36 



Fishery Bulletin 89(1), 1991 



10 cm of the sea surface so would 

 more accurately be called a 'hypo- 

 neuston' net. Temperatures and 

 salinities measured during collec- 

 tions containing chaetognaths 

 were averaged at each positive 

 station (Figs. 2 and 3). 



Flaccisagitta enflata, Sagitta 

 tenuis, Ferosagitta hispida, and, 

 to a lesser extent, S. helenae and 

 Pterosagitta draco were absent 

 or uncommon in temperatures 

 less than about 9°C (Figs. 2, 3), 

 while few Parasagitta elegans, 

 Mesosagitta minima, and Ptero- 

 sagitta draco were found in 

 warmest temperatures. Serrato- 

 sagitta tasmanica was present in 

 a very wide range of both tem- 

 perature and salinity. Numbers 

 of Pterosagitta draco were re- 

 duced in lower salinities as well 

 as low temperatures; occurrences 

 were in salinities higher than 



34 %o except in the summer of 

 1976. Sagitta helenae and Meso- 

 sagitta minima were more fre- 

 quent and numerous in higher 

 salinities, while S. tenuis was ab- 

 sent from salinities greater than 



35 %o. Other species in Figures 

 2 and 3 were captured in various 

 salinities. 



Interspecific association 



Before examining association be- 

 tween pairs of species, the data 

 were first tested for overall asso- 

 ciation using a matrix of the pres- 

 ence or absence of the 15 most 

 common chaetognaths in 716 col- 

 lections. Schluter's (1984) index 

 of overall association (VR here, as in Ludwig and 

 Reynolds 1988) for these 15 species was 2.108, indicative 

 of a net positive association among the species. The null 

 hypothesis of no association was rejected (W = 1509; 

 90% probability 654.9<W 779.3). 



Among paired-species associations, most statistical- 

 ly significant coefficients (P<0.05) were positive (Table 

 5). Significant negative associations (C 8 = -0.15 to 

 -0.73) were limited to six pairings of various species 

 with Parasagitta elegans and the pair Sagitta tenuis- 

 Mesosagitta minima. The sole significant positive asso- 

 ciation of P. elegans (P<0.05) was with Serratosagitta 



tasmanica. Highest positive coefficients included asso- 

 ciations among (1) the other most frequent chaeto- 

 gnaths, Serratosagitta tasmanica, Mesosagitta mini- 

 ma, and Flaccisagitta enflata (C 8 = 0.18 to 0.27); (2) 

 deeper-living or outer shelf chaetognaths Flaccisagitta 

 hexaptera, Eukrohnia hamata, Pseudosagitta lyra, 

 Mesosagitta decipiens, and Krohnitta subtilis (C 8 = 

 0.11 to 0.30); and (3) the seasonal warm-water species 

 K. pacifica, Serratosagitta serratodentata, Ferosagitta 

 hispida, and Sagitta tenuis (C 8 = 0.09 to 0.26). Sagitta 

 helenae and Pterosagitta draco shared positive associa- 

 tions with all three groups. 



