32 



D. A. HANCOCK AND A. C. SIMPSON 



but on areas with a high natural population of shore crabs, these enter the 

 pots and deter the entry of whelks (B, F). In addition, dead crab bait seems 

 to have a deterrent effect on the entry of crabs. 



(3) Competition between the bait and natural food available, which will vary 

 from place to place and year to year. 



(4) Seasonal effects on the feeding behaviour of the species, e.g. laboratory 

 experiments have shown that the feeding of whelks is at a minimum during 

 the summer, but greatest in spring, and this was reflected in commercial 

 catches (Fig. 2). Similarly, lobsters feed most actively in the summer and 

 catches are then at their maximum. 



AVERAGE CATCH IN lOO POTS ON EACH DAY FISHED 



IsIo1nId1jIfImIaIm1jIj1aIs1qinIdijifIm1a1mIJIjiaIsio 



TOTAL CATCH PER CALENDAR MONTH 



Fig. 2. — Landings of whelks by commercial boats at Whitstable, 1957-9. 



(5) Competition from the pots of other fishermen — here the direction of 

 tidal flow related to the position of bait and prey is important. 



(6) The design of the pots, e.g. some lobster pots retain lobsters more 

 efficiently than others. 



(7) The frequency with which the traps are emptied, and the frequency with 

 which the bait is renewed. Whelk pots left down for more than one day at 



