Michigan Department of Conservation
Research and Development Report No. 107
Institute for Fisheries Research Report No. 1738, 1967
Rate of Escape of Fish from Trap Nets
Mercer H. Patriarche
Fishery biologists are well aware that stationary
trapping devices usually are selective with respect to species and size of fish they
capture and retain. This source of bias can significantly affect catch indices,
population estimates, and computations of growth and mortality rates. In this paper I
discuss the rate of escape fish of various species and sizes from trap nets of the
kind described by Crowe (1950) and Latta (1959). This experiment was prompted by
casual observations that, even though some fish if left in a net overnight were still
present the following day, there were also instances when fish escaped during the
interval between lifts.
Hansen (1944) tested to ability of certain species
to escape fyke nets in Illinois lakes and found that both the bluegill
(Lepomis macrochirus) and largemouth bass (Micropterus salmoides) were
adept at escapement. One-third of the bluegills and 37% of the bass escaped in a
23-hour period. Over a 2-day period (51 hours) in another lake, 86% of the bluegills
and 20% of the bass left the nets. Schupp (1965) observed a pronounced increase in
fish catches when the nets were lifted at 2-hour intervals rather than once a day.
Latta (1959), seeking an explanation for size selectivity among fish large enough to
be retained by the trap nets, speculated that some sort of behavior pattern probably
was responsible, and cited several instances where more larger fish were retained than
small ones. He further postulated that the “peck order” described by Gerking
(1957) might be a factor.