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

The key variables analysed were the percentage abnormal carapace assessed in the fieldusing all 1599 observations (a Binomial proportions model), the distribution of countsaccording to highest lesion class (a Poisson linear model), and HSI (Normal model). In theseanalyses, ‘crab category’ was always significant (P ≤ 0.05), justifying its inclusion as astratifying term. The relevant means are listed in Table 6.Table 6. Mean values and standard errors (s.e.) for the crab categories.Hepato-somatic index s.e. Percent abnormal s.e.Female large 0.059 0.002 3.8 0.8Female small 0.064 0.004 1.8 0.7Male legal 0.043 0.003 7.1 1.7Male undersize 0.056 0.002 2.5 0.7Regarding locations and sampling events, the only significant (P ≤ 0.05) effect was for theHSI, where combined results for June/July (0.061 ± 0.002) were higher than those forApril/May (0.050 ± 0.002). Results for HSI are to be expected given HSI is generally highestduring the non-reproductive period for crabs (winter), and then decreases as crabs move intotheir reproductive season and energy stores are utilised in gonad production (Table 7).Table 7. Mean values and average standard errors for hepato-somatic index and per cent abnormal foreach location and sampling event.Location Hepato-somatic index Per cent abnormalApril/May June/July April/May June/JulyFitzroy River 0.046 0.060 4.5 1.4Bundaberg 0.050 0.061 3.7 3.1The Narrows 0.055 0.059 3.2 5.2Port Development Area 0.057 0.068 8.8 4.4Hamilton Point 0.050 0.061 3.1 3.7Calliope River 0.049 0.063 5.8 2.7Rodds Bay 0.043 0.056 2.3 2.4(average s.e.) 0.004 (average s.e.) 2.0June/July also sees similar or lower percentages of abnormal crabs than April/May for allsites except for the Narrows, while no significant difference was detected between Gladstoneand the reference sites.Possibly due to the low number of abnormal crabs (58), there were no significant effects forlocation or trip on the distributions of these counts (P = 0.14 and 0.13 respectively). Thedistribution of observed lesions across sites is shown in Table 8.Table 8. Lesion categories as observed in the field, according to categories described by Andersen, 2001.Where individual crabs had more than one lesion, only the most severe lesion was included.LocationLesion CategoryL1 L2 L3 L4 L5Fitzroy River 2 6 1 1 4Bundaberg 0 1 1 2 2The Narrows 1 0 2 2 1Port Development Area 2 5 1 1 1Hamilton Point 0 2 1 2 2Calliope River 1 1 2 1 0Rodds Bay 1 3 0 4 145