NOAA TECHNICAL MEMORANDUM

NMFS-SEFC-254

Evaluation of the Impacts of Turtle

Excluder Devices (TEDS) on Shrimp

Catch Rates in the Gulf of Mexico

and South Atlantic, March 1988

through July 1989

BY

Maurice Renaud, Gregg Gitschlag, Edward Klima,

Arvind Shah, James Nance, Charles Caillouet,

Zoula Zein-Eldin, Dennis Koi and Frank Patella

U.S. DEPARTMENT OF COMMERCE

Robert A. Mosbacher, Secretary

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

John A. Knauss, Administrator

NATIONAL MARINE FISHERIES SERVICE

William W. Fox, Jr., Assistant Administrator for Fisheries

MAY 1990

This Technical Memorandum series is used for documentation and timely communication

of preliminary results, interim reports, or similar special-purpose information. Although

the memoranda are not subject to complete formal review, editorial control, or detailed

editing, they are expected to reflect sound professional work.
NOTICE:

The National Marine Fisheries Service (NMFS) does not approve, recommend

or endorse any proprietary product or material mentioned in this publication.

No reference shall be made to NMFS, or to this publication furnished by

NMFS, in any advertising or sales promotion which would indicate or imply

that NMFS approves, recommends, or endorses any proprietary product or

proprietary material mentioned herein or which has as its purpose any intent

to cause directly or indirectly the advertised product to be used or purchased

because of this NMFS publication.

This report should be cited as follows:

Renaud, Maurice, Gregg Gitschlag, Edward Klima, Arvind

Shah, James Nance, Charles Caillouet, Zoula Zein-Eldin,

Dennis Koi and Frank Patella. 1990. Evaluation of the

Impacts of Turtle Excluder Devices (TEDS) on Shrimp

Catch Rates in the Gulf of Mexico and South Atlantic,

March 1988 through July 1989. NOAA Technical

Memorandum, NMFS-SEFC-254

Copies may be obtained by writing:

National Marine Fisheries Service

Galveston Laboratory

4700 Ave. U

Galveston, TX 77551
TABLE OF CONTENTS

EXECUTIVE SUMMARY .................................................... iv

INTRODUCTION .......................................................... 1

MATERIALS AND METHODS ................................................. 3

Recruitment of Vessels ................................................ 3

Positioning of Net Types .............................................. 3

Identification of Study Sites ............................................ 4

Observer Training ..................................................... 5

Gear Tuning/Control Tows .............................................. 6

Data Collection ....................................................... 6

Shrimp ............................................................ 7

Commercial Shrimp Catch .......................................... 8

Fish ............................................................. 8

Sea Turtles ...................................................... 9

Other Catch ..................................................... 10

Tow Duration .................................................... 10

Bottom Type ..................................................... 10

TEDS and Trawling Equipment ..................................... 10

Gear Performance ................................................ 11

Seasons ......................................................... 11

Statistical Analyses ................................................. 12

Multivariate Analyses ........................................... 12

General Linear Model Analyses ................................... 12

Additional Analyses ............................................. 13

Biological Models ............................................... 13

RESULTS .............................................................. 15

Descriptive Data Summary ............................................. 15
Trips ........................................................... 15

Paired Data ..................................................... 15

Performance of TED-equipped and Standard Nets........................ 16

CPUE Comparisons with the Commercial Fleet........................ 18

Correlations .................................................... 18

Multivariate Paired T-test ........................................... 19

Multivariate Paired t-test for Quad-rigged Vessels by Tow..........19

Multivariate Paired t-tests for Quad-rigged Vessels by Trips.......22

Multivariate Paired t-tests for Twin-rigged Vessels by Tow.........24

General Linear Model Analyses ......................................... 24

Paired Data ..................................................... 24

Quad-rigged Trawl Data Paired by Tow ............................ 26

Quad-rigged Trawl Data Paired by Trip ........................... 26

Twin-rigged Trawl Data Paired by Tow ............................ 27

Twin-rigged Trawl Data Paired by Trip ........................... 27

Quad-rigged vs Twin-rigged Vessels .............................. 27

Overall ......................................................... 27

Turtle Captures ...................................................... 28

Biological Yield Models .............................................. 30

DISCUSSION ........................................................... 31

Gear Performance ..................................................... 32

Relationships Between Standard and TED-Equipped Nets....................33

Comparison Between Standard and TED-equipped Nets.......................34

Seasons ......................................................... 34

Areas ........................................................... 35

Net Type ........................................................ 36

ii
Biological Model ..................................................... 37

Turtle Capture ....................................................... 40

SUMMARY .............................................................. 44

ACKNOWLEDGMENTS ..................................................... 48

REFERENCES ........................................................... 50

LIST OF TEXT TABLES .................................................. 53

LIST OF TEXT FIGURES ................................................. 55

TEXT TABLES .......................................................... 57

TEXT FIGURES ......................................................... 74

LIST OF APPENDICES ................................................... 96

APPENDIX I ........................................................... 98

APPENDIX II ......................................................... 146

APPENDIX III ........................................................ 153

iii
EXECUTIVE SUMMARY

Trained National Marine Fisheries Service observers

collected information from March 1988-July 1989 on catch rates of

shrimp and finfish from commercial shrimp vessels voluntarily

participating in this study. Data were compared between TEDequipped nets (Georgia TED with and without an accelerator

funnel) and standard shrimp nets. This represents partial

fulfillment of OMB and House Appropriations Committee

requirements with respect to TEDS and their economic impact on

the shrimp fishery.

This report summarizes preliminary results through July

1989, including 4159 hours of fishing time. When the study is

completed in September 1990, a comprehensive economic analysis

Will be completed with these data by Texas A&M University.

Fishing areas, times and length of tows were controlled by the

vessel captain. The catch rates of the vessels participating in

the program were not significantly different than the catch rates

of commercial shrimp fleets fishing in the same area during the

same time frame. We feel that the results of this observer

program are representative and meaningful in terms of the

evaluation of TEDS under commercial conditions.

Standard and TED-equipped nets appeared to operate similarly

with respect to types and frequency of problem tows. Whe n

problems with the fishing gear occurred, the TED-equipped nets

lost more shrimp and finfish than standard nets.

Differences in the CPUEs between standard and TED-equipped

iv
nets were compared using multivariate paired t-tests. Overall, a

10% loss of shrimp was experienced for quad-rigged vessels,

whereas, the overall loss for twin-rigged vessels was about 2%.

In general, for quad-rigged vessels, there were significant mean

differences in the paired catch rates between the standard and

TED nets for both shrimp and finfish. In all cases, the overall

mean differences between CPUEs of standard and TED nets were

positive, indicating the standard nets caught more shrimp and

finfish than TED-equipped nets. The mean differences in the

seasonal shrimp catch rates were less than 0.9 lbs/hr, without

including trynet data and 1.4 lbs/hr with trynet catch added to

the trailing net. Shrimp CPUEs ranged seasonally from a gain of

0.1 lbs/hr to a loss of 1.4 lbs/hr. CPUEs vary seasonally and

only during the winter months were there no significant

differences in the overall shrimp catch rates between standard

and TED-equipped nets; during all other seasons, differences were

significant. The overall finfish CPUEs were 74.0 and 64.5 lbs/hr

for standard and TED nets, respectively, or a mean difference of

9.4 lbs/hr.

Significant differences were noted between the shrimp catch

rates of the two TED types. When the Georgia TED without a

funnel was compared with a standard net, the catch rate for the

standard net was 7.2 lbs/hr and 5.9 lbs/hr for the TED-equipped

net, or a difference of 1.3 lbs/hr. The Georgia TED with the

funnel caught 5.9 lbs/hr compared to 6.7 lbs/hr for the standard

net, or a difference of 0.7 lbs/hr.

V
For twin-rigged vessels, the overall shrimp CPUE with TEDequipped nets ranged from 2% better than the standard net to 18%

worse than the standard nets with a trynet adjustment. No

significant difference was observed in the overall catch rates

between TED and standard nets for twin-rigged vessels.

Yield was modeled to determine what impact various levels

of shrimp loss would have on the overall population. Overall

decrease of 10% in fishing mortality rate resulted in no

detectable change in the overall yield of both brown and white

shrimp fisheries and a 2% decrease in the yield for the pink

shrimp fishery.

A total of 40 turtles were caught in the observer program,

of which 27 were caught along the Atlantic coast and 13 were

caught in the Gulf of Mexico. Nine of the 40 turtles came aboard

unconscious and 36 were released alive. The estimated total

capture of turtles using 1988 fishing effort is 14,112 for the

Gulf of Mexico and 14,986 turtles for the Atlantic Ocean. The

capture rate of sea turtles in the Gulf of Mexico was similar to

earlier studies, but apparently declined in the Atlantic.

vi
Evaluation of the Impacts of Turtle Excluder Devices (TEDS)

on Shrimp Catch Rates in the Gulf of Mexico and South Atlantic,

March 1988 through July 1989

Prepared by

Maurice Renaud, Gregg Gitschlag, Edward Klima,

Arvind Shah, James Nance, Charles Caillouet,

Zoula Zein-Eldin, Dennis Koi, and Frank Patella

INTRODUCTION

The National Marine Fisheries Service (NMFS) promulgated

regulations which required the use of Turtle Excluder Devices

(TEDs) on offshore shrimp vessels beginning in June 1987 (Federal

Register, 1987), depending upon vessel size, geographic location,

and fishing area. Due to a series of judicial, Congressional and

administrative actions, TED regulations were not fully

implemented region-wide until May 1, 1990.

Both the Office of Management and Budget (OMB) and the House

Appropriations Committee in 1988 required certain studies and

reports relating to TED use and testing and evaluating the

impacts of TED use on fishermen and sea turtles. The OMB

required a study on whether or not TEDS are effectively excluding

turtles and the House Appropriations Committee required a study

on the full economic impact of TEDS. This report is in partial

fulfillment of both those requirements. NMFS, in cooperation

with the shrimp industry, initiated a TED Evaluation Program on

March 5, 1988. The overall goal of this program was to determine
the impacts of the utilization of certified TEDS on commercial

shrimp trawlers operating on the South Atlantic and Gulf of

Mexico coasts. Funding was provided by NMFS, the Marine

Fisheries Initiative program (MARFIN), and the Gulf and South

Atlantic Fisheries Development Foundation.

This program, initiated in March 1988, will continue through

September 1990. We are reporting on observations from March 1988

through July 1989. The program is aimed at comparing shrimp catch

rates of TED-equipped trawls with those of standard trawls

without TEDS in selected shrimp fishing areas of the southeast

region. For this purpose, trained observers were placed on

shrimp vessels operating off the coasts of Texas, Louisiana,

Mississippi, Alabama, Florida (Gulf and Atlantic), Georgia and

South Carolina. Results will be used in a comprehensive economic

analysis of the impact of TEDS on the shrimp industry which is

currently being conducted by Texas A&M University. The analysis

should be available by the end of this year.

Specific objectives of the TED evaluation program are to:

1) Compare catch rates of shrimp for TED-equipped trawls

and standard trawls without TEDS in representative

shrimp fishing areas of the Gulf and Atlantic coasts of

the U.S. by season,

2 ) Provide data, results and a biological simulation model

to the Economics Analysis Branch of the NMFS for an

economic evaluation of impacts of TEDS.

2
MATERIALS AND METHODS

Recruitment of Vessels

Vessels were recruited through the assistance of NMFS port

agents, NOAA Sea Grant Marine Advisory Agents, regional shrimp

associations and industry contacts. Participation in the study

by shrimpers was strictly voluntary. Vessels and crews were not

government leased or chartered. A payment of $lOO/day was

sometimes provided by the Gulf and South Atlantic Fisheries

Development Foundation, generally when TEDS were not required by

law. This was an incentive for vessel owners to allow NMFS

personnel to collect data while on board their vessels. All

participating vessels had appropriate federal authorization to

use TEDS in one-half the trawls when a NMFS observer was on

board. Eighteen shrimp vessels used in the study were quadrigged (two trawls towed on each side), and one was twin-rigged

(one trawl towed on each side). Analyses of data from quadrigged and twin-rigged vessels will be discussed separately.

Positioning of Net Types

Trips were designed initially to have a TED-equipped net

paired with a standard net on each side of the vessel. The

assignments of TEDS to inboard or outboard positions were made

with the assumption that these positions would be reversed on

subsequent trips. Several vessels refused to participate unless

we placed the TEDS in certain configurations. Consequently, we
have recorded almost every possible TED and standard net position

configuration.

Identification of Study Sites

Initially, observers were placed on shrimp vessels in each

of the four major Gulf of Mexico offshore fishing areas:

Louisiana, Texas, south Florida, and Alabama-Mississippi. Of 600

planned observer days, 240 were scheduled for Louisiana, 200 for

Texas, 100 for Florida and 60 for Mississippi-Alabama. The

respective percentages of combined five year (1981-1986) shrimp

landings from these fishing areas were 49%, 33%, l0%, and 8%. We

intended that areas with higher production be allotted greater

amounts of observer effort, although not necessarily in direct

proportion to production. Planned observer effort was increased

somewhat in Alabama-Mississippi and in the primarily hard bottom

south Florida area to provide sufficient data for statistical

analysis of TED performance under the special conditions

encountered in these areas. One hundred observer days were also

scheduled for the South Atlantic. Observer days were targeted

for the peak regional shrimping seasons in each area.

The study depended on shrimpers volunteering to let NMFS

personnel collect data on board their vessels. Due to limited

response by shrimpers, we collected data from virtually any

vessel whose owner or captain would allow us aboard. Since one

of the principal objectives of this study was to evaluate the

effect of the use of TEDS on commercial shrimping, the shrimpers

decided where and when to fish and which certified TED to use.

4
Our only NMFS stipulations were that the shrimper had to use

federally approved TEDS and to keep catches from each net

separated from each other.

Observer Training

All observers were required to have at least a bachelors

degree in science and some college course work in biology. The

observers received general training in the form of:

1) presentation of background information on TED research, 2)

review of TED Regulations, 3) review of diagrams of trawls and

TED's, 4) discussions on how changes in trawling gear affect the

fishing configuration and shrimp catchability of trawls

(published material also provided for reference), 5) discussions

of general procedures for the TED study, 6) review of diagnostic

keys for identification of sea turtles, shrimp and fish 7) review

of detailed instructions for filling out all data sheets, 8)

discussions of the most common errors made on data sheets and how

to avoid them, and 9) presentations of the guidelines for

summarizing data into trip reports and trip summaries for outside

circulation. Approximately 12 hours of video tapes were utilized

to familiarize observers with sea turtle biology, shrimp trawling

activities, terminology of trawling gear, effects of gear

alterations on shrimp catchability of trawls, a variety of TEDS,

installation procedures for TEDS, the performance of TEDS

underwater and a special video showing all of the required

procedures for data collection.
Observers also received two to three days of intensive

training aboard shrimp vessels. This included all procedures

necessary to collect data and fill out data sheets properly. A

review of the identification of shrimp and fish species was also

made at this time. After their training was completed, observers

were dispatched from the NMFS Galveston Laboratory to commercial

shrimping vessels working off the coasts of South Carolina,

Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas.

Gear Tuning and Control Tows

The fishing efficiency of all nets used in this study was

standardized by NMFS or Texas A&M Sea Grant gear specialists

during a participating vessel's initial trip. Control tows were

made using standard nets which were adjusted to catch

approximately-equal amounts of shrimp. Vessel captains were

briefed by gear specialists about the proper installation of

TEDS. Once TEDS were installed, the gear specialist made

necessary modifications to the rigging for the proper operation

of the TED, based upon his experience and observation of similar

catch rates between standard and TED-equipped nets. This

procedure was usually accomplished in 2-3 days. The captain was

responsible for gear tuning after the departure of the gear

tuner. Variation in the tuning ability of captains can

contribute to variation seen in the TED data.

Data Collection

Every phase of the operation was explained to captains to

insure that they understood exactly what data NMFS needed to

6
collect. Otherwise every effort was made to minimize the

observers influence on normal fishing activities. The primary

requirement was that catches from each net be kept separated from

all others so the total weight of shrimp from each trawl could be

recorded. Captains of the vessels were requested to examine the

data collected by the NMFS observer and to sign the data sheets

to verify their accuracy. Copies of the completed data sheets

were mailed to the vessel captain and owner for their record.

Shrimp. If necessary, the back deck of the vessels was

partitioned into sections with wooden beams to prevent the

catches of the trawls from mixing. A sample of approximately 50

pounds was shovelled from the contents of each trawl into

standard sized plastic shrimp baskets (70 lb capacity). Thus a

quad-rigged vessel produced four samples per tow and a twinrigged two samples per tow. Shrimp and fish were separated from

each sample. The total weight (to the nearest lb) of brown,

pink, and white shrimp (Penaeus sp.) combined was recorded for

each net for each tow. Another weight was recorded for each

additional commercial shrimp species. In order for total weights

to be standardized, the observer noted catch as heads on or heads

off.

For each net the number of shrimp (heads on) in

approximately 5 lb of the basket sample was recorded. Observers

were instructed in selecting a representative group of shrimp

that was not biased according to shrimp size. In those cases in

which the shrimper discarded small shrimp, procedures were
modified to include only the size range of shrimp retained by the

shrimpers.

For one tow each day, total length (length from tip of

rostrum to tip of telson) in mm was measured for a representative

sample of 200 shrimp. Fifty shrimp came from each net if the

vessel was quad-rigged or 100 shrimp from each net if the vessel

was twin-rigged. Shrimp with broken telsons, broken tails,

broken rostrums, and crushed shrimp were not measured. These

samples included all sizes of shrimp captured by the trawl

including the size ranges not kept by the shrimper.

Commercial Shrimp Catch. Catch per unit effort (CPUE) in

lbs/day, heads off, from NMFS port agent interviews of the shrimp

fishery were compared with CPUE data from our observer trips.

These comparisons were used to determine the similarity between

this study's CPUEs and those reported by the commercial fleet

from the same areas and times.

Fish. The most abundant finfish species was inferred for

each trawl by casual observation. A group weight was recorded

for the fish sorted from the basket sample taken from each

trawl. For each trawl, a combined weight was recorded of all

fish too large to fit into the basket. Since the total weight of

shrimp was also recorded for each trawl, the total weight of fish

per trawl could be estimated assuming direct proportion:

8
weight, Ss = sample shrimp weight, St = total shrimp

weight, and FL = combined weight of fish too large to

fit in basket.

Once each day (usually the last tow), finfish in basket

samples taken from one TED-equipped and one standard trawl were

sorted by selected species, counted, and weighed by species. The

selected species included Atlantic croaker, spot, seatrout (all

species), longspine porgy, flounder (all species), snapper (all

species), mackerel (all species), redfish and grouper (all

species). All other fish species were weighed together as a

miscellaneous category. Beginning in mid-1989, additional MARFIN

funding allowed for increased fish sampling aboard some Gulf of

Mexico vessels. Once each day, every fish in the basket sample

taken from each trawl of a given tow was measured and identified

to species.

Sea Turtles. For each turtle caught, the date, location,

depth of capture, type of net (TED-equipped, standard or try

net), species, length (straight and curved), width (straight and

curved), weight (if possible), and condition (conscious,

unconscious, fresh dead, dead but not fresh) were recorded. All

turtle sightings were also noted. Dead turtles were 1) marked

with spray paint, flipper-tagged and returned to the sea for

possible return through the sea turtle stranding and salvage

network (STSSN) or 2) returned to the laboratory for autopsy.

Living turtles were flipper-tagged and released.
Other Catch. For each trawl a group weight was recorded for

each species (other than commercial shrimp) which was retained

aboard for consumption or sale. This included catch such as

lobster, stone crab, blue crab, red snapper, flounder, etc. When

a species was arbitrarily removed from one trawl but also

appeared in other trawls, or if it was not possible to determine

which trawl the catch came from, then the group weight was

recorded for all trawls combined.

Tow Duration. Tow duration was defined as the time the

brake was set on the winch at the beginning of the tow to the

time when the winch was engaged and the brake released to

retrieve the trawl from the bottom.

Bottom Type. Bottom type was characterized as rough or

smooth and hard or soft. If nets were snagged or torn, then the

bottom was considered rough. A smooth bottom, such as mud or

shell hash, had little or no topographic relief and would not

snag or tear nets. When in doubt, the vessel captain was

consulted. Hard bottom was defined as any bottom other than mud,

and mud was considered soft bottom.

TEDS and Trawling Equipment. TEDS were characterized as to

type, panel bar spacing, presence or absence of an accelerator

funnel (Appendix III, Figure l), size of opening to exclude

turtles, etc. In some areas, when TEDS were repeatedly bent.

during fishing activities new TEDS constructed from larger gauge

pipe were purchased to minimize the problem. Prior to making

experimental tows, a variety of measurements such as length of

10
headrope and footrope, lazy lines, leglines, size of trawl mesh

and other data were recorded to characterize each trawl. This

allowed for the standardization of shrimp and fish catch between

vessels using different sizes of gear. If a trawl was later

modified by captain or crew, the modifications were also

recorded.

Gear Performance. Each net was characterized by an

operation code based on its performance in the water (Appendix

II, Table 1). A net towed without incident was coded 'Z'. Other

codes were used to describe any problems encountered, such as

tangling of trawl doors, the cod end bag coming untied, etc. Two

codes were occasionally required to describe trawl performance.

Information on debris clogging the TEDS was recorded.

Debris was defined as items that were caught in the trawl which

required special effort to remove and/or discard. Some of these

included large loggerhead sponges, tree trunks or branches,

tangled cable, lobster pots, and TV sets.

Not all data were used in the analyses of shrimp and fish

catch. Data from nets with operation codes A, B, C, E, F, L, M,

O, S and Z and combinations were used for analyses. Codes D, G,

H, I, J, K, N, P, Q, R, T and U reflect uncollected data or nonTED related problems affecting catch so these data were not used

in analyses.

Seasons. For analytical purposes seasons were defined as

winter (DEC-FEB), spring (MAR-MAY), summer (JUN-AUG) and fall

(SEP-NOV).

11
Statistical Analyses

Multivariate Analyses. Multivariate paired t-tests were

performed on paired data to test the null hypothesis of equal

catch per unit effort (CPUE, lbs/hr) for shrimp and finfish

simultaneously for both the standard and TED-equipped trawls.

Data were paired either by tow or by trip for quad-rigged and

twin-rigged vessels for these analyses. This test is discussed

in detail by Morrison (1976). The null hypothesis was:

Univariate adjusted paired t-tests were. performed whenever the

above null hypothesis was rejected. Also, the confidence

intervals on each of the parameters (stated in the above null

hypothesis) were constructed.

General Linear Model Analyses. General linear model (GLM)

analyses were performed on four data sets, including quad-rigged

and twin-rigged vessels, each with TED-equipped and standard

trawls paired by tow and by trip using SASTM, (Statistical

Analysis System, SAS Institute, Inc., Cary, N.C.). The GLM was

used to compare standard and TED-equipped nets. The dependent

variables used in the GLM analyses included differences between

standard and TED-equipped nets for catch, ln(catch), CPUE and

ln(CPUE), ratios of catches and CPUEs in TED-equipped and

standard nets and the logarithmic transformations of these ratios

12
and shrimp loss (gain) rates in TED-equipped nets as compared to

standard nets.

Milliken and Johnson (1984) discussed GLM methods,

underlying assumptions, problems and interpretations for

unbalanced experiments in multiway treatment structures with

missing data such as the paired data from the TED evaluation

study. A discussion of the GLM methods, assumptions and analyses

used in this study is included in Appendix I.

Additional Analyses. Other statistical analyses of the data

included frequency distributions, correlations, linear

regressions, t-tests and paired t-tests, mean, standard

deviation, confidence intervals and other descriptive statistics

(Sokal and Rohlf, 1981).

Biological Models. Deterministic population models were

produced for all three shrimp species by linking a Ricker-type

yield per recruit model to recruitment estimates that were

independent of parent stock (Ricker, 1975; Nichols, 1984; Nance

and Nichols, 1988). Recruitment level was set at the geometric

mean for the 1960-1988 period. Averages of estimates for 1985-

1988 fishing mortality (F) derived from virtual population

analysis were used as the baseline for current conditions. Yield

estimates were made for all three species for a range of "F"

multiplier, values ranging from 0-2 by 0.002 increments. Tables

of these yield estimates were used to determine effects of TED

equipped nets on the overall shrimp yield in the Gulf of Mexico.

13
This was possible because yield estimates (Yt are a direct result

of fishing mortality rates (Royce, 1972). The yield model was:

Yt = Ft Nt Wt dt

where,

Nt is the number of animals (R) in a cohort

subject to fishing (F) and natural (M)

mortality at a given time (t),

the formula is:

Ft is the fishing mortality at a given time

Wt is the average weight of an individual at time

t, estimated from growth equations.

Fishing mortality rate (F) is the product of two separate

variables; i.e., a catchability coefficient (q) and directed

nominal fishing effort (f).

F = q f

TED-equipped nets influence fishing mortality by affecting shrimp

catchability and not fishing effort (f). Any percentage change

in shrimp catchability caused by TED-equipped nets is assumed to

be directly reflected by an equal percentage change in fishing

mortality. This is based on an assumption of direct

proportionality between change in CPUE and change in q. Thus,

any change in CPUE as a result of TED use is translated into a

proportional change in q.

14
RESULTS

Descriptive Data Summary

Trips. For each geographic area, the frequency of trips is

shown by season (Figs. 1 and 2). Of 32 trips in the Gulf of

Mexico, 27 trips employed Georgia TEDS equipped with accelerator

funnels and 5 trips employed Georgia TEDS without funnels. This

contrasts with the Atlantic coast where funnels were used on only

1 trip of 16. Most trips occurred during the summer which, along

with the fall, is generally considered part of the peak shrimping

season in all areas except southwest Florida where highest shrimp

production occurs during winter and early spring. In the Gulf of

Mexico, 11 trips were made during summer, 8 in fall, 7 in winter

and 6 in spring. In the Atlantic, 12 trips were in the summer

and 4 in winter. The Morrison "Soft" TED, a NMFS-type TED, and a

homemade TED were used on a limited number of trips: however,

sample sizes were not large enough for analysis.

A twin-rigged vessel was only used in Texas. Three twinrigged trips were made during the fall and winter using the

Georgia TED without a funnel. Four trips were made in the fall

using a Georgia TED with a funnel.

Paired Data. When at least one TED-equipped net and one

standard net were towed simultaneously from a given vessel, the

resulting data were considered to be a valid pair. In cases

where two or more of either net type were towed, the data from

the like nets were averaged to create a single standard-TED pair.

15
During one trip, Georgia TEDS with and without funnels were

towed simultaneously. For this trip and for each tow, one of the

two TED-equipped nets was randomly selected along with a randomly

selected standard net to make a pair. Two artificial "subtrips" were created from the original trip - one contained the

Georgia TEDS with funnels and the other included Georgia TEDS

without funnels. Figures 3 and 4 show the frequencies of TEDstandard data pairs with usable operational codes by geographic

area and season.

In the Gulf of Mexico, information from 488 data pairs

(quad-rigged and twin-rigged combined) was collected from tows

using Georgia TEDS equipped with accelerator funnels, and 61

pairs without funnels. There were 22 data pairs in the Atlantic

for Georgia TEDS with accelerator funnels and 231 without

funnels. In the Atlantic, approximately 67% of the sampling was

during summer and the remainder during winter.

About 8% of the data pairs by tow were collected from a

twin-rigged vessel operating off the Texas coast. Thirty-six

data pairs by tow were collected in the fall for Georgia TEDS

equipped with funnels. Twenty-three data pairs were collected

during fall and 5 during winter for tows using Georgia TEDS

without funnels.

Performance of TED-equipped and Standard Nets. The total

number of nets towed was 3,808; 3640 tows on quad-rigged vessels

and 168 tows on twin-rigged vessels. Standard nets and nets

equipped with Georgia TEDS, with and without funnels, composed

16
3,641 of the 3,808 tows. The frequency of net tows (quad- and

twin-rigged vessels combined) with each operation code was

tabulated by TED type (Appendix II, Tables 2 and 3). Percentage

of successful tows, those with no gear-related problems

attributable to TEDS (Table 1) was similar between standard and

TED-equipped nets. About 93.7% of all standard net tows, 91.1%

of all net tows of Georgia TED-equipped nets without funnels, and

89.8% of all net tows of Georgia TED-equipped nets with

accelerator funnels were successful (Table 1). Thus the

differences in success between standard nets and TED-equipped

nets with and without funnels are 3.9% and 2.6% respectively.

Operation codes not included as successful represent tows with

problems that may or may not be associated with the presence of

TEDS. This represented only 6.3%, 8.9% and 10.2% of the net

tows for standard nets, Georgia TED-equipped nets without funnel,

and Georgia TED-equipped nets with funnel, respectively.

Operation code frequencies of net tows for TED-equipped and

standard nets were similar in all cases except for net tows with

codes F and O. One percent of standard net tows were coded F

(gear fouled, typically entangled in itself) compared with 5.1%

of net tows using Georgia TED-equipped nets without funnels and

1.3% of net tows using Georgia TED-equipped nets with funnels.

Code O (gear fouled on object or object caught in net) occurred

in 0.7% of standard net tows, 0.02% of net tows of Georgia TEDequipped nets without funnels, and 2.7% net tows of Georgia TEDequipped nets with funnels. Based on operation codes, it appears

17
that the percentages of successful tows were very similar between

standard nets and nets equipped with Georgia TEDS with or without

funnels.

CPUE Comparisons with the Commercial Fleet. Average CPUE of

shrimp calculated on a trip by trip basis for standard nets

monitored on commercial vessels participating in the TED observer

program was compared to CPUE for standard nets on other

commercial vessels fishing in the same areas and time.

Information on non-participating commercial vessels was obtained

through interviews by NMFS port agents. Values were summarized

by season and statistical subarea (Table 2, Appendix III, Figure

2). Standard net CPUEs of commercial vessels with observers were

not significantly different (P = 0.65) from CPUEs on other

commercial vessels. In four of seven cases, overall shrimp catch

from standard nets on TED observer vessels had a higher CPUE than.

standard nets on other commercial vessels. Four of the

comparisons ranged between -4.0 and +8.2 lb per hr and three

comparisons were within 1.5 lb per hour (Table 2). It is felt

that TED observer vessels were representative of other commercial

vessels in the fleet fishing in similar places at the same time.

Correlations. There were significant correlations between

standard and TED-equipped nets paired by tow (all areas, seasons,

and vessels; Appendix II, Tables 4 and 5) with respect to shrimp

catch, shrimp catch adjusted for try net catch, shrimp CPUE and

shrimp CPUE adjusted for try net catch (Figs. 5-8). Correlation

coefficients ranged from 0.91 to 0.95. No apparent differences

18
were observed among areas, seasons and vessels (quad-rigged or

twin-rigged).

Within standard and TED-equipped nets, significant

correlations were present between shrimp catch rates and fish

catch rates (pounds/tow and CPUEs) both for data adjusted with

try net catch and data not adjusted with try net catch (Figs. 9

and 10; Appendix III, Figs. 2-8). The adjustment for try net

catch was made by adding the shrimp weight (heads off) from the

try net to the shrimp weight (heads off) of the inboard net towed

on the same side as the try net. Although significance was

probably due to the large sample sizes, the small r values ranged

from 0.10 to 0.17.

Multivariate Paired T-test

Multivariate Paired t-test for Quad-rigged Vessels by Tow.

A multivariate paired t-test discussed by Watson et al. (1986)

was used on data paired by tow to compare TED-equipped and

standard nets with regard to shrimp and finfish CPUE. The data

collected for TED-equipped and standard nets during different

seasons, areas and TED types provide strong evidence to refute

the null hypothesis of no difference between the CPUE for shrimp

and finfish in standard versus TED-equipped nets. The

differences tested simultaneously for finfish and shrimp (Tables

3 and 4) were significant at P values usually much less than

0.01. The P value is the probability of obtaining differences at

least as large as the observed difference between CPUEs of TEDequipped and standard nets when the null hypothesis is true. P

19
values less than 0.05 are judged to be indicative of significant

difference. Significant mean differences were observed not only

when viewing the simultaneous comparisons of catch rates of TEDequipped and standard nets overall, but also for different

months, areas and times (day/night combinations). The only

exception was found during the winter period. However, rejection

of the null hypothesis does not indicate which of the two mean

differences, that for shrimp or for fish, have caused rejection

of the null hypothesis. The same methodology used by Watson et

al. (1986) and discussed by Morrison (1976) to control

experimental error rate was used here to test for shrimp and

finfish mean differences between the standard and TED-equipped

trawlsseparately. When viewing only the mean difference in CPUE

for shrimp, there were significant mean differences between TED

and standard nets for most comparisons. The only exceptions were

for the winter period, areas 9-12, statistical area 28 and

combined day and night trawls. This indicates that there was

usually a significant mean difference in shrimp CPUE between

standard and TED-equipped nets during most fishing operations

regardless of the TED type.

For the Gulf and South Atlantic combined, mean differences

of shrimp catch rate between standard and TED-equipped nets

appear to be slight; 10% overall for quad-rigged vessels and.2%

for twin-rigged vessels. The mean differences range from 0.5 to

0.9 lb per hour of fishing without including trynet catch. Mean

differences ranged from 0.7 to 1.3 lb per hour of fishing when

20
trynet catch was included. When adjustments for try net catch

were not included in the analysis, Georgia TEDS with funnels lost

an average 0.5 lb of shrimp per hour as compared to standard nets

and Georgia TEDS without funnels lost an average 0.9 lb of shrimp

per hour as compared to standard nets. Likewise, the mean

difference in the catch rates of finfish was significant between

the standard and TED-equipped nets, primarily due to a lower

catch rate for TED-equipped nets as compared to standard nets.

The finfish CPUE mean differences between TED-equipped and

standard nets ranged from 8.3 to 11.5 lb per hour. Although this

is a small mean loss, it clearly shows a significant reduction in

the finfish by-catch with the Georgia TED either with or without

a funnel.

All shrimp vessels normally fish with a try net in front of

one of their nets. In this volunteer study the positioning of

the nets was not directed by NMFS; therefore, the number of times

the try net would be positioned in front of a standard or a TEDequipped net was not randomly determined. In reviewing all of

the data, of a total of 877 paired tows in which a try net was

involved, 664 (76%) of these had the try net positioned in front

of the standard net, while only 213 (24%) were positioned in

front of the TED-equipped net (Table 5).

Try net catch was added to the net directly behind it.

Therefore, in 76% of the cases the catch was added to the

standard net and in only 24% of the cases was it added to the

TED-equipped net. Since these are quad-rigged vessels, it is

21
probably inaccurate to assume that all of the catch caught by the

try net would go into the net immediately behind it. Most

likely, were the try net not present, some of the shrimp would

have been captured by the outboard net. Therefore, we also

compared the mean CPUEs without try net catch added in for

standard and TED-equipped nets. Table 6 describes this

relationship. When the try net was in front of the standard net,

the mean catch rate of shrimp was 6.9 lbs per hour. However, the

catch rate for TEDS with and without funnels was the same, 5.9

lb/hr with or without try net in front of the TED-equipped net.

This shows that the try net had an effect of at least 6% (on the

average) on the catch rates of shrimp in the standard net,

therefore, corrections based on try net data increased the

difference between the standard and TED in all cases.

The mean difference in shrimp CPUE between TED-equipped and

standard nets (Table 7) was greater when there were problems with

the nets during a tow, than when there were none (1.4 lb vs 0.4

lb). This was also true for fish CPUEs (16.7 lb vs 7.3 lb).

Similar results were found when try net catches were added to the

inboard nets directly behind them.

Multivariate Paired t-tests for Quad-rigged Vessels by

Trips. Multivariate paired t-tests for quad-rigged vessels were

also conducted by trip. Results are listed in Tables 8 and 9.

In contrast to the analysis by tows, significant differences were

the exception rather than the rule. When try net adjustments

were not included, the overall CPUE mean difference between

22
standard and TED-equipped net was significant for both shrimp and

fish. However, one TED type (Georgia TED without a funnel)

showed a significant difference overall for shrimp alone as well

as fish alone, whereas the Georgia TED with a funnel had no

significantly different CPUE values. Thus, the null hypothesis

of no difference was not rejected for this TED type. There were

virtually no significant differences for shrimp CPUE by season

(except for summer) nor area except for statistical areas 30-

32. There were slightly different results when the try nets were

included in the analysis. Significant mean differences were

noted overall and by all TED types used.

Generally, the shrimp catch rate mean differences between

standard and TED-equipped nets were slight; without try nets the

mean differences ranged from 0.4 lb to 1.0 lb per hour and when

try net adjustments were included the mean differences ranged

from 0.7 lb to 1.2 lb per hour. Mean differences in the catch

rates of shrimp between the standard nets and TED-equipped nets

without funnels were the highest whether or not the try net

adjustment was included. Conversely, mean differences in catch

rates between standard and TED-equipped nets for the Georgia TED

with a funnel were 0.4 lb per hr without try net adjustment and

0.7 lb per hr with try net.

The mean differences in the catch rates of finfish were also

apparent when each TED type was compared to standard nets (a

difference of 3.9 lb per hour for Georgia TEDS with a funnel

compared to 12.0 lb per hour for Georgia TEDS without a funnel).

23
The TED-equipped net with funnel did not significantly reduce the

mean CPUE as compared to the standard net. However, TEDequipped nets without funnels did reduce CPUE significantly.

Multivariate Paired t-tests for Twin-rigged Vessels by Tow.

In contrast to the analysis performed for quad-rigged vessel

tows, significant mean differences were the exception rather than

the rule on the twin-rigged vessel (Table 10). One TED type

(Georgia TED without a funnel) showed a significant mean

difference overall, for shrimp alone, but not for fish alone.

The other TED type (Georgia TED with a funnel) had no significant

mean difference between CPUE values. There were no significant

mean differences overall, or for areas, month or day/night

combinations.

Shrimp catch rate mean differences between standard and TEDequipped nets ranged from negative 0.2 lbs per hour to 1.4 lbs

per hour. The Georgia TED without a funnel had the greatest mean

difference in catch rates.

Fish catch rate mean differences between standard and TEDequipped nets were all less than ±l.0 lb per hour. No

significant mean difference in fish catch between net types

occurred in this analysis.

General Linear Model Analyses

Paired Data. General linear model (GLM) analyses were

performed on paired data for standard vs TED-equipped trawls

(Appendix I, Tables 1-4). The four data sets analyzed were the

24
same as those in the multivariate paired t-test and were

represented by combinations of quad-rigged and twin rigged

trawlers, with TED-standard net pairings by tow and by trip. In

some cases, the great imbalance of the data sets (Appendix I,

Table 1) prevented evaluation of the effects of Region (R) or

Season (Q), but the effect of TED type (T) could be evaluated in

all four data sets (Appendix I, Tables 3 and 4). A complete

description of the variables, analyses, assumptions and results

is found in Appendix I.

Two sets of GLM analyses, one with and one without

adjustment for try net catches of shrimp (Table 11), used as

dependent variable the difference between natural logarithms of

shrimp catches in standard and TED-equipped trawls. In these

analyses, the independent variables and interactions in the GLM

accounted for greater proportions of variation in the dependent

variable than in the other models we tested (see Appendix I,

Table 3).

For all models tested, the residuals had a mean of zero,

thus fulfilling one assumption of the analysis (Appendix I, Table

3). However, those in which the difference between logarithms of

catches was used as the dependent variable (i. e. those with high

coefficients of determination) produced low coefficients of

skewness and kurtosis for the residuals, thus closely

approximating the additional assumption of normality of residuals

required for GLM analysis (Table 11). Among these models, those

in which region was the classification variable produced the

25
highest coefficients of determination, followed by those in which

season was the classification variable, and finally by those in

which TED type was the classification variable (Table 11). This

indicated that more variation in these dependent variables was

accounted for by region than season, and more by season than TED

type.

Quad-rigged Trawl Data Paired by Tow. When the Least

Squares Means (LSMs) of these best dependent variables for quadrigged trawlers with data paired by tow were tested to determine

whether they differed from zero, the LSMs for the difference

between logarithms of shrimp catches were not significantly

different from zero for Georgia TEDS without funnels, for regions

18-21; 1-8, and >21, and season (Table 12). Still fewer LSMs

were not significantly different from zero when the try net

adjustment was applied, including those for regions 9-12, l-8 and

>21, and seasons spring and fall. Thus, the adjustment for try

net catch affected the results of the comparison between the

logarithms of shrimp catch in standard and TED-equipped trawls by

reducing the number of cases in which LSMs were significantly

different from zero.

Quad-rigged Trawl Data Paired by Trip. For quad-rigged

vessel data paired by trip, LSMs of the difference between

logarithms of shrimp catches were not significantly different

from zero for regions 9-12, l-8 and >21 and seasons winter and

spring (Table 12). The LSM for fall was not estimable due to

data imbalance.

26
Twin-rigged Trawl Data Paired by Tow. For twin-rigged

vessel data paired by tow, the effects of region and season could

not be tested by GLM due to data imbalance, so only TED type was

used as a classification variable (Table 11). For data paired by

tow, the LSMs of the difference between logarithms of shrimp

catches were not significantly different from zero for both TED

types when there was no adjustment for try net catch of shrimp,

and the LSM for Georgia TEDS with funnels did not differ

significantly from zero when the try net adjustment was made

(Table 12).

Twin-rigged Trawl Data Paired by Trip. For twin-rigged

vessel data paired by trip, none of the LSMs for differences

between logarithms of shrimp catches differed significantly from

zero for the two TED types, both with and without the try net

correction (Table 12).

Quad-rigged vs Twin-rigged Vessels. General results for

twin-rigged trawls paired by tow and for both quad-rigged and

twin-rigged trawls paired by trip undoubtedly were affected by

the smaller sample sizes (Appendix I, Table 1). Also the

sampling unit in the study was the tow. Therefore, GLM analyses

of data paired by tow should be considered superior to those for

data paired by trip.

Overall. In no cases were the negative LSMs (i.e. those

suggesting a gain in natural logarithm of shrimp catch by TEDequipped trawls) significantly different from zero (Table 12).

27
Turtle Captures

Forty sea turtles (alive or fresh dead) were captured on

vessels participating in this study. They consisted of 32

loggerheads (Caretta caretta), 6 Kemp's ridleys (Lepidochelys

kempi), and 2 hawksbills (Eretmochelys imbricata). Thirty-five

were caught in standard shrimp trawls, 4 in try nets and 1 in a

TED-equipped trawl (Table 13, Fig. 11). Refer to Appendix III

(Figs. 9-12) for the seasonal breakdown of turtle captures. The

loggerhead caught in the TED-equipped trawl was entangled in the

accelerator funnel. It was subsequently tagged and released

alive. Four of the turtles (2 loggerheads, 1 Kemp's ridley and 1

hawksbill) captured in standard shrimp trawls could not be

revived after several hours of resuscitation and were presumed

dead. Three of these were painted and thrown overboard. One

loggerhead was autopsied within 2 days of capture, but the

internal organs were too decomposed for analysis. No painted

carcasses were reported by the Sea Turtle Stranding and Salvage

Network. The remaining 36 turtles were tagged and released

alive. Three turtles were captured off Louisiana, 10 off the

west coast of Florida, 23 off the east coast of Florida, 3 off

Georgia and 1 off South Carolina. No turtles were captured off

Texas.

Catch rates of turtles in standard shrimp nets varied by

region and season (Table 14). Four turtles captured in try nets

were not used in the calculations for this Table. Fishing effort

was standardized to 100 ft headrope per tow using the formula,

28
Turtle mean CPUE (R) and its 95% confidence interval (C.I.) were

calculated according to Snedecor and Cochran (1967) for ratio

estimates using the formula,

The total annual capture of turtles by the commercial shrimp

fleet was projected using the 5 million hours of fishing effort

in the Gulf of Mexico and 0.5 million hours of fishing effort in

the Atlantic for calendar year 1988 (Table 14). Effort values

from 1988 were used for our projection since fishing effort in

the Gulf of Mexico has been increasing at a rate of approximately

7.5% per year since 1980; Atlantic effort, although fluctuating

as compared to the Gulf of Mexico, was also high in 1988. Based

on 5 million hours of fishing effort, we estimated 14,112 turtle

captures by the commercial fleet in the offshore Gulf of Mexico

during 1988, and 14,986 turtle captures in 0.5 million hours of

29
fishing effort in the Atlantic. Mortality rates for turtles

captured in trawls cannot be accurately estimated because

survival of released turtles us unknown.

Biological Yield Models

Ricker-type (Ricker, 1975) yield models for each of the

three major shrimp species show the same basic curve shape (Nance

et al. 1989). The curves shown in Fig. 12 are very flat around

the region where yield estimates are plotted for current fishing

mortality rates (F-multiples = 1.0). Thus, with current fishing

patterns and current fishing mortality rates, little increase or

decrease in yield is predicted with the minor reductions in F

that would be expected due to small losses of shrimp by TEDS.

A decrease of 10% in F (loss of 10% of shrimp catch with a

TED-net compared to a standard net) would result in an estimated

0% change in overall-yield in both the brown and white shrimp

fisheries and a 2% decrease in the yield for the pink shrimp

fishery. A decrease of 20% in F would result in an estimated

decrease in overall yield of 1% in the white shrimp fishery, 2%

in the brown shrimp fishery and 5% in the pink shrimp fishery.

These estimated decreases in overall yield for each fishery are

so small that year to year variability in recruitment and growth

rates would tend to overshadow any losses from TED usage.

30
DISCUSSION

This report is based on data collected by NMFS observers

during cooperative cruises with the shrimp industry participants.

Since this was a voluntary program, area and time of sampling

could not be controlled, resulting in great imbalances in the

data set by region, season and TED type. During the first year

of the study we focused our efforts on primarily one design and

obtained relatively good coverage for Georgia TEDS with and

without funnels.

Along the Atlantic coast we had adequate samples from

Georgia TEDS without funnels, but virtually no samples from

Georgia TEDS with funnels. There was high sampling effort during

the summer and winter months, but almost no sampling during

spring and fall. Conversely, in the Gulf of Mexico most sampling

was with Georgia TEDS with funnels and very little sampling with

Georgia TEDS without funnels. We collected sufficient data off

the Texas coast during the peak shrimping seasons of summer and

fall, and off the southwest Florida coast during peak shrimping

seasons of winter and spring. However, off the Louisiana coast,

we obtained minimal information during summer and fall, the time

of peak shrimp abundance in that area.

In general, the results are functions of the type of TED

predominating in an area and the specific times and places

fished. Catch rates for TEDS along the Atlantic coast are

31
characteristic of the Georgia TED without funnel, the primary

gear tested in that area, and catch rates in the Gulf of Mexico

reflect Georgia TEDS with funnels. Thus, there is confounding

among area (Atlantic, Gulf of Mexico), TED-type and season.

Gear Performance

Overall, there was a high degree of similarity in shrimp

catchability between TED-equipped and standard nets. When there

were problems with both the TED-equipped and standard nets, TEDequipped nets lost proportionally more shrimp and finfish than

standard nets. Standard nets, even with problems, retained more

of the shrimp and finfish catch than the TED-equipped nets. Any

debris that clogged or choked the net would undoubtedly affect

the performance of an operating TED, either keeping the door open

continually or jamming the door so that both shrimp and finfish

could easily escape. Standard nets did not have an escape door

through which shrimp and fish could exit. When problems were

encountered, catch rates were reduced by approximately 1.4 lbs/hr

for shrimp, and by around 16.7 lbs/hr for finfish. However, the

overall percentage of problems was low both with and without

TEDS, with good gear performance about 90% for all nets.

Although there are areas within the Gulf and Atlantic where

tow problems are more frequent, for example, the rough bottom

areas of Florida's Tortugas fishing grounds, our sampling was not

adequate to document all these areas. Problems were more random

than systematic and occurred in both standard and TED-equipped

32
nets. Overall, there was a high degree of similarity in gear

performance between these types of nets. Further, we found that

the average catch per unit effort (CPUE) of observer boats was

similar to the CPUE of the commercial fleet for that given area

and time. Thus, our sampling efforts did represent commercial

shrimping at that time and for that given area. Therefore, the

results of this program are meaningful in terms of evaluation of

TEDS under commercial conditions.

Relationships Between Standard and TED-Equipped Nets

There was a very strong correlation (r ranged from 0.87 to

0.95) between the lbs of shrimp/hr caught in a standard net and

the lbs of shrimp/hr caught in a TED-equipped net for all areas,

seasons and vessels. This indicates a strong linear relationship

between catch rates of shrimp of both net types.

We also examined the relationship between the catch of

shrimp and fish. Although the r2

 values were low, the

correlations between the fish and shrimp catch rates were highly

significant. Because of the impact of fish on the shrimp catch,

we used the multivariate paired t-tests analysis as the "best"

statistical means for simultaneously comparing catch rates

between TED and standard nets.

General Linear Model (GLM) analyses for unbalanced data were

also performed. The "best" models were those in which the

dependent variable was represented by the difference between the

natural logarithm of shrimp catch in standard vs TED-equipped

nets, or the natural logarithm of the ratio of shrimp catches in

33
TED-equipped vs standard nets. Because of inherent difficulties

with interpretation of GLMs and the greatly imbalanced data sets,

we felt that these statistical tests were inferior to those of

the multivariate paired t-tests, but they provided another way of

describing differences between standard and TED-equipped nets.

Nevertheless, the results of the GLM indicated that more

variation in the dependent variables was accounted for by region

than season, and more by season than by TED type. They also show

that when mean differences were significant there was a shrimp

loss by TEDS, but gains in shrimp catch by TED-equipped nets were

not significant.

Comparison Between Standard and TED-equipped Nets

Seasons. The differences in the CPUEs using multivariate ttests for simultaneous evaluation of overall catch rates clearly

show significant mean differences between standard and TEDequipped nets. Further, there are significant mean differences

in the overall catch rates between the two TED types for both the

shrimp and finfish. We have plotted these differences to show

the relationship between standard and TED CPUEs by season, for

shrimp and finfish (Figs. 13 and 14). In all cases the shrimp

and finfish CPUEs for the TED were significantly less than CPUEs

for the standard net. However, the fact that the shrimp CPUE

mean differences were not very large is of practical importance.

CPUEs varied between seasons just as abundance of shrimp on the

fishery grounds also varies between seasons. The differences in

34
shrimp CPUE between net type varied seasonally and ranged from a

low of 0.1 lbs/hr in winter to a high 1.4 lbs/hr during summer.

The standard net caught, on the average, larger amounts of

finfish than the TED-equipped net for the same season (Fig. 14).

As an example, during the spring months the standard net caught

89.3 lbs/hr fish, whereas the TED-equipped net caught only 85.6

lbs/hr for a difference of approximately 3.7 lbs/hr; during the

summer months the standard net caught 69.3 lbs/hr and the TEDequipped net 53.9 lbs/hr or a difference of approximately 15.4

lbs/hr of fishing. This reduction in the finfish catch was

statistically significant during the summer months but not

significant during any other season.

Areas. We also examined the difference in catch rates

between standard and TED-equipped nets by geographical area.

Again, shrimp and finfish catch rates for TEDS were lower than

catch rates for the standard net. Differences in shrimp CPUE

between net types were significant in all areas except Cape

Canaveral. In the Cape Canaveral area (Fig. 15) the shrimp catch

rates for the standard net were 4.7 lbs/hr, whereas for the TEDequipped net it was 4.4 lbs/hr or a difference of only 0.3

lbs/hr. In other Atlantic coast areas the shrimp catch rates

averaged 8.8 lbs/hr in the standard net, but only 7.2 lbs/hr in

the TED-equipped net, a difference of 1.6 lbs/hr. Shrimp CPUE

differences by net type in the Gulf of Mexico were much less,

ranging from 0.5 lbs/hr to 0.8 lbs/hr.

35
Area differences may be confounded with those from net

type. Georgia TEDS without funnels predominated on vessels on

the Atlantic coast whereas those with funnels dominated in the

Gulf of Mexico. The effectiveness of the TED-type may influence

the catch rates of shrimp. By-in-large, gear specialists have

reported that the Georgia TED with funnel is more effective in

retaining shrimp than the same TED without a funnel (personal

communication, John Watson, NMFS, Pascagoula, MS).

Overall finfish catch rates differed significantly between

TED-equipped and standard nets. Comparisons by geographical area

showed significant differences for only a few areas (Fig. 16).

The catch rate of finfish by area was also different for TEDequipped or standard nets. The Louisiana coast of the Gulf of

Mexico had the highest finfish catch rates: 114 lbs/hr with the

standard net as compared to 110.9 lbs/hr for the TED-equipped

net, a difference of about 3.1 lbs/hr. Finfish catch rate

differed significantly between TED-equipped and standard nets

only in southwest Florida and the Atlantic coasts. The reason

for this difference is unclear. The Atlantic coast catch rates

were 82.6 lbs/hr for the standard net and 62.2 lbs/hr for the

TED-equipped net (a difference of 20.4 lbs/hr). In southwestern

Florida, rates were 46.9 lbs/hr and 40.3 lbs/hr for the standard

and TED-equipped net, respectively.

Net Type. Shrimp catch rates were reviewed for the two TED

types. Catch rate for the standard net was 7.2 lbs/hr versus 5.9

lbs/hr for the net equipped with a Georgia Jumper without a

36
funnel, a difference of 1.3 lbs/hr (Fig. 17). For quad-rigged.

vessels, the standard net caught 6.7 lbs/hr and the Georgia TED

with funnel caught 5.9 lbs/hr for a difference of 0.7 lbs/hr.

Overall, there appeared to be some dissimilarity in the shrimp

catch rate differences when the two TED types were compared (see

above).

For twin-rigged vessels, the catch rate for the standard net

was 9.9 lbs/hr versus 10.2 lbs/hr for the Georgia Jumper with a

funnel, however, without the funnel the Georgia Jumper's catch

rate was 5.2 lbs/hr versus 6.0 lbs/hr for the standard net (Fig.

18). A major difference was observed in the loss rate of shrimp

depending on the type of TED. The Georgia Jumper with the funnel

was clearly superior and showed no significant difference in

shrimp loss when compared to the standard net.

Likewise, the overall difference of finfish catch rates

between standard and TED-equipped nets were compared for each of

the two TED types (Fig. 19). These data showed a significant

reduction in fish catch for both TED types. The Georgia TED with

and without a funnel reduced the finfish catch rate by 11.5

lbs/hr and 8.3 lbs/hr, respectively.

Biological Model.

Shrimp catch rates by TED-equipped nets were usually lower

than those in standard nets and mean rates varied from 2% better

to 15% worse for quad-rigged vessels. When the catch of shrimp

in the try nets was added to the catch in the inboard net

immediately behind the try net, the results indicated that the

37
mean loss rate ranged from 3% loss to approximately 18% loss for

the Georgia TED without a funnel. As previously stated, we feel

that the try net adjustment is biased in favor of standard nets

because 76% of all the tows with the try net were in front of the

standard net and only 24% were in front of the TED-equipped net.

When we compared shrimp CPUEs between standard and TED-equipped

nets there was a 6% mean difference in catch rates with the try

net adjustment. Although there appears to be an inherent bias

within the try net adjustments, we have provided analyses both

with and without try net adjustments. Whether the range in the

CPUE data is +2% to -15% (e.g., without try net adjustments) or a

loss of 3-18%, there is, in every case except one, a loss in

shrimp catch rate. However, for twin-rigged vessels the overall

mean catch in shrimp CPUE was not significantly different between

TEDS and standard nets (Table 10). As discussed previously, the

multivariate paired t-test analysis shows that these differences

were significant overall. We have demonstrated that the shrimp

loss rate is relatively small practically, ranging from 0.2

lbs/hr to 1.6 lbs/hr, depending upon the area, season, and TED

type. Therefore, we have taken the opportunity to determine what

this loss rate would mean to total production in the shrimp

fishery. Yield curves have been generated for each of the shrimp

fisheries by using models to determine total yield with a variety

of different fishing pressures (Fig. 12). At present levels of

fishing effort (F-multiplier = 1.0) each curve is very flat to

either side (Nance et al., 1989). Thus, because of the flat38
topped nature of the curve at the present level of fishing, any

increases in fishing mortality rates would not increase the yield

of shrimp. Likewise, a decrease in fishing mortality rates of

10 or 20% would not significantly decrease the overall production

of shrimp.

We have assumed 1) that a shrimp escaping through either a

TED-equipped net or a standard net will not die because of that

episode (no increase in natural mortality rates), and 2) that

such escaping shrimp will join the remaining population, will

grow and experience the same natural mortality as the rest of the

stock. Phares (1978), describing the selectivity of shrimp nets,

showed a loss rate of shrimp varying by area and season, with an

extensive size range of lost shrimp. Therefore, we have assumed

that mortality incurred by shrimp escaping from TED-equipped nets

would be no greater than that experienced from standard nets. In

fact, the survival rate of shrimp escaping from TED-equipped nets

might be increased because the opening in the TED-equipped net is

larger than the mesh openings in the cod end of a standard net.

If there were a decrease of 20% in the catch rate and this

translated to a fishing mortality decrease of 20%, we would

estimate a resultant decrease in overall yield of only 1% in the

white shrimp fishery, 2% in the brown shrimp fishery, and

approximately 5% in the pink shrimp fishery. By this we mean

that there is ample fishing effort on the grounds to capture the

animals for that given year-class, and that a reduction in the

fishing mortality rate due to loss of shrimp by TEDS will not

39
greatly affect the overall yield. Although this decrease may, in

fact, impact a given individual fisherman on any particular tow,

what he loses in that tow will still be available to him for

capture by succeeding tows that day or the next and might even be

accessible to him within the next couple of months.

The fishery yield could benefit overall if effort is

concentrated on young small emigrating shrimp that have growth

potential exceeding the reduction due to natural mortality. Thus

the overall yield could be enhanced through reduction in growth

overfishing (Klima et al., 1982; Nance et al., 1989; Nichols,

1982). The lowering of shrimp catch rates due to TEDS may not be

viewed as all unfortunate depending on the time of year when this

occurs.

Turtle Capture.

During the study, turtles were captured in all regions

except the western Gulf (statistical areas 18-21), an area where

we had considerable observer effort. This is not to imply that

turtles are not caught by shrimp trawlers off the state of Texas.

In May 1989, a commercial shrimper fishing off Freeport caught a

loggerhead turtle in approximately 10 fathoms of water. Further,

Henwood and Stuntz (1987) identified 16 loggerheads and 4 Kemp's

ridley turtles taken by shrimpers in the western Gulf for a catch

rate of 0.002±0.001 (turtles/net hour) for loggerhead turtles.

Whether the capture rate is at the same level today is unknown.

The data for strandings in 1986-1987 show a large number of

turtles along the Texas coast (Fig. 20). The proportion of those

40
strandings due to shrimping is unknown at present. However, the

turtle stranding rate decreased during June when the offshore

waters were closed to all shrimping except to daytime shrimping

in 0-4 fathoms. Most strandings occurred in March, April, May

and again in July and August and the remaining fall months. Up

to 51 of these strandings in 1986 were possibly related to

removal of oil platforms using explosives, as documented by Klima

et al. (1988). Since 1987, the removal of oil platforms has been

controlled by the Minerals Management Service and NMFS through a

Section 7 Consultation under the Endangered Species Act and an

intensive observer program. There have been no documented turtle

mortalities resulting from platform removals since that date.

At-sea capture of turtles was highest along the Atlantic

coast and especially high off Cape Canaveral and Mayport, FL.

Also, a high capture rate was found off southwest Florida on the

Sanibel fishing grounds. Three sea turtles were caught off the

panhandle of Florida during the spring of 1989.

In spring, loggerheads concentrate along the east coast of

Florida from Brevard to Palm Beach counties (Thompson, 1988). In

the fall, they migrate to southeast U.S. waters and the Gulf of

Mexico. In the Gulf of Mexico, loggerheads appear to concentrate

along the central-west coast of Florida. Aerial surveys during

the early to mid 1980s showed the ratio of loggerhead turtle

sightings for the northwestern Gulf to northeastern Gulf to be

about 1 to 25. Loggerheads also nest along the Florida west

41
coast, but only sporadically elsewhere along the Gulf of Mexico

coast.

Fishing effort in the Gulf of Mexico has been increasing at

a rate of approximately 7.5% per year since 1980 (Fig. 21); in

the Atlantic, fishing fluctuates greatly from year to year

depending upon the abundance of shrimp with no apparent trend

since 1982 (Fig. 22). Nevertheless, the fishing power in the

Atlantic and the Gulf of Mexico is at extremely high levels and

turtles that are found on shrimping grounds are certainly

vulnerable to capture by shrimp trawlers as calculated by Henwood

and Stuntz (1987). Those authors estimated 12,947 turtle

captures based on 4.3 million hours of fishing effort in the Gulf

of Mexico, and 33,871 turtle captures in 0.7 million hours of

fishing effort in the combined inshore and offshore of the

Atlantic. Our estimate of 14,112 turtles captured in the Gulf of

Mexico in 5 million hours accompanies a 16% increase in fishing

effort but only a 8% increase in captures. We estimated 14,986

turtle captures in the Atlantic based on 0.5 million hours of

offshore effort. Henwood attributes 67% of the Atlantic effort

to offshore fishing. Adjustment of their earlier results to

reflect only offshore effort reduces the capture estimate to

22,694 turtles in approximately 0.47 million hours. Our estimate

of 14,986 turtle captures represents a decrease of 34% despite a

6% increase in shrimping effort in the offshore Atlantic.

1

Personal Communication (1990), Dr. Terry Henwood, NOAA, SEFC,

NMFS, 9450 Koger Blvd., St. Petersburg, FL 33702.

42
Our data document turtle capture rates by season and area.

The data also clearly indicate that TEDS do significantly reduce

the capture of turtles by shrimp trawlers in commercial

operations.

43
SUMMARY

This report represents partial fulfillment of OMB and House

Appropriations Committee requirements with respect to TEDS and

their economic impact on the shrimp fishery. Information on the

performance of standard and TED-equipped nets was collected by

National Marine Fisheries Service (NMFS) observers placed on

commercial shrimp vessels in the Atlantic and Gulf of Mexico.

Vessel captains permitted NMFS observers to collect catch rate

and net performance information from simultaneously towed

standard and TED-equipped nets. Sampling areas, times and length

of tows were controlled by the captain. From March 1988 through

July 1989, a total of 48 trips encompassing 4,159 fishing hours

were conducted resulting in a total of 776 paired tows. All of

the data collected were used in the analyses with the exception

of cases when the cod end became untied, nets were badly torn or

non-TED related problems affected the catch.

Due to the voluntary nature of the program, we were unable

to control areas and times of sampling, so there were great

imbalances in the data set. Along the Atlantic coast, we

obtained adequate samples with Georgia TEDS without funnels but

virtually no samples with Georgia TEDS with funnels. There was a

dearth of sampling with Georgia TEDS without funnels along the

Gulf of Mexico; there was satisfactory sampling with Georgia TEDS

with funnels in most areas but only during peak fishing seasons.

44
Standard and TED-equipped nets appeared to operate similarly

with respect to types and frequency of problem tows. When

problems with the fishing gear occurred, the TED-equipped nets

lost more shrimp and finfish than standard nets.

The catch rates of the observer vessels participating in

this program were not significantly different from the catch

rates for the commercial fleets fishing in the same area during

the same time frame. Therefore, we feel that the results of this

observer program are representative and meaningful in terms of

the evaluation of two types of Georgia TEDS under commercial

conditions.

This voluntary program precluded choosing the location of

the try net. The captain made that decision and in 76% of the

tows, the captain located the try net in front of the standard

net. To compensate for the location of the try net we either

omitted its catch or added its catch to the trailing net. This

adjustment increased the catch in standard nets by 6% while

having no apparent effect in the catch of the TED-equipped net.

Multivariate paired t-tests were judged the most appropriate

means for comparing differences in the CPUEs between standard and

TED-equipped nets. In general, for quad-rigged vessels, there

were significant mean differences in the paired catch rates

between the standard and TED-equipped nets for both shrimp and

finfish. In all cases, the overall mean difference between CPUEs

of standard and TED-equipped nets were positive, indicating that

standard nets caught more shrimp and finfish than TED-equipped

45
nets.. The mean differences in the seasonal shrimp catch rates

were less than 0.9 lbs/hr without including try net data and 1.4

lbs/hr with try net catch added to the trailing net. Shrimp CPUE

ranged seasonally from a gain of 0.1 lbs/hr to a loss of 1.4

lbs/hr. CPUE varied seasonally and only during the winter months

were there no significant differences in the overall shrimp catch

rates between standard and TED-equipped nets. During all other

seasons differences were significant.

The overall finfish CPUEs were 74.0 and 64.5 lbs per hour

for standard and TED nets respectively or a mean difference of

9.4 lbs per hour.

Differences in shrimp and finfish catch rates between

standard and TED-equipped nets varied by geographic area, and in

all cases catch rates were less in TED-equipped than in standard

nets. Differences in the shrimp CPUE were significant in all

geographical areas with the exception of Cape Canaveral.

Significant differences were noted between the shrimp catch

rates of the two TED types. When the Georgia TED without a

funnel was compared with the standard net, the catch rate for the

standard net was 7.2 lbs/hr and 5.9 lbs/hr for the TED-equipped

net, or a difference of 1.3 lbs/hr. The Georgia TED with the

funnel caught 5.9 lbs/hr compared to of 6.7 lbs/hr for the

standard net, or a difference of 0.7 lbs/hr. Differences between

TED-types may be confounded with areal and seasonal factors.

The overall finfish catch rates were also significantly

reduced by both the Georgia TED with and without a funnel as

46
compared to a standard net. The mean differences were 8.3 and

11.5 pounds per hour respectively for the Georgia TED with and

without a funnel.

For twin rigged-vessels, the overall shrimp CPUE with TEDequipped nets ranged from 2% better than the standard net to 18%

worse than the standard nets with a try net adjustment. No

significant difference was observed in the overall catch rates

between TED and standard nets for twin-rigged vessels. However,

there was a significant difference in the catch rates between the

Georgia TED without a funnel and the standard net, but no

difference with the Georgia TED with a funnel and the standard

net.

Yield was modeled to determine what impact various levels

of shrimp loss would have on overall shrimp production. Overall,

a decrease of 10% in fishing mortality rate resulted in no

detectable change in the overall yield for both brown and white

shrimp fisheries and a 2% decrease in the yield for the pink

shrimp fishery. A decrease of 20% in F decreased the overall

yield 1% in the white shrimp fishery, 2% in the brown shrimp

fishery, and approximately 5% in the pink shrimp fishery.

A total of 40 turtles were caught in the observer program,

of which 27 were caught along the Atlantic coast and 13 were

caught in the Gulf of Mexico. Nine of the 40 came aboard

unconscious, and 36 were released alive. The estimated total

capture of turtles using 1988 fishing effort is 14,112 for the

Gulf of Mexico and 14,986 turtles for the Atlantic Ocean.

47
ACKNOWLEDGMENTS

We would like to acknowledge the assistance of several

organizations and their personnel for a tremendous amount of

assistance in keeping this study active for the past 17 months.

Tom Murray (Gulf and South Atlantic Fisheries Development

Foundation) provided funding for the purchase of many of the TEDS

used in the study and the $lOO/day incentive for shrimpers to

participate in the study. Sea Grant Marine Advisory Agents and

personnel from Texas (Gary Graham and Hollis Forrester),

Louisiana (David Bankston and Paul Coriel), Mississippi (David

Veal), Georgia (Dave Harrington and Paul Christian), and South

Carolina (David Smith) assisted in the recruitment of vessels for

the study and some of the gear tuning on the shrimp vessels.

NMFS Port Agents in Brownsville, TX (Kit Doncaster, Edie

Hernandez), Port Aransas, TX (Mary McGee), Freeport, TX (Dick

Allen), Port Arthur, TX (Madeline Bailey), Houma, LA (Kathy

Hebert and Ed Voisin), Golden Meadow, LA (Gary Rousse), Cameron,

LA (Patrick Walther), New Orleans, LA (Lee Usie), Key West, FL

(Ed Little), Cape Canaveral (Claudia Dennis) Ft. Meyers, FL (Tom

Hebert), Brunswick, GA (Dan Foster) and Charleston, SC (Ann

Jennings and John Devane) assisted in the recruitment of vessels

for the study. The Texas and Louisiana Shrimpers Associations

also assisted in vessel recruitment for our study. Will Seidel,

John Watson, Windy Taylor, Dale Stevens, James Barber and Rodney

Sawyer (NMFS, Pascagoula) assisted in vessel recruitment TED

construction, gear tuning and background information on the

48
development of the TED, its installation and proper use. We

would also like to thank those who participated in two TED

Workshops (Dr. Charles Gates, TAMU; Dr. Scott Nichols, NMFSPascagoula, Michael Parrack, NMFS-Miami, Gary Graham, Sea Grant

and David Harrington, Sea Grant) for specific guidance concerning

data analysis. Much credit also goes to the NMFS observers

(Galveston Laboratory) that have painstakingly collected the data

for this project. Finally, we would like to acknowledge the

shrimpers that participated in the study.

49
Federal Register, 1987. 52(124):24244-24262.

Henwood, T. A. and Stuntz, W. E. 1987. Analysis of sea turtle

captures and mortality during commercial shrimp trawling.

Fishery Bulletin (1987) 85(4):813-17.

Klima, E. F., K. N. Baxter and F. Patella. 1982. A review of

the offshore shrimp fishery and the 1981 Texas Closure.

Mar. Fish. Rev. 44:16-30.

Klima, E. F., Gitschlag, G. R. and M. L. Renaud. 1988. Impacts

of the explosive removal of offshore petroleum platforms on

sea turtles and dolphins. Mar. Fish. Rev. 50(3):33-42.

Milliken, G. A. and D. E. Johnson. 1984. Analysis of

messy data, vol. I: Designed experiments. Lifetime Learning

Publications, A Division of Wadsworth, Inc., Belmont, CA,

473 p.

Morrison, D. F. 1976. Multivariate statistical methods.

McGraw-Hill Publ., N.Y., 415 p.

Nance, J. M., E. F. Klima, K. N. Baxter, F. J. Patella and D.

B. Koi. 1989. Review of the 1988 Texas Closure for the

shrimp fishery off Texas and Louisiana. NOAA Tech. Memo,

NMFS-SEFC 218. 87 p.

Nance, J. M. and S. Nichols. 1988. Stock assessment for

brown, white and pink shrimp in the U.S. Gulf of Mexico,

1960-1986. NMFS-SEFC-NOAA Technical Memorandum No. 203,

64 p.

50
Nance, J. M., E. F. Klima and T. E. Czapla. 1989. Gulf of

Mexico shrimp stock assessment workshop. NOAA Tech. Memo.,

SEFC-NMFS-239. 41 p.

Nichols, S. 1982. Impacts on shrimp yield of the 1981

Fishery Conservation Zone closure off Texas. Mar. Fish.

Rev. 44:31-37.

Nichols, S. 1984. Updated assessments of brown, white and

pink shrimp in the U.S. Gulf of Mexico. Paper presented at

the SEFC Stock Assessment Workshop. Miami, Fl., May 1984.

Phares, P. L. 1978. An analysis of some shrimp trawl mesh size

selection data. Report prepared for the Gulf of Mexico

Fishery Management Council. 37 p.

Ricker, W. E. 1975. Computation and interpretation of biological

statistics of fish populations. Bull. Fish. Res. Bd.

Canada. 191:1-382.

Royce, W. F. 1972. Introduction to the Fishery Sciences.

Academic Press, N. Y., N. Y.

Snedecor, G. W. and W. G. Cochran. 1967. Design and analysis

of sampling. Chapter 17. In: Statistical Methods. Iowa

State University Press. Ames, Iowa. pp. 504-539.

Sokal, R. R. and F. J. Rohlf. 1981. Biometry. W. H. Freeman and

Co., N. Y., 857 p.

Thompson, N. B. 1988. The status of loggerhead, Caretta

caretta; Kemp's ridley, Lepidochelys kempi; and green,

Chelonia mydas, sea turtles in U. S. waters. Marine

Fisheries Review (1988), 50(3):16-23.

51
Watson, J. W., Mitchell, J. F. and Shah, A. 1986. Trawling

Efficiency Device: A New Concept for Selective Shrimp

Trawling Gear. Marine Fisheries Review (1986), 48(1):1-9.

52
LIST OF TEXT TABLES

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Table 9.

Table 10.

Table 11.

Table 12.

Frequency of operation codes for standard net, Georgia

TED without funnel, and Georgia TED with a Funnel..........57

CPUE (lbs/hr) comparisons of observed catch rates with

standard nets vs commercial catch rates; by trip...........58

Results of multivariate paired t-test for quad-rigged

vessels; all data without try nets. Comparisons between

CPUE (lbs/hr) of standard and TED-equipped nets; by tow....59

Results of multivariate paired t-test for quad-rigged

vessels; all data with try nets included. Comparisons

between CPUE (lbs/hr) of standard and TED-equipped nets;

by tow ................................................ ...... 60

Number of tows in which try net was in front of standard

or TED-equipped net; Georgia TED types combined............61

Comparison of mean CPUE (lbs/hr) with and without try net

for standard and TED-equipped nets; Georgia TED types

combined ................................................ 61

Comparison of mean CPUE (lbs/hr) and their differences for

standard and TED-equipped nets (Georgia TED types combined)

with and without trawling problems.........................62

Results of multivariate paired t-test for quad-rigged

vessel; all data without try nets. Comparisons between

CPUE (lbs/hr) of standard and TED-equipped nets; by trip...63

Results of multivariate paired t-test for quad-rigged

vessel; all data with try nets. Comparisons between CPUE

(lbs/hr) of standard net and TED-equipped nets; by trip....64

Results of multivariate paired t-test for twin-rigged

vessel; all data with try nets. Comparisons between CPUE

(lbs/hr) of standard and TED-equipped nets; by tow.........65

Results of General Linear Model (GLM) analyses of paired

observations from TED-equipped and standard trawls with

TED type (T), Region (R) and Season (Q) as classification

variables and with selected continuous variables as

covariates (see Appendix II text for description of

symbols used for dependent and continuous variables).......66

Least squares means (LSMs) of dependent variables for

various TED types, Regions and Seasons (Q) in General

Linear Model (GLM) analyses of paired observations for

TED-equipped and standard trawls (see Appendix II text

for description of symbols used for dependent variables)...69

53
Table 13. Turtle captures by area, net type and species..............71

Table 14. Standard Net Data: observer effort, turtle captures, CPUE

(turtles/hr), commercial shrimping effort, estimated

captures of sea turtles in the Gulf of Mexico and the

southern North Atlantic by season for 1988.................72

Table 15. TED Net Data: observer effort, turtle captures, CPUE

(turtles/hr), commercial shrimping effort, estimated

captures of sea turtles in the Gulf of Mexico and the

southern North Atlantic by season for 1988.................73

54
LIST OF TEXT FIGURES

Figure 1. Frequency of trips using Georgia TEDS (with funnels) by

season and area (N = 28) .......................... 74

Figure 2. Frequency of trips using Georgia TEDS (without funnels)

by season and area (N = 20) ......................... 75

Figure 3. Frequency of standard and Georgia TED (with funnel) tow

data pairs by season and area (N = 510)....................76

Figure 4. Frequency of standard and Georgia TED (without funnel)

tow data pairs by season and area (N = 292)................77

Figure 5. Ted shrimp catch vs standard shrimp catch, not adjusted

for try net catch, all areas/vessels combined. Data

paired by tow (N = 770) ......................... . 78

Figure 6. Ted shrimp catch vs standard shrimp catch, adjusted for

try net catch, all areas/vessels combined. Data paired

by tow (N = 770) ......................... . 79

Figure 7. Ted shrimp CPUE (lbs/hr) vs standard shrimp CPUE, not

adjusted for try net catch, all areas/vessels combined.

Data paired by tow (N = 770) ..................... . 80

Figure 8. Ted shrimp CPUE (lbs/hr)vs standard shrimp CPUE, adjusted

for try net catch, all areas/vessels combined. Data

paired by tow (N = 770) ...................... . 81

Figure 9. Standard shrimp CPUE (lbs/hr) vs standard fish CPUE, not

adjusted for try net catch, all areas/vessels combined.

Data paired by tow (N = 770) ..................... . 82

Figure 10. Standard shrimp CPUE (lbs/hr) vs standard fish CPUE,

adjusted for try net catch, all areas/vessels combined.

Data paired by tow (N = 770) ....................... 83

Figure 11. Location of turtle captures ........................ 84

Figure 12. Yield curves .......................... . 85

Figure 13. Differences in CPUE (lbs/hr) of shrimp between standard

and TED-equipped nets, by season. Solid topped bars

represent significant differences between standard and

TED nets. Data paired by tows (N = 706). Quad-rigged

vessels only ........................... . 86

55
Figure 14. Differences in CPUE (lbs/hr) of finfish between standard

and TED-equipped nets, by season. Solid topped bars

represent significant differences between standard and

TED nets. Data paired by tows (N = 706). Quad-rigged

vessels only ............................................... 87

Figure 15. Differences in CPUE (lbs/hr) of shrimp between standard

and TED-equipped nets, by area. Solid topped bars

represent significant differences between standard and

TED nets. Data paired by tows (N = 706). Quad-rigged

vessels only...............................................88

Figure 16. Differences in CPUE (lbs/hr) of finfish between standard

and TED-equipped nets, by area. Solid topped bars

represent significant differences between standard and

TED nets. Data paired by tows (N = 706). Quad-rigged

vessels only ............................................... 89

Figure 17. Differences in CPUE (lb/hr) of shrimp between standard

and TED-equipped nets for quad-rigged vessels. All area

and seasons combined. Solid topped bars represent

significant differences between standard and TED nets.

Data paired by tows (N = 706). Quad-rigged vessels

only ............................................... 90

Figure 18. Differences in CPUE (lb/hr) of shrimp between standard

and TED-equipped nets for twin-rigged vessels. All area

and seasons combined. Solid topped bars represent

significant differences between standard and TED nets.

Data paired by tows (N = 70). Quad-rigged vessels

only ............................................... 91

Figure 19. Differences in CPUE (lb/hr) of finfish between standard

and TED-equipped nets for quad-rigged vessels. All area

and seasons combined. Solid topped bars represent

significant differences between standard and TED nets.

Data paired by tows (N = 706). Quad-rigged vessels

only ............................................... 92

Figure 20. Turtle stranding frequency by year in statistical areas

17-21 ............................................... 93

Figure 21. Effort in the offshore Gulf of Mexico shrimp fishery.......94

Figure 22. Effort in the offshore Atlantic shrimp fishery.............95

56
Table 1. Frequency of operation codes for standard net,

Georgia TED without funnel, and Georgia TED with

a Funnel.

A. By Group

a Group 1 = operation codes A, B, C, E, F, N, O, S,

multiple codes containing one of these letters.

T plus

These codes

reflect gear-related problems which may or may not be

attributed to TEDS.

b Group 2 = operation codes G, I, J, K, L, M, P, Q, U, Z, plus

multiple codes containing only these letters. These codes

reflect tows with no gear-related problems attributable to TEDS.

57
Table 2. CPUE (lbs/hr/4 nets) comparisons of observed catch rates of standard nets with

commercial catch rates; by season and statistical area. Data are from 39 trips on

twin and quad-rigged observer vessels in the Gulf of Mexico and interviews of the

commercial shrimp fleet.

58
Table 3. Results of multivariate paired t-test for quad-rigged vessels: all

data without try nets. Comparisons between CPUE (lbs/hr) of standard

and TED-equipped nets: by tow.

a TED type 4 has no funnel; TED type 9 has a funnel.

59
Table 4. Results of multivariate paired t-test for quad-rigged vessels: all

data with try nets included. Comparisons between CPUE (lbs/hr) of

standard net and TED-equipped nets: by tow.

TED type 4 has no funnel; TED type 9 has a funnel.

60
Table 5. Number of tows in which try net was in front of standard

or TED-equipped nets; Georgia TED types combined.

Table 6. Comparison of mean CPUE (lbs/hr) with and without try net

for standard and TED-equipped nets; Georgia TED types

combined.

61
Table 7. Comparison of mean CPUE (lbs/hr) and their differences for

standard and TED-equipped nets (Georgia TED types combined) with

and without trawling problems.

No problem tows: operational codes A, E, F, O, S, B, C, Z, L (refer to

Appendix )

Problem tows: all other operational codes (refer to Appendix )

62
Table 8. Results of multivariate paired t-test for quad-rigged vessels: all

data without try nets. Comparisons between CPUE (lbs/hr) of standard

and TED-equipped nets; by trip.

TED type 4 has no funnel; TED type 9 has a funnel.

63
Table 9. Results of multivariate paired t-test for quad-rigged vessels: all

data with try nets. Comparisons between CPUE (lbs/hr) of standard

net and TED-equipped nets: by trip.

a TED type 4 has no funnel; TED type 9 has a funnel.

64
Table 10. Results of multivariate paired t-test for twin-rigged vessels; all

data with try nets. Comparisons between CPUE (lbs/hr) of standard

and TED type nets by tow.

a

 TED type 4 has no funnel; TED type 9 has a funnel.

65
Table 11. Results of General Linear Model (GLM) analyses of paired observations from TED-equipped and standard trawls with TED

(T), Region (R) and Season (Q) as classification variables and with selected continuous variables as covariates

(see Appendix II text for description of symbols used for dependent and continuous variables).

66
Table 11. (cont).

67
Table 11 (cont).

Mean square residual.

The mean of the residuals was zero in all GLM models shown in this table.
Table 12. Least squares means (LSMs) of dependent variables for various TED types, Regions and Seasons (Q) in General Linear Model

(GLM) analyses of paired observations for TED-equipped and standard trawls (see Appendix II text for description of symbols

used for dependent variables).

69
Table 12 (cont).

a

 ns indicates that the LSM was not significantly different from zero at P<=0.05; otherwise the LSM was significantly different from

zero.

b

 NE indicates that the LSM was not estimable because of data imbalance (insufficient sample size).

70
Table 13. Turtle captures by area, net type and species.

71
Table 14. Standard net data: observer effort, turtle captures, CPUE (turtles/hr), commercial shrimping effort, estimated captures of

sea turtles in the Gulf of Mexico and the southern North Atlantic by season for 1988.

72
Table 15. TED net data: observer effort, turtle captures, CPUE (turtles/hr), commercial shrimping effort, estimated captures of sea

turtles in the Gulf of Mexico and the southern North Atlantic by season for 1988.

73
Figure 1. Frequency of trips using Georgia TEDs (with funnels) by season and

area (N = 28).

74
Figure 2. Frequency of trips using Georgia TEDs (without funnels) by season and

and area (N = 20).

75
Figure 3. Frequency of standard and Georgia TED (with funnel) tow data pairs

by season and area (N = 510).

76

FIGURE 5. TED SHRIMP CATCH VS STANDARD SHRIMP CATCH,

NOT ADJUSTED FOR TRY NET CATCH,

ALL AREA/VESSELS COMBINED

N = 770
FIGURE 6. TED SHRIMP CATCH VS STANDARD SHRIMP CATCH,

ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770
FIGURE 7. TED SHRIMP CPUE (LBS/HR) VS STANDARD SHRIMP CPUE (LBS/HR),

NOT ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770
FIGURE 8. TED SHRIMP CPUE (LBS/HR) VS STANDARD SHRIMP CPUE (LBS/HR),

ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770
FlGURE 9. TED SHRIMP CATCH VS TED FlSH CATCH

NOT ADJUSTED FOR TRY NET CATCH

ALL AREAS/VESSELS COMBINED

N = 770
FIGURE 10. TED SHRIMP CATCH VS TED FlSH CATCH

ADJUSTED FOR TRY NET CATCH

ALL AREAS/VESSELS COMBINED

N = 770

Figure 12. Yield curves.

85
Figure 13. Differences in CPUE (Ibs/hr) of shrimp between standard and TEDequipped nets, by season. Solid topped bars represent significant

differences between standard and TED nets. Data paired by tows

(N = 706). Quad-rigged vessels only.

86
Figure 14. Differences in CPUE (Ibs/hr) of finfish between standard and TEDequipped nets, by season. Solid topped bars represent significant

differences between standard and TED nets. Data paired by tows

(N = 706). Quad-rigged vessels only.

87
Figure 15. Differences in CPUE (Ibs/hr) of shrimp between standard and TEDequipped nets, by area. Solid topped bars represent significant differences

between standard and TED nets. Data paired by tows (N = 706). Quadrigged vessels only.

88
Figure 16. Differences in CPUE (Ibs/hr) of finfish between standard and TEDequipped nets, by area. Solid topped bars represent significant

differences between standard and TED nets. Data paired by tows

(N = 706). Quad-rigged vessels only.

89
Figure 17. CPUE (Ibs/hr) of shrimp in standard and TED-equipped nets for

quad-rigged vessels. All areas and seasons combined. Solid topped

bars represent significant differences between standard and TED nets.

Data paired by tows (N = 706).

90
Figure 18. CPUE (Ibs/hr) of shrimp in standard and TED-equipped nets for

twin-rigged vessels. All areas and seasons combined. Solid topped

bars represent significant differencesbetween standard and TED nets.

Data paired by tows (N = 70).

91
Figure 19. CPUE (Ibs/hr) of finfish standard and TED-equipped nets for

quad-rigged vessels. All areas and seasonscombined. Solid topped

bars represent significant differences between standard and TED nets.

Data paired by tows (N = 706).

92
Figure 20. Turtle stranding frequency by year in statistical areas 17 - 21.

93

Figure 22. Effort in the offshore Atlantic shrimp fishery.

95
LIST OF APPENDICES

APPENDIX I.

Table 1.

Table 2.

Table 3.

Table 4.

APPENDIX II.

GENERAL LINEAR MODEL ANALYSES OF DATA FROM STANDARD

AND TED-EQUIPPED TRAWLS PAIRED BY TOW AND BY TRIP,

FOR QUAD-RIGGED AND TWIN-RIGGED TRAWLERS..............98

Frequency of levels within classification variables

used in GLM analyses of paired observations from

TED-equipped and standard trawls.....................114

Descriptive statistics for dependent and continuous

variables used in GLM analyses of paired observations

from TED-equipped and standard trawls...............122

Results of GLM analyses of paired observations from

TED-equipped and standard trawls with TED type, Region

and Season as classification variables and with

selected continuous variables as covariates..........l30

Lease squares means of selected dependent variables

various TED types, Regions and Seasons in GLM

analyses of paired observations for TED-equipped

and standard trawls ....................... .140

APPENDIX TABLES......................................146

Table 1. Summary of operation codes for trawl performance..........147

Table 2. Frequency of operation codes for standard net, Georgia

TED without funnel, and Georgia TED with a funnel.........148

Table 3. Frequency of operation codes for standard net, Morrison

"Soft" TED, a NMFS-type TED and a homemade TED............149

Table 4. Summary of regression analyses on twin-rigged vessels:

Ted-equipped vs standard shrimp nets. By area and season;

data paired by tow........................................150

Table 5. Summary of regression analyses on quad-rigged vessels:

Ted-equipped vs standard shrimp nets. By area and season;

data paired by tow ........................... . 151

APPENDIX III. APPENDIX FIGURES ........................... .153

Figure 1. Schematic diagram of the end of a shrimp trawl containing

a Georgia TED and an accelerator funnel...................154

Figure 2. NMFS statistical areas in the Gulf of Mexico and south

Atlantic ............................. . 155

Figure 3. Standard shrimp catch vs standard fish catch, not

96
Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

adjusted for try net catch,

Data paired by tow. N = 770

all areas/vessels combined.

.................... . 156

Standard shrimp catch vs standard fish catch, adjusted

for try net catch, all areas/vessels combined. Data

paired by tow. N = 770 .................... . 157

TED shrimp catch vs TED fish catch, not adjusted for try

net catch, all areas/vessels combined.

tow. N = 770

Data paired by

......................... . 158

TED shrimp catch vs TED fish catch, adjusted for try net

catch, all areas/vessels combined. Data paired by tow.

N = 770 ............................ . 159

TED shrimp CPUE vs TED fish CPUE, not adjusted for try

net catch, all areas/vessels combined.

tow. N = 770

Data paired by

........................... . 160

TED shrimp CPUE vs TED fish CPUE, adjusted for try net

catch, all areas/vessels combined. Data paired by tow.

N = 770 ........................... . 161

Locations of winter turtle captures (Dec, Jan, Feb)........ 162

Figure 10. Locations of spring turtle captures (Mar, Apr, May)....... 163

Figure 11. Locations of summer turtle captures (Jun, Jul, Aug)....... 164

Figure 12. Locations of fall turtle captures (Sep, Oct, Nov)......... 165

97
APPENDIX I

GENERAL LINEAR MODEL ANALYSES OF DATA FROM STANDARD AND TEDEQUIPPED TRAWLS PAIRED BY TOW AND BY TRIP, FOR QUAD-RIGGED

AND TWIN-RIGGED TRAWLERS

98
METHODS

General linear model (GLM) analyses were performed on four

data sets of paired TED-equipped and standard trawls, using SASTM

(Statistical Analysis System, SAS Institute, Inc., Cary, N.C.).

The four data sets were represented by combinations of quadrigged and twin-rigged trawlers with pairings by tow and by trip.

The data paired by tow included TED-equipped and standard trawls

towed simultaneously, one pair per tow. Pairing by trip produced

one pair per trip. For quad-rigged trawlers, the pairs were

standardized to one TED-equipped and one standard net by

averaging the TED-equipped trawls together and the standard

trawls together by tow. Pairing by trip involved summing over

tows in a trip.

GLM analyses were used because all four data sets were

unbalanced (Appendix I, Table 1); i.e., the number of

observations was not the same for all levels of any given

classification variable, and some combinations of classification

variables contained no observations at all (they had empty

cells). These analyses were used to "screen" the data sets to

determine which GLM models were better suited to describe the

data and underlying assumptions. They also can be compared with

results of the multivariate, paired t-test described elsewhere in

this report, since they were applied to the same four data sets.

If either shrimp or fish data in a given pair were missing, then

the record for that pair was rejected from the GLM analyses of

paired data. For quad-rigged trawlers, there were 706

99
observations (pairs) by tow and 41 observations by trip. For

twin-rigged trawlers, there were 64 observations by tow and 7

observations by trip.

Symbols used for dependent, classification and continuous

variables in the GLM analyses of paired data are given below:

Symbol Description

Two TED types including Georgia TED and

Georgia TED with funnel;

Towing velocity (knots);

Tow duration (hours);

Natural logarithm of H;

Five regions represented by groupings of

shrimp statistical subareas including Texas

(18-21), Louisiana (13-17), MississippiAlabama (9-12), West Florida (l-8) and

Atlantic coast (> 21).

Four seasons represented by groupings of

months into winter (Dec-Feb), Spring (MarMay), Summer (Jun-Aug) and Autumn (Sep-Nov);

100
Water depth (fathoms);

Natural logarithm of D;

Shrimp catch (pounds) per net tow or catch

per trip in TED-equipped trawls:

Shrimp catch (pounds) per net tow or catch

per trip in standard trawls;

Shrimp catch (pounds) per net tow or catch

per trip in TED-equipped trawls, adjusted by

the addition of shrimp caught in the try net

to the net immediately behind it;

Shrimp catch (pounds) per net tow or catch

per trip in standard trawls, adjusted by the

addition of shrimp caught in the try net to

the net immediately behind it;

Projected fish catch (pounds) per net tow or

catch per trip in TED-equipped trawls

(projected from the sample proportion of

shrimp to fish and the shrimp catch):

101
Projected fish catch (pounds) per net tow or

catch per trip in TED-equipped trawls

(projected from the sample proportion of

shrimp to fish and the shrimp catch);

Natural logarithm of ST;

Natural logarithm of SS;

Natural logarithm of STadj;

Natural logarithm of SSadj;

Natural logarithm of FT;

Natural logarithm of FS;

Shrimp catch (pounds) per unit effort (hours)

in TED-equipped trawls, ST/H;

Shrimp catch (pounds) per unit effort (hours)

in standard trawls, SS/H;

Shrimp catch (pounds) per unit effort (hours)

in TED-equipped trawls, adjusted by the

addition of shrimp caught in the try net to

the net immediately behind it, STadj/H;

102
Shrimp catch (pounds) per unit effort (hours)

in standard trawls, adjusted by the addition

of shrimp caught in the try net to the net

immediately behind it, SSadj/H;

Fish catch (pounds) per unit effort (hours)

in TED-equipped trawls, FT/H;

Fish catch (pounds) per unit effort (hours)

in the standard trawls, FS/H;

Natural logarithm of SCPUET;

Natural logarithm of SCPUES;

Natural logarithm of SCPUETadj;

Natural logarithm of SCPUESadj;

Natural logarithm of FCPUET;

Natural logarithm of FCPUES;

103
Proportion that shrimp catch in TED-equipped

trawls represented as compared to that in

standard trawls, ST/SS;

Proportion that shrimp catch in TED-equipped

trawls represented as compared to that in

standard trawls, adjusted by the addition of

the shrimp caught in the try net to the net

immediately behind it, STadj/SSadj;

Proportion that fish catch in TED-equipped

trawls represented as compared to that in

standard trawls, FT/FS;

Percentage shrimp loss (note that a negative

loss is a gain) by TED-equipped trawls, l00(1

- RS);

Percentage shrimp loss by TED-equipped

trawls, adjusted by the addition of shrimp

caught in the try net to the net immediately

behind it, l00(1 - RSadj); and

Percentage fish loss by TED-equipped trawls,

l00(1 - RF).

104
The subscript T was used to designate TED-equipped trawls

and the subscript S was used to designate standard trawls. The

subscript adj was used to indicate data adjusted by the addition

of catch from the try net to the net immediately behind it,

whether the net was standard or TED-equipped. Thus, the

adjustment applied only to one net in each quad-rigged tow or

each twin-rigged tow.

Milliken and Johnson (1984) discussed the GLM methods,

underlying assumptions, problems and interpretations for

unbalanced experiments in multiway treatment structures with

missing data. In the TED evaluation study, classification

variables (main effects) such as TED type (T), Region (R) and

Season (Q) represented the treatments. The analyses also

considered continuous variables (covariates) such as duration of

tow (H), towing speed (V) and water depth (D) or logarithmic

transformations of H and D. The classification variables were

the main effects and the continuous variables were covariates in

the GLM models tested. Interactions were also included in some

of the GLM models.

Such multiway treatment structure combined with all possible

interactions produced large numbers of missing cells, so the sums

of squares for some of the high order interactions were not

estimable. Therefore, we included only three main effects and

all a-factor interactions in the model, when TED type, Region and

Season were used together in a GLM analysis, and only one main

effect and either all 2-factor or both a-factor and 3-factor

105
interactions when TED type, Region or Season were treated one at

a time in separate analyses. However, all analyses in which TED

type, Region and Season were included together in a GLM model

were later discarded because the Least Squares Means (LSMs) for

these classification variables were not estimable because of data

imbalance.

GLM was used to determine which the models tested accounted

for the greatest proportion of the total sum of squares as shown

by the coefficient of variation (r2), as well as to determine

which models met the assumptions of mean zero and normality of

the residuals. When they were estimable, LSMs also were

estimated for each classification variable and were tested to

determine if they were significantly different from zero. When

the test involved a mean difference, whether constructed from

untransformed or transformed data, this was equivalent to testing

whether or not there was a significant difference between

standard and TED-equipped trawls. When the test involved a

proportion (ratio), this was equivalent to testing whether or not

it differed significantly from zero.

The major problem impacting the GLM analyses of the paired

data was the considerable imbalance of the data set. Some

'combinations of main effects were never observed; i.e., they had

empty cells. Also, for those cells containing data, the number

of observations was not equal from cell to cell. One simple

example will suffice for explanation. Georgia TEDS without

funnels and Georgia TEDS with funnels were the dominant TED

106
types, so observations for other TEDS were excluded from the GLM

analyses of paired data. Five Regions were defined as groupings

of shrimp statistical subareas. For the experimental structure

to have been balanced in regard to these two main effects of TED

type and Region, both TED types should have been tested the same

number of times in each Region. If one or the other TED type was

not tested in a given Region, that combination of TED type and

Region was not observed, thus causing an empty cell in the

experimental structure. If given combinations of TED type and

region contained data, but the number of observations varied from

cell to cell, then the experiment was unbalanced with regard to

sample size or the number of times a particular TED type by

Region combination was tested. NMFS had little if any control

over either type of imbalance (missing cells and unequal sample

size), because the study involved voluntary participation by

shrimpers who decided when and where to fish, so it was not a

controlled experiment.

Many statistical packages can calculate test statistics for

experiments with missing treatment combinations and unequal

sample sizes, and SASTM is among them. However, Milliken and

Johnson (1984) remarked that they knew of no package [of

statistical procedures] that handles the analysis of such data

adequately or completely. Whenever there are missing treatment

combinations, certain hypotheses involving the parameters

corresponding to the missing cells generally cannot be tested

107
without making some assumptions about these parameters (Milliken

and Johnson, 1984).

For example, in the two-factor case involving missing cells

in the combination of TED type and Region, the required

assumption would be that there is no interaction between TED type

and Region. Without experimental evidence to support this

assumption, such an assumption should not be made. Thus, in the

absence of evidence justifying an assumption of no interaction

between main effects, we cannot validly make such an assumption.

Because we were not able to build full models with all

interactions (because of the tremendous imbalance in the data),

it was not possible to obtain an experimental error term with

which to test the higher order interactions for significance.

Any main effects and interactions incorporated into our GLM

analyses were tested against the residual mean square which could

have included higher order interactions.

This residual mean square was an extremely crude "error"

variance. In addition, because the F tests were not based on

expected mean squares in some cases they may not have been exact

or appropriate.

We used the "effects model" approach (Milliken and Johnson,

1984, Chapter 14) to GLM analysis. The Type IV analysis was

chosen, since none of the main effects hypotheses tested by Types

I-III analyses are entirely satisfactory when there are missing

treatment combinations, because they rarely have reasonable

interpretations. Type IV hypotheses are interpretable. However,

108
the results obtained by Type IV analysis depend on what the

treatments are called and how they are numbered. SASTM GLM

indicates this situation by placing an asterisk on the printed

degrees of freedom and noting that "OTHER TYPE IV TESTABLE

HYPOTHESES EXIST WHICH MAY YIELD DIFFERENT SS."

Another problem caused by the imbalanced data was that some

LSMs were still not estimable, even when TED type, Region and

Season were used one at a time in a model along with 2-factor and

3-factor interactions.

In a multivariate GLM with interactions, the term residual

is used to denote variability remaining after the variation

attributable to the main effects, covariates and interactions has

been accounted for. In our models with one main effect, up to

four continuous variables, and either all a-factor or all 3-

factor interactions, or both, the residual mean square could have

contained variance components represented by higher order

interactions as well as containing the so-called experimental

error. If the assumption of zero interactions were incorrect for

these higher order interactions, then the residual mean square

would have been too large and the resulting F values for

significance test would have been correspondingly too small

(Milliken and Johnson, 1984). Consequently, if there were

significant higher order interactions, they would not have been

discovered by our analyses, and the significance of some main

effects, covariates and lower order interactions included in our

models might have been masked (ibid.). The consequence of this

109
situation is that the significance tests of the LSMs were highly

conservative. Thus, if a LSM was shown to be Significantly

different from zero, its significance occurred despite a

potentially inflated residual mean square.

Assumptions of the GLM analysis are that (1) sampling within

treatments (groups representing main effects) must be random, (2)

the error term or residual must be an independent normally

distributed, random variable with mean zero, (3) the variances of

treatments must be homogeneous, and (4) the main effects must be

additive.

RESULTS

Appendix I, Table 1 gives the number of observations for

each level of each classification variable used in the GLM

analyses. Part A is for data paired by tow and Part B for data

paired by trip for quad-rigged trawlers. Part C is for data

paired by tow and Part D for data paired by trip for twin-rigged

trawlers. The imbalance is obvious in these data.

Appendix I, Table 2 gives the descriptive statistics for all

dependent and continuous variables used in our GLM analyses, for

data paired by tow (A) and by trip (B) for quad-rigged trawlers,

and by tow (C) and by trip (D) for twin-rigged trawlers.

Appendix I, Table 3 shows the particular dependent and

independent variables used in each GLM analysis on data paired by

tow and by trip for quad-rigged and twin-rigged trawlers, and the

110
variance of residuals (s2

), coefficient of determination (r2

),

and analysis of the residuals (coefficients of skewness and

kurtosis) for each. Analysis of the residuals indicated the

degree to which a chosen model fulfilled the requirements of a

mean of zero and normality of the residuals required by GLM

analysis. The coefficient of determination indicated the

proportion of variation in the dependent variable that was

accounted for by the independent variables and interactions in

each model tested. Note that for data paired by trip, tow

velocity and water depth could not be included as continuous

variables because they varied from tow to tow in a trip.

Appendix I, Table 4 gives the LSMs for each dependent

variable by TED type, Region and Season, for data paired by tow

and by trip for quad-rigged and twin-rigged trawlers. An "ns"

next to a LSM indicates that it was not significantly different

from zero at P<=0.05. Non-significance was the exception rather

than the rule, since most LSMs were significantly different from

zero. An "NE", in the table indicated that the LSM was not

estimable because of data imbalance. Occasionally, these

significance tests produced what might appear to be ambiguous

results: e.g., one LSM might have been significantly different

from zero, while another of the same magnitude or larger might

not have been significantly different from zero. This was

another result of the imbalance in the data since significance

depends in part on degrees of freedom associated with the test

111
statistic, and the sample size was not the same for all levels of

a given classification variable (See Appendix I, Table 1).

In most cases the GLM models that produced the highest

coefficients of determination (r2

) and the lowest skewness and

kurtosis coefficients for the residuals were those involving the

difference between the natural logarithms of shrimp catches in

standard vs TED-equipped trawls, both with and without the try

net correction (Appendix I, Table 3). Appendix I, Table 4 shows

which LSMs were significantly different from zero and which were

not for various levels of TED type, Region and Season.

The LSMs of the ratios of shrimp catches were all

significantly different from zero, for both TED-types, all

Regions and all Seasons, both with and without the try net

correction (Appendix I, Table 4). When the dependent variable

involved a difference between standard and TED-equipped nets,

whether or not logarithms had been used, the LSM was an estimate

of the mean difference. If this LSM was significantly from zero

it indicated that there was a significant difference between

standard and TED-equipped nets. The sign of this difference

indicated whether TEDS lost (+) or gained (-) shrimp as compared

to standard nets.

The GLM analyses as well as other analyses applied to data

paired by tow should be considered superior to those applied to

data paired by trip. First of all, the sampling unit in the TED

evaluation study was the individual tow, not the trip (Appendix

I, Table 3). Secondly, pairing by trip collapsed the data from

112
individual tows in a trip into one pair per trip, thus reducing

sample size and masking tow to tow variation. Finally, pairing

by trip produced inconsistent results, increasing the

coefficients of determination for some GLM analyses but

decreasing them for others as compared to results for GUI

analyses of data paired by tow.

113
Appendix I. Table 1. Frequency of levels within

classification variables used in GLM

analyses of paired observations from

TED-equipped and standard trawls.

A. Data paired by tow (706 observations, quad-rigged trawlers)

114
Appendix I. Table 1. (cont.)

115
Appendix I. Table 1. (cont.)

B. Data paired by trip (41 observations, quad-rigged trawlers)

116
Appendix I. Table 1. (cont.)

Georgia TED with funnel

117
Appendix I. Table 1. (cont.)

C. Data paired by tow (64 observations, twin-rigged trawlers).

Six observations were excluded from the analyses because

fish data were not collected on 6 tows.

118
Appendix I. Table 1. (cont.)

119
Appendix I. Table 1. (cont.)

D. Data paired by trip (7 observations, twin-rigged trawlers)
Appendix I. Table 1. (cont.)

4. Combined

121
Appendix I. Table 2. Descriptive statistics for dependent and

continuous variables used in GLM analyses Of

paired observations, from TED-equipped and

standard trawls.

A. Data paired by tow (706 observations, quad-rigged trawlers)

122
Appendix I. Table 2 (cont).

123
Appendix I. Table 2 (cont).

124
Appendix I. Table 2 (cont).

125
Appendix I. Table 2 (cont).

C. Data paired by tow (64 observations, twin-rigged trawlers)

126
Appendix I. Table 2 (cont).
Appendix I. Table 2 (cont).

D. Data paired by trip (7 observations, twin-rigged trawlers)
Appendix I. Table 2 (cont).

129
Appendix I. Table 3. Results of General Linear Model (GLM) analyses of paired observations from TED-equipped and standard

trawls with TED type (T), Region (R) and Season (Q) as classification variables and with selected

continuous variables as covariates (see Appendix I text for description of symbols used for dependent

and continuous variables).

A. Data paired by tow (706 observations, quad-rigged trawlers)

130
Appendix I. Table 3 (cont).
Appendix I. Table 3 (cont).

132
Appendix I. Table 3 (cont).

133
Appendix I. Table 3 (cont).

134
Appendix I. Table 3 (cont).

135
Appendix I. Table 3 (cont).

136
Appendix I. Table 3 (cont). 

137
Appendix I. Table 3 (cont).

138
Appendix I. Table 3 (cont). 

139
Appendix I. Table 4. Least squares means (LSMs) of selected dependent variables for various TED types, Regions and Seasons in

General Linear Model (GLM) analyses of paired observations for TED-equipped and standard trawls. (see

Appendix I text for description of symbols used for dependent and continuous variables).

A. Data paired by tow (706 observations, quad-rigged trawlers)

140
Appendix I. Table 4 (cont).

141
Appendix I. Table 4 (cont).

142
Appendix I. Table 4 (cont).
Appendix I. Table 4 (cont).

144
Appendix I. Table 4 (cont).

145
APPENDIX II

APPENDIX TABLES

146
Appendix II. Table 1. Summary of operation codes for trawl

performance.

A = Nets not spread; typically doors are flipped or doors hung

together so net could not spread.

B = Gear bogged: the net has picked up a quantity of sand or mud

such that the net can not be easily towed.

C = Bag choked; the catch in the net is prevented from getting

into the bag by something (grass, sticks, turtle, etc.)

clogging net or by the twisting of the lazy-line.

D = Gear not digging; the net is fishing off the bottom due to

insufficient weight.

E = Twisted warp or line; the cables composing the bridle get

twisted (from passing over blocks which occasionally must be

removed before continuing to fish). Use this code if catch

was affected.

F = Gear fouled; the gear has become entangled in itself.

Typically this involves the webbing and some object like a

float or chains.

G = Bag untied; bag of net not tied when dragging net.

H = Rough weather; if the weather is so bad fishing is stopped,

then the previous tow should receive this code if the rough

conditions affected the catch.

I = Torn webbing or lost net; usually results from hanging the

net and tearing it loose.

tears if at all.

The net comes back with large

Do not use this code if there are only a

few broken meshes. Continue using this code until net is

repaired or replaced.

J = Dumped catch; tow was made but catch was discarded, perhaps

because of too much trash, fish, sponge. Give reason in

Comments.

K = No pick up: tow made but net not dumped on deck because nets

are brought up, boat changes location and nets are towed more

before decking.

L = Hung up; untimely termination of a tow by a hang. Specify

trawl(s) which were hung and caused lost time in Comments.

M = Bags dumped together and catches not separated.

N = Net did not fish; no apparent cause.

O = Gear fouled on object; typically a log caught in bag or TED.

Net may be towed but performance is affected.

in Comments.

Give specifics

P = No measurement taken of shrimp or total catch.

Q = Cable breaks and net lost. Describe in Comments.

R = Net caught in wheel.

S = Tickler chain fouled or tangled.

T = Other Problems

U = TED's tied shut.

Z = Successful tow

147
Appendix II. Table 2. Frequency of Operation Codes For

Standard Net, Georgia TED without

funnel, and Georgia TED with a Funnel.

148
Appendix II. Table 3. Frequency of Operation Codes For Standard

Net, Morrison TED, Saunder's TED, and

Golden TED.

*These operational codes reflect tows with no gear related problems

attributal to TEDS.

149
Appendix II. Table 4. Summary of Regression Analyses on Twin-Rigged Vessels: TED-equipped vs Standard Shrimp

Nets. By area and season; data paired by tow.

GT/NF = GEORGIA TED WITHOUT A FUNNEL

GT/WF = GEORGIA TED WITH A FUNNEL

TEDCPUSH = CPUE OF SHRIMP IN TED NET NOT ADJUSTED FOR TRY NET

STDCPUSH = CPUE OF SHRIMP IN STANDARD NET NOT ADJUSTED FOR TRY NET

TEDSH = CATCH OF SHRIMP IN TED NET NOT ADJUSTED FOR TRY NET

STDSH = CATCH OF SHRIMP IN STANDARD NET NOT ADJUSTED FOR TRY NET

TEDCPUTR = CPUE OF SHRIMP IN TED NET ADJUSTED FOR TRY NET

STDCPUTR = CPUE OF SHRIMP IN STANDARD NET ADJUSTED FOR TRY NET

TEDSHTR = CATCH OF SHRIMP IN TED NET ADJUSTED FOR TRY NET

STDSHTR = CATCH OF SHRIMP IN STANDARD NET ADJUSTED FOR TRY NET

TEDFI = CATCH OF FISH IN TED NET NOT ADJUSTED FOR TRY NET

STDFI = CATCH OF FISH IN STANDARD NET NOT ADJUSTED FOR TRY NET

a These slopes are not significantly different from 1.

150
Appendix II. Table 5. Summary of Regression Analyses on Quad-Rigged Vessels: TED-equipped vs Standard Shrimp

Nets. By area and season; data paired by tow.

151
Appendix II. Table 5 (continued). Summary of Regression Analyses on Quad-Rigged Vessels: TED vs Standard Shrimp

Nets. By area and season; data paired by tow.

GT/NF =

GT/WF =

TEDCPUSH =

STDCPUSH =

TEDSH =

STDSH =

TEDCPUTR =

STDCPUTR =

TEDSHTR =

STDSHTR =

TEDFI =

STDFI =

GEORGIA TED WITHOUT A FUNNEL

GEORGIA TED WITH A FUNNEL

CPUE OF SHRIMP IN TED NET NOT ADJUSTED FOR TRY NET

CPUE OF SHRIMP IN STANDARD NET NOT ADJUSTED FOR TRY NET

CATCH OF SHRIMP IN TED NET NOT ADJUSTED FOR TRY NET

CATCH OF SHRIMP IN STANDARD NET NOT ADJUSTED FOR TRY NET

CPUE OF SHRIMP IN TED NET ADJUSTED FOR TRY NET

CPUE OF SHRIMP IN STANDARD NET ADJUSTED FOR TRY NET

CATCH OF SHRIMP IN TED NET ADJUSTED FOR TRY NET

CATCH OF SHRIMP IN STANDARD NET ADJUSTED FOR TRY NET

CATCH OF FISH IN TED NET NOT ADJUSTED FOR TRY NET

CATCH OF FISH IN STANDARD NET NOT ADJUSTED FOR TRY NET

a These slopes are hot significantly different from 1.

152
APPENDIX III

APPENDIX FIGURES

153
Figure 1. Schematic diagram of the end of a shrimp trawl

containing a Georgia TED and an accelerator

funneI.

154
Figure 2. NMFS statistical areas in the Gulf of Mexico and south Atlantic.

155
FIGURE 3. STANDARD SHRIMP CATCH VS STANDARD FISH CATCH,

NOT ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770

156
FIGURE 4. STANDARD SHRIMP CATCH VS STANDARD FlSH CATCH,

ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770

157
FIGURE 5. TED SHRlMP CATCH VS TED ASH CATCH,

NOT ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770
FlGURE 6. TED SHRIMP CATCH VS FlSH CATCH

ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770
FlGURE 7. TED SHRIMP CPUE (LBS/HR) VS TED FISH CPUE (LBS/HR)

NOT ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770

FlSH POUNDS/HR IN TED-EQUIPPED NET

160
FlGURE 8. TED SHRIMP CPUE (LBS/HR) VS TED FlSH CPUE (LBS/HR)

ADJUSTED FOR TRY NET CATCH,

ALL AREAS/VESSELS COMBINED

N = 770

FISH POUNDS/HR IN TED-EQUIPPED NET

161
162
163
164
165