Comparison of underwater visual methods for assessing temperate rocky reef fish communities and the effectiveness of spatial marine conservation areas
Date
2018-09-04
Authors
Burke, Lily Anne-Marie
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Abstract
Precise and accurate species abundance and distribution data are important for making effective ecological conservation and management decisions. These data are often challenging to obtain, especially in marine environments where the logistical and technical difficulties of working underwater can limit the precision and accuracy of detection. The chosen survey methodology, along with the study design, will determine the extent to which species’ spatial or temporal variability in abundance and distribution may be investigated. Different observational methods may yield different results. I explore how the methodology used to collect sample measurements of fish abundance and diversity in marine environments can influence your understanding of the focal population and the effectiveness of spatial marine conservation measures.
I compare inshore rockfish abundance and fish diversity estimates between paired towed video and baited video surveys and between dive and baited video surveys conducted on temperate rocky-reefs in the nearshore Northeast Pacific on the coast of British Columbia, Canada. I test if the baited video survey data yield equivalent insight to those data derived from the methods commonly used in shallow (dive surveys) and deeper waters (towed video surveys). Paired dive and baited video surveys took place inside and outside of spatial marine conservation areas designated for inshore rockfish called Rockfish Conservation Areas. I test whether the baited video data generate the same conclusions about Rockfish Conservation Area effectiveness as data derived from the dive surveys, and whether the Rockfish Conservation Areas have greater inshore rockfish abundance and fish diversity than paired locations outside the conservation areas.
I find similar inshore rockfish abundance estimates between towed and baited video, but baited video surveys detect a greater number of unique species than the towed video surveys. The dive surveys detect greater inshore rockfish abundance and fish diversity than the baited video surveys, but the baited video data yield equivalent insight on Rockfish Conservation Area effectiveness to data derived from the dive surveys.
I find little evidence that inshore rockfish recovery is influenced by Rockfish Conservation Area protection. When data were combined across all sites sampled, Rockfish Conservation Areas did not produce more inshore rockfish, bigger rockfish, or greater fish diversity than paired sites outside of Rockfish Conservation Areas, whether measured using a dive survey or a baited video survey. However, I did observe a positive effect of Rockfish Conservation Area protection for some of the individual Rockfish Conservation Areas surveyed that rated as having a high Conservation Score. This suggests certain Rockfish Conservation Areas may be effective conservation areas for inshore rockfish recovery.
The differences I observe in inshore rockfish abundance and fish diversity between the paired surveys reveals the methodology used can influence species abundance and diversity estimates. Baited video surveys are a low cost and effort methodology that can be used to examine inshore rockfish abundance and fish diversity over rocky reefs from nearshore waters down to depths greater than 20 m, and to monitor the effectiveness of spatial marine conservation areas.
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Keywords
baited video, towed video, dive surveys, underwater survey comparison, rockfish, Rockfish Conservation Areas, spatial marine conservation measures