I received your questions, and have provided some brief responses, hopefully they answer your questions.
Looking at the pictures you provided, the fish appears to have had its gills eaten, probably by a gull or similar bird, so it could have been transported by a bird to the spot you found it?
Just a thought, but it is also possible the fish was living nearby.
1) Are there catfish living and breeding in the Tongariro River?
They don’t breed in the river itself, as their preferred spawning habitat is in the warm shallow margins of the lake, particularly around raupo swamp.
2) Is DOC monitoring catfish in Taupo lake and rivers?
This monitoring is intended to help us understand the diet, population and distribution trends of the catfish.
3) If catfish are in the Tongariro River, what if anything can be done to control their spread?
Catfish have been present in the lake for over 3 decades, and we expect that in this time they have reached the full extent of their likely range. Based on our monitoring the department has no concerns for the likelihood of catfish infesting the Tongariro, as its temperature and flow rate are generally outside the preferred habitat of catfish. The preferred habitat is warm water and shallow, sandy or muddy substrate and weed beds.
4) Has DOC got a catfish operational plan?
If by this question you mean to ask if the department has a plan for the eradication of catfish from the lake the answer is no. Our operations extend only to monitoring the catfish population and diet.
5) Does it include a program to counteract the damage they do to native fish populations?
No. The Ministry for Primary Industry has the responsibility for managing invasive species such as catfish, and there are no plans to undertake control programs in the lake at this time.
6) If they get abundant up the rivers how will this affect trout spawning? I read they love eating the trout eggs?
The department does not have any concerns in this regard, as per question 3 above.
7) Also, will the condition of the Taupo trout be affected with the competition for food from the catfish?
The condition of trout in the lake is mainly dependent on the productivity of plankton in the pelagic zone of the lake, as plankton abundance underpins the entire food chain of the lake.
Operations Manager Taupo Fishery
Turangi Office | Central North Island Region
G Level 1, 69 Town Centre, Turangi 3330
E 0211658663 or (07) 384 7116
Department of Conservation, Te Papa Atawhai www.doc.govt.nz