Long- time salmon angler turns to science

Angler John Hodgson measures the water temperature on the Waimakariri River

When 82-year-old John Hodgson heads out to fish the Waimakariri he doesn’t just take his fishing tackle, his thermometer and notebook are always handy too.

For the last eight years Mr Hodgson has been testing a theory that salmon migration is affected by river and ocean temperatures.

Underlying his research is a concern over the effect that water takes have on salmon migration: “These braided rivers heat up quite a lot in the summer naturally, but add to that the water abstraction for irrigation and you start see an effect.”

Mr Hodges started fishing for trout in 1955 on the Selwyn River and then went on to develop a passion for salmon fishing in the 1970s – a devotion that continues today.

Around eight years ago he started to notice a pattern around when the salmon were moving up the river and decided to test this theory.

On his weekly fishing trips throughout the season he measures the water temperatures from a site between the highway bridges on the Waimakariri and ocean temperatures at Kairaki.

He then correlates this with anecdotal evidence on how many salmon are moving up the river from discussions with fellow angers.

“When I turn up at MacIntosh’s or Kairaki on the Waimak the first thing they [the salmon anglers] ask me is ‘what’s the temperature today, John?’ They all know me there,” he says.

Although the Waimakariri River has been the focus of most of his study due to the proximity to his home, Mr Hodgson also records the temperature when he fishes the Rakaia, Rangitata and Hurunui Rivers.

Although he has not finished his research early indications are that if the river is too warm salmon will not enter. “My early findings are that the braided rivers will increase in temperature up to five degrees on a sunny day, and when you combine this with low flows you can get quite warm rivers. You would be very lucky to catch a salmon if the river is over 17 degrees Celsius. It makes them very uncomfortable because of the lack of oxygen,” he says.

Mr Hodgson is an active member of the NZ Salmon Anglers and over the years has been involved in enhancement activities such as planting salmon eggs in tributary streams of the Waimakariri River and writing submissions on resource management issues.

“Fishing is a disease” says Mr Hodgson, who clearly has no qualms about his affliction.

ends

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