In situ Ichthyoplankton Imaging System (ISIIS): system design and preliminary results

Robert K. Cowen,Cedric M. Guigand

Limnol. Oceanogr. Methods 6:126-132 (2008) | DOI: 10.4319/lom.2008.6.126

ABSTRACT: Over the last two decades, there has been an accelerating advancement of acoustic and optical plankton samplers, opening many opportunities for fine-scale studies of plankton distribution. To date, however, the imaging systems have been limited in the volume of water being sampled, thereby restricting their utility to quantifying highly abundant, small zooplankton like copepods, but not relatively rarer, larger ichthyo- and other meso-zooplankton (e.g., larval decapods, salps, pteropods, ctenophores, etc.). Here we describe an imaging system, In situ ichthyoplankton imaging system (ISIIS), that is capable of In situ (i.e., noninvasive) sampling of sufficiently large volumes of water at very high resolution, allowing quantitative measurement of these rare plankton, while at the same time also recording the smaller more abundant taxa. Capitalizing on state-of-the-art digital line scan cameras and high-throughput computer data transfer and storage, combined with shadow photographic lighting techniques, we have designed and built a towed system capable of imaging at 68-micron pixel resolution, yet with up to a 20-cm depth of field (with a 14-cm field of view). This system is coupled with various environmental sensors (e.g., CTD, fluorometer), enabling the evaluation of fine-scale, taxon-specific distributions in relation to environmental conditions. Field testing demonstrated high-resolution imagery of plankters, while quantitatively imaging >70 L s-1 continuously for a 78-min trial.