Post-release mortality caused by commercial longline fishing leading coastal shark populations to decline

Contributor – Nick Whitney, Anderson Cabot Center for Ocean Life, New England Aquarium (USA)

Bycatch has long been an issue in commercial longline fisheries, and whilst there are blanket regulations in place requiring fishermen to release some species which could be accidentally caught, a recent study has found that some are more vulnerable than others.

Dr. Nick Whitney, senior scientist at the New England Aquarium’s Anderson Cabot Center for Ocean Life in Massachusetts described how there is a general feeling that released shark bycatch will return to a normal way of life. The study, however, proves that this is not the case for several of the more vulnerable species, such as the blacktip and spinner sharks.

Photo credit: New England Aquarium

A “post-release mortality rate” describes the death rate of animals who are caught as bycatch, and which are then subsequently released. A high post-release mortality rate is typically therefore seen in more vulnerable species, where capture stress leads to physical or physiological trauma.

Where “at-vessel mortality” is easy to quantify, since this bycatch is already dead upon landing; calculating a post-release mortality rate can be challenging. Regulations are therefore heavily reliant on estimations using data from other species, which may not be an accurate reflection of the impact of longline fisheries on shark populations.

This landmark study quantified post-release mortality rates by combining blood-stress physiology with accelerometer data from CTL G6a+ data loggers. The activity-based accelerometer data (together with pressure and temperature data also captured by the logger), combined with blood samples taken from the same individuals, provides evidence of the sharks’ post-release behaviour and therefore the impact of the capture stress.

The G6a+ loggers - which were attached to the dorsal fin - recorded tri-axial acceleration at 25Hz, pressure (depth) at 1Hz and temperature at a 30 second rate. The float package (pictured below) enabled the study to retrieve the archival G6a+ loggers (which need to be physically recaptured and downloaded before they can be redeployed) by utilising corrosive wire to ensure removal from the sharks, and incorporating a VHF transmitter from Advanced Telemetry Systems (USA) to facilitate recovery.

Photo credit: New England Aquarium

The use of retrievable and reusable dataloggers for this study allowed for some of the largest sample sizes (over 300 sharks tagged from 5 species) of any shark post-release mortality study. Such studies typically use satellite tags which are single-use and are approximately three times the cost of our acceleration data loggers (Lear and Whitney, 2016). The study found that the capture response of sharks varies greatly by species – with hardier species such as sandbar, tiger, and bull sharks displaying great resiliency while other species such as blacktip and spinner sharks may die at a rate of 41 to 71% after they are caught and released.

The findings of the study suggest that seasonal restrictions and limited soak times could reduce post-release mortality rates for some species, and that such rates can vary greatly depending on the species and fishery.

Source:

Whitney NM, Lear KO, Morris JJ, Hueter RE, Carlson JK, Marshall HM (2021) Connecting post-release mortality to the physiological stress response of large coastal sharks in a commercial longline fishery. PLoS ONE 16(9): e0255673.

https://doi.org/10.1371/journal.pone.0255673

References:

Lear, K.O., Whitney, N.M. (2016) Bringing data to the surface: recovering data loggers for large sample sizes from marine vertebrates. Anim Biotelemetry 4, 12

https://doi.org/10.1186/s40317-016-0105-8

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/]

Best practice for storing your Data Storage Tags

With our production facility currently closed, some of us have been able to continue working from home and keeping up important discussions with customers (new and existing) about their upcoming requirements. One key thing we have learned here, though, is that it is likely that we will see fieldwork being delayed or postponed for significant periods of time, either due to a lack of safe working environments (e.g. social distancing), or with budgets being re-evaluated and resources being restricted.

So, with this in mind, I have written up this short, informative guide on best storage practice for your tags so that they can continue to contribute to your studies for as long as possible.

STORAGE

How should I store my tags?

We recommend that optimal storage for tags would be at room temperature, perhaps in a cupboard or a drawer. You should refrain from storing the tags in the fridge or in areas that are likely to get very warm as this will be detrimental for the battery. Due to their small size, the batteries are vulnerable to temperature extremities and, as such, have reduced performance levels in temperatures around 0°C and over 34°C.

When the tags are not in use, they should be stored in Deep Sleep mode to preserve battery life.

What will this mean for battery life?

Due to what’s called quiescent current draw, the tags will naturally lose battery power over time, even if they are not used. We estimate that the tags will lose approximately 1 month of battery life over a 12-month period whilst in Deep Sleep mode.

What is “quiescent current draw”?

It’s an electronics term which means “background current” – representing reduced battery voltage over time where electronic circuitry continues to run in the background, drawing current to power itself.

What is “Deep Sleep” mode?

Deep Sleep mode is the tag’s version of “standby”, where power can be saved by disabling primary operations. In this mode, a tag cannot log any data and does not maintain its internal clock. As a result, less of the electronic circuitry is used and the current draw from the circuit board is minimised, thus saving battery life.

You can activate Deep Sleep mode in one of two ways, but both require the use of the DST Host Software:

1. Once you have inserted a tag into an interface and selected “Connect”, you should navigate to the “Tag” tab along the top menu row and then select “Set Deep Sleep”.

2. Alternatively, if the tag has recorded data which has not yet been downloaded, you should proceed to “Download” this data first. Upon completing the download, the software will ask if you wish to store the tag in Deep Sleep mode.

Some additional things to consider:

• All new tags are shipped to the customer in Deep Sleep mode

• Placing a tag into an interface which is plugged into the PC will wake the tag out of Deep Sleep after 5 seconds, even without clicking “Connect” in the software

• Deep Sleep mode is not activated automatically at any time

• If you set Deep Sleep mode before the end of a deployment, then the tag will stop logging data at the time that Deep Sleep is activated

• Likewise, if you set up a new deployment with the tag and then set Deep Sleep mode, the tag will not begin logging at your start date as it is not maintaining its internal clock. You should only
  consider setting Deep Sleep mode after setting up a new deployment if the period between deploying the tag using the software and physically attaching the tag to a creature/object is more than a week or so. In that case, do not forget to manually set the clock (“Deploy” > “Set Clock”) before you release the tag, or it will not record any data!

DEPLOYMENT

Should I carry out any additional processes before deploying?

Yes, we suggest the following precautionary checks before deployment:

1. Visually check the tags – specifically, checking to see there are no clear defects on the outer casing or with the black urethane resin which covers the sensor

2. Connect to the tags using the DST Host software – you may need clean the communication pins with a pointed tool (such as a sharp, pointed scalpel) if these tags have been used previously, as there may be some debris/dirt present

3. Check the tag battery voltage – you can access live sensor readings by navigating to the “Tag” tab along the top menu row of the DST Host software, then selecting “View Sensors”. Whilst the battery voltage figure provided is only indicative, it will help you to set your expectations for tag performance. For example, if your tag displays a battery voltage <2.90V, then the tag is nearing the end of its lifetime and may only achieve a shorter deployment

What should I do if I cannot establish connection with the tag?

1. As mentioned previously, your first check should be to clean the communication pins. If the tag has been used before then it is quite possible that some dirt or debris could remain in the communication pins due to their concave shape. Any debris could block an electrical connection between the tag’s communication pins, and the spring pins in the interface (reader).

2. Secondly, you should check to see whether the PC you are now using is the same PC that
   was used to connect to the tags previously. It may be that, whilst you have the DST Host software installed, you may not have the correct drivers for the USB interface installed on this machine. You can find the drivers on the USB stick provided with your order, or directly from the FTDI website: www.ftdichip.com/Drivers/VCP.htm

   You should select the ‘setup executable’ option on the right hand side of the table, selecting from the row which matches your operating software.

If you have tried both steps above and still cannot communicate with the tags, it may simply be that the tag battery has expired.

What should I do if the tag battery has expired?

If you have data on the tag which you cannot retrieve due to battery expiry, please contact us on info@cefastechnology.co.uk and request to return your tag(s). We can carry out a free-of-charge data retrieval procedure to attempt to recover any data stored in the tag’s memory.

To conclude, we anticipate being able to reopen our production facility in the coming weeks, and so we remain available to receive orders and discuss your needs. Please do not hesitate to get in touch if we can be of assistance!

Stay safe, and we hope to speak to you soon.

The Mystery of European Eel migration

Contributors - Pieterjan Verhelst, University of Ghent (Belgium)
- David Righton, Cefas (UK)

European eels migrate from rivers all over Europe to the Atlantic to spawn. Very little is known, however, about their exact spawning location. Belgian researchers from the University of Ghent, Flanders Marine Institute and the Research Institute for Nature and Forest have been working with Cefas scientists to gain a greater understanding of how the eels migrate from Belgium.

Acoustic telemetry can provide detailed location information around coastal areas where networks of transmitters are plentiful. Outside of the acoustic network range, Cefas Technology data loggers can reveal information about the eels’ behaviour as they head out to the open ocean.

Since 2018, Pieterjan (PJ) Verhelst has been using G5 pop-off Data Storage Tags (pDST) to study eel behaviour. Housed within a bright orange flotation collar; these units detach from the eels after a pre-programmed data logging period (utilising the in-built pressure & temperature sensors). Upon release, the units float to the surface and wash up on shore, often being discovered by walkers or beachcombers.

To-date, the 2018 tagging work has yielded more than 15 datasets, with further work in 2019 starting to yield a lot more. Within the past month alone, eight units have been washed ashore in the aftermath of storms Ciara, Dennis and Jorge.

PJ’s studies have revealed – for the first time – that eels migrating from Belgium have traversed the English Channel and headed for a longer journey, continuing west, to the presumed spawning grounds in the Sargasso Sea.

Last week, PJ found himself in the news, reporting on his studies to the BBC. You can watch the video here.

Behavioural ecology of European seabass off the West Coast of France

Declining European seabass (Dicentrarchus labrax) numbers in the Irish Sea, Celtic Sea, English Channel and southern North Sea required detailed assessments of stocks to be carried out.  This led to a collaborative project between Ifremer, CLS (Space Oceanography Division), Institut Telecom/Telecom Bretagne, Parc Naturel Marin d’Iroise in the Iroise Natural Marine Park, a marine protected area around Brittany, western France. The project aimed to provide biological evidence to support the implementation of conservation measures to save the declining stocks.

A total of 246 G5 Long-Life Data Storage Tags were deployed in the summers of 2010, 2011 and 2012. Fish were caught by professional fishers in either Ushant or Raz de Sein waters but, due to difficulties in navigating the Iroise Sea, two methods of tagging were practiced. The first involved a support vessel where seabass were tagged and released on the same day. The second method transported fish to a shore-based location where the fish would be kept overnight before being released the next day.

In order to increase the return rate of the tags, they were supplied housed in a bright orange flotation collar (Fig. 1). The tags were surgically implanted into the peritoneal cavity with an external Floy Tag® for identification purposes.

Fig 1. A G5 Long-Life fitted with a flotation collar

Until the end of 2016, 36 individuals were recovered. 38.9% of returns were as a result of the tags drifting to the shore and being found (made possible by the flotation collars). The remainder of the recoveries were caught by fisherman or through the sale channel.

Researchers used the hidden Markov model for fish geolocation to infer the seabass’ movement from release to recapture. Analysis of the data revealed a spatial structure to the stocks, with individuals exhibiting either migration or residency behaviours.

The study demonstrated how archival loggers can be used to investigate species’ behavioural patterns in the long-term and could therefore influence conservation actions.

References:

de Pontual, H., Lalire, M., Fablet, R., Laspougeas, C., Garren, F., Martin, S., Drogou, M., Woillez, M. (2019), ‘New insights into behavioural ecology of European seabass off the West Coast of France: implications at local and population scales’, ICES Journal of Marine Science, Volume 76, Issue 2, pp. 501-515

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/