Preface This manual was developed based on maerial presened during several sock assessmen raining courses sponsored by he Alanic Saes Marine Fisheries Commission, and supplemened by class lecure noes of Dr. Joseph T. DeAleris, Professor of Fisheries and Aquaculure, Universiy of Rhode Island. I is inended o be used as a reference for sock assessmen biologiss and sudens, and as a course handbook for fuure ASMFC sock assessmen raining courses. ii
Acknowledgmens The Commission would like o hank all of hose people who assised wih he sock assessmen raining courses including Dr. Lisa Kline (ASMFC), Dr. Alan Temple (U.S. Fish and Wildlife Service, Naional Conference and Training Cener), Dr. Joseph T. DeAleris (Universiy of Rhode Island), Mr. Najih Lazar (Rhode Island Division of Fish and Wildlife), and all he preseners and lecurers (Dr. Don Orh, Virginia Tech; Dr. Joseph DeAleris; Mr. Mark Gibson, Rhode Island Division of Fish and Wildlife; Mr. Najih Lazar; Dr. Wendy Gabriel, Naional Marine Fisheries Service; Dr. Jeremy Collie, Universiy of Rhode Island; and Dr. Josef Idoine, Naional Marine Fisheries Service). We are graeful o he Naional Conference and Training Cener (U.S. Fish andwildlife Service, Shepherdsown, WV) and he Universiy of Rhode Island for assising wih he developmen of he raining courses, and for providing access o classrooms and compuer faciliies. Graeful appreciaion is exended o Dr. Mahew Miro (ASMFC/Rhode Island Division of Fish and Wildlife) for reviewing he documen and providing useful commens and suggesions, and Ms. Vanessa Jones (ASMFC) and Ms. Laura Lee (ASMFC) for assisance wih formaing and ediing. Special hanks go o Dr. DeAleris for providing his lecure noes, ime, and experience o his manual. iii
Table of Conens Preface... ii Acknowledgemens... iii Lis of Figures... viii Lis of Tables... xiii Inroducion o Fish Sock Assessmen, Fisheries Managemen, Fisheries and Fishery-Dependen Daa, and Research Surveys and Fishery-Independen Daa Joseph T. DeAleris and Laura G. Skrobe... I - 1 Background... I - 1 Fisheries Managemen... I - 1 Fish Sock Assessmen... I - 3 Fisheries and Fishery Dependen Daa...I - 4 Hooks and Line Gear... I - 4 Pos and Traps... I - 5 Dragged Gear... I - 7 Seines... I - 9 Gillnes... I - 11 Fishery-Dependen Daa and Analyses... I - 12 Research Surveys... I - 13 Bibliography... I - 15 Mahemaics and Biosaisics Review Joseph T. DeAleris...II - 1 Funcions...II - 1 Powers and Logarihms...II - 6 Transforming or Linearizing Funcions...II - 7 Differenial Calculus...II - 9 Inegral Calculus...II - 12 Differenial Equaions...II - 14 Descripive Saisics...II - 15 Hypohesis Tesing...II - 18 Fiing Models o Daa...II - 19 Exercises...II - 21 Bibliography...II - 23 Growh Joseph T. DeAleris and Laura G. Skrobe... III - 1 Inroducion... III - 1 Von Beralanffy Growh Equaion... III - 3 Esimaing Lengh... III - 3 iv
Esimaing Weigh... III - 5 Esimaing Age... III - 6 Esimaing Growh Equaion Parameers... III - 6 Gulland-Hol Mehod... III - 6 Ford-Walford Plo... III - 8 Non-linear Regression Mehods... III - 1 Gomperz Growh Equaion... III - 11 Exercises... III - 12 Bibliography... III - 13 Esimaion of Moraliy Raes Don Orh, Najih Lazar, and Joseph T. DeAleris... IV - 1 Inroducion... IV - 1 Esimaing Toal Moraliy from Cach Curve Analysis... IV - 8 Esimaing Toal and Fishing Moraliy from Tagging Experimens... IV - 1 One Time Releases or Single Census (Peersen Type)... IV - 11 Recapures in a Series of Years from a Single Year Release... IV - 12 Esimaing Naural Moraliy from Fishing Moraliy and Effor Daa... IV - 14 Oher Mehods for Esimaing Naural Moraliy... IV - 15 Exercises... IV - 17 Bibliography... IV - 18 Seleciviy of Marine Fish Harvesing Gears: General Theory, Size Selecion Experimens, and Deerminaion of Size Selecion Curves Joseph T. DeAleris... V - 1 Background... V - 1 Lieraure Review... V - 1 General Theory... V - 2 Logisic Cumulaive Disribuion Funcion... V - 2 Normal Probabiliy Disribuion Funcion... V - 5 Field Experimens and Esimaion of Size Selecion Curves... V - 7 Exercises... V - 12 Bibliography... V - 15 Developmen and Applicaion of Yield per Recrui and Spawning Sock per Recrui Models Joseph T. DeAleris and Najih Lazar... VI - 1 Background... VI - 1 Analyical Soluion... VI - 1 Discree Time Model... VI - 8 Exercises... VI - 18 Bibliography... VI - 19 Producion Models Joseph T. DeAleris...VII - 1 Inroducion...VII - 1 v
Populaion Growh and Regulaion...VII - 1 Surplus Producion Model...VII - 6 Schaefer Model...VII - 7 Fox Model...VII - 9 Exercises...VII - 14 Bibliography...VII - 15 Sock and Recruimen Joseph T. DeAleris... VIII - 1 Inroducion... VIII - 1 Biological Processes... VIII - 1 Measuremen of Spawning Sock and Recruimen... VIII - 1 Basic Principles of he S-R Relaionship... VIII - 2 Beveron-Hol Model... VIII - 2 Ricker Model... VIII - 3 Shephard Model... VIII - 4 Esimaion of S-R Parameers... VIII - 5 Spawning Sock per Recrui and Seady Sae... VIII - 9 Exploied Populaion Trajecories... VIII - 1 Environmenal Effecs on he S-R Relaionship wih Exploiaion... VIII - 1 Exercises... VIII - 12 Bibliography... VIII - 14 Sampling Mehodology Review Jeffrey Brus and Carolyn Belcher... IX - 1 Inroducion... IX - 1 Sampling Design... IX - 1 Simple Random Sampling... IX - 2 Sraified Random Sampling... IX - 3 Sysemaic Sampling... IX - 6 Mulisage Sampling... IX - 9 Resampling Mehods... IX - 9 Boosrap... IX - 1 Jack Knife... IX - 12 Fishery Dependen and Independen Sampling Mehods... IX - 12 Recreaional Fisheries... IX - 12 Commercial Fisheries... IX - 13 Resource Surveys... IX - 14 Effor Sandardizaion... IX - 15 Exercises... IX - 18 Bibliography... IX - 2 Sequenial Populaion Analysis: Age and Lengh Srucured Assessmen Models Joseph DeAleris and Laura Skrobe... X - 1 Background... X - 1 Formulaion of he Governing Equaions for SPA... X - 2 vi
Projecion Models: Age-Based... X - 4 Projecion Models: Lengh-Based... X - 5 Rerospecive Models: Age-Based... X - 8 Rerospecive Models: Lengh-Based... X - 15 Excercises... X - 21 References... X - 23 Cach Survey Analysis Jeremy Collie... XI - 1 Background... XI - 1 Cach Survey Analysis... XI - 1 Derivaion of he Collie-Sissenwine Mehod... XI - 2 Fiing he Collie-Sissenwine Mehod o Daa... XI - 3 Applying he Collie-Sissenwine Mehod o King Crabs... XI - 5 Brisol Bay... XI - 6 Mone Carlo Simulaions... XI - 11 Boosrapping he Abundance Esimaes... XI - 17 Conclusions... XI - 17 Exercises... XI - 21 Bibliography... XI - 24 Biomass Dynamic Models Joseph DeAleris and Laura Skrobe...XII - 1 Inroducion...XII - 1 Model Formulaion...XII - 1 Exercises...XII - 11 References...XII - 13 A Review of Fish Sock Assessmen Daa and Models and he Resuling Biological Reference Poins Used in Fisheries Managemen Joseph DeAleris and Laura Skrobe... XIII - 1 Inroducion... XIII - 1 Index Daa... XIII - 2 Yield Per Recrui Models... XIII - 2 Spawning Sock Biomass and Egg Per Recrui Models... XIII - 3 Surplus Producion Models... XIII - 4 Sock-Recruimen Models... XIII - 7 Age and Lengh Srucured Models... XIII - 8 Inegraing Models... XIII - 9 Conrol Rules... XIII - 1 References... XIII - 11 Appendix 1: Insrucions for Yield per Recrui Tables... A1-1 Appendix 2: Answers o Examples... A2-1 Appendix 3: Answers o Exercises... A3-1 vii
Lis of Figures Inroducion o Fish Sock Assessmen, Fisheries Managemen, Fisheries and Fishery Dependen Daa, and Research Surveys and Fishery Independen Daa Figure 1: Boom longline gear... I - 5 Figure 2: Crab po... I - 6 Figure 3: Pound ne... I - 7 Figure 4: Oyser dredge... I - 8 Figure 5: Oer rawl... I - 9 Figure 6: Purse seine... I - 1 Figure 7: Sink gill ne... I - 11 Figure 8: Poomac River blue crab harves and licenses issued... I - 12 Figure 9: Esimaed number of marine recreaional fishing rips in Rhode Island from MRFSS survey... I - 13 Mahemaics and Biosaisics Review Figure 1: Funcion y = f(x)...ii - 1 Figure 2: Linear funcion: y = ax+b...ii - 2 Figure 3: Special cases of linear funcions...ii - 2 Figure 4: Effecs of slope a on he linear funcion...ii - 3 Figure 5: The quadraic funcion: y = A(x-x )(x-x 1 )...II - 3 Figure 6: Parabola: y = -Ax 2 + Axb...II - 4 Figure 7: Exponenial funcions: y = a x...ii - 4 Figure 8: Asympoic funcion: y = 1-e -x...ii - 5 Figure 9: Power funcions: y = x N...II - 6 Figure 1: Non-linear and linear forms of y = Ae -zx...ii - 8 Figure 11: Non-linear and linear forms of y = bx-ax 2...II - 9 Figure 12: Non-linear and linear forms of y = f(x)...ii - 1 Figure 13: Funcions y = bx ax 2 and y = b-2ax...ii - 11 Figure 14: The inegral of a funcion y = f(x)...ii - 12 Figure 15: Lengh-frequency disribuion...ii - 17 Figure 16: Mean and confidence inervals of fish fork lenghs...ii - 19 Figure 17: Linear and non-linear models for he weigh-lengh relaionship W =.5545L 3.1273...II - 2 Growh Figure 1: Growh curve for lengh where L is he maximum lengh ha can be achieved... III - 1 Figure 2: Growh curve for weigh where W is he maximum weigh ha can be achieved... III - 2 Figure 3: Muli-modal lengh-frequency disiribuion... III - 2 Figure 4: The linear relaionship beween growh (dl/d) and lengh (L )... III - 3 Figure 5: The correced von Beralanffy growh funcion for lengh ( ) L (1 K L e )... III - 4 Figure 6: The effec of he value of he growh coefficien (K) on he growh curve... III - 5 viii
Figure 7: Gulland Hol plo of growh rae agains mean lengh... III - 7 Figure 8: Ford-Walford plo of growh a ime +T versus lengh a ime... III - 9 Esimaion of Moraliy Raes Figure 1: Schemaic diagram of inpus and losses o a sock... IV - 1 Figure 2: Relaionship beween he rae of loss (dn/d) and populaion size (N)... IV - 2 Figure 3: Exponenial decay curves for Z =.2,.5, 1., and 2. wih recruimen N = 1 fish... IV - 3 Figure 4: Type 1 fishery... IV - 5 Figure 5: Type 2 fishery... IV - 5 Figure 6: Exponenial decay of cohor number when M =.2 and F =.1 Applied a c age 3... IV - 7 Figure 7: The linearized exponenial decay funcion: lnn = Z + b... IV - 8 Figure 8: Cach curve analysis... IV - 9 Figure 9: Observed and prediced populaion size... IV - 9 Figure 1: Ln(recapures) versus ime for agged winer flounder... IV - 13 Figure 11: Plo of Z = qf + M. In his example, q =.13 and M =.2118... IV - 14 Figure 12: Linear regression of Z agains f o solve for M... IV - 15 Seleciviy of Marine Fish Harvesing Gears: General Theory, Size Selecion Experimens, and Deerminaion of Size Selecion Curves Figure 1: Probabiliy of selecion following a logisic cumulaive disribuion funcion... V - 3 Figure 2: Regression of ln(p/(1-p)) vs L... V - 4 Figure 3: Logisic cumulaive disribuion funcion (LCDF) seleciviy curves... V - 5 Figure 4: Probabiliy of selecion following a normal probabiliy disribuion funcion... V - 6 Figure 5: Linear regression of ln(c B /C A ) for wo similar gears ha follow NPDF... V - 6 Figure 6: Normal probabiliy disribuion funcion (NPDF) seleciviy curves... V - 7 Figure 7: Resuls of he covered cod-end experimen... V - 9 Figure 8: Analysis and resuls of NPDF seleciviy analysis... V - 11 Developmen and Applicaion of Yield per Recrui and Spawning Sock per Recrui Models Figure 1: Yield per recrui as a funcion of fishing moraliy... VI - 7 Figure 2: Funcional characerisics of an unfished cohor of an idealized roundfish... VI - 11 Figure 3: Funcional characerisics of an unfished cohor of an idealized roundfish... VI - 12 Figure 4: Selecion characerisics of harvesing gears used on he cohor of idealized roundfish... VI - 13 Figure 5: Isopleh diagrams expressed as a percenage of maximum for size selecion based on a LCDF... VI - 14 Figure 6: Isopleh diagrams expressed as a percenage of maximum for size ix
selecion based on a NPDF... VI - 15 Figure 7: Effec of seepness of he LCDF on he cohor of an idealized roundfish... VI - 16 Figure 8: Effec of he sandard deviaion of he NPDF for he cohor of an idealized roundfish... VI - 17 Producion Models Figure 1: The rae of change of populaion number (dn/d) as a funcion of populaion size (N) for r >, =, and <...VII - 2 Figure 2: Populaion rajecories for densiy independen growh where r >, =, and <...VII - 3 Figure 3: Birh (b) and deah (d) raes incorporaing densiy dependence...vii - 4 Figure 4: Parabolic model relaing densiy dependen rae of populaion change o populaion size...vii - 5 Figure 5: Logisic model describing populaion number as a funcion of ime...vii - 6 Figure 6: Schaefer model relaing yield o effor...vii - 8 Figure 7: Time hisory of cach and effor...vii - 1 Figure 8: Linearizaion of he Schaefer model and he bes fi regression...vii - 11 Figure 9: Non-linear Schaefer model bes fi o he cach and effor daa...vii - 12 Figure 1: Linearizaion of he Fox model and he bes fi regression...vii - 13 Figure 11: Non-linear Fox model bes fi o he cach and effor daa... VII 13 Sock and Recruimen Figure 1: The Beveron-Hol S-R relaionship wih changing values of A... VIII - 3 Figure 2: The Ricker S-R relaionship a various a and b values... VIII - 4 Figure 3: The Shephard S-R relaionship a various, K, and values... VIII - 5 Figure 4: Applicaion of S-R daa in he linearized Beveron-Hol S-R relaionship... VIII - 6 Figure 5: Applicaion of S-R daa in he Beveron-Hol S-R relaionship... VIII - 7 Figure 6: Applicaion of S-R daa in he linearized Ricker S-R relaionship... VIII - 8 Figure 7: Applicaion of S-R daa in he Ricker S-R relaionship... VIII - 8 Figure 8: Inersecion of SSBPR funcions a various fishing moraliy levels (F), wih a Beveron-Hol S-R relaionship... VIII - 9 Figure 9: Two-sage life hisory rajecory based on he inersecion of S-R and SSBPR relaionships... VIII - 1 Figure 1: Effec of environmenal suiabiliy on he S-R and SSBPR relaionships...viii 11 Sequenial Populaion Analysis: Age and Lengh Srucured Sock Assessmen Models Figure 1: Trajecory of cohor number for a life span of 5 years, where naural moraliy is M =.7 or 5% annual loss.... X - 3 Figure 2: Von beralanffy growh funcion for he pond fish when K = 1. and L = 4 cm... X - 3 Figure 3: Trajecory of cohor number for F =.7 and M =.7... X - 5 Figure 4: Number of fish remaining in a cohor as a funcion of he lengh wih naural moraliy only... X - 7 x
Figure 5: Number of fish remaining in cohor number as a funcion of lengh... X - 7 Figure 6: Cohor Number as a funcion of ime, during one year, showing Pope's age-based approximaion wih cach aken insananeously a mid-year...x - 9 Figure 7: Cohor approximaion as a funcion of lengh wihin a lengh class, showing Jones' lengh-based approximaion wih cach aken insananeously a mid-lengh wihin he range... X - 15 Cach Survey Analysis Figure 1: Plo of cach per uni effor (n i /f/ I ) versus he cumulaive cach (x i ) for a lobser populaions: redrawn from Delury (1947)... XI - 2 Figure 2: Annual iming of xcrab moling, rawl survey, and commercial fishery... XI - 6 Figure 3: Abundances of Brisol Bay red king crabs measured wih a rawl survey and esimaed wih cach-survey analysis. The consan naural moraliy rae, M, was.36 and he variable Ms are from Zheng e al 1995. Adaped from Collie and Kruse (1998) wih permission... XI - 7 Figure 4: Legal male abundance, harves rae, and naural moraliy of Brisol Bay king crabs. Adaped from Collie and Kruse (1998) wih permission... XI - 9 Figure 5: Sensiiviy of he cach-survey analysis o errors in he inpu daa. Each panel shows he deviaion of he simaed cachabiliy coefficien from is known value of 1 wih errors in he inpu value of T (rue value =.25), M (rue value=.3), or (rue value = 1). Larger circles indicae a poorer fi of he cach-survey analysis. Adaped from Collie and Kruse (1998) wih permission... XI - 1 Figure 6: Flow char if he sequence of seps in he Mone Carlo simulaion process... XI - 12 Figure 7: Disibuions of q relaive o rue value of 1. in Mone Carlo simulaions wih differen magniudes of measuremen error. Each box plo summarizes he disribuion of 2 q values. The whie bar is he median and he box conains he second and hird quariles. The doed line exends 1.5 imes he inerquarile disance and he horizonal lines are ouliers. The hree numbers under each box indicae he sandard deviaion of measuremen errors, he correlaion of measuremen errors, and process error sandard deviaion (from lef o righ). Adaped from Collie and Kruse (1998) wih permission... XI - 13 Figure 8: Comparison of he effec of measuremen and process error on he esimae of pos-recrui abundance. Each solid line is one simulaion.... XI - 14 Figure 9: Disribuion of q relaive o known value of 1. in Mone Carlo simulaions wih differen magniudes of boh measuremen and process error. The explanaion of he box plos is he same as for Figure 7. Adaped from Collie and Kruse (1998) wih permission.... XI - 16 Figure 1:Relaive abundances of Kodiak red king crabs meaured wih a po survey and esimaed wih cach-survey analysis. The consan M was.36 and he variable Ms were scaled o ocean emperaure anomalies. Adaped from Collie and Kruse (1998) wih permission... XI - 18 xi
Figure 11:Flow char of he sequence of seps in he boosrap process... XI - 19 Figure 12:Boosrap abundance esimaes for Brisol Bay and Kodiak red king crabs. Adaped from Collie and Kruse (1998) wih permission... XI - 2 Biomass Dynamic Models Figure 1: Effec of he inrinsic rae of growh (r) on he sock biomass rajecory (B A )...XII - 3 Figure 2: Effec of he inrinsic rae of growh (r) on he sock biomass growh rae (db/d) as a funcion of biomass (B)...XII - 3 Figure 3: Effec of a consan cach rae of 1 m on he sock biomass rajecory...xii - 4 Figure 4: Effec of increasing cach from o 5 m on he sock biomass Trajecory...XII - 5 Figure 5: Effec of an oscillaing cach wih a period of 1 years and a maximum of 15 m on he sock biomass rajecory...xii - 5 Figure 6: Effec of an oscillaing cach wih a period of 1 years and a maximum of 25 m on he sock biomass rajecory...xii - 6 Figure 7: Time-series plo of cach and observed and esimaed indices of relaive abundance...xii - 8 Figure 8: Time-series plo of cach and observed and esimaed CPUE...XII - 9 A Review of Fish Sock Assessmen Daa and Models and he Resuling Biological Reference Poins Used in Fisheries Managemen Figure 1: Indices of relaive abundance based on survey and fishery daa... XIII - 2 Figure 2: Y/R model showing Y MAX, F MAX, and F.1... XIII - 3 Figure 3: SSB/R model showing F 1, 2, and 3%... XIII - 4 Figure 4: Yield-sock biomass model showing MSY and B MSY... XIII - 5 Figure 5: Cach-fishing effor model showing MSY and F MSY... XIII - 6 Figure 6: Yield-fishing effor model showing revenue and coss... XIII - 7 Figure 7: Sock-recruimen relaionship showing B MSR and B... XIII - 8 Figure 8: Inegraed S-R and SSB/R plos... XIII - 9 Figure 9: Harves conrol rule based on biomass levels relaive o B MSY and fishing moraliy raes relaive o F MSY... XIII - 1 xii
Lis of Tables Mahemaics and Biosaisics Review Table 1: Lengh daa grouped ino ineger caegories...ii - 17 Esimaion of Moraliy Raes Table 1: Proporional decrease in populaion over ime... IV - 4 Table 2: Relaionship beween insananeous naural moraliy, annual percen loss, and life span... IV - 6 Table 3: Values of naural moraliy derived using Hoenig (1983)... IV - 16 Seleciviy of Marine Fish Harvesing Gears: General Theory, Size Selecion Experimens, and Deerminaion of Size Selecion Curves Table 1: Resuls of he covered cod-end experimen... V - 9 Developmen and Applicaion of Yield per Recrui and Spawning Sock per Recrui Models Table 1: Yield per recrui for M/K =.5... VI - 5 Table 2: Yield per recrui for M/K = 2.... VI - 6 Producion Models Table 1: Trawl cach and effor daa wih CPUE...VII - 11 Table 2: Trawl cach and effor daa wih ln(cpue)...vii - 12 Sampling Mehodology Review Table 1: Possible sysemeaic samples and sample size for populaion of A = 4 and k - 6... IX - 7 Sequenial Populaion Analysis: Age and Lengh Srucured Sock Assessmen Models Table 1: Age-based projecion of cohor abundance and cach... X - 5 Table 2: Lengh-based projecion of cohor abundance and cach... X - 8 Cach Survey Analysis Table 1: Adapaions of he DeLury mehod... XI - 2 Table 2: Dynamics of size and shell age for king crabs... XI - 6 Table 3: Resuls of Mone Carlo simulaions of cach-survey analysis... XI - 15 xiii
INTRODUCTION TO FISH STOCK ASSESSMENT, FISHERIES MANAGEMENT, FISHERIES AND FISHERY-DEPENDENT DATA, AND RESEARCH SURVEYS AND FISHERY-INDEPENDENT DATA Background Joseph T. DeAleris and Laura G. Skrobe Universiy of Rhode Island Kingson, RI A fish populaion is a group of inerbreeding fish ha is characerized by is own birh rae, growh rae, age srucure, and deah rae. A fish sock is ofen referred o as ha porion or subse of a fish populaion ha is subjec o exploiaion or harves. Fish socks may respond differenly o exploiaion because of differences in reproducive, growh, and naural moraliy raes. Therefore, fish socks are considered discree unis for managemen purposes. The purpose of fish sock assessmen is o evaluae he saus of a fish sock and o predic how he sock will respond o various exploiaion or harves scenarios. The curren saus of a sock is characerized by esimaing sock parameers such as moraliy (naural and fishing), abundance, biomass, age srucure, and growh rae. The fuure saus of a sock is prediced by modeling he process of sock change over ime in response o managemen, using he previously esimaed sock parameers. Fisheries managemen is he process by which we aemp o conrol fish sock abundance by regulaing harves. Fisheries managemen decisions are made in an aemp o mee predeermined objecives concerning fuure sock saus based on biological, sociological, economic, and poliical inpus. The hisory of fish sock assessmen and fishery resource managemen began wih he erroneous assumpion ha he ocean s resources were unlimied. Thomas Huxley concluded in 1884 ha fish were so abundan and fecund, and man s abiliy o harves hem was so limied, ha fish populaions were immune o man s aciviies. Shorly hereafer, a he urn of he cenury, he Inernaional Council for he Exploraion of he Sea (ICES) iniiaed he collecion of commercial cach daa o respond o concerns of overfishing and depleed fish socks. World Wars I and II allowed worldwide fish socks o rebuild, bu overfishing in he las fify years has driven socks o record low levels. Fisheries Managemen The Magnuson Fishery Conservaion and Managemen Ac, enaced in 1976, empowered he federal governmen o regulae fishing from 3 o 2 miles off he coass of he Unied Saes. The Ac creaed eigh regional fishery managemen councils ha are charged wih he responsibiliy of developing fishery managemen plans (FMPs) for socks wihin heir region. Council members include represenaives from each sae who hen represen he regulaory, recreaional, commercial, and conservaion consiuencies. Each council has an execuive direcor and saff o assis in he preparaion of FMPs. I - 1
NMFS is mandaed by Congress o collec and analyze daa on he saus of he fishery resources off he coass of he Unied Saes and on he fisheries. NMFS hen provides his informaion o he managemen councils for heir use. Addiionally, he councils have commiees and panels ha provide furher echnical assisance o he council saff and members on scienific and sociological issues relaed o he FMPs. Rules for he developmen of FMPs are referred o as he 62 guidelines, and provide direcions for he definiion of overfishing, he esablishmen of measures o preven overfishing, and he developmen of a program for rebuilding a sock if overfishing already exiss. Public inpu and commen is sough hroughou he FMP developmen process. FMPs are modified hrough plan amendmens ha also allow for public inpu and commen. However, if condiions in he fishery are changing rapidly, framework acion noices are used o allow managemen o keep pace wih an evolving fishery. The original Magnuson Ac and he recenly re-auhorized Magnuson-Sevens Ac provide naional sandards for he managemen of fishery resources. The Ac has many sandards i aemps o achieve, including promoe conservaion and uilizaion of he fishery resources based on he bes scienific informaion available, seek o promoe opimum susainable yield while prevening overfishing, and proec he habias for fishery resources. The full ex can be found a www.nmfs.gov/sfa/magac. Afer he fishery managemen plan amendmen or noice acion has proceeded hrough he regulaory process, i is published in he federal regiser. Managemen measures become federal regulaions which are enforced by NMFS law enforcemen agencies, he U.S. Coas Guard, and ohers. Violaions are subjec o civil and criminal sancions. Civil sancions include wrien warnings, fines issued by Noices of Violaions and Assessmen (NOVA), forfeiure of seized propery including cach, vessels, and equipmen, and finally, permi sancions. In addiion o he regional managemen councils, here are hree regional inersae fishery managemen commissions esablished by federal law: he Alanic Saes Marine Fisheries Commission (ASMFC), he Gulf Sae Marine Fisheries Commission, and he Pacific Saes Marine Fisheries Commission. These commissions include hree represenaives from each sae in he region, again represening various consiuencies. Recenly, hese commissions were charged by Congress o promoe and encourage managemen of inerjurisdicional marine resources. The Alanic Coasal Fisheries Cooperaive Managemen Ac passed by Congress in 1993 charged he ASMFC wih he responsibiliy of developing FMPs for ransboundary, migraory coasal species. For example, in 1998, he ASMFC developed a FMP for American lobser, a resource harvesed from Maine o Virginia. The main managemen sraegies used o conrol harves raes include resricing effor and resricing harves. U.S. fisheries have radiionally been open-enry or open-access fisheries. Since he passage of he Magnuson Ac, here has been seady growh in he harvesing capaciy. Thus, as we ener he weny-firs cenury, here is excess capaciy or over-capializaion in our fisheries, resuling in overfishing of limied resources. To limi or resric overfishing, I - 2
managemen has responded in some fisheries by issuing seasonal or annual oal allowable cach (TAC) regulaions (i.e. resricing harves). These quoas resul in derby fisheries where individual fishermen aemp o cach as much as hey can, as quickly as hey can, unil he quoa is reached and he fishery closed. These derbies resul in emporary marke glus and lower prices paid for cach o fishermen. Oher mehods o conrol fishing moraliy include limiing effor by closing fishing areas during specific imes o proec spawning aggregaion of fish or nursery areas, allowing vessels only limied number of days a sea, resricing he vessel size, horsepower, or he amoun of gear fished. The mos conroversial effor-conrol measure, however, is limied enry. This is a fundamenal change in he radiional open-access fishery managemen policy in he U.S. Limied enry begins wih a moraorium on new licenses. A relaed issue is he ransferabiliy of licenses, i.e., can an individual sell his license, or can poenial new enrans o he fishery apply o a loery o ener he fishery, as exising paricipans leave he fishery. Anoher aspec of limied enry is he provision for propery righs hrough individual ransferable quoas (ITQ). Afer conrolling access o he fishery wih a moraorium on new licenses, fishermen are individually awarded a porion or allocaion of he TAC each year, and ha share is ransferable o oher fishermen via direc sale. Thus larger, more efficien harvesers are able o purchase he shares of he smaller, less efficien harvesers. This resuls in consolidaion of harvesing capaciy and increased economies of scale. Typically, limis are placed on he oal number of shares an individual or corporaion may acquire so as o avoid monopoly siuaions. Fish Sock Assessmen The mos recen Repor on he Saus of Fisheries of he Unied Saes published every year by he Naional Marine Fisheries Service (NMFS) indicaes ha 98 fish socks naionwide are considered overfished. Fisheries managers have he responsibiliy o properly manage hese fish socks for he long-erm benefi of boh he fish socks and he human populaion. Managemen decisions are made based on informaion derived hrough he various mehods of fish sock assessmen. Used properly, hese mehods will allow overfished socks o rebuild and will ensure harves pressure does no exceed susainable levels. A sock assessmen repor ypically includes he following secions: 1. Descripion of he fisheries ha inerac wih he sock and he presenaion of fisherydependen daa (landings, effor, ec.). 2. Resuls of research surveys ha provide fishery-independen daa on abundance and samples for biological analysis. 3. Life hisory characerisics of he resource including naural moraliy, growh, and mauriy. I - 3
4. Populaion and fishery parameers ha may include sock-recruimen relaionships, esimaion of exploiaion raes, yield per recrui and spawning sock/egg per recrui models, surplus producion models, and sock abundance indices. 5. Biological reference poins based on he previous models and analyses. 6. Review of managemen objecives and alernaive acions o achieve a susainable fishery. Fisheries and Fishery-Dependen Daa A wide array of gear ypes are used o harves fishery resources commercially and recreaionally. The principal gears are: hook and line, pos and raps, rawls and dredges, seines, and gillnes. Hooks and Line Gear Hook and line fishing mehods have evolved from he simple ac of aaching bai o a line, lowering ha line ino he sea, hen carefully rerieving bai wih a prey sill aached feeding. This mehod of fishing is referred o as bobbing and is praciced oday in Chesapeake Bay by recreaional fishermen using a chicken neck aached o a line for he purpose of harvesing blue crabs. The modern ben hook is believed o have evolved from a naural horn hook, and from sone and carved shell hooks. The simples form of hook and line fishing is he handline. I consiss of a line, sinker, leader, and a leas one hook. There are boh recreaional and commercial handline fisheries in he U.S. In he New England area, handlines are used o harves bluefin una from small vessels. In fac, alhough his is a echnologically sophisicaed fishery wih fish finding and navigaion elecronics, i is sill conduced by individual or pairs of fishermen in small boas (< 1 m), so i may be considered an arisinal fishery. Recreaionally, handlines are used in ice fishing. The mos basic pole and line fishery is a bamboo pole wih a shor line and hook aached. Recreaionally, hese are used o cach small fish in a wide variey of fisheries. The addiion of a reel o sore he line was a significan improvemen o pole and line gear, and is again used in recreaional and commercial fisheries. The reel, pole, and line gear is probably he mos widely used recreaional fishing gear; i is used in freshwaer and marine fisheries in a wide variey of forms from fly fishing o offshore rolling for large pelagic billfish. Wih he guiding philosophy ha if one hook is good, many hooks are beer, commercial fishermen developed boom longline gear (Figure 1). The principle elemen of his gear is he mainline or groundline ha can exend up o 5 km in lengh. Branching off he mainline a regular inervals are leaders or snoods, and hooks. Anchors hold each end of he mainline in place and surface buoys aached via floa lines o he anchors mark he locaion of he gear. The mainline was iniially consruced of naural fiber lines, which was replaced by a hard-lay, wised, arred nylon, and now monofilamen and wire cables are ypically used. Leaders were iniially ied o he mainline, and now hey ypically snap-on o he mainline allowing separae sorage of he hooks and leaders and he mainline. All boom-se, longline gear, is considered I - 4
fixed and passive because once deployed he gear does no move and he fish volunarily akes he hook. Figure 1. Boom longline gear (USDOI Circular 48). On he eas coas of he U.S., here is an acive pelagic longline fishery for large highly migraory pelagic species, in paricular, swordfish, una, and shark. A ypical vessel, 2 m in lengh, fishes a 1 km mainline and abou 5 hooks on a 12 hour soak. The gear is fixed wih respec o he waer, bu can drif over he seabed as much as 1 km in an overnigh-soak. The gear is passive, in ha fish are araced o he hook wih bai, ligh sicks, and someimes noise makers, and volunarily ake he gear. The ar of aracing fish or squid o a lure wih hooks moving up and down is called jigging. Jigging is conduced by hand, wih a reel, pole and line, or using jigging machines ha are programmed o move he lure in a paricular way. Finfish usually ake he hook wih heir mouh, bu are occasionally snagged. In conras, squid are almos always snagged by he hooks. Thus, jigs are classified as eiher acive or passive depending on he mehods of capure. Pos and Traps The essenial elemen of any po or rap fishing gear is a non-reurn device ha allows he animal o volunarily ener he gear, bu makes escape difficul, if no impossible. The erminology used o idenify pos and raps is also confusing, as boh erms have been applied o he small porable, 3-dimensional gear. In his manual, a po is defined as a small, porable, 3-dimensional device, whereas a rap is idenified as a large, permanen, 2-dimensional gear. The principle of operaion of po gear is ha animals ener he device seeking food, sheler, or boh. The non-reurn device, while allowing he animal o ener he gear, resrics escape. The holding area reains he cach unil he gear is rerieved. Bai is placed in a bag or cage wihin I - 5
he po. Culling rings or escape vens are added o he exerior wall of he po o allow for he release of undersize sub-legal animals. Finfish, shellfish, and crusaceans are all harvesed wih pos in he esuarine, coasal, and offshore waers of he U.S. The blue crab fisheries conduced in he inshore waers of he mid and souh Alanic regions use a wire mesh po (Figure 2). The design of he po incorporaes wo secions, an upsairs and downsairs. Crabs araced by bai ener he downsairs via one of wo o four enrance funnels. Once in he po, he escape reacion is o swim upward, so a pariion wih wo funnels separaes he wo secions. The upsairs secion serves o hold he cach for harves. Escape vens or cull rings may be insalled in he po o reduce juvenile bycach. Crab pos are usually fished as singles and are hauled by hand from small boas or wih a po hauler in larger vessels. Crab pos are generally fished afer an overnigh soak, excep early and lae in he season. Figure 2. Crab po (Sundsrom 1957). Traps are generally a large scale, 2-dimensional device ha uses he seabed and sea surface as boundaries for he verical dimension. The gear is fixed, ha is i is insalled a a locaion for a season, and is passive, as he animals volunarily ener he gear. Traps consis of a leader or fence ha inerrups he coas parallel o he migraory paern of he arge prey, a hear or parlor ha leads fish via a funnel ino he bay secion, and a bay or rap secion ha serves o hold he cach for harves by he fishermen. The non-reurn device is he funnel linking he hear and bay secions. The bay, if consruced of webbing, is harvesed by concenraing he cach in one corner, a process referred o as bagging or hardening he ne. The cach is removed by brailing wih a dip ne. The advanages of raps are ha he cach is alive when harvesed, resuling in high qualiy; ha he gear is very fuel efficien; and ha here is he poenial for very large caches. The disadvanages are ha he iniial cos of he gear is high, ha here is compeiion for space by oher users of he esuarine and coasal ecosysem, and finally ha he fish mus pass by he gear o be capured, so any aleraions in migraory roues will radically affec cach. On he mid-alanic coasal plain, large raps consruced of webbing hang from sakes ha are pounded ino he unconsolidaed seabed and are locally referred o as pound nes (Figure 3). I - 6
These raps are usually se a poins or capes ha fish end o migrae around. The leader secions are 1 o 6 m in lengh, saring in shallow waer (< 2 m), and ending in waer dephs of 1 o 15 m. The hear secions lead o single or double funnels ha lead ino he bay secion. The gear capures boh pelagic and demersal species. Dragged Gear Figure 3. Pound ne (Sundsrom 1957). Fishing gear ha is dragged or owed over he seabed or hrough he waer is referred o as mobile gear. The dragged gears include a bag consruced of webbing or rings and chain links ha collec he cach. These are exclusively acive fishing gears, in ha he animals do no volunarily ener he gear, bu are eiher swep up from he seabed or filered from he waer by he gear. Towed gear evolved from he need of man o harves more efficienly, and ha required collecing from more waer or he boom. Towed gear was iniially deployed from hand-powered boas, hen sailing vessels, and finally from large ships wih engines greaer han 1 horsepower. Mechanizaion of hese fisheries wih engines and winches enabled larger gear o be owed faser and handled wih less labor. The earlies dragged gear was probably some form of small rake used o collec shellfish owed by a hand-paddled canoe. As we ener he weny-firs cenury, he larges gear is a pelagic fish rawl wih a mouh opening in excess of 1 x 1 m, owed by a vessel larger han 1 m in lengh wih an engine of 2 horsepower or more. Dredges are rake-like devices, equipped wih bags o collec he cach. They are ypically used o harves molluscan shellfish from he seabed, bu occasionally are used o arge crusacean, finfish, and echinoderm species. Dredges are designed o harves boh epifauna and infauna; however, he specific design deails of he gear are very differen. In esuarine waer, dredges are used o harves oysers. The oyser is a sessile organism, generally growing in reef-like habias. The oyser dredge consiss of a seel frame.5 o 2. m I - 7
in widh, wih an eye and nose or ongue, and a blade wih eeh (Figure 4). Aached o he frame is he ow chain or wire, and a bag o collec he cach. The bag is consruced of rings and chain-links on he boom o reduce he abrasive effecs of he seabed, and wine or webbing on op. The dredge is owed slowly (< 1 m/sec) in circles, from vessels 7 o 3 m in lengh. Compared o shaf ongs or paen ongs, he oyser dredge is very efficien. In many regions, oyser dredging is allowed only on privae or leased oyser beds, and prohibied on public beds. However, in he Maryland porion of Chesapeake Bay, dredging is permied on public beds, bu only under sail, so as o mainain inefficiency, hus allowing for a radiional fishery. Figure 4. Oyser dredge (Sundsrom 1957). Blue crabs are harvesed during he winer monhs wih large dredges similar o oyser dredges. The blue crab, suscepible o pos during he acive summer monhs, are dorman in he winer monhs, and burrow ino sof esuarine booms. Sern-rig dredge boas ( 15 m in lengh) ow wo dredges in andem from a single chain warp. The dredges are equipped wih long eeh (1 cm) ha rake he crabs ou of he boom. This same gear is used o harves whelk in he summer and mussels in he fall from Chesapeake Bay. Again, as fishermen sough o increase efficiency and ow vessels became larger, dredges evolved ino beam rawls so as o capure finfish. The seel frame became larger and ligher, and he bag became larger and funnel shaped, so as o concenrae he cach in a cylindrical-shaped, webbing secion, referred o as he codend. The firs beam rawls were owed by sailing vessels, bu oday large beam rawls wih mouh openings of 15 o 2 m, are owed from boh sides of modern, high horsepower rawlers. Oer rawls developed as fishermen sough o furher increase he horizonal opening of he rawl mouh, bu wihou he cumbersome rigid beam (Figure 5). In he lae 188s, Musgrave invened he oer board, a waer-plane device ha when used in pairs, each owed from a separae wire, served o open he ne mouh horizonally and hold he ne on he boom. Iniially, all oer boards were conneced o he wing ends of he rawl, as hey are oday in he shrimp rawl fishery. In he 193s, he Dan Leno gear developed by Frenchmen, Vigarnon and Dahl, allowed he oer boards (doors) o be separaed from he rawl wing ends using cables or ground gear. I - 8
This echnology increased he effecive area swep by rawls from he disance beween he ne wings o he disance beween he doors. The ground gear can be as long as 2 m, hus increasing he area swep by he rawl by as much as hree fold. Figure 5. Oer rawl (Sundsrom 1957). Boom rawl fisheries are prosecued for demersal species on all coass of he U.S. In he norheas, vessels from 15 o 5 m fish in waers ranging from 1 o 4 m in deph. Small mesh nes are used o capure norhern shrimp, whiing, buerfish, and squid. Large mesh rawls are used o harves cod, haddock, flounder, and oher large species. These rawls are ypically rigged wih long ground wires ha creae sand clouds on he seabed, herding he fish ino he rawl mouh. In he souheas and Gulf coas areas, small mesh rawls are used o harves shrimp. Pelagic fishes are harvesed using off-boom or midwaer rawl nes. The nes mus be aimed or direced a specific concenraions of fish. Therefore, he fishermen mus be able o idenify he locaion of fish boh laerally and verically, and o direc he pelagic rawl o ha posiion. Seines Fishing gear ha is used o encircle marine resources eiher on he seabed or in he waer column are classified as surround gear. Because he area enclosed by he gear is limied, he gear is direced or aimed a idenified concenraions of fish. Surround gear are ofen referred o as seine nes. The simples form of seine is a single wall of webbing wihou a bag, conneced a each end o poles ha are handled by fishermen. The ne is pulled hrough he shallow waer collecing finfish, crusaceans, mollusks, ec., and finally dragged up ono a beach where he cach is sored. The webbing is of variable mesh size, bu is usually very small, (abou.5 cm), as he gear is ypically used o harves bai fish for recreaional hook and line fisheries. Typically a recreaional or subsisence beach seine is abou 2 m in lengh and 1. o 1.5 m in heigh wih a I - 9
1. cm mesh size. Commercial beach seines range in lengh from 2 o 4 m and are equipped wih a bag in he cener or side. The long-haul seine is se and hauled in shallow waer esuaries from a boa (abou 15 m). The ne is a single wall of small mesh webbing (< 5 cm) and is usually greaer han 4 m in lengh and abou 3 m in deph. The end of he ne is aached o a pole driven ino he boom and he ne is se in a circle so as o surround fish feeding on he idal fla. Afer closing he circle, he ne is hauled ino he boa, reducing he size of he circle, and concenraing he fish. Finally, he live fish are brailed or dip-need ou of he ne. Seine nes are also used on pelagic fishes. However, he ne mus be designed o close a he boom. The nes are floaing, ha is he buoyancy on he floa line exceeds he weigh of he webbing and leadline. The gear fishes from he air-sea inerface o he deph of he webbing. The gear is se in a circle around an idenified school of pelagic fishes hen closed off on he boom, so as o preven he escape of he fish. The purse seine is closed using a coninuous purse line (Figure 6). Funcionally, purse seines are used o surround a concenraion of fish, hen he purse seine is hauled in so as o close he boom of he ne. Figure 6. Purse seine (Sundsrom 1957). The pureic power block developed in he early 195s, was a significan mechanizaion of he purse seine fishery. The V-shaped sheave, aached o a beam end and powered by a hydraulic moor, has replaced 1 o 2 men ha used o haul in he long wings of he small seines (3 m) used o harves menhaden in Chesapeake Bay. The larges purse seines now used on una, fish in he open ocean and are more han 2 m in lengh and 2 m in deph. Wihou he power block, hese fisheries would no have developed. I - 1
Gillnes Gillnes include a group of fishing gear ypes where animals are capured by a wall of webbing in he waer column or on he boom. The animals are capured by wedging, gilling, or angling. Gillnes operae principally by wedging and gilling fish, and secondarily by enangling. The nes are a single wall of webbing wih floa and lead lines. The nes are designed and rigged o operae as eiher sink or floaing nes, and are anchored or drifing. The webbing is usually monofilamen nylon due o is ransparency; bu mulifilamen, synheic or naural fibers are also used. Anchored sink gillnes are used o harves demersal fish along all coass of he U.S. The nes are rigged so ha he weigh of he leadline exceeds he buoyancy of he floaline, hus he ne ends he seabed and fishes ino he near boom waer column (Figure 7). Anchors are used a eiher ends of he ne o hold he gear in a fixed locaion. The nes vary in lengh from 1 o 2 m and in deph from 2 o 1 m. Muliple nes are aached ogeher o form a sring of nes, up o 2 m in lengh. In shallow waer, sink gillnes may fish from boom o surface, if he webbing is of sufficien deph. Figure 7. Sink gillne (Sundsrom 1957). Gillnes are also designed so as o floa from he sea surface and exend downward ino he waer column and are used o cach pelagic fish. In his case, he buoyancy of he floaline exceeds he weigh of he leadline. Floaing gillnes are anchored a one end or se-ou o drif usually wih he fishing vessel aached a one end. Anchored floaing gillnes are used in shad fisheries on he eas coas. Offshore, large mesh drif nes are se for swordfish and oher large pelagic fishes. I - 11
Fishery-Dependen Daa and Analyses The Naional Marine Fisheries Service (NMFS) and sae agencies collec cach and effor daa on he recreaional and commercial fisheries, so as o monior he saus of he fishery resource socks and o esimae fishing moraliy. From hese daa and analyses, and in conjuncion wih fishery-independen daa sources (scienific surveys) and analyses, fishery scieniss are able o predic he oucomes of various managemen alernaives. In he commercial fisheries, landings daa is colleced from fishermen s logbooks and rip ickes, dockside inerviews by por agens, monhly summaries from dealers, or oher means. However, landings daa may no be enirely represenaive of he acual cach, due o a-sea discards. Daa on discards is colleced by a-sea observers who sample he enire cach, hen noe discards and landings. Sea-sampling is usually only conduced on a subse of he fishing flee due o he high cos of saffing hese programs, bu he observed discard raes are exrapolaed o he enire flee, so as o develop complee esimaes of age/size-specific cach. Discards are proraed ino he landings based on heir age/size and gear-specific survival probabiliy. Effor in commercial fisheries is ofen based on license daa according o gear ype, vessel onnage, days a sea or fishing, or he amoun of gear se and soak ime. Wihin a specific fishery, here is a sandardized uni of effor, for example, one day fishing by boom rawl for a 5 o 99 on vessel. Oher classes of rawl vessels, boh smaller and larger, are hen compared o he sandard vessel in erms of cachabiliy and raed accordingly. An example of fishery-dependen daa can be seen in Figure 8. The Poomac River blue crab harves ime series of boh cach and effor was obained from hisorical commercial harves and license daa from he Poomac River Fisheries Commission. Figure 8. Poomac River blue crab harves and licenses issued. Recreaional fisheries landing saisics are colleced by por-based samplers who conduc inercep inerviews wih fishermen reurning from a day of fishing a sea. These daa are supplemened wih he Marine Recreaional Fishery Saisics Survey (MRFSS). The MRFSS is I - 12
a series of surveys iniiaed by NMFS saring in 1979 o obain sandardized and comparable esimaes of paricipaion, effor, and cach by recreaional anglers in he marine waers of he Unied Saes. The MRFSS collecs recreaional fisheries daa using boh dockside inercep and elephone surveys. The inercep survey collecs daa on he number, weighs, and lenghs of fish caugh by species, sae and couny of residence, and avidiy level (e.g. rips per year, mode of fishing, and primary area of fishing). The elephone survey collecs daa on he presence of marine recreaional anglers in he household, number of anglers per household, number of fishing rips in a 2-monh period, he mode of each rip, and he locaions (couny) of each rip. The esimaed number of marine recreaional fishing rips in Rhode Island from he MRFSS Survey can be seen in a ime series of recreaional effor (Figure 9). Millions of Trips 1.8 1.6 1.4 1.2 1..8.6.4.2. 1975 198 1985 199 1995 2 Year Figure 9. Esimaed number of marine recreaional fishing rips in Rhode Island from MRFSS Survey. Research Surveys NMFS and sae agencies also collec and analyze daa on fishery resources independen of he recreaional and commercial harvesing secors. NMFS uilizes a flee of research vessels operaed by he Naional Oceanographic and Amospheric Adminisraion (NOAA) o collec his daa. Surveys conduced by NMFS range from marine mammal populaion couns o plankon surveys. The rawl surveys for fish provide an independen index of relaive abundance of species aken by he sampling gear ha can be compared o fishery cach per uni effor, also an index of relaive abundance. When he wo indices ogeher rack rends of increasing or decreasing abundance, here is greaer confidence in he conclusions drawn from hese analyses. The fishery-independen surveys also provide biological samples for he sudy of age and growh, moraliy, fecundiy, and oher life hisory characerisics, in addiion o allowing for he collecion of oceanographic daa ha is used o develop ecological models relaing fish abundance and disribuion o environmenal condiions. I - 13
Fishery-independen surveys follow a rigorous mehodology ha is designed o resul in saisically valid samples, aken in a consisen and reproducible manner. The proocol for boom rawl surveys usually follows a random sraified design. The coninenal shelf waer is divided ino similar sraa by laiude and deph zone, so as o reduce sample variabiliy wihin sraa and herefore increase he precision of abundance esimaes. Wihin sraa, saion locaions are seleced randomly, so as o remove possible biases and o mee saisical design requiremens. Survey daa is used o develop a fishery-independen index of relaive abundance (CPUE), so emporal consisency in sampling is exremely imporan. Considerable effor is expended o ensure ha each ow of he rawl is exacly he same as every oher ow wihin each survey, and beween pas and fuure surveys. Small changes in sampling mehod or gear may resul in subsanial changes in cachabiliy of ha gear, so any changes are avoided or invesigaed horoughly via paired comparison mehods prior o implemenaion. I - 14