Detection and characterisation of derelict creel fleets to evaluate marine megafauna entanglement risk in Scottish waters – CreelMap Final Project Report.

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Summary
Creel fisheries, using fleets of baited pots or ‘creels’ to catch Nephrops, lobsters and crabs, are an
important component of the inshore, and to a lesser extent offshore, Scottish fishing sector.
Unfortunately, this fishery has also been implicated in accidental lethal entanglements of marine
mammals and other megafauna, notably minke whales, humpback whales and basking sharks. It is not
clear how much of this impact is caused by creel fishing gears (fleets) that are actively fishing and
regularly tended, vs. fleets that have been lost due to storms or interactions with other fishers. Loss
rates of creels are poorly characterised but anecdotal records suggest they may be considerable. Once
fleets of creels are lost, there is little information about the entanglement risks they continue to pose
(in addition to wider concerns about damage to sensitive habitats and chemical pollution as they
slowly degrade). To address ongoing impacts of creel fisheries on species of conservation concern in
Scotland, it is essential to understand the distribution and configuration of, and risks posed by, derelict
creel fleets.
The CreelMap project sought to evaluate a combination of different towed side-scan sonar (SSS)
systems and in-situ observations by Remotely Operated Vehicle (ROV) to assess whether these tools
can efficiently detect and locate derelict creel fleets, an essential first step towards considering
potential recovery. Several different kinds of SSS systems were tested by towing them behind the SAMS
research vessel Seol Mara in inshore waters adjacent to the Scottish Association for Marine Science
(SAMS) in western Scotland, between August 2023 – May 2024. A subset of likely survey targets was
subsequently observed directly through deploying an ROV during December 2023 – June 2024, again
from RV Seol Mara. Results revealed that SSS systems operating at frequencies ≥500 kHz) were able to
reliably identify creels, and when operated at higher frequencies could discriminate groundlines.
However, the quality of the SSS data was strongly influenced by the movement of the vessel in
response to wave and wind conditions. ROV observations revealed varying amounts of epifaunal
growth present on both creels and accompanying groundlines. A single derelict creel fleet was found
by the ROV; counter to expectations, the groundline was partially buried in the sediment rather than
floating in the water column. As no attempt was made to recover the fleet, the composition of the
groundline presently remains unknown.
Under suitable conditions, SSS systems are powerful tools for the discovery and mapping of derelict
creel fleets that can subsequently be examined in more detail, for example with ROVs, potentially
offering a distinct advantage over other derelict gear types (e.g. gillnets) that may be more difficult to
detect. A constraint of the system tested was the need for deployment from a surface vehicle which
restricted the area and increases the costs of surveying. Deploying SSS systems from automated
surface vehicles (ASVs) or automated underwater vehicles (AUVs) may in future enable more efficient
surveying across larger, and deeper areas. No attempt was made in this project to recover the
discovered fleet, but developing the capacity to do so is an important priority. The ability to detect and
observe derelict creel fleets in situ will also facilitate future studies to better understand the behaviour
of discarded or lost ropes and lines, to improve evaluation of long-term entanglement risks.