Effect of supplementary stocking of juvenile brown trout, Salmo trutta, on yield in a Norwegian mountain reservoir

Abstract

The effect of supplementary stocking of juvenile (age 0+), hatchery-reared, brown trout, Salmo trutta L., on annual yields was assessed in a Norwegian mountain reservoir between 1979 and 2007. Fishing was mainly carried out by local fishermen with benthic gillnets. During the study period, annual stocking ranged from 0 to 52 500 fish (19.8 ha )1 ). No stocking has been carried out since 1997. Annual yield varied from 1650 to 5653 kg, corresponding to 0.62-2.13 kg ha )1 . Exploitation rate in terms of number of gillnets and mean weight of 6+ fish (age when catchable size was reached) explained 64% of the variability in catches. Stocked fish contributed very little to the yield or catch-per-unit-effort, exhibiting no positive correlation with stocking density. The lack of contribution from stocked fish was probably caused by a competitive bottleneck in the eroded epibenthic zone, causing high juvenile mortality. If stocking continues, it is recommended that fish with body lengths >15-20 cm are used. K E Y W O R D S : compensatory stockings, habitat shift, hatchery-reared fish, natural recruitment, survival, yield.

Social, economic and ecological objectives of inland commercial and recreational fisheries

“…It also recognised that management conflicts and synergies exist between recreational and commercial fisheries (Dorow et al 2010;Syrja¨nen & Valkeaja¨rvi 2010), aquaculture and other aquatic resource users (Rask et al 2010;. These arise, for example, from stocking and introductions to meet angler demand (Baer & Brinker 2010;Hesthagen et al 2010) vs protection of biodiversity (Dorow et al 2010) or development of water resource schemes vs fisheries interests. As a consequence, there is a need to balance promotion of aquaculture and inland fisheries with biodiversity protection.…”

“…2010; Sutela & Vehanen 2010). These arise, for example, from stocking and introductions to meet angler demand (Baer & Brinker 2010; Hesthagen et al. 2010) vs protection of biodiversity (Dorow et al.…”