Whale Interactions with Wave Device Cables

The presence of wave energy devices off the Pacific coast of the United States could pose a threat to Pacific gray whales. The whales migrate approximately 15,000 - 200,000 km round trip between their primary feeding grounds in the Bering and Chukchi Seas and their calving and primary breeding grounds in Baja California, Mexico. Investigations using conceptual and individual-based models may help shed light on the interactions that can be expected.

 

A single device within a migratory corridor poses little threat to a migrating gray whale, as there is a huge chance for avoidance even if the whale doesn't have the ability to detect and evade the device. However, as more devices are installed and organized into an array that can span several kilometers, the threat grows. In an array, many devices are linked together and share anchors, mooring lines, buoys, and export cables. The result is a complex, net-like geometric configuration. Little is known about the sensory of gray whales or their reactions to detect and avoid the wave array matrix. If the whale is unable to successfully avoid the array, the whale is likely committed to attempting to navigate through the matrix, as whales are unable to reverse direction.

 

Conceptual models can identify a number of possible encounters unique to each device studies (OPT Power Buoy, Pelamis Wave Energy Converter P2, and Wave Dragon) and can identify the starting conditions of the whales characterized by velocities associated with common behaviors like traveling, feeding, and breaching. The next step is using IBMs as simulations to assess the global consequences of local interactions by members of a population. A variety of individuals (a gray whale or cow-calf pair) defined by attributes including cross-section width, gender, age, size or volume, energetics (i.e., breathing rate) could be generated to mimic the variety in the population. The environment where the interactions occur should be defined by the conditions of the migratory corridor (i.e., benthic topography data), the presence or absence of predatory orca pod, and the arrangement and mooring line configuration of the array. In this way, it is possible to generate an infinite number of whale variables that are described by the cross-section (individual or pod size) and other physical attributes, sensory capabilities and maneuverability, and reaction/tendency toward evasion. These models are set up to track the designed whale through time steps and detect whether an individual whale (with a set of specific characteristics) evades the array or describes a collision event. In this way it is possible to start mapping the global consequences for the Pacific gray whale population given the local actions of individuals encountering a proposed wave array.

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