Mouse-Eating Trout - 2009/2010 the year of the Mouse
2009 Newsflash!
Season 2009/20010 is set to be another Year of the Mouse!
That's not a Chinese Year thing, instead it means that New Zealand Fly fishing rivers will be full of large mouse-eating trout.
May 2009 : Year of Mouse news update
Put simply, the Beech trees have a bumper flowering season, which causes an abundance of seeds for the mice population along the rivers, which then get gobbled up by passing trout, leading to large mouse eating trout in the early season coming up (from October 2009). The year of the Mouse stays long in the memory for those who experience it.
See below, for the latest news extract and the full story of the phenomenon as previously reported on this website.
| Department of Conservation alert after flower deluge
The full effect of a bumper flowering of beech trees throughout the country is not likely to be felt until next spring, according to the Conservation Department's Nelson Lakes area office biodiversity programme manager, Dave Rees. Favourable climatic conditions cause the trees to produce increased quantities of flowers and seeds in what is known as a mast year. The abundance of that food on the forest floor leads to a surge in the numbers of rats and mice ... The effects of the beech mast in the area would likely not be felt until the breeding season in the spring. Extracts from an orignal article in The Marlborough Express. |
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By Gavin James and Steve Fox
New Zealand has an international reputation for having a pristine backcountry trout fishery where anglers have the opportunity to catch large, wild trout. Yet as anglers who fish backcountry rivers know, these fish, while sometimes large, are normally long rather than well conditioned. Every few years, however, this pattern seems to change with some unusually high conditioned fish being caught. During the last two summers this has been particularly evident with numerous reports of record size trout being caught throughout the country. As a consequence, there has been much talk in angling clubs and reports in the popular press about the size of some of the fish caught and the apparent importance of mice as food for trout. Our recent capture of a large brown trout containing mice stimulated our scientific curiosity and prompted an investigation into what is actually known of the relationship between mice and trout. |
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We have attempted to provide some answers here to the more commonly asked questions that perplex anglers. What causes good beech tree seeding years, or "masting" years in botanical terms, and can they be predicted? What is the link between beech seeding and "mice plagues" and for that matter why do mice apparently enter the water so readily and end up becoming food for trout?
Why do only some trout seem to catch on to this new food source and does this phenomenon only happen in New Zealand? Beech tree seeding has been the subject of scientific interest since the late 1950s, when it was first hypothesized that the sporadic seeding of beech trees leads to a cascading increase in the number of rodents, then stoats, and subsequent predation on native birds. |
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Such a scenario is of concern to conservationists, as beech trees (Notholagus spp.) either dominate or are present in approximately 70% of New Zealand's native forests. While there has been no research on the link between beech seeding and trout growth, recent studies on food webs within beech forests are beginning to shed some light on the relationship.
On average, beech trees in New Zealand produce seeds in large quantities every three to five years. However, the last two years have been unusual in that seeding has occurred in consecutive years. Some forest communities have been studied for as long as 35 years and there is general consensus that temperature has a large role to play in triggering beech seeding. |
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Hot conditions in summer stimulate flower bud formation, but it is actually the following summer before the beech trees produce flowers and several months after that (Febuary to May) before the seeds are shed. Thus there is a lag over a year between the warm temperatures and the production of beech seeds. The seeds then lie on the ground all winter and germinate in spring. Within a single year the intensity of seeding often varies between different locations and beech species, although overall there is significant synchrony among all the beech species over at least the entire South Island and lower North Island. Some seeds are produced in most years, but the amount varies extremely widely, from only one to five seeds per m2 in the lowest years to more than 12,000 per m2 in the highest.
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In spite of temperature being a major factor in triggering beech seed production, there are different explanations for the mechanisms involved. One view is that the warmer temperatures result in increased photosynthesis and therefore greater production of flower buds. Another view is that temperature is merely a cue for flower production. It has recently been shown that beech gains a major pollination benefit from flowering synchronously at intervals, giving support to the second (cueing) theory.
Different beech tree species apparently do seed simultaneously across various regions of the country, suggesting that there are large-scale climatic factors involved, notably El Nino and La Nina. However, it is also true that local factors, such as aspect and elevation, can modify the timing and intensity of masting on a local basis. |
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