669 



AbStfelCt.— This study examined 

 the catch from gill nets set on nearshore 

 rocky reefs around the Kaikoura Pen- 

 insula on the east coast of the South 

 Island of New Zealand. The combined 

 catch of 114 net sets of three net mesh 

 sizes (2.5", 3.5", and 4.5") was analyzed 

 for the mode of entanglement of cap- 

 tured fish and for duration effects on 

 fish. Fusiform species were commonly 

 gilled and wedged, whereas laterally 

 compressed species usually became 

 tangled by fins or spines; these patterns 

 appeared to be a consequence of the 

 behavioral and morphological charac- 

 teristics unique to each species. The av- 

 erage fork length of caught fish in- 

 creased with mesh size for gilled and 

 wedged fish but not for those that were 

 tangled. Within each mesh size, en- 

 tangled fish tended to have the largest 

 mean fork length, gilled fish were in- 

 termediate in mean fork length, and 

 wedged fish had the smallest mean fork 

 length. Nets of 2.5" mesh size caught 

 the most fish over all set durations. 

 There was no significant difference be- 

 tween a 6-hour set and a 15-hour set in 

 the number of fish or number of spe- 

 cies caught. The proportion of damaged 

 fish in the landed catch was small for 

 nets of all three mesh sizes set for six 

 hours but increased markedly for set 

 times that were longer. Clearly both 

 mesh size, as well as morphological and 

 behavioral differences between species 

 affect the susceptibility of individual 

 fish to gill nets. 



Gillnetting in southern New Zealand: 

 duration effects of sets and 

 entanglement modes of fish 



Michael J. H. Hickford 

 David R. Schiel 



Department of Zoology, University of Canterbury 

 Private Bag 4800. Christchurch, New Zealand 

 e-mail address Mike@zool canterbury .ac.nz 



Manuscript accepted 16 April 1996. 

 Fishery Bulletin 94:669-677 ( 1996). 



Different species of fish are not 

 equally vulnerable to a given method 

 of fishing. Gill nets, in particular, are 

 highly selective in terms of the sizes 

 and species of fish they catch 

 (Hamley, 1975; Boy and Crivelli, 

 1988). There are many factors, how- 

 ever, other than the species or size 

 of a fish that can influence the sus- 

 ceptibility of a fish to being caught 

 in a gill net. Hamley (1975) listed 

 these factors as the reaction offish 

 to nets, the different behavior offish 

 around nets, the type of net con- 

 struction, the hanging coefficient, 

 net saturation and characteristics 

 of nets, such as their visibility, elas- 

 ticity of meshes, and filament size. 

 Dimensional characteristics of 

 fishes, such as length-weight rela- 

 tionships (Kipling, 1957), length- 

 condition relationships (Regier, 

 1969), and length-girth relation- 

 ships (Kawamura, 1972), can also 

 influence selectivity. 



It is generally agreed that a given 

 mesh size provides a size selection 

 for a particular species that is char- 

 acterized by a lower size limit, be- 

 low which fish are small enough to 

 pass through the mesh without hin- 

 drance, and by an upper size limit, 

 above which fish are too large to 

 enter the mesh and become en- 

 tangled (Hamley, 1975). Between 

 these limits the length-frequency 

 distribution of the catch is approxi- 

 mately normal, with a mode at the 

 length where the corresponding 



girth measure is slightly greater than 

 the mesh perimeter (McCombie and 

 Fry, 1960; Berst, 1961; Garrod, 1961; 

 McCombie and Berst, 1969). 



The number offish caught in gill 

 nets does not necessarily increase 

 in direct proportion to the time that 

 nets are in the water (Kennedy, 

 1951). Van Oosten (1935) showed 

 that gill nets left for eight nights 

 caught only 47 percent more fish 

 than the same nets left for four 

 nights, whereas if the catch increased 

 in direct proportion to the time fished, 

 the increase would have been 100 per- 

 cent. The presence of captured, strug- 

 gling fish and of dead fish may result 

 in the efficiency of gill nets decreas- 

 ing with time (Kennedy, 1951). 



The analysis of catches of fish 

 taken in gill nets is complicated by 

 the passive nature of this type of 

 fishing gear (Berst and McCombie, 

 1963). Several factors affect gill-net 

 catches, such as the movement of 

 fish, the shape and structure of the 

 fish, and the associative pattern or 

 grouping of the individuals of any 

 species or assemblage of species 

 (Moyle, 1950). 



The aim of the present study was 

 to analyse the size range and abun- 

 dance of the most common fish spe- 

 cies in gill-net catches from near- 

 shore reefs in southern New Zea- 

 land. The data for this analysis were 

 derived from the catch of nets used 

 for comparison of reef fish popula- 

 tions previously assessed by visual 



