Evaluation and Reflection page

There have been lots of informal discussion and questions. In terms of the requirements you need to make a record of these. You also need to keep a logbook where you can record more personal thoughts/evaluations, if you don't want to post them here.

HR - Is the decline of the Grey Mullet in fish catches on the North Island partly as a consequence of the reduced recruitment of young fish from the estuaries which are infested with Gambusia?

HR - The shape of the female fish we are catching has changed. Any ideas of how to quantify/measure this?

Listen to this!!



HR - Should we expect a difference in the growth rates of fish in the breeding & non-breeding season? Is it statistically significant and is there some genetic control of this?

HR - What will happen with the males, with respect to their growth over the season?

HR - Seems like the females will all be LARGE (> 21 mm TL) when they start breeding again. What a great way to kick start the re-population exercise.

HR - With the modification of the minnow trap to catch Gambusia and the use of light as a bait, could we test different colours of lights = different wavelengths to get an idea of which one wavelength works the best?

Hr - Daylength = 12h30 long = magical figure for Gambusia breeding. = 11 March stop and 3 October start. Last fertilization 11 March = last babies 11 April = 4 weeks later = few juveniles after this time. Start breeding 3 October = 12h31 = young born 3 November = 5 mm long. Caught in sampling two weeks later (17 November) at minimum. PREDICTION Expect juveniles of this year’s breeding in sampling around about 17 November!
WRONG!! Hr caught a juvenile (139 mm long) and 5 females showing black spots on 6 September. Back to the drawing board - sigh!!!

Gambusia 2011.
Breeding trends and the number of large and small fish over the last two years have been the same, until this year it seems. The only difference, it seems, is that we had a really mild winter up until about the end of August and then we had a sharp cold snap. There was no die off of adult fish as had been recorded before and it seem like the survival of large fish through the winter was going to be good. Then the cold snap hit! There was a major die off of large sized fish at about the time they should have been starting to breed. Not surprisingly this has had a major impact on the increase in number over the last couple of months (end of November 2011). The trends that are being recorded are interesting but the season is not yet complete, so watch this space. There is a suggestion that to control populations of Gambusia, in this stream anyway, a sudden cold snap in early spring might do the business. More to follow

There are suggestions that Banded Kokopu are feeding on Gambusia in the swamp part of the stream. Kokopu grow faster here than anywhere else in the catchment. They have been recorded to feed mostly on terrestrial insects which are derived from the closed canopy that is part of their habitat. While there are some overhanging trees in the swamp where the kokopu live, it is nothing like the habitat they occupy further upstream, so where is the extra food coming from that is promoting this fast growth. There are no Gambusia further upstream but they are present in the swamp, so that might be it. I have no doubt that kokopu will eat gambusia if given half a chance, but it would be nice to know if they would eat them on a regular basis. Is this an indication of the ecosystem evolving to deal with the introduction of Gambusia? W shouldn't be surprised that this might happen.


Results from walk down the stream 1 August 2009

Thanks to Peter Crossley for coming along and sharing his knowledge about the fish/aquatic life of the stream.

A discussion, after we had spent an extra hour more than we planned to, came up with these ideas:- In order of priority:-

1.) We need to identify the route that the water takes under the main sewer pipe that leads to the stream and out to sea. This is a matter of priority for a number of reasons:- a) A pulse of whitebait could potentially restock the stream with native species very quickly.
b) A known transit area could be quite easily monitored for fish going up and down stream and would be a useful indicator of fish movements at different times of the year. There is a report from the Council that identifies this issue and it is currently being sourced.

2.) The source of the 'Fe pollution' above the waterfall needs to be identified and remedied. The source of the Fe contamination is a bacteria, so it is not pollution. It can lead to anaerobic conditions though and that is not good for fish.

3.) We need to trial and develop the floating traps for catching Gambusia. These will allow us to sample the rest of the stream, where our big net is not so easy to use. First trial of the traps went OK - they were not tampered with and one adult INANGA was caught. There is an issue with the light. The trap with the diffuse light in it had no fish in it and the light in the trap with the fish in was not working and seems to be US. We need to find a light that will (a) provide a concentrated beam and (b) last overnight. Ideas welcome.


Winter of 2011 is unseasonably warm up to now (3 degrees in Auckland) and this has resulted in a large number of adult fish surviving for much longer into the winter than in the past. They have probably all died now as a result of the cold weather but time will tell. The trend for water temperature is a steady increase since trapping started and the response from the Gambusia has been interesting. Not fully analyzed yet but worth putting down. The cold snap in early spring put paid to these adult fish. There are now few adults surviving and their breeding seems to have been delayed by a month at least. Watch this space.

Banded Kokopu surveys

We have caught heaps of kokopu in Le Roy's stream in all habitats that have been sampled. We have some evidence that a pollution event in one of the tributaries killed all the resident large fish and that they were replaced by a number of small juvenile fish a short time later. We will monitor this situation with interest. In total we have caught 400 odd individiual fish in the stream, although some of these will have been caught more than once, so the actual number caught is much less than this. We have caught 51 individuals at least once and this is likely to be more as the analysis of the photographs is not yet complete.

We also surveyed the Waiurutoa stream and that is also full of banded kokopu, but they are all mostly small individuals, suggesting an event which has reduced the numbers of larger fish at some point in the recent past. The diversity of fish in this stream is higher than that in Le Roy's and there are Common and Giant Bullys, as well as large numbers of Inanga and no Gambusia. The estuarine part of the stream has large numbers of Cockabullies, which are totally absent in Le Roy's.

A brief survey, of the estuarine portion, in the summer of 2010/11 when a comparison of the two streams was made had these results:- Le Roy's stream - Heaps of Gambusia, some Inanga, Adult Giant Bullys and Large Long-finned Eels (> 50 cm long). Waiurutoa stream:- No Gambusia, Cockabullies, Common Bullys, Heaps of Inanga and small Long-finned Eels (<10 cm long). Is this an indication of the impact of Gambusia? In Le Roy's only those fish that actively prey on them were present in reasonable numbers, whereas in the stream where they are absent, the diversity and number of smaller (more impacted?) species was higher. It warrants a more complete survey.

Do Banded Kokopu change their spots? If not, then photo's of both sides of the fish will enable them to be identified indefinitely. How variable is the pattern also?

Debris collected from downstream of some of the pools did not result in any young fish, after it was immersed in water in 2010. Searches for eggs did not reveal any either. Searches for eggs on the sides of the pools inhabited by breeding sized fish did not reveal any eggs either. Sigh!! We need to look harder or in a different place!! NO - recent data analysis and new knowledge indicates that the debris was collected far too late and that any eggs present in the debris would have hatched before it was collected. These data show that the kokopu spawned in late May/early June and these are the dates to target if we hope to find eggs in the flood debris. Watch this space.

Lots of 'debris' in the traps set above the waterfall and close to it on the downstream side. Is this an indicator for suitable waters for the kokopu we have caught? Those traps set in the swamp, in which we caught kokopu had NO DEBRIS in them at all!. Different water conditions entirely. Is this 'debris' amount quantifiable somehow and should it be?

Gambusia and Inanga feeding together on the same material and in the same way = snatching it from the surface. Is this the area of competition between the two species?