Workshop to Design an Experiment

to Determine the Effects of Longline

Gear Modification on Sea Turtle

Bycatch Rates

(Workshop para a elaboração de

uma experiência que possa diminuir

as capturas acidentais de tartarugas

marinhas nos Açores)

2-4 September 1998

Horta, Azores, Portugal

Edited by:

Alan B. Bolten

Helen R. Martins

Karen A. Bjorndal

U.S. Department of Commerce

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

NOAA Technical Memorandum NMFS-OPR-19

December 2000
Copies of this report may be obtained from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161 USA

(703) 487-4650

(800) 336-4700 (rush orders)

This technical memorandum series is used for documentation and timely

communication of preliminary results, interim reports, or similar specialpurpose information. Although the memoranda are not subject to complete

formal review, editorial control, or detailed editing, they are expected to

reflect sound professional work. The views and conclusions expressed by the

authors are not necessarily those of the National Marine Fisheries Service. In

addition, the mention of trade names or commercial firms is for information

only and does not imply endorsement by the National Marine Fisheries

Service.

This report was prepared in fulfillment of reference order 40AANF804175

issued to the Archie Carr Center for Sea Turtle Research.

Suggested Citation:

Bolten, A. B., H. R. Martins, and K. A. Bjorndal, editors. 2000. Workshop to

design an experiment to determine the effects of longline gear modification on

sea turtle bycatch rates. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-OPR19, 50 p.
Workshop to Design an Experiment to

Determine the Effects of Longline Gear

Modification on Sea Turtle Bycatch Rates

(Workshop para a elaboração de uma

experiência que possa diminuir as capturas

acidentais de tartarugas marinhas nos Açores)

2-4 September 1998

Horta, Azores, Portugal

Edited by

Alan B. Bolten

Archie Carr Center for Sea Turtle Research

and Department of Zoology

P.O. Box 118525

University of Florida

Gainesville, FL 32611 USA

Helen R. Martins

Departamento de Oceanografia e Pescas

Universidade dos Açores

PT-9900 Horta Portugal

Karen A. Bjorndal

Archie Carr Center for Sea Turtle Research

and Department of Zoology

P.O. Box 118525

University of Florida

Gainesville, FL 32611 USA

NOAA Technical Memorandum

NMFS-OPR-19

December 2000

U.S. Department of Commerce

Norman Y. Mineta, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service

Penelope D. Dalton, Assistant Administrator for Fisheries

Table of Contents 

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .v 

Workshop Agenda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vi 

Workshop Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .x 

Opening Remarks (Abertura) 

Helen R. Martins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 

The Swordfish Fishery in the Azores: an Overview 

Alexandre Aires da Silva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 

Information on Accidental Capture of Marine Turtles in the Azores 

(Informação disponível sobre a pesca acidental de tartarugas nos Açores) 

Manuel F. Serpa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 

Turtle Bycatch Study in the Longline Fisheries of the Azores 

R. Prieto, R. Ferreira, and A. Silva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 

Observation Program for Fisheries in the Azores (POPA): 

Aspects Related to Marine Turtles 

(Programa de Observação para as Pescas dos Açores (POPA): 

Aspectos relacionados com Tartarugas Marinhas) 

Rogério Feio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 

Approach to the Experimental Design and Review of the Experimental 

Variables with the Objective of Stimulating Discussion 

(Aproximação ao desenho experimental e revisão das variáveis experimentais, 

com o objectivo de estimular a discussão) 

Eduardo Isidro and Mário Pinho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 

Experiment to Evaluate Gear Modification on Rates of Sea Turtle Bycatch in the 

Swordfish Longline Fishery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 

Statistical Power of the Azores Longline Experiment 

Jerry A. Wetherall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44 

Closing Remarks (Comentários de encerramento) 

Helen R. Martins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 

Acknowledgments 

 This workshop was funded by the U.S. National Marine Fisheries Service. Additional 

support was provided by the University of the Azores, Department of Oceanography and 

Fisheries; the Azores Ministry of Agriculture and Fisheries; and the Archie Carr Center for Sea 

Turtle Research, University of Florida. We are grateful for the support of Barbara Schroeder and 

Earl Possardt of the U.S. National Marine Fisheries Service. 

v 
Workshop to Design an Experiment to Determine the Effects of Longline 

Gear Modification on Sea Turtle Bycatch Rates 

Agenda 

1 September 1998: All out of town participants arrive in Horta 

2 September 1998: Workshop Day 1 (Location: Camara do Comercio) 

9:30 – 10:00 Opening. Helen Martins (Workshop Moderator) 

 Introduction of Participants 

 Welcome. Helder da Silva

 Workshop Schedule. Alan Bolten

10:00 – 10:50 Background Presentations (Background presentations will be limited to 

15 minutes with an additional 10 minutes for discussion) 

 Objectives of the Workshop. Mário Pinho and Eduardo Isidro 

 Review of swordfish longline fishery in the Azores 

 (techniques, equipment, bait, etc.). Alexandre Silva

10:50 – 11:15 Coffee Break 

11:15 – 12:30 Background Presentations, continued 

 Review of available information on turtle bycatch in longline 

fisheries in the Azores. Manuel Serpa

 Review of longline observer program in the Azores. Rui Prieto 

presented by Alexandre Silva 

 Review of POPA (Observer program for fisheries in the Azores) with 

respect to sea turtle observations. Rogério Feio 

12:30 – 14:00 Lunch (We will eat as a group at O Barao) 

14:00 – 14:30 Review of life history of sea turtles in the waters around the Azores. 

Alan Bolten 

14:30 – 15:30 Presentation of an experimental design to stimulate discussion 

Eduardo Isidro and Mário Rui Pinho

15:30 – 16:00 Coffee Break 

16:00 – 17:30 Experimental Design and Analysis 

 Discussion of experimental variable, design and analysis 

17:30 Adjourn Day 1 

3 September 1998: Workshop Day 2 

vi 
9:30 – 11:00 Review of Day 1. Alan Bolten

 Schedule of Day 2 

 Development of experimental design and analysis. 

11:00 – 11:30 Coffee Break 

11:30 – 12:30 Development of experimental design and analysis, continued 

12:30 – 14:00 Lunch (We will eat as a group at O Barao) 

14:00 – 15:30 Development of experimental design and analysis, continued 

15:30 – 16:00 Coffee Break 

16:00 – 17:30 Finalize experimental design and analysis 

 Begin discussion on the logistics for conducting the experiment 

(time of year, location, boats, etc) and development of budget 

17:30 Adjourn Day 2 

4 September 1998: Workshop Day 3 

9:30 – 11:00 Review of Day 2. Alan Bolten

 Schedule of Day 3 

 Discuss and finalize logistics for conducting the experiment. 

11:00 – 11:30 Coffee Break 

11:30 – 12:30 Develop budget for conducting the experiment. 

12:30 – 14:00 Lunch (We will eat as a group at O Barao) 

14:00 – 15:30 Finalize budget for conducting the experiment. 

15:30 – 16:00 Coffee Break 

16:00 – 17:30 Workshop Review and Conclusions. 

 Distribute assignments for Workshop Report 

 Adjourn Workshop 

vii 
Workshop para a elaboração de uma experiência que possa diminuir as 

capturas acidentais de tartarugas marinhas nos Açores 

Agenda 

1 de Setembro 1998: Chegada dos convidados à cidade de Horta (Alojamento: Horta Hotel) 

2 de Setembro 1998: Workshop Dia 1 (Localização: Câmara do Comércio, Travessa 

da Misericórdia) 

9:30 - 10:00 Abertura. Helen Martins (Moderadora do Workshop) 

 Apresentação dos Participantes 

 Boas vindas. Helder da Silva 

 Agenda do Workshop. Alan Bolten 

10:00 - 10:50 Apresentações genéricas (As apresentações terão um limite máximo de 

15 minutos, com 10 minutos adicionais para a discussão) 

 Objectivos do Workshop. Mário Pinho e Eduardo Isidro

 Síntese da pesca do Espadarte com palangre, nos Açores (técnicas, 

 equipamento, isco, etc.). Alexandre Silva 

10:50 - 11:15 Intervalo para Café 

11:15 - 12:30 Apresentações genéricas, continuação 

Revisão da informação disponível sobre o capturas acidentais de 

tartarugas em pesca de palangre, nos Açores. 

Manuel Fernando Serpa

 Análise do programa de observação da pesca de palangre nos 

Açores. Rui Prieto, apresentado por Alexandre Silva

Análise do POPA (Programa de Observadores para as Pescas dos 

Açores) no que diz respeito a observações de tartarugas marinhas. 

Rogério Feio 

12:30 - 14:00 Almoço (A refeição será em grupo, no restaurante O Barão) 

14:00 - 14:30 Estudo da vida das tartarugas marinhas nas águas dos Açores. 

Alan Bolten 

14:30 – 15:30 Apresentação de um desenho experimental, a fim de estimular a 

discussão. Eduardo Isidro e Mário Pinho 

15:30 - 16:00 Intervalo para Café 

16:00 - 17:30 Desenho Experimental e Análise 

 Discussão das variáveis experimentais, desenho experimental e analise. 

viii 
17:30 Encerramento do Dia 1 

3 de Setembro 1998: Workshop Dia 2

9:30 - 11:00 Síntese do Dia 1. Alan Bolten

 Agenda para o Dia 2 

 Desenvolvimento do desenho experimental e análise 

11:00 - 11:30 Intervalo para Café 

11:30 - 12:30 Desenvolvimento do desenho experimental e análise (continuação) 

12:30 - 14:00 Almoço (A refeição será em grupo no restaurante O Barão) 

14:00 - 15:30 Desenvolvimento do desenho experimental e análise, (continuação) 

15:30 - 16:00 Intervalo para Café 

16:00 - 17:30 Finalização do tema: Desenho Experimental e Análise 

 Começo da discussão sobre logística no decorrer da experiência (altura 

do ano, localização, embarcações, etc.) e estipulação de um orçamento 

17:30 Encerramento do Dia 2 

4 de Setembro 1988: Workshop Dia 3 

9:30 - 11:00 Síntese do Dia 2. Alan Bolten

 Agenda para o Dia 3 

 Discussão e conclusão sobre a logística para o decorrer da experiência 

11:00 - 11:30 Intervalo para Café 

11:30 - 12:30 Elaboração do orçamento para a concretização do projecto. 

12:30 - 14:00 Almoço (A refeição será em grupo no restaurante O Barão) 

14:00 - 15:30 Finalização da estipulação do orçamento para a concretização do projecto 

15:30 - 16:00 Intervalo para Café 

16:00 - 17:30 Síntese do Workshop e Conclusões 

 Distribuição de tarefas para o Relatório do Workshop 

 Encerramento do Workshop

ix 
Workshop Participants 

A. Director of Fisheries of the Regional Government of the Azores 

Helder da Silva 

B. University of the Azores, Department of Oceanography and Fisheries, Horta 

Alexandre Silva 

Eduardo Isidro 

Helen Martins 

João Tátá Regala 

Jorge Fontes 

Manuel Fernando Serpa 

Mário Pinho 

Rogério Ferreira 

Rogério Feio 

Verónica Neves 

C. Directorate of the Nature Conservation Service of the Azores

Manuel Veríssimo 

D. Commercial fishermen 

Genuíno Madruga, Horta 

Jorge Gonçalves, Horta 

José Sebastião Nunes, Corvo 

José Maria Ferreira Faria, Flores 

E. Participants from the United States 

Alan Bolten (Archie Carr Center for Sea Turtle Research, University of Florida) 

Jerry Wetherall (US National Marine Fisheries Service, Hawaii) 

x 
Opening Remarks 

Helen R. Martins 

Departamento de Oceanografia e Pescas 

Universidade dos Açores 

PT-9900 Horta, Portugal 

E-mail: hmartins@dop.uac.pt 

Ladies and gentlemen, 

I am very happy to have the honour to open this workshop and to be your moderator 

during these 3 days. I do think that we have managed to bring together the best people possible 

to reach our objective. 

First of all it is important that we get to know each other well in order to have a fruitful 

discussion. I would ask each of you to present yourselves by your name, place of work, and other 

information of interest. My name is Helen Martins or Helena Martins in Portuguese version. I am 

a researcher at the Department of Fisheries and Oceanography (DOP) of the University of the 

Azores, where I have worked for the last 22 years. (Other participants who introduced 

themselves in turn were: Helder Marques da Silva, Alexandre Silva, Eduardo Isidro, João Tátá 

Regala, Manuel Fernandes Serpa, Mario Pinho, Rogério Ferreira, Rogério Feio, Veronica Neves, 

Manuel Verissimo, Genuino Madruga , Jorge Gonçalves, José Sebastião Nunes, Jose Maria 

Ferreira Faria, Alan Bolten, and Jerry Wetherall). 

The topic of this workshop is the problem of marine turtles. These turtles constitute a 

group of ancient reptiles that already lived in the oceans more than 100 million years ago and 

existed in the time of the dinosaurs. They represent a distinct part of the bio-diversity of our 

planet. In the 18th and 19th centuries turtles were very abundant, and populations existed with 

more than a million individuals. However, during the last hundreds of years humans have 

destroyed the ability of turtles to maintain their numbers which have decreased drastically 

through intentional and accidental capture by fishermen, destruction of feeding areas and resting 

places, destruction of nesting beaches, and, more recently, pollution of the oceans. 

Today almost all populations show decline, some at a drastic pace and some are already 

extinct. Worldwide, there is a growing concern with accidental capture of sea turtles in 

commercial fisheries. Today all the turtle species in the Azores (5 species) are included in the 

Red List of IUCN as endangered and all marine turtles are included in CITES and in CMS. It is 

evident that a program to protect these animals from extinction has to be carried out on a global 

scale and through governments, scientists, fishermen and the general public. I do think that here 

in the Azores we have the opportunity to achieve such a collaboration. The result of this 

workshop may have importance also for other regions of the world's oceans. 

Thank you! 

1 
Abertura 

Minhas Senhoras e Meus Senhores 

Estou muito contente por ter a honra de abrir este Workshop e para ser a sua moderadora 

durante estes 3 dias. Penso que conseguimos reunir as melhores cabeças possíveis para chegar ao 

nosso objectivo. 

Antes de mais é importante que nos conheçamos bem para ter uma discussão frutífera. 

Peço a cada um que diga o seu o nome e o seu local de trabalho e outras observações de 

interesse. Eu chamo-me Helen Martins ou Helena Martins na versão Portuguesa. Sou 

investigadora de Departamento de Oceanografia e Pescas, onde trabalhei deste o princípio, ou 

seja desde hà 22 anos. (Outros participantes: Helder Marques da Silva, Alexandre Silva, Eduardo 

Isidro, João Tátá Regala, Manuel Fernandes Serpa, Mario Pinho, Rogério Ferreira, Rogério Feio, 

Veronica Neves, Manuel Verissimo, Genuino Madruga , Jorge Gonçalves, José Sebastião Nunes, 

Jose Maria Ferreira Faria, Alan Bolten, Jerry Wetherall.) 

O nosso assunto neste Workshop é o problema das tartarugas marinhas. Estas tartarugas 

são um grupo de repteis muito antigos. Já existiam nos mares há 100 milhões de anos, viviam no 

tempo dos dinossáurios, e representam uma parte distinta da biodiversidade do mundo. Nos 

séculos XVIII e XIX as tartarugas eram muito abundante e tiveram populações que contavam um 

milhão ou ainda mais. Mas nas últimas centenas de anos o Homem destruiu a habilidade das 

tartarugas de manter os seus números, que baixaram drasticamente através de capturas 

intencionais e capturas acidentais da pesca, destruição de áreas de alimentação, destruição dos 

locais de desova e descanso e, mais recentemente, a poluição dos oceanos. 

Hoje em dia quase todas as populações estão em declínio, algumas a um ritmo drástico e 

outras já estão extintas. Cada vez mais há uma crescente preocupação para as capturas acidentais. 

Hoje em dia todas as tartarugas dos Açores (5 espécies) estão incluídas na lista vermelha 

da União Internacional de Conservação da Natureza como em perigo ou vulneráveis e todas as 

tartarugas marinhas estão incluídas na Convenção de Comercio Internacional de Espécies em 

Perigo de Fauna e Flora Selvagem (CITES) e na Convenção de Conservação de Espécies 

Migratórios de Animais Selvagens (CMS). É evidente que uma força para proteger estes animais 

da extinção tem que ser exercida a uma escala global e através da colaboração entre governos, 

cientistas, pescadores e o publico em geral. Eu penso que aqui nos Açores temos a oportunidade 

de conseguir uma colaboração deste género. Os resultados deste workshop podem ter 

importância também para outras regiões dos oceanos. 

Obrigada! 

2 
The Swordfish Fishery in the Azores: an Overview 

Alexandre Aires da Silva 

Departamento de Oceanografia e Pescas 

Universidade dos Açores 

PT-9900 Horta, Portugal 

E-mail: alexsilva@dop.uac.pt 

This paper aims to provide a background about the swordfish fishery in the Azores within the 

scope of the I Workshop on Sea Turtle Bycatch, Horta, 2-4 September 1998. 

Historical Background of the Fishery 

The swordfish (Xiphias gladius) fishery in the Azores has already been described 

(Pereira, 1988; Simões and Silva, 1994; Simões, 1995). The fishery started in 1987 following the 

strong incentives for swordfish exploitation given by the VII Azorean Fisheries Week as well as 

the good experimental fishing results obtained during 1985-1986 (Fernandes 1987, Pousa, 1987). 

Prior to 1987, the capture of swordfish in the Azores was considered a bycatch of the demersal 

fishery with landings not exceeding 30 tons per year. 

Fleet Identification 

The longline fleet targeting swordfish in the Azores can be first divided into two main 

components according to place of registration: Azores and Mainland Portugal fleets. The 

Azorean fleet can be further classified into three main components according to physical 

characteristics of the vessels and fishing regime: the open-deck wooden boats (ODWB), smallsize cabin-deck boats (CDB1) and large size cabin-deck boats (CDB2). The average physical 

characteristics for each of the fleet components are given in Table 1. 

Table 1. Average physical characteristics for each component of the swordfish fleet 

operating in the Azores. ODWB: open-deck wooden boats; CDB1: small-size cabin-deck 

boats; CDB2: large-size cabin-deck boats; MPB - Mainland Portugal boats. 

Fleet Fleet component Overall length (m) Engine power (HP) Gross tonnage (GRT)

ODWB 10 37 5

Azores CDB1 14 173 27

CDB2 28 581 157

Mainland Portugal MPB 26 516 122

The open-deck wooden boats (ODWB; Figure 1.A) consist of small-size fishing boats 

mainly operating within 3 miles off the coasts of S. Miguel Island (Simões, 1995). This artisanal 

fleet fishes for swordfish during the summer season and shifts to the demersal fish community in 

winter months. Longline sets with an average number of 800 hooks-per-set are carried out on a 

3 
daily trip basis. The open-deck wooden boats entered into the fishery in 1991, and have 

increased in numbers from that year (Figure 2.A). Seventeen fishing permits were given to this 

fleet component in 1998. 

Like the ODWB fleet component, the small-size cabin-deck boats (CDB1; Figure 1.B) 

target swordfish during the summer season and shift to the demersal fish community in winter 

months. This type of boat lacks freezing capacity, staying for about one week at sea. One 

longline set is carried out per day using an average number of 1500 hooks. The fishing effort is 

mostly localized around the coastal areas and the fishing banks of the Central Island Group. This 

fleet component exhibited a strong increase in numbers during the early 1990s, peaking at 40 

permits in 1993 (Figure 2.A). After that period, the number of permits given to component CDB1 

has declined continuously to 26 in 1998. 

Large-size cabin-deck boats fishing for swordfish throughout the year represent the third 

Azorean fleet component (CDB2; Figure 1.C). This component conducts fishing campaigns that 

can take about a month at sea due to the large freezing capacity of the vessels. One longline set 

with an average number of 2500 hooks is carried out on a daily basis. During the winter months 

the large-size cabin-deck boats extend their fishing areas outside the Azorean EEZ. Number of 

fishing permits for the component CDB2 reached a maximum of 20 permits in 1994, then 

declined to 9 permits in 1998 (Figure 2.A). 

The Mainland Portugal fleet fishing for swordfish in the Azores is similar to the Azorean 

CDB2 component in physical characteristics of vessels and fishing regime (cf. Table 1; Figure 

1.C). This fleet mostly lands in the Portuguese and Spanish Mainland, in the harbors of Aveiro 

and Vigo, respectively. Unlike the Azorean fleet, the number of fishing permits given to the 

Mainland fleet exhibited a strong increasing trend during the 1990s (Figure 2.B). A total of 15 

permits was given to this fleet in 1998. 

Fishing Gear and Methods 

The longline gear consists of a mainline to which branchlines with hooks are sequentially 

attached at a fixed distance (Figure 3). The mainline is suspended in the water column with a 

system of buoys attached by floatlines. The gear configuration can slightly change according to 

the maximum desired fishing depth (i.e., changing the length of the floatlines). 

Two different types of longline gear are used in the swordfish fishery in the Azores: the 

Spanish and the US longline. Although both gears mostly use hook number 17/0, they differ in 

the type of the mainline, arrangement of gear components, and crew number (Fernandes, 1987). 

The type of mainline used in the Spanish longline is twisted polyethylene. In the US gear, 

the mainline is 3.50 monofilament nylon. All of the gear components of the Spanish longline 

(i.e., the mainline, branchlines and buoys) are assembled on land. The US longline components 

are stored separately onboard, with the gear being continuously prepared during the set. Lastly, 

the operation of the two types of gear involves a different crew number. The fishing crew for 

Spanish longline requires 15 men; this number is reduced to 7 men for US longline operation. 

4 
Although the Azorean fleet has adopted both the Spanish and US gears, the acceptance of 

the former has been gradually increasing in the region. The Mainland Portugal fleet mainly 

operates with the US longline gear. 

The swordfish fishing is carried out during night hours due to the negative phototropism 

exhibited by the species. For this purpose, the longline set finishes at dusk and the hauling 

operation starts at dawn. While the main type of bait used by the Azorean longline fleet is 

Spanish mackerel (Scomber japonicus), the Mainland Portugal fleet uses squid as well. The use 

of light-sticks in the swordfish fishery in the Azores is not a common practice. 

Fishing Areas 

Most of the fishing effort carried out by the Azorean and Mainland Portugal swordfish 

fleets is carried out in the waters around the Azores. A total of 5774 longline sets was reported in 

fishing logbooks during the period 1993-1998 (see Figure 4 for distribution map). A proportion 

of 87.2% (n=5037) of these fishing operations are confined to the area 36-48o N, 18o-42o W 

(ICES X), which contains most of the Azorean EEZ. Although the incidence is low, the 

distribution of the Portuguese longline fleet in the North Atlantic extends to the waters off the 

Iberian Peninsula and the African coast. 

Identification of Bycatch 

Bycatch of the swordfish fishery in the Azores consists mainly of pelagic sharks, 

particularly the blue shark (Prionace glauca) and the shortfin mako (Isurus oxyrinchus) (Silva et 

al., 1996). Other species–such as the common thresher (Alopias vulpinus), bigeye thresher 

(Alopias superciliosus), smooth hammerhead (Sphyrna zygaena), tope (Galeorhinus galeus) and 

the galapagos shark (Carcharhinus galapaguensis)–are also represented in the shark bycatch. 

The bigeye (Thunnus obesus) and blue marlin (Maikaira nigricans), respectively, represent most 

of the tuna and billfish bycatch. 

Bycatch of marine turtles in longlines targeting swordfish in the Azores is poorly known. 

Information on this issue was presented during this workshop (see Serpa and Prieto et al. in this 

volume). The loggerhead turtle (Caretta caretta) is the species most commonly caught. The 

leatherback (Dermochelys coriacea) has already been recorded during longline experimental 

fishing activities carried out by the Department of Oceanography and Fisheries, University of the 

Azores (Silva et al., 1996). 

The bycatch of marine birds associated with the longline fishery in the Azores is virtually 

unknown. 

Fishing Seasons 

Two fishing seasons can be identified for the longline fishery targeting swordfish in the 

Azores: swordfish season and blue shark season. Catch rates for blue shark and swordfish exhibit 

a pronounced seasonal and asynchronic nature (Figure 5). While the highest catch levels of the 

former species are obtained in the Spring, the fishing season for the latter targeted species is 

5 
from May to December. Blue shark bycatch represents a major proportion of the total catch taken 

by the fishery, reaching a minimum of 22% and a maximum of 86%, respectively, during 

October and May (Figure 6). Shortfin mako catch levels are less than 5% of the total catch 

during the entire year. 

Landings of Swordfish and Pelagic Sharks 

Reported landings of swordfish, blue shark and shortfin mako in the Azores during the 

period 1993-1997 are shown in Figure 7. Landings of swordfish exhibit a peak of 463 metric 

tons (mt) in 1995, followed by a decline to 178 mt in 1997. Reported catches of blue shark 

increased from 1993 to 1996, peaking in 1996 at 328 mt. After that period, landings declined to 

92 mt in 1997. Although the discard levels associated with the swordfish fishery are not 

quantified, blue shark discards by the Azorean longline fleet are believed to be high. This 

conclusion is supported by the non-existence of a stable market and little demand for blue shark 

products within the Azorean region. Discard levels for this species by the Mainland's longline 

fleet are known to be extremely low. This results from the existence of two asynchronic fishing 

seasons for the targeted swordfish and for blue shark in the Azores (Figure 5), and the increasing 

demand for shark products in European markets (Fleming and Papageorgiou, 1997). 

Landings of shortfin mako in the region averaged about 8.2 mt per year during 

1993-1997, with a maximum of 12 mt landed in 1995. Discard levels for this shark are extremely 

low due to the high quality of its meat. 

6 
Literature Cited 

Fernandes, L. 1987. Pesca Experimental de espadarte nos Açores com Palangre de deriva. VII 

Semana das Pescas dos Açores 1987: 121-126 

Fleming, E. H. and P. A. Papageorgiou. 1997. Shark fisheries and trade in Europe. TRAFFIC 

Europe, Brussels, Belgium. 78 p. 

Pereira, J. 1988. La pecherie de l'espadon aux Acores. ICATT, Coll. Vol. Sci. Papers

SCRS/87/85, Vol. XXVII (2): 318-320. 

Pousa, A. G. 1987. Como se trabaja al espadarte. VI Semana das Pescas dos Açores 1986: 269-

271. 

Silva, H. M., A. A. Silva & P. Simões. 1996. Relatório do cruzeiro de grandes pelágicos 

realizado durante o Outono 93/Primavera 94 nos Açores (ARQPAÇO-01-O93/P94).

Arquivos do DOP, Série Cruzeiros, 1 (1996). ISSN 0873-2876. 

Simões, P. and H. M. Silva. 1994. Caracterização da pesca de espadarte (Xiphias gladius) em 

águas Açoreanas: período 1987-92. XIII Semana das Pescas dos Açores 1994:203-222. 

Simões, P. 1995. The swordfish (Xiphias gladius L. 1758) fishery in the Azores, from 1987 to 

1993. ICCAT, Coll. Vol. Sci. Papers SCRS/94/109, Vol. XVIV (3): 126-131. 

7 
Figure 1. Components of the longline fleet fishing for swordfish in the Azores: 

A - Azorean open-deck wooden boats (ODWB); 

8 
Figure 1. Components of the longline fleet fishing for swordfish in the Azores: 

B - Azorean small-size cabin-deck boats (CDB1); 

9 
Figure 1. Components of the longline fleet fishing for swordfish in the Azores: 

C - large-size cabin-deck boats from the Azores and Mainland Portugal (CDB2; 

 MPB)

10 
0

5

10

15

20

25

30

35

40

45

50

1990 1991 1992 1993 1994 1995 1996 1997 1998

Year

Number of boats

ODWB CDB1 CDB2

A) Azorean fleet

0

5

10

15

20

25

1990 1991 1992 1993 1994 1995 1996 1997 1998

Year

Number of permits

B) Mainland fleet

Figure 2. Number of fishing permits (=boats) for the longline fishery in the Azores, 1990-

1998. 

A - Azorean fleet (ODWB - open-deck wooden boats; CDB1 - small size cabin-deck 

 boats; CDB2 - large-size cabin-deck boats). 

 B - Mainland Portugal fleet. 

11 
Figure 3. Longline gear. 

12 
Figure 4. Longline sets reported in Portuguese fishing logbooks, 1993-1998. The 

rectangular area represents the ICES area X which contains most of the Azorean EEZ. 

13 
0

100

200

300

400

500

600

700

800

900

1000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

CPUE (Kg of PGO / 1000 hooks)

0

50

100

150

200

250

300

350

400

450

CPUE (Kg of SWO / 1000 hooks)

Blue shark (PGO) Swordfish (SW O)

Figure 5. Monthly mean catch rates of swordfish (SWO) and blue shark (PGO) in the 

Azores, 1993-1998. Vertical lines represent 95% confidence intervals of the mean estimates. 

14 
0

10

20

30

40

50

60

70

80

90

100

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Percentage (% )

SWO PGO IOO

Figure 6. Monthly mean catch proportions of swordfish (SWO), blue shark (PGO) and 

shortfin mako (IOO). Vertical lines represent 95% confidence intervals of the mean 

estimates. 

15 
0

50

100

150

200

250

300

350

400

450

500

1993 1994 1995 1996 1997

Year

Landings (mt)

SWO PGO IOO

Figure 7. Yearly landings (metric tons) of swordfish (SWO), blue shark (PGO) and shortfin 

mako (IOO) in the Azores, 1993-1997.

16 
Information on Accidental Capture of Marine Turtles in the Azores 

Manuel F. Serpa 

Departamento de Oceanografia e Pescas 

Universidade dos Açores 

PT-9900 Horta, Portugal 

E-mail: fserpa@dop.uac.pt 

Unfortunately nothing has previously been recorded on accidental capture of sea turtles 

by the longline fleet in the Azores. This report is based on the personal experience of the author 

who has had the opportunity to take part in several longline fishing surveys from 1989 to 1996. 

This is a summary of my experiences. 

November 1989 to February 1990, F/V “António Duarte”. Experiment with winter longlining 

for tuna. 

Results of 32 sets: 910 blue sharks, 114 swordfish, 3 bigeye, 2 albacore, 8 mako sharks, 2 

loggerheads and 3 leatherback turtles. 

Remarks: The small number of turtles was due to the fact that it was winter and that the target 

species was tuna which means that the lines were set too deep to catch turtles. 

June to September 1990, F/V “IMAQ FISH”. Experiment with longlining for tuna from 

Azores to Canada. However, as few tuna were caught, the gear was changed to target swordfish. 

Results from 30 settings: 4 bigeye, 7 yellowfin, 9 bluefin, 38 blue sharks, 39 swordfish, 20 

loggerheads and 3 leatherback turtles. 

Remarks: Several turtles were caught in June and July, always on the hooks close to the buoys. 

At the end of July, we caught several large turtles (20 – 30 kg) WNW of Flores, Azores. Farther 

north, when 300 nautical miles from the Grand Bank, no more turtles were seen. 

November 1990, F/V “IMAQ FISH”. Experiment in longlining for swordfish. 

Results: 2 bluefin, 1 bigeye, 2 yellowfin, 1 albacore, 4 mako sharks, 104 swordfish, 8 

loggerheads and 3 leatherback turtles.

March to April 1991. Japanese longliner for tuna. 

Results: 3 loggerheads, and 2 leatherback turtles.

Remarks: Very few turtles due to low temperature (15o to 16o C) and that the line was set as deep 

as 80 m, the target species being tuna. 

September to October 1996, F/V “S. Miguel”. Longlining for swordfish. 

Results in 22 sets: 10 tons of swordfish, 12 tons of shark, 0.5 tons of tuna, and about 100 

loggerhead turtles.

Remarks: 90% of the turtles were caught at Mar da Prata, south of S. Miguel and the Bank of S. 

Mateus, south of Pico. The water temperature was 20-22° C. The bait was 75% mackerel and 

25% squid. 

17 
November to December 1996, F/V “Mar de Cristal”. Longlining for swordfish. 

Results in 16 sets: 8 tons of swordfish, 6 tons of shark, 300 kg of bigeye, and 40 loggerhead 

turtles, with an average weight of about 30 kg. 

Remarks: Each set had an average of 900 hooks. The bait was 75% mackerel, 15% squid, and 

10% shark filets. The number of fishing boats in the area varied from 2 to 4. Most of the turtles 

were captured in November at the bank of S. Mateus, south of Pico, where up to 6 were taken in 

one day. 

Concluding Remarks 

The turtles seem to be more likely to be caught from June to the middle of August, and 

most of them were caught when the fisheries were directed at swordfish. One also observes that 

the majority are caught on hooks close to the buoys. 

My experience is that, at the end of the summer when few turtles are seen on the surface, 

the turtles that are caught are larger. Thus, in July and August one finds individuals of variable 

sizes, while from September onwards one finds more larger individuals. From my experience, 

the number of turtles caught in the fisheries diminishes from the end of August to the middle of 

September and increases again in October and November especially under favorable weather 

conditions. 

Most of the turtles are not hauled onboard. Especially on the larger vessels, they are 

rejected by the fishermen by cutting the line. Only rarely, when the sea is smooth, is the turtle 

freed from the hook onboard and put out to sea. 

The number of turtles that manage to free themselves from the hook at sea is 

insignificant. This only happens with large boats at great speed under bad weather conditions. 

Only once in my experience was a turtle hauled aboard dead. In general, the turtles did 

not show signs of being weak or tired. 

I hope that through discussion and dialogue it will be possible to develop these ideas as 

well as other questions regarding the accidental capture of turtles. 

18 
Informação disponível sobre a pesca acidental de tartarugas nos Açores 

Infelizmente pouco ou nada existe de informação registado em qualquer organismo 

oficial, no entanto e dentro do possível, tentarei dar alguns registos pessoais, outros através de 

diálogos com mestres de outras embarcações e também através da assistência de algumas 

descargas. 

Irei começar por capturas recentes em duas embarcações no ano de 1996, visto ser 

aquelas que tenho um registo mais concreto: 

Em Setembro e Outubro no palangreiro ‘S.Miguel’, capturou-se cerca de 100 tartarugas 

em 22 lances, 15 deles junto às ilhas dos grupos Oriental e Central e nalguns bancos; os restantes 

7 lances foram efectuados mais distantes, mais precisamente no Banco Voador, Banco Sarda e 

um no Banco Gigante. Nos primeiros 15 lances foram capturadas cerca de 90% de tartarugas 

com maior incidência no Mar de Prata, ilha de S. Miguel e Baixo de S. Mateus, ilha do Pico. As 

capturas foram de 10 toneladas de espadarte, 12 toneladas de tubarão, 0.5 tonelada de atum e 

cerca de 100 tartarugas careta como já mencionado. A temperatura das águas variou de 20-22 

graus Celsius. A média de anzóis foi de 1000. O isco variou em 75% cavala e 25% lula. 

Em Novembro e parte de Dezembro, o palangreiro polivalente Mar de Cristal, capturou 

cerca de 40 tartarugas em 16 lances, todos eles junto aos Bancos de S. Mateus, Banco de Açor e 

Mata de Prata. Dois deles foram efectuados junto à ilha de S. Miguel. As tartarugas foram 

capturadas na maioria no mês de Novembro e junto ao Baixo de S. Mateus, tendo-se capturado 6 

exemplares num só dia. Capturou-se na totalidade 8 toneladas de espadarte, 6 toneladas tubarão, 

300 kg de atum patudo e cerca de 40 tartarugas careta como acima mencionado. As tartarugas 

em média tinham um peso de 30 kg, a média de anzóis por lance foi de 900. O isco foi em 

percentagem de 75% de cavala, 15% de lula e 10% de filete de tubarão. O número de 

embarcações na zona variava de 2 a 4. 

Posso desde já mencionar que nos meses de Julho e Agosto encontrámos indivíduos de 

vários pesos e comprimentos, a partir de Setembro já encontrámos indivíduos mais seleccionados 

e com maior peso. Poderá isto significar que os indivíduos mais pequenos atravessam as nossas 

águas nos meses mais quentes, mais concretamente em Julho e parte de Agosto. 

Numa outra experiência minha, a bordo de um atuneiro palangreiro japonês, nos meses 

de Março e Abril de 1991 nos mares dos Açores, onde obtivemos alguns exemplares não 

representativos, na ordem de 3 a 5 exemplares, sendo dois deles tartarugas de couro. O número 

reduzido de exemplares poderá estar relacionado com dois factores: a temperatura reduzida que 

variou à superfície entre 15 e 16 graus e também pelo facto da pesca ser dirigida ao atum rabilo, 

ou seja, feita a grandes profundidades, ficando o longline a uma média de 80 metros de 

profundidade. 

Ainda outra experiência foi levada a cabo, a bordo de um palangreiro dinamarquês/ 

canadiano ‘IMAQ FISH’, dirigida ao atum rabilo. A campanha teve início em Junho de 1990 

tendo terminado em Setembro do mesmo ano, esta campanha foi efectuada por mim e por outro 

19 
colega, tendo sido iniciada nos mares dos Açores até à costa do Canadá. Em virtude das capturas 

baixas em tunídeos e de ocorrência de grandes quantidades de espadarte, alterou-se o palangre, 

dirigindo-se apenas para esta espécie. 

Nesta campanha, capturou-se vários exemplares de tartarugas, mais precisamente, nos meses de 

Junho e Julho, sendo estes sempre recolhidos nos anzóis junto das bóias. 

Nos finais de Julho, quando nos afastámos para WNW da ilha das Flores, surgiram sempre 

alguns indivíduos de grande porte (entre 20/30 kg). No entanto, à medida que subíamos para 

Norte a cerca de trezentas milhas do Grand Bank, deixámos de capturar qualquer exemplar. 

As capturas dos 30 lances foram de 4 patudo (bigeye), 7 galha-à-ré (yellowfin), 9 rabilo 

(bluefin), 38 tintureira (blue shark), 39 espadarte (swordfish), 20 tartarugas careta (Caretta 

caretta) e 3 tartarugas de couro (Dermochelys coriacea). Com a mesma embarcação fez-se ainda 

uma experiência ao espadarte, no mês de Novembro, resultante do número de espécies 

capturadas na experiência anterior e dos maus resultados em espécies de tunídeos.Embora a 

época propícia já tivesse passado, ainda capturou-se 11 exemplares de tartarugas careta (Caretta 

caretta), 3 tartarugas de couro (Dermochelys coriacea) tendo uma delas pesado 415 kg; a pesca 

foi feita mais à superfície e as temperaturas das águas mantiveram-se entre os 19 e 18 graus 

Celsius. Em resumo, as capturas totais foram de 2 rabilo, 1 patudo, 2 galha-á-ré, 1 voador, 3 

tintureiras, 4 rinquim, 104 espadartes, 11 tartarugas (8 tartaruga careta e 3 tartarugas de couro). 

Campanha de atum com palangre na embarcação ‘António Duarte’. Esta experiência foi 

levada a cabo nos meses de Novembro e Dezembro de 1989 e Janeiro e Fevereiro de 1990, tendo 

como objectivo o atum de Inverno. Em 32 lances efectuados, capturou-se 910 tintureira, 114 

espadarte, 3 patudo, 2 voador, 8 rinquim , 3 tartarugas de couro e 2 tartarugas careta. O pequeno 

número de tartarugas capturadas deveu-se à época do ano e também ao palangre ser dirigido ao 

atum, ficando este a maior profundidade. 

Em resumo, poder-se-á concluir que as tartarugas incidem mais nos meses de Junho, 

Julho e parte de Agosto, capturando-se mais indivíduos quando a pesca é dirigida a espadarte. 

Verificou-se que a maior parte dos indivíduos são capturados nos anzóis junto às bóias. Nas 

minhas experiências verifiquei de que à medida que o Verão avançava, os indivíduos eram na 

sua maioria de grande porte e poucos se avistavam à superfície. Ainda fiquei com a ideia de que, 

nos fins de Agosto até meados de Setembro, parece ser mais reduzido o número de tartarugas, 

surgindo novamente em Outubro e Novembro, em especial quando as condições climatéricas são 

favoráveis. 

Queria também salientar, que grande parte das tartarugas ou até mesmo a sua maioria, são 

rejeitadas ao mar pelos pescadores sem entrar no navio, muito em especial, nos palangreiros de 

maior profissionalismo e de grande porte. Na alagem do palangre, o tempo perdido com uma 

tartaruga bastaria, para recolher dois a três anzóis, daí não haver motivação para recolher para 

bordo as tartarugas, sendo na sua maior parte cortadas pelo estralho. Só raramente, quando as 

condições do estado do mar e a pescaria é favorável é que as tartarugas são desiscadas do anzol e 

largadas ao mar. 

Posso adiantar com alguma segurança que, o número de tartarugas a desprenderem-se dos 

anzóis durante a alagem é quase insignificante, apenas poderá acontecer esporadicamente num 

20 
grande palangreiro a grande velocidade, na época de Inverno onde as condições do mar são 

muito desfavoráveis. 

Posso concluir que em todas as campanhas efectuadas por mim, só uma vez foi registado 

a recolha de uma tartaruga sem vida e raramente outras vinham com aparência de cansaço e 

fraqueza. 

Espero que, em discussão e diálogo possamos definir com maior rigor estas ideias assim 

como outras questões. 

21 
Turtle Bycatch Study in the Longline Fisheries of the Azores 

R. Prieto, R. Ferreira, and A. Silva 

Departamento de Oceanografia e Pescas 

Universidade dos Açores 

PT-9900 Horta, Portugal 

E-mail: rprieto@dop.uac.pt 

Abstract 

A study was conducted to try to quantify the bycatch of marine turtles by the longline 

fisheries in the Azores. The sampling method was designed to provide information about the 

fishery and associated bycatch as catch per unit effort and biological data on the turtles and other 

species caught accidentally, especially blue sharks. The mean capture for 1000 hooks per month 

varied between 0.036 and 0.753, respectively, in May and July, with the number of turtles 

captured per set between 0 and 7. Most of the turtles were hooked in the mouth. Of the 27 turtles 

captured, 19% were caught on hooks baited with mackerel, 11% with squid, and the remaining 

(70%) with unidentified bait. Only one of the 27 turtles was found dead. The data presented 

constitute the preliminary results from the study. We plan to put more observers on longline 

fishing boats during the coming months. 

Introduction 

During recent years there has been increasing concern regarding the accidental capture of 

turtles in longline fisheries as a threat to some populations. A few years ago this fishery was 

considered to cause little harm to turtle populations (Hillestad et al., 1995), but further studies on 

population dynamics and accounts from fishermen in some areas indicate otherwise. It is 

probable that the impact the fishery has on turtle populations varies with area and the different 

techniques used. 

To better understand this impact and manage turtle populations affected by this fishery, it 

is critical to quantify the capture rates and compare the results from different areas and 

techniques to develop management strategies wherever necessary. The study presented here was 

designed to address this problem and to serve as a guideline in the design of more complex and 

broader studies. 

Overview of Sea Turtle Biology in the Azores

In the Azores EEZ, loggerheads (Caretta caretta) constitute the overwhelming majority 

of marine turtles, whereas green turtles (Chelonia mydas) and leatherback turtles (Dermochelys 

coriacea) occur occasionally (Martins, pers. comm.). Studies of size distribution, tagging and 

recapture experiments (Carr, 1986; Bolten et al., 1993, 1995) and more recently of genetics 

(Bolten et al., 1998) show that the post-hatchling loggerheads from the east coast of North 

America are carried by the oceanic currents to the eastern Atlantic, through the Azores, Madeira, 

22 
Canary Islands, and perhaps the Cape Verde Islands. The movements of these turtles are 

probably associated with the North Atlantic Gyre System, and the duration of the pelagic stage is 

estimated to be between 10-12 years (Bolten et al., 1995). 

The pelagic-stage loggerheads found around the Azores have curved carapace lengths 

varying between 10 and 60 cm, with a mean of 33.6 cm, and represent an early stage of the life 

history of the turtles nesting in the southeastern United States and Yucatan Peninsula. The 

loggerhead turtles frequenting the Azores waters are thus immature animals, which have a high 

probability of reaching maturity and are therefore very important to the maintenance of the 

population. 

Study Design

The longline fishery in the Azores is supposed to be directed at swordfish (Xiphias 

gladius), but recent studies show that two main seasons occur, and the catch between February 

and June is composed mainly of blue sharks (Prionace glauca). Between June and December the 

catch is mostly composed of swordfish (see Silva in this volume). The gear can also differ, and 

two different set-ups are used which fish at distinct depths. 

The study was designed to cover the two seasons, and efforts were made to sample the 

two set-ups. In order to carry out this study, some companies fishing in the Azores with longline 

gear were contacted, and they agreed to take onboard one observer to monitor the fishery. The 

sampling method was designed to provide information about the fishery and associated bycatch 

as catch per unit effort and biological data on the turtles and other species, especially blue sharks. 

Whenever a turtle was caught, the observer would stop any other work to record the data on the 

turtle and to attend to it, if necessary. 

The data collected for turtles were: 

1. Species 

2. Measurement of the curved carapace length 

3. Collection of skin sample for DNA analysis 

4. Capture 

• Method of capture (hook or entanglement) 

• Condition (dead; weak; strong) 

• Position of hook or entanglement 

• Position of the hook in the digestive tract (if applicable) 

5. Other pertinent observations 

After the data were collected, the turtle was tagged and released, and observations were 

made on its behavior. In the case of a dead turtle, the right front flipper and stomach were frozen. 

The first observer was put on the fishing boat "Altair" in May, and the sampling was 

made between May and August. The observer trained one of the fishermen, and during the 

months of June and July, this fisherman collected the data. 

Preliminary Results 

23 
The data presented below constitute the preliminary results from the study and are 

presented only to give an idea of the benefits a program of observers could bring to the 

understanding of the sea turtle longline bycatch. 

The size frequency of loggerhead turtles (Caretta caretta) caught in the swordfish fishery 

between May and August is presented in Figure 1. The mean capture for 1000 hooks per month 

varied between 0.036 and 0.753 (Figure 2), respectively, in May and July with the number of 

turtles captured per set between 0 and 7. 

Of the 27 turtles captured, most of them (25) were hooked in the mouth; only one was 

hooked in the eye, and another in the flipper. Except for one turtle with a hook in the junction of 

the jaw that could not be removed, all of the turtles that were brought onto the boat were freed 

from hooks and lines. Only one of the 27 turtles was dead. In addition, the fishermen reported an 

undetermined number of turtles captured in June that were not hauled onto the boat due to their 

large size (two of them were leatherback turtles, and the others were loggerheads). These turtles 

were set free by cutting the line attached to the hook and thus the position of the hook is not 

known. 

The relation between capture and the baits used is presented in Figure 3. Of the 27 turtles 

captured, 19% were caught on hooks baited with mackerel, 11% with squid, and the remaining 

(70%) with unidentified bait. 

Conclusions

The results of this study are preliminary, and we intend to put more observers on longline 

fishing boats during the coming months. It is, thus, too soon to draw any conclusions about the 

bycatch of marine turtles around the Azores in this fishery. Nonetheless, we believe that as data 

are collected in this way, there will be a better understanding of the magnitude of the bycatch, as 

well as of the way in which it occurs. In addition, information on other species can also be 

gathered in this way and can help in the management of the fishery. 

The work achieved during this first phase was not only encouraging scientifically. It also 

showed that a close collaboration with the fishermen could produce good results regarding the 

conservation of turtles. The fishermen on "Altair" and the owner of the company were very 

receptive to the study and even eager to learn how they could help the turtles. It is reasonable to 

think that more fishermen and companies would be receptive not only to have other observers 

onboard, but also, in some cases, to try alternative techniques to reduce the bycatch, if this is 

proved to be necessary. 

Literature Cited

Bolten, A. B., K. A. Bjorndal, H. R. Martins, T. Dellinger, M. J. Biscoito, S. E. Encalada, and B. 

W. Bowen. 1998. Transatlantic developmental migrations of loggerhead sea turtles 

demonstrated by mtDNA sequence analysis. Ecological Applications 8:1-7. 

24 
Bolten, A. B., K. A. Bjorndal, and H. R. Martins. 1995. Life history of the loggerhead sea turtle, 

Caretta caretta, (Reptilia: Cheloniidae), in the Atlantic. Bol. Mus. Mun. Funchal 4:115-

122. 

Bolten, A. B., H. R. Martins, K. A. Bjorndal, and J. Gordon. 1993. Size distribution of pelagicstage loggerhead sea turtles (Caretta caretta) in the waters around the Azores and 

Madeira. Arquipélago 11A:49-54. 

Carr, A.1986. Rips, FADs, and little loggerheads. BioScience 36:92:-100. 

Hillestad, H. O., J. I. Richardson, C. McVea, Jr., and J. M. Watson, Jr. 1995. Worldwide 

incidental capture of sea turtles. Pages 189-496 in K. A. Bjorndal, editor. Biology and 

Conservation of Sea Turtles, revised edition. Smithsonian Institution Press, Washington, 

D.C., USA. 

25 
26 

0

1

2

3

4

5

6

40 42 44 46 48 50 52 54 56 58 60 62 64

Curved Carapace Length (cm)

Frequency

Figure 1: Size distribution of loggerheads (n = 18) captured by longline fisheries around the 

Azores. 
0

0.2

0.4

0.6

0.8

1

1.2

May June July August

Month

Captures / 1000 hooks

2/25

9/25

8/5

10/19

N = 29

Figure 2. Mean capture of loggerhead sea turtles in longline fisheries around the Azores. 

Fractions above the bars represent the number of turtles caught per number of sets. Error lines 

represent the error at a confidence level of 0.95. 

27 
28 

Unknown

70%

Mackerel

11%

Squid

19%

Figure 3: Distribution of bait type for loggerhead turtles captured in the longline fishery around 

the Azores. 
Observation Program for Fisheries in the Azores (POPA): 

Aspects Related to Marine Turtles 

Programa de Observação para as Pescas dos Açores (POPA) 

Aspectos relacionados com Tartarugas Marinhas 

Rogério Feio 

Departamento de Oceanografia e Pescas 

Universidade dos Açores 

PT-9900 Horta, Portugal 

E-mail: rogerio@dop.uac.pt 

English Summary 

As part of the Observer Program for the Fisheries of the Azores (POPA), information 

related to sightings and tagging of turtles is also collected. That information is recorded by the 10 

observers contracted for POPA on the tuna fishing vessels. All of the data presented here are 

related to the sampling period between 15 May and 31 July 1998. One of the objectives of this 

work is to relate the turtle sightings to the environmental conditions (temperature, beaufort and 

visibility). The results revealed no significant relation between temperature and turtle abundance. 

There is a very significant relation between visibility and beaufort (state of the sea) and the 

number of turtle sightings. This relationship suggests that atmospheric conditions can interfere 

with the detection of turtles at sea and that better environmental conditions improves the 

detection by the observers. From a total of 390 sighted individuals, 50 were tagged, 

corresponding to 12.8%. The tagged individuals had a minimum curved carapace length of 17 

cm, a maximum of 55 cm, and a mean of 33.5 cm. 

O POPA é uma proposta apresentada pelo DOP/UA que permite, por um lado, conhecer 

de forma objectiva as suspeitas que recaem sobre os pescadores açorianos relativamente à 

captura ilegal de cetáceos e, por outro lado, recolher dados sobre as pescas e espécies marinhas 

açorianas. 

O POPA surge como consequência final dos vários contactos entre as partes interessadas 

na implementação deste programa (Industria Concerveira -COFACO-, Associação de Armadores 

da Pesca do Atum e Similares dos Açores -APASA- , Departamento de Oceanografia e pescas da 

Universidade dos Açores -DOP/UA-, “Earth Island Institute”, Serviço Açoreano de Lotas -

LOTAÇOR-, “University of Hawaii” e a conserveira “Starkist Seafood”), com o patrocínio da 

Direcção Regional das Pescas dos Açores. Estes contactos surgiram como consequência do 

acordo de princípios em que estas entidades reconhecem que o POPA possa ser organizado e 

gerido pelo Centro do IMAR - Instituto do Mar da Universidade dos Açores (DOP/UA), de 

modo a poder contribuir para a atribuição do estatuto “dolphin safe” ao atum capturado nos 

Açores. 

29 
O objectivo fulcral do POPA, tendo por base uma inegável qualidade científica, é o de 

assegurar que não haja mortalidade intencional nem perseguição deliberada de cetáceos pelas 

tripulações das embarcações atuneiras. Este objectivo será assegurado pela presença de 

observadores embarcados nos navios atuneiros. Aproveitando este facto, pretende-se obter 

complementarmente dados científicos sobre cetáceos e outras espécies marinhas (caso das 

tartarugas e aves marinhas), bem como sobre a pescaria (capturas, esforço de pesca, 

preenchimento de diários de bordo, etc.). 

No decorrer das campanhas de observação os 10 observadores contratados para o POPA, 

recolheram informação relacionada com avistamentos e marcação de TARTARUGAS. Os 

resultados obtidos são consequência de uma primeira abordagem estatística resultante da base de 

dados do POPA ainda em desenvolvimento. Esta fase do trabalho corresponde a uma abordagem 

preliminar que relaciona os avistamentos de tartarugas com as condições ambientais do meio 

(temperatura, beaufort e visibilidade). 

 Os resultados demonstram uma relação significativa entre o estado do mar (Beaufort) e o 

número de tartarugas avistadas, G = -0,40; p = 0,00; n = 74 (figura 1). No caso da visibilidade vs

o tartarugas avistadas verifica-se também uma relação significativa entre as variáveis, G = -0,49; 

p = 0,00; n = 74 (figura 2). Os resultados obtidos revelam que condições ambientais influenciam 

a detecção de tartarugas por parte do observador e sugerem que melhores condições ambientais 

favorecem essa detecção. 

Beaufort

Tartarugas Avistadas

-5

5

15

25

35

45

55

012345

Figura 1 - Relação entre o Beaufort (estado do mar) e o número de tartarugas avistadas. 

30 
 

Visibilidade

Tartarugas Avistadas

-5

5

15

25

35

45

55

Muito Boa Boa Media Má

Figura 2 - Relação entre a visibilidade e o número de tartarugas avistadas. 

No que diz respeito ás classes de comprimento dos indivíduos marcados, os resultados revelam 

um comprimento médio da carapaça de 37,5 cm, tendo sido o comprimento máximo de 55 cm e 

o mínimo de 17 cm, para o total de 50 indivíduos marcados (figura 3). 

Classes de Comprimento (cm)

No de Indivíduos

0

1

2

3

4

5

6

7

8

9

10

10 15 20 25 30 35 40 45 50 55

Figura 3 - Classes de comprimento das 50 tartarugas marcadas. 

31 
Approach to the Experimental Design and Review of the Experimental Variables 

with the Objective of Stimulating Discussion 

Aproximação ao desenho experimental e revisão das variáveis experimentais, 

com o objectivo de estimular a discussão 

Eduardo Isidro and Mário Pinho 

Departamento de Oceanografia e Pescas 

Universidade dos Açores 

PT-9900 Horta, Portugal 

E-mail: eduardo@dop.uac.pt 

English Summary 

The loggerhead sea turtle, Caretta caretta, comprises a part of the bycatch of the 

swordfish longline fishery. The available information on this fishery and respective bycatch is 

scarce. Thus, it is difficult at this point to elaborate a clear sampling and experimental design. 

The objective of this presentation is to perform a brief review of hook fishing aspects and 

selectivity properties, as well as to summarize the main experimental variables and the possible 

types of the experiments to compare them. As any experiment has its own set of assumptions and 

difficulties, at the end, two types of experiments will be discussed – experiments in captivity and 

experimental fishing – with the objective of stimulating further discussion. 

Sumário 

A tartaruga Caretta caretta é capturada acidentalmente na pesca de palangre do 

espadarte. A informação estatística e biológica disponível, não permite, nesta altura, elaborar um 

desenho experimental claro. O objectivo desta apresentação é o de rever brevemente os aspectos 

da pesca com anzol e as suas características selectivas, assim como o de rever as principais 

variáveis experimentais e o tipo de experiências que se podem fazer para as testar. Como cada 

experiência tem os seus pressupostos e dificuldades, submete-se à discussão, no final e com o 

objectivo de estimular a discussão, dois tipos de experiências: experiências em cativeiro e pesca 

experimental. 

Introdução 

O método científico consiste em analisar o problema, formular uma ou mais hipóteses, 

testar essas hipóteses através de experiência(s) cujos resultados, após tratamento matemático ou 

estatístico, conduzam à rejeição ou aceitação das hipóteses iniciais. Qualquer exercício de 

desenho experimental está, assim, dependente do problema e das hipóteses levantadas, e tentará, 

à priori, responder a três tipos de questões: Como recolher a informação necessária para testar a 

hipótese, onde e quando recolher essa informação e quantas amostras serão necessárias (Krebs, 

1989). 

32 
Tipo de experiências 

Uma forma simples de classificar as experiências consiste em dividi-las em dois grandes 

grupos - manipuláveis e observacionais (Scheiner & Gurevitch, 1993) - sendo óbvio que esta 

classificação é muito artificial e que a maior parte das experiências caiem necessariamente entre 

estes dois tipos opostos (ver fig. 1). 

Tomando a pesca comercial como uma experiência, uma vez que ela é uma fonte de 

dados cuja análise poderá servir para encontrar padrões temporais e espaciais correlacionáveis 

quer com a biologia das espécies quer com a estratégia ou com o regime de pesca, tudo o que se 

pode dizer é que dificilmente poderá responder ao problema posto neste "workshop" - desenho 

de uma experiência com o objectivo de determinar o efeito de algumas modificações no palangre 

de meia água, utilizado na pesca do espadarte, de forma a diminuir a captura acidental de 

tartarugas - mas que, todavia, deve ser compreendida em detalhe. A informação existente sobre a 

pescaria do espadarte e sobre as respectivas capturas acidentais, nomeadamente as de tartaruga, é 

muito escassa, e pouco ajuda na elaboração de um desenho experimental. Apesar disso, a análise 

prévia das capturas da pesca do espadarte (ver Silva, neste volume) já responde à pergunta de 

quando se deve fazer uma pesca experimental nos Açores. A resposta é, obviamente, na altura 

em que a captura acidental de tartarugas é maior, i.e., entre Junho e Outubro. 

Convém, nesta altura, salientar que o problema que se está a analisar neste workshop é 

bastante complexo e que uma revisão da bibliografia sobre a selectividade do anzol mostra que 

este assunto ainda não está bem resolvido (ver McCracken, 1963; Pope et al., 1975; Ralston, 

1982; Morais, 1990; Lokkeborg & Bjordal, 1992; Kenchington, 1993; Otway & Craig, 1993; 

Erzini et al., 1995, 1997; Millar, 1995; Sousa, 1996; Sousa et al., in press). De facto, caso se opte 

por uma pesca experimental, há que entender que há muitos factores em jogo, alguns difíceis de 

controlar e medir (e.g. interacções inter/intra específicas, comportamento perante a arte, factores 

ambientais, etc.), que podem aumentar de tal forma a variabilidade das capturas que só uma 

amostragem enorme poderá tornar o efeito dos tratamentos estatisticamente detectáveis. Isto 

significa que, com o conhecimento disponível, é difícil prever quanto tempo ou quantos lances 

ou quantas amostras serão necessárias para que, através de uma pesca experimental, se obtenha a 

informação suficiente para testar o efeito de determinadas variáveis. Significa também que, neste 

caso, é aconselhável testar um número reduzido de factores ou variáveis e recolher o maior 

número possível de amostras (executar um número elevado de lances). 

 

Considerando o que se disse no parágrafo anterior, não se deve, por isso, esquecer as 

experiências em tanques ou gaiolas, uma vez que elas permitem controlar melhor uma série de 

factores adicionais, isolar os tratamentos e replicar experiências. No entanto, é de salientar que a 

execução deste tipo de experiências será sempre difícil nos Açores, por falta de locais naturais 

adequados (i.e. pouco expostos a uma acção intensa do mar, no caso das gaiolas), e que não há 

informação suficiente sobre o stress, e consequentes alterações comportamentais, induzido pelo 

cativeiro nas tartarugas. A alteração do comportamento dos animais em cativeiro é de facto o 

maior "handicap" deste tipo de experiências, levando, frequentemente, o investigador a preferir a 

pesca experimental. 

33 
Pesca com anzol e variáveis principais 

Independentemente do tipo de arte de anzol utilizada, podem-se distinguir três etapas na 

captura com anzol: atracção, captura e escape (Bjordal, 1981). Em cada uma destas etapas, os 

factores ou variáveis que possivelmente terão maior influência e que são mais facilmente 

manipuláveis encontram-se sublinhados na tabela 1. 

Conclusões 

Nesta apresentação e nas apresentações anteriores, ficou claro que o conhecimento actual 

sobre a pesca do espadarte e sobre o "bycatch" de tartarugas é insuficiente quer nos Açores, quer 

noutras áreas de pesca, e que é importante que esta informação comece a ser recolhida num 

futuro próximo. Ficou também claro que as variáveis a testar, para responder ao problema posto 

neste workshop seriam: Tipo e tamanho de isco, tipo e tamanho de anzol, profundidade de pesca 

e tipo de estralho. O possível efeito de atracção das bóias foi também mencionado. Algumas 

destas variáveis, nomeadamente o tamanho do anzol e tipo de estralho, embora importantes na 

captura acidental de tartarugas, teriam certamente um impacto muito grande no rendimento da 

pesca do espadarte, pelo que quaisquer medidas baseadas no resultado desta experiência seriam 

difíceis de implementar. Sugere-se assim que estas variáveis não sejam testadas e que se focalize 

a atenção nas restantes variáveis. O tipo e tamanho de isco deve também merecer mais alguma 

reflexão como variável a analisar, uma vez que a Caretta caretta parece ter uma alimentação 

generalista (Preen, 1996) e que a alteração do isco também pode conduzir a alterações 

significativas nos rendimentos de pesca (ver e.g. Lokkeborg & Bjordal, 1993). 

Como base para a discussão que se segue, apresenta-se um esquema de um palangre de 

meia-água, cujo desenho e características deverão ser definidas e completadas, tendo como 

objectivo a pesca experimental (Fig. 2), embora se insista que se debata previamente a 

possibilidade da realização de algumas experiências em cativeiro. Neste aparelho há ainda que 

prever a colocação de instrumentação para monitorizar o comportamento da arte (e.g. TDRs) e a 

sistematização da amostragem de forma a que a sua aplicação no campo seja tão simples quanto 

possível, que os dados resultantes sejam tratados como se o processo fosse verdadeiramente 

aleatório e que a informação recolhida seja tão completa quanto possível de forma a que se possa 

tirar algumas conclusões sobre a interacção entre as variáveis, o comportamento da espécie e 

alguns factores ambientais. Deve-se ainda acrescentar que, de acordo com as conclusões 

anteriores, a pesca experimental deverá ser feita entre Junho e Outubro, num local onde seja mais 

provável encontrar tartarugas e espadarte, com um aparelho de características idênticas, mas com 

uma dimensão ligeiramente menor que o utilizado na pesca comercial (i. e. com um menor 

número de anzóis, porque o processamento de pescado e informações a registar tornam a alagem 

mais morosa). 

Bibliografia

Bjordal, A. 1981. Engineering and fish reaction aspects of longlining - a review. ICES 

C.M./B:35, 22 p. 

Erzini, K., J. M. S. Gonçalves, L. Bentes, and P. G. Lino. 1995. Small hook longline selectivity 

study. Commission of the European Communities, DG XIV/C/1 ref. BIOECO/93/04. 

34 
Erzini, K., J. M. S. Gonçalves, L. Bentes, and P. G. Lino. 1997. Short communication. Fish 

mouth dimensions and size selectivity in a Portuguese long-line fishery. Journal of 

Applied Ichthyology 13:41-44. 

Kenchington, T. J. 1993. Estimation of the functional form of selectivity by baited hooks: a 

graphical approach. Canadian Journal of Fisheries and Aquatic Sciences 50:772-780. 

Krebs, C. J. 1989. Ecological methodology. New York, Harper Collins, 654p. 

 

Lokkeborg, S. and A. Bjordal. 1992. Species and size selectivity in longline fishing: a review. 

Fisheries Research 13:311-322. 

 

McCracken, F. D. 1963. Selection by cod-end and hooks on cod, haddock, flatfish and redfish. 

ICNAF Special Publication 5:131-155. 

 

Millar, R. B. 1995. The functional form of hook and gillnet selection curves cannot be 

determined from comparative catch data alone. Canadian Journal of Fisheries and 

Aquatic Sciences 52:883-891. 

Morais, P. J. 1990. Selectividade do anzol relativamente ao Pagellus bogaravero (Goraz) e ao 

Helicolenus dactylopterus dactylopterus (Boca negra), pescados nos Açores. Faro, 

Universidade do Algarve, 74p. 

 

Otway, N. M. and J. R. Craig. 1993. Effects of hook size on the catches of undersized snapper 

Pagrus auratus. Marine Ecology Progress Series 93:9-15. 

Pope, J. A., A. R. Margetts, J. M. Hamley, and E. F. Akyuz. 1975. Manual of methods for fish 

stock assessment. Part III - Selectivity of fishing gear. FAO Fisheries Technical Paper 

41:1-65. 

Preen, A. R. 1996. Infaunal mining: A novel foraging method of loggerhead turtles. Journal of 

Herpetology 30:94-96. 

Ralston, S. 1982. Influence of hook size in the Hawaiian deep-sea handline fishery. Canadian 

Journal of Fisheries and Aquatic Sciences 39:1297-1302. 

 

Scheiner, M. S. and J. Gurevitch, Eds. 1993. Design and analysis of ecological experiments. 

London, Chapman & Hall, 445p. 

Sousa, F. 1996. Estudo da eficiência relativa e selectividade do palangre fundeado na pesca 

demersal Açoreana. Unidade de Ciências e Tecnologias dos Recursos Aquáticos. Faro, 

Universidade do Algarve, 72p. 

 

35 
Sousa, F., E. Isidro, and K. Erzini. In press. Semi-pelagic longline selectivity for two demersal 

species from the Azores: the black spot sea bream (Pagellus bogaraveo) and the rockfish 

(Helicolenus dactylopterus dactylopterus). Fisheries Research. 

36 
EXPERIÊNCIAS

(Experiments)

MANIPULÁVEIS

(Manipulative)

OBSERVACIONAIS

(Observational)

LABORATÓRIO,

TANQUES, GAIOLAS

(Lab., Tanks, Cages)

PESCA EXPERIMENTAL

(Experimental fishing)

PESCA COMERCIAL

(Commercial fishing)

Figura 1 - Tipos de experiências. 

37 
Refletor de radar

Bóias de sinalização Flutuador

Linha da bóia 

Linha madre

Anzol Estralho

Bloco 1 Bloco ?

BASKET

50m

Figura 2 - Esquema geral de um palangre de meia água, a ser completado através da discussão. 

38 
Tabela 1 - Etapas da captura com anzol e variáveis principais. As variáveis consideradas mais 

importantes estão sublinhadas. 

ETAPAS VARIÁVEIS 

ATRACÇÃO: 

(Attraction) 

Isco, profundidade, variáveis ambientais vs factores biológicos 

da espécie (e.g. correntes, luz ou transparência da água, 

distribuição vertical e horizontal da espécie, comportamento 

alimentar, atracção pelas boias, etc.). 

CAPTURA: 

(Capture) 

Tamanho e forma do anzol vs factores biológicos da espécie 

(outros factores e.g. espaçamento dos anzóis, saturação do 

aparelho, competição inter e intraespecífica, comportamento 

alimentar, tamanho da boca, etc.). 

ESCAPE: 

(Escape) 

Tamanho e forma do anzol, tipo de estralho vs factores 

biológicos da espécie (outros factores e.g. aprendizagem através 

de contactos prévios com a arte, comportamento alimentar e 

forma como engole o anzol, etc.). 

39 
Experiment to Evaluate Gear Modification on Rates of Sea Turtle Bycatch 

in the Swordfish Longline Fishery 

Objective 

Conduct an experiment to evaluate effects of gear modification on rates of sea turtle 

bycatch in the swordfish longline fishery in the Azores. The primary variables to be evaluated 

are hook shape (“J” Anchora vs. Mustad circle/curve), bait (squid vs. mackerel), and buoy line 

depth (3 fathoms vs. 6 fathoms). Although the primary objective is to evaluate rates of sea turtle 

bycatch, the effect of gear modification on the location of hooking (e.g., mouth vs. esophagus) 

will also be evaluated. The location of hooking has very important implications for the survival 

of the hooked turtles. 

Justification 

1. Results from this experiment will have broad application and can be applied to swordfish 

longline fisheries around the world. 

2. The sea turtle population impacted by the swordfish longline fishery in the Azores is the 

early juvenile pelagic stage for turtles that nest in the southeast USA. 

Background 

The problem of sea turtle bycatch in longline fisheries has been recognized worldwide 

(for review, see Balazs and Pooley 1994, Williams et al. 1996). Bolten et al. (1994) presented 

preliminary data on bycatch of loggerhead sea turtles (Caretta caretta) in the swordfish longline 

fishery in the Azores. The waters around the Azores are an important developmental habitat for 

the pelagic stage of the Atlantic loggerhead population. Using mtDNA sequence analyses, 

Bolten et al. (1998) determined that the source rookeries for this pelagic population are primarily 

in the southeastern USA. Therefore, the nesting population of loggerheads in the southeast USA 

is the primary population impacted by the swordfish longline fishery in the Azores. 

Design of the Experiment 

An experiment was designed using “American Gear” configuration (nylon line with steel leader) 

with the following three variables: 

1. hook type: “J” Ancora 17/0 (Spanish) vs. Mustad circle/curve 

2. bait: squid vs. mackeral 

3. depth of buoy line: 3 fathoms vs. 6 fathoms. 

Workshop participants identified other variables (e.g., light sticks), but there was consensus that 

the three variables chosen were the most important. The experiment will be conducted during 

the 4 primary months of the swordfish fishery in the Azores (June, July, October, and 

November). A commerical longline fishing vessel (with a commercial crew) from the Azores 

will be chartered to conduct the experiment. The experiment will consist of a minimum of 60 

40 
sets (approximately 15 sets per month) with 960 hooks per set. For each set at each of the two 

buoy line depths (3 fathoms [n = 30 sets] or 6 fathoms [n = 30 sets]), the experimental design 

will allow for the following comparisons to be statistically evaluated: 

Hook 1A vs. Hook 2B

 480 hooks for each treatment 

Bait LC vs Bait CD 480 hooks for each treatment 

Hook1 Bait L vs Hook1 Bait C vs Hook2 Bait L vs Hook2 Bait C 

 240 hooks for each treatment 

A Hook 1 = “J” Ancora 

B

 Hook 2 = Circle/Curve Mustad 

C

 Bait C = Cavala = mackerel 

D Bait L = Lula = squid 

The following diagram illustrates the experimental array. The starting order of bait and 

hook type will be randomized each day to avoid position effect within a gear array. Because 

every experimental variable change is associated with a major gear change, this experimental 

array will faciliate changes in variables and data collection. For example, bait type will change 

at every large buoy and hook type will change at every radar reflector buoy. 

 |> |> |> |> 

OoooOoooOoooOoooOoooOoooOoooOoooOoooOoooOoooOoooOoo... continued 

|____||____||___||____||___||____||___||___||____||___||____||___||___... 

Bait C L C L C L C L C L C L C 

(n=24 hooks for each bait unit = basket) 

|__________________||________________||_________________||________... 

 Hook 1 Hook 2 Hook 1 Hook 2 

n=96 hooks n=96 n=96 n=96 

|> = radar reflector buoy 

O = large buoy 

o = small buoy 

1. The buoy line will be either 3 fathoms or 6 fathoms 

2. There will be 6 hooks (with 9-meter leaders) on each mother line; hooks will be spaced at 25-

30 m. 

41 
Schedule 

An excellent window of opportunity now exists to pursue this experiment in the Azores because 

of both political will and interest from the commercial longline fleet in the Azores. We propose 

that the experiment begin in June 1999. 

Literature Cited 

Balazs, G.H. and S.G. Pooley. 1994. Research plan to assess marine turtle hooking mortality: 

results of an expert workshop held in Honolulu, Hawaii, November 16-18, 1993. NOAA 

Technical Memorandum NOAA-TM-NMFS-SWFSC-201. 166 pages. 

Bolten, A.B., K.A. Bjorndal, H.R. Martins, T. Dellinger, M.J. Biscoito, S.E. Encalada and B.W. 

Bowen. 1998. Transatlantic developmental migrations of loggerhead sea turtles 

demonstrated by mtDNA sequence analysis. Ecological Applications 8:1-7. 

Bolten, A.B., K.A. Bjorndal and H.R. Martins. 1994. Life history model for the loggerhead sea 

turtle (Caretta caretta) population in the Atlantic: Potential impacts of a longline fishery. 

Pages 48-54 in G.H. Balazs and S.G. Pooley (eds.), Research Plan to Assess Marine 

Turtle Hooking Mortality: Results of an Expert Workshop Held in Honolulu, Hawaii, 

November 16-18, 1993. NOAA Technical Memorandum NMFS-SWFSC-201. 

Bolten, A.B., J.A. Wetherall, G.H. Balazs, and S.G. Pooley (compilers). 1996. Status of marine 

turtles in the Pacific Ocean relevant to incidental take in the Hawaii-based pelagic 

longline fishery. NOAA Technical Memorandum. NOAA-TM-NMFS-SWFSC-230. 

167 pages. 

Williams, P., P.J. Anninos, P.T. Plotkin, and K.L. Salvini (compilers). 1996. Pelagic longline 

fishery-sea turtle interactions: Proceedings of an industry, academic and government 

experts, and stakeholders workshop held in Silver Spring, Maryland, 24-25 May 1994. 

NOAA Technical Memorandum. NMFS-OPR-7. 77 pages. 

Witzell, W.N. and J. Cramer. 1995. Estimates of sea turtle by-catch by the U.S. pelagic longline 

fleet in the western north Atlantic Ocean. NOAA Technical Memorandum NMFSSEFSC-359. 14 pages. 

______________________________________________________________________________ 

Editors' Note 

The Workshop presented in these proceedings brought together scientists, managers, commercial 

fishermen, and conservationists to identify the important variables for an experiment and to 

develop the experimental design reported above. However, following the Workshop, further 

power analyses of the experimental design (see J. Wetherall's chapter in this report) indicated 

that the number of variables should be reduced to ensure that statistically rigorous analyses 

would be possible. The US National Marine Fisheries Service awarded the Archie Carr Center 

42 
for Sea Turtle Research at the University of Florida a contract to conduct the modified 

experiment in collaboration with the University of the Azores (DOP/Horta). The modified 

experiment will evaluate the effect of 3 different types of hook (Mustad # 76800 D 9/0 [straight J 

hook], Mustad # 76801 D 9/0 [reversed/offset J hook], Mustad # 39960 ST 16/0 [circle hook]) on 

sea turtle bycatch and the target species in the swordfish longline fisheries in the Azores. There 

are to be 100 sets of 1500 hooks per set with the hook types individually alternating throughout 

the set with bait kept constant (squid). There will be 8 hooks between each buoy to ensure that 

hook type and hook position vary relative to the buoys. The experiment is to be conducted from 

July - December 2000. 

43 
Statistical Power of the Azores Longline Experiment 

Jerry A. Wetherall 

National Marine Fisheries Service 

2570 Dole Street 

Honolulu, HI 96822 USA 

email: jwethera@honlab.nmfs.hawaii.edu 

Objective

The objective of this analysis was to estimate the statistical power of F tests of the main 

treatment effects in a 2-way factorial experiment with 3 treatment levels for the first factor 

(factor A) and 2 levels for the second factor (factor B), assuming both effects are fixed. This 

ANOVA design is applicable to a swordfish longline experiment planned for the Azores to 

assess the effects of longline gear manipulation on incidental take rates of loggerhead turtles. 

Each longline set is considered a randomized block or replicate and the experimental sampling 

unit is assumed to be a 24-hook basket of longline gear. Within each longline set, each of the 6 

treatment combinations is repeated 7 times. 

For the purposes of this exercise assume that the factors have independent and additive 

effects; i.e., there are no treatment interactions. Let Fij denote the average treatment response 

within an experimental unit (i.e., the mean number of turtles taken per 24-hook basket) when 

factor A is at level i and factor B is at level j (i=1, 2, 3; j=1, 2). In terms of the experimental 

factors, the mean response for treatment combination {i,j} is: 

Fij = F11 + (i - 1) δA + (j - 1) δB for i = 1, 2, 3 and j = 1, 2

where F11 is the average response under "base conditions", defined as the treatment combination 

giving the lowest average take rate. The symbols δA and δB are increments in the mean response 

relative to the base conditions associated with factors A and B, respectively. In a balanced 

experiment with this design the overall mean take rate for the experiment is:

F = F11 + δA + 2 δB. 

where a dot subscript indicates averaging over all levels of a factor. 

Under the 2-way ANOVA, F statistics are generated that provide tests of the null 

hypotheses: 

AH0: Fi. = F for all i 

 and BH0: F.j = F for all j

against the alternative that at least one of the marginal means for each factor differs from F. 

The power of the F tests was estimated with respect to specific alternative hypotheses. In 

particular, power was computed with respect to the alternative hypotheses: 

44 
AHA: F1. = F - δA

F2. = F

F3. = F + δA

and BHA: F.1 = F - 2 δB

F.2 = F + 2 δB

These are equivalent to: 

AHA: F2. = F1. + δA

F3. = F1. + 2 δA

and BHA: F.2 = F.1 + δB

Azores Design

For the Azores experiment, the A factor was assumed to be hook type, to be studied at 3 

levels: circle hook, straight J hook and offset J hook. The B factor is bait type, to be tested at 2 

levels: squid and mackerel. The table of treatment means looks like this: 

Bait Type

Hook Type

Squid Mackerel 

Row 

Means 

Circle F11 F12 F1.

Straight J F21 F22 F2.

Offset J F31 F32 F3.

Column Means F.1 F.2 F

It was assumed that under current conditions swordfish longliners in the Azores use primarily 

straight J hooks baited with either squid or mackerel. Thus current conditions are essentially 

indicated by the second row mean, F2. (the shaded cell in the table above). Note that the average 

take rate in the experiment, F, will be equal to F2., the assumed mean take rate for the "current" 

conditions. 

45 
Parameter Settings 

Statistical power of the F test depends on (1) sample size (number of experimental 

sampling units); (2) the magnitude of the treatment effects to be detected; (3) variation in 

treatment effects (responses) among sampling units; and (4) Type I error probability (α level). 

These conditions were specified as follows: 

(1) The overall sample size was fixed at 80 longline sets x 6 treatment combinations x 7 repeat 

observations or 3,360 baskets. Each longline set (replicate) involves 42 baskets and 1,008 hooks. 

(2) The magnitude of the treatment effects depends on the average take rate under base 

conditions (F11), and the increments (δA and δB) associated with each factor. Data collected by 

observers in the Azores fishery during May-December 1998 (151 observed sets) indicate a mean 

take rate of 0.19 turtles per 1,000 hooks under current conditions. In keeping with the design 

assumption above, this take rate is therefore regarded as an estimate of F2. and F. For simplicity, 

it was also assumed that δA = δB = δ. Further, the increment δ was expressed as a fraction of the 

current mean take rate: δ = γF2. where the parameter γ ranges from 0 up to a maximum value 

dependent on the design. In the Azores design, γ has a maximum value of 2/3. Using these 

relationships, the mean take rate under base conditions (F11) can be computed for any feasible 

combination of F2. and γ. Values of the other cell means follow readily from the design 

assumptions and constraints. 

(3) Sampling variance refers to the variance in turtle takes at the scale of the sampling unit, i.e., 

per 24-hook basket. A related measure of variability for which estimates are more readily 

available is the variance in mean turtle take per 1,000 hooks as computed among sets; this is 

proportional to the variability in take rate among baskets. It is convenient to specify the level of 

variability in terms of the parameter ω, the ratio of the variance in take per 1,000 hooks at the set 

level to the mean take rate. In the Azores fishery, the observer data indicate that ω = 0.95, i.e., 

the number of takes per 1,000 hooks at the set level is approximately a Poisson variate (ω = 1.0). 

The information about take rate variability under current conditions, combined with other 

assumptions (e.g., how the mean and variance of take rate are related; see below) allows us to 

compute average rate variability for the entire experiment. 

(4) Type I error in the F tests was set at 5% (i.e., α = 0.05). 

Computational Method 

Power was estimated for several combinations of F2. and γ, with F2. ranging from 0.2 to 

2.0 and γ from 0.1 to the maximum value of 0.67 (Tables 1 and 2). The lowest value of F2.

considered is 5-10 times lower than the mean take rate reported at the 1998 Horta planning 

meeting (the latter figure was apparently based on summary information from a couple of 

observer trips). 

Power was estimated by simulating the longline experiment 500 times under each set of 

conditions, conducting the appropriate ANOVA F tests, and observing the proportion of times 

46 
AH0 and BH0 were rejected under the specified alternative hypotheses. Take data for each basket 

in an experiment were generated from a stochastic model of the take process parameterized with 

the appropriate take rate distribution. The model invented for this purpose was a 2-stage 

Bernoulli-Poisson mixture model. This model assumes that each basket of hooks deployed has a 

specified probability β of not encountering turtles at all, e.g., due to patchiness of the turtle 

distribution; in this event none are taken. If a basket does encounter turtles (with probability 1 - 

β) the number of turtles taken (including possibly 0) is Poisson with a specified mean take rate. 

The β parameter was estimated from the current take rate conditions, and a Poisson parameter 

was computed for each cell of the design based on the value of β and the expected take rate in 

the cell. For purposes of the simulation, the minimum value of ω at the basket level was set at 

1.01 (i.e., take rates were always over-dispersed). This is just slightly greater than the variance 

indicated by the observer program data. Likewise, the minimum take rate considered was 0.2, 

slightly higher than the estimated current conditions. 

Power estimates derived from the simulations were checked against the power curves 

published by Pearson and Hartley (Biometrika, Vol. 38, 1951, p. 112) and reprinted in various 

other references. These curves are based on the non-central F distribution. The non-centrality 

parameters required to use the power charts were calculated in each simulation as a function of 

the sample size, overall variance, proportional effect, and other parameters. In each case, 

comparisons of simulation results with charted values showed the simulation results to be 

accurate. 

Results

Results are given in Tables 1 and 2. The first row in each table is for F2. = 0.2, roughly 

the current conditions in the fishery. In this case reasonable power levels (say, > 80%) with 

respect to AH0 cannot be achieved under the design constraints assumed (Table 1). Tests of BH0

are even less powerful than those for AH0, for effects of the same magnitude (Table 2). 

In the second row of results, which assume F2. = 0.5, power is greater but differences 

between marginal means of the A-factor will need to be 60% or greater for reasonably powerful 

tests of AH0. Tests of BH0 are still not possible with sufficient power. 

With F2. = 1.0, there is sufficient power to detect differences between marginal means of 

the A-factor greater than about 40% and differences among marginal means of the B-factor 

greater than about 60%. 

With F2. = 2.0, there is sufficient power to detect differences between marginal means of 

the A-factor greater than about 30% and differences among marginal means of the B-factor 

greater than about 45%. 

Comments

(1) Power would be increased by accepting a higher level of Type I error (say α = 0.10), but I 

have not computed these cases. 

47 
(2) Other things remaining equal, the power of the F tests can be increased by dropping one of 

the experimental factors, resulting in a single-factor experiment with the same total sample size, 

or to increase the sample size, e.g., by increasing the number of sets. For example, with a 

proportional difference of γ = 0.5 in a single-factor experiment studying factor A at 3 levels, the 

F test would have a power of about 80% when the current mean take rate is 0.5 turtles per 1,000 

hooks. Under the 2-factor design, the power is only 65% (Table 1). 

(3) Here it was assumed that the response variable was simply the number of turtles taken in a 

basket. For treatments like hook type, however, the appropriate variable may be more complex, 

e.g., involving not only take rate but some score related to severity of injuries sustained in the 

hooking, etc. How should this be handled? 

Table 1. Approximate power of F test for detecting proportional differences in the mean take 

rate of turtles (γ) between 3 hook types given assumed current mean take rate (turtles per 1,000 

hooks, F2.). Assumes α = 0.05 and ω = 1.01. 

γ

F2.

0.1 0.2 0.3 0.4 0.5 0.6 0.67 

0.2 <0.30 <0.30 <0.30 <0.30 0.32 0.38 0.46 

0.5 <0.30 <0.35 0.31 0.43 0.65 0.79 0.88 

1.0 <0.30 0.30 0.47 0.75 0.91 0.98 >0.99 

2.0 <0.30 0.43 0.79 0.96 >0.99 >0.99 >0.99 

48 
Table 2. Approximate power of F test for detecting proportional differences in the mean take 

rate of turtles (γ) between 2 bait types given assumed current mean take rate (turtles per 1,000 

hooks, F2.). Assumes α = 0.05 and ω = 1.01 . 

γ

0.1 0.2 0.3 0.4 0.5 

F2.

0.6 0.67 

0.2 <0.30 <0.30 <0.30 <0.30 <0.30 <0.30 0.31 

0.5 <0.30 <0.30 <0.30 0.30 0.35 0.47 0.56 

1.0 <0.30 <0.30 0.31 0.42 0.60 0.76 0.84 

2.0 <0.30 0.30 0.47 0.72 0.88 0.97 0.99 

49 
Closing Remarks

Helen R. Martins 

According to our first agenda our Director, Ricardo Santos, was to have closed this workshop. 

However, as he had to be away on other duties, the task was left to me. 

First of all, I would like to thank profoundly our colleague Alan Bolten for the initiative, 

enthusiasm and patience he has shown in order to bring the workshop to a successful conclusion, 

and also Jerry Wetherall of the National Marine Fisheries Service who came a long way from 

Hawaii to support us. We are very grateful to the fishermen who sacrificed their time to help us 

with their expertise. 

A special thank you to my colleagues at DOP who presented information that made us better 

understand our objective. 

Many thanks to all of you! 

Comentários de encerramento 

Segundo a primeira teríamos o nosso Director Ricardo Santos a afzer o encerram, ento do 

workshop. Porém, ele teve outros compromissos e a tarefa passou para mim. 

Antes de mais, quero agradecer profundamente ao nosso colega Alan Bolten pela sua iniciativa, 

entusiasmo e paciência com o fim a levar a cabo com sucesso este projecto e ao Jerry Wetherall 

do National Marine Fisheries Service do E.U.A. que fez a longa viagem do Hawaii para nos 

apoiar e aos pescadores que fizeram o sacrifício de nos dar algum do seu precioso tempo para 

nos ajudar. Também agradeço aos meus colegas no DOP que apresentaram comunicações para 

nos ajudar a perceber melhor o nosso objectivo. 

Para todos, muito obrigada! 

50