669 Abstract.-This study examined thecatchfrom gill nets seton nearshore Gillnetting in southern New Zealand: rocky reefs around the Kaikoura Pen­ insula on the east coast of the South duration effects of sets and Island of New Zealand. The combined catch of 114 net sets ofthree net mesh entanglement modes of fish sizes (2.5",3.5", and 4.5") was analyzed for the mode of entanglement of cap­ Michael J. H. Hickford tured fish and for duration effects on fish. Fusiform species were commonly David R. Schiel gilled and wedged, whereas laterally Department of Zoology. University of Canterbury compressed species usually became Private Bag 4800. Christchurch. New Zealand tangled byfins or spines; these patterns appeared to be a consequence of the e-mail address:Mil<[email protected] 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 Different species of fish are not girthmeasureis slightlygreaterthan tangled fish tended to have the largest mean fork length, gilIed fish were in­ equallyvulnerable to a given method the mesh perimeter (McCombie and termediate in mean fork length, and offishing. Gill nets, inparticular, are Fry, 1960; Berst, 1961; Garrod, 1961; wedged fish hadthe smallest meanfork highly selective in terms ofthe sizes McCombie and Berst, 1969). length. Nets of 2.5" mesh size caught and species of fish they catch The number offish caught in gill the most fish over all set durations. (Hamley, 1975; Boy and Crivelli, nets does not necessarily increase There was no significant difference be­ tween a 6-hour set and a 15-hour set in 1988). There are many factors, how­ in direct proportion to the time that the number of fish or number of spe­ ever, other than the species or size nets are in the water (Kennedy, cies caught. The proportion ofdamaged ofa fish that can influence the sus­ 1951). Van Oosten (1935) showed fish in the landed catch was small for ceptibility of a fish to being caught that gill nets left for eight nights nets of all three mesh sizes set for six in a gill net. Hamley (1975) listed caught only 47 percent more fish hours but increased markedly for set times that were longer. Clearly both these factors as the reaction offish than the same nets left for four mesh size, as well as morphological and to nets, the differentbehavioroffish nights, whereasifthecatchincreased behavioral differences between species around nets, the type of net con­ indirect proportion to thetimefished, affect the susceptibility of individual struction, the hanging coefficient, theincreasewouldhavebeen 100 per­ fish to gill nets. net saturation and characteristics cent. Thepresence ofcaptured, strug­ ofnets, such as theirvisibility, elas­ glingfish andofdeadfish mayresult ticity of meshes, and filament size. in the efficiency ofgill nets decreas­ Dimensional characteristics of ing with time (Kennedy, 1951). fishes, such as length-weight rela­ The analysis of catches of fish tionships (Kipling, 1957), length­ taken in gill nets is complicated by condition relationships (Regier, the passive nature of this type of 1969), and length-girth relation­ fishing gear (Berst and McCombie, ships (Kawamura, 1972), can also 1963). Severalfactors affect gill.net influence selectivity. catches, such as the movement of Itis generally agreed that a given fish, the shape and structure ofthe mesh size provides a size selection fish, and the associative pattern or for a particular species thatis char­ grouping of the individuals of any acterized by a lower size limit, be­ species or assemblage of species low which fish are small enough to (Moyle, 1950). pass through the mesh withouthin­ The aim ofthe present study was drance, and by an upper size limit, to analyse the size range and abun­ above which fish are too large to dance ofthe most common fish spe­ enter the mesh and become en­ cies in gill-net catches from near­ tangled (Hamley, 1975). Between shore reefs in southern New Zea­ these limits the length-frequency land. The datafor this analysis were distribution ofthe catch is approxi­ derived from the catch ofnets used Manuscript accepted 16 April 1996. mately normal, with a mode at the for comparison of reef fish popula­ Fishery Bulletin 94:669-677 (1996). length where the corresponding tions previously assessed by visual 670 Fishery Bulletin 94(4). 1996 survey (Hickford and Schiel, 1995) and from gill nets have been "gilled." Ifthe mesh encircling the body thatwere usedfor behavioral observations. By record­ was posterior to the base ofthe pectoral fin, the fish ingthe morphological features ofthe catch, along with was determined to have been "wedged." Ifa fish was the form ofentanglement, the primaIyfactors that de­ held because mesh had snagged an appendage, such termine the vulnerability ofindividual species to par­ as the fins, spines, teeth, or maxilla, or ifthe fish's ticular mesh sizes could be identified. Analysis ofthe struggling had simply enveloped it in the mesh, it quantity and quality ofthe catch landed from gill nets was described as "tangled." Careful handling of the set for various periods should yield an optimum set nets resulted in very few "drop-outs" from the net. time that will maximize landings and reduce wastage. However, any fish that were loose in the net were excluded from subsequent entanglement analysis. Entanglement data were collated for each species Materials and methods in each mesh size. Because the species composition of individual net sets was so variable and because The gillnet catch analyzed in this study was pooled many species were caught only in a small proportion from several experiments. Consequently, the result­ of sets, the analyses ofentanglement data were re­ ing sampling design is not orthogonal. The netting HLticted to the five most commonly caught spedes. was done on rocky reefs around the Kaikoura Penin­ This produced a 5x3x3 contingency table, in which sula on the east coast ofNew Zealand's South Island the number of fish caught were categorized accord­ (42°25'S, 173°42'E) from 8 January 1993 to 26 Feb­ ing to species, mesh size, and entanglement mode. ruary 1993. The nets (Table 1) were set from a 6­ This table was analyzed by using a log-linear model meterrunabout and hauledin by hand. Each netwas that required thirteen iterations for the G-value to be setin a random direction and the ends were anchored minimized. ( IaGI < 0.001; Sakal and Rohlf, 1981). The withweights andmarkedwith surface buoys. At least odacidOdaxpulluswas the only species caughtinlarge 10 meters separated any two nets. The nets were set enough numbers across most net sets for individual on the bottom at depths ranging from 3 to 15 meters statistical analysis ofentanglement to be done. and for periods of11-17 hours.At all sites thebenthic The duration ofeach net set was recorded. Two set habitattype hadbeen described (Hickford andSchiel, times were chosen for analysis: a 6-h daytime set 1995) and the fish populations had been surveyed from late morning to late afternoon and a 15-h night with visual transects by divers immediately before set from late afternoon to early morning. The num­ the nets were set. At the end ofall sets, the nets were beroffish and number ofspecies caught during each placed inbins andbrought backto the laboratory with set were compared.Acomparison ofthe capture rates fish still entangledinthemeshfor analysis ofthecatch. ofcommon species was also made between day and The combined catch of114 net sets ofthree mesh sizes night sets andbetween mesh sizes. Eachfish caught over a single known habitat type (rocky pinnacles, was given a condition index according to the degree of mixed. algae [Hickford andSchiel, 1995]) was analyzed.. damage it had sustained while in the net (Table 2). As each fish was removed from the net, its species and fork length (mm) were recorded as was the method by which each fish had become trapped in Results the mesh. If a fish was held by the mesh encircling its body between the posterior edge ofits operculum The 114 net sets caught 1,165 fish from 14 families and the base ofits pectoral fin, it was determined to (Table 3). The odacid Odax pullus (46% of the total Table 1 Table 2 The dimensions ofthe gill nets used in fishing during this Descriptions of the indices used to categorize the condi­ study. Mesh size is given in inches by the manufacturers tion offish landed in gill nets. andismeasured as the diagonal length ofa stretched mesh. Filament size is the diameter ofthe monofilament. Condition index Damage Net and mesh dimension Measurement No damage Chafing or scale loss from contact with gill net Net length (m) 30 30 30 Minor damage Minor lesions; fin or eye damage Net height (m) 1.80 1.75 1.72 Mejor damage Mejor lesions; flesh loss or sea lice Mesh size (inches) 2.5 3.5 4.5 damage Filament size (mm) 0.36 0.48 0.58 Severe damage Loss ofskeletal material Hickford and Schiel: Gillnetting in southern New Zealand 671 Table 3 The species, common name, fisheries code, and number offish caught in each ofthe three mesh sizes and in total. The number of individual net sets are shown in parentheses under the mesh size. No. offish Mesh size Family and Common Fisheries 2.5" 3.5" 4.5" 'lbtal no. species name code (29) (30) (55) (114) Myliobatidae Myliobatis tenuicaudatus (Hector, 1987) Eagle ray EGR 0 1 0 1 Moridae Latella rhacinus (Bloch and Schneider, 1801) Rock cod ROC 2 1 0 3 Pseudophycis bachus (Bloch