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Turbulence profiler about to be deployed next to a longline (Photo: Craig Stevens) Sampling from an instrumented platfom next to a longline (Photo: Craig Stevens) dedicated research station in central Jutland. Mussels are passive, so they cannot adjust their position (well, not quickly) to improve their feeding. Locating the crop requires knowledge and forethought to maximise feeding rates and minimise the accumulation of waste deposits. This might seem simply a matter of locating them in the fastest-fl owing water. However, competing use of water space and the limited working depths mean the answer is not always that simple. The New Zealand team is providing expertise to the project team about how to observe and measure the currents moving through and around the farm. The water stratifi cation means fl ow can also move under and over the farm. With low fl ows and lots of stratifi cation, the water around the mussels can be quickly stripped of food. The key to replenishment is knowing the degree of turbulent mixing that refreshes the water and food supply right near the mussels. Without this, models are just nice pictures. How will the Danish project help New Zealand aquaculture development? Stevens says the most important lesson learnt from the Danish project is that we need to embrace complexity. The Limfjorden Jutland is a micro-tidal system, and so fl ushing is mainly driven by large storms which are hard to predict. Measurements taken show the clear effects on the fl ow from farms surrounding the basin that is guiding the water fl ow in certain ways. This farm-effect must be built into predictive models of the system to determine the best strategy to maximise feeding and minimise the accumulation of waste deposits. Another key factor is the water is quite strongly stratifi ed compared to New Zealand coastal waters. This makes the shallow Limfjorden effectively much deeper in terms of how nutrients are passed around and so more comparable to New Zealand waters. A number of strategies are possible to maximise feeding and growth, given this stratifi cation, based around understanding the seasonal variations in stratifi cation and how the crop can be varied with this both in season and spatially throughout a farm. Working on the Danish project has been quite challenging, says Stevens. It's a very complex system and an ambitious research programme. but it brings substantial, high-level benefi ts to New Zealand. The Danish wind energy industry is a relevant example and has proven the benefi ts of building a knowledge- based sector around an industry and so corner the market internationally in terms of ideas and staying at the leading edge. If we can build on this with mussels at a national level, New Zealand stands to keep a hand on the tiller in terms of leading mussel aquaculture. We are world leaders in understanding how suspended culture effects and is affected by fl ow variability. This will become more and more important as aquaculture space is limited. So while we are exporting our skills and knowledge it's a two-way street. By working with top-level scientists in complementary science areas we bring home a range of ideas about how to improve our own approaches to understanding environmental infl uences on production, impacts and how to turn ideas into benefi ts for society. Also, using mussels to soak up excess nutrients is highly relevant to ideas about how to mitigate fi sh farm effects. Stevens says New Zealand's involvement in this international project is part of a broad initiative to have a much more knowledge-based approach to working with, and using, our oceans and coastal waters. The basic tools for quantifying transport and mixing seawater and the nutrients carried with it can be applied to a wide range of sectors, including energy supply, biosecurity, future climate forecasting and food production. The challenge is connecting the improvements in understanding how the ocean works to the particular needs of each sector. NOVEMBER/DECEMBER 2011 ■ NZ AQUACULTURE ■ 15