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

There were significant differences between the two reference sites for most conditions in Trip1, Trip 2 or both (P < 0.05). Some differences would be expected due to the difference inlatitude and habitat structure. Reference sites were chosen to the north and south ofGladstone to balance these effects.Skin condition: Skin redness has been reported and investigated in a wide range of fishspecies including sharks. Pathology investigation of skin redness in Phase 1 showedinflammation, erosion, scarring, bleeding, cell death and swelling, but no causative agentwas identified.Skin redness was further investigated in Phase 2. The broad range of time taken to processsamples allowed changes in observed skin redness over time to be documented. Fish werephotographed in the field as they were caught, and again in the laboratory as part of thenecropsy examination. Fish were stored in plastic bags on ice, and took between zero and17 hours to process. Data showed that skin condition and fin condition ratings were affectedby time since death (P < 0.05), and that there was a significant interaction with fish species.This means that changes in skin condition through time are different according to species. Inboth barramundi and mullet, the proportion of fish with a skin condition other than normalincreased over time (P = 0.010 and 0.056, respectively). There was no significant differencebetween the relationships observed in Gladstone and reference sites. This indicates that thereddening of fish over time is not a phenomenon specific to Gladstone Harbour.Not enough bull sharks were caught for the above statistical analysis, although the limitedevidence did suggest a similar pattern. Photographic evidence allowed for visiblecomparison of the fish over time, and showed that skin redness developed in some sharksand other fish post mortem (Figure 38).BarramundiCommercial catchBetween 2000 and 2010, the reported commercial catch of barramundi in the entireGladstone region (S30) ranged between 3.97 t (2009) and 16.77 t (2005) with an annualaverage of 10.8 t. In 2011, the influx of barramundi from Lake Awoonga into the system sawthe commercial catch rise to an unprecedented high of 248.31 t (Figure 3). Of this total, 130 twas captured between July and September 2011. Logbook data supplied by commercialfishers for 2012 shows that the recorded catch returned to historical levels.25