Video capture of crustacean fisheries data as an alternative to on-board observers

Abstract

For EU member states to meet the requirements of the Marine Strategy Framework Directive and the reformed Common Fisheries Policy, it will be necessary to improve data collection related to many fisheries that are at present subject to relatively little monitoring or scientific research. This study evaluated the use of on-board camera systems to collect data from Cancer pagurus and Homarus gammarus fisheries. We evaluated the reliability of the hardware and its ability to collect images of sufficient accuracy and precision compared with using on-board observers. Fishers and on-board observers passed animals removed from traps across a defined area. The relationship between the in situ and predicted measurements of carapace length of lobsters or carapace width (CW) of crabs was investigated. The mean difference between the predicted and real crab measurements was −0.853 mm with a standard error of 0.378 mm. Suggesting that the model tends to underestimate the real CW slightly. The mean difference between predicted and real data for lobsters was 0.085 mm with a standard error of 0.208 mm. Sex allocation for crabs based on video images was 100% accurate. All male lobsters were correctly assigned. For lobsters >86 mm in length, the correct female sex allocation was 100% accurate. For smaller lobsters, the accuracy of sex allocation decreased to a low of 51% in lobsters <70 mm. Camera systems were found to be a suitable method for collecting data on the size and sex of crabs and lobsters. The error attributable to using video data rather than manual measurement was less than 3 mm, which is sufficient to detect growth increments in these species. The requirements to collect basic species data are increasing and the ability to do so without on-board observers will reduce the cost implications of these requirements. Future computer automation of image extraction and measurements will increase the application of video systems for data collection.

Accurate estimation of fish length in single camera photogrammetry with a fiducial marker

“…This level of error is comparable to that observed by Hold et al (2015) who used a fiducial marker to estimate carapace size in crab and lobster where the mean differences between estimated and actual lengths were 0.1 % and 0.6 % respectively. Similar mean differences have been reported when using paired lasers (Deakos 2010, 0.4 % in Manta alfredi), or multi-camera systems (Rosen et al 2013 1.0 % in 3 fusiform fish species).…”

“…In contrast, OpenCV and Python offer greater platform agnosticism, with support across MS Windows, Mac OS, Android, Linux and other platforms. Hold et al (2015) found that radial distortion was limited by ensuring the subject was centred in the FoV (also see Rodgers et al, 2017). The parallax effect was empirically controlled with a 2 nd order linear model with FoV as a predictor.…”

“…Potential applications include remote electronic monitoring (virtual observation) of commercial fisheries to assess catch (e.g. White et al, 2006;Chang et al, 2010;Hold et al, 2015; Bartholomew et al, 2018) and bycatch (e.g. Bartholomew et al, 2018), ecological studies using fixed cameras (e.g.…”

“…Neuswanger et al, 2016). Accurate length estimates have also been derived by deployment of a simpler system by analysing images captured with a single camera and a physical fiducial marker of known length (Hold et al, 2015;van Helmond, Chen, & Poos, 2017).…”

Remote electronic monitoring as a potential alternative to on-board observers in small-scale fisheries

“…Studies have been carried out to measure the effectiveness of REM systems at monitoring industrial fishing activities, including target catch (Ames et al, 2007;Hold et al, 2015;Kindt-Larsen et al, 2011;Stanley et al, 2009) (c) Fig. 1.…”