OCS Study 

MMS 2000-087 

Estimation of Fisheries Impacts 

Due to Underwater Explosives 

Used to Sever and Salvage Oil and 

Gas Platforms in the U.S. Gulf of Mexico 

Final Report 

U.S. Department of the Interior MW Minerals Management Service 

Gulf of Mexico OCS Region 
OCS Study 

MMS 2000-087 

Estimation of Fisheries Impacts 

Due to Underwater Explosives 

Used to Sever and Salvage Oil and 

Gas Platforms in the U.S . Gulf of Mexico 

Final Report 

Authors 

Gregg R. Gitschlag 

Michael J . Schirripa 

Joseph E . Powers 

Prepared under MMS 

Interagency Agreement 17912 

by 

National Marine Fisheries Service 

Southeast Fisheries Science Center 

Miami, Florida 33149 

Published by 

U.S. Department of the Interior New Orleans Minerals management Service 

Gulf of Mexico OCS Region April 2001 

111 

DISCLAIMER 

This report was prepared under contract between the Minerals 

Management Service (MMS) and the National Marine Fisheries 

Service . This report has been technically reviewed by the MMS, 

and it has been approved for publication . Approval does not 

signify that the contents necessarily reflect the views and 

policies of the MMS, nor does mention of trade names or 

commercial products constitute endorsement or recommendation for 

use . It is, however, exempt from review and compliance with the 

MMS editorial standards . 

REPORT AVAILABILITY 

Extra copies of this report may be obtained from the Public 

Information Office (Mail Stop 5034) at the following address : 

U .S . Department of the Interior 

Minerals Management Service 

Gulf of Mexico OCS Region 

Public Information Office (MS 5034) 

1201 Elmwood Park Boulevard 

New Orleans, Louisiana 70123-2394 

Telephone : (504)-736-2519 or 

1-800-200-GULF 

CITATION 

Suggested Citation : 

Gitschlag, G . R ., M . J . Schirripa, and J . E . Powers . 2000 . 

Estimation of fisheries impacts due to underwater explosives 

used to sever and salvage oil and gas platforms in the U .S . 

Gulf of Mexico : Final report . OCS Study MMS 2000-087 . 

Prepared by the National Marine Fisheries Service . U .S . 

Dept . of the Interior, Minerals Mgmt . Service, Gulf of 

Mexico OCS Region, New Orleans, LA . 80 pp . 

v 

PREFACE 

The title of this study, "Estimation of Fisheries Impacts Due to 

Underwater Explosives Used to Sever and Salvage Oil and Gas 

Platforms in the U .S . Gulf of Mexico," is somewhat of a misnomer . 

There are a wide variety of oil and gas structures in addition to 

platforms . Data analysis included extrapolation of results to 

other structure types in addition to those commonly referred to 

as platforms . A detailed explanation appears in the report . Also, 

no distinction was made between petroleum and gas structures . 

ACKNOWLEDGMENTS 

We gratefully acknowledge the hard work and dedication of the 

many NOAA divers and field personnel who participated in the 

study, including but not limited to David Atkinson, Christie 

Daniels, Brett Dodson, Sanford Evans, Garry Gana, Shawn Hussong, 

Michael Loeffler, Logan Respess, Ricardo Rubiano, and Ron Wooten . 

We also acknowledge the U .S . Navy divers from the Explosive 

Ordnance Disposal Mobile Unit SIX Detachment TWO, Ingleside, TX, 

who asssited with field work at one platform removal site . We 

thank Scott Allman, Breck Bacon, Tommy Gottreau, Aly Hakam, James 

Kiesler, Vernon Luning, George Santos, Greg Schulte, and Dean 

Whittaker for assistance in providing platforms for the study . 

Christopher Legault and Clay Porch assisted with the stock 

assessment analysis . Dr . Andre Landry identified fish measuring 

<8 cm that were collected under one platform . Todd Kihle and Jo 

Williams assisted with preparation of tables and figures . Special 

thanks are due to Dr . Ann Bull, the MMS COTR for the study. In 

addition to actively participating in several cruises, her 

understanding of offshore and underwater research greatly 

facilitated her COTR duties to the benefit of the project . 

Gregg R . Gitschlag, Michael J . Schirripa, Joseph E . Powers 

Vii 

Executive Summary 

According to data from the National Marine Fisheries 

Service (NMFS) Platform Removal Observer Program which includes 

removals in both federal and state waters, from 1989-98 a total 

of 958 structures were salvaged using explosives for an annual 

average of roughly 96 structures . One obvious consequence of 

using explosives is a negative impact on fish . There has 

previously been no attempt to quantify the impacts of explosive 

platform removal on fish populations . Of special concern is the 

commercially and recreationally important red snapper (Lutjanus 

campechanus) which occurs at many of these structures . The red 

snapper continues to be the subject of intense government 

regulation as this species is severely overfished and there are 

significant problems in the long-term viability of the stock 

(Goodyear and Phares 1990 ; Goodyear 1996 ; Cowan 1998 ; Schirripa, 

1998) . 

Fishery managers attempt to track the size and status of 

stocks using mathematical equations which include variables 

relating to recruitment and mortality . The results of such stock 

assessment analyses provide managers with critical information 

needed to manage fisheries . This study quantifies the mortality 

of fish species resulting from explosive platform removals . For 

the first time, mortality estimates from platform removals were 

used in stock assessment analyses to determine the relative 

importance of this mortality compared with other sources of 

mortality such as commercial and recreational fishing, trawl 

bycatch, and discards . As a result, stock assessments may be 

improved through addition of this new parameter into stock 

assessment equations . 

The most severely impacted fish species at explosive 

structure removals in order of abundance were Atlantic spadefish 

(Chaetodipterus faber), blue runner (Caranx crysos), red snapper 

(Lutjanus campechanus), and sheepshead (Archosargus 

probatocephalus) . These four species accounted for 86% of 

estimated mortality . Numbers of all other impacted species were 

far below those of the top four . Of the species encountered in 

these field studies, only red snapper, gag and red drum have 

stock assessments conducted on them by the National Marine 

Fisheries Service . For red snapper, even when the mortality 

estimate was doubled, impacts were estimated to be small, well 

within the variation of our current assessments, and would not 

alter current determinations of status or current management 

recovery strategies . Similarly, current methods of assessment 

would not detect the even smaller changes in magnitude of gag and 

red drum . Results indicated no significant difference in 

estimated mortality of red snapper by depth, longitude, platform 
V ill 

age, season, surface salinity, and surface temperature in the 

study area (14-32 m)during May to September . These analyses 

suggest no appropriate strata for expansion of mortality data to 

the greater Gulf of Mexico and indicate that platforms in the 

water depths studied can be included in a single group for the 

purpose of estimating fish mortality due to explosive platform 

removals . Although the effects of structure complexity on fish 

abundance was not an objective of this study, unpublished data 

from the National Marine Fisheries Service indicated structure 

complexity may directly influence observed mortality . This 

parameter was integrated into the sensitivity analysis for stock 

assessment . A significant difference in red snapper length at 

removals in 20-30 m water depths vs those at shallower and deeper 

depths was also incorporated into the analysis . 

Future impacts to the red snapper stock were predicted based 

on forecasts of future structure removals reported by Pulsipher 

et al . (in press) . Estimates of future mortality were higher than 

current estimates but less than the doubled value of current red 

snapper mortality which was used in these stock assessment 

analyses . Consequently, future red snapper mortality estimates at 

explosive structure removals fall within the variation of our 

current assessments . Given the assumptions used in these 

forecasts, predicted future mortality would not alter current 

determinations of stock status or current management recovery 

strategies for red snapper . However, should future facts alter 

the validity of these assumptions, then these predictions should 

be revised accordingly . 

Three important caveats should be remembered when 

interpreting these results . First, species composition and 

abundance can change in water depths deeper than those 

encountered during this study . Second, sample size was small, 

only nine platforms out of more than 4,000 structures present in 

the U.S . Gulf of Mexico . Finally, all sampling was conducted 

during the months of May through September . 
ix 

TABLE OF CONTENTS 

D n r'-"P 

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi 

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii 

1 .0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

2 .0 Study Site Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

3 .0 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

3 .1 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

3 .2 Fish Tagging Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

3 .3 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

3 .3 .1 Mortality Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

3 .3 .2 Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 11 

3 .3 .3 Population Estimates and Mortality Rates . . . . . 13 

3 .3 .4 Quantitative Impact on Selected Fish Stocks . .13 

3 .3 .4 .1 Red Snapper Stock Assessment 

Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

3 .3 .4 .2 Gag ( Mycteroperca microlepis) Stock 

Assessment Methodology . . . . . . . . . . . . . . . 18 

3 .3 .4 .3 Red Drum ( Sciaenops ocellatus ) Stock 

Assessment Methodology . . . . . . . . . . . . . . . 18 

4 .0 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

4 .1 Fish < 8 cm TL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

4 .2 Estimated Mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

4 .2 .1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

4 .2 .2 Mortality by Depth and Longitude . . . . . . . . . . . . . 24 

4 .2 .3 Mortality by Season . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

4 .2 .4 Mortality by Platform Age . . . . . . . . . . . . . . . . . . . . 34 

4 .2 .5 Mortality by Surface Temperature and 

Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

4 .2 .6 Estimated Mortality by Platform Size . . . . . . . . . 34 

4 .3 Length-Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

4 .4 Population Estimates and Mortality Rates . . . . . . . . . . . . 35 

4 .5 Fish Density Around Platforms . . . . . . . . . . . . . . . . . . . . . . . 44 

4 .6 Comparison of Estimated Mortality and Size of 

Positively and Negatively Buoyant Fish . . . . . . . . . . . . . . 44 

4 .7 Assessing Impacts (1989-98) . . . . . . . . . . . . . . . . . . . . . . . . . 50 
X 

4 .7 .1 Impacts on Red Snapper (1989-98) . . . . . . . . . . . . . 50 

4 .7 .2 Impacts on Gag (1989-98) . . . . . . . . . . . . . . . . . . . . . 53 

4 .7 .3 Impacts on Red Drum (1989-98) . . . . . . . . . . . . . . . . 53 

4 .8 Assessing Future Impacts on Red Snapper(1999-2023) . .53 

5 .0 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

5 .1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

5 .2 Depth and Longitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S5 

5 .3 Season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 

5 .4 Platform Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 

5 .5 Surface Temperature and Salinity . . . . . . . . . . . . . . . . . . . . 58 

5 .6 Platform Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 

5 .7 Length-Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 

5 .8 Population Estimates and Mortality Rates . . . . . . . . . . . . 59 

5 .9 Fish Density Around Platforms . . . . . . . . . . . . . . . . . . . . . . . 60 

5 .10 Comparison of Positively and Negatively Buoyant 

Fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

5 .11 Estimating Red Snapper Impacts across the U .S . 

Gulf of Mexico Using Stock Assessment Techniques . . . . 61 

5 .11 .1 Structure Complexity and Red Snapper 

Mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

5 .11 .2 Water Depth and Structure Removal . . . . . . . . . . . 62 

5 .11 .3 Red Snapper Length by Water Depth . . . . . . . . . . . 63 

5 .11 .4 Assessment of Impacts on Red Snapper 

(1989-98) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

5 .11 .5 Assessing Future Impacts on Red Snapper 

(1999-2023) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 

5 .12 Sources of Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 

6 .0 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 

Appendix I Pre-detonation Visual Fish Surveys . . . . . . . . . . . . 77 

Appendix II Common and Scientific Names of Collected 

Fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 
X1 

LIST OF FIGURES 

pArF 

Figure 

1 Map of study sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

2 Schematic of sampling design showing transect lines, 

circular surveys, and sampling area under platform . . . . . . . . 5 

3 Schematic of transect line sampling showing 100 m 

line secured to the platform at one end and weighted 

and staked to the sea floor at the other . . . . . . . . . . . . . . . . . .? 

4 Schematic of circular surveys within 25 m of platform . . . . . 8 

5 Schematic of circular surveys at distances greater than 

25 m from platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

6 Schematic of sampling under a platform . . . . . . . . . . . . . . . . . . . 10 

7 Estimated age frequency of annual platform mortality of 

red snapper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

8 Estimated mortality at platforms by water depth and 

species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

9 Estimated mortality at platforms by longitude and 

species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

10 Estimated mortality at platforms by month and species . . . . 27 

11 Estimated mortality at platforms by platform age and 

species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

12 Estimated mortality at platforms by surface water 

temperature and species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

13 Estimated mortality at platforms by surface water 

salinity and species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

14 Estimated mortality at platforms by platform size and 

species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

15 Length-frequency (TL in cm) of Atlantic spadefish by 

platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

16 Length-frequency (TL in cm) of blue runner by platform . . . 39 

17 Length-frequency (TL in cm) of gray triggerfish by 

platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

18 Length-frequency (TL in cm) of mangrove snapper by 

platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

19 Length-frequency (TL in cm) of red snapper by platform . . . 42 

20 Length-frequency (TL in cm) of sheepshead by platform . . . . 43 

21 Summary of fish collections by platform . . . . . . . . . . . . . . . . . . 45 

22 Red snapper assessment results including platform 

removals using Data Set E (represents arbitrary doubling 

of moderate to high estimate of red snapper mortality at 

platforms) compared to base case assessment (base) . . . . . . . 52 

X111 

LIST OF TABLES 

Table 

PAGE 

1 Characteristics of platforms studied . . . . . . . . . . . . . . . . . . . . . . . 3 

2 Estimated platform mortality at age (numbers of red 

snapper) for each mortality estimate (Data Sets A-E) . . . . . . 16 

3 A . Mortality at age of red snapper including directed 

fisheries mortality (including release mortality) and 

bycatch (from Schirripa and Legault 1999) . B . Proportion 

of additional mortality from platform removals using Data 

Set E (double the moderate to high estimate of annual red 

snapper mortality at platform removals based on 1989-98 

data) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

4 Estimated mortality and descriptive statistics by species 

and platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

5 A . Gulf of Mexico gag catch at age (without platform 

removal estimates) . B . Estimated number at age . C . 

Estimated fishing mortality rate at age . . . . . . . . . . . . . . . . . . . 20 

6 Catch at age of red drum (without platform removal 

mortality) from most recent assessment (Porch 2000) . . . . . . . 21 

7 Estimated mortality of the five most impacted species . . . . . 23 

8 ANOVAs for estimated mortality by test parameter for the 

six most impacted species and all species combined . . . . . . . . 33 

9 GLM analysis of total length by depth (<20 m vs >20 m) and 

longitude (<92° vs >92°) for most impacted species . . . . . . . . . 36 

10 Mean total total length by depth (<20 m vs >20 m) for 

most impacted species and all species combined . . . . . . . . . . . . 36 

11 Recapture rates (100 x number of tags recovered/number of 

tags released) for tag-recapture study . . . . . . . . . . . . . . . . . . . . 36 

12 Population estimates by species and platform . . . . . . . . . . . . . . 37 

13 Mortality rates (100 x estimated mortality/population 

estimate) by species and platform . . . . . . . . . . . . . . . . . . . . . . . . . 37 

14 Comparison of red snapper mortalities collected at the 

surface (floaters) with estimated mortality from the sea 

floor (sinkers) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 

15 Comparison of total length of positively (floater) and 

negatively (sinker) buoyant red snapper by platform . . . . . . . 49 

16 Changes in red snapper management benchmarks from base 

case assessment when refitting estimation models using 

platform removal Data Set E (double the moderate to high 

estimate of annual red snapper mortality at platform 

removals based on 1989-98 data) . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 

17 Estimated number of dead fish floating at the surface 

after detonations during 1986-98 . . . . . . . . . . . . . . . . . . . . . . . . . . 51 
X1V 

18 Description of data used in stock assessment sensitivity 

analysis for red snapper mortality at explosive structure 

removals in >7 m depths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 
1 .0 INTRODUCTION 

The first offshore energy platform in the Gulf of Mexico was 

built in 1942 (Pulsipher et al, in press) . As of January 31, 2000 

there were 3,967 oil and gas structures) present in federal 

waters of the Gulf of Mexico . Federal regulations require removal 

of these structures within one year of lease termination . 

According to data from the National Marine Fisheries Service 

(NMFS) Platform Removal Observer Program which includes removals 

in both federal and state waters, from 1989-98 a total of 958 

structures were salvaged using explosives for an annual average 

of roughly 96 structures . For the same period, MMS data for 

federal waters indicate underwater explosives were used in 64% of 

all removals (submerged wells not included in these data) . In the 

most common explosive removal method, 40-50 lb charges are 

detonated inside the pilings and well conductors at a minimum 

depth of 5 m below the sea floor (MMS requirement) . Consequently, 

hundreds of pounds of explosives, primarily Comp-B and C-4, are 

used at most offshore platform removals . 

Offshore platforms function as artificial reefs attracting a 

wide variety of marine life as well as an abundance of anglers 

(Hastings et al . 1976 ; Sonnier et al . 1976 ; Dugas et al . 1979 ; 

Gallaway 1980 ; Continental Shelf Associates 1982 ; Gallaway and 

Lewbel 1982 ; Gallaway and Martin 1980 ; Ditton and Auyong 1984 ; 

Witzig 1986 ; Reggio 1987 ; Stanley and Wilson 1989 ; ScarboroughBull and Kendal) 1990 ; Stanley and Wilson 1990 ; Rooker et al . 

1997) . One obvious consequence of using explosives to remove 

offshore structures is a negative impact on fish . Although 

offshore platforms have been the subject of much scientific study 

over the years, there has previously been no attempt to quantify 

the impacts of explosive platform removal on fish populations . Of 

special concern is the commercially and recreationally important 

red snapper (Lutjanus campechanus) which occurs at many of these 

structures . The red snapper continues to be the subject of 

intense government regulation as this species is severely 

overfished and there are significant problems in the long-term 

viability of the stock (Goodyear and Phares 1990 ; Goodyear 1996 ; 

Cowan 1998 ; Schirripa, 1998) . 

Fishery managers attempt to track the size and status of 

stocks using mathematical equations which include variables 

relating to recruitment and mortality . The results of such stock 

assessment analyses provide managers with critical information 

needed to manage fisheries . This study attempts to quantify the 

mortality of fish by species resulting from explosive platform 

Michelle Morin, Minerals Management Service, 1201 Elmwood Park Boulevard, New Orleans, LA 70123 . 

Personal communication. 
z 

removals . For the first time, mortality estimates from platform 

removals were used in stock assessment analyses to determine the 

relative importance of this mortality compared with other sources 

of mortality such as natural and fishing mortality . As a result, 

stock assessments may be improved through addition of this new 

parameter into stock assessment equations . 

2 .0 STUDY SITE SELECTION 

Although this study was intended to sample a total of 10 

platforms, sufficient data to estimate fish mortality were 

collected at 9 of 10 study sites off the Louisiana and Texas 

coasts in water depths ranging from 14-32 m (Table l, Figure 1) . 

Field work spanned seven sampling seasons from 1993-1999 

primarily due to restrictions relating to structure type, water 

depth, season, and cooperation from platform owners . Structures 

in very shallow water were thought to lack key species of 

interest, particularly red snapper . Intensive underwater sampling 

required substantial amounts of bottom time . This limited study 

depths to a maximum of approximately 36 m . Also, best results 

were obtained when sampling was conducted as soon as possible 

after explosives were detonated . This minimized fish loss from 

the sea floor due to predation and allowed samples to be 

collected before decomposition of dead fish resulted in 

subsequent bloating and floating of carcasses to the surface that 

could occur within 24 h of detonation . Loss of dead fish from the 

sea floor could cause gross underestimates of fish mortality . Due 

to safety considerations platform salvage work halted while 

research divers collected samples in close proximity to the 

platform . Despite a dive contingent which usually numbered a 

dozen or more, this generally meant that the platform owner would 

incur additional costs of thousands or tens of thousands of 

dollars for a 5 h work delay . To accommodate diving operations 

and reduce cost overruns, removals occurring during the winter 

weather season from December through April were not targeted for 

inclusion in the study . For these reasons, selection of the ten 

study sites is best characterized as opportunistic rather than 

random . 

3 .0 MATERIALS AND METHODS 

3 .1 Sampling 

Although sampling techniques were refined during the study, 

basic sampling design is summarized in Figure 2 . After detonation 

of explosives, dead fish either floated to the surface or sank to 

the sea floor . To assess the impact on fish populations, field 

personnel operating from inflatable boats used dip nets to 
Table 1 . Characteristics of platforms studied . 

Platform ID I SMI 23 WD 30 ST 146 SS 158 WC 172 WC 173 WC 181 SS 209 GA 288 SS 2141 

Depth (m) 25 13 .7 28 16.8 14.6 14.6 17.6 

Depth (ft) 82 45 92 55 48 48 58 

Platform age (yr) 33 39 16 12 23 19 17 

Longitude (°W) 91 .88 89.62 90.5 91 .03 93 .23 93 .18 93 .2 

Surface temperature (°C) 29 30 26 30.5 30.5 29 32 .1 

Surface salinity (ppt) 33 26 18 23 25 24 

Month of removal 8 7 5 7 8 9 7 

Year removed 94 94 95 93 95 95 97 

Volume (m) 7050 9809 6860 3310 1037 1927 1408 

Mortality was not estimated at this location because only surface fish collections were conducted. 

32 22.9 36 

105 75 118 

37 31 24 

90.87 94.7 90.86 

31 28 29 

28.8 28.5 30 

7 5 6 

98 99 97 

5696 2290 29860 

W 
97°W 

100 km 

960W 95°W 94°W 930W 920W 91°W 90°W 

f\ LOUISIANA 

~rJ r ..,o.~., N, New Orleans 

Galvest '-"WC 172--;)- 8P~ W C 173 

SS 158 "" 

TEXAS .WC 181 SM123 --> 

-=GA 288 . ." 73m ST 146 

/ ' .55m, 

- --~-

:r : . 

v --~ SS 207 \ SS 214 

x pus ----

insti 

mnsviue 

J e iq m ~ 

', 30°N _ 

~29°N 

W D 30 

28°N 

27°N 

26°N 

A 

Figure 1 . Map of study sites . Dark circles represent platforms where fish mortality was 

estimated from samples collected at the sea surface and bottom . The white 

circle represents a platform where only sea surface sampling was conducted . 
100 m 

50 m 

25 m 

/ Platform 

Under platform 

"" Transect 

Circular survey 

Figure 2 . Schematic of sampling design showing transect lines, circular surveys, and 

sampling area under platform . 
6 

collect all dead fish that floated to the surface while divers 

manually sampled dead fish that sank to the sea floor . Dives were 

delayed a minimum of 30 minutes after detonation to allow fish to 

die and sink to the bottom . Three techniques were employed to 

sample dead fish from the sea floor beneath and around the 

platform : transect lines, circular surveys, and sampling frames . 

One hundred meter transect lines radiating out from the base of 

the platform were sampled by divers . Two hundred meter transects 

were surveyed at one platform . Transect width varied with 

underwater visibility but was either 2 or 4 m . Two person dive 

teams were always used during collections . Divers lined up on 

opposite sides at one end of a transect line . Each diver grasped 

the transect line in one hand and used their outstretched arms to 

estimate a transect width of either 1 or 2 m on each side of the 

line . At the first study site divers used mesh bags to collect 

discrete samples of dead fish in 5 m increments along the 100 m 

transect line . This proved to be too time consuming so 25 m 

increments were sampled at all but the final study site where the 

25 m area nearest the platform was divided into two 12 .5 m 

segments (Figure 3) . 

A second technique was used to assess fish mortality around 

the platform . At the first study site, 44 square frame nets 

measuring 13 .4 m2 each were deployed on the sea floor around the 

platform within a radius of 100 m . A buoyed line attached to the 

frames allowed easy retrieval from a vessel after explosives were 

detonated . At subsequent platform removals these nets were 

replaced with circular surveys performed by divers . One end of a 

3 .35 m long PVC pipe was staked to the sea floor . Using the pipe 

as a distance gauge, divers collected dead fish as they swam the 

pipe in a circle using the staked end of the pipe as a pivot 

point . Twenty-four circular surveys measuring 6 .7 m in diameter 

and 35 .3 m2 were sampled within 100 m of the structure . Samples 

within 25 m (Figure 4) of the structure were collected along 

guidelines secured to the base of the platform to insure there 

was no overlap between circular and transect surveys . Beyond 25 m 

there was little chance of overlap, and a compass and range 

finder were generally used to locate sampling sites within 

selected quadrants around the platform (Figure 5) . 

Dead fish which fell to the sea floor beneath the platform 

were collected using rectangular sampling frames of various 

designs and dimensions (Figure 6) . One inch galvanized pipe 

frames measuring 3 x 3 m were initially used to accommodate 

potentially large fish kills beneath the platform . These frames 

featured mesh that could be pursed with a draw string to prevent 

fish loss during retrieval to the surface with lift bags . When 

large fish kills were not encountered, these heavy, cumbersome 

frames were replaced with lightweight PVC frames without mesh . 

Divers manually placed fish from the sampling frame into mesh 
Figure 3 Schematic of transect line sampling showing 100 m line secured to the plattorm 

at one end and weighted and staked to the sea floor at the other . Divers 

deployed from an inflatable boat and followed the buoy line down to the transect 

line . Divers collected all dead fish within a predetermined sampling width, 

either 1 or 2 m, on each side of the transect . Fish samples were generally 

bagged in 25 m increments which allowed calculation of fish estimates at 

different distances around the platform . Bags with fish were clipped back onto 

the transect line and empty bags were used for collections along the next 

section until the entire line was sampled . 

J 
00 

y ` ~ - 

Platform leg 

Guideline 

Sampling area 

Sample 

marker 

Figure 4 . Schematic of circular surveys within 25 m of platform . To prevent overlap with 

transect line sampling, a guideline was used to mark locations of circular 

surveys adjacent to the platform . Divers descended along the platform leg and 

followed the guideline to the marker to begin sampling . 
BUOY 

Descent / Ascent line 

Point of 

rotation 

Clump 

weight 

Stake 

3.4 m 

Figure 5 . Schematic of circular 

Buoys were set using 

Using the staked end 

fish in sampling bags 

a marker stuck in the 

survey . 

Start-stop 

marker 

PVC pipe 

surveys at distances greater than 25 m from platform . 

a compass and range finder to mark sampling locations . 

of a 3 .4 m long PVC pipe as a pivot point, divers collected 

as they swam a circle . When underwater visibility was low, 

sea floor was used to indicate the start-stop point of the 

110 
0 

4:4 

4K 

T` -

49 

Sampling frame 

Figure 6 . Schematic of sampling under a platform . Sampling frames constructed of PVC pipe 

were placed beneath the platform . Lines securing the frames to the platform 

served as rope highways during night dives and when visibility was poor . Divers 

manually collected all fish that fell within the borders of the sampling frame . 
11 

bags . At the large platform at West Delta Block 30, structural 

members were also used to delineate sampling areas on the sea 

floor . For further information about diving operations, diver 

training, and sampling at offshore platforms consult Gitschlag 

(1995) . 

3 .2 Fish Tagging Study 

To estimate fish population size prior to detonation of 

explosives, a fish mark recapture study was conducted . Fish were 

captured on rod and reel using assorted hook sizes . Traps were 

occasionally used to supplement catches . Total length and species 

were recorded for each fish landed . Fish were tagged with plastic 

t-bar tags using tagging guns . Only fish that were alive and in 

good condition were released . 

3 .3 Analysis 

3 .3 .1 Mortality Estimates 

Data recorded for dead fish collected after the explosion 

included species identification, total length, weight, and tag 

presence or absence . Unless otherwise stated, all results refer 

to fish greater than or equal to 8 cm total length since this was 

the minimum size consistently collected by hand by divers . Seafloor surface areas were calculated for each region surrounding 

the platform in 25 m increments out to 100 m. Fish density was 

determined for each 25 m band around the platform . The ratio of 

total area to sample area within each band was calculated and 

multiplied by fish density to determine estimated fish mortality 

for that region . Mortality estimates for each region were summed 

to provide a total estimate of fish mortality from the sea floor 

surrounding the platform . The area immediately under the 

platform, called the footprint, was determined mathematically 

after subtracting areas where well conductors penetrated the sea 

floor . Samples from the footprint area were pooled and fish 

mortality was estimated as described above . Finally, the estimate 

from the 100 m area surrounding the platform was combined with 

that of the footprint and added to the surface mortalities to 

provide a total mortality estimate for each platform . 

3 .3 .2 Statistical Analysis 

Mortality estimates at each platform by species and for all 

species combined were partitioned into a series of two sample 

tests to analyze various factor effects . Prior to analysis, data 

were tested for normality using the Kolmogorov-Smirnov test and 

for equality of variance using the F-test . When no significant 
12 

differences were found at P<=0 .05, single factor ANOVA was used . 

When either test showed rejection of the null hypothesis, data 

were transformed using square root and re-tested . In one case 

where data passed the normality test but transformation did not 

reduce variance, ANOVA was used when variance was somewhat 

heteroscedastic (P=0 .03 for red snapper analysis by longitude) . 

Due to unequal sample sizes, GLM (general linear model) was 

used for multivariate analysis for both mortality and length 

data . Due to the large sample size of length measurements for 

each of the top five impacted species except mangrove snapper, 

length data were not subjected to the same rigorous testing for 

normality and homogeneity of variance prior to GLM analysis in 

keeping with the Central Limit Theorem . After GLM analysis, plots 

of means by standard deviations were reviewed to assess patterns 

indicative of unequal variance . None were observed . When 

significant differences were found with GLM, main effects were 

further analyzed using Tukey-Kramer studentized range test for 

paired comparisons . For analysis of length of positively 

(floating) and negatively buoyant (sinking) red snapper at each 

platform, data were not normally distributed and the 

nonparametric Mann-Whitney test was used . Data at two platforms 

were log transformed to reduce heteroscedasticity (F-test P=0 .02 

for Block 23 and P=0 .04 for Block 181) . 

For mangrove snapper length, sample size was small in some 

depth-longitude cells so normality and variance testing was 

performed . Although mangrove snapper length by depth zone was not 

normally distributed, variance was equal and Mann-Whitney test 

was used for paired comparisons of three depth zones (<20 m vs 

20-30 m, <20 m vs >30 m, and 20-30 m vs >30 m) . Mangrove snapper 

lengths were log transformed to equalize variance for comparison 

of two depth zones (<20 m vs > 20 m) . 

Estimated mortality by year and platform volume were 

analyzed using the Spearman rank correlation coefficient (Glantz 

1992) . Volume was calculated by multiplying the footprint area of 

the platform by water depth . This provided an overestimate of 

platform volume because, except in shallow water, the footprint 

area on the sea floor is larger than the deck area at the sea 

surface . 

Analysis of fish density around platforms used actual, not 

estimated, numbers of fish . To approximate the normal 

distribution, transect data were transformed by log (density + 1) . 

All species were grouped together and analyzed using a two sample 

t-test assuming unequal variance . According to the Central Limit 

Theorem, confidence in the results of this procedure increases 

with increasing sample size because the distribution of the 

sample mean approaches a normal distribution . Similar procedures 

were used for analysis of circular survey data . 
13 

3 .3 .3 Population Estimates and Mortality Rates 

Estimates of pre-detonation fish populations were calculated 

using the ratios of tagged to untagged fish as follows : 

Nb = Na x Ntv/Nta 

where Nb is the number of live fish present before blasting, 

Na is the number of dead fish collected after blasting, 

Ntb is the number of fish tagged and released before blasting, 

and Nta is the number of dead tagged fish collected after 

blasting . This equation was used to estimate pre-detonation 

population sizes by species . A total fish population estimate was 

not calculated because species composition of fish tagged prior 

to detonations differed from that of dead fish collected after 

detonations . This was a consequence of selectivity of fishing 

gear used to catch live fish for pre-detonation tagging . 

Mortality rates were calculated for species at platforms 

where both pre-detonation population estimates and postdetonation mortality estimates were determined . Dividing the 

mortality estimate by the population estimate yielded the 

mortality rate . 

3 .3 .4 Quantitative Impact on Selected Fish Stocks 

The inherent uncertainty in expanding red snapper mortality 

from "per platform" estimates to annual estimates was 

acknowledged and accounted for in the evaluation of impacts by 

including three different versions of the estimate for recent 

mortality and two versions for future mortality : 

Data Set A : Low estimate of annual red snapper mortality based 

on structure removal data from 1989-98 : estimated 

annual mortality of 29,046 fish . 

Data Set B : Moderate to high estimate of annual red snapper 

mortality based on structure removal data from 

1989-98 : estimated annual mortality of 41,200 

fish . 

Data Set C : Low estimate of future annual red snapper 

mortality based on forecasts of annual structure 

removals for 1999-2023 : estimated annual mortality 

of 43,157 fish . 

Data Set D : High estimate of annual red snapper mortality 

based on forecasts of annual structure removals 

for 1999-2023 : estimated annual mortality of 
14 

66,435 fish . 

Data Set E : This data set represents an arbitrary doubling of 

Data Set B to establish some limits on possible 

impacts given uncertainties in estimation of 

platform mortality : estimated annual mortality of 

82,400 fish . 

Low (Data Set A), moderate to high (Data Set B), and double the 

moderate to high estimates (Data Set E) of annual red snapper 

mortality at explosive platform removals were calculated based on 

information obtained from this and other studies from 1989-98 

(see Discussion for details) . Similar procedures were used to 

develop Data Sets C and D to assess future impacts on red snapper 

based on a forecast of future platform removals (Pulsipher et 

al ., in press) . 

3 .3 .4 .1 Red Snapper Stock Assessment Methodology 

Length frequencies of red snapper were converted to age 

frequencies using Table 1 of Schirripa and Legault (1999), the 

most recent red snapper stock assessment analyses . The resulting 

age-frequency (Figure 7) and platform mortality at age (for each 

year class, Table 2) indicate that age two was the modal age of 

platform mortality . Stock assessment analysis was performed on 

the doubled data set to establish bounds on the purported impact . 

The additional mortality at age (1989-98) implied by the doubled 

estimate was added to each year of the annual fishing induced 

mortality at age estimated from other sources : commercial, 

recreational, discard mortality and bycatch (Table 3) . The stock 

assessment analysis in Schirripa and Legault (1999) was then 

repeated using the mortality at age including Data Set E for each 

year, 1989-98 . 

Note that the assessment analyses in Schirripa and Legault 

(1999) have evolved in their complexity from earlier work 

(Goodyear and Phares 1990, Goodyear 1989) . The current methods 

use the same population model ; however, improvements in 

statistical fitting algorithms have allowed the relaxation of 

assumptions used previously . These improvements have included : 1) 

mortality at age is not assumed to be known with certainty and 

statistical variation in mortality is accounted for in the 

fitting ; 2) selectivity at age from each fishery is estimated 

through the fitting procedure, rather than being imposed through 

an external assumption ; and 3) the stock recruitment model 

(needed for calculating management benchmarks) is fit 

simultaneously with other variables rather than being fit after 

the fact . Details of these modifications are given in Schirripa 

and Legault (1999) . 
15 

0 .35 

0.3 

0.25 

c 

0.2 

L 

0 .15 

0.1 

0 .05 

0 

Age 

Figure 7 . Estimated age frequency of annual platform mortality of 

red snapper . 

0 2 4 6 8 10 12 14 16 >17 
16 

Table 2 . Estimated platform mortality at age (numbers of red 

snapper) for each mortality estimate (Data Sets A - E) . 

Age 

Data A Data B Data C Data D Data E 

0 27 39 42 65 80 

1 2935 4148 4423 6809 8445 

2 9784 13923 14599 22473 27874 

3 8704 12327 12860 19796 24554 

4 2809 3985 4149 6387 7922 

5 1334 1896 1971 3034 3763 

6 843 1185 1237 1904 2362 

7 550 788 820 1262 1566 

8 427 602 629 968 1201 

9 321 451 474 730 905 

10 186 264 279 429 533 

11 283 398 420 647 802 

12 36 52 54 83 103 

13 211 300 318 490 607 

14 111 154 160 246 305 

15 14 26 28 43 53 

16 72 99 105 162 200 

17 84 117 123 189 235 

>17 315 446 466 717 890 

Total 29046 41200 43157 66435 82400 

Data Set A: Low estimate of annual red snapper mortality based on structure removal data from 

1989-98. 

Data Set B: Moderate to high estimate of annual red snapper mortality based on structure 

removal data from 1989-98 . 

Data Set C: Low estimate of future annual red snapper mortality based on forecasts of annual 

structure removals for 1999-2023 . 

Data Set D: High estimate of annual red snapper mortality based on forecasts of annual structure 

removals for 1999-2023. 

Data Set E: This data set represents an arbitrary doubling of Data Set B to establish some limits 

on possible impacts given uncertainties in estimation of platform mortality. 
Table 3 . A . Mortality at age of red snapper including directed fisheries mortality 

(including release mortality) and bycatch (from Schiripa and Legault 1999) . 

B . Proportion of additional mortality from platform removals using Data Set E 

(double the moderate to high estimate of annual red snapper mortality at 

platform removals based on 1989-98 data) . 

A. 

Year Age 0 

1984 8045789 

1985 5070414 

1986 10842855 

1987 8827322 

1988 10246806 

1989 16479304 

1990 15994584 

1991 20893292 

1992 16086854 

1993 18256121 

1994 19752131 

1995 19966959 

1996 13140123 

1997 15104940 

1998 16526770 

B. 

Year Age 0 

1989 0.001 

1990 0.001 

1991 0.000 

1992 0.001 

1993 0.000 

1994 0.000 

1995 0.000 

1996 0.001 

1997 0.001 

1998 0.001 

Avg. 0.001 

Age 1 Age 2 

7302444 506023 

12371844 432742 

7392935 595474 

14100342 324418 

11636915 672163 

10180341 444697 

35611302 286573 

24191064 639866 

12985745 299222 

14202511 362664 

21180642 311503 

23153641 188159 

22019964 232382 

24125247 333637 

9469581 218530 

Age l Age 2 

0.003 0.055 

0.001 0.086 

0.001 0.038 

0.002 0.082 

0.002 0.068 

0.001 0.079 

0.001 0.130 

0.001 0.106 

0.001 0.074 

0.003 0.112 

0.002 0.083 

Age 3 

864375 

339458 

723587 

979206 

536294 

1049868 

613345 

609185 

1996646 

1183261 

885412 

797526 

806827 

1153038 

803275 

Age 3 

0.008 

0.013 

0.013 

0.004 

0.007 

0.009 

0.010 

0.010 

0.007 

0.010 

0.009 

Age 4 

540476 

302873 

120196 

273198 

599219 

135491 

393603 

284748 

225908 

1508757 

702375 

461400 

783925 

885121 

1125239 

Age 4 

0.028 

0.010 

0.013 

0.017 

0.002 

0.005 

0.008 

0.005 

0.004 

0.003 

0.010 

Age 5 Age 6 Age 7 

270269 127047 30311 

260491 152088 73475 

205164 203251 100490 

44206 101539 126078 

144512 27728 78146 

236220 69519 15217 

31700 67176 25476 

225460 19545 42668 

143947 157250 16675 

60209 49074 91187 

718076 18205 13368 

244759 300186 7043 

259742 175625 239360 

356024 127735 108431 

452510 152838 55392 

Age 5 Age 6 Age 7 

0.010 0.023 0.079 

0.075 0.023 0.047 

0.010 0.080 0.028 

0.016 0.010 0.072 

0.039 0.032 0.013 

0.003 0.086 0.090 

0.010 0.005 0.171 

0.009 0.009 0.005 

0.007 0.012 0.011 

0.005 0.010 0.022 

0.018 0.029 0.054 

Age 8 

39326 

19594 

44564 

64519 

111708 

49015 

6541 

17351 

41639 

14434 

29594 

4858 

5020 

178746 

52581 

Age 8 

0.018 

0.138 

0.052 

0.022 

0.063 

0.031 

0.186 

0.180 

0.005 

0.017 

0.071 

Age 9 

24281 

29908 

12127 

25668 

61296 

76716 

23053 

4826 

18803 

46772 

5920 

11564 

3127 

4235 

97317 

Age 9 

0.007 

0.023 

0.110 

0.028 

0.011 

0.090 

0.046 

0.170 

0.126 

0.005 

0.062 

Age 10 Age 11 

14530 15416 

21538 14256 

19847 15603 

6331 9900 

24391 5918 

44447 17890 

37293 21861 

18569 32722 

5657 22958 

24905 8234 

23644 15015 

2632 11964 

7215 1671 

2816 6716 

2511 1778 

Age 10 Age 11 

0.018 0.006 

0.022 0.005 

0.043 0.003 

0.142 0.004 

0.032 0.013 

0.034 0.007 

0.305 0.009 

0.111 0.062 

0.285 0.015 

0319 0.058 

0.131 0.018 

Age 12 

20249 

16145 

11092 

7740 

9177 

4311 

8782 

20762 

41467 

35108 

5707 

8500 

7897 

1592 

4464 

Age 12 

0.141 

0.069 

0.029 

0.015 

0.017 

0.106 

0.071 

0.077 

0.381 

0.136 

0.104 

Age 13 

15126 

21952 

13487 

5499 

7203 

6572 

2127 

8850 

26483 

64271 

27407 

3521 

5886 

7680 

1106 

Age 13 

0.046 

0.143 

0.034 

0.012 

0.005 

0.011 

0.087 

0.052 

0.040 

0.276 

0.071 

Age 14 Age 15+ 

12203 60674 

16571 77366 

19531 91445 

6776 59906 

5132 61561 

5050 41309 

3290 25304 

2241 30905 

11163 38440 

40825 65438 

55113 112695 

18116 120108 

2554 115397 

5851 123459 

5544 104431 

Age 14 Age 15+ 

0.010 0.038 

0.016 0.062 

0.024 0.051 

0 .005 0.041 

0 .001 0.024 

0 .001 0.014 

0.003 0.013 

0.021 0.014 

0.009 0.013 

0.010 0.015 

0.010 0.029 

J 
18 

In conjunction with the red snapper stock assessment 

analysis using the additional mortality from Data Set E, 

management benchmarks and population characteristics were 

recalculated . These included : fishing mortality rate at which the 

slope of the yield-per-recruit curve is one tenth of what it is 

at the origin (F0 .1) ; the fishing mortality rate that maximizes 

yield-per-recruit (Fmax) ; the fishing mortality rate which 

reduces spawning potential ratio to 20%, 30%, and 400 of what it 

would be with no fishing (F20%SPR, F20%SPR, F40%SPR) ; the fishing 

mortality rate that would eventually produce maximum sustainable 

yield (FMSY) ; and the most recent estimate of fishing mortality 

rate (for 1998, F1998) . Additionally, Maximum Sustainable Yield 

(MSY), the biomass that would support the taking of MSY (BMSY), 

and the spawning stock in number of eggs that would support MSY 

(SSMSY) were also calculated . The results were compared to 

results from the base case stock assessment (Schirripa and 

Legault 1999) . 

3 .3 .4 .2 Gag (Mycteroperca microlepis) Stock Assessment 

Methodology 

Gag, a popular recreational and commercial grouper, were 

present in the platform removal samples (Table 4) . The mean 

number of gag killed per platform (only 1 .6) was expanded to an 

annual estimate equivalent to the ratio of red snapper in Data 

Set E relative to the mean kill per platform removal 

(82,400/514 .7) . This yielded an annual platform removal kill of 

256 gag per year (under Data Set E assumptions) . This value was 

compared to the results of the most recent gag stock assessment 

(Schirripa and Legault 1997) which are reproduced in Table 5 . 

3 .3 .4 .3 Red Drum (Sciaenops ocellatus) Stock Assessment 

Methodology 

Red drum were also present in low numbers in the platform 

removal samples (Table 4) . The mean number of red drum killed per 

platform removal (6 .0) was expanded to an annual estimate 

equivalent to the ratio of red snapper in Data Set E relative to 

the mean kill per platform (82,400/514 .7) . This yielded an annual 

platform removal kill of 961 red drum per year (under Data Set E 

assumptions) . This value was compared to the results of the most 

recent red drum stock assessment (Porch 2000) which are 

reproduced here in Table 6 . 
Table 4 . Estimated mortality and descriptive statistics by species and platform. 

SPECIES SMI 23 WD 30 ST 146 SS 158 WC 172 WC 173 WC 181 SS 209 GA 288 Total Mean Std error Std dev Var 

95% 

confidence 

level 

Almacojack 29 0 1 0 0 0 0 0 0 30 3 3 10 9? 7 

Atlantic bumper 0 0 0 0 46 201 0 0 0 247 .7 22 67 4471 SI 

Atlantic croaker 

Atlantic spade8sh 

0 

2069 

0 

631 

0 

698 

0 

1689 

0 

911 

7 

1068 

0 

2401 

0 

633 

0 

2774 

7 

1-875 

I 

1431 

I 

375 824 

5 

679238 634 

Atlantic thread herring 0 0 0 0 0 I 0 0 0 I 0 0 0 (> 

5 

Belted sand bass I 1 0 0 0 1 0 17 0 0 29 3 2 6 40 

Bermuda drub 0 0 0 0 0 0 43 0 0 43 5 5 14 304 11 

Black drum 0 19 6 0 2 14 0 0 3 44 5 2 7 48 5 

Blue runner 611 33 1592 1069 219 0 684 13 646 4867 541 181 542 294154 417 

Blutspotted searobin 0 0 0 0 I 0 0 0 0 1 0 0 0 0 0 

Chub mackerel 0 0 0 0 0 0 0 0 4 4 0 0 1 2 I 

Cocoa damselfish 0 0 0 0 0 0 4 0 0 4 0 0 1 2 I 

Crevalle jack 0 0 0 0 5 0 0 0 0 5 1 

7 

1 

7 

2 

22 

2 

487 17 

Cubbyu 0 0 0 0 0 0 0 0 66 66 

Gag 6 6 2 0 0 0 0 0 0 14 2 1 3 7 2 

Gray triggerRsh 144 1 16 116 13 0 22 43 44 399 44 17 52 2685 40 

Great barracuda 5 0 0 0 0 0 0 0 0 5 1 1 

Guaguanche 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 

Gulf toadfish 0 0 0 0 0 0 0 0 24 24 3 3 8 63 6 

Hardhead catfish 0 6 0 0 4 397 0 0 0 407 45 44 132 17466 101 

Harvest fish 0 0 0 0 0 5 0 00 0 5 1 1 2 2 1 

L11dyfish 0 3 0 0 0 0 0 0 0 3 0 0 1 I 1 

L na er 34 0 60 0 1 0 0 193 8. 371 41 22 65 5197 50 ane s pp 

Leopard toadfish 53 0 0 0 0 0 0 0 0 53 6 6 18 317 14 

Lookdown 0 3 0 0 0 0 0 0 0 3 0 0 1 I I 

Mangrove snapper 63 364 240 44 1 1 0 3.4 64 1100 1 .. 49 146 2132 . II . 

Molly miller 0 0 0 0 0 0 4 0 0 4 0 

2 

0 

2 

1 

7 

2 

54 

I 

6 

Mullet 0 22 0 0 0 0 0 0 0 22 

Ocean triggerfish 0 0 2 0 0 0 0 0 0 2 0 

6 

0 

4 

I 

12 

0 

141 

I 

9 

Pigfish 23 0 0 0 3 0 0 0 31 57 

Pinfish 0 0 0 0 0 3 0 0 17 20 2 2 6 33 4 

Planehead lilefish 44 0 0 0 0 0 0 0 0 44 5 5 1S 213 11 

Red drum 0 0 0 35 0 0 0 0 19 54 6 4 12 156 10 

Red snapper 1193 24 298 296 498 709 709 418 487 4632 515 111 332 110174 255 

Remora 0 0 0 0 13 0 0 0 0 13 1 1 4 19 3 

Rock hind 0 0 9 0 0 0 7 0 5 22 2 1 4 14 3 

Scaled sardine 0 0 0 0 8 0 0 0 0 8 1 1 3 7 Z 

Scamp 3 0 0 0 0 0 0 0 0 3 0 0 1 

Schoolmaster 9 0 0 0 0 0 0 0 0 9 1 1 3 

Scrawled file0sh 0 0 0 0 0 0 4 0 0 4 0 0 I 3 

30 4 

Sergeant major 0 0 0 0 5 16 0 0 0 21 2 2 5 

Sharksucker 0 0 0 0 0 3 0 0 0 3 0 0 1 I I 

Sheepshead 330 1007 1 .0 395 457 386 968 61 370 4094 455 110 329 108436 253 

Silk snapper 0 0 0 39 0 0 0 0 0 39 4 4 13 166 10 

Silver trout 0 0 140 0 1 0 0 0 0 141 16 16 47 -173 36 

Spanish sardine 0 0 0 0 0 1 0 0 0 1 0 0 0 0 (1 

Speckled trout 0 3 0 0 0 0 0 

0 

0 

0 

0 

464 

3 

464 

0 

5. 

0 

52 

1 

155 23929 I 119 

Tomtate 

lf h 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 0 0 16 16 2 5 30 4 

Unknown damse is 

0 0 27 0 27 3 3 9 81 7 

Unknown ee1 0 0 0 0 0 

0 38 39 4 4 13 161 10 

Unknown soapfish 0 0 1 0 0 0 0 

0 52 6 5 15 231 12 

Unknown 0 6 0 0 0 0 0 

10 

46 

5 53 97 11 6 17 303 13 

Whitespottedsoapfish 23 0 3 0 4 0 

1 1 2 3 1 

Yellow drub 1 0 0 0 0 0 0 2 5 8 

I 2 4 2 

Yellowtail snapp er 6 0 0 0 0 0 0 0 0 6 I 

Total 4657 2128 3188 3682 2193 2812 4874 1765 5216 30513 3390 429 1288 1658640 990 
20 

Table 5 . A . Gulf of Mexico gag catch at age (without platform 

removal estimates) . B . Estimated number at age . 

C . Estimated fishing mortality rate at age . All tables 

are from most recent assessment (Schirripa & Legault 

1990) . 

A. Catch at age 

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 

0 59221 17064 21342 14255 1068 119235 4402 64897 858 5892 6184 

1 150908 72295 73647 93977 44157 6239 186202 20761 293570 4570 40385 

2 187199 141039 153511 134722 64317 95021 9592 383520 38167 579451 12745 

3 137228 130462 157149 111652 68312 90321 100872 8076 360526 35789 499217 

4 121975 107169 116331 87660 70015 82589 78855 73083 1981 224942 15467 

5 92876 71323 77917 62485 48354 60262 59415 64918 11315 699 88126 

6 55241 38484 45741 38867 32296 32872 37890 47029 13893 3108 325 

7 26739 18265 23514 20851 20965 18430 19099 26062 14064 4192 1717 

8 12104 8837 10046 9442 12559 9747 10293 11592 9326 5081 2513 

9 4594 3756 4262 3100 6513 4842 5265 5790 4495 3901 3114 

10 1605 1480 1268 1046 2365 2147 2664 2740 2336 2065 2398 

11 976 1055 585 274 1212 945 1805 2345 1918 2099 2552 

Total 850666 611229 685313 578331 372133 522650 516354 710813 752449 871789 674743 

Annual Ave of Total = 649679 .1 

B . Number at age 

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 

0 1094081 931874 756028 564509 43760 2441090 218696 3297382 85338 976042 252318 

1 1006385 886835 786259 630946 472669 36675 1990625 184154 2777948 72656 834626 

2 807251 726637 696374 608568 456145 365956 25798 1540989 139291 2119309 58303 

3 552892 521915 495078 457567 399351 333116 227266 13370 972240 84666 1289343 

4 371871 349175 328764 281211 290735 280568 203357 102856 4116 504744 39947 

5 222007 207623 201698 175782 161201 185584 165298 102426 21916 1723 227606 

6 109492 105629 112972 101860 93725 94144 104175 87534 28804 8478 839 

7 50693 43525 55464 55137 51881 50906 50739 54759 32205 12029 4435 

8 20248 19099 20658 26106 28254 25358 26837 26082 23186 14785 6490 

9 7443 6347 8317 8553 13771 12771 12851 13621 11790 11373 8043 

10 2844 2203 2023 3246 4505 5869 6533 6216 6397 6009 6193 

11 1729 1570 934 850 2309 2583 4426 5320 5252 6108 6591 

Total 4246936 3802432 3464569 2914335 2018306 3834620 3036601 5434709 4108483 3817922 2734734 

C. Fishing mortality rate at age 

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 

0 0.06 0.0199 0.0309 0.0276 0.0266 0.054 0.0219 0.0214 0.0109 0.0065 0.0267 

1 0.1757 0.0918 0.1062 0.1744 0.1059 0.2018 0.106 0.1292 0.1206 0.0701 0.0535 

2 0.2861 0.2337 0.27 0.2713 0.1643 0.3264 0 .5073 0 .3106 0.3479 0.347 0.2674 

3 0.3096 0.3122 0.4156 0.3035 0.203 0.3435 0.6428 1 .0282 0.5056 0.6012 0.5348 

4 0.4328 0.3988 0.4761 0.4065 0.2989 0.3791 0.5358 1 .3961 OJ21 0.6464 0.5348 

5 0.5928 0.4586 0.5332 0.4789 0.3878 0.4274 0.4857 1 .1186 0.7997 O.569 0.5348 

6 0.7725 0.4942 0.5673 0.5247 0 .4604 0.4681 0.4931 0.8499 0.7232 0.4981 0.5348 

7 0.8261 0.5953 0.6036 0.5186 0.5658 0.4902 0.5154 0.7094 0.6285 0 .467 0.5348 

8 1 .0101 0 .6814 OJ318 0.4896 0.6441 0.5297 0.5282 0.644 0.5623 0.4588 0.5348 

9 1 .0674 0.9932 0.7908 0.4909 0.703 0.5203 0.5764 O.6058 0.5241 0.4577 0.5348 

10 09188 1 .2468 1 .0962 0 .4234 0.82 0.4968 0.5728 0.6367 0.4957 0.4588 0.5348 

11 0.9188 1 .2468 1 .0962 0.4234 0.82 0.4968 0.5728 0.6367 0.4957 0.4588 0.5348 

Ages 3-20 0.8399 0.9805 0.8987 0.4372 0.6824 0.4791 0.5599 0.742 0.551 0.4858 0.5348 

Ages 3-15 0.8095 0.878 0.8227 0.4425 0.6295 0.4722 0.5549 0.7825 0.5722 0.4962 0.348 

Ages 6-15 0.9189 1 .0245 0.9271 0.464 0.7293 0.4989 0 .555 O.6629 0.5412 0.4634 0.5348 
Table 6 

Year 

1979 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

1992 

1993 

1994 

1995 

1996 

Catch at age of red drum (without platform removal mortality) from most recent 

assessment (Porch 2000) . 

Age 

0 1 2 3 4 5 6 7 8 9 10+ 1 Total 

1223084 4684690 709840 92050 97256 

663585 3694230 1262266 120094 69124 

981272 1994110 1081798 442832 99963 

1755830 3308810 832672 308113 170404 

475074 3881589 1845374 310492 206858 

426804 2390703 1660383 452747 380959 

510186 3709014 2176560 815334 417795 

614832 3646962 1866425 252018 110609 

648498 2095886 1384156 151684 41402 

440500 1062259 931303 145979 29404 

368500 460121 857058 138123 50965 

574500 396099 535085 117468 22372 

970500 2319526 654009 99601 53300 

759800 1578037 1667890 60833 24962 

876400 1217060 1590896 233959 17041 

914900 1884994 1290323 228481 84922 

817500 2127316 1812427 192410 101655 

677300 1232365 1253477 121355 52221 

135919 178673 121113 141873 72783 431952 7889233 

72896 172633 221795 150351 176186 626671 7229831 

53528 78330 171767 220642 149507 798426 6072175 

72370 60050 80289 176060 226106 971668 7962371 

173902 98398 74226 99249 217539 1480621 8863322 

270300 306508 162009 122186 163367 2795218 9131183 

484652 478113 532728 281456 212304 5141256 14759398 

41997 53657 52648 58655 30993 589525 7318320 

25393 14012 17177 16848 18771 198592 4612420 

1960 5151 2751 3373 3309 42687 2668676 

5416 6037 5295 2829 3467 47287 1945097 

829 4902 3127 2742 1465 26287 1684877 

1414 13382 6196 3952 3466 35078 4160424 

3269 10685 7954 3683 2349 22908 4142370 

1863 15513 9538 7099 3287 22543 3995199 

1056 8233 14131 8686 6465 23527 4465720 

6929 7458 8579 14723 9050 31251 5129299 

12543 36396 6347 7302 12532 34302 3446139 

Mean 1989-96 = 3621141 

N 
22 

4 .0 RESULTS 

4 .1 Fish < 8 cm TL (Total Length) 

With the exception of this section, results describe only 

fish greater than or equal to 8 cm in total length . This appeared 

to be the minimum size which divers routinely collected by hand . 

At one site where a large number of very small fish were 

observed, all fish no matter what size were painstakingly 

collected within a single 1 .5 X 1 .5 m frame on the sea floor 

beneath the platform . Specimens included 117 vermilion snapper 

(Rhomboplites aurorubens), 6 round scad (Decapterus punctatus), 2 

lane snapper (Lutjanus synagris), and 2 scaled sardine (Harengula 

pensacolae) . Mortality of small vermilion snapper measuring < 8 

cm TL within the footprint area of this platform was estimated at 

approximately 5,900 . Estimated mortality of all small fish in the 

footprint area alone exceeded 6,200 compared with a total 

estimated mortality (footprint area plus 100 m radius) of 

approximately 4,900 for fish measuring >8 cm . 

4 .2 Estimated Mortality 

4 .2 .1 Overview 

Total estimated mortality per platform ranged from 1,765-

5,216 with a mean of 3,390, standard error 429, and 95% 

confidence level of 990 . Four species including Atlantic 

spadefish (Chaetodipterus faber), blue runner (Caranx crysos), 

red snapper, and sheepshead (Archosargus probatocephalus) 

accounted for 86% of the total estimated mortality . Inclusion of 

mangrove snapper (Lutjanus griseus), the species with the next 

highest estimated mortality, raised this value to 90% (Table 7) . 

Descriptive statistics for all species collected are presented in 

Table 4 . Although gray triggerfish ranked only eighth in mean 

estimated mortality it was noteworthy because it was the only 

species outside of the top five that was collected at eight of 

nine platforms studied . Mean estimated mortality per platform was 

1,431 for Atlantic spadefish, 541 for blue runner, 515 for red 

snapper, 455 for sheepshead, 122 for mangrove snapper, and 44 for 

gray triggerfish . Range in estimated mortality by platform was 

631-2,774 for Atlantic spadefish, 0-1,592 for blue runner, 24-

1,193 for red snapper, 61-1,007 for sheepshead, 0-364 for 

mangrove snapper, and 0-144 for gray triggerfish . Standard error 

was 275 for Atlantic spadefish, 181 for blue runner, 111 for red 

snapper, 110 for sheepshead, 49 for mangrove snapper, and 17 for 

gray triggerfish . For other species, estimated mortality per 

platform exceeded 200 only once out of nine platforms studied . 

These species included Atlantic bumper (Chloroscombrus chrysurus, 
23 

Table 7 . Estimated mortality of the five most impacted species . 

Total % of total 

estimated estimated 

Species ~ mortality mortality 

Atlantic spadefish 12875 42 

Blue runner 4867 16 

Red snapper 4632 15 

Sheepshead 4094 13 

Mangrove snapper 1100 4 

Total 27568 90 
24 

201), hardhead catfish (Arius fells, 397), and tomtate (Haemulon 

aurolineatum, 464) . 

Atlantic spadefish occurred in large, tightly knit schools 

that remained in close contact with the structure, usually within 

roughly 20-40 m . Blue runner were found at platforms in both 

large and small schools . Blue runner ranged more widely around 

platforms than did Atlantic spadefish, sometimes on the order of 

several hundred meters, and may escape serious impact from 

explosives if they are further from the platform at the instant 

charges are detonated . Red snapper occurred at all platforms 

studied . Estimated mortality ranged from the low hundreds to over 

a thousand except at the shallowest structure where mortality was 

24 . Sheepshead also occurred at all study sites . This species was 

found right at the structure rather than ranging at some 

distance . Estimated mortality was generally in the low to mid 

hundreds but exceeded one thousand at one platform . Mangrove 

snapper were numerous at two-thirds of the study sites and were 

much less abundant than red snapper . Gray triggerfish were found 

at all but one platform studied but always in modest numbers 

(usually less than 100) compared with the more abundant schooling 

species such as Atlantic spadefish and red snapper . Tomtate were 

only found at one structure (Galveston Area Block 288) where they 

were abundant . Hardhead catfish were found at three platforms . 

Nearly 400 hardhead catfish were estimated at one platform 

although estimated mortality at two other structures was four and 

six . Atlantic bumper were only reported at two platforms with 

values estimated at 46 and 201 . Mean mortality per platform for 

other species of interest including gag grouper, lane snapper, 

and red drum was 2, 41, and 6, respectively . 

Fish mortality resulting from the use of underwater 

explosives may be affected by many factors including but not 

limited to water depth, platform location, platform age, platform 

size and complexity, salinity, temperature, weight of explosives 

used in structure removal, and seasonal and annual variations . A 

series of graphs plotting estimated mortality by each of these 

parameters appears in Figures 8-14 . 

4 .2 .2 Mortality by Depth and Longitude 

Estimated mortality by depth was plotted for each species 

and for all species combined (Figure 8) . The graph for all 

species combined was very similar to that for Atlantic spadefish 

which accounted for 42% of total estimated mortality . Mortality 

plots for all species combined showed a steady increase with 

water depth from 14 m to a maximum at 23 m followed by a 

continuous decline with further increase in depth . Estimated 

mortality at the maximum study depth (32 m) was nearly the same 

as that at the shallowest study depth (14 m) . Estimated mortality 
25 

6000 

All species 

x'5000 

0 4000 

E 

-3000 

m 

E 2000 

w 1000 

3C 

~ 2°. 

2( 

E 

'v 1~ 

E 1( .N 

w 

1800 

1500 

0 1200 

E 

900 

600 .y 

300 

160 

x,140 

10 15 20 25 30 35 

Depth Iml 

Blue runner 

10 15 20 25 30 35 

Depth (m) 

m 120 

r 

E 100 

80 

E 60 

'-~; 40 

w 20 

400 

350 

c0 300 

E 250 

-0 200 

E 150 

100 

50 

Mangrove snapper 

'A I 

10 15 20 25 30 35 

Depth (m) 

1400 Red snapper 

>, 1200 

1000 -

0 

800 

600 \ / \ / 

400 

200 

Depth (m) 

1200 

1000 

0 800 

E 

-0 600 

400 . N 

W 200- 

10 15 20 25 30 35 

Depth (m) 

Figure 8 . Estimated mortality at platforms by water depth and 

species . 

Depth (m) 

Depth (m) 
26 

E 

-a3000 

a1 

2000 

w 1000 

30( 

4--25( 

6000 

5000 

0 4000 

400 

,, 350 

1800 

Mangrove snapper 

300 

250 

-0 200 

a? 

150 

100 

w 

50 

89 90 91 92 93 94 95 

Longitude 

0 20( 

E 

~ 15( 

E 10( .y 

w 5( 

1400 

>. 1200 

1000 

0 

E 800 

600 

.N 400 

200 

12( 

Z. 10( 

0 8 

E 

6( 

4( 

w 2 

Red snapper 

89 90 91 92 93 94 95 

Longitude 

89 90 91 92 93 94 95 

Longitude 

Figure 9 . Estimated mortality at platforms by longitude and 

species . 

1600 

m 1400 

0 1200 

E 1000 

800 

600 

400 

200 

160 

x,140 

120 

100 

All species 

89 90 91 92 93 94 95 

Longitude 

Blue runner 

89 90 91 92 93 94 95 

Longitude 

Gray triggerfish 

80 

E 60 

'y 40 

w 

20 

Longitude 

Longitude 
27 

6000 

5000 

m 

0 4000 

3000 

.N E 2000 

w 1000 

3000 

T 2500 

0 2000 

E 

-0 1500 

1000 

500 

1800 

1600 

1400 

0 1200 

1000 

All species 

4 5 6 7 8 9 10 

Month 

4 5 6 7 8 9 10 

Month 

Blue runner 

400 

,, 350 

300 

E 250 

200 

E 150 

100 

50 

1400 

>. 1200 

1000 

0 

E 800 

600 

.N 400 

200 

12 

X10 

Mangrove snapper 

5 6 7 8 9 10 

Month 

snapper 

800 

E 600 

400 

200 

4 5 6 7 8 9 10 

Month 

160 

x,140 

120 

100 

v 80 

60 

=Cn 40 

w 20 

r 

o $ 

E 

~ 6 

m 

E 

4 

.y 

w 2 

4 5 6 7 8 9 10 

Mnnth 

4 5 6 7 8 9 10 

Month 

Figure 10 . Estimated mortality at platforms by month and species . 

Month 
28 

6000 

5000 

0 4000 

400 

350 

E 

3000 m 

.N 2000 

w 1000 

All species 

0 5 10 15 20 25 30 35 40 45 

Platform age (yr) 

3000 

2500 

82000 

E 

1500 

E 1000 .N 

500 

1800 

1600 

1400 

0 1200 

E 1000 

800 

600 

400 

200 

160 

,, 140 

0 5 10 15 20 25 30 35 40 45 

Platform age (yr) 

Atlantic spadefish 

i Blue runner 

0 5 10 15 20 25 30 35 40 45 

Platform age (yr) 

4 Gray triggerfish 

m 120 

r 

100 

80 

60 

'y 40 

w 

20 

0 5 10 15 20 25 30 35 40 45 

Platform age (yr) 

i Mangrove snapper 

300 

250 

200 

150 

100 

w 50 

0 5 10 15 20 25 30 35 40 45 

Platform age (yr) 

1400 

1200 

1000 

0 

E 800 

600 

.N 400 

200 

1200 

L~1000 

0 800 

E 

600 

400 

200 

Red snapper 

0 5 10 15 20 25 30 35 40 45 

Platform age (yr) 

Sheepshead 

Platform age (yr) 

Figure 11 . Estimated mortality at platforms by platform age and 

species . 
29 

6000 

5000 

4000 

E 

3000 

E 2000 

" N 

w 1000 

n 

3000 

2500 

All species 

/V 

24 25 26 27 28 29 30 31 32 33 

Surface temperature (°C) 

0 2000 

E 

-0 1500 

1000 .N 

500 

n 

24 25 26 27 28 29 30 31 32 33 

Surface temperature (°C) 

1800 

1600 

1400 

a 1200 

1000 

800 

600 

400 

200 

0 

160 

x,140 

Blue runner 

24 25 26 27 28 29 30 31 32 33 

Surface temperature (°C) 

Gray triggerfish 

120 

V0 100 

-0 80 

60 

, 40 

w 

20 

n 

24 25 26 27 28 29 30 31 32 33 

Surface temperature (°C) 

400 

,350 

Mangrove snapper 

300 

250 

200 

150 

100 

W 

50 

n 

1400 

1200 

1000 

24 25 26 27 28 29 30 31 32 33 

Surface temperature (°C) 

Red snapper 

0 

E 800 

10 

600 

400 

200 

0 

120( 

100( 

0 801 

E 

601 

E 401 

.N 

w 20, 

L4 Lo LO L/ Lo Ly 3V 31 3L 013 

Surface temperature (°C) 

Figure 12 . Estimated mortality at platforms by surface water 

temperature and species . 

LY LJ GO L! GO L7 JV JI JG JJ 

Surface temperature (°C) 
30 

6000 

L~5000 

4000 

3000 

E 2000 

.N 

W 1000 

350 

0 

300( 

~ 250( .m 

r 20D 

E 

1501 

E 1001 

W 501 

Y 

15 17 19 21 23 25 27 29 31 33 35 

Surface salinity (ppt) 

1800 

1600 

1400 

0 1200 

1000 

800 

600 

400 

200 

0 

160 

x,140 

m 120 

r0 100 

~ 80 

60 

C~ 4u 

w 

20 

n 

Blue runner 

15 17 19 21 23 25 27 29 31 33 35 

Surface salinity (ppt) 

15 17 19 21 23 25 27 29 31 33 35 

Surface salinity (ppt) 

>, 300 

250 

snapper 

E 200 

150 

100 

N 

W 50 

0 

1200 

1000 

15 17 19 21 23 25 27 29 31 33 35 

Surface salinity (ppt) 

snapper 

m 

0 800 

E 

-0 600 

2 

400 

.y 

200 

0 

120( 

1001 

a 801 

E 

601 

401 

w 20, 

15 17 19 21 23 25 27 29 31 33 35 

Surface salinity (ppt) 

Figure 13 . Estimated mortality at platforms by surface water 

salinity and species . 

10 11 1V 41 4J 40 4/ 4V 01 00 01) 

Surface salinity (ppt) 

I O I / I ZI L I LJ LJ LI LZI 01 JJ JO 

Surface salinity (ppt) 
31 

6000 

5000 

0 4000 

3000 

2000 .N 

w 1000 

300 

250 

0 20a 

E 

-0 15C 

r 

~ 10C .N 

w 5( 

P\ 

0 2000 4000 6000 8000 10000 12000 

Platform volume (cubic m) 

400 

350 

300 

250 

200 

E 150 

100 

w 

50 

1400 

1200 

1000 

800 

600 

400 

200 

i mangrove snapper 

0 2000 4000 6000 8000 10000 12000 

Platform volume (cubic m) 

Red snapper 

0 2000 4000 6000 8000 10000 12000 

Platform volume (cubic m) 

1800 Blue runner 

1500 

0 1200 

E 

900 

600 .N 

300 

0 2000 4000 6000 8000 10000 12000 

Platform volume (cubic m) 

160 

x,140 

m 120 

r 

E 100 

80 

E 60 

, 40 

w 

20 

12C 

10C 

ca 

E 

-a 6( 

4C .N 

w 2C 

0 2000 4000 6000 8000 10000 12000 

Platform volume (cubic m) 

Figure 14 . Estimated mortality at platforms by platform size and 

species . 

0 2000 4000 6000 8000 10000 12000 

Platform volume (cubic m) 

0 2000 4000 6000 8000 10000 12000 

Platform volume (cubic m) 
32 

of blue runner varied widely from 0-1592 . Plots showed highest 

values at depths between 17-28 m . Estimated mortality of gray 

triggerfish at three platforms in depths less than 15 m was low, 

13 or less . At greater depths values ranged from 16-144 . 

Mortality of mangrove snapper was highest at the shallowest 

platform, 14 m, located off the Mississippi delta in an area at 

least occasionally influenced by lenses of clearer, offshore 

water . At platforms deeper than 20 m mangrove snapper mortality 

estimates displayed a general increase with depth . In contrast, 

mortality estimates for red snapper were lowest at the shallowest 

study site but were relatively high and quite variable (296-1193) 

at increased depths . Mortality estimates for sheepshead were 

highly variable at depths below 20 m but continuously decreased 

at greater depths . 

Estimated mortality for each species and all species 

combined was compared for water depths <20 m versus >20 m using 

ANOVA (Table 8) . Despite general trends described above, a 

significant difference (P=0 .05) was found only for sheepshead 

with estimated mortality continuously decreasing at depths 

greater than 20 m. 

Longitude was used as an indication of platform location 

along the east-west axis through the study area . Graphs of 

estimated mortality by longitude showed a high degree of 

variability for Atlantic spadefish, blue runner, sheepshead, and 

all species combined (Figure 9) . Peaks in estimated mortality for 

gray triggerfish occurred at mid-longitudes while other values 

were much lower . For mangrove snapper highest mortality occurred 

east of 91° . This contrasted with red snapper where highest 

values were observed at higher longitudes to the west . 

Estimated mortality for each species and all species 

combined was compared for longitude <92° versus >92° (longitude 

of Lafayette, Louisiana is 92°) using ANOVA (Table 8) . There was 

no significant difference (P>0 .05) for any species except 

mangrove snapper (P=0 .01) . 

To further focus on platform location as a factor in 

determining the extent of impacts due to underwater explosives, 

GLM two factor analysis with interaction for 3 depths (<20 m, 20-

30 m, >30 m) by 2 longitudes was used to analyze differences in 

estimated mortality . No significant difference (P>0 .05) was found 

for depth and longitude interaction for Atlantic spadefish, blue 

runner, gray triggerfish, mangrove snapper, red snapper, 

sheepshead, and all species combined . 

4 .2 .3 Mortality by Season 

Mortality assessments at explosive platform removals were 

conducted during May, July, August, and September . Time frame of 

the study spanned late spring through summer . Graphs of estimated 
Table 8 . ANOVAs for estimated mortality by test parameter for the six most impacted 

species and all species combined . 

Blue Gray Mangrove Red Sheeps- Spaderunner tri erfish snapper snapper bead fish All 

Depth 0.42 0.25 0.19 0.53 0.05 0.74 0 .55 

<20m vs >20m 

Longitude 0.49 0.27 0.01 0.52 0.37 0.27 0 .46 

<=92 and >92 

Platform age 0.32 0.51 0.09 0.91 0.93 0.78 0.92 

<25yr. vs >25yr. 

Season 0.09 0.68 0.53 0.59 0.34 0.59 0.35 

Spring (May) vs Summer (Jul, 

Aug, Sep) 

Surface temperature 

<30°C vs >=30°C 

Surface salinity 

<=26ppt vs >26ppt 

0.43 0.75 0.61 0.23 0.34 0 .51 

0.51 0.21 0 .21 0 .40 0.33 0 .47 

I 0.25 

0.61 

W W 
34 

mortality by month indicated extreme month to month variability 

(Figure 10) . Estimated mortality for each species and all species 

combined was compared for spring (May) versus summer (JulySeptember) using ANOVA (Table 8) . There was no significant 

difference (P>0 .05) for Atlantic spadefish, blue runner, gray 

triggerfish, mangrove snapper, red snapper, sheepshead, or all 

species combined . 

4 .2 .4 Mortality by Platform Age 

Graphs of estimated mortality by platform age indicated 

great variability (Figure 11) . Estimated mortality for each 

species and all species combined was compared for platform age 

<25 yr vs >25 yr using ANOVA (Table 8) . No significant difference 

(P>0 .05) was found for Atlantic spadefish, blue runner, gray 

triggerfish, mangrove snapper, red snapper, sheepshead, or all 

species combined . 

4 .2 .5 Mortality by Surface Temperature and Salinity 

Surface temperature ranged from 26-32°C with a mean of 30°C 

while surface salinity ranged from 18-33 ppt with a mean of 26 

ppt . Separate graphs of estimated mortality by temperature and 

salinity showed high variability for Atlantic spadefish, blue 

runner, gray triggerfish, mangrove snapper, red snapper, 

sheepshead, and all species combined (Figures 12 and 13) . No 

significant difference (P>0 .05) in estimated mortality was found 

for surface water temperature (<30°C vs >=30°C) or salinity (c=26 

vs >26 ppt ; Table 8) . 

4 .2 .6 Estimated Mortality by Platform Size 

The volume of water enclosed within the boundary of the 

platform served as an index of platform size . Plots of estimated 

mortality by platform size are shown in Figure 14 . Estimated 

mortality by platform size was analyzed using Spearman rank 

correlation coefficients . P values ranged from >0 .2 to >0 .5 for 

Atlantic spadefish, blue runner, gray triggerfish, red snapper, 

sheepshead, and all species combined, but was <0 .02 for mangrove 

snapper . This indicated no correlation between estimated 

mortality and platform volume for any species except mangrove 

snapper . 

4 .3 Length-Frequency 

Although a sufficient number of transect, circular, and 

frame samples were collected from the sea floor to estimate total 

mortality at nine of ten platforms studied, sampling of dead fish 
35 

floating on the surface was completed at all ten locations . 

Graphs of total length by species and platform appear in Figures 

15-20 . GLM was used to analyze length by depth, longitude, and 

their interaction for surface and bottom fish collections at all 

platforms combined . Depth zones were defined as <20 m and >20 m 

and longitude was partitioned into groups <92° and >92° . 

Significant differences in total length (P<=0 .003) were found for 

all three parameters for blue runner, red snapper, Atlantic 

spadefish, sheepshead, and all species combined (Table 9) . 

Mangrove snapper lengths also varied significantly (P<0 .03) with 

depth, but longitude was not tested due to small sample size at 

longitudes above 92° . Mean lengths of blue runner (36 .3 vs 30 .6 

cm), mangrove snapper (48 .5 vs 34 .9 cm), and sheepshead (40 .9 vs 

34 .6 cm) were greater in deeper water while red snapper (36 .0 vs 

37 .3 cm) and Atlantic spadefish (27 .8 vs 31 .1 cm) were smaller 

(Table 10) . Larger fish were found east of 92° for blue runner 

(35 .7 vs 30 .6 cm) and red snapper (36 .7 vs 35 .8) but not for 

Atlantic spadefish (28 .0 vs 31 .0 cm) and sheepshead (33 .3 vs 38 .7 

cm) . 

4 .4 Population Estimates and Mortality Rates 

Pre-detonation population estimates were calculated whenever 

tag/recapture studies provided sufficient data . In most 

tag/recapture experiments using conventional techniques, 

recapture rates of 2-5 % are anticipated . Recovery rates as high 

as 73% (Table 11) attest to the effectiveness of sampling with 

explosives . Red snapper estimates at 7 platforms ranged from 503-

1943 with a mean of 905 and standard error of 196 (Table 12) . 

Atlantic spadefish population estimates at three platforms ranged 

from 1432-1782 with a mean of 1564 and standard error of 110 . At 

four platforms gray triggerfish were estimated to number 63-131 

with a mean of 104 and standard error of 16 . The blue runner 

population was estimated at 558 at one platform while almaco jack 

(Seriola rivoliana) numbered only 28 at another platform . 

Mortality rates were determined for species and platforms 

where pre-detonation population estimates were calculated (Table 

13) . Mortality rate is the estimated mortality divided by 

population estimate . Rates for red snapper varied from 59-88% 

with a mean of 71% and standard error of 4 . Atlantic spadefish 

rates ranged from 72-135% with a mean of 108 and standard error 

of 19 . Mortality rates for gray triggerfish varied from 68-1250 

with a mean of 81 and standard error of 30 . Mortality rates for 

blue runner and almaco jack were 123% and 104%, respectively . 
36 

Table 9 . GLM analysis of total length by depth (<20m vs >20m) 

and longitude (<92~ vs >92c)) for most impacted species . 

Depth 

P values 

Longitude Interaction N 

Atlantic spadefish 0 .000 0.000 0 .000 4020 

Blue runner 0.000 0.000 0.000 845 

Mangrove snapper 0.027 - - 562 

Red snapper 0.000 0.003 0.000 2983 

Sheepshead 0.000 0.000 0.000 1993 

All species 0 .000 0 .000 0 .000 11964 

Table 10 . Mean total length by depth (<20m vs >20m) for the most 

impacted species and all species combined . 

<20m n I >20m n 

_ . ., . . 

Blue runner 

Mangrove snapper 

Red snapper 

Sheepshead 

All species 

31 .1 2271 

30.6 342 

34.9 245 

37.3 904 

34.6 1591 

33 .0 

27.8 1749 

36.3 503 

48.5 317 

36 .0 2079 

40 .9 402 

33 .9 

Table 11 . Recapture rates (100 x number of tags recovered / 

number of tags released) for tag-recapture study . 

Platform 

Species I SMI ST SS WC WC WC SS GA 

23 146 158 172 173 181 209 288 

Almaco jack 25 

Atlantic spadefish 13 

Blue runner 

Gray triggerfish 24 13 

Red snapper 41 49 

72 34 

29 

30 

73 19 20 62 44 
Table 12 . Population estimates by species and platform . 

Platform 95% 

Species I SMI ST SS WC WC WC SS GA I Std Std confidence 

Almaco jack 28 

Atlantic spadefish 

Blue runner 

Gray triggerfish 129 

Red snapper 1943 503 

1432 1477 1782 

558 

93 63 

597 1091 1048 601 553 

28 0 

1564 110 190 36258 473 

558 

95 19 33 1092 82 

905 196 517 26754 478 

Table 13 . Mortality rates (100 x estimated mortality / population estimate) by species 

and platform . 

Platform 95% 

Species ( SMI ST SS WC WC WC SS GA I Std Std confidence 

23 146 158 172 173 181 209 288 Mean error dev Var level 

Almaco jack 

Atlantic spadefish 

Blue runner 

Gray triggerfish 

Red snapper 

104 

112 

61 

118 72 135 

123 

125 68 

59 83 65 68 70 88 

104 0 

108 19 32 1044 80 

123 

102 17 30 874 73 

71 4 11 121 10 

W 

J 
38 

GVV 

T16 

U 

~ 12 

ii 

4 

WD 30 N=315 

0 depth=l4m 

0 - 

0 -

0 

0 

200 

T 160 

U 

120 

80 

40 

GA 288 N=471 

depth=23m 

140 

120 

U >,100 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

N C80 7 

60 

40 

20 

WC 172 N=569 

depth=l5m 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

200 

WC 173 N=616 

160 >1 I ~ depth=15m 

U 

120 

~ 80 

40 

80 

~ 60 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

c a) 

~ 40 

2 

" 20 

200 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

T 160 

U 

12 0 

d $0 

40 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

250 

SMI 23 N=671 

T 200 depth=25m 

U 

150 -

7 

100 -

LL -

50 

80 

60 

c 

40 

a) 

U- 20 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

ST 146 N=180 

depth=28m 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

100 

80 

U 

60 

40 

20 

60 

OC 40 

N 

7 

Q 

20 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

SS 214 

depth=32m 

5 10 15 20 25 30 35 40 45 50 55 5 10 15 20 25 30 35 40 45 50 55 

Length (cm) Length (cm) 

Figure 15 . Length-frequency (TL in cm) of Atlantic spadefish by 

platform . 
39 

8 

v6 

c 

a' 4 

a) 

LL 2 

40 

~ 30 

WD 30 N-9 

depth=l4m 

Length (cm) 

c 

20 

CU 

LL 10 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

WC 173 

(No blue runner collected) 

100 

T 80 

60 

~ 40 

20 

100 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

SS158 N=116 

depth=l7m 

U 80 

60 

~ 40 

20 

30 

25 

OC 20 

X 15 

10 

5 

GA 288 N=67 

depth=23m 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

40 

]SMI 23 N=72 

>1 30 depth=25m 

/ \ 

c 

20 

a) 

LL 10 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

300 

250 

200 

150 

100 

50 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

4 

]SS 209 N=4 

03 

r depth=32m 

c 

02 

LL 1 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

40 

]SS 214 N=70 ,, 

0 I ~ depth=32m 

c 

20 

a) 

u- 10 

5 10 15 20 25 30 35 40 45 50 55 5 10 15 20 25 30 35 40 45 50 55 

Length (cm) Length (cm) 

Figure 16 . Length-frequency (TL in cm) of blue runner by 

platform . 
40 

2 

T 

U 

C (D 1 

4 

v3 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

WD 30 N=1 

depth=l4m 

c 

Q 

U_ i 

6 

WC 173 

T 

c4 

(No gray triggerfish collected) 

ti 2 

GA 288 N=21 

depth=23m 

5 10 15 20 25 30 35 40 45 50 55 5 10 15 20 25 30 35 40 45 50 55 

Length (cm) Length (cm) 

7 

v 5 

c a> 4 

~3 

~ 2 

1 

5 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

SS 158 Ndepth=17m 

T4 

U 

c 3 

22 

~i 

1 

12 

10 

U a 

C 

N 6 

v 

4 

2 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

10 

>, 8 

U 

c 6 

~ 4 

2 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

8 

]SS 209 N=19 

~, depth=32m 

1 

c 

°' 4 Q 

U- 2 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

15 

T12 

U 

c 9 

~ 6 

3 

Length (cm) Length (cm) 

Figure 17 . Length-frequency (TL in cm) of gray triggerfish by 

platform 
41 

100 

,, 80 

U 

y 60 

(D 40 

20 

2 

T 

U 

C 

N ,~ 

Q a) 

15 25 35 45 55 65 75 

Length (cm) 

WD 30 N=223 

depth=l4m 

in I I I I t~, 

2 

15 25 35 45 55 65 75 

Length (cm) 

C 

~ 1 

9 

U 

C 6 

N 

15 25 35 45 55 65 75 

Length (cm) 

°' 3 

WC 181 

(No mangrove snapper collected) 

15 25 35 45 55 65 75 

Length (cm) 

8 

v 6 

C 

~ 4 a 

U- 2 

GA 288 N=17 

depth=23m 

15 25 35 45 55 65 75 

Length (cm) 

10 

SMI 23 N=37 

T 8 depth=25m 

U 

C 6 

~ 4 

2 

15 25 35 45 55 65 75 

Length (cm) 

18 

15 ST 146 ~ N=66 

~ depth=28m 

C 

Cr 9 

6 

3 

Length (cm) 

60 

S209 N=142 

>1 45 death=32m 

C 

30 

1` 15 

20 

L>, 15 

c 

X10 

u- 5 

Length (cm) 

SS 214 N=55 

depth=32m 

15 25 35 45 55 65 75 

Length (cm) 

Figure 18 . Length-frequency (TL in cm) of mangrove snapper by 

platform . 
42 

18 

15 

a 

~ 12 

a~ 9 

a 

2 6 

WD 30 N=24 

depth=l4m 

100 

>, 80 

U 

60 

~ 40 

20 

10 20 30 40 50 60 70 80 90 

Length (cm) 

3 

10 20 30 40 50 60 70 80 90 

Length (cm) 

140 

>.105 

U 

C 

70 

N 

35 

50 

10 20 30 40 50 60 70 80 90 

Length (cm) 

40 

U 

~ 30 

~ 20 

10 

9 

10 20 30 40 50 60 70 80 90 

Length (cm) 

U 

C 

7 

Q 

~' 3 

60 

10 20 30 40 50 60 70 80 90 

Length (cm) 

SS 158 N=33 

depth=17m 

~ 45 

c 

30 

a) 

U- 15 

250 

200 

U 

c: 150 

7 

N 100 

LL 

50 

GA 288 N=244 

depth=23m 

10 20 30 40 50 60 70 80 90 

Length (cm) 

120 

90 

c 

60 

30 

120 

>. 90 

U 

C 

60 

30 

10 20 30 40 50 60 70 80 90 

Length (cm) 

SS 209 N=370 

depth=32m 

10 20 30 40 50 60 70 80 90 

Length (cm) 

200 

SS 214  N=425 

'\ >1 150 depth=32m 

c 

100 

U- 50 

10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 

Length (cm) Length (cm) 

Figure 19 . Length-frequency (TL in cm) of red snapper by 

platform . 
43 

300 

250 

200 

150 

100 

50 

WD 30 

N=698 

depth=l4m 

45 

30 

Q 

15 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

160 

WC 172 

120 N=328 

c 

~' 80 Q 

L` 40 

50 

25 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

T 40 

U 

~, 30 

220 

10 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

T 20 

U 

~ 15 

~ 10 

5 

250 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

T 200 

U 

150 

N 

50 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

60 

SMI 23 

45 ] N=142 

c 

30 

GA 288 

N=109 

depth=23m 

LL 15 

Length (cm) 

40 

]ST 146 

~ 30 N=67 

c 

20 

a) 

" 10 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

25 

,, 20 

U 

ca) 15 

~ 10 

U_ 

5 

5 10 15 20 25 30 35 40 45 50 55 

Length (cm) 

30 

~ 20 

N 

Q 

UE 10 

5 10 15 20 25 30 35 40 45 50 55 5 10 15 20 25 30 35 40 45 50 55 

Length (cm) Length (cm) 

Figure 20 . Length-frequency (TL in cm) of sheepshead by platform . 
44 

4 .5 Fish Density Around Platforms 

A summary of the locations of all underwater fish collections 

appears in Figure 21 . Numbers of fish collected along transect 

line surveys from eight platforms were analyzed using the two 

sample t-test . There was a significant difference (P<0 .001) in 

fish density (log (density + 1) transformed) for samples collected 

at 0-25 m (0 .027 fish/m3) and 25-50 m (0 .002 fish/m3) distances 

from platforms along transect lines . Using data from circular 

surveys collected at 0-6 .7 m and 18 .3-25 .0 m from the platform, 

two sample t-test indicated a significant difference (P=0 .003) 

between samples . Fish density was higher closer to the platform 

(0 .051 fish /M3 VS 0 .007 fish/m3) . Fish density for transect data 

collected between 50-75 m and 75-100 m from platforms averaged 

0 .001 and 0 .000 fish/m3 . 

4 .6 Comparison of Estimated Mortality and Size of Positively and 

Negatively Buoyant Fish 

Table 14 shows no consistent relationship between the number 

of red snapper carcasses collected at the surface and the 

estimated number of red snapper which sank to the sea floor after 

detonations . Results for all fish species combined were also 

highly variable . Paired t-test of log transformed ratios of 

positively (floating) to negatively buoyant (sinking) fish showed 

a significant difference between red snapper and all species 

combined . More red snapper floated to the surface than sank at 4 

of 8 study sites compared with only 2 of 9 study sites for all 

fish species combined . Ratios of floating to sinking red snapper 

ranged from 0 .03-6 .74 per platform while the range for all 

species combined was 0 .03-1 .47 . At the upper end of the range, 

more red snapper floated than sank by a factor of 6 .74 . Extremely 

low values indicate that few fish floated to the surface . A ratio 

of 0 .03 means that an estimated 33 times more fish sank to the 

sea floor than floated to the surface . Results for all species 

combined indicate that more fish generally sink than float and 

that actual total fish mortality may be considerably more than 

what is observed at the surface . 

GLM analysis of red snapper length by factors of platform 

and buoyancy showed a significant difference (P<0 .01) for both 

factors and interaction . Mann-Whitney tests used to compare 

length of floating vs sinking red snapper at each platform showed 

mixed results . A significant difference (P<0 .05) in total length 

of positively vs negatively buoyant fish was found at four 

platforms, but no difference was apparent at four other platforms 

(Table 15) . Mean total length was larger for positively buoyant 

fish at all platforms except one in 15 m of water where 

negatively buoyant fish were significantly larger . Difference 
45 

C. 

LEGEND 

--- 2m wide transect 

4m wide transect 

D Platform 

O Circular survey (35.3m2) 

Square frame nets (13.4rrV) 

X;~,- Direction of surface current 

Figure 21 . Summary of fish collections by platform . Number of 

fish collected by divers is shown in the schematics . 

The number inside the square at the center represents 

fish sampled beneath the platform . Circled values 

indicate circular surveys . Numbers adjacent to 

vertical and horizontal lines are transect line 

samples . 

a. Platform : WD 30 July 1994 

Depth: 14m 

Surface Collection : 358 

Bottom Collection : 327 

Platform : WC 172 August 1995 

Depth: 15m 

Surface Collection : 1311 

Bottom Collection : 182 

Platform : WC 173 September 1995 

Depth: 15m 

Surface Collection : 866 

Bottom Collection : 254 
46 

d. Platform : SS 158 July 1993 

Depth: 17m 

Surface Collection : 109 

Bottom Collection : 317 

N strong 

.' 

. ~ 

0: 0, 

P3, 

0: ee 

.r, 0 ~c 

~ _, . 

-0 - ~ 3 9"- Fez t 0 0 4i 

06 ---

0 " , 10 

25m ~ 

5 

75m 

10efn 

f 

m 

LEGEND 

--- 2m wide transect 

- 4m wide transect 

D Platform 

O Circular survey (35.3rrf) 

Square frame nets (13.40) 

Direction of surface current 

Figure 21 Cont . Summary of fish collections by platform . Number 

of fish collected by divers is shown in the 

schematics . The number inside the square at the 

center represents fish sampled beneath the 

platform . Circled values indicate circular 

surveys . Numbers adjacent to vertical and 

horizontal lines are transect line samples . 

e. Platform : WC 181 July 1997 

Depth: 18m 

Surface Collection : 380 

Bottom Collection : 1067 

Platform : GA 288 May 1999 

Depth : 23m 

Surface Collection : 75s 

Bottom Collection : ass 
47 

h. Platform : ST 146 May 1995 

Depth: 28m 

Surface Collection : 782 

Bottom Collection : 182 

N 0 

0 0 a 

~ 

z 

1s, 

- - 

0 

---?- . 3 _ 

is

_116 

7 _ _OJ _ -0 --- 0 

- 

100m 

I . 

Platform : SS 209 

Depth: 32m 

Surface Collection: 861 

Bottom Collection : 144 

N 

100m 

LEGEND 

--- 2m wide transect 

4m wide transect 

O Platform 

O Circular survey (35.3mz) 

Square frame nets (13.4rrfl 

Direction of surface current 

Figure 21 Cont . Summary of fish collections by platform . Number 

of fish collected by divers is shown in the schematics . The 

number inside the square at the center represents fish sampled 

beneath the platform . Circled values indicate circular surveys . 

Numbers adjacent to vertical and horizontal lines are transect 

line samples . 

9~ Platform : SMI 23 August 1994 

Depth: 25m 

Surface Collection : 1283 

Bottom Collection : 529 
48 

Platform: SS 214 

Depth: 32m 

Surface Collection : 1232 

Bottom Collection : p 

N 

D 

00m 

LEGEND 

--- 2m wide transect 

4m wide transect 

D Platform 

O Circular survey (35.3m2) 

Square frame nets (13.4rr2) 

Direction of surface current 

Figure 21 Cont . Summary of fish collections by platform . Number 

of fish collected by divers is shown in the schematics . The 

number inside the square at the center represents fish sampled 

beneath the platform . Circled values indicate circular surveys . 

Numbers adjacent to vertical and horizontal lines are transect 

line samples . 
49 

Table 14 . Comparison of red snapper mortalities collected at the 

surface (floaters) with estimated mortality from the sea floor 

(sinkers) . 

Ratio Percent 

Platform Floaters Sinkers Total floater/sink floater/total Depth m 

WC 172 417 81 498 5 .15 84 15 

WC 173 120 589 709 0.20 17 15 

SS 158 10 286 296 0.03 3 17 

WC 181 73 636 709 0 .11 10 18 

GA 288 202 285 487 0.71 41 23 

SMI23 714 479 1193 1 .49 60 25 

ST 146 238 58 296 4.10 80 28 

SS 209 364 54 418 6.74 87 32 

Total 2138 2468 4606 46 

Table 15 . Comparison of total length of positively (floater) and 

negatively (sinker) buoyant red snapper by platform . 

MannMean TL N Mean TL N Whitney 

Platform floaters floater sinker sinker P De th m 

WC 172 34.1 416 40.1 17 0 .06 15 

WC 173 44.4 120 43 .1 83 0 .45 15 

SS 158 56.8 10 45.7 23 0.01 17 

WC 181 49 .6 73 30 .9 138 0 18 

GA 288 31 .5 202 25 .1 42 0 23 

SMI23 33 .1 714 29 .3 81 0.01 25 

ST 146 44.7 238 40.2 5 0.4 28 

SS 209 38.5 361 38 9 0.68 32 
50 

between mean lengths of positively and negatively buoyant red 

snapper ranged from -6 .0 to 18 .7 cm . These two platforms were in 

depths of 15 and 18 m, respectively . Combining all positively 

buoyant fish yielded a mean of 36 .7 cm while the mean for all 

negatively buoyant fish combined was 34 .1 cm . The difference 

between these means was 2 .6 cm . Since results did not show a 

consistently significant difference between length of positively 

and negatively buoyant fish at individual platforms and since the 

overall difference in mean length of positively and negatively 

buoyant fish was small, it should be acceptable to utilize 

historical data from the NMFS Platform Removal Observer Program, 

which is only available for positively buoyant fish, to enhance 

the present data set with additional red snapper lengths . 

4 .7 Assessing Impacts (1989-98) 

4 .7 .1 Impacts on Red Snapper (1989-98) 

Red snapper stock assessment analysis including mortality 

from explosive structure removals was conducted using the Data 

Set E structure removal estimate (arbitrary doubling of the 

moderate to high estimate to provide an upper limit of 

mortality) . Results were compared to the base case assessment 

from Schirripa and Legault (1999 ; Figure 22) . Benchmark 

comparisons appear in Table 16 . The impact of including platform 

removal Data Set E was that abundance estimates were almost 

indistinguishable from the original assessment (Figure 22) . The 

differences were well within the statistical estimation variances 

for the original assessment . 

The additional mortality from explosive removals (Data Set 

E) altered management benchmarks, as well, (Table 16) with the 

fishing mortality and MSY benchmarks decreasing 3% or less and 

stock size benchmarks increasing less than 1% . The present 

management strategy of the Gulf Council is robust to these 

changes in benchmarks, i .e . the recovery strategy would function 

approximately the same with or without the platform removal 

inclusion . Again, note that these changes are well within the 

original estimation variation . Finally, note that these results 

are designed to evaluate bounds on the purported impacts by using 

Data Set E . Actual impacts are likely to be less . 

Red snapper mortality from explosive structure removals was 

compared to other sources of mortality . The doubled red snapper 

mortality estimate resulting from explosive structure removals 

was divided by the combined mortality from commercial and 

recreational fishing, release mortality, and bycatch for each age 

class and year (Table 3B) . When tabled values of these 
51 

Table 16 . Changes in red snapper management benchmarks from base 

case assessment when refitting estimation models 

using platform removal Data Set E (double the 

moderate to high estimate of annual red snapper 

mortality at platform removals based on 1989-98 

data) . 

Base Platform % Change (P-B)IB 

F0.1 0.096 0.093 -3 .04% 

Fmax 0.125 0.121 -3 .03% 

F20%SPR 0.169 0 .165 -2 .78% 

F30%SPR 0.126 0 .122 -2 .80% 

F40%SPR 0.095 0.093 -2 .83% 

Fmsy 0 .118 0.115 -2 .99% 

Fcurrent 0.474 0.444 -6 .32% 

MSY (million pounds) 107.995 106.146 -1 .71% 

Bmsy (million pounds) 3930.31 3940.31 0.25% 

SSmsy (million eggs) 7 .76E+09 7 .78E+09 0.22% 

F0.1 Fishing mortality rate at which the slope of the yield-per-recruit curve is one tenth of what it is at 

the origin . 

Fmax Fishing mortality rate that maximizes yield-per-recruit . 

F20%SPR Fishing mortality rate which reduces spawning potential ratio to 20% of what it would be with no 

fishing 

F30%SPR Fishing mortality rate which reduces spawning potential ratio to 30% of what it would be with no 

fishing 

F40%SPR Fishing mortality rate which reduces spawning potential ratio to 40% of what it would be with no 

fishing 

Fmsy Fishing mortality rate that would eventually produce maximum sustainable yield 

Fcurrent Most recent estimate of fishing mortality rate (for 1998, F1998) 

MSY Maximum sustainable yield 

Betsy Biomass that would support the taking of MSY 

Ssmsy Spawning stock in number of eggs that would support MSY 

Table 17 . Estimated number of dead fish floating at the surface 

after detonations during 1986-98 (data provided by 

NMFS Platform Removal Observer Program) . 

Average Total 

number estimated Minimum Maximum 

Number of floating number value value 

of fish aer of floating estimated estimated 

Structure type structures structure fish per structure per structure 

Platform 742 567 420932 0 8875 

Submerged well 57 133 7554 0 1105 

Caisson 252 109 27372 0 2738 

Flare pile 7 41 285 0 200 
52 

120000000 

100000000 

80000000 

-0 E 60000000 

40000000 

20000000 

0 

-~ Platform 

Age 0 ~ Base 

Platform 

--- Base 

100000000 

10000000 - 

1000000 

100000 

1984 

84 86 88 90 92 94 96 98 0 3 6 9 12 15 

Year Age 

3500000 

3000000 

2500000 

2000000 

1500000 Z 

1000000 

500000 

0 

uuuuuuuuu 

100000000 

10000000 

1000000 

100000 

84 86 88 90 92 94 96 98 0 3 6 9 12 15 

Year Age 

800000 

700000 

600000 

500000 

400000 

0300000 

200000 

100000 

0 

100000000 

10000000 

1000000 

100000 

84 86 88 90 92 94 96 98 0 3 6 9 12 15 

Year Age 

1200000 

1000000 

800000 

600000 

400000 

200000 

0 

100000000 

10000000 

1000000 

100000 

10000 _ 

84 86 88 90 92 94 96 98 0 3 6 9 12 15 

Year Age 

Figure 22 . Red snapper assessment results including platform 

removals using Data Set E (represents arbitrary doubling of 

moderate to high estimate of red snapper mortality at platforms) 

compared to base case assessment (base) . 
53 

proportions were averaged by age class, results showed that 

mortality from explosive structure removals represented the 

following percentage of other combined mortality : 1% or less for 

ages 0, l, 3, 4, and 14 ; 1-5o for ages 5, 6, 11, and 15+ ; 5-10% 

for ages 2, 7, 8, 9, and 13 ; and 10-13% for ages 10 and 12 . Note 

that these calculations were based on the doubled estimate of red 

snapper mortality at explosive structure removals to provide a 

boundary for purported impacts . 

4 .7 .2 Impacts on Gag (1989-98) 

Annual estimated mortality of gag at explosive platform 

removals (under Data Set E assumptions ; see Discussion) is 256 

fish per year . Comparison with results from the most recent gag 

stock assessment (Table 5) indicates this represents 0 .04% of the 

average annual mortality from other sources . Current methods of 

assessment would not detect such small changes in magnitude . 

4 .7 .3 Impacts on Red Drum (1989-98) 

The annual estimated mortality of red drum at explosive 

structure removals (under Data Set E assumptions) is 961 fish per 

year . Comparison with results from the most recent red drum stock 

assessment (Table 6) shows this is 0 .03% of the average annual 

mortality from other sources . Such a small change is 

indistinguishable using current methods of assessment . 

4 .8 Assessing Future Impacts on Red Snapper (1999-2023) 

The procedures described above provide an analysis for the 

period 1989-98 and can be used to assess the present status of 

the red snapper stock . During this ten year period, a total of 

958 structures were removed from federal and state waters of the 

Gulf of Mexico using explosives for an annual average of about 

96 . However, a recent forecast for 1999-2023 estimates the 

number of annual structure removals (both mechanical and 

explosive) in federal waters to increase to 186 (Pulsipher et al, 

in press) . This value was adjusted (see Section 5 .11 .5) to yield 

an estimated annual average of 129 explosive structure removals 

in both state and federal waters for 1999-2023 . The high estimate 

of mortality (assuming equal red snapper mortality at all 

structure types) based on these increased removals yields a 

projected annual mortality at explosive structure removals of 

66,435 red snapper for 1999-2023 . Although this is more than the 

41,200 annual estimate for 1989-1998, it is still considerably 

less than the 82,400 value used in the 1989-98 stock assessment 

analysis which represents double the annual 1989-98 estimate . 

Consequently, the impact of a projected increase in average 
54 

annual explosive structure removals is not expected to be 

distinguishable from benchmarks assuming other influencing 

factors remain constant and removal forecasts are accurate . 

Another consideration in assessing future red snapper stocks 

relates to habitat . Various estimates place the increase in Gulf 

of Mexico reef habitat due to offshore platforms at 10-25% . 

Pulsipher et al . (in press) predict the number of platforms in 

federal waters will decrease from 3,687 in 1999 to 2,612 in the 

year 2023, a reduction of 1,075 platforms or about 29% . This is 

certainly a substantial loss of habitat . The question of whether 

offshore platforms represent critical habitat that increases fish 

numbers rather than simply redistributing individuals has long 

been debated . If offshore oil and gas structures prove to be 

critical habitat, then a reduction in stock size may accompany 

the large reduction in structure numbers from the Gulf of Mexico . 

5 .0 DISCUSSION 

5 .1 Overview 

one obvious finding from this study is the lack of 

significant differences in estimated mortality as a function of 

test parameters including depth, longitude, surface temperature 

and salinity . This was due to a variation in fish abundance 

between platforms, small sample size in some cells, and a 

generally limited range over which variables were tested . For 

example, there was general consistency in platform complexity and 

a fairly narrow range in depth, surface salinity and surface 

temperature . Estimated mortality of fish at a given platform 

within study depths from 14-28 m ranged from approximately 2,000-

5,000 for fish measuring greater than 8 cm TL . Depending on one's 

perspective, it appears that platforms with similar 

characteristics may have quite different numbers of fish impacted 

by explosives since mortality differed by more than a factor of 

two for the highest and lowest estimates . Conversely, a range of 

2,000-5,000 may be considered fairly narrow considering the 

difficulty and complexity involved in field sampling, the many 

variables that can affect fish distribution at platforms, and 

wide ranges in fish populations reported from month to month by 

other researchers (Putt 1982 ; Stanley and Wilson 1996a ; Stanley 

and Wilson 1997) . 

To understand fish mortality we must first understand fish 

distribution at offshore structures . Any factor affecting fish 

distribution at platforms may affect mortality . For example, at 

West Delta Block 30, the easternmost platform studied in 14 m of 

water, 493 Atlantic spadefish and little else were tagged in May . 

When explosives were finally detonated about 30 days later, only 

9 of 315 spadefish collected had tags . Although no snapper of any 
55 

species were captured during pre-detonation tagging operations at 

this site, 220 mangrove snapper were collected dead after 

detonations with a total estimated mortality of 364 . Fish 

distribution at West Delta Block 30 was influenced by a lens of 

clear water that moved into the area during the 30 day period 

between tagging and blasting . In areas such as this where more 

than a hundred structures can be viewed with the naked eye from 

atop the removal platform, movement of fish between structures is 

not surprising . It is clear that fish populations at platforms 

are dynamic and fish are not as habitat faithful as once thought . 

In general, failure to detect a significant difference in 

various parameters tested in this study does not indicate that 

these factors may not affect fish distribution . It does indicate 

that parameter values encountered during the study were not 

dissimilar enough to cause differences in fish distribution given 

the small number of platforms studied . For at least some 

parameters, when a sufficient change occurs in values beyond the 

ranges found in this study, fish assemblages and resulting 

fishery impacts will undoubtedly change . For example, species 

distribution in general has been reported to change as fish move 

from shallower to deeper water in relation to changing seasons 

and temperatures (Bradley and Bryan 1974 ; Hastings et al . 1976) 

5 .2 Depth and Longitude 

Attempts have been made to characterize fish assemblages at 

platforms by depth (Gallaway and Lewbel 1982 ; Stanley and Wilson 

in press) . Based on observations at some 20 platforms off 

Louisiana and 18 off Texas, Gallaway and Lewbel (1982) suggested 

three depth zones of fish assemblages at platforms : the coastal 

zone ranged from 0-30 m, the offshore zone from 30-60 m, and the 

bluewater zone deeper than 60 m . These depth ranges are, of 

course, general in nature and gradual rather than acute changes 

in fish assemblages can be expected in transitional depths . 

Gallaway and Lewbel (1982) observed variation between the coastal 

and offshore zones in general abundance of certain species . 

Using estimated mortality as an indication of abundance 

permits comparison with these earlier studies . The only platform 

we investigated in the offshore zone was at 32 m which could be 

considered a transitional location between zones . Consequently, 

it was not surprising to see both similarities and differences in 

our results and those reported by Gallaway and Lewbel . These 

authors reported sheepshead and gray triggerfish were present but 

not abundant in the offshore zone which corresponded with our 

results . We observed tomtate at only one structure but they were 

abundant . This is noteworthy because Gallaway and Lewbel (1982) 

described a high abundance of tomtate in this same field nearly 

20 years ago . They also reported the absence of large schools of 
56 

tomtate at Louisiana structures . Although these authors observed 

high numbers of Atlantic spadefish at intermediate depth zones 

eventually decreasing with increasing depth in the bluewater 

zone, we found a decreasing, but insignificant, trend in 

abundance to 32 m . In contrast to their finding of large schools 

of lookdown at coastal Louisiana platforms, we estimated 

mortality for all nine platforms combined at only three 

individuals . Gallaway and Lewbel (1982) reported smaller schools 

of red snapper in 0-30 m depths, but, again, our results showed 

no statistical difference in estimated red snapper mortality by 

depth . However, anecdotal reports describe thousands of dead red 

snapper floating to the surface after explosives were detonated 

at platforms in deeper water . 

Red snapper mortality at explosive structure removals may 

increase in the offshore and bluewater zones . During 1989-98 an 

annual average of 5 platforms and 3 submerged wells were removed 

with explosives in the bluewater zone (NMFS Platform Removal 

Observer Program unpublished data) . Although bluewater platforms 

will have to be removed at some time in the future, they 

currently represent a minor portion of explosive removals . 

Results for major impacted species corresponded with those 

of Stanley and Wilson (in press) . At their 20 m study site, the 

most abundant species included Atlantic spadefish, red snapper, 

blue runner, and sheepshead in that order . While our study ranked 

blue runner slightly ahead of red snapper, red snapper was only 

one percentage point ahead of blue runner in Stanley and Wilson's 

results . 

Although some differences between Louisiana and Texas 

platforms were noted by Gallaway and Lewbel (1982), only one 

Texas platform was included in the present study . Consequently, 

it is not surprising that results from our analysis of estimated 

mortality and fish length by longitude did not parallel those of 

this earlier work . 

5 .3 Season 

This study was not designed to address seasonal and annual 

variations in fish mortality at platforms . Studies of blasting 

impacts were only conducted during May, July, August and 

September which encompasses late spring and summer . The number of 

platforms studied annually was one in 1993, two in 1994, three in 

1995, and one each in 1997, 1998, and 1999 . Since it was 

impossible to sample any platform more than once (platforms were 

removed), it is not surprising that graphs of estimated mortality 

by year also showed great variability . Lack of significant 

differences in mortality during these few months does not mean 

that seasonality plays no important role in fish distribution and 

abundance at offshore platforms . Seasonal changes in fish 
57 

abundance are well documented for the Gulf of Mexico (Gallaway 

1980 ; Gallaway et al . 1981 ; Mosley 1966 ; Bradley and Bryan 1975 ; 

Lukens 1981 ; Fable et al . 1981 ; Reagan 1985 ; Sutter and McIlwain 

1987) . Large differences can occur not only between seasons but 

also on a monthly basis . Fish population size was observed to 

vary by a factor of two to five from month to month (Putt 1982 ; 

Stanley 1994) . Heavy fishing pressure on red snapper may 

contribute to seasonal lows in summer abundance at some platforms 

(Gallaway 1980) . Given the small sample size and large monthly 

variation found in our study, it is clear that these results 

should not be used as an indicator of trends in seasonal or 

annual fish mortality at individual platform removals . 

Unpublished data collected by one of the authors (G . 

Gitschlag) from 1987-98 documents explosive removals in the U .S . 

Gulf of Mexico . Fifty-nine percent of explosive removals at 

structures classified as platforms by the NMFS Platform Removal 

Observer Program occurred from May through September and 84% from 

May through December . Relatively few removals occur during winter 

months when costs escalate due to severe weather . For structures 

of all types, 610 of removals occurred during May-September and 

85% from May-December . Consequently, distribution of fish during 

winter months is not a major factor affecting mortality related 

to explosive removals because few removals occur during this 

period . 

5 .4 Platform Age 

Platform age less than 25 yr vs greater than 25 yr was not a 

significant factor affecting fish mortality at platforms . Age of 

structures studied was from 12-39 years while 4 of 9 platforms 

exceeded 30 years . Based on this platform age structure, fish 

communities had ample time for development at all study sites . 

One noteworthy platform was South Marsh Island Block 23, a 33 

year old structure located in 25 m of water at longitude 91 .88° . 

This platform had previously been part of a larger three 

structure complex interconnected by above water bridges . The 

other two platforms, a 4 pile and a 6 pile structure, were 

removed 11 months earlier using over 318 kg (700 lb) of 

explosives . Since these explosions may have decimated the fish 

population at all three structures, the remaining platform offers 

insight into the extent of recolonization achieved by fish 

species during this 11 month period . Apparently, this was ample 

time to achieve repopulation . Total estimated mortality at this 

platform ranked second out of the nine platforms studied while 

red snapper mortality ranked first exceeding the second ranked 

platform by 68% . 

Colonization of newly installed platforms occurs quite 

rapidly and mature fish assemblages can be anticipated at all but 
58 

the very youngest platforms . Lukens (1981) reported full 

colonization of Gulf of Mexico artificial reefs can occur within 

15 months . Stanley and Wilson (1991) also found structure age was 

not a significant factor in explaining fish abundance at 

platforms . Generally, it is the older platforms that are removed . 

Relatively few very young platforms are salvaged . Thus platform 

age does not appear to be an important parameter affecting 

mortality of fish at explosive platform removals . 

5 .5 Surface Temperature and Salinity 

Surface temperature ranged from 26-32°C . No significant 

difference in estimated mortality was found at water temperatures 

< 30°C vs >=30°C . Bottom temperature ranged from 22-27°C . Although 

fish distribution is certainly affected by extreme salinity and 

temperature, these were not encountered during the study . 

Although low salinities may be encountered near areas affected by 

large freshwater outflow from rivers, this study was not designed 

to assess this influence . Red snapper have been collected at 

temperatures ranging from 13-28 C° (Rival 1970, Roe 1976) and 

have survived repetitive 20 min laboratory exposure to about 45 

ppt (Huff and Burns 1981) . In general, during seasons when most 

platform removals occur, natural fluctuations in salinity and 

temperature are not expected to be an important factor affecting 

fish distribution at offshore platforms . 

Surface salinity ranged from 18-33 ppt with an average of 26 

ppt . Variation in surface salinity (<=26 vs >26 ppt) did not have 

a significant effect on mortality estimates . Fish appeared to be 

unaffected by fluctuations within this range . Bottom salinity was 

less variable (25-33 ppt) . 

5 .6 Platform Size 

Gallaway and Lewbel (1982) reported that abundance of 

Atlantic spadefish was directly proportional to platform size . 

Stanley and Wilson (1991, in press) reported structure size 

affected fish density with higher density at mid-size platforms . 

Ogawa et al . (1977) and Rousenfell (1972) also found fish 

abundance was directly correlated with reef size . In contrast, 

anecdotal information provided to the author by a professional 

snapper fisherman indicated that one of his largest catches 

occurred on a submerged structure about the size of a barrel . We 

found no significant difference in estimated fish mortality 

resulting from explosive platform removals as a function of 

platform size . Perhaps size alone does not determine fish 

abundance at offshore platforms . 
59 

5 .7 Length-Frequency 

Analysis of length-frequency data provided an opportunistic 

glimpse of possible relationships between fish size, water depth 

and geographic location (longitude) of platforms . For a thorough 

investigation, a much larger sample of platforms is obviously 

required . Results for the five major species impacted at 

explosive structure removals did not indicate a general trend of 

larger fish being taken in deeper water . Three species (blue 

runner, sheepshead, and mangrove snapper) exhibited larger mean 

lengths at depths greater than 20 m while two others (Atlantic 

spadefish and red snapper) did not . Further analysis of red 

snapper data indicated significantly smaller fish at 20-30 m 

platform depths than at shallower and deeper depths . Combining 

additional red snapper data from the NMFS Platform Removal 

Observer Program provided similar results . It is recommended that 

additional data from other sources be combined for further 

testing which should consider more depth zones as well as capture 

seasons . This is necessary to account for migration across depth 

zones at various times of the year . 

Although fish length varied significantly by longitude for 

each species tested, no general trend in size was observed for 

platforms east of 92° vs west of 92° . Size and growth are complex 

variables and are affected by many parameters . The significant 

interaction effect may serve as an indicator of the importance of 

multiple parameters in determining fish size . 

5 .8 Population Estimates and Mortality Rates 

Fishing equipment used in tag and release experiments did 

not collect representative samples of all species . Population 

estimates were only calculated when sufficient data were 

obtained . Consequently, estimated mortality for all species 

combined provided the only index of total fish abundance . Average 

total estimated mortality (3390) was about four times lower than 

the estimated abundance (13,444) reported by Stanley and Wilson 

(in press) at a single platform in 22 m of water . This difference 

may be partially due to differences in methodology . Acoustic 

sampling of live fish used by Stanley and Wilson reportedly had a 

minimum target size of 2 .5 cm total length (Love 1971) which was 

considerably smaller than the 8 cm minimum used in the present 

study . Large numbers of fish less than 8 cm were collected at 

only one structure where estimated mortality of these small fish 

exceeded 6200 in the area immediately under the platform . 

Population estimates based on tag/recapture studies assume 

that 100% of tagged fish survive and mix with the population . 

Great care was taken to release only fish that appeared to be in 

good condition . However, external inspection may not always 
60 

provide a good index of internal trauma (Gitschlag and Renaud, 

1994) and some fish may succumb after release . Survival depends 

on many factors including where the fish was hooked, handling of 

fish, depth of capture (especially for physoclistic species), and 

abundance of predators in the area . When fish with gas bladders 

are retrieved rapidly to the surface during capture, the gas 

within the bladder can expand and cause serious internal damage . 

If survival of tagged and released fish is less than 1000 then 

population estimates will be higher than actual and estimated 

mortality due to explosives will be low . This may in part account 

for some of the low mortality estimates found for red snapper . 

When estimated mortality in this study exceeds population 

estimates, estimated mortality is recommended as a superior 

indicator of population size . 

However, some low rates were real and not artifacts . On the 

rare occasions when divers encountered good visibility during 

post-detonation dives, considerable variation was observed . In 14 

m of water at the largest platform studied, dives made within 

hours of the detonation showed a wide variety of fish species 

swimming beneath the platform . At another removal at 18 m depth, 

divers observed nearly complete mortality with the water column 

essentially devoid of any swimming fish . 

5 .9 Fish Density At Platforms 

While it is widely known that fish congregate at platforms 

and other offshore structures, data which quantitatively describe 

this phenomenon are limited (Gallaway et al . 1981, Gallaway and 

Lewbel 1982 ; Continental Shelf Associates 1982 ; Putt 1982 ; 

Stanley 1994 ; Stanley and Wilson 1996a ; Stanley and Wilson 1996b ; 

Stanley and Wilson 1997 ; Stanley and Wilson in press) . Dead fish 

that sink to the sea floor may provide an index of pre-detonation 

fish density at various distances around platforms . However, when 

fish swimming in the water column are killed by explosives, they 

may not fall directly to the sea floor . Currents may move 

carcasses laterally during descent . Also, hydrodynamic 

characteristics of the carcass may cause lateral movement during 

descent even in the absence of current . In this study a 

moderately strong current was only present at one platform in 18 

m of water in Ship Shoal Block 158 . Data from this platform were 

not included in the analysis of fish density . 

For platforms at depths of 14-32 m, results from the present 

study showed fish density decreased dramatically beyond 18 m . 

This compared well with results from Stanley and Wilson (in 

press) who found an area of influence of 18 m around two 

platforms in depths of 22 m and 60 m. Stanley and Wilson (1996b ; 

1997) also reported a near field area of influence of 16 m on the 

continental shelf where water depth was 25 m. Gerlotto et al . 
61 

(1989) reported fish densities adjacent to a platform were 5 to 

50 times greater than 50 m away . Stanley and Wilson's highest 

mean densities were roughly an order of magnitude larger than 

those in the present study . This difference may in part be 

related to methodology . Recall that Stanley and Wilson's 

technique detected fish with a minimum size of 2 .5 cm in contrast 

to an 8 cm minimum in the present study . 

5 .10 Comparison of Positively and Negatively Buoyant Fish 

When fish are killed by explosives some sink to the sea 

floor while others float to the surface . Extensive efforts were 

made to collect all dead fish which floated to the sea surface 

after explosives were detonated . In contrast, a sample was taken 

of dead fish which sank to the sea floor and an estimate of 

mortality was calculated mathematically . If a consistent 

mathematical relationship exists between the number of fish which 

float and the number which sink, then we need only to sample 

carcasses at the surface to obtain reliable estimates of total 

mortality . This would be extremely economical compared to the 

cost of fielding a team of divers to collect samples from the sea 

floor . Unfortunately, the ratio between positively and negatively 

buoyant fish varied widely with more fish floating to the surface 

at some explosive platform removals and more sinking to the sea 

floor at others . 

5 .11 Estimating Red Snapper Impacts across the U.S . Gulf of 

Mexico Using Stock Assessment Techniques 

Key information required in stock assessment includes the 

number and size of fish killed each year . In order to estimate 

total annual mortality associated with explosive structure 

removals in the U .S . Gulf of Mexico, we must first consider two 

important factors that may affect fish distribution : structure 

complexity and water depth . Size of fish mortalities must also be 

determined . 

5 .11 .1 Structure Complexity and Red Snapper Mortality 

There is a wide variety of oil and gas structures in the 

Gulf of Mexico including but not limited to platforms . The NMFS 

Platform Removal Observer Program collects data at all explosive 

structure removals in both state and federal waters of the U .S . 

Gulf of Mexico and its embayments . Data files maintained by this 

program define a platform as a multi-pile structure, a caisson as 

a single pile structure which is generally freestanding but 

occasionally connected to a platform, a flare pile as a single 

pile structure usually associated with a platform, and a 
62 

submerged well as a single pile extending some distance above the 

sea floor but not approaching the sea surface . The platform 

category includes a wide range of structures, some quite large 

with dozens of pilings . In many cases several platforms are 

placed close together in complexes connected above water via 

walkways . NMFS data for 1989-98 showed that 70% of all explosive 

structure removals were platforms, 23% were caissons, 6% were 

submerged wells, and 1% were flare piles . Platform removals 

exceeded caisson removals by a factor of three and were 

justifiably the focus of the present study . 

Data from the NMFS Platform Observer Program include visual 

estimates of dead, floating fish made opportunistically after 

explosives are detonated . These estimates can be extremely crude 

for large fish kills that are difficult to count accurately . They 

can also provide very accurate information in cases where few 

fish float to the surface as might be anticipated at single pile 

structures if they do not attract large numbers of fish . Data 

collected from 1989-98 show the average number of floating fish 

per structure was approximately 567 for platforms, 109 for 

caissons, 41 for flare piles, and 133 for submerged wells (Table 

17) . We cannot conclude that fish mortality at caissons was less 

than half that observed at platforms because the present study 

showed no consistent relationship between observed surface 

mortality and total mortality . Nevertheless, the data clearly 

indicate that fish mortality at caissons was not trivial despite 

the disparity in complexity between platforms and caissons . 

In addition to the volume of water encompassed within the 

boundary of the platform, the number of pilings at a platform can 

serve as an indication of structure complexity . Structure 

complexity was fairly consistent in the present study . Eight of 

the nine platforms studied were small, four pile structures 

ranging in depth from 15-32 m . One larger, 24 pile structure was 

located in 14 m of water where total estimated fish mortality was 

second lowest and red snapper mortality was nearly zero . This 

provides strong evidence that, contrary to popular belief, 

structure size alone may not be the most important factor in 

determining fish population size . 

5 .11 .2 Water Depth and Structure Removal 

Although no significant difference in estimated mortality by 

water depth was found in this study, on a larger scale, water 

depth does affect fish distribution and should be considered a 

potential factor affecting the calculation of total annual fish 

mortality at explosive structure removals . Depths of platforms 

used in the study can be compared with historical data from the 

NMFS Platform Removal Observer Program . From 1989-98, 33% (319) 

of explosive structure removals occurred in 14-32 m, while 43% 

(420) were in shallower water and 24% (228) in deeper water . 
63 

After more of the older structures in shallow water are removed, 

removal depth should increase over time as deeper water 

structures increase in number and age . Maximum depth for a 

platform removal was 114 m . Only eight structures, all submerged 

wells, were removed at greater depths with a maximum of 394 m . 

Caisson removals rarely exceeded 30 m in depth . 

5 .11 .3 Red Snapper Length by Water Depth 

As discussed earlier, total length of red snapper varied 

significantly by depth zone although the mean difference was 

small . A significant difference (P<0 .001) was found for depths 

<20 m vs >20 m . Further analysis indicated a difference for red 

snapper lengths taken from 20-30 m vs those from shallower (<20 

m) and deeper (20-30 m) depths . This did not follow the intuitive 

expectation of larger fish occurring in deeper water . Also, it 

posed a problem in determining how to expand these results to 

structure removals outside the depth range of the study . 

To further investigate the relationship between red snapper 

length and water depth, additional sources of data were explored . 

Lengths for red snapper collected from both sea surface and sea 

floor in the present study were combined with length data for 

floating red snapper collected opportunistically by personnel 

from the NMFS Platform Removal Observer program at various 

explosive structure removals from 1987-1998 . This contributed an 

additional 13,527 red snapper lengths for a total of 16,510 

collected at 116 explosive structure removals . Pooling of these 

data was justified for several reasons . Since the objective is to 

assess red snapper mortality at all explosive structure removals, 

it is advisable to utilize the largest possible data set 

representing as many of these removals as possible from all depth 

zones where red snapper were collected . In the present study, 

only 4 of 8 platforms showed a significant difference between 

length of red snapper collected at the surface and those 

collected at the sea floor . The overall mean length of positively 

buoyant fish was only 2 .6 cm more than that of negatively buoyant 

fish . Analysis of the combined data set using GLM single factor 

analysis and Tukey-Kramer studentized range test for paired 

comparisons yielded results similar to the previous findings . 

There was a statistical difference in red snapper length due to 

depth (P<0 .00) and the difference was in the 20-30 m strata . 

5 .11 .4 Assessment of Impacts on Red Snapper (1989-98) 

Ideally, mortality estimates for additional depth strata and 

structure type would provide information for the missing cells of 

the study prior to developing an estimate for total fish 
.p 

Table 18 . Description of data used in stock assessment sensitivity analysis for red 

snapper mortality at explosive structure removals in >7 m depths . 

Annual Annual 

number of Estimated estimated RS 

explosive red snapper mortality at 

structure Structure mortality explosive structure 

Data Set Estimate Period removals types included per structure removals 

A Low 1989-98 56.4 Platforms & well jackets 515 29,046 

B Mod-High 1989-98 80 Ally 515 41,200 

C Low 1999-2023 83.8 Platforms & well jackets 515 43,157 

D Mod 1999-2023 129 All' 515 66,435 

E 2xB 1989-98 160 Ally 515 82,400 

"All" includes platforms, well jackets, caissons, flare piles, and submerged wells. 
65 

mortality in the U .S . Gulf of Mexico . Since these data are not 

now and may never become available, another strategy was 

implemented . A sensitivity analysis provided a reasonable index 

to make this assessment . 

Low, moderately high, and very high estimates of red snapper 

mortality were determined (Table 18) . Estimates of total 

mortality were based on structure type while size composition was 

weighted by water depth . To provide a low estimate of mortality 

due to explosives we assumed no red snapper were killed at 

caissons and flare piles while mortality at other structure types 

was the same as that obtained in the present study . For the 

moderately high estimate, we assumed mortality was the same at 

all structure types including caissons and flare piles . Finally, 

we doubled the moderately high value to obtain a very high 

estimate of red snapper impacts . 

Information collected by the NMFS Platform Removal Observer 

Program was used to further refine the analysis . The depth range 

at which red snapper were collected was 7-114 m (22-375 ft) . 

Consequently, structures in water depths less than 7 m were not 

included in the red snapper analysis . Rivas (1970) and Moseley 

(1966) reported red snapper taken as shallow as 9 m and 14 m, 

respectively while Bradley and Bryan (1975) collected snapper as 

shallow as 5 .5 m in trawls . Although dead, floating fish were not 

collected at every structure removal monitored by NMFS observers 

from 1987-98, observers did perform fish collections at 321 

structures at depths from 7-114 m and 22 structures at shallower 

depths to a minimum of 2 m . 

Red snapper length records from the present study were 

combined with those from the NMFS Platform Removal Observer 

Program as described above . Although no significant difference in 

estimated mortality was detected at depths <20 m vs >30 m, there 

was a significant difference in red snapper length at depths from 

20-30 m. Consequently, all length records were sorted into two 

depth zones (7-20 m and >30 m vs 20-30 m) as were counts of 

explosive structure removals . Estimated annual red snapper 

mortality per structure (515) was multiplied by the ten year 

(1989-98) average annual number of explosive structure removals 

in each depth zone (from NMFS Platform Removal Observer Program 

data) to yield an estimate of red snapper mortality for each 

depth zone . Red snapper lengths in each depth zone were expanded 

by replication to equal these estimates . 

These expanded data sets were used in stock assessment 

analysis to determine the effect of mortality due to explosive 

structure removal on the overall stock . Despite natural variation 

in the data and possibly higher mortality at depths greater than 

study depths, doubling the moderately high estimate is expected 

to provide a value that far exceeds the actual mortality . 

Of the species encountered in these field studies, only 

three have stock assessments conducted on them : red snapper, gag 
66 

and red drum . Of these, estimated mortality of red snapper at 

platform removals was 331 times that for gag and 86 times that 

for red drum . Yet even when the estimate of red snapper mortality 

was doubled, the impacts were estimated to be small, well within 

the variation of our current assessments, and would not alter 

current determinations of status or current management recovery 

strategies . Therefore, it is not scientifically meaningful to 

develop quantitative mitigation strategies for platform removal 

based on these results . However, there are several general points 

about mitigation that may be made . Results indicated that smaller 

(younger pre-spawning) fish are likely to be the most affected 

age-groups in platform removal for nearly all species . Thus, a 

goal of any mitigation strategy would be to reduce the mortality 

overall and reduce it on young (small) fish disproportionately . 

If particular times or areas can be defined in which overall 

abundance on platforms or abundance of small fish on platforms is 

likely to be reduced, then platform removals could be focused in 

those times and areas . Unfortunately, the data from the nine 

platform removals do not provide consistent advice in this 

regard . Knowledge of the biology of the species involved would be 

more useful than quantitative analysis that might be done with 

the existing data . In general, water depths where red snapper 

occur are also characterized by platforms . One exception is 

movement of fish out of shallow water during winter with 

decreasing water temperature . Thus, explosive removal of 

platforms in shallow water during winter might be expected to 

reduce impacts on red snapper and other fish species . 

Sampling strategies to improve the precision of the 

determinations of impact and mitigation options should take two 

forms : 1) increase precision of the "per platform" mortality 

estimates by increasing the number of platforms sampled ; and 2) 

detect the effect of other factors on mortality by stratifying 

the platform sampling . Of these two, stratified sampling will 

likely be of the greatest benefit in reducing uncertainty . 

Factors that are likely to have an effect are depth, geographical 

area and season . These effects are likely to be different between 

species . With the present sample of nine platforms, the data are 

not sufficient to design stratified sampling regimes . Thus, 

generally increasing the number of platforms sampled would be 

useful in both reducing variation in the mean kill per platform 

estimate, but more importantly it would provide further guidance 

as to the important factors for more detailed sampling designs . 

Of course, the cost of increased sampling would have to be 

evaluated in light of the expected impacts of platform removals 

on the stocks discussed above . 
67 

5 .11 .5 Assessing Future Impacts on Red Snapper (1999-2023) 

This analysis utilized data from NMFS, MMS, and Pulsipher et 

al . (in press) . Unlike data from the NMFS Platform Removal 

Observer Program, the MMS data set did not include subsea wells, 

flare piles or any removals that occurred in state waters . These 

two data sets were used together in conjunction with Pulsipher's 

forecast of future platform removals to assess future impacts on 

red snapper . If explosives continue to be used at approximately 

64% of all removals', then fish populations at 119 platforms and 

caissons (0 .64 x 186 predicted annual platform removals) will be 

impacted annually . Using MMS data, this represents an increase of 

59% ((119-75)/75) over the 1989-1998 period . As of January 31, 

2000, 8 .8% (351 of 3967) of structures present in the Gulf of 

Mexico were in depths less than about 7 m . Reducing the 119 

predicted explosive removals by this factor yields 109 . From 

1989-98 NMFS recorded an additional 126 removals in depths >7 m 

including submerged wells and flare piles in federal waters and 

structures of all types in state waters . This represents 10 .8% 

(126/1172) of all removals (explosive and non-explosive) in the 

1989-98 MMS data base . Assuming this ratio remains constant in 

the future, the total number of explosive structure removals 

predicted annually will increase by an additional 20 (0 .108 x 

186) to provide a total of 129 (109 + 20) annual explosive 

structure removals in depths >7 ml . This is a moderately high 

estimate based on all structure types having the same mortality 

of red snapper . A low estimate of 83 .8 structures per year was 

obtained by deleting caissons, flare piles, and submerged wells 

from the NMFS data along with similar structure designations in 

the MMS data set . 

5 .12 Sources of Error 

Transect lines provided continuous sampling from the 

platform out to a distance of 100 m while circular surveys 

provided discrete, discontinuous samples . Circular surveys and 

sampling frames provided more accurate information than transect 

lines where transect widths (thus sampling area) were 

approximated, not measured . Transect width was designed to be 

either 1 or 2 m depending on underwater visibility . Distance was 

estimated using the armspread of divers to approximate 2 m . 

Divers with both longer and shorter armspreads were used during 

the study . Whenever possible, transect and circular survey data 

were combined to estimate total mortality so any small 

discrepancy would be even further diluted . Sampling of dead fish 

under the platform was highly accurate . Percent coverage of the 

footprint area under the platform by sampling frames ranged from 

12-83% with an average of 28% . Similarly, virtually every dead 
68 

fish observed at the surface was collected . 

Mortality estimates for certain platforms were probably 

slightly low for several reasons . Divers could not collect more 

fish than were present but they could fail to collect all fish 

due to poor visibility . At Ship Shoal Block 158, the only site 

where there was a substantial current, sample bags for the 

downcurrent transect line were lost during retrieval . Divers who 

collected the samples reported large numbers of fish which was 

anticipated due to the strongly directional current moving fish 

carcasses as they sank to the sea floor . 

If the assumption of decreasing mortality with increasing 

distance from platform is true, then other factors tended to 

slightly overestimate mortality . This is due to a continuous 

decrease in the ratio of sampling to total area as one proceeds 

away from the platform . This would tend to slightly overestimate 

mortality based on transect line and circular survey data . For 

example, the total area of the 12 .5-25 m band around a platform 

is larger than the 0-12 .5 m band, but the sampling area was 

constant throughout the entire 0-25 m region along the transect 

line . Similar reasoning holds for pooling of the two innermost 

circular surveys (0-6 .7 m and 18 .3-25 m) . Thus samples taken 

closer to the platform had a somewhat higher weighting in the 

overall average . 

Exceptions could occur in the case of schooling species such 

as blue runner which were often observed at greater distances . 

Mortality then becomes a matter of chance depending on where a 

school is at the instant explosives are detonated . Another 

exception was identified at a platform in 18 m of water . No fish 

were collected in 7 of 8 circular surveys conducted at a distance 

of 50 m . Four fish including 3 red snapper and a sheepshead were 

collected in a sample which happened to be located adjacent to a 

large debris pile . It appears that fish were attracted to the 

debris on the otherwise barren sea bottom . Presence of structure 

around platforms probably affects fish distribution and hence 

mortality resulting from explosive platform removal . 

In general, positive and negative sources of error probably 

cancel each other out or result in slightly low estimates . 

Exceptions include cases when samples with large numbers of fish 

were lost . Overall, final estimates appear to be accurate and 

variance in estimated mortality by species indicates real 

differences between platforms . 

Data analysis indicated that future estimates can be 

improved somewhat by partitioning the area within 25 m of the 

platform into more than one sampling region . While increments of 

5 m proved to be too time-consuming given most logistical 

situations, partitioning of the 0-25 m area around the platform 

into two sampling regions, as was done at the last study site, 

Galveston Block 288, worked well . 
69 

6 .0 SUMMARY 

l . The most severely impacted fish species in order of abundance 

were Atlantic spadefish, blue runner, red snapper, and 

sheepshead . These five species accounted for 86% of estimated 

mortality . Numbers of all other impacted species were far below 

those of the top four . 

2 . Of the fish species encountered in these field studies, only 

three have stock assessments conducted on them : red snapper, gag 

and red drum . For red snapper, even when the mortality estimate 

was doubled, impacts were estimated to be small, well within the 

variation of our current assessments, and would not alter current 

determinations of status or current management recovery 

strategies . Similarly, current methods of assessment would not 

detect the even smaller changes in magnitude of gag and red drum . 

3 . In general, results indicated no significant difference in 

estimated mortality of red snapper by depth, longitude, platform 

age, season, surface salinity, and surface temperature in the 

study area (14-32 m) during May to September . 

4 . These analyses suggested no appropriate strata for expansion 

of mortality data to the greater Gulf of Mexico . Consequently, 

platforms in the water depths studied can be included in a single 

group for the purpose of estimating fish mortality due to 

explosive platform removals . 

5 . Although the effects of structure complexity on fish abundance 

was not an objective of this study, unpublished data from the 

National Marine Fisheries Service indicated structure complexity 

may directly influence observed mortality . This parameter was 

integrated into the sensitivity analysis for stock assessment . 

6 . A significant difference in red snapper length at removals in 

20-30 m water depths vs those at shallower and deeper depths was 

also incorporated into the analysis . 

7 . Future impacts to the red snapper stock were predicted based 

on forecasts of future structure removals reported by Pulsipher 

et al . (in press) . Although estimates of future mortality were 

higher than current estimates, they were still within the 

variation of our current assessments . Given the assumptions used 

in these forecasts, predicted future mortality would not alter 

current determinations of the status of the red snapper stock or 

current management recovery strategies . 
70 

8 . Two important caveats should be remembered when interpreting 

these results . First, species composition and abundance can 

change in water depths deeper than those encountered during this 

study . Second, sample size was small . Only nine to ten platforms 

were sampled out of more than 4,000 structures present in the 

U .S . Gulf of Mexico . 
71 

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62 :1397-1403 . 

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74 

petroleum structures as artificial reefs . OCS Report/MMS87-

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76 

Interior . Minerals Management Service . 
77 

Appendix I 

Pre-detonation Visual Fish Surveys 

Minerals Management Service requested performance of visual 

fish surveys to be patterned after Bohnsack and Bannerot (1986) . 

These researchers described the use of stationary visual census 

techniques for use on coral reefs . In general, protocols included 

divers listing all fish species observed in 5 min within an 

imaginary cylinder with a 7 .5 m radius extending from sea surface 

to bottom . With the exception of schooling fish which were 

counted as soon as they were observed, divers counted the number 

of individuals observed for each species recorded during a second 

5 minute session performed immediately after the first . The 

authors reported underwater visibility generally exceeded 12 m. 

Key differences in the environmental conditions encountered 

during our study in the northern Gulf of Mexico and Bohnsack & 

Bannerot's study in the Florida Keys prevented duplication of 

their protocols . Underwater visibility in our study was as low as 

2 m or less and never allowed divers to visually sample the 

entire water column . Although visual surveys were conducted using 

a reduced survey radius appropriate to the visibility 

encountered, it was determined that using these values to 

calculate fish densities and generate fish population estimates 

would result in severe errors . It was impossible to determine 

when the same individuals made multiple passes through a given 

survey area . On many occasions it was obvious that fish were 

swimming through multiple survey areas and being counted by more 

than one diver during the same 5 minute survey period, yet it was 

impossible to document how often this occurred . Reduced survey 

distance in our study may have affected which species were 

observed since some species approach divers much more closely 

than others . By the end of our study it became clear that the 

procedures described by Bohnsack and Bannerot were not directly 

applicable to our study sites . Consequently, fish survey data 

were not used to estimate fish population size . 

79 

Appendix II 

Common and Scientific Names of Collected Fish 

Common name 

Almaco jack 

Atlantic bumper 

Atlantic croaker 

Atlantic spadefish 

Atlantic thread herring 

Belted sand bass 

Bermuda chub 

Black drum 

Blue runner 

Bluespotted searobin 

Chub mackerel 

Cocoa damselfish 

Crevalle jack 

Cubbyu 

Gag 

Gray triggerfish . 

Great barracuda 

Guaguanche 

Gulf toadfish 

Hardhead catfish 

Ladyfish 

Lane snapper 

Leopard toadfish 

Lookdown 

Mangrove snapper 

Molly miller 

Mullet 

Ocean triggerfish 

Pigfish 

Pinfish 

Planehead filefish 

Red drum 

Red snapper 

Remora 

Rock hind 

Scaled sardine 

Scamp 

Schoolmaster 

Scrawled filefish 

Sergeant major 

Sharksucker 

Scientific name 

Seriola rivoliana 

Chloroscombrus chrysurus 

Micropogonias undulatus 

Chaetodipterus faber 

Opisthonema oglinum 

Serranus subligarius 

Kyphosus sectatrix 

Pogonias chromis 

Caranx crysos 

Prionotus roseus 

Scomber japonicus 

Pomacentrus variabilis 

Caranx hippos 

Equetus umbrosus 

Mycteroperca microlepis 

Balistes capriscus 

Sphyraena barracuda 

Sphyraena guachancho 

Opsanus beta 

Arius felis 

Peprilus paru 

Lutjanus synagris 

Opsanus tau 

Sel ene vomer 

Lutjanus griseus 

Blennius cristatus 

Mugil (sp .) 

Canthidermis sufflamen 

Orthopristis chrysoptera 

Lagodon rhomboides 

Monocanthus hispidus 

Sciaenops ocellatus 

Lutjanus campechanus 

Remora remora 

Epinephelus adscensionis 

Harengula pensacolae 

Mycteroperca phenax 

Lutjanus apodus 

Aluterus scriptus 

Abudefduf saxatilis 

Echeneis naucrates 
80 

Sheepshead 

Silk snapper 

Silver trout 

Spanish sardine 

Speckled trout 

Tomtate 

Whitespotted soapfish 

Yellow chub 

Yellowtail snapper 

Archosargus probatocephalus 

Lutjanus vivanus 

Cynoscion nothus 

Sardinella anchovia 

Cynoscion nebulosus 

Haemulon aurolineatum 

Rypticus maculatus 

Kyphosus incisor 

Ocyurus chrysurus 
F . 

P 

The Department of the Interior Mission 

Q4r+r.. - 2 

o`` '= As the Nation's principal conservation agency, the Department of the Interior has responsibility 

for most of our nationally owned public lands and natural resources . This includes fostering 

a ~ 

;.1 

sound use of our land and water resources ; protecting our fish, wildlife, and biological diversity; 

preserving the environmental and cultural values of our national parks and historical places; 

"` and providing for the enjoyment of life through outdoor recreation . The Department assesses 

our energy and mineral resources and works to ensure that their development is in the best 

interests of all our people by encouraging stewardship and citizen participation in their care. 

The Department also has a major responsibility for American Indian reservation communities 

and for people who live in island territories under U.S . administration . 

The Minerals Management Service Mission 

As a bureau of the Department of the Interior, the Minerals Management Service's (MMS) 

primary responsibilities are to manage the mineral resources located on the Nation's Outer 

Continental Shelf (OCS), collect revenue from the Federal OCS and onshore Federal and Indian 

lands, and distribute those revenues . 

Moreover, in working to meet its responsibilities, the Offshore Minerals Management Program 

administers the OCS competitive leasing program and oversees the safe and environmentally 

sound exploration and production of our Nation's offshore natural gas, oil and other mineral 

resources. The MMS Minerals Revenue Management meets its responsibilities by ensuring the 

efficient, timely and accurate collection and disbursement of revenue from mineral leasing and 

production due to Indian tribes and allottees, States and the U .S. Treasury. 

The MMS strives to fulfill its responsibilities through the general guiding principles of : (1) being 

responsive to the public's concerns and interests by maintaining a dialogue with all potentially 

affected parties and (2) carrying out its programs with an emphasis on working to enhance the 

quality of life for all Americans by lending MMS assistance and expertise to economic 

development and environmental protection .