ANGLING EXPERIMENTS WITH CARP (CYPRINUS CARPIO L.) II. DECREASING CATCHABILITY THROUGH ONE-TRIAL LEARNING by J. J. BEUKEMA* (Organization for the Improvement of Inland Fisheries, Utrecht & Zoological Laboratory, State University of Groningen, The Netherlands) A. INTRODUCTION In the course of the fishing season catches per angling-hour tend to decrease in heavily fished waters. Such a decrease is not invariably accompanied by an equally steep decrease of the stock of fish present (e,g., WATERS, 1960). It may even occur when all captured fishes are returned to the water (WESTMAN et al., cited from BENNET, 1962: 244). A decreasing vulnerability of the fish to angling may be assumed in such cases. It may be caused by the ability of the fishes to learn to avoid baits presented upon hooks, as has been observed in aquarium experiments (HUTCHENS & WITT, both cited from BENNET, l.c.). Decreasing vulnerability to angling of carp, observed consistently in intensively fished ponds, is analyzed in the following paper by means of controlled angling for individually tagged carp in closed, drainable ponds. * Present address: Netherlands Institute for Sea Research, Texel, The Netherlands. 82 B. MATERIAL AND METHODS Data were gathered during the same or similar angling
Netherlands Journal of Zoology (in 2003 continued as Animal Biology) – Brill
Published: Jan 1, 1969
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