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Sep 10, 2022 509 likes •636 views

Understanding the potential for marine megafauna entanglement risk from marine renewable energy developments Steven Benjamins, Violette Harnois, Helen Smith, Lars Johanning, Lucy Greenhill, Caroline Carter, Ben Wilson www.sams.ac.uk

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Steven Benjamins, Violette Harnois, Helen Smith, Lars Johanning, Lucy Greenhill, Caroline Carter, Ben Wilson

Understanding the potential for marine megafauna entanglement risk from marine renewable energy developments

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Entanglement

Global conservation

problem for many species

Involves ropes, chains, etc.
Are MRE moorings a risk?

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Marine megafauna

Legal requirements (e.g. EC Habitats Directive) necessitate risk assessment

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Review of entanglement

Fisheries
Aquaculture
Subsea cables
Moorings & anchors

Heezen, B.C. 1957. Whales entangled in deep sea

cables. Deep Sea Research, 4, 105-115.

Photograph was provided courtesy of NOAA Fisheries Alaska Marine Mammal Stranding Program. Photographs were originally collected under NOAA Fisheries permit #932-1905. Case study submitted under NOAA Ref. No. KW-KOD2012-FW01

Main group of concern: Baleen whales Additional concern:

Derelict fishing gears

snagged in moorings

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Risk assessment: Mooring modelling

Simulated floating structure
6 different mooring configurations:

– Catenary

With chain
With chain and Nylon
With chain and Polyester

– Catenary with accessory buoy – Taut

With Nylon

– Taut with accessory buoy

Mooring behaviour was simulated across wave

periods of 1-10 s, wave heights of 1, 5, 10 m

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Risk assessment: Mooring modelling

Tension characteristics
Swept volume
Curvature

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Risk factors: Mooring design

Tension characteristics
Swept volume
Curvature

Taut Catenary with chain/Nylon Taut Catenary with chain/Nylon

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Risk factors: Mooring design

Tension (high = good; low = bad)
Swept volume (small = good; large = bad)
Curvature (limited = good; large = bad)

3 2 1

H = 5 m

3 2 1

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Risk factors: Biology

Body size (small = good; large = bad)
Flexibility (flexible = good; rigid = bad)
Sensory systems (long-range = good;

short-range = bad)

Feeding mode (pursuit hunting = good;

lunge feeding = bad)

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Relative risk assessment

Species group

Catenary & chain Catenary & chain & nylon Catenary & chain & polyester Taut & nylon Catenary & accessory buoy Taut & accessory buoy

Cetaceans Baleen whales Large whales Medium-sized whales Toothed whales Sperm whale Medium-sized whales and dolphins Small whales, dolphins and porpoises Pinnipeds Seals Sea lions/fur seals Sea turtles Sharks Basking sharks Other large sharks Ocean sunfish

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Conclusions

Very limited data on non-fisheries entanglements
Mooring entanglement risk likely low for most megafauna
Possible exception: Baleen whales
Mooring design influences relative risk; assessment approach to

be refined as more data become available

Important to consider risk early during project development
Risks around arrays will depend upon device distribution,

densities, extent of mooring sharing between devices

Need to assess risk of derelict fishing gears