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Science Manual – Using Video Images for Fisheries Monitoring 3

2.1.2 Sizing

A simple method of sizing by reference point has been integrated into both the image

processing techniques outlined in this report (Fishtick and DVMD). The user clicks

on two points within the view a known distance apart (at approximately the same

distance from the camera as the fish) in order to calibrate, before measuring the fish.

A simple calculation then determines fish length from the calibration. All that is

needed for this method to work are a number of markers at known distances from the

camera. This method can therefore work with all of the systems described in Table

2.1. However, under certain conditions, it may not be possible to place markers or to

accurately estimate the distance of the fish from the camera, for example with

upward-looking cameras with no structure in the view.

2.1.3 Fish behaviour

Avoid mounting equipment in areas where fish may hold. This may mean deploying

on the downslope of a Denil or Larinier pass.

2.2 Logistics

2.2.1 Mains power

Some system configurations may not lend themselves to running on battery-powered

systems, even with an on-site method of keeping the batteries charged. Wide fish

passes which require lots of lighting are an example. Strategic or long-term

monitoring sites would also benefit from mains power; it may be more cost-effective

to install mains power where equipment is likely to be deployed for a number of

years.

There are plenty of options for powering a system where mains power is not

available (Section 3.2). Low-power charging options are not included in the system

descriptions here, as they are very site-specific. Add whatever is chosen to the total

cost of the system

2.2.2 Equipment maintenance

Don’t forget to factor the time needed to clean cameras, light panels and white

boards into your fish counter budget. During the summer months cameras will need

to be cleaned at least every two weeks. Sites where debris is likely to accumulate

will need regular checking and maintenance all year round.

2.2.3 Access to equipment

Equipment maintenance should be borne in mind when planning a fish pass counter

site, as you will need to be able to access equipment over a range of river flows. You

are likely to lose data if you have a fish pass in the middle of a river with only wading

access. As soon as the flows increase, you will be unable to safely reach the

equipment to clean cameras, remove debris or repair any damage.

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