Diving a little deeper on floating offshore wind

Humpbacks lunge-feeding

A few weeks back we published a newsletter on foundations and bases for offshore wind turbines – and how the masts are secured, either on the seafloor, or floating. A lot is known about masts secured to the seabed, as variations of these have been used over the last decade in Europe (although some of the impacts on marine wildlife are just being discovered).

But the interactions and impacts with floating structures are an open question, as there is only one floating farm in place in Norway, and the habitat there is not the same as the “call” and development areas off the California coast. The state of Maine is developing “Aqua Ventus” a demonstration floating wind project which many will be observing closely. But this is a single “semi-submersible” floating platform.

What is being proposed off the California Central Coast is 400 square mile web of tethered spars, semi-submersibles, and tension-leg platforms, all interconnected with electrical power cables suspended at 100m – 150m below the surface. So we will be transforming what has been open ocean throughout the 30-million-year evolution of mysticetes into a forest of obstacles – of which we can safely speculate that they don’t have the adaptive vocabulary to understand the risks posed by these structures.

Whales that have been feeding in open ocean will be confronting and colliding with cables and floating structures as they feed, and migrate. Putting this in perspective, rorquals (blue, fin. Sei, Brydes, and Minke whales) lunge feed on aggregations of small fish and marine invertebrates throughout the water column, down to 300m. This involves their acceleration up to 6m. sec-1 (~20km.hr-1) opening their jaws up to 90 degrees from their body, capturing their body-weight in food-laden water, closing their jaws, and expelling the water through their baleen.

Lunge feeding is a remarkable, but safe procedure in open water. But executing this maneuver in a forest of floating structures interconnected with cables, and tethered to the seafloor with more cables poses a number of potential threats. This situation may be exacerbated by the tendency of forage fish to aggregate around mid-water column structures. Do the rorquals and humpbacks (which also lunge-feed) have the senses and perceptual vocabulary to avoid these collisions?

The folks at the Bureau of Ocean Energy Management (BOEM) explain this away with a snappy little animation illustrating how a mother whale leaves her baby at the surface while she forages amongst the cables and tethers, with the happy ending of her reuniting to her baby. What if she returns with a broken jaw?

Can these whales learn how to navigate around these obstacles and avoid harm?

We are about to find out…