Tuesdays with Turtles – Why Adult Turtles Die so You Can Eat Fish

An interesting paper featuring a North Carolinian turtle researcher Larry Crowder from Duke University:

Blackwell Synergy – Conservation Biology, Volume 21 Issue 1 Page 79 – February 2007 (Full Text)

Abstract: Although some sea turtle populations are showing encouraging signs of recovery, others continue to decline. Reversing population declines requires an understanding of the primary factor(s) that underlie this persistent demographic trend. The list of putative factors includes direct turtle and egg harvest, egg predation, loss or degradation of nesting beach habitat, fisheries bycatch, pollution, and large-scale changes in oceanographic conditions and nutrient availability. Recently, fisheries bycatch, in particular bycatch from longline fisheries, has received increased attention and has been proposed as a primary source of turtle mortality. We reviewed the existing data on the relative impact of longline bycatch on sea turtle populations. Although bycatch rates from individual longline vessels are extremely low, the amount of gear deployed by longline vessels suggests that cumulative bycatch of turtles from older age classes is substantial. Current estimates suggest that even if pelagic longlines are not the largest single source of fisheries-related mortality, longline bycatch is high enough to warrant management actions in all fleets that encounter sea turtles. Nevertheless, preliminary data also suggest that bycatch from gillnets and trawl fisheries is equally high or higher than longline bycatch with far higher mortality rates. Until gillnet and trawl fisheries are subject to the same level of scrutiny given to pelagic longlines, our understanding of the overall impact of fisheries bycatch on vulnerable sea turtle populations will be incomplete

Adult sea turtle killing by humans occurs due to

  1. Harvest, killing them deliberately for food
  2. Incidental bycatch in fishing nets
  3. Habitat loss

The paper focuses on long line fishing and its effects on turtle mortality. So, if like me, you’re not a fisherperson, what is long line fishing and what are some other kinds of fishing techniques that have effects of sea turtles? Well, the Duke Project GloBal research team on studying bycatch has a nice primer. Some highlights:

  1. Longlines: As the word suggests, longlines are very long (>10 km) lines of 2000+ individually baited hooks that drift close to the surface and are used to catch tuna, swordfish, halibut, etc. Crowder’s paper suggests that while each individual longline hook has low probability of catching a turtle, because of their number and ubiquitousness, they catch many many turtles.
  2. Gillnets: These are giant rectangular mesh nets, either stationary or drifting, that catch marine life indiscriminately. There’s not much that can be done by way of reducingsea turtle catch in gillnets, except monitoring, observation and just using less of them
  3. Trawls: Big funnel shaped bags that catch fish. Bottom trawling fishing boats used to, and still catch turtles at an alarming rate. Trawls are now (at least in the U.S and other “developed” countries) required to be outfitted with Turtle Excluder Devices (TEDS) to let turtles swim to safety.
  4. Purse Seines: These are weighted on the bottom and float at the corners. They are indiscriminate, and especially hard on dolphins. It appears that mitigation efforts aimed at reducing dolphin mortality have the unintended effect of increasing sea turtle catch. Battle of the cute species!!

Take home message? Catching fish causes a lot of turtles to die. While trawl fishing is the worst culprit, it is also the most studied and the technique for which a viable mitigation strategy exists. THe other kinds of fishing are less studied, and there is precious little that can be done to avoid sea turtle bycatch.

Happy fishing!

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  1. i think you should have a little more information, and make the words a little more bigger.I realy could not see the words at all.So can you please email me a better copy thats all i ask for.

    my turtle is dying and i don’t know wat to do he is not eating none of the food we give him. We brought him home on June the 13 2009 at J&A’s 99 cent store for $8.99 i dont think that is a good store they only have chinease people working there and they can’t understand english at all that gets on my nerves i hate chinease people please read this message.

    A’ Sha

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