It was almost 12 months ago to the day that I wrote in this column: “Four Mile Hole in Kakadu National Park will not be opened this year due to massive infestation with the floating aquatic weed: salvinia. “Apparently, 95% of this iconic lagoon is covered; and although the closure is deemed temporary, don’t hold your breath waiting for it to reopen.” Four Mile Hole is a very special lagoon on the Wildman River system, and I first brought attention to the pending salvinia infestation back in July 2014, when it was still minor. Nothing seemed to happen after that until, two years later, it had to be closed as you were flat out seeing any water through it for the entire lagoon. Although I was critical of what appeared to be a total lack of aggressive action to save the lagoon, I also wrote: “To be fair, ongoing disastrous wet seasons have mitigated against the salvinia scourge being flushed down to the salt water where it would die. “Maybe we’ll get an all mother of wet seasons this year, and it will be flushed away. “But is that the ‘active management’ we’re told will happen: pray for a good wet season?” Well lo and behold, we actually did get an all mother of wet seasons this year, and there is great news because of it. According to Anthony Mann, Kakadu’s Program Manager (weeds, feral animals & fire): “Four Mile Hole was closed during the 2016 dry season due to a severe outbreak of salvinia, and a low density of weevils. “The poor wet season of 2015/16 and warm temperatures created ideal conditions at Four Mile Hole for the weed to flourish – and perhaps too hot and dry for the survival of weevils. “As such, salvinia ended up covering approximately 95% of the area, thereby preventing any access to the water body. “The area was closed to prevent any disturbance and potential spread of the weed to other areas. “The return of a ‘normal’ wet season in 2016/17 has resulted in a flushing out of Four Mile Hole - and the majority of the salvinia infestation has been cleared out. “As such, this area will re-open to the public in 2017. “It is expected to open within the next two weeks.” So there you go: we’re back on track with this iconic barra fishing hole. Anthony was also able to shed some light on how it is proposed to deal with future salvinia infestation: “Salvinia is very difficult to control, due to its rapid rate of spread – in ideal conditions it can double in size in less than 3 days. “Kakadu National Park uses a biological control agent as the primary method of salvinia control: the salvinia weevil, Cyrtobagous salviniae. “They’re only small (2-3mm long), but they can help control salvinia infestations by eating the rhizomes and young leaves, causing the plant to sink. “If conditions are right, the weevils can breed on the salvinia and increase their consumption of plant material, and they gradually eat their way through the infestation. “However, the weevils will never completely remove an infestation – as they will start to die off as the extent of salvinia diminishes. “So over time, the salvinia and the weevils undergo a cycle of boom and bust,” Anthony said. “Gundjeijmi Aboriginal Corporation has recently established a breeding facility for salvinia weevils in Jabiru, with support from Kakadu National Park and NT Weeds Branch. “This facility will breed weevils in captivity (in large tanks) for release into priority salvinia infestations in Kakadu, including Four Mile Hole. “If successful, this will enable the release of thousands of weevils per year into existing salvinia infestation,” Anthony explained. My understanding is that the goal is to produce tens of thousands of weevils – many times more than before – and really attack the salvinia infestations at Four Mile Hole and elsewhere in Kakadu. That’s great news, and park management is to be commended for taking such positive action. Anthony did say: “It will really depend on how successful the breeding facility is, but we will release as many as we can breed – and will keep releasing them as they continue to breed.” That is just perfect! PHOTOS: Steve Castle (left) with an extremely-rare NT wahoo is helped by Darwin Bluewater Charters crew member, Gary Lee.
Brian Caruthers, pictured here with deckie Rueben Raymond, also fished with Darwin Bluewater Charters and caught this ripper sailfish.
Ben Peel with daughter Tilly, 4, and one of her seven barra caught down the Daly River.
