NEFSC Trawl Warp
and Gear Performance Review
Updated 1/22/03

Survey Trawl
Experiment Data

Jan 13-14 Workshop
Working Papers


Trawl Performance
Oct. 2-3



Invited participants

consensus report

Trawl Observation
Cruise Concludes

Survey Trawl
Observation Cruise

Experimental Design

Scientific Party

What does
the survey say
about Cod?

Warp Declaration
CLF et al. V. Evans

Delaware II Warp Measurements

Albatross IV Warp Measurements

Survey Gear Types

Albatross IV

Delaware II

Why Conduct
Research Vessel

Fishermen's Reports

NOAA Office
of Marine Aviation
and Operations

NEFSC Main Page

WHAT HAPPENED? Acting on the advice of industry members, we inspected the trawl cables (warp) on the NOAA Ship Albatross IV' s sampling equipment on September 3, 2002.

We found that the marks on the cable attaching scientific survey gear to the vessel were not at true 50 m length intervals they are intended to indicate. The marks are used by the vessel crew to determine how much cable is deployed. The cable was most recently replaced in February 2000, and used in eight bottom trawl surveys, beginning with Winter 2000 and ending with Spring 2002.

WHAT HAVE YOU DONE ABOUT IT? The cable has been correctly marked and installed, and is in use on the Autumn 2002 survey. Similar measures were made on the NOAA Ship Delaware II on 9/16-17/02. Those marks are all within 1 m or less of true 25 and 50 m intervals, varying randomly between less than 1" and 38.4". The cable has been remarked using methods similar to those used to remark the Albatross's cable.

The NOAA Administrator, Vice Admiral (ret.) Conrad C. Lautenbacher, has issued further directives to all vessels NOAA uses for trawl surveys to perform similar checks and intends to revisit ship procedures to assure consistent operations.

HOW DID IT HAPPEN? We are investigating this further along with NOAA's Office of Marine and Aviation Operations (OMAO), the line office of NOAA responsible for vessels and vessel operations. It appears that the wire was either not marked correctly upon installation, or that its configuration has changed with use.

WHAT DOES IT MEAN? At times more cable was deployed on one side of the trawl net than on the other.

This is a matter of inches at shorter lengths, and more pronounced as more cable is deployed. For example, with 100 m (328 ft) of cable deployed, just under 1 inch more cable was out on one side; at 300 m (984 ft) the difference was just under 6 ft. Of all tows made in the surveys, 75% deploy 300 m of cable or less.

As a result, the gear may have fished differently from prior surveys, and data collected (catch per tow, for example) may have been influenced in a way that should be accounted for before those data are used by scientists. When we understand what the effect was, we can likely compensate if the differences are significant.

WILL THIS CHANGE THE SCIENTIFIC ADVICE ON STOCK STATUS? We don't know. When we better understand if there was an effect, and how significant it may have been, we can answer that question.

WHEN WILL YOU KNOW? We are working on this problem now. A preliminary review of existing data sets does not reveal an obvious effect attributable to the change in cable. However, it will take time to reliably document how the gear performed and how that might have influenced catch.

HOW WILL YOU KNOW? Through field work with the gear and by analyzing data collected pre- and post-cable change.

Field work: The NOAA Ship Albatross IV is presently conducting the 2002 Autumn bottom trawl survey. Between September 13 and 16, video equipment and additional net sensor equipment was brought aboard. Work is ongoing to properly install and test this equipment. Beginning September 25, the video and net sensor equipment will be used in experimental tows to both directly and numerically document net performance. Individuals from the region's commercial industry and the fishery management councils will be part of the scientific crew during these observations. Additional work will then be conducted which will further document gear performance. This work will be nested within ongoing research cruises throughout October.

Analyses: Directly following the experimental work, a workshop will be convened to examine the data collected and produce a report. The workshop will be public, with invited members to include scientists familiar with fishery survey practices, commercial fishermen and gear providers, the region's fishery management councils.. The workshop will produce a report that can then be used in updating groundfish assessments as planned during mid-October.

We are reanalyzing data sets from the last two year's surveys now to look for an effect by species, geographic area, or depth. We are looking at any data sets that might provide a basis for identifying and quantifying this effect, if any: Canadian survey indices on Georges Bank, inshore state surveys, any differences between observed and predicted indices derived from our most data-rich indices, and analyses simulating the effect in assessments across species and age groups.

WHAT IS YOUR "GUT" FEELING ABOUT THE EFFECTS ON SURVEY RESULTS? It is important that we know, not speculate.

Over the 40 year history of the survey, we have performed several major recalibrations of the gear in order to keep our results consistent within the time series. If we can detect and quantify this effect, we can likely account for it as well.

WHAT WILL YOU DO WITH NEW INFORMATION? We will use it to update any analyses that have already been performed and make revised information available.

DOES THIS MEAN THERE IS MORE COD? Too early to say. However, the relative trends in cod stocks derived from the survey to date agree with similar trends derived from Canadian surveys and from state inshore surveys for the years in question.

WHAT DOES THIS MEAN FOR AMENDMENT 13? We are obligated to act on the best available scientific information and intend to do so. The present FMP development allows for incorporation of new biological and fishery-based information. Much depends on three factors: how quickly the effect of gear misrigging on survey results can be reliably quantified, whether there is an effect attributable to cable differences, and how significant the effect is.
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(File Modified Feb. 05 2007)