Distance travelled or number of encounters, in other words, increases with the fish swimming speed, which is dependent on the fish size (Rudstam et al, 1984;Anderson, 1998;Jepsen et al, 1999;Čech and Kubečka, 2002;Jacobsen et al, 2002;Porch et al, 2002). Thus, the overestimation could be evoked by different sizes of compared species.…”

A Bioenergetics Approach to Modeling Striped Bass and Threadfin Shad Predator‐Prey Dynamics in Lake Powell, Utah‐Arizona

“…Within each year, catches from all gill nets were summed and divided by total effort to estimate reservoirwide catch per unit effort (CPUE). Gill-net CPUE data were adjusted for mesh-size selectivity (Helser et al 1998), and encounter probability (Rudstam et al 1984;Porch et al 2002).…”