NELSON MARLBOROUGH FISH & GAME
Winter is here and all over the country trout are in spawning mode.
Currently, brown trout are close to finishing their annual breeding duties, with rainbow trout spawning commencing in the following couple of months.
Like salmon, trout will spawn in their place of birth, and can travel some way to get there.
Conversely, where salmon perish once their duties are done, trout generally survive the ordeal and can return year after year to spawn.
If conditions allow, trout can live well over a decade, meaning a single fish can contribute to many years of recruitment.
Watching spawning trout is a unique and fascinating experience; after finding a mate and reaching their intended destination, trout will scratch around to locate the ideal gravels – generally around pebble size - small enough to dig up but not so small as to get washed away.
The pair go on their sides and flick up gravel to create a bed, where eggs are deposited and fertilized, then covered up similarly to create what is termed a trout ‘redd’. Once complete, one or both fish will defend their redd for some weeks, guarding it against disturbance by other spawning trout. Trout redds can be easy to identify, commonly seen as an oval area of clean ‘scrubbed’ gravel, and in shallow water areas such as the tail of a pool.
From then it’s up to nature to determine the survivability of their progeny: the more stable the water, the better for trout recruitment.
Generally, it is the months that follow that are the most important.
Eggs incubating in the gravel are vulnerable to smothering from sediment through stream bed disturbance, especially during base flows.
Similarly, as newly-hatched trout emerge from the gravel, they are most vulnerable to flood events. One or two stable winter/spring periods will see successful recruitment and transition from juveniles into medium and large-sized fish – meaning a booming fishery and happy anglers as we are currently experiencing in the region.
On the other hand, damaging floods or in-stream disturbances through this crucial time can have flow-on consequences for trout numbers, which become apparent in the following years. Likewise, drought or low-water periods can also impact trout and native fish abundance.
Fish & Game staff monitor trout spawning activity in many rivers and streams, which are mostly achieved via foot surveys, counting trout redds and spawning fish and assessing spawning habitat. Comparisons can be made year-to-year if a waterway is surveyed regularly or on an ad-hoc basis to paint a picture of the fishery. Frequently our spawning results and habitat assessments are used to inform on specific RMA matters.
As an example, Fish & Game actively engage with TDC river engineers/Taylors contractors over river works within trout spawning waters so winter channel stabilisation work can still be achieved, whilst minimising damage to trout spawning activity.
Fish & Game are also happy to work with landowners wishing to undertake winter instream works at sites that trout may potentially use, the goal being to assess where most activity is occurring to ensure works will not cause significant unintended consequences for the trout population breeding cycle. Call 03 544 6382 for more information.
