Proxy Measures of Fitness Suggest Coastal Fish Farms Can Act as Population Sources and Not Ecological Traps for Wild Gadoid Fish

Background: Ecological traps form when artificial structures are added to natural habitats and induce mismatches between habitat preferences and fitness consequences. Their existence in terrestrial systems has been documented, yet little evidence suggests they occur in marine environments. Coastal fish farms are widespread artificial structures in coastal ecosystems and are highly attractive to wild fish. Methodology/Principal Findings: To investigate if coastal salmon farms act as ecological traps for wild Atlantic cod (Gadus morhua) and saithe (Pollachius virens), we compared proxy measures of fitness between farm-associated fish and control fish caught distant from farms in nine locations throughout coastal Norway, the largest coastal fish farming industry in the world. Farms modified wild fish diets in both quality and quantity, thereby providing farm-associated wild fish with a strong trophic subsidy. This translated to greater somatic (saithe: 1.06–1.12 times; cod: 1.06–1.11 times) and liver condition indices (saithe: 1.4–1.8 times; cod: 2.0–2.8 times) than control fish caught distant from farms. Parasite loads of farm-associated wild fish were modified from control fish, with increased external and decreased internal parasites, however the strong effect of the trophic subsidy overrode any effects of altered loads upon condition. Conclusions and Significance: Proxy measures of fitness provided no evidence that salmon farms function as ecological traps for wild fish. We suggest fish farms may act as population sources for wild fish, provided they are protected from fishing while resident at farms to allow their increased condition to manifest as greater reproductive output.Funding was provided by the Norwegian Research Council Havet og kysten program to the CoastACE project (no: 173384)

Site fidelity in breeding Common Eider Somateria mollissima females

We studied nest-site and post-nesting feeding site fidelity in a population of Common Eiders Somateria mollissima in North Norway during five consecutive breeding seasons (1986-90). Twenty-five per cent of the females that nested successfully and none of the unsuccessful females returned to the same nest . Whether females nested at the same site was independent of nesting variables other than total clutch loss . Similarly, nest-site fidelity did not result in nesting variables different from those of females which changed their nest-site. In contrast, fidelity to post-nesting feeding sites was very high (92%). Females that showed post-nesting feeding site fidelity did not have a higher rate of nest-site fidelity than than other birds in the population . We therefore contend that in Common Eiders fidelity to a specific nest-site is less important than fidelity to the postnesting feeding site . Going to areas where the female knows that sufficient food can be found is very important for both the female and her brood. In comparison to other duck species with more specific nest-site requirements (cavity-nesting ducks), Common Eiders have a low return rate to previous nest-sites, and we suggest that this reflects a difference in the availability of suitable sites

The diets of sympatric wintering populations of Common Eider Somateria mollissima and King Eider S. spectabilis in Northern Norway

Atotal of 2534 food items of 42 species (exclusive eggs of fish) were identified in the diet of Common Eiders Somateria mollissima (1650 items of 34 species) and King Eiders S. spectabilis (884 items of 35 species) from Troms in northern Norway in April/May. Both species had been feeding on much the same prey species but in quite different proportions . The diet of Common Eiders was dominated by Mytilus edulis (46.3% wet wt .), eggs of Cyclopterus lumpus (25.9%) and other molluscs, Modiolus modiolus (7 .3%), Modiolaria discors (2 .1%) and Arctica islandica (2 .8%) . King Eiders feed mainly on echinoderms, Ophiopholis aculeata (27.1%), Strongylocentrotus droebachiensis (22.7%) and Asterias rubens (15.1 %). Otherimportant King Eiderfood items were molluscs, Modiolaria discors (4 .8%), Modiolus modiolus (3 .6%) and Trophonopsis clathratus (4 .3%). King Eiders had a broader diet than Common Eiders (average number of food species per individual 6.9 vs . 3.6), and thecalculated diet overlap was 0.15. The differences in the diet observed is most likely a result of King Eiders feeding at greater depths than Common Eiders

The occurrence of reindeer calves in the diet of nesting Golden Eagles in Finnmark, northern Norway

To assess the importance of semi-domesticated reindeer Rangifer tarandus calves in the diet of Golden Eagles Aquila chrysaetos, in Finnmark (northern Norway), we collected prey remains at 37 nests over six years (2001-2006). The study area was divided into 1) a fjord area, which is an important calving area for reindeer, and 2) an inland area where few reindeer give birth. 469 prey items were collected over the years. The diet of eagles was numerically dominated by birds (73% of collected prey items), especially willow/rock ptarmigan Lagopus spp. (51%), while mammals made up 27%, with mountain hare Lepus timidus as the most common species. Remains of reindeer calves were found in half of the nests studied and made up 8.5% of the collected prey items: 13.2% in the fjord area and 6.5% in the inland area. There was a higher chance of finding reindeer calves at nests in the fjord area than inland, and in nests situated in birch forest than in pine forest. The number of reindeer calves in the Golden Eagle diet in Finnmark corroborates well other studies from northern Fermoscandia. The importance of the Golden Eagle as a predator on reindeer can't, however, be assessed here