SCREENS & FEEDERS
PRODUCTION OF SPAWNING
STONES FOR FRESHWATER TROUT
A
mobile screen is proving its versatility by making an unusual contribution to the freshwater environment. For the past three years, Veljekset Kokkonen, a crushing contractor in Lieksa, eastern Finland, has used its Metso Lokotrack ST2.8 mobile scalper to screen various sizes of crushed stone for sand, gravel and soil, and for a highly specialised use – spawning stones to help endangered freshwater trout breed. These spawning stones aim to restore the extremely threatened freshwater trout in the Naarakoski rapids, on the Lieksanjoki watercourse. The beautiful territory is on the lower course of the famous Ruunaa fishing and nature conservation area. The freshwater trout wander from the lakes to the upper courses of rivers to breed. For this, they need proper-sized stones. The smaller stones are needed to successfully lay their eggs and the larger stones, about the size of a human head, protect the precious first moments of the trout babies. Juha-Pekka Kokkonen, the man in charge of crushing and screening at Veljekset Kokkonen, has overseen the operation of the Lokotrack ST2.8 screen at the company’s Pekkilä soil extraction area in Lieksa. “We screen three sizes of natural stones from the gravel bank,” Kokkonen said. “The sizes of the spawning stones vary between 30-60mm, 20-100mm and 100-250mm. More than 1300m2 of gravel is being processed. “Working with the screen is fast. We use an eccentric throw of 14mm, and the screen accepts as much feed as the excavator is capable of putting in. “We use punch plates in three sections on the screen’s upper deck and a steel mesh in one section, as well as on the lower deck.” Veljekset Kokkonen purchased its first mobile crushing equipment from Metso in the early 1980s and then acquired a trackmounted two-stage plant. The Lokotrack ST2.8 screen was delivered in 2016. “Based on our first experiences, ST2.8 is a screen that gets the job done,” Kokkonen said. “So far, everything has worked well. A Finnish product is a safe choice, because it means that spare parts and maintenance services are locally available when needed. 42
Quarry June 2019
The Lokotrack ST2.8 screen quickly produces spawning stones of different sizes.
Juha-Pekka Kokkonen.
The fry stones, sized 20-100mm, will make it safer for the landlocked trout to reproduce in the rapids.
“Good fuel economy is an added bonus for us, enhancing the cost-effectiveness of screening. The efficient screen consumes about 12 litres per hour, which is not much for an hourly screening capacity of more than 200 tonnes.” Veljekset Kokkonen’s operations are based on three pillars: construction sector transport services, contracting, and crushing and screening. The family company operates mainly in eastern Finland and employs 20 people. It crushes and screens roughly half a million tonnes of aggregates annually. As many of Veljekset Kokkonen’s clients are small producers, the equipment is transported from one place to another about 40 times a year. Veljekset Kokkonen screens the spawning
stones for Kuopion Teho-Louhinta, the company in charge of submerging the stones in the Naarakoski rapids, commissioned by the Centre for Economic Development, Transport and the Environment for North Karelia. The work has provided the landlocked fish with new and better spawning sites. The spawning stones meet an important need: natural stocks of landlocked trout can be found in only a few headwaters in Finland. In rapids with a stone and gravel bottom, only about one per cent of the fish stock develop into fry. The Metso Lokotrack ST2.8 scalping screen is available in Australia through national distributor Tutt Bryant Equipment. • Source: Metso
