Blogposts: 2024

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.

Two recent examples of the ongoing issue of marine entanglements were reported to the Scottish Marine Animal Stranding Scheme (SMASS) team last week. The first was a 9.60m long female humpback whale which washed ashore in Granton, Edinburgh on the 29th September. This whale had several skin abrasions highly consistent with rope entanglements. A week later and 100 miles north, a 5.75m long female minke whale washed ashore in Johnshaven on the Aberdeenshire coast. Due to issues with access and disposal, we weren’t able to do a full necropsy on either case, however thanks to the help of SMASS volunteers, we have tissue samples, measurements and detailed images of both animals and are confident that entanglement was the most likely cause of death.

Both of these were sub-adult animals in moderate body condition, suggesting they had been successfully feeding prior to becoming entangled. The humpback whale had bruising and abrasions across the throat pleats and around the pectoral fin consistent with some sort of rope. The minke whale had much more obvious signs of entanglement, with a deep encircling laceration around the tailstock and twin linear lesions on the underside of the fluke consistent with a rope which was under tension and had dug so far into the into the tissue it had almost amputated the fluke, most likely whilst the animal was still alive. As we often find, neither whale stranded with any material remaining attached, meaning it is not possible to say if this was active fishing gear, marine debris or rope from a non- marine source. This also highlights the significant welfare and conservation issues caused by entanglement around Scotland.