Odd Terje Sandlund

Coregonid introductions in Nor- way: well-intended and successful, but destructive

The introduction of coregonids, mainly whitefi sh (Coregonus lavaretus (L.)), into new localities together with the enhancement of existing stocks was actively pursued in southern Norway from around 1850 until the 1960s, with 1875 to 1925 being the most intensive period. According to the offi cial records of the relevant management authorities and other documentation, whitefi sh were released into approximately 150 localities, mostly in south-east and central Norway. Introductions often led to subsequent (secondary) spreading to downstream localities, and in some cases or at a later stage to other lakes or reservoirs through tunnels constructed in association with hydropower development. The estimated number of native whitefi sh populations in Norway was approximately 360, while at present time there are approximately 900 populations. Some recipient localities were fi shless lakes, while many contained other species such as brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.)). Whitefi sh were relatively successful in establishing viable and abundant populations in many lakes, sometimes with a quite devastating impact on native fi sh populations, mainly planktivorous species such as Arctic charr. Vendace (C. albula (L.)) was also introduced into around 16 lakes during the period 1859 to 1890, but only in one of these cases was a viable population established. In this paper we summarize the available information about coregonid introductions in Norwegian lakes, and discuss how it has changed fi sh diversity. We discuss the factors leading to population establishment or failure and how these introductions have impacted native fi sh populations, as well as the value of fi sheries in some of the lakes. The management policies behind these fi sh cultivation practices and the historical development of management principles are also discussed.

European smelt (Osmerus eperlanus) eats all; eaten by all: Is it a key species in lakes?

The concept o f keystone species is controversial and often confused with dominant species. A modem definition is a species whose impact on the ecosystem is far greater than expected from its biomass (POWER & MILLS 1995, POWER et al. 1996). European smelt (Osmerus eperlanus) is mainly considered a pelagic zooplanktivore species, but investigations have shown that it eats larger pelagic animals as well as small fish, and that it is phytoplanktivorous in its larval stages (SVÃRDSON 1976, NILSSON 1979, NA:SJE et al. 1987). Moreover, it utilizes the epibenthic habitat to prey on epibenthic invertebrates (SANDLUND et al. 1980, 1985a). European smelt is also an important prey species, eaten by a number of sympatric fish species (NILSSON 1979). It has been dubbed a buffer species by SvÃRDSON (1976). Thus, European smelt is an important component in a large number of trophic interactions in the pelagic ecosystem. In many Scandinavian cases, the presence o f smelt is also considered a prerequisite for the occurrence of the desired large-bodied predatory brown trout (Salmo trutta) (SANDLUND & NA:SJE 2000). In this paper we review data on trophic position o f European smelt in the pelagic zone of Norwegian Lake Mjosa and discuss its role in the pelagic ecosystem.

Whitefish Fisheries in Mountainous Southeastern Norway: Abundant Resources, but Scarce Fishermen

Abstract Commercial utilization of inland fish resources can constitute an important addition to other economic activities in rural communities. Based on a case study of commercial whitefish fishery in Lake Femund, a mountain lake in southeastern Norway, this article outlines experience gained and indicates some of the general problems related to this type of economic activity. They concern aspects such as resource biology, product development and marketing, economic management, and staff recruitment. An initial hypothesis of the study was that commercial fishery would have a significant impact on the whitefish stock, causing fluctuations in yield and consequent variations in the economy of the fishery. Therefore, the study included an analysis of marketing possibilities for whitefish products, as well as of the social and socioeconomic conditions sustaining whitefish fishery in the local community. Nearly 20 years of data show that commercial fishery in Lake Femund, with a yield of up to 1 kg per ha, has a low to moderate exploitation rate. Thus, fishery itself does not generate fluctuations in the fish population that would influence yields. The major restrictions on the enterprise are related to other aspects, such as problems of economic and technical management of this specialized small-scale industry, difficulties in the recruitment of fishermen to a short-season fishery in a time when the employment pattern in the community is changing from seasonal activities in agriculture to full-time employment in manufacturing and services, and the challenge of developing and marketing competitive products for a niche market.