Comparison of the species composition, catch rate, and length distribution of the catch from trap nets with three different mesh and throat size combinations

摘要

Trap nets of varying design are commonly used to assess fish populations, but the effect of the design on gear selectivity is not well known. In particular, it may be advantageous to use multiple net designs with different mesh and throat sizes to maximize the catch of specific length-classes and to minimize the risk of predation on small fish by larger fish. We compared the species composition, catch rate, and length distribution of fishes caught by three trap net designs with dimensions differing only in mesh size and throat size (0.6-cm delta mesh and 3.8-cm X 3.8-cm square throats, 1.3-cm square mesh and 7.6-cm X 7.6-cm square throats, or 2.5-cm square mesh and 12.7-cm X 12.7-cm square throats). A total of 3,473 fish of 18 species were captured from Sandy Lake, Portage County, Ohio, during 24 sample dates from June to August 1999. The large net design had a significantly higher average number of species captured (mean = 11) than the medium or small net design (means = 9 and 8, respectively). Whereas nets with larger mesh and throat size combinations typically caught larger fish for the six most commonly captured species, only rarely did nets capture fish as large or as small as possible based on their physical dimensions. Specific length-classes of some species were not captured in the nets or were very net design specific, indicating a possible difference in trap net vulnerability of different ontogenetic stages. We conclude that data from trap nets with different mesh and throat sizes should not be directly compared with each other, and that multiple net mesh and throat sizes (or even multiple gear types) should be used when a more complete picture of fish length and abundance is desired.