Last month I returned from sea after two back-to-back trips where I tested the efficiency of mitigation measures in reducing seabird mortality on longline hooks. Similarly Martin was at-sea at the same time performing the same experimental work on a different vessel.
As well as participating in the capsule experiment (see previous diary entry), our main aim was to finish the collection of at-sea data that we started this time last year. The experiment was set up to identify whether tori lines reduce seabird mortality in pelagic longline fisheries. We have had the full support from Pelagic Resources Department of the National Department of Aquatic Resources to carry out our studies and on completing the studies the results look very promising.
From the data we collected in 2009 we felt sure that we were going to be able to show confidently that our mitigation measure was effective, but we knew we would need more data to make firm conclusions. During 2009-10 we completed eight fishing trips on commercially-rigged vessels. During days when longline gear was set without using a tori line, a total of 25 birds were caught. However, on lines set under the protection of a tori line not a single bird was killed.
The tori line did become entangled with fishing gear on a high proportion of the days it was used. In these cases the weak-link we have included close to the end of the tori line breaks and the rest of the tori line is left flying and still prevents seabirds gaining access to the baited hooks.
We are very pleased with the results as they show that the tori line is efficient at reducing seabird mortality in Uruguay, and as such we have a mitigation measure that we can apply to prevent seabird bycatch.
Obviously we still have a lot to do, including testing ways to increase the sink rate of fishing gear, and improving the use of night setting as a standard practice as these measures are complimentary and work best when used in combination.
For the tori line, we need to reduce the entanglements to make sure it is a measure that the fleet will use voluntarily and achieving this is a big challenge for 2011.
Beyond the positive results we were also paying close attention to the different species that attend the vessels and we had some interesting visitors. Two species in particular caught my attention. The presence of the Wandering albatross, which were around the vessel on every day of my time at sea, arrived in groups of several individuals. We see a peak in abundance of this species at this time of year in Uruguay as the female birds from the South Georgia population are starting to leave the chicks on the nests and head up to feeding grounds off Uruguay.
The other species that caught my eye was the Sooty albatross. To date, Martin and I have few records of this species in Uruguay, which has prevented us from identifying a seasonal trend. The closest breeding populations are at Tristan da Cunha and Gough Island, an oceanic archipelago and home to huge numbers of seabirds.
Many species, such as the Spectacled petrel and Yellow-nosed albatross arrive here from the archipelago and so we had imagined that the Sooty albatross would be associated with the same migration. Fortunately these last trips provided plenty of new data on this species, and helped me understand more about where they forage.
Such new experiences are common during trips at-sea on fishing vessels. There is always something new to learn about albatross and petrels in the South Atlantic and this, without doubt, is what gives me a lot of motivation to continue working onboard and observing these magnificent birds.