Assessing seabird bycatch vulnerability where floated demersal longlines are used

Contributor: Yann Rouxel, Bycatch Project Officer, The Royal Society for the Protection of Birds (RSPB)

Whilst many Data Storage Tag applications involve tagging creatures directly; others, such as The RSPB’s project looking at minimising seabird bycatch, sees G5 Long-Life tags attached to floated demersal longlines. Commencing in January 2020, the project set out using the DSTs to identify the sinking profile of commercially used floated demersal longlines used notably by fishing vessels in offshore Scottish waters (UK Seafood Innovation Fund, 2020).

Almost a quarter of the global seabird population is at risk of bycatch; and longlines, when sinking slowly, make baits readily available to foraging seabirds in surface waters (UK Seafood Innovation Fund, 2020).

Inserting the DSTs into a specially-designed protective housing protected them from physical damage whilst attached to the lines. Applying the DSTs directly to the fishing gear (Fig. 2) helped the project team to determine its sinking speed which in turn informs bycatch vulnerability for seabirds.

Fig 1. A G5 Long-Life DST being inserted into a Protective Tag Holder

Fig 2. Photo credit: Juan Pablo Forti

The optional Dive-Logging feature utilised means that the 2Hz fast logging data block could be activated using the wet switch, rather than using the standard sample rate, which would have filled the memory with non-relevant data from before the longline was submersed and after it was brought back in. In addition to the benefit of preserving memory space for critical dive profiles and the consequent saving of battery life, it also facilitated more flexibility when it came time to physically dropping the lines, as recording was triggered by entry to the water rather than a pre-determined time.

The deployed tags were retrieved from the longline after each fishing operation; data was downloaded, and then tags were redeployed. The data retrieved from the tags will contribute towards the development of effective seabird bycatch mitigation measures.

The project has since been finished and the team is now exploring potential follow-up projects, to develop and test at-sea bycatch mitigation measures including of longline designs that sink faster.

This project was funded by the Seafood Innovation fund (SIF), thus was presented on the SIF website:

https://www.seafoodinnovation.fund/projects/developing-a-floated-demersal-longline-design-that-minimises-seabird-bycatch-fs031/

The RSPB’s official Twitter page: https://twitter.com/Natures_Voice

The RSPB’s official Facebook page: https://www.facebook.com/RSPBLoveNature/

BirdLife International on Twitter: https://twitter.com/BirdLife_News

The UK Seafood Innovation Fund on Twitter: https://twitter.com/SeafoodFund

References

UK Seafood Innovation Fund (2020), Developing a floated demersal longline design that minimises seabird bycatch, Accessed 24th June 2020 [https://www.seafoodinnovation.fund/projects/developing-a-floated-demersal-longline-design-that-minimises-seabird-bycatch-fs031/]

Tracking sea trout kelts to establish marine migration routes

Contributor – Céline Artero, Game and Wildlife Conservation Trust (UK)

Migration routes of sea trout kelts in the Tamar and Frome estuaries (UK) & Bresle estuary (France) are relatively unknown. The SAMARCH (SAlmonid MAnagement Round the CHannel) project uses acoustic technology alongside our G5 Standard Data Storage Tag to better understand the kelts’ use of these transitional and coastal waters. It is hoped that the data retrieved from the tags will help to inform authorities of the salmonids’ behavioural pattern and thus reduce the risk to them.

The tags are housed inside a flotation collar (Fig. 1) and inserted into the body cavity alongside an acoustic tag, which provides rough location information. If the location of the fish is known, electrofishing is used as the recapture method. Alternatively, if the tag naturally releases from the kelt (when the fish dies), it would float and wash up onto shore, either on a beach (if the fish died at sea) or by the river’s edge if the fish was returning to its natal river. The bright orange colouring of the flotation collars makes them easier to spot by members of the public, who could read the return information on the label, encapsulated within the float.

Fig 1. A G5 Standard DST with collar float attachment, next to a sea trout kelt

Returned tags are then re-connected to a PC and data is downloaded from them. Temperature and pressure data recorded by the G5 DSTs will be analysed using the Hidden Markov Model to reconstruct the sea trout kelts’ migration path and swimming behaviour.

A benefit of using archival loggers in this study (in addition to acoustic tags) is that they can provide additional information on mortality rates during the migration. Acoustic technology alone can provide location information as the tags pass through detection gates deployed downstream. Whilst you can infer mortality from non-detection between downstream gates; there are distinct patterns in archival tag data which represents a mortality event, such as sudden raised temperatures (through predation) or depth readings nearing zero (tag separated from the fish and floating to the surface, again perhaps through predation). In this case, by logging temperature and pressure at a 2-minute rate, Céline and her team can capture mortality information whilst also ensuring the longest possible logging duration.

Deployment of the tags started in the winter of 2018-19, where 116 individuals were tagged. The project – running until the end of 2021 – plans to tag a further 150 individuals during winter 2019-20.

Other organisations associated with the project:

• Environment Agency

• Agrocampus Ouest

• Office Français de la Biodiversité

• Institut National de la Recherche Agronomique

Find out more:

Facebook:           Operation Tagback

www.samarch.org/project-information/fish-tracking/