Gladstone Fish Health Investigation 2011 - 2012 - Western Basin ...

Appendix B – Statistical report: Gladstone Harboursampling trips 2012OVERVIEWThis report describes the statistical analyses of the fisheries data collected on two sampling trips, fromtargeted sites around Gladstone Harbour as well as from two reference sites (Fitzroy River andBundaberg). Section 1 outlines the statistical methods employed. Section 2 covers the results for thespecies that were not submitted to the laboratory, and illustrates that there were no apparent problemsamongst these species. The comprehensive Section 3 outlines the results for the important and targetedfish species submitted to the laboratory (barramundi, bull sharks, mullet and queenfish), at both the trip /location level, and then combined into regional comparisons. Sections 4 to 6 then repeat thiscomprehensive presentation of results separately for three key species, namely barramundi, mullet andmudcrabs respectively. For bull sharks, there were insufficient numbers to conduct separate analyses. Forqueenfish, the observed percentages of diseased individuals were too low to warrant separate analyses.1. STATISTICAL METHODSAll analyses were conducted using GenStat (2011). General linear models (McCullagh and Nelder 1989)were used for the continuous variables. Generalised linear models (McCullagh and Nelder 1989) wereadopted for the discrete (categorical) data, using the Poisson distribution with a log link for counts, andthe Binomial distribution with the logit link function for binary (percentage) data.As there was incomplete coverage in the three‐way design matrix (fish by location by trip – see Table 1.1),it was important to account for this in the analyses, and to correctly adjust the resultant means. Figure 1.1demonstrates the large differences between fish species for the hepatosomatic index. This shows that any‘ raw’ averages (for each trip and location) will depend heavily on the balance of fish being caught, inparticular,the number of bull sharks.Table 1.1. Distri bution of catches by species and locations.Barra. Bull shark Grin ner Her ring Mullet Pra wn Queenfish ThreadfinFitzroy R 68 7 115 115 21 200 12 200Bundaberg 20 1 18 110 26 200 36 125Hamilton Pt 31 1 0 0 0 0 0 0Calliope R 23 3 0 0 18 0 14 0Harbour 7 0 46 120 0 174 0 220Spoil Grounds 0 0 0 0 0 0 5 0Upp. Boyne R 21 1 0 0 20 0 0 0Low Boyne R 32 10 0 0 20 0 4 0Rodds Bay 9 0 0 0 20 0 0 0Lake Awoonga 5 0 0 0 0 0 0 0102