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

Byoliveridley

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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  • Tuesdays with Turtles – Gahirmatha Arrribada Hatchings

    Byoliveridley

    In case I forgot to mention, the Olive Ridley arribada started during the 2nd week of February, so about 50 days later, here they are, the “millions” of hatchlings.

    The Hindu News Update Service

    Olive Ridley hatchlings emerge in Gahirmatha

    Kendrapara (Orissa), April 10. (PTI): Millions of tiny olive ridley sea turtle hatchlings are now emerging out of nests at the Gahirmatha beach in Orissa’s Kendrapara district, wildlife officials said on Monday.

    The eggs laid by thousands of adult females in the Nasi-2 and Babubali islands in the Gahirmatha marine sanctuary have began to hatch over the last two days, they said.

    Wildlife officials stationed at the nesting grounds were witness to the phenomenon, but tourists and researchers were not allowed into the unmanned territory close to the Wheeler’s island where a defence test range is located.

    India’s intermediate range nuclear-capable missile Agni III is likely to be test fired from there some time this week, defence sources said.

    You know what, the fact that this area is under close military supervision because of India’s grandiose missile dreams may not be sucha bad thing (sacrilege!!!). The area is under so much development pressure that even military operations are better than the alternative.

    For more about the Gahirmatha area, visit the official website. At this point in time, the Arribada is very tourist unfriendly, and there are few, if any volunteering opportunities. I will keep any eye open for changes

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  • Tuesdays with Turtles – Lighsticks Kill

    Byoliveridley

    Following up on the fishing issues from last week, here’s word that lights used to lure tuna towards longline fisheries attract juvenile sea turtles as well.

    Article – Science & Technology – Lightsticks may hold deadly attraction for sea turtles

    RALEIGH, N.C. Longline fishermen use lightsticks similar to the glowing tubes that delight trick-or-treaters to lure tuna and swordfish to baited hooks. New research by University of North Carolina-Chapel Hill scientists suggests that for endangered sea turtles the lights may hold a fatal attraction.

    Lab experiments by Ken Lohmann, a University of North Carolina biology professor and John Wang, a graduate who is now a research associate at the University of Hawaii and National Marine Fisheries, found that young loggerhead turtles in a tank tended to swim toward lights.

    It’s well known that hatchling turtles on a beach will crawl toward lights as they try to find the surf. But researchers did not know whether juvenile loggerheads in the water shared that attraction. Young loggerhead and leatherback sea turtles, which are protected because of declining numbers, are inadvertently hooked during longline fishing.

    Well, not so surprising, is it? Bioluminescence is a common enough phenomenon that especially at night, animals will be attracted to light as it can signal food. It’s tricky, but when you try to catch fish, tyou will catch other animals as well. So, when you change something about the way you catch fish, you need to study how it affects other endangered species…

    Off topic, but it is ironic that I read this in the ocregister, which is a newspaper from Orange County, California. It reported on work done by UNC Chapel Hill, which is in Orange County, North Carolina.

  • 100s of turtles die in Andhra Pradesh

    Byoliveridley

      I have written about turtle excluder devices (TEDs) and how they save adult turtles lives previously. So, this story is an utterly avoidable tragedy brought about by the lack of implementation of laws regulating the use of TEDs.

    The death of hundreds of Olive Ridley turtles along the Paravada coast in December 2007 had occurred due to failure of the trawlers to install the mandatory turtle excluder device. Lab tests conducted at Andhra University and Veterinary Biological Research Institute, Hyderabad ruled out the largescale death of the endangered species due to consumption of toxic contents discharged by industries located nearby or on account of rise in the seawater temperature.“We didn’t find any abnormal pollution levels. The washing ashore of carcasses was not a localised phenomena as dead turtles were found all along the coast up to Srikakulam during the year-end – the breeding season,” P.J. Vijaykar, Divisional Forest Officer told The Hindu on Wednesday.

    The Hindu : Andhra Pradesh / Visakhapatnam News : Olive Ridley death riddle solved

    Andhra Pradesh was supposed to be a success story with the TEDs. This from an article by Kartik Shanker, one of SSTCN’s founding members…

    In India, the parallel cases of Orissa and Andhra Pradesh demonstrate how a TED programme should not (and should) be implemented. In Orissa, the polarization between the fishing community and conservationists has prevented the introduction of TEDs, while in Andhra Pradesh, TEDs were introduced by the state Fisheries Department with appropriate demonstration and training programmes (see Shanker and Pilcher, 2003).

    So, this occurrence in Andhra Pradesh is quite disheartening and speaks to the large gaps that lie between legislation, policy and implementation in India.

    Cross Posted at SSTCN

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  • |

    Killer nets reinstated

    Byoliveridley

    Council Decisions: March 2006

    Drift Gillnet Management

    The Council adopted a recommendation to NMFS to authorize an exempted fishing permit (EFP) that would allow drift gillnet fishing in the current August 15-November 15 closed area. The EFP fishery would be governed by several requirements for all vessels, including, to carry an observer; to limit total fishing effort in the EFP fishery to 300 sets; to immediately cease the EFP fishery if, and when, two leatherback sea turtles were encountered by the fishing gear; and to immediately cease the EFP fishery if one mortality or serious injury occurred to any of the following marine mammals: short-finned pilot whale, sperm whale, fin whale, gray whale, humpback whale, or minke whale.

    And, with that, starts the rather egregious practice of drift gillnet fishing. The restrictions seem fairly tight, an observer on every boat, and end to the fishery after two incidences of capture. There is definitely more than meets the eye here, I don’t know what. Drift gillnet fishing is well documented to cause turtle catch, this from the 1998 Fishery Bulletin for 1990-1995

    In the drift gillnet fishery, seven out of 387 mammals observed entangled were released alive. In the set gillnet fishery, five out of 1,263 mammals observed entangled were released alive. Estimates of incidental kill are presented along with estimates of entanglement for species that were observed to be released alive. For the period under consideration, the estimated mortality for the drift gillnet fishery was over 450 marine mammals each year. A total of 20 turtles and 3 seabirds were observed entangled during the entire period. The most frequently entangled species in this fishery were common dolphins, Delphinus spp., and northern elephant seals, Mirounga angustirostris. Estimated cetacean mortality in the driftnet fishery decreased from 650 in 1991 to 417 in 1995; pinniped mortality decreased from 173 in 1991 to 116 in 1995. Estimated cetacean mortality in the set gillnet fishery ranged from a high of 38 in 1991 to a low 14 in 1993; pinniped mortality rose to a high of 4,777 in 1992 and then decreased to 1,016 in 1995. We postulate that there has been a decline in the number of pinnipeds and cetaceans in the setnet fishery owing to area closure. No similar proposal can be made for the driftnet fishery. The most frequently entangled mammals in the setnet fishery were California sea lions, Zalophus californianus, and harbor seals, Phoca vitulina. Six turtles and 1,018 seabirds were estimated entangled in this fishery during the NMFS Observer Program from July 1990 to December 1995.

    So what’s the deal, this thing caught 20 turtles in 5 years, so it is going to catch turtles, no doubt about it. Anyone who does not get what the death of one adult sea turtle means read this. Sea turtles are wonderfully fragile animals given their size, they take long to mature sexually, they do not breed all that much and less than 1% of turtle hatchlings survive to adulthood. Leatherbacks are highly endangered.

    I have a feeling that this is the first part of a one-two punch intended to reinstate the famed turtle killer long line swordfish nets on the pacific coast. The “proof” that these nets do not catch turtles will be used to lobby for longline swordfishing in, oh say three months?

5 Comments

  1. Pingback: Tuesdays with Turtles - Lighsticks Kill « The Olive Ridley Crawl
  2. Pingback: 100s of turtles die in Andhra Pradesh « The Olive Ridley Crawl
  3. Pingback: 100s of turtles die in Andhra Pradesh « Students’ Sea Turtle Conservation Network

  4. 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.

    love,
    A’ Sha
    Harris

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