DTU Aqua's research into marine living resources expands knowledge and develops methods that can support management decisions for a sustainable utilization of fish and shellfish stocks
Main themes within marine living resources research
DTU Aqua's research into marine living resources has four main themes:
- Surveying and fisheries monitoring methods and analysis
We are constantly developing methods to collect and process data to describe the current status of and trends in fish stocks based on the best available information. This involves work to assess the amount and distribution of fish and other commercially relevant marine species. For that end we develop methods and tools to monitor and analyse these stocks as well as the effort, distribution and catches in fisheries.
- Stock identification and vital statistics
We develop methods for a fast and precise processing of individual fish to identify their species and population affiliation. We examine the length, weight, sex and maturity and determine the age of the fish. The fish we measure come from sampling of catches from the fishery and from scientific surveys. Data is then converted into estimates of trends in stock size and biomass, and the average growth, reproduction and mortality rates of individual fish.
- Data handling methods and statistical stock assessment models
Data from fisheries sampling and surveys are entered into data bases with public access. We construct and offer dedicated software to extract, combine, analyse and illustrate the extensive information that has been gathered by international scientific collaboration. Further, we develop novel but rigorous statistical models to analyse and predict population trends and their uncertainties, telling us to what extent these stocks can be exploited.
- Process-oriented models and analysis of fisheries management strategies
We develop process-based mathematical models that can describe the spatial behaviour and life cycle of individual organisms in the 3D marine environment taking into account both hydrographic and biological influences. In this way we can predict e.g. larval drift and population distribution of the fish stocks, spatial connectivity of stocks as well as growth and survival of individual fish, based on physiological relations. The work addresses the aspect of scaling from individual level dynamics to population level where a spatial structure emerges in the models from underlying biological and oceanographic processes.
Why do we carry out research into marine living resources?
The overall goal of DTU Aqua’s research into marine living resources is to help ensure the sustainable utilization of ecologically and commercially important fish and shellfish stocks. Fisheries are dependent on there being enough fish and shellfish in the sea, both now and in the future. So although predictions into the future are highly uncertain we have the goal to strengthen the scientific basis for fisheries advice and to contribute to management strategies that are robust to changes in the dynamics of the populations and their ecosystems.
The specific aim for the research area is therefore to increase our knowledge of the biological mechanisms behind population fluctuations, and to develop the appropriate mathematical and statistical models to be able to assess the development in the amount of fish in the different stocks in the sea, how they distribute and the level of exploitation they can sustain within a reasonable prediction horizon.
Even though survey technology is constantly developing, e.g. acoustic and visual methods like echo sounders, sonars and video cameras, you cannot count the number of fish in the sea like you count birds flying in the sky or deer in a field. Therefore, indirect methods have to be used to estimate the amount of fish in the different stocks in the sea. Here data from the fishery on removal of fish by the catches is extremely useful combined with independent surveys supplying trends and indices of population abundance and distribution.
When we combine these data with measurements of size and age of the fish we can follow the decline in numbers of fish in each year class and thereby estimate the annual mortality rate. This mortality is a combination of fishing mortality and mortality from natural causes like predation and death at spawning and old age. If we can estimate natural mortality we can also calculate fishing mortality and address the impact of fishery. Estimating fishing mortality is one of the fundamentals of the most advanced stock assessment approaches, the so called analytical assessment.
How do we carry out the research?
Data about fish stocks and quantities and species caught originates from landing statistics, fishermen's logbooks (which provide information on species, quantities and areas), samples from fisheries collected by DTU Aqua at different ports, and on board fishing vessels and from DTU Aqua's scientific expeditions. This data includes gender, age, size, maturity, genetics, etc. and is used to identify populations and their respective age compositions.
We apply all this information and data in formalised statistical models to estimate the fishing mortality, the biomass of the stock and the number of recruits in each new generation. We use a statistical approach since it gives us the opportunity to rationally select the best model setting for our analysis and provides us with uncertainty estimates of the above estimated parameters to judge whether estimated population changes are significant. The stock assessment models are made freely accessible and transparent in open source user friendly portals. It is the intension that anybody with an interest in fisheries is able to reproduce exactly what the scientists have built their fisheries advice on.
When the studied systems are highly complex, process-oriented models offer a simplified view of ecosystem dynamics. Since model parameters are highly uncertain and process representation is simplified, process-oriented models can only offer a semi-realistic description, where the approximate effects of biological end environmental mechanisms can be assessed. Such semi-realistic explorations are useful in many situations, where there is not sufficient data to support a data-driven assessment of the question of interest and this allows us to estimate the response-envelope of the ecosystem to anthropogenic drivers, e.g. climate change and changed fishing patterns. These models also guide the development of underlying biological models used in stock assessment work towards a more realistic process representation that makes better usage of biological knowledge and derived ecosystem properties.
What is the research used for?
The research into marine living resources is used to give advice on the development and current status of the individual stocks and how much can be caught in fisheries without endangering the recruitment of new generations to the population. Advice also considers a healthy ecosystem functioning such as there being enough fish in the stock to provide food for predators higher up in the food chain. Based on the scientific advice managers will negotiate and set TACs and fishing quotas as well as in other ways regulate the fisheries.
Research therefore forms the basis for DTU Aqua's consultancy services for Danish and international authorities involved with fisheries. Our primary customers are the Ministry of the Environment and Food of Denmark, the International Council for the Exploration of the Sea (ICES) and the European Union (EU).
With an increasing request for the statistical assessment models (e.g. www.stockassessment.org ) and other products (e.g. IBMLIB) of the research area, international collaboration has expanded. DTU Aqua thus delivers models and participates in the advice process in collaboration with e.g. Fisheries and Oceans, Canada (DFO), and National Oceanic and Atmospheric Administration, USA (NOAA).
Results from the research are also included in assessments of the ecosystems where clients e.g. are Baltic Marine Environment Protection Commission (HELCOM) and the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR).
DTU Aqua collaborates extensively with the fishing industry and recreational fishermen to collect data, perform pilot studies and perform studies on new management initiatives, for example on the industrial sandeel fishery, implications of the landing obligation and management of the mixed herring stock fishery in the Kattegat-Skagerrak and the North Sea.