some of the differences noted when comparing, for Instance, sardine vs. herring 

 and single vs. double hooking, and It follows that multiple hooking of the baits 

 may reduce the amount of bait stealing. Double-hooked baits should withstand a 

 greater amount of pulling before coming off than single-hooked baits, for only a 

 slight tug and twist on a single-hooked sardine or herring will take It off the 

 hook. 



Sea Condition 



Loss of bait during the fishing and retrieving period over and above 

 that removed by animals must be the result of motion of the baited hooks. Aside 

 from the setting and hauling periods the only source of motion Is the action of 

 the sea (Ignoring movement of the line by hooked fish) during the fishing period. 

 An indication of the effect of the motion of the sea on bait loss may be obtained 

 from an examination of the rate of return with relative hook depth. Data from the 

 early cruises indicated a progressive increase in the number of baits retrieved 

 with increase in the relative hook depth (table 15). Vlhen this is considered in 

 the light of a parallel increase in the catch with relative depth (table 16), It 

 becomes evident that either bait stealing is less operative at greater depths or 

 some other environmental factor or factors give the bait a better chance to remain 

 on the deeper hooksl/. There is no evidence of a decrease in bait stealing with 

 depth, but there is a possibility that the action of the sea on the gear varies 

 Inversely with depth. This could arise if the wave-induced up and down movement 

 of the buoys were transmitted with diminishing Intensity to the deeper hooks. To 

 investigate this relationship, one end of a model longllneS/ was raised to various 

 heights simulating the effect of wave action on the gear. Accurate measurements 

 of the usual seas (3 to 8 feet) encountered could not be made because of the small 

 size of the model; however, Indications showed an inverse displacement of hooks 

 with depth; e.g., a 10-foot movement gave relative motions of 1.6, 1.4, and 1.0 

 feet for the shallow, intermediate, and deep hooka respectively. 



The effect of the sea-induced motion may also help to explain the 

 persistently higher sardine returns as compared to the herring when considering 

 single-hooked baits. The larger eye diameter of the herring and its relatively 

 narrower cranial width (fig. 5) make it more apt to drop off the hook if the hook 



is moved up and down by the sea. 



Since it appears that loss 

 of bait Is related to relative differ- 

 ences in the fiunount of motion within 

 sets of gear, it might be expected 

 that under different sea conditions 

 bait loss may vary. This is borne 

 out by the lower returns of single- 

 hooked sardines with increasing sea 

 intensities (fig. 6, table 17). If 

 the sea varies during the course of 

 experiments on type of bait and 

 method of hooking, the relative re- 

 turns should be different under dif- 

 ferent sea intensities. In the 

 following sections, the experiments 

 are re-examined to ascertain whether 

 the significant Interaction chi- 



squares noted in several experiments could have been caused by changes in relative 



bait retention induced by variations In sea Intensity. 



SARDINE 



HERRING 



Figure 5. 



-Lateral and dorsal views 

 of the sardine and herring 

 baits. 



1/ The problem of whether increased catch at greater depths is a function of 



better bait return is not under consideration. However, it is evident from a 

 comparison of tables 15 and 16 that the catch increased more rapidly with 

 depth than the bait return. Indicating some Independence of the two events. 



5/ The longline model was made of chain axid was proportional to the dimensions 



of the real gear. The chain was allowed to sag freely giving a catenary curve 

 like that assumed to exist during fishing. 



17 



