190 | Chapter 10
the seabed to catch, for example, Patagonian Toothfish. During setting,
as the line streams astern, there is a short period, only a few seconds,
when each baited hook has not sunk far. It can be grabbed by a bird,
perhaps an albatross, which is then hooked and pulled underwater.
Hours later the bird’s sodden drowned corpse comes back to the surface
along with the retrieved line and the catch. A useless, unnecessary death,
and a stain on humanity’s stewardship of the seas.
To mitigate this problem, responsible for hundreds of thousands of
bird deaths every year, various partial solutions are available. For exam-
ple, setting at night is less likely to cause bird deaths simply because most
species are then less active. Streamer lines, flapping in the wind astern
of the vessel, frighten birds away from the danger zone in the immediate
wake behind the propeller.
Another protective trick is to deliver the baited hook to an under-
water depth beyond the reach of diving birds as speedily as possible.
This can be achieved by using weighted lines or passing the line through
an underwater setting tube. Such measures are especially important in
the case of White- chinned Petrels, an abundant species of the Southern
Ocean and a prominent scavenger behind fishing boats. Indeed they are
the seabirds most commonly killed by Southern Hemisphere longline
fisheries. These petrels are more active at night than most other species
and consequently benefit little from night- time line- setting. They are
also proficient divers, with the habit of bringing baited hooks to the
surface. There, amid the throng of jostling birds, they may be displaced
by larger albatrosses but, of course, the albatross risks paying a fatal price
for its poor manners in muscling the petrel away from the baited hook.
Researchers from the FitzPatrick Institute of African Ornithology,
situated on the elegant campus of the University of Cape Town, wanted
to know the depth of White- chinned Petrel dives.^15 Using data from
nine time- depth recorders deployed on breeding White- chinned Petrels,
they found that 95 percent of dives were to depths less than 8 metres,
but the deepest dives were to 16 metres. These depths may be unimpres-
sive compared to those reached by shearwaters, auks, and penguins
(Chapter 9), but the information is worrying. Best practise protocols
for longlining stipulate that the line should be at least 5 metres down
once it extends beyond the coverage of the streamer or ‘tori’ lines astern.