| 1. |
- Hansen, Henry H., et al.
(författare)
-
Projecting fish community responses to dam removal – Data-limited modeling
- 2023
-
Ingår i: Ecological Indicators. - : Elsevier. - 1470-160X .- 1872-7034. ; 154
-
Tidskriftsartikel (refereegranskat)abstract
- Modeling fish community responses to dam removal is an emerging field of study as dam removals become more common, but uncertainties concerning recovery time and community stability remain. In Europe, an EU-wide biodiversity strategy plans to restore around 25,000 km of rivers to free-flowing status, which emphasizes the importance of being able to predict fish community responses after dam removal. We developed a multi-species size spectrum model for a fish community in the Mörrum River in Sweden to identify possible outcomes after a dam was removed in 2020. Electrofishing monitoring before the dam removal was used to calibrate the model. We projected multiple scenarios into the future to explore patterns of community stability, individual species responses, and recovery time while varying parameters related to dam removal mortality, base resource rate change, and maximum recruitment change. We created 30 hypothetical scenarios using an abrupt change perspective (parameters are step-based) and 30 scenarios using a gradual change perspective (parameters are smooth). In both perspectives, dam removal mortality and a decreasing resource rate reduced community biomass and delayed recovery time compared to pre-dam removal conditions. Our results demonstrate that recovery from a dam removal scenario is not necessarily a benefit for all species. In scenarios where dam removal practices or dam failures cause high mortality events and sustained impacts on base trophic level resources, recovery of pre-removal biomass may take decades, while community stability may be unstable for twice that time-period. Our study shows that size spectrum models can be applied to dam removal scenarios to explore potential recovery outcomes, particularly from a risk avoidance perspective. A benefit of using such an approach is the relatively low data requirements needed to perform projections (e.g., present species, fish growth rates, relative fish abundance). Implementing this model in other river systems, particularly at the reach scale, can help river restoration and management assess tradeoffs associated with different habitat restoration approaches prior to committing to a dam removal plan.
|
|
| 2. |
- Neuenfeldt, Stefan, et al.
(författare)
-
Feeding and growth of Atlantic cod (Gadus morhua L.) in the eastern Baltic Sea under environmental change
- 2020
-
Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 77:2, s. 624-632
-
Tidskriftsartikel (refereegranskat)abstract
- Five decades of stomach content data allowed insight into the development of consumption, diet composition, and resulting somatic growth of Gadus morhua (Atlantic cod) in the eastern Baltic Sea. We show a recent reversal in feeding level over body length. Present feeding levels of small cod indicate severe growth limitation and increased starvation-related mortality. For young cod, the low growth rate and the high mortality rate are manifested through a reduction in size-at-age. The low feeding levels are likely the result of a decrease in benthic prey abundance due to increased hypoxic areas, while decreasing abundances of pelagic species in the area of cod distribution have prevented a compensatory shift in diet. Our study emphasizes that environmental forcing and the decline in pelagic prey caused changes in consumption and growth rates of small cod. The food reduction is amplified by stunted growth leading to high densities of cod of smaller size competing for the scarce resources. The average growth rate is negative, and only individuals with feeding levels well above average will survive, though growing slowly. These results suggest that the relation between consumption rate, somatic growth and predatorprey population densities is strongly environmentally mediated.
|
|
| 3. |
- Wang, Wei, et al.
(författare)
-
Anthropogenic forcing of fish boldness and its impacts on ecosystem structure
- 2021
-
Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 27:6, s. 1239-1249
-
Tidskriftsartikel (refereegranskat)abstract
- Modified fish behaviors in response to anthropogenic stressors, such as chemicals, microplastics, acoustic emissions and fisheries, are a debated driver of change in freshwater ecosystems and oceans. Our ability to judge the severity of observed behavioral responses is hampered by limited knowledge regarding how subtle behavior modifications in prey fish affect ecosystems. Here we show that anthropogenic stressors affecting fish boldness are not expected to cause population collapse, but rather elusive effects on fish length, population biomass, reproduction and ecosystem state shifts. We use a physiologically structured population model (three trophic levels), well fed with empirical data, to simulate how previously suggested alterations of fish boldness traits due to anthropogenic stressors affect ecosystem structure. Our results suggest that these stressors may cause ecosystem structure effects, such as skewed size distributions, reduced fish biomass and reduced reproduction success, by altering the foraging behavior of fish. However, the specific structure effects depend on where the boldness-shyness continuum change occurs and on the species-specific life stages. The model also highlights somewhat counterintuitive effects leading to possible extinction of predators when the foraging behavior of the prey is hampered. We conclude that anthropogenic forcing of fish behavior may be a hidden mechanism behind ecosystem structure changes in both freshwater and marine ecosystems.
|
|
