http://lod.bco-dmo.org/id/dataset/2789
eng; USA
utf8
dataset
Highest level of data collection, from a common set of sensors or instrumentation, usually within the same research project
Biological and Chemical Oceanography Data Management Office (BCO-DMO)
Unavailable
508-289-2009
WHOI MS#36
Woods Hole
MA
02543
USA
info@bco-dmo.org
http://www.bco-dmo.org
Monday - Friday 8:00am - 5:00pm
For questions regarding this resource, please contact BCO-DMO via the email address provided.
pointOfContact
2009-06-25
ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data
ISO 19115-2:2009(E)
Low-Profile, Low-Bycatch Gillnets, Gulf of Maine, Stellwagon Bank, 2000-2002: catch data from F/V Lady Irene NEC-MP2000-1 in the the Gulf of Maine from 2000-2002 (NEC-CoopRes project)
2005-09-01
publication
2005-09-01
revision
BCO-DMO Linked Data URI
2005-09-01
creation
http://lod.bco-dmo.org/id/dataset/2789
Michael Pol
principalInvestigator
Biological and Chemical Oceanography Data Management Office (BCO-DMO)
Unavailable
508-289-2009
WHOI MS#36
Woods Hole
MA
02543
USA
info@bco-dmo.org
http://www.bco-dmo.org
Monday - Friday 8:00am - 5:00pm
For questions regarding this resource, please contact BCO-DMO via the email address provided.
publisher
Cite this dataset as: Pol, M. (2005) Low-Profile, Low-Bycatch Gillnets, Gulf of Maine, Stellwagon Bank, 2000-2002: catch data from F/V Lady Irene NEC-MP2000-1 in the the Gulf of Maine from 2000-2002 (NEC-CoopRes project). Biological and Chemical Oceanography Data Management Office (BCO-DMO). (Version final) Version Date 2005-09-01 [if applicable, indicate subset used]. http://lod.bco-dmo.org/id/dataset/2789 [access date]
Low-Profile, Low-Bycatch Gillnets, Gulf of Maine, Stellwagon Bank, 2000-2002: catch data Dataset Description: <h3>Testing of Low-Profile, Low-Bycatch Gillnets</h3>
<p><strong>Project Leader</strong>:<br />
<em>Michael Pol, </em>Massachusetts Division of Marine Fisheries<br />
<strong>Additional Project Participants:</strong><br />
<em>H. Arnold Carr, </em>Massachusetts Division of Marine Fisheries<br />
<em>Robert MacKinnon, </em>Massachusetts Gillnetters' Association</p>
<p>"Two experimental gillnets were tested that are designed to reduce or eliminate the bycatch of cod while targeting flatfish species. Both experimental designs reduce the vertical profile of the nets in the water. One experimental design modifies a foam-core floatline by adding lead every few feet; the other net replaces the gillnet's floatline with another leadline so that the net lies nearly completely on the bottom. Both are 8 meshes deep (MD) and have different floatation and hanging ratios. The nets were quantitatively compared to standard gillnets (25 MD) to determine their effectiveness in reducing cod bycatch. The nets with lower vertical profiles have been shown to reduce the catch of legal cod, but not discarded cod. Catch rates of flatfish could not be compared, due to low catch numbers. Filming with an underwater camera indicated that the orientation of the nets was different than anticipated. Research has continued on these gillnets with additional funding the Northeast Consortium in FY2001." <em>extracted from: Summary of Completed Cooperative Research Projects Funded by the Northeast Consortium, January 2006</em></p>
<p><strong>Parameter names and Descriptions</strong> each with a different form of flotation on the headline.<br />
A: had floats<br />
B: had foamcore and lead<br />
C: had foamcore only<br />
D: second leadline in place of floatline "NK" indicates species "not known".</p>
<p>Related data objects:<br />
<a href="http://nec.whoi.edu/jg/serv/nec/Gear/gillnets_summary.html0%7Bdir=nec.whoi.edu/jg/dir/nec/Gear/,info=nec.whoi.edu/jg/info/nec/Gear/gillnets_summary%7D">Total weights from all net configurations</a><br />
<a href="http://nec.whoi.edu/jg/serv/nec/Gear/gillnets_temp.html0%7Bdir=nec.whoi.edu/jg/dir/nec/Gear/,info=nec.whoi.edu/jg/info/nec/Gear/gillnets_temp%7D">Gillnet bottom temperatures </a></p> Methods and Sampling: <p>Several important conclusions can be drawn from these results. First, we confirm that the traditional industry-developed cod and flatfish gillnets are each effective at targeting cod and flatfish; the cod gillnet was especially selective for legal-sized cod, with a small bycatch of spiny dogfish. The relatively small bycatch of spiny dogfish differs from He's (2006) similar study, although this difference may be due to densities of dogfish rather than gear design. Secondly, the experimental designs reduced cod catches in the flatfish gillnet by 49% and 58%, demonstrating that the floatline modifications were effective in avoiding cod. Catches of cod below MLS, following removal of one anomalous set, were reduced at levels approaching the 0.05 significance level. Catches of legal-sized yellowtail and winter flounder in experimental nets were not different from catches in the standard flatfish gillnet. Further, catches of undersized winter flounder were also significantly lower in the experimental designs. These results Testing of Low-Profile, Low Cod-Bycatch Gillnets 16 indicate that adoption, mandated or voluntary, of the modified gillnet designs would lead to reductions in cod bycatch compared to standard flatfish gillnets.</p>
<p>The lengths of flatfish caught in the experimental gillnets, as reflected in lengthfrequency distributions, were not different from the standard flatfish gillnet. This result indicates that adoption of these designs would not lead to any reduction in the landed value of flatfish catches due to size differences. In short, evidence was found to reject the first null hypothesis and, with the caveats of one anomalous set and p-values close to 0.05 in the case of sublegal cod, that the experimental designs do catch cod (above and below MLS) at a lower rate than the standard flatfish net (Hypothesis 1). No evidence was found to refute the null hypothesis for cod length that all flatfish designs would catch cod of similar lengths (Hypothesis 2). No evidence was found to refute Hypothesis 3 (All flatfish designs, experimental and standard, would catch flatfish at similar rates) for yellowtail above and below MLS, and winter flounder above MLS. It was rejected for winter flounder below MLS. Lastly, no evidence was found to reject Hypothesis 4. All flatfish nets caught similar lengths of flatfish. The experimental nets therefore performed as hoped, improving the standard flatfish design by reducing cod bycatch, while also reducing winter flounder below MLS, too.</p>
Funding provided by National Oceanic and Atmospheric Administration (NOAA) Award Number: ZZ-487
completed
Michael Pol
508-990-2860x116
1213 Purchase St., 3rd floor
New Bedford
MA
02740
USA
mike.pol@state.ma.us
pointOfContact
asNeeded
Dataset Version: final
Unknown
haul_group
year_start
ship
trip_id
month_local
day_local
year
date_local
lat
lon
net_config
haul
set_begin_date
set_begin_hr
haul_end_date
haul_end_hr
duration
total_species_caught
species
kd_flag
weight
Gillnet
theme
None, User defined
No BCO-DMO term
year_start
ship
month_local
day_local
year
date_local
latitude
longitude
species scientific name (binomial)
featureType
BCO-DMO Standard Parameters
Gillnet
instrument
BCO-DMO Standard Instruments
NEC-MP2000-1
service
Deployment Activity
the Gulf of Maine
place
Locations
otherRestrictions
otherRestrictions
Access Constraints: none. Use Constraints: Please follow guidelines at: http://www.bco-dmo.org/terms-use Distribution liability: Under no circumstances shall BCO-DMO be liable for any direct, incidental, special, consequential, indirect, or punitive damages that result from the use of, or the inability to use, the materials in this data submission. If you are dissatisfied with any materials in this data submission your sole and exclusive remedy is to discontinue use.
NorthEast Consortium
http://northeastconsortium.org/
NorthEast Consortium
The Northeast Consortium encourages and funds
cooperative research and monitoring projects in the Gulf of Maine and Georges Bank that have effective,
equal partnerships among fishermen, scientists, educators, and marine resource managers.
At the 2008 Maine Fisheremen's Forum, the Northeast Consortium organized a session on data collection and availability. Participants included several key organizations in the Gulf of Maine area, sharing what data are out there and how you can find them.
The Northeast Consortium has joined the Gulf of Maine Ocean Data Partnership. The purpose of the GoMODP is to promote and coordinate the sharing, linking, electronic dissemination, and use of data on the Gulf of Maine region.
The Northeast Consortium was created in 1999 to encourage and fund effective, equal partnerships among commercial fishermen, scientists, and other stakeholders to engage in cooperative research and monitoring projects in the Gulf of Maine and Georges Bank. The Northeast Consortium consists of four research institutions (University of New Hampshire, University of Maine, Massachusetts Institute of Technology, and Woods Hole Oceanographic Institution), which are working together to foster this initiative.
The Northeast Consortium administers nearly $5M annually from the National Oceanic and Atmospheric Administration for cooperative research on a broad range of topics including gear selectivity, fish habitat, stock assessments, and socioeconomics. The funding is appropriated to the National Marine Fisheries Service and administered by the University of New Hampshire on behalf of the Northeast Consortium. Funds are distributed through an annual open competition, which is announced via a Request for Proposals (RFP). All projects must involve partnership between commercial fishermen and scientists.
The Northeast Consortium seeks to fund projects that will be conducted in a responsible manner. Cooperative research projects should be designed to minimize any negative impacts to ecosystems or marine organisms, and be consistent with accepted ethical research practices, including the use of animals and human subjects in research, scrutiny of research protocols by an institutional board of review, etc.
NEC
largerWorkCitation
program
Northeast Consortium: Cooperative Research
http://northeastconsortium.org/
Northeast Consortium: Cooperative Research
<p>The Northeast Consortium encourages and funds cooperative research and monitoring projects in the Gulf of Maine and Georges Bank that have effective, equal partnerships among fishermen, scientists, educators, and marine resource managers.</p>
<p>The Northeast Consortium seeks to fund projects that will be conducted in a responsible manner. Cooperative research projects are designed to minimize any negative impacts to ecosystems or marine organisms, and be consistent with accepted ethical research practices, including the use of animals and human subjects in research, scrutiny of research protocols by an institutional board of review, etc.</p>
NEC-CoopRes
largerWorkCitation
project
eng; USA
oceans
the Gulf of Maine
2005-09-01
Georges Bank, Gulf of Maine
0
BCO-DMO catalogue of parameters from Low-Profile, Low-Bycatch Gillnets, Gulf of Maine, Stellwagon Bank, 2000-2002: catch data from F/V Lady Irene NEC-MP2000-1 in the the Gulf of Maine from 2000-2002 (NEC-CoopRes project)
Biological and Chemical Oceanography Data Management Office (BCO-DMO)
Unavailable
508-289-2009
WHOI MS#36
Woods Hole
MA
02543
USA
info@bco-dmo.org
http://www.bco-dmo.org
Monday - Friday 8:00am - 5:00pm
For questions regarding this resource, please contact BCO-DMO via the email address provided.
pointOfContact
http://lod.bco-dmo.org/id/dataset-parameter/13645.rdf
Name: haul_group
Units: unknown
Description: <p>sampling phases -- hauls grouped by time of the year</p>
http://lod.bco-dmo.org/id/dataset-parameter/13646.rdf
Name: year_start
Units: unknown
Description: <p>the year the sampling started for each sampling interval</p>
http://lod.bco-dmo.org/id/dataset-parameter/13647.rdf
Name: ship
Units: unknown
Description: <p>name of ship setting haul</p>
http://lod.bco-dmo.org/id/dataset-parameter/13648.rdf
Name: trip_id
Units: unknown
Description: <p>unique identifier for each ship/vessel trip</p>
http://lod.bco-dmo.org/id/dataset-parameter/13649.rdf
Name: month_local
Units: unknown
Description: <p>month of year, local time, (from date_local)</p>
http://lod.bco-dmo.org/id/dataset-parameter/13650.rdf
Name: day_local
Units: unknown
Description: <p>day of month, local time, (from date_local)</p>
http://lod.bco-dmo.org/id/dataset-parameter/13651.rdf
Name: year
Units: unknown
Description: <p>year local time (from date_local)</p>
http://lod.bco-dmo.org/id/dataset-parameter/13652.rdf
Name: date_local
Units: unknown
Description: <p>date the net was hauled up and the fish were removed, local time,<br /> reported as mo/day/yr.</p>
http://lod.bco-dmo.org/id/dataset-parameter/13653.rdf
Name: lat
Units: unknown
Description: <p>latitude associated with trip_id</p>
http://lod.bco-dmo.org/id/dataset-parameter/13654.rdf
Name: lon
Units: unknown
Description: <p>longitude associated with trip_id, negative = West</p>
http://lod.bco-dmo.org/id/dataset-parameter/13655.rdf
Name: net_config
Units: unknown
Description: <p>"treatment" -- Four strings of eight nets each were set, <br />each with a different form of flotation on the headline. <br />A: had floats <br />B: had foamcore and lead <br />C: had foamcore only D: second leadline in place of floatline</p>
http://lod.bco-dmo.org/id/dataset-parameter/13656.rdf
Name: haul
Units: unknown
Description: <p>the order in which the four gillnet strings were recovered</p>
http://lod.bco-dmo.org/id/dataset-parameter/13657.rdf
Name: set_begin_date
Units: unknown
Description: <p>date when nets were set</p>
http://lod.bco-dmo.org/id/dataset-parameter/13658.rdf
Name: set_begin_hr
Units: unknown
Description: <p>time when nets were set</p>
http://lod.bco-dmo.org/id/dataset-parameter/13659.rdf
Name: haul_end_date
Units: unknown
Description: <p>when hauling of endline begins</p>
http://lod.bco-dmo.org/id/dataset-parameter/13660.rdf
Name: haul_end_hr
Units: unknown
Description: <p>time when hauling of endline begins</p>
http://lod.bco-dmo.org/id/dataset-parameter/13661.rdf
Name: duration
Units: unknown
Description: <p>how long did the set last in hours</p>
http://lod.bco-dmo.org/id/dataset-parameter/13662.rdf
Name: total_species_caught
Units: unknown
Description: <p>includes both those kept and those discarded</p>
http://lod.bco-dmo.org/id/dataset-parameter/13663.rdf
Name: species
Units: unknown
Description: <p>common name of fauna caught <br />"NK" indicates species "not known".</p>
http://lod.bco-dmo.org/id/dataset-parameter/13664.rdf
Name: kd_flag
Units: unknown
Description: <p>disposition of the fish: (K)ept or (D)iscarded</p>
http://lod.bco-dmo.org/id/dataset-parameter/13665.rdf
Name: weight
Units: unknown
Description: <p>total weight of all fish caught, in pounds</p>
GB/NERC/BODC > British Oceanographic Data Centre, Natural Environment Research Council, United Kingdom
Biological and Chemical Oceanography Data Management Office (BCO-DMO)
Unavailable
508-289-2009
WHOI MS#36
Woods Hole
MA
02543
USA
info@bco-dmo.org
http://www.bco-dmo.org
Monday - Friday 8:00am - 5:00pm
For questions regarding this resource, please contact BCO-DMO via the email address provided.
pointOfContact
761301
https://datadocs.bco-dmo.org/file/A88rLkgh1gV3D4/lolo_gillnets.csv
lolo_gillnets.csv
Primary data file for dataset ID 2789
download
https://osprey.bco-dmo.org/dataset/2789/data/download
download
onLine
dataset
<p>Several important conclusions can be drawn from these results. First, we confirm that the traditional industry-developed cod and flatfish gillnets are each effective at targeting cod and flatfish; the cod gillnet was especially selective for legal-sized cod, with a small bycatch of spiny dogfish. The relatively small bycatch of spiny dogfish differs from He's (2006) similar study, although this difference may be due to densities of dogfish rather than gear design. Secondly, the experimental designs reduced cod catches in the flatfish gillnet by 49% and 58%, demonstrating that the floatline modifications were effective in avoiding cod. Catches of cod below MLS, following removal of one anomalous set, were reduced at levels approaching the 0.05 significance level. Catches of legal-sized yellowtail and winter flounder in experimental nets were not different from catches in the standard flatfish gillnet. Further, catches of undersized winter flounder were also significantly lower in the experimental designs. These results Testing of Low-Profile, Low Cod-Bycatch Gillnets 16 indicate that adoption, mandated or voluntary, of the modified gillnet designs would lead to reductions in cod bycatch compared to standard flatfish gillnets.</p>
<p>The lengths of flatfish caught in the experimental gillnets, as reflected in lengthfrequency distributions, were not different from the standard flatfish gillnet. This result indicates that adoption of these designs would not lead to any reduction in the landed value of flatfish catches due to size differences. In short, evidence was found to reject the first null hypothesis and, with the caveats of one anomalous set and p-values close to 0.05 in the case of sublegal cod, that the experimental designs do catch cod (above and below MLS) at a lower rate than the standard flatfish net (Hypothesis 1). No evidence was found to refute the null hypothesis for cod length that all flatfish designs would catch cod of similar lengths (Hypothesis 2). No evidence was found to refute Hypothesis 3 (All flatfish designs, experimental and standard, would catch flatfish at similar rates) for yellowtail above and below MLS, and winter flounder above MLS. It was rejected for winter flounder below MLS. Lastly, no evidence was found to reject Hypothesis 4. All flatfish nets caught similar lengths of flatfish. The experimental nets therefore performed as hoped, improving the standard flatfish design by reducing cod bycatch, while also reducing winter flounder below MLS, too.</p>
from Cruise: NEC-MP2000-1 Several important conclusions can be drawn from these results. First, we confirm
that the traditional industry-developed cod and flatfish gillnets are each effective at
targeting cod and flatfish; the cod gillnet was especially selective for legal-sized cod,
with a small bycatch of spiny dogfish. The relatively small bycatch of spiny dogfish
differs from He’s (2006) similar study, although this difference may be due to densities
of dogfish rather than gear design. Secondly, the experimental designs reduced cod
catches in the flatfish gillnet by 49% and 58%, demonstrating that the floatline
modifications were effective in avoiding cod. Catches of cod below MLS, following
removal of one anomalous set, were reduced at levels approaching the 0.05 significance
level. Catches of legal-sized yellowtail and winter flounder in experimental nets were not
different from catches in the standard flatfish gillnet. Further, catches of undersized
winter flounder were also significantly lower in the experimental designs. These results
Testing of Low-Profile, Low Cod-Bycatch Gillnets 16
indicate that adoption, mandated or voluntary, of the modified gillnet designs would lead
to reductions in cod bycatch compared to standard flatfish gillnets.
The lengths of flatfish caught in the experimental gillnets, as reflected in lengthfrequency
distributions, were not different from the standard flatfish gillnet. This result
indicates that adoption of these designs would not lead to any reduction in the landed
value of flatfish catches due to size differences. In short, evidence was found to reject the
first null hypothesis and, with the caveats of one anomalous set and p-values close to 0.05
in the case of sublegal cod, that the experimental designs do catch cod (above and below
MLS) at a lower rate than the standard flatfish net (Hypothesis 1). No evidence was
found to refute the null hypothesis for cod length that all flatfish designs would catch cod
of similar lengths (Hypothesis 2). No evidence was found to refute Hypothesis 3 (All
flatfish designs, experimental and standard, would catch flatfish at similar rates) for
yellowtail above and below MLS, and winter flounder above MLS. It was rejected for
winter flounder below MLS. Lastly, no evidence was found to reject Hypothesis 4. All
flatfish nets caught similar lengths of flatfish. The experimental nets therefore performed
as hoped, improving the standard flatfish design by reducing cod bycatch, while also
reducing winter flounder below MLS, too.
Specified by the Principal Investigator(s)
<p>Four types of gillnets were constructed for this study. Each gillnet was 91 m (300 ft) long. Two complete sets of nets (48 nets) were constructed. All reported gillnet characteristics are nominal. The standard flatfish, lead-added, and dual leadline nets were identically designed except for the construction of the floatline. Each type was constructed of light green (mesh size: 178 mm (7 in)), monofilament mesh webbing with a diameter of 0.47 mm, twenty-five meshes deep. The leadline was 91 m (50 fm) of 23 kg/183 m (50 lb/100 fm) leadline. The floatline of the standard flatfish net consisted of 91 m (50 fm) of 13 mm (0.5 in) diameter foamcore float line with built-in floatation (1.7 oz./yd (52.5 g/m)). The leadadded design was made with a floatline the same as the standard flatfish net, but with flat pieces of lead weight wrapped around the floatline every 9 m (5 fm). The dual leadline net was made with the floatline and leadline consisting of 91 m (50 fm) of 23 kg/ 183 m (50 lb/100 fm) leadline. This net had no floatline as it is normally defined. The standard cod net was used to determine if cod were present in the study area. It was designed following industry practice, and differed from the other three nets in color, twine diameter, leadline weight, and hanging ratio. It was constructed of light green monofilament mesh webbing (mesh size: 178 mm (7 in)) with a diameter of 0.57 mm, twenty-five meshes deep. The floatline was 91 m (50 fm) of 9.5 mm (0.375 in) twisted polyethylene (PE) floatline with one deepwater gillnet float every fathom, or fifty floats per net. Each float provided approx. 3 oz. (85 g) of flotation. The leadline was 91 m (50 fm) of 29 kg/ 183 m (65 lb/100 fm) leadline. Eight nets of the same design were tied into a string; one string of each design was set in the same general location. The geographical arrangement of the strings was changed each time the nets were hauled, based on a modified Latin square design to reduce bias. In general, strings were set and hauled following normal commercial fishing practice. However, soak times were limited to overnight (~24 h), shorter than standard when targeting flatfish. This shorter soak time was selected to allow more rapid testing and to increase survival of discarded fish. A 'set' was defined as each instance of a net being hauled and its catch quantified. Strings were fished on consecutive days whenever possible.</p>
<p>Testing was halted for safety reasons and scientific validity when weather conditions were poor. Bottom temperatures were collected by probes attached to nets during the May 2001 and February 2002 testing periods. Soak durations were defined as the difference between the time when the setting of the nets began until the end of the hauling of the nets. On trips where the gear was set and not hauled, set times were recorded by the vessel captain. When only the time that setting ended was recorded, an estimate of the begin time was made by using other set durations for that vessel. When no set time was recorded, soak times were estimated using water temperatures collected by sensors attached to three of the four nets, if available. Durations were used to normalize catches to lb/hr.</p>
<p>Modified box-and-whisker plots were constructed for catch rates (lb/hr) of cod and yellowtail flounder separately above and below minimum landing size (MLS) and for winter flounder above MLS. Box-and-whisker plots give a visual representation of the distribution of the catch rates for each net by set. The box ends are defined as the first and third quartile of all observed catch rates for that net. The median is a solid line through the box. The mean is represented by a plus sign. The whiskers at either end extend to the most extreme data point, except where those points exceed 1.5 times the length of the quartile box. More extreme points are shown as solid dots. Box-and-whisker plots typically cannot be used for hypothesis testing.</p>
<p>To determine the appropriate statistical test, Bartlett's test for homogeneity of variance (Sokal and Rohlf 1995) was first employed; catch rates (lb/hr) were found to be heteroscedastic, making use of ANOVA or t-tests for catch comparisons inadvisable unless transformed. As an alternative to transforming data, the non-parametric randomization test (Sokal and Rohlf 1995, Rago 2004) was chosen to compare the catch of several species and size groups in each experimental net (lead-added and dual leadline) against the control, the standard flatfish net. Using this method, mean differences in catch rates were compared set-by-set for cod, yellowtail and winter flounders above and below MLS. Sets that had zero catches in all four designs were excluded from analysis.</p>
<p>The observed mean difference between the catch rate in each experimental string and the standard flatfish string for each set was compared to a distribution of 1000 or more differences determined from random assortments of the pool of catch data. The p-value was defined as the percentage of the mean differences more extreme than the observed difference. Length-frequencies of target species were pooled and compared between the standard net and each of the control nets using the Kolmogorov-Smirnov test (Sprent 1989). Sample sizes were adjusted for cluster effects following the methods of Pennington et al. (2001). One day of filming was conducted with an underwater remotely-operated vehicle (ROV) to examine the underwater profile of individual nets.</p>
from Cruise: NEC-MP2000-1 Four types of gillnets were constructed for this study. Each gillnet was
91 m (300 ft) long. Two complete sets of nets (48 nets) were constructed. All reported
gillnet characteristics are nominal.
The standard flatfish, lead-added, and dual leadline nets were identically designed
except for the construction of the floatline. Each type was constructed of light green
(mesh size: 178 mm (7 in)), monofilament mesh webbing with a diameter of 0.47 mm,
twenty-five meshes deep. The leadline was 91 m (50 fm) of 23 kg/183 m (50 lb/100 fm)
leadline.
The floatline of the standard flatfish net consisted of 91 m (50 fm) of 13 mm (0.5
in) diameter foamcore float line with built-in floatation (1.7 oz./yd (52.5 g/m)). The leadadded
design was made with a floatline the same as the standard flatfish net, but with flat
pieces of lead weight wrapped around the floatline every 9 m (5 fm). The dual leadline
net was made with the floatline and leadline consisting of 91 m (50 fm) of 23 kg/ 183 m
(50 lb/100 fm) leadline. This net had no floatline as it is normally defined.
The standard cod net was used to determine if cod were present in the study area.
It was designed following industry practice, and differed from the other three nets in
color, twine diameter, leadline weight, and hanging ratio. It was constructed of light
green monofilament mesh webbing (mesh size: 178 mm (7 in)) with a diameter of 0.57
mm, twenty-five meshes deep. The floatline was 91 m (50 fm) of 9.5 mm (0.375 in)
twisted polyethylene (PE) floatline with one deepwater gillnet float every fathom, or fifty
floats per net. Each float provided approx. 3 oz. (85 g) of flotation. The leadline was 91
m (50 fm) of 29 kg/ 183 m (65 lb/100 fm) leadline.
Eight nets of the same design were tied into a string; one string of each design
was set in the same general location. The geographical arrangement of the strings was
changed each time the nets were hauled, based on a modified Latin square design to
reduce bias. In general, strings were set and hauled following normal commercial fishing
practice. However, soak times were limited to overnight (~24 h), shorter than standard
when targeting flatfish. This shorter soak time was selected to allow more rapid testing
and to increase survival of discarded fish. A “set” was defined as each instance of a net
being hauled and its catch quantified.
Strings were fished on consecutive days whenever possible. Testing was halted
for safety reasons and scientific validity when weather conditions were poor. Bottom
temperatures were collected by probes attached to nets during the May 2001 and
February 2002 testing periods.
Soak durations were defined as the difference between the time when the setting
of the nets began until the end of the hauling of the nets. On trips where the gear was set
and not hauled, set times were recorded by the vessel captain. When only the time that
setting ended was recorded, an estimate of the begin time was made by using other set
durations for that vessel. When no set time was recorded, soak times were estimated
using water temperatures collected by sensors attached to three of the four nets, if
available. Durations were used to normalize catches to lb/hr.
Modified box-and-whisker plots were constructed for catch rates (lb/hr) of cod
and yellowtail flounder separately above and below minimum landing size (MLS) and for
winter flounder above MLS. Box-and-whisker plots give a visual representation of the
distribution of the catch rates for each net by set. The box ends are defined as the first and
third quartile of all observed catch rates for that net. The median is a solid line through
the box. The mean is represented by a plus sign. The whiskers at either end extend to the
most extreme data point, except where those points exceed 1.5 times the length of the
quartile box. More extreme points are shown as solid dots.
Box-and-whisker plots typically cannot be used for hypothesis testing. To
determine the appropriate statistical test, Bartlett’s test for homogeneity of variance
(Sokal and Rohlf 1995) was first employed; catch rates (lb/hr) were found to be
heteroscedastic, making use of ANOVA or t-tests for catch comparisons inadvisable
unless transformed. As an alternative to transforming data, the non-parametric
randomization test (Sokal and Rohlf 1995, Rago 2004) was chosen to compare the catch
of several species and size groups in each experimental net (lead-added and dual leadline)
against the control, the standard flatfish net.
Using this method, mean differences in catch rates were compared set-by-set for
cod, yellowtail and winter flounders above and below MLS. Sets that had zero catches in
all four designs were excluded from analysis. The observed mean difference between the
catch rate in each experimental string and the standard flatfish string for each set was
compared to a distribution of 1000 or more differences determined from random
assortments of the pool of catch data. The p-value was defined as the percentage of the
mean differences more extreme than the observed difference.
Length-frequencies of target species were pooled and compared between the
standard net and each of the control nets using the Kolmogorov-Smirnov test (Sprent
1989). Sample sizes were adjusted for cluster effects following the methods of
Pennington et al. (2001).
One day of filming was conducted with an underwater remotely-operated vehicle
(ROV) to examine the underwater profile of individual nets.
Specified by the Principal Investigator(s)
asNeeded
7.x-1.1
Biological and Chemical Oceanography Data Management Office (BCO-DMO)
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For questions regarding this resource, please contact BCO-DMO via the email address provided.
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Gillnet
Gillnet
PI Supplied Instrument Name: Gillnet PI Supplied Instrument Description:Two experimental gillnets were tested that are designed to reduce or eliminate the bycatch of cod while targeting flatfish species. Both experimental designs reduce the vertical profile of the nets in the water. One experimental design modifies a foam-core floatline by adding lead every few feet; the other net replaces the gillnet's floatline with another leadline so that the net lies nearly completely on the bottom. Both are 8 meshes deep (MD) and have different floatation and hanging ratios. The nets were quantitatively compared to standard gillnets (25 MD) to determine their effectiveness in reducing cod bycatch. Instrument Name: Gillnet Instrument Short Name:Gillnet Instrument Description: Gillnetting uses curtains of netting that are suspended by a system of floats and weights; they can be anchored to the sea floor or allowed to float at the surface. A gillnet catches fish by their gills because the twine of the netting is very thin, and either the fish does not see the net or the net is set so that it traps the fish. Community Standard Description: http://vocab.nerc.ac.uk/collection/L05/current/65/
Cruise: NEC-MP2000-1
NEC-MP2000-1
F/V Lady Irene
vessel
NEC-MP2000-1
Michael Pol
http://northeastconsortium.org/ProjectFileDownload.pm?report_id=564&table=project_report
Report describing NEC-MP2000-1
F/V Lady Irene
vessel