Visual acuity and olfatory sensitivity in the swordfish (Xiphias gladius) for the detection of prey during field experiments using the surface longline gear with different bait types

Abstract

During a total of 20 sets carried out on board a surface longliner, the different degrees of effectiveness obtained in the capture of swordfish were evaluated using 5 different bait types (natural, artificial and mixed). The results point to substantial and significant differences in the CPUEs obtained among the different bait types tested to catch swordfish. However, the results show few mean differences that were not statistically significant between the CPUEs obtained using natural bait (control) or mixed bait consisting of artificial bait on the outside -which in itself was of null effectiveness- into which was inserted a piece of natural bait, concealed from view. Both types of bait (control and mixed) were effective in the capture of swordfish despite the differences in constitution and properties. On the basis of these results, it is possible to make an indirect assessment of the importance of visual and odor stimuli in the swordfish to detect and carry out the final attack on its prey. Odor was found to be the key element in this process.