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Trawling for Science

May 12, 2013

by S.W. Ross (UNCW, 7 May 2013)

deploying the trawl

Science team and crew members get ready to deploy the trawl. Image courtesy of Liz Baird, Deepwater Canyons 2013 Expedition, NOAA-OER?BOEM/USGS

On this cruise the ROV Jason II is our main science sampling tool; however, underwater vehicles cannot stay on the bottom indefinitely nor can they collect every type of sample needed.  We use a variety of gear specific to different needs, and many types of nets are included in our arsenal of sampling gear.  On this cruise we are using a bottom otter trawl to collect fishes and invertebrates.  This is a small net (16 ft wide) that is held open by water pressure on otter doors (rectangular wood boards weighted with steel).  Most of this sampling takes place at night after ROV operations, but if the weather is too rough for the ROV, we will trawl during the day, sometimes in very deep water (1670 + m).  All of our tows are only 30 min, and this matches our data over the last 12 years, yielding a consistent data set for us to compare samples from the Gulf of Mexico to the Mid-Atlantic.  While the tows are short, the actual time to conduct deep-water tows can be long because the amount of wire we must let out is 2.5-3 times the water depth. For deep trawls we have out 4,000 m of wire; thus, one tow will require 5 hours of vessel time.

sorting the catch from the trawl

Kirstin Meyer sorts the catch from the trawl. Image courtesy of Liz Baird, Deepwater Canyons 2013 Expedition, NOAA-OER/BOEM/USGS

Despite this long time commitment, trawling can be very productive and can give us data not available from other methods.  For example, this project has many objectives related to deep-sea corals.  Our last two trawl samples from water depths around 1,600 m yielded a number of solitary corals, and most of these came up alive.  These would have been hard to find with the ROV or other gear, and they will be used by our genetics team, the coral biologist, for our trophic objectives, and for distributional data.  The trawl also gave us several species of invertebrates and fishes not yet seen on the cruise.  These are used for several purposes (feeding studies, reproduction biology, ecology).  All data are useful and fit together to give us a better understanding of this poorly known ecosystem.

working up the catch from the trawl

Science team members work up the catch from the trawl, including sorting, measuring and preserving the samples. Image courtesy of Liz Baird, Deepwater Canyons 2013 Expedition, NOAA-OER/BOEM/USGS

While trawls produce a lot of our seafood, and as noted above can be valuable for science, they can also cause damage to bottom habitats.  We have seen lost trawl nets in these canyons wrapped around rocks and corals.  In addition, large commercial trawls catch a lot of animals that are not used, are discarded dead, and are thus wasted.  Fishermen do not want to lose their gear and many are very concerned about conservation.  Technological improvements (better bottom maps, better navigation, sensors on nets) are allowing trawling to become more efficient and less damaging; future improvements will continue to help these valuable fisheries.

3 Comments leave one →
  1. May 12, 2013 12:15 pm

    You mentioned that damage can be detected in the deep water canyon area where trawlers have lost equipment and left their “footprint” in the habitats. Are any offshore areas protected from commercial fishing like National Parks are protected on land?

    • lizbaird permalink
      May 13, 2013 2:38 pm

      from John Tomczuk
      Thank you for your good question. Similar to National Parks on land, Marine Protected Areas (MPAs) serve to protect and conserve our marine resources. However, the approaches for setting aside MPAs vary from region to region and are complex to say the least. They are based on the intended goals and objectives for these areas to provide regulatory control or prohibit specific types of activities known to harm the resources. An MPA by definition is considered any area of the marine environment that has been reserved by federal, state, territorial, commonwealth, tribal, or local laws or regulations to provide lasting protection for part or all of the natural and cultural resources therein.
      For example, in the South Atlantic region there are several deepwater MPAs established through a process between the Regional Fishery Council and the Federal government. The established MPAs are designed to protect a fish species and vary in size from a couple square miles to over several square miles. Additionally, in June 2010 new management measures based on years of research proposed by the region were approved to protect over 23,000 square miles of habitat (approximately twice the size of Maryland) as Coral Habitat Areas of Particular Concern (CHAPCs). These areas, CHAPCs contain a variety of habitat including deep-sea stony coral reefs and a range of fish species. The MPAs in return serve as an opportunity for scientists, resources managers, and policy makers to monitor the areas to learn more about the resources and ocean health, as well as track their effectiveness.

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