Tactical Research Fund: Development and deployment of sterile ‘Judas fish’ to assist carp eradication in Lake Sorell, Tasmania - surgical and chemical sterilisation
Critically, sterile Judas fish need to be developed/deployed by spring of 2013, before remaining females from the 2009 cohort begin to mature. Delay in project commencement beyond 2012 spring will critically hamper carp eradication in Tasmania.
To date, Integrated Carp Management (ICM) strategy has resulted in eradication of carp from Lake Crescent and contained their population to Lake Sorell, repeatedly demonstrating an ability to fish down new cohorts rapidly. Use of radio-tagged "Judas" male carp to locate and remove aggregations has been the largest contributor (e.g. accounting for >80% of carp captured in Lake Crescent). Despite low adult carp numbers spawning occurred in Lake Sorell (2009), prompted by exceptionally high water levels. Relatively large size of the lake (than Crescent) and resource limitations did not help. Male Judas carp were implicated in this recruitment prompting their removal and replaced by juvenile Judas in 2011- ID feeding aggregations; mature Judas also ID spawning aggregations.
In absence of Judas technique, it is deemed impossible to achieve control let alone eradication, prompting preliminary sterilization trials in 2010. Albeit with low success rate (1/11) the trials were encouraging with further comparative anatomical examinations revealing valuable clues for future refinement. In light of this progress multiple sterilized fish will be ready for deployment by October 2013, should the refinement/experiments commence this spring (2012). Two annual carp programme reviews (10-11 May 2011 and 19-20 May 2012) have recommended the technique/s be developed systematically—including alternative approaches along with hormonal, histological, behavioural and fertility assessment.
Primary objective is to develop/deploy behaviourally least compromised sterile Judas fish. Fish with compromised reproductive behaviour though not preferred are useful in betraying the numerically dominant non-reproductive aggregations.
Expected outcomes will contribute to long-term goals of recreation and commercial fishing sectors in inland waters of Tasmania, with likely interest to other states.
Final report
In a world first, the project successfully developed reliable procedures for surgical sterilization of male carp and demonstrated that these when deployed as sterile ‘Judas’ fish are as competent as male ‘Judas’ carp in betraying the locations of feral populations thus assisting their capture. Significantly, the sterile Judas fish will mitigate future risks associated inadvertent contributions to spawning and recruitment. The sterile Judas carp are now an integral component of the ongoing carp eradication program at Lake Sorell, Tasmania.
Following the discovery of the carp Cyprinus carpio in lakes Crescent and Sorell in 1995, the Inland Fisheries Service (IFS) decided to eradicate both the populations. While, the Lake Crescent population has been successfully eradicated, the Lake Sorell population has been lingering, owing to inadvertent spawning and recruitment in 2009 —contributed by Judas carp, which are otherwise central to the eradication strategy at the lakes. Responding to the crisis and urgent need to mitigate future recruitment risks this project explored chemical and surgical sterilization options with a view to replace male ‘Judas’ carp with sterile ‘Judas’ carp.
The primary objective of the project was to develop reliable sterilization technique/s that did not significantly compromise the behavior of the sterilized individuals. Behavioral integrity of the sterilized individuals when fitted with radio-transmitters and deployed as Judas fish (i.e. to assimilate and integrate seamlessly into the wild populations) was/is critical to betraying the locations of aggregations allowing targeted fishing and removal of feral populations.
Keywords: Common carp, Cyprinus carpio, steroid hormones, Superlorin, testis, tubectomy, Radio-tracking, Ultra sound.
