Development and experimental assessment of an underwater video technique for assessing fish-habitat relationships

Developing tools that aquatic managers can use to understand the impact of human development on fish habitat is important in an era where our aquatic resources are under increasing pressure. To this end, we examined whether an underwater video camera was useful for quantifying fish habitat use in inland lakes by 1) examining patterns in fish habitat use, residency time and feeding behaviour among habitat types, 2) determining the precision and statistical power of the aforementioned estimates, and 3) assessing whether our habitat-specific camera estimates were reflective of whole-system estimates. Lastly, we used our protocol in an experimental situation to test site-specific fish habitat use at sites where habitats were manipulated (removed or added). We demonstrated that our underwater video protocol could successfully capture site-level habitat use that corresponded with whole-system abundance estimates, addressing the concern that habitat-based surrogates of fish productivity be validated on a whole-system scale. Unfortunately, our underwater video technique was unable to discriminate fish habitat use patterns among simple habitat types and unable to consistently separate differences in among-habitat fish feeding and residency behaviours. Our ability to detect a difference was low in all among-habitat comparisons. In the aquatic systems where habitat was added, we documented a significant shift in fish habitat use towards the addition sites and away from control sites, but no corresponding increase in system-wide fish biomass or production; no changes were apparent in the habitat removal lakes. A combination of longer filming duration, more filming sites or changing to a mobile transect method would likely address the data deficiencies that limited our ability to make site-level inferences about fish habitat use.