Freshwater Fish and Bugs in the Gilbert River
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November 2007 Northern Guf Resource Management Group Freshwater fish and bugs in the Gilbert River Inside : Collecting the facts Increasing local awareness 2 During June 2006, the Depart- catching fish, the scientists thing in this short newsletter Fishing with electricity 2 ment of Primary Industries and enjoyed fantastic local hospi- will interest you. Fisheries (DPI&F) and Ecowise tality and support, for which The information gathered will Where are the fish? 3 Environmental Pty Ltd surveyed we were most grateful. assist the NGRMG and locals the fish and visible aquatic In this newsletter you will find to make and contribute to Water quality and habitat 3 invertebrates (bugs) in the Gil- out how an electrofisher management decisions for the bert River catchment. The works, how we determined northern Gulf region. Floods and flows are vital 3 survey was initiated by the the health of the Gilbert River Northern Gulf Regional Man- catchment and why aquatic agement Group (NGRMG) to Aquatic macroinvertebrates 4 habitat is important. This is a address the lack of knowledge quick summary of the findings of the diversity of life in the No water - what happens? 5 and an explanation of the region’s waterways. importance of maintaining Over a 10 day period, 20 sites river flows and floods. A Acknowledgements 5 were sampled to identify the much more detailed report is visible bugs, which fish and available from the NGRMG Recommendations 6 how many lived there, and how office. healthy the catchment was at So whether you are keen List of fish found 7 the time. While the trip was fisher, a budding naturalist or hectic and involved being just interested in the water bogged, bush bashing, croco- quality and aquatic biodiver- dile wrestling and of course Special points of sity of the local area, some- Surveying near Mt Surprise interest: 1557 fish measured Gilbert catchment clean and healthy 38 fish species found 9 fish species re- The fish and invertebrate to access funds to reduce community, water quality and weed and pig infestations. corded for the first aquatic habitat in the Gilbert time in the Gilbert At the sites surveyed, current catchment are in a very pasture condition had no ob- 2 totally new species healthy state. The obvious vious influence on fish diver- and 3 requiring fur- threats to this healthy status sity or abundance or water ther investigation are weeds and feral pigs. quality. Weeds can smother trees and 3599 “bugs” col- grazing land. Pigs destroy However any changes in wa- Attempting to get the boat to the lected river and lagoon banks and ter management practices will water need careful consideration as 75 families of degrade water quality. river flows are the single most aquatic invertebrates The technical report from this important factor influencing (bugs) study will assist the NGRMG catchment health. Page 2 Increasing local awareness An important part of this basic habitat assessments. project was to increase the All landholders were supplied capacity of NGRMG staff with a written summary of and Gulf residents to under- aquatic habitat, water quality stand and become familiar Station owners/managers participated and fish species found in their with the different ways to in sampling at most sites waterbodies. describe and assess catchment condition. Feedback from participants was extremely positive and Several members of the requests for return visits have NGRMG, local residents and been received. landholders participated in field sampling which provided The skills learned will assist them with basic aquatic ecol- landholders to develop farm ogy skills. This included iden- management plans and to tification of fish and bug spe- understand “jargon” often cies, measurement and inter- used by government consulta- Savannah guides also partici- pretation of water quality and tive committees. pated in sampling Backpack electrofisher in a small wa- terbody Catching fish with electricity Electrofishing is the best way fluence its effectiveness, in- unconscious for up to 90 sec- “it’s powerful enough to capture large numbers of cluding water hardness, water onds. And before you ask, yes to kill a human yet fish fish quickly with no harm to temperatures and operator it does stun crocodiles … are only unconscious the fish. We use two types of skill. It is not as easy as it briefly! for up to 90 seconds” electrofishers. For very small looks and requires lots of Fish were identified and up to waterbodies we have a back- experience to pick the most 20 of each species measured pack unit powered by a bat- effective settings to collect and recorded then returned tery, and for everywhere else, whatever fish are present. An unharmed to the water. a boat mounted unit powered electric current basically an- by a 7.5KVA generator. aesthetizes fish. We use up to Any fish that were “new” or 1000 volts and 7 or more different were preserved and Electrofishing only works in sent to the Queensland Mu- freshwater. Many factors in- amps, more than enough to kill a human, yet fish are only seum for positive id. What about river frontage land condition? “Most pleasing was the lack of urban rubbish” At each site the condition of “wet” had just finished, a lot to manage. land adjacent to the water- of it was weeds and grass spe- No link was found between body was assessed using the cies not desired by the grazing GLM land condition, water ABCD rating system adopted industry. This meant most quality, fish distribution or by the Grazing Land Manage- sites were rated C. The best abundance. Whether this ment (GLM) project (A = rating was a B and two sites remains the same throughout excellent to D = poor). Our rated D. the year is unknown. assessment was reviewed by a The greatest disturbance to What was noticeable through- member of the GLM team river banks was caused by pigs out the catchment was the (Kev Shaw) from photos. which contributed to the sites absence of rubbish. Obviously While most sites had good with a “D” rating. Unfortu- the community cares about its ground cover because a good nately this damage is difficult catchment. Page 3 Where are the fish? While site specific data was 195m above sea level (AHD). Three species, the Papuan kept confidential by request, Only two fish species were river sprat, northwest glassfish trends within the fish popula- found at all sample sites: and freshwater anchovy, were tion on a catchment scale spangled perch and rainbow- only found in offstream la- were obvious. No secret fish- fish. Five fish species were goons. ing spots revealed in this seg- found only above 195m AHD Sites closer to the coast Fish captured during ten minutes ment … sorry. while 12 species were only tended to have a greater Barramundi were scarce in the found below. number of fish species. middle to upper reaches of The most widespread and Even more species are likely the catchment despite suitable common species of interest to to exist in the lower reaches habitat. The timing and size anglers include sleepy cod, of the Gilbert River. However of the wet season may influ- archerfish, sooty grunter, gulf wet weather prevented access. ence how far and where bar- grunter and barramundi. ramundi travel. It appears that The great news was that no There were also eight differ- feral or exotic fish were de- in 2006, barramundi were ent species of catfish. limited to areas less than tected. Sleepy cod being measured Water quality and habitat “excellent” Water quality across the Dissolved oxygen, pH, tem- the more oxygen there was in catchment was generally ex- perature and turbidity (water the water and the more spe- cellent. One spring had sur- clarity) were also measured. cies it contained. prisingly low conductivity Water in offstream lagoons Fish habitat was excellent at (almost as pure as rainwater). tended to be cloudier than the most sites, with overhanging instream waterholes. This is Conductivity is basically a trees, snags and aquatic plants Water quality monitoring measurement of dissolved usually because floodplain plentiful. Erosion and silta- minerals. Spring and bore lagoons are filled by sediment tion was generally low with water normally contains high laden floodwaters. the exception of one site levels of dissolved minerals Dissolved oxygen is critical to which had major pig damage. and is classified as “hard”. aquatic life. All sites had good The banks had been uprooted The reasons for such a low levels of oxygen. We found and the water quality was also reading are a mystery. that the wider the water body, lower than at similar sites. Floods and flows are vital According to historical re- Fish within the Gilbert catch- and the juveniles don’t get an cords, rainfall is surprisingly ment require both flood peaks opportunity to migrate up- evenly distributed across the and a good steady flow in the stream and across floodplains. Gilbert catchment. There is river to move about, spawn Managers (this includes land- distinct seasonality though, and access permanent water holders) of streams within the with most rain falling between to sustain them through the catchment require a good November and March. This dry season. Reduced floods understanding of the flow does not always translate to or flows will reduce fish distri- characteristics and their rela- regular river flows. The only bution, abundance and diver- tionship with aquatic ecology. months to always have some sity. The timing of the flows Any development that is likely flow are February and March. is also important to species to change the flow of streams There may be multiple flood such as barramundi that move within the Gilbert catchment peaks in between low or no between salt and freshwater.