| 1. |
|
|
| 2. |
- Kaspersson, Rasmus, 1978, et al.
(författare)
-
Effects of density on foraging success and aggression in age-structured groups of brown trout
- 2010
-
Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472. ; 79:3, s. 709-715
-
Tidskriftsartikel (refereegranskat)abstract
- The benefit of monopolizing a limited resource is influenced by competitor density and by the relative competitive ability of defenders and intruders. Nevertheless, few studies have investigated the effect of density on resource defence in groups with large asymmetries in competitive ability, as a consequence of, for example, age and/or body size. We used two age classes (i.e. size groups) of stream-living brown trout, Salmo trutta, to investigate this issue. While old (and large) trout are assumed to be superior during interference competition, younger individuals may be both numerically dominant and constitute more than half of the total population biomass. In this experiment, the ability of one yearling to monopolize a concentrated food source was observed at four densities of under-yearlings (zero, two, six and 12) in an indoor seminatural stream. We predicted that the success of defence would decrease with increasing under-yearling density and that the frequency of defence (i.e. aggression) would peak at an intermediate density. As predicted, yearlings made significantly more unsuccessful foraging attempts and adopted darker body coloration at high density of under-yearlings, suggesting increased stress levels. However, in contrast to our second prediction, the number of aggressive interactions increased progressively with density. These novel findings suggest that the cost of defence increases with under-yearling density, probably as a consequence of stress from interference with under-yearlings employing alternative competitive strategies. However, the difference in size seems to enable yearlings to defend the food resource at higher density of competitors than predicted from the resource defence theory.
|
|
| 3. |
- Kaspersson, Rasmus, 1978, et al.
(författare)
-
Habitat exclusion and reduced growth: a field experiment on the effects of inter-cohort competition in young-of-the-year brown trout
- 2012
-
Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 169:3, s. 733-742
-
Tidskriftsartikel (refereegranskat)abstract
- Competition during the juvenile phase is a key process for regulating density in organisms with high fecundity. Juvenile density-dependent bottlenecks may become even more pronounced if several cohorts compete, but this has received relatively limited attention in previous literature. We performed a manipulation experiment in seven coastal streams to investigate the presence of inter-cohort competition, using habitat selection, body-size and density of newly emerged (age-0) brown trout (Salmo trutta) as response variables. The trout population (age ≥1 fish) was estimated using electro-fishing prior to the emergence of fry (April–May) and was either removed (manipulated sections) or maintained (control sections). Age-0 habitat selection was examined in June while density and body-size was evaluated in October (end of the growth season). We found that age-0 trout selected habitats that were located further from riffles (nursery habitats) in the absence of age ≥1 trout, suggesting a niche overlap between cohorts in the habitat dimension and, hence, that both inter-cohort competitive interactions and ontogenetic preference may influence habitat utilisation in the wild. Furthermore, we also found age-0 body-size to be significantly larger in manipulated sections and negatively related to its own density. We argue that competition from older cohorts influence the availability of age-0 feeding territories at the critical phase of emergence with secondary negative effects on age-0 growth. These results not only have implications for understanding the mechanisms of density dependence but can also provide valuable knowledge to the management of salmonid populations and their habitats in the wild.
|
|
| 4. |
- Stålhammar, Martin, et al.
(författare)
-
Effects of lure type, fish size and water temperature on hooking location and bleeding in northern pike (Esox lucius) angled in the Baltic Sea
- 2014
-
Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 157, s. 164-169
-
Tidskriftsartikel (refereegranskat)abstract
- In recreational fishing, catch and release (C&R), where fish are released alive after capture, is commonly adopted to minimize fishing mortality. Injuries from hooking and the mode of de-hooking can affect survival probability, and the choice of angling gear can affect injury severity. We show for C&R angling for northern pike (Esox lucius) in the Baltic Sea that hooking location and size of fish captured vary among lure types. Hooking in gills and aorta increased bleeding severity, which was generally expressed more strongly in larger pike. Our results supported the notion that anglers can minimize injury in northern pike angling by the choice of appropriate gear. In addition, our study is one of the first to show that hooking location is also affected by water temperature; low temperatures tended to result in deeper hooking. Despite this, water temperature did not affect level of bleeding in pike, and low water temperatures may be beneficial as they likely reduce the overall stress response in released pike. (C) 2014 Elsevier B.V. All rights reserved.
|
|
