Analyse this…

As we embark on our second season of data collection in Lithuania, we highlight what we learned from analysing our first season’s data.

While raw figures might make interesting reading, when it comes to thinking about bycatch, we need to analyse our data to draw useful conclusions about how effective our net panels might be in reducing seabird mortality in gillnet fisheries.

One of the difficulties with almost all bycatch data, irrespective of fishery or accidentally captured species, is that it is usually a rare, sporadic event – this means that our data set contains lots of zeros, when there was no bycatch at all. Most means of analysis don’t cope particularly well with this – but thankfully, there are ways!

Without getting into the details (we will aim to publish our results in full once we have completed our next field season), the mean number of birds caught per set was about a third lower in our experimental sets with net panels (mean of 0.37 birds/set) than control sets (0.54/set). While this is an encouraging result, this difference was not statistically significant. Given this outcome, we are undertaking further trials this winter in Lithuania, continuing to conduct paired trials to bottom-out whether these net panels might have utility in reducing seabird bycatch in the Baltic. The signs are encouraging, but more work is required!

One interesting (and statistically significant!) result is that total fish catch was actually higher in the nets carrying panels compared to standard gillnets (a graph below if you’re interested!). This is an important result, as technical mitigation is unlikely to be popular with fishermen if it negatively affects catch. We’ll continue to keep a close eye on how net panels affect target catch…

total catch

 Total fish catch in control and experimental nets. Horizontal lines are the median, boxes the interquartile range, error bars the 95% CI, and dots are final outliers

Thanks to Alex Bond of RSPB for carrying out the analysis!

Stopping gillnet bycatch – how do we do it?

Spring is arriving all over Europe, and everyone is looking forward to longer days, more sunshine and wildlife waking up again. I love spring myself, and I’m not a glutton for punishment, but I have been casting my mind back to a snowy week in West Virginia, USA, at the end of January.

It’s not because I’m pining for the cold, but because it was then that we ran a workshop with the American Bird Conservancy focussing on the development of technical measures to reduce bycatch in gillnet fisheries. Working with researchers, fishermen, NGOs and sensory ecologists from across the world, we were looking to go beyond national and species-group silos to discuss innovative ideas to reduce gillnet bycatch – something which we are actively trying to tackle in Lithuania as part of this project.

The core purpose of the workshop was to come up with some specific project proposals to test ideas for bycatch mitigation, ideally with a cross-taxa focus – covering at least two out of three of birds, turtles and marine mammals. If you’re a bycatch geek, we hope to post a link to the full report of the workshop here soon – so keep your eyes peeled. In the meantime, here are few reflections from the workshop from me:

We need to work across species and sectors

Gillnet bycatch is a global issue of major concern – as sea turtle expert Bryan Wallace put it: ‘Net bycatch has the highest cumulative severity across air-breathing megafauna taxa of any major fishing gear category’. There is thus much to be gained by working across species groups. The literature on mitigating this problem is far richer for e.g. cetaceans than it is for seabirds. Ideas that have shown potential for one species (or group of species) could show promise for others – see, for example, John Wang’s work on net lighting for turtles – how might this apply to velvet scoter or bottlenose dolphins?

Something that came up time and again at the workshop was the need to work with fishermen. Fishermen understand their gear, have insights into interactions with non-target species and understand the practical realities of deploying mitigation measures in their fishing operations. This approach is central to what we are doing with the Seabird Task Force, and is an approach that BirdLife truly pioneered with the Albatross Task Force.

We need to better understand interactions with gillnets

Turtles, seabirds and marine mammals often become entangled in nets away from the human gaze, which means our understanding of how bycaught animals interact with gillnets is poor. Better understanding othese interactions – perhaps utilising advancing camera technology – will surely help us unlock solutions. It might allow us to key in on particular aspects of behaviour around nets to reduce the likelihood of entanglement.

We need to approach the problem from a sensory ecology perspective

Or in more straightforward language – we need to understand how species see, hear, feel (perhaps even smell and taste!) the world, so that we can design appropriate mitigation measures. I won’t spend much time on this here, but you can read a blog I wrote about it here – where you can also access the paper this blog was based on.

We need to get out there and test stuff!

The only way we will develop solutions is to get out on vessels and start testing some ideas! Don’t get me wrong – I’m not suggesting slap-dash poor experimentation without proper thought. Well thought-out ideas, understanding the fundamentals of sensory ecology and thinking about the type of interaction an animal has with a net are all important – that’s why I mention them first – but we need to start getting our hands salty and seeing what works and what doesn’t. It’s in that spirit that the Seabird Task Force was founded, and it’s in that spirit that we hope to find solutions to the problem of gillnet bycatch in the Baltic – and beyond.

Lessons on gillnet bycatch: the US case study

Gillnet fisheries are not uniform in nature across the globe – different species are targeted via different mesh sizes, fishing techniques and positioning of the net in the water column.Gillnet bycatch is also not a problem restricted to a single country or even sea basin – there are recorded instances all over the world. What we hope, however, is that a suite of mitigation measures can be devised to reduce bird bycatch wherever gillnet fishing occurs. The work of the Seabird Task Force in Lithuania is our first step on this path.Some of the only research done to date on seabird bycatch mitigation in gillnet fisheries was done in the Puget Sound, USA, by Ed Melvin, a well-respected seabird bycatch specialist based at Washington State University. His work, back in the 1990s, resulted in the development and adoption of modified bycatch-reducing nets in the sockeye salmon fishery that operates in the Sound.

 In September 2014, Rory Crawford, Senior Policy Officer with the BirdLife International Marine Programme, and Rex Harrison, a salmon gillnet fisherman from Filey Bay in the UK, went to the Puget Sound on a ‘GAP2 Exchange’ to meet with sockeye fishermen, the management authorities, and Ed Melvin himself – all with a view to understanding more about what knowledge we might be able to take back and apply to other fisheries. This video, produced by GAP2, neatly summarises Rory and Rex’s trip, and highlights BirdLife’s approach to finding solutions to bird bycatch – one of collaboration and mutual understanding with fishermen.Many thanks to GAP2 for funding Rory and Rex’s exchange trip, and for promoting collaboration between fishermen, scientists, NGOs and policy makers.