Many coastal and estuarine fisheries around Australia are now dominated by recreational fishing. This poses a problem for assessment and sustainable fisheries management because recreational catch and effort are difficult to track. While creel surveys and diary angler-type approaches can provide information on catch composition and catch rates, critical information on fishing effort is generally missing. This project has trialled the use of boat ramp cameras to obtain data on overall recreational boat fishing effort in Port Phillip Bay and the adjacent Western Port Bay in Victoria.
Seven cameras have been installed since spring 2014. Each camera takes a photograph every 2 minutes, which results in well over 20,000 images per camera each month. Due to the time-intensive nature of the image analysis (viewing), we have explored sub-sampling approaches to provide an acceptable estimate of overall effort while requiring fewer images to be viewed.
We performed sub-sampling estimates of the total catch using 20 – 50 percent of the total available images, and tested randomization routines using whole days or in hourly blocks, and also a routine which focussed more effort on times of expected activity (pre-dawn and pre-dusk). Sampling in hourly blocks randomized across all days of the study produced estimates with greater than 80 percent accuracy using less than 30 percent of total images, although the error rate increased as the total effort in the underlying data decreased.
An alternative approach to reducing the total number of images is to use activity sensor software that is programmed so that the cameras take photographs only when a specific type of motion is detected in a set field of view. We present preliminary results on the performance of the activity sensor software, and prospects of this approach.