Drones detect illegal and derelict crab traps in a shallow water estuary

Abstract

The issues surrounding illegal, unregulated and unreported fishing, and that of abandoned, lost and discarded fishing gears, leading to ghost fishing, are intensifying. Estuarine crab trapping is likely subject to high levels of illegal and potential ghost fishing, because it also has good economic incentives regarding potential catch, low gear acquisition costs and accessible fishing grounds. To improve the efficiency and effectiveness of fisheries monitoring, control and surveillance operations, the efficacy of small consumer‐grade drones for sighting traps in an estuary in NSW, Australia, was tested. Twelve sets of two flights were undertaken at 20 and 30 m altitude over a 600‐m stretch of estuary for 5 days to quantify the detectability of submerged mesh traps of three different mesh colours. The drone was able to detect the majority of traps efficiently, with depth in relation to water clarity being the main factor affecting detection. In shallow water, detection rates were high for all mesh colours, but in the slightly deeper placements, orange traps were more readily detected. This study demonstrates that drones could be an efficient and reliable tool for rapidly assessing areas for illegal and derelict traps and can be supplemented into land or vessel‐based fisheries operations.

Inter‐ and intra‐specific interactions affecting crustacean trap fisheries—Implications for management

“…The possibility that European lobster catch rates in commercial fisheries are affected by a density-dependent factor is difficult to detect and compensate for routinely; this can distort the relationship between fishing effort and fishing mortality, which strongly influences the possibility of stock collapse when effort is high . These biases warrant further study using a combination of fishery data and fishery-independent survey methods, such as visual surveillance including the use of remote surveillance (Bloom et al, 2019), capture-mark-recapture (Clark, Jury, Goldstein, Langley, & Watson, 2018;Øresland, Oxby, & Oxby, 2018;Skerritt, Fitzsimmons, Polunin, Berney, & Hardy, 2012) or electronic tagging (Lees et al, 2018;Skerritt et al, 2015), as well as supporting studies of the encounter rate and capture process.…”

Beach safety: can drones provide a platform for sighting sharks?

“…Similarly, sighting rates for dugong (Dugong dugon) decreased with water depth and turbidity (Pollock et al 2006;Hodgson et al 2013). In deeper water, wavelengths of light are either scattered or absorbed before reflecting off the substrate, creating a darker ocean colour and masking the grey shark-like colour of the analogues (Bloom et al 2019). Conversely, in shallower water, where the depth of sightability is greater than the water depth, light is reflected from the sand or reef substrate, giving the water a lighter appearance and allowing better contrast with the silhouette.…”

Riverine Plastic Litter Monitoring Using Unmanned Aerial Vehicles (UAVs)

“…UAVs are increasingly used for long-term monitoring efforts such as wildlife surveys [16,17], coastal erosion surveys [18,19], and beach litter monitoring [20]. Although some research has been done using UAVs for monitoring purposes in the dynamic riverine environment [21][22][23], to date, no efforts have been made to broaden the application of UAVs for the monitoring of particle fluxes. We foresee many opportunities in usage of UAVs for plastic debris monitoring, both in data acquisition and in data processing.…”