Growing juvenile lobsters in salmon farms as part of an integrated multi-trophic aquaculture (IMTA) system is showing promising signs, according to researchers at the University of Stirling, reports Bonnie Waycott.
IMTA involves farming different species from different levels of the food chain in the same space, where the by-products (such as waste) from one species can become inputs (such as fertilisers or food) for another. Although significantly widespread in Asia, in most of Europe, including the UK and Ireland, this is still primarily in the research or experimental stage with a need to better understand the relationships between different species within the system to make the shift from research to commercialisation. In this sense, pilot-scale studies are becoming increasingly important.
One such study is highlighting the potential of growing juvenile lobsters outside salmon pens as an IMTA. Led by researchers at the University of Stirling in Scotland and the Marine Institute in Ireland, the study was part of a €7 million EU H2020 research project called TAPAS (Tools for Assessment of Aquaculture Sustainability), which aimed to develop new, improved tools and approaches to support the planning, licensing and management of aquaculture sustainability. It was also part of a wider case study within TAPAS focusing on IMTA in Ireland and their potential to increase sustainability and provide ecosystem services and wider benefits to society.
“Wild populations of European lobster have declined due to overfishing, and restocking programmes rely on hatchery-grown lobsters that are released into the wild,” said Anastasios Baltadakis, lead author of the study and a TAPAS-funded PhD researcher at the University of Stirling, and Joanne Casserly, Scientific and Technical Officer with Foras na Mara, the Marine Institute.
“Studies have shown that lobsters that are acclimatised in the natural environment following the hatchery stage have improved survival. It was hypothesised that growing lobsters in containers next to salmon would provide a source of food via the waste and the cage would act as a shelter from rough weather conditions,” they said.
“The Marine Institute operates a marine research site at Lehanagh Pool in Beirtreach Bui Bay Connemara in the west of Ireland. This is a pilot-scale experimental marine site that is licensed for several different species of finfish, shellfish and seaweed and this is where the work was carried out.”
The salmon and lobster study involved fieldwork and sampling at the IMTA site and lab-based work. In-situ measurements of water quality parameters and sediment were taken and hydrographic data were collected to understand environmental conditions. In order to assess differences in growth, the team also measured the carapace length of lobster juveniles at both the IMTA site and a control site. Lobster muscle samples were also collected for fatty acid and stable isotope analysis to evaluate the uptake of wastes and assess any influence on growth.
Because the study was experimental and used a novel combination of species in an open water system, there were many uncertainties and questions surrounding the results. Baltadakis and Casserly said that it also wasn’t clear whether the lobsters would directly utilise waste from salmon production and whether there would be any effects, but analysis revealed that the lobsters did uptake waste, indicating a trophic relationship between the two systems. Carapace length revealed no noticeable effects on growth between the IMTA site and control site, although the lobsters at the IMTA site did appear more robust.
“The study site is a pilot-scale experimental IMTA site, so this would influence the results as the amount of waste that was entering the environment from the cage was considerably less than would occur at a commercial scale salmon farm. If this work was upscaled then there may be a more noticeable effect on growth. However, further work is needed to assess the optimal amount of waste that lobsters could be exposed to and this would involve further fieldwork and hydrodynamic modelling,” Baltadakis and Casserly stated.
IMTA covers a huge variety of species combinations in different system set-ups and offers a host of benefits. For example, extractive species can remove some of the waste generated by higher trophic organisms so there may be bio-mitigation advantages. IMTA also maximises the use of space while the diversity of species can offer extra economic benefits. Diversifying production through IMTA may also provide additional food crops and/or an extra source of income. Hopes are high that a lobster/salmon IMTA would support restocking activities and help wild lobster populations. The waste from the salmon provides a food source and the pens can be a shelter and mooring point for the lobsters so they can acclimatise in the environment before being released. This could be seen as a type of ecosystem service, with salmon aquaculture providing wider societal benefits.
But further research into the feasibility of a lobster/salmon IMTA is still required. There is also a need to evaluate the implications of lobsters eating waste from salmon on their physiology/reproductive capacity and determine if there are benefits for post-release survivability. The practicalities of setting up such an IMTA at a commercial farm site would also need some consideration. Chemotherapeutants, which are sometimes used on salmon farms, may negatively affect lobsters so a lobster/salmon IMTA could only be set up a site such as the one used in the study where no chemotherapeutants are used, said Baltadakis and Casserly.
“IMTA is not a one-size-fits all concept and different types will have their own benefits and challenges,” they said.
“Through our work, we aimed to established if there would be a trophic link between the salmon to the lobster whereby any waste from salmon production would be utilised as a nutrient input for the lobster. Now that the study has confirmed this, further research can take place to assess interest amongst industry and address other questions surrounding this type of system. At the Lehanagh Pool site, the Marine Institute will continue to work with lobster and investigate different production methods and benefits to local stakeholders and the inshore fishing community.”
The University of Stirling and the Marine Institute have several research projects looking at IMTA systems with a range of species combinations and environments. The Marine Institute is currently involved in a number of EU-funded research projects focused on the sustainable development of aquaculture and IMTA. Work with novel species such as lobster continued in the H2020 IMPAQT project towards validating IMTA and is progressing in another project, the ASTRAL project, developing new, resilient and profitable value chains in aquaculture.