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MISSION DISPATCH 8 June 9, 2005 | Julian Partridge | San Clemente Basin (off the coast of S. California) 
Nearly 20 years ago, my work on the ecology of animal vision led me to study deep-sea fish.
The visual world of deep-sea animals is difficult for us to imagine: an environment in which
sunlight is reduced to dim blue remnants of bright surface sunlight, or to pitch blackness
punctuated only by flashes of blue bioluminescent light made by the animals themselves.
This visual environment has led to the evolution of some extraordinary adaptations.
Participating in some fifteen deep water cruises on British, German and US research ships,
I have worked at understanding the spectral sensitivity and physiological adaptations of
vision in deep sea fish and crustaceans.
This cruise on R/V New Horizon gave an excellent opportunity for a new direction of research - behavioural observations of living animals. Dr Tamara Frank, our cruise leader from HBOI, has recently developed a new midwater trawl which utilises a closing cod end. By towing this net very slowly and closing the cod end at depth, animals are brought to the surface in excellent condition and can then be maintained in cooled aquaria on board ship. Tammy also supplied the HBOI kreisel: a temperature controlled, circular-cross section aquarium in which delicate animals can be maintained and observed for many hours. The Kreisel gently circulates cold seawater to keep animals away from the sides and surfaces of the aquarium. Midwater animals rarely encounter such hard surfaces in their natural lives and do not survive long without such specialist care. 
Using the kreisel my colleague Ron Douglas and I have been able to investigate the way in which the squid Histioteuthis orientates itself and its unusual eyes. Histioteuthis is extraordinary in having one small eye and one large: the latter tubular in shape, with a yellow lens and reduced field of view. Various ideas have been proposed for how Histioteuthis uses its eyes: the larger yellow-lensed eye perhaps being for breaking the bioluminescent camouflage of overhead animals to see their silhouettes against the remnants of down-welling light. Using the kreisel, and by video recording in both visible and infra-red light, we have been able to observe the way Histioteuthis orientates its body and its eyes in response to gravity and directed illumination. This is a step further to understanding the natural history of this extraordinary animal. Not only does the combination of careful capture with the closing cod end, and careful maintenance in the kreisel, allow us to make scientific observations of deep-sea animals, but also it provides an opportunity for filmmaking for wider purposes. Working with professional filmmaker Dr John Ruthven, Ron and I have filmed a wide variety of living deep sea animals. This footage, in HDTV format, will be valuable both to scientists and educators, and also has the potential to be incorporated into TV programs which will engage the public in deep-sea biology. 
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