PhD students

Daniel Rooth

Title of the PhD project
Rewilding marine coastal ecosystems – fish community dynamics in transplanted eelgrass habitats

Supervisors
Mikael van Deurs, Ole Henriksen and Christian Skov, DTU Aqua

Background of the project
Anthropologically induced effects such as eutrophication and hypoxia in marine coastal environments are today widespread and often severe, resulting in habitat loss, reduced biodiversity and trophic cascades. Loss of important habitats can delay or hinder the recovery and integration of fish populations into the ecosystem. Restoration and transplantation of habitats such as eelgrass meadows have proven successful in terms of promoting taxonomic biodiversity and abundance of slow-moving marine fauna. By reintroducing these habitat types to the ecosystem, complex three-dimensional structures may provide refuge as well as foraging opportunities for invertebrates, fish and other organisms, forming biodiversity hotspots. However, knowledge of the effect on community dynamics, behaviour and biodiversity of fish in these environments, remain insufficient. 

About the project
The objective of this PhD project is to study the fish community dynamics in relation to the coastal habitats such as transplanted- and naturally occurring eelgrass. The potential re-colonisation of fish communities associated with the transplantation of eelgrass will be investigated with a strong emphasis on the roles of top- and mesopredators. With public collaboration together with recreational anglers, continuous monitoring of degraded areas is carried out whilst evaluating ecosystem function of eelgrass- and stony reef habitats. 

Perspectives
The PhD project contributes to a deeper understanding of the biodiversity and community dynamics, including predator-prey interactions and habitat preferences, of marine fish in shallow coastal waters, with the hopes of contribute to improving rewilding efforts in restored marine areas. The project will also critically assess various underwater monitoring methodologies commonly used to assess fish, in a complex coastal ecosystem, as well as involving local anglers and volunteers.

Markus Varlund Strange

Title of the PhD project
Cormorant and seal predation on fish in inner Danish waters

Supervisors
Nis Sand Jacobsen, Lotte Kindt-Larsen and Niels Jepsen, DTU Aqua

Background of the project
Many species are struggling in the inner Danish waters compared just 50 years ago, and some of our previously most important fisheries there have declined or even closed. These fish stocks have been subject to several different stressors, i.e., overfishing, food scarcity, parasites, oxygen depletion, predation, etc. For mitigation efforts to be successful, it is essential to disentangle the effects of the stressors, and especially understand the natural components. One of these is predation from seals and cormorants, which have both increased dramatically since the 1970’s.

About the project
My project aims to quantify the natural mortality of cod, herring, and various flatfish due to seals and cormorants, both in the current situation and historically. This is achieved through a combination of empirical diet data from the predators, and modelling approaches. The diet data are acquired from otoliths in seal scats and cormorant pellets, and the modelling framework includes a stochastic stock assessment model, and a spatiotemporal species distribution model. The culmination of the project is a management strategy evaluation, where I will investigate the effects of different seal and cormorant management scenarios. 

Perspectives
This project will increase our understanding of predators’ role in the recovery process of deteriorated fish stocks, and enable informed decision-making on management of conflict species. Furthermore, as numerous fish stocks worldwide are in poor condition and human-wildlife conflicts occur everywhere, results from this project can inspire managers all over the world. Lastly, the project will also contribute to the ongoing efforts of developing methods for including good estimates of natural mortality in fish stock assessments.

Previous PhD student within the research area Ecosystem based Marine Management

Katrina Bromhall
The effect of modified and lightweight fishing gears on benthic macrofauna

Isabella Kratzer
Gillnet modifications to reduce bycatch of harbor porpoises

Gildas Glemarec
Bycatch of seabirds in Danish gillnet fisheries – assessing scale and testing mitigation

Elliot John Brown
Habitat Suitability for Juvenile Flatfish of the Inner Danish Waters

Louise Dahl Kristensen
The importance of habitat structure for the distribution and behaviour of demersal fish

Lotte Kindt-Larsen
Management of fisheries in harbour porpoise (Phocoena phocoena) marine protected areas

Karin Olsson 
Trait-based analysis of reproductive strategies among marine fish

Teunis Jansen
North Sea Mackerel or Mackerel in the North (Sea)?