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Latin american journal of aquatic research

On-line version ISSN 0718-560X

Lat. Am. J. Aquat. Res. vol.37 no.3 Valparaíso  2009

 

Lat. Am. J. Aquat. Res., 37(3): 327-346, 2009
DOI: 10.3856/vol37-issue3-fulltext-5

Research Article

 

The deep-sea shrimp fishery off Brazil (Decapoda: Aristeidae): development and present status

La pesquería de gambas de profundidad en Brasil (Decapoda: Aristeidae): desarrollo y estado actual

 

Rodrigo Dallagnolo1, José Angel Alvarez Perez1, Paulo Ricardo Pezzuto1 & Roberto Wahrlich1

1Universidade do Vale do Itajaí, Centro de Ciencias Tecnológicas da Terra e do Mar Rúa Uruguai 458, CEP 88.302-202, Itajaí, SC, Brazil. Corresponding author: Rodrigo Dallagnolo (rdallagnolo@univali.br)


ABSTRACT. The development of a deep-sea fishery for aristeid shrimps off Brazil is reviewed from its early days in 2002. Descriptive data were collected by observers on board 75 directed fishing trips conducted in the study period, with a total of over 15,000 monitored trawls. An incipient fishing phase took place between No-vember 2000 and October 2002, when aristeid shrimps were occasionally reported in the bycatch of operations mostly targeting the Argentine hake (Merluccius hubbsi). After that, a directed fishery was established for these resources. All nine vessels involved in this fishery (one national and eight chartered) concentrated on 11 limited grounds between 700 and 800 m deep and 18°S and 34°S. The main species caught between November 2002 and May 2007 was the "carabinero" Aristaeopsis edwardsiana (456,710 kg), followed by the "moruno" Aristaeomorpha foliácea (121,497 kg), and then the "alistado" Aristeus antillensis (27,919 kg). The trawlers operate in conjunction, such that the total area of each fishing ground was swept at least twice. This harvest pattern substantially reduced "carabinero" catch rates from 14 kg hour-1 in the first sampled trimester to 4 kg hour-1 in the last. Despite the inferred biomass reduction of this species, the fishery has continued without a formal management plan.

Keywords: trawl fishery, deep-water shrimps, Aristeidae, Brazil.


RESUMEN. Se revisa el desarrollo de una pesquería en aguas profundas dirigida a gambas aristeideas en Brasil. Desde su inicio, en 2002, los datos descriptivos fueron obtenidos por observadores a bordo de 75 viajes de pesca realizadas en ese período que resultaron en más de 15.000 arrastres monitoreados. Una fase incipiente de la pesquería se estableció entre noviembre de 2000 y octubre de 2002, cuando gambas aristeideas fueron registradas en la captura accidental de operaciones de pesca dirigidas principalmente a la merluza-argentina (Merluccius hubbsi). A ésta sobrevino una fase dirigida en que participaron nueve arrastreros (uno nacional y ocho arrendados). Estos buques concentraron sus operaciones en 11 fondos de pesca angostos entre 700 y 800 m de profundidad y los paralelos 18°S y 34°S. Las principales especies capturadas entre noviembre de 2002 y mayo de 2007 fueron el "carabinero" Aristaeopsis edwardsiana (456,710 kg), seguido del "moruno" Aristaeomorpha foliácea (121,497 kg), y el "alistado" Aristeus antillensis (27,919 kg). Los arrastreros operaran de forma agregada y esto hace que el area total de cada zona de pesca haya sido arrastrada al menos dos veces. Este patrón de explotación ha producido reducciones substanciales en las tasas de captura del "carabinero" que varió de 14 kg hora-1 en el primer trimestre de monitoreo a 4 kg hora-1 en el último. A pesar de la aparente reducción de biomasa de esta especie, la pesquería ha continuado sin un plan formal de manejo.

Palabras clave: pesca de arrastre, gambas de aguas profundas, Aristeidae, Brasil.


INTRODUCTION

The recent development of deep-water fisheries off Brazil has been strongly influenced by a foreign vessel-chartering program implemented by the Brazilian government in 1998. From 2000 onwards, large ves-seis operating gillnets, longlines, trawls, and traps occupied virtually unexplored areas of the continental slope and established unprecedented fishing regimes on shellfish and finfish species, including deep-sea crabs (Chaceon notialis and C. ramosaé), the argentine shortfin squid (Illex argentinus), the monkfish (Lophius gastrophysus), the Argentine hake (Merluccius hubbsi), and others (Pérez et al., 2003). Because these chartered operations were intensely monitored by observers and VMS (satellite vessel monitoring systems) as part of their legal obligations, a large amount of ishing and biological data was made avail-able and used in the elaboration of preliminary stock assessments and management plans for these resources (Pérez et al., 2002a, 2002b, 2003, 2005; Wahrlich et al., 2004; Pérez & Wahrlich, 2005; Pezzuto et al., 2006a).

As these slope fisheries intensified, principally off the southeastern and southern sectors of the Brazilian coast, new resources were recorded as bycatch components, most notably, the valuable deep-sea shrimps of the family Aristeidae. In late 2002, as productive concentrations of these resources were identified, a new directed trawl fishery began to develop, the latest and deepest since the onset of the chartering program (Pezzuto et al., 2006b; Pérez et al., 2009a).

This paper reviews the initial five years of the deep-sea shrimp fishery off the Brazilian coast, adding complementary new data on the early development phase (2000-2004) previously described by Pérez et al. (2009a) and Pezzuto et al. (2006b). The study also characterizes the temporal and spatial trends of the fishery through the subsequent, more dynamic period (2004-2007).

MATERIAL AND METHODS

Fishing data were obtained from commercial operations conducted on the continental slope off the southeastern and southern sectors of the Brazilian coast, delimited by the parallels 18°S and 34°S and by the 200 to 1000 m isobaths (Fig. 1). This gives a surface area of 250,000 km2, averaging 1,600 km in length and 150 km in width and characterized by topographic irregularities including plateaus and submarine can-yons (Zembruscki, 1979).


Figure 1. Study area in southeastem and southern Brazil, with an emphasis on the continental slope between 200 m and 1000 m depth and the latitudinal limits of the aristeid shrimp trawling operation sectors. Abbreviations refer to major states inthe study area: MG: Minas Gerais, ES: Espirito Santo, RJ: Río de Janeiro, SP: São Paulo, SC: Santa Catarina, RS: Rio Grande do Sul, and PR: Parana.

Figura 1. Área de estudio en el sureste y sur de Brasil con énfasis en el talud continental entre 200 y 1000 m de profundidad y límites latitudinales de los sectores de operación de la pesca de arrastre dirigida a las gambas aristeideas. Las abreviaturas se refieren a los estados en el area de estudio, MG: Minas Gerais, ES: Espirito Santo, RJ: Río de Janeiro, SP: São Paulo, SC: Santa Catarina, RS: Río Grande do Sul y PR: Paraná.

All analyzed data originated from satellite VMS and observers on board all chartered-fleet fishing operations conducted from October 2000 to May 2007. Each trawl conducted by chartered vessels within this period was described by position, date, time, and depth (m) at deployment and retrieval, as well as the trawl speed (knots), trawl duration (h), head rope length (m), mesh size at cod-end (mm), and catch composition (kg). The nationalized trawler was the only one not subjected to the VMS or obligatory observers. Logbooks were the only source of this vessel's catch and effort information, as provided by the vessel skipper for nine fishing trips between 2005 and 2006.

Catch (kg), effort (trawled hour), and catch rate (kg hour-1 ) variability were summarized by year and trimester, considering the different aristeid shrimp species separately. Spatial patterns of the fishing area occupation, catch, and effort were analyzed through VMS-generated individual positions during the fishing trips as well as geographic trawl positions as recorded by observers. Deployment and retrieval positions for individual trawls conducted by the entire fleet in each year were plotted on a cartographic basis and fishing sectors were delimited, following Pezzuto et al. (2006b): (a) northern, between 18°20'S and 22°S; (b) central, between 22°S and 26°S; and (c) southern, between 26°S and the southernmost limit of the Brazilian EEZ (Fig. 1). Fishing sectors were further subdivided into fishing grounds as delimited by the isobaths that enclosed 80% of the fishing trawls. Each fishing ground was referenced by a capital letter N, C, or S, according to the sector (northern, central, or southern) in which it was identified and followed by a number that increased from south to north (i.e. Cl was the southernmost fishing ground of the central fishing sector).

The surface areas of ishing sectors and fishing grounds were calculated by transforming latitude and longitude coordinates into UTM and then converting these into metric units. All geometric coordinates were referenced on the basis of Datum SAD 1969 (South American Datum) and their transformations consid-ered three UTM zones that cover southeastern and southern Brazil (UTM 22, UTM 23 and UTM 24).

RESULTS

Trawlers, gear, and trawling operations

A total of sixteen chartered trawlers operated in the Brazilian slope waters since the year 2000. Two of them, "Joana" and "Nuevo Apenino", recorded aristeid shrimps as bycatch components. For another eight trawlers, these shrimps were the main target species. All shrimp trawlers were longer than 30 m, powered by approximately 1,000 HP engines, and capable of performing fishing trips lasting over one month (Table 1).

A variety of trawl nets were employed by these vessels, most of them differing in head rope length, which ranged from 45 to 95 m, and mesh size, which ranged from 40 to 80 mm (Figs. 2a and 2b).


Figure 2. Distribution of the a) head rope length and b) codend mesh size used in the fishing nets for the capture of aris-teid shrimps off Brazil between November 2002 and May 2007. The vessels are identified as: ALB (Albamar). CGR (Costa Grande), FAV (Favaios), KAY (Kayar), LCAST (Lago Castiñeras), MMA (Mar María), NOE (Noé), and TBl (TBl). The box in the middle indicates the quartiles of the distribution and the median (horizontal line). The "whiskers" show the largest/smallest observations that fall within a distance determined to be 1.5 times the length of the box.

Figura 2. Distribución de a) las dimensiones de la relinga y b) de la malla del copo de la red utilizados en las redes de arrastre para la captura de gambas aristeideas en la costa de Brasil entre noviembre de 2002 y mayo de 2007. Se identifican los buques por las abreviaciones ALB (Albamar), CGR (Costa Grande), FAV (Favaios), KAY (Kayar), LCAST (Lago Castiñeras), MMA (Mar María), NOE (Noé) e TBl (TBl). La "caja" central indica los quartiles de la distribución y la mediana (línea horizontal). Las lineas "wiskers" representan las mayores/ menores observaciones dentro de un rango definido como 1,5 veces el largo de la "caja".

Excluding those fishing operations where deep-sea shrimps were considered to be by-catch, a total of 75 fishing trips, around 15,000 trawls, and over 63,000 trawled hours were focused on aristeid shrimps off southeastem and southem Brazil from 2002 to 2007 (Table 1). Trawl velocity ranged between 2 and 3 knots, although faster (4.0- 4.5 knots) and slower (under 2.0 knots) trawls were also recorded (Fig. 3a). The duration of trawls was normally distributed around a mean value of 4.06 h (±0.007 SE) (Fig. 3b). The product of both variables (trawl velocity and duration) allowed us to estímate that each trawl swept an aver-age linear extensión of approximately 21 km, with maximum values of 73 km (Fig. 3c). Wing spread was estimated as approximately half of the head rope length as proposed by Sparre & Venema (1997). This measure, when multiplied by the trawl length values, indicated that each trawl swept a mean surface area of 0.73 km2 (Fig. 3d). However, this surface frequently surpassed 1 km2 and reached 2.3 km2 in extreme cases.


Figure 3. Fishing strategies adopted by the chartered trawlers for the aristeid shrimp fishery off Brazil between November 2002 and May 2007.

Figura 3. Estrategias de pesca empleadas por los arrastreros arrendados en la pesca de gambas aristeideas en la costa de Brasil entre noviembre de 2002 y mayo de 2008.

Catch composition

Altogether, these trawlers caught approximately 600 ton of deep-sea shrimps. The "carabinero" shrimp (Aristaeopsis edwardsiana) was the most abundant in the catches, followed by the "moruno" shrimp (Aris-taeomorpha foliácea) and finally the "alistado" shrimp (Aristeus antillensis) (Table 2). Catches of all three species increased steadily until 2005, a trend also ob-served in the total effort as expressed either in number of trawls or trawled hours. In 2006, the fishing effort decreased around 26% (trawled hours) and 24% (number of trawls), coinciding with a 45% and 66% decrease in catches of "carabinero" and "alistado" shrimps and a 21% increase in "moruno" shrimp catches.

Retained and commercialized bycatch were mainly the deep-sea crab Chaceon spp. (128,950 kg), the Argentine hake Merluccius hubbsi (71,426 kg), the gulf hake Urophycis cirrata (25,076 kg), the monkfish Lophius gastrophysus (20,305 kg), and the Argentine shortfin squid Illex argentinus (49,887 kg) (Table 2). In addition, catches included a variety of discarded shellfish and finfish species typical of the lower slope. Although a comprehensive qualitative and quantitative analysis of discards has not been completed, the preliminary identification of specimens collected by observers included bonefishes of the family Synaphobranchidae, Macrouridae, Trachichtidae, Berycidae, Astronestidae, Oreosomatidae, Ipnopidae, Alocephalidae, Ophidiidae, and others. Invertebrates have also been frequently reported and collected, including deep-sea corals such as Flabellum cf. alabastrum (Pires, 2007).

Fishery history

The Portuguese vessel "Joana" was the first trawler to opérate under the chartering program and reported the first catches of "alistado" shrimps in nine out of 300 trawls conducted in late 2000 - early 2001 (Figs. 4a and 4b). One of them at occurred at 32°S (300 m depth; 2.1 kg) and the others were recorded off the coast of the states of São Paulo and Rio de Janeiro at 23°S (384-460 m depth; 18.9 kg) (Table 3). In 2002, the trawler "Costa Grande" operating on slope areas (366.9 m ± 6.3 SE) and targeting mainly monkfish and hake concentrations (Fig. 4c) conducted exploratory trawls in areas deeper than 500 m on two occasions, resulting in new catches (177.3 kg) of aristeid shrimps, particularly in the vicinity of the 700 m iso-bath (Fig. 4d, Table 3). Also in 2002, the trawler "Nuevo Apenino", fishing for hake off the coasts of São Paulo and Rio de Janeiro states (Fig. 4e), conducted 27 trawls in areas deeper than 500 m; most of these produced positive catches of "carabinero" shrimps (Fig. 4f). These were the largest catches recorded during the early development phase (676.67 kg) and also the highest catch rates reported until then (8.9 kg hour1 ± 2.5 SE) (Table 3).


Figure 4. Geographic position of all fishing tows (left column) and of the fishing tows with incidental catches of aristeid shrimp fishery (right column) conducted by the vessels Joana (a and b), Costa Grande (c and d) and Nuevo Apenino (e andf).

Figura 4. Posición geográfica de todos los lances de pesca (columna de la izquierda) y de los lances de pesca con capturas incidentales de gambas aristeideas (columna de la derecha) realizados por los buques Joana, (a y b) Costa Grande (c y d) y Nuevo Apenino (e y f).

Further concentrations of "carabinero" and "alistado" shrimps were also found in exploratory fishing conducted by the trawler "Mar Maria" in the northern sector of the Brazilian coast, off the coasts of the states of Amapá and Para, between 1°-6°N and 45o-51°W (Asano-Filho et al., 2005; Pezzuto et al., 2006b; Pérez et al., 2009a) (Table 3). Whereas all aristeid shrimp catches reported above were minor compo-nents of the total catches, they were profitable enough to stimulate a new fishing phase, the deepest ever recorded in the country (Pezzuto et al., 2006b; Pérez et al., 2009b). Thus, the chartered trawlers "Costa Grande" and "Mar María" pioneered the fishery, targeting aristeid shrimps in 2003 with lower slope trawling operations (Fig. 5). In the following year, as the former vessels abandoned Brazilian waters, five new trawlers entered the fishery under the chartering program composing, in 2003 and 2005, the largest fleet operating simultaneously on these slope areas. In 2006, this fleet was reduced to four units, including a new nationalized vessel. In 2007, only the latter vessel and "Mar María" maintained their operations on aristeid shrimps of Brazil (Fig. 5).

Until the end of 2004, the central (22-26°S) sector concentrated all the fishing effort. In 2005, the new vessels "Favaios", "Albamar", "Lago Castiñeras", and "Kayar" started to fish in the northern (north of 22°S) and southern (south of 26°S) sectors, thereby expand-ing the fishery to the entire latitudinal extensión of the slope off southeastern and southern Brazilian (Fig. 5).


The "carabinero" shrimp dominated the catches in all fishing sectors and was particularly abundant in the central sector and virtually the only species caught in the southern sector. The "moruno" shrimp, which is the second species in terms of total catches, was caught predominantly in the central sector, although catches in 2005 were considerably higher in the northern sector. The "alistado" shrimp was caught most abundantly in the northern sector throughout the entire fishing period (Table 4). The fishing effort was particularly concentrated in the central sector, peaking in 2005 with 2,911 trawls and 11,844 trawled hours ex-erted on this sector. In 2007, the effort tended to be evenly distributed throughout the entire fishing area.


Table 4. Geographic distribution of the fishing effort and catches of aristeid shrimps of Brazil between November 2002 and May 2007. Number of tows (tows); trawling hours (trawl); and catches of Aristaeopsis edwardsiana, Aristaeomorpha foliácea and Aristeus antillensis.

Tabla 4. Distribución geográfica del esfuerzo pesquero y capturas de gambas aristeideas en la costa de Brasil entre noviembre de 2002 y mayo de 2007. Número de arrastres (tows); horas de arrastre (trawl); capturas de Aristaeopsis edwardsiana, Aristaeomorpha foliácea y Aristeus antillensis.

Fishing grounds and intensity

In all fishing sectors, the trawls tended to concentrate on a narrow bathymetric stratum between 700 and 750 m depth (Fig. 6). An analysis of the distribution of ishing trawls on a finer spatial resolution allowed the definition of particular fishing grounds within the defined sectors where fishing activity was intense.


 

Figure 6. Distribution of individual tow depths in opera-tions targeting aristeid shrimps off Brazil by latitudinal sector between November 2002 and May 2007. The box in the middle indicates quartiles of the distribution and the median (horizontal line). The "whiskers" show the largest/smallest observations that fall within a distance determined to be 1.5 times the length of the box. Observations falling outside the referred limits are shown sepa-rately as individual dots.

Figura 6. Distribución de las profundidades de los lances de pesca dirigidos a la captura de las gambas aristeideas por sector latitudinal en la costa de Brasil entre noviembre de 2002 y mayo de 2007. La "caja" central indica los quartiles de la distribución y la mediana (línea horizontal). Las líneas "whiskers" representan las menores/mayores observaciones dentro de un rango definido como 1,5 veces el largo de la "caja". Observaciones fuera de los límites referidos son representadas por separado como puntos individuales.

The central sector enclosed four localized fishing grounds intensely exploited since 2002 (Fig. 7a). The first trawling operations targeting "carabinero" shrimp concentrations occupied a northern fishing ground (C3). In the following year, the fishing area extended southwards, promoting the occupation of ishing grounds Cl and C2. By 2005, the last fishing ground (C4) was established in the northern extreme of this sector (Fig. 7a).


 

Figure 7. Fishing grounds on the middle slope of the a) central, b) north, and c) south sectors used by the char-tered trawlers for the aristeid shrimp fishery off Brazil.

Figura 7. Áreas de pesca en el talud central de los sectores a) central, b) norte y c) sur utilizados por los arrastre-ros fletados en la captura de gambas aristeideas en la costa de Brasil.

The exploitation of the northern sector began in 2004 and was concentrated in two well-defined fishing grounds (N2 and N4) (Fig. 7b). In the following year, a small fishing ground was established on the western side of the Besnard seamount, a component of the "Vitória-Trindade" chain (N3). In 2006-2007, a last fishing ground began to be exploited at the southern extreme of this sector (NI) (Fig. 7b). Three fishing grounds were exploited within the southern sector between 2005 and 2007 (SI, S2, S3) (Fig. 7c); a major submarine canyon separates S1 and S2.

The surface area of all the fishing grounds was lim-ited, ranging between 125 km2 and 1,227 km2 (Table 5). In the central sector, the largest fishing grounds, C2 and C3, were trawled for almost 30,000 hours in total, accumulating nearly 45% of all fishing effort. The entire surface area of the fishing grounds Cl, C2, and C3 was swept approximately two times. C4, the last ground to be fished by the trawl fleet, was swept 1.5 times over nearly one year of exploration (Fig. 8a). Most of the trawling efforts in the northern sector were concentrated in grounds N2 and N3 (Table 5). These grounds and N4 were fully swept at least 2.5 times, whereas NI was swept 1.5 times. In the case of N3, which only began to be explored after mid-2005, the activity was much more intense than in the other grounds; in only six months, its surface area had been completely swept twice (Fig. 8b). In the southern sector, grounds SI and S3 concentrated most of the trawling effort (Table 5) and had their entire surface areas swept once (Fig. 8c). Nevertheless, these grounds were less trawled than those of the central and northern sectors.


Table 5. Catches, fishing effort, and surface areas of the fishing grounds explored by the chartered trawlers targeting aristeid shrimps off Brazil between November 2002 and May 2007. NA: tows conducted outside the fishing grounds and northof 18°20'S.

Tabla 5. Capturas, esfuerzo de pesca y area de los fondos de pesca explotados por arrastreros arrendados para la pesca de gambas aristeideas en la costa de Brasil entre noviembre 2002 y mayo 2007. NA: arrastres realizados fuera de los fondos de pesca y al norte de 18°20'S.


 

Figure 8. Cumulative curves of the area swept daily by the aristeid shrimp trawl fishery off Brazil. values were weighted by the surface of each fishing ground within the latitudinal sectors a) south, b) central, and c) north. Vertical lines delimit the years of exploitation.

Figura 8. Curvas cumulativas de las areas barridas diariamente por la pesca de arrastre dirigida a las gambas aristeideas en la costa de Brasil. Los valores fueron ponderados por la superficie de cada area de pesca dentro de los sectores latitudinales sur (a), central (b) y norte (c). Las líneas verticales delimitan los años de explotación.

The largest catches of "carabinero" shrimps were recorded in fishing grounds C2 and C3. The largest catches of "moruno" shrimp originated firom fishing grounds C3, C4, and NI. The largest catches of "alistado" shrimp were obtained in fishing grounds N2 and N4. In the central sector, the "carabinero" shrimp dominated the trawlers' catch except for the fishing ground C4, where "moruno" shrimp catches surpassed those of all other species (Table 5). However, an in-creasing proportion of the latter species was noticeable in the catches of 2006, particularly in fishing grounds Cl, C2, and C3, as the proportion of "carabinero" shrimp declined (Fig. 9).


 

Figure 9. Relative composition of the three species of aristeid shrimps in annual catches obtained by operations in the fishing grounds of the central sector, southeastern Brazil. Data firom 2007 refer to the first semester only.

Figura 9. Composición relativa de las tres especies de gambas aristeideas en las capturas anuales obtenidas en las areas de pesca del sector central, sureste de Brasil. Datos de 2007 se refieren al primer semestre.

In the northern sector, this trend was not observed with the same clarity (Fig. 10). The proportion of shrimp species in the catches firom fishing ground NI remained stable, whereas the proportion of shrimp species alternated in the catches firom fishing grounds N2,N3, and N4 (Fig. 10).


 

Figure 10. Relative composition of the three species of aristeid shrimps in annual catches obtained by operations in the fishing grounds of the north sector, southeastern Brazil. Data firom 2007 refer to the first semester only.

Figura 10. Composición relativa de las tres especies de gambas aristeideas en las capturas anuales obtenidas en las areas de pesca del sector norte, sureste de Brasil. Datos de 2007 se refieren al primer semestre.

Catch rate

The "carabinero" shrimp sustained the highest mean catch (14 to 4.7 kg hour-1 ) rates throughout the entire period (2004-2007) (Fig. 11). These rates tended to decline locally and were generally higher as the different fishing sectors were exploited for the first time (Table 6).


 

Figure 11. Mean yields (kg hour-11) and standard errors (vertical bars) of Aristaeopsis edwardsiana for each quarter of the trawl fishery off Brazil in the a) central sector, b) north sector, and c) south sector.

Figura 11. Rendimientos medios (kg hora-1) y error patrón (líneas verticales) de Aristaeopsis edwardsiana en cada trimestre de la pesquería de arrastre en la costra de Brasil, a) sector central, b) sector norte y c) sector sur.


Table 6. Annual meanyields (kg hour-11) of Aristaeopsis edwardsiana, Aristaeomorpha foliacea, and Aristeus antillensis obtained by chartered trawlers within each latitudinal sector. Standard errors are given between brackets.

Tabla 6. Rendimientos anuales (kg hora-1) de Aristaeopsis edwardsiana, Aristaeomorpha foliácea y Aristeus antillensis obtenidos por arrastreros arrendados dentro de los sectores latitudinales. Valores del error estándard entre paréntesis.

Annually, mean catch rates declined steadily in all fishing sectors. In the central sector, mean catch rates decreased 61% between 2002 and 2007. The same was observed in the northern sector, where mean catch rates declined 36% from 2004 to 2006, increasing slightly in 2007. In the southern sector, catch rates dropped 26% in the first year of exploitation (2005-2006), stabilizing in 2007. "Carabinero" shrimp catch rates also exhibited seasonal variations, peaking every year in the fourth trimester. This pattern has been consistently observed in the central and southern sectors and is less pronounced in the northern sector.

The catch rates for "moruno" shrimp were generally lower than those of the "carabinero" shrimp (6.3 to 0.76 kg hour-11) (Fig. 12). The annual variation of the former, however, exhibited a contrasting pattern in relation to the latter species i.e., it tended to increase in the last years of deep-sea shrimp exploration. In the central and northern sectors, the catch rates increased 327% and 835% from 2002 to 2006 (Table 6). In 2006, the "moruno" shrimp catch rates were comparable with those of the "carabinero" shrimp, unlike the early fishery, when the latter species was significantly more productive. Within-year catch rate variations were clearly distinguished in the northern sector, with peaks in the fourth trimester. In the central sector, seasonal variations were not as clearly defined, al-though lower catch rates were generally obtained for each year in the first trimester.


 

Figure 12. Mean yields (kg hour-11) and standard errors (vertical bars) of Aristaeomorpha foliácea for each quarter of ishery off Brazil in the a) central sector and b) north sector.

Figura 12. Rendimientos medios (kg hora-1) y error patrón (líneas verticales) de Aristaeomorpha foliácea en cada trimestre de la pesquería de arrastre en la costa de Brasil, a) sector central y b) sector norte.

Catch rates of the "alistado" shrimp were, on aver-age, the lowest among deep-sea shrimps (2.4 to 0.005 kg hour-1 ) (Fig. 13). In the northern sector, however, the contribution of this species to the total aristeid shrimp catch was significantly higher than in the central sector, where it never surpassed 1.0 kg hour-1 (Table 6). In the northern sector, catch rates de-creased around 65% between 2004 and 2007. In contrast with the other deep-sea shrimps exploited off Brazil, no within-year cyclic variation could be distinguished for the catch rate of "alistado" shrimps.


 

Figure 13. Mean yields (kg hour-11) and standard errors (vertical bars) of Aristeus antillensis for each quarter of ishery off Brazil in the a) central sector and b) north sector.

Figura 13. Rendimientos medios (kg hora-1) y error patrón (líneas verticales) de Aristeus antillensis en cada trimestre de la pesquería de arrastre en la costa de Brasil, a) sector central y b) sector norte.

DISCUSSION

The descriptive analysis of the first five years of deep-sea shrimp exploration off Brazil revealed general patterns closely resembling aristeid fisheries else-where in the world. In French Guiana, the main fishing grounds are located between 400 and 900 m deep and most catches occur in the second half of the year in the vicinity of the 700 m isobath (Guéguen, 2000). Trawl surveys conducted in that area in 1990 obtained shrimp catch rates ranging between 13.2 and 40.6 kg hour-1 ("carabinero") and 0.09 and 0.74 kg hour-1 ("alistado") (Guéguen, 1998, 2000, 2001). In the Mediter-ranean Sea, the "gambero rosso" (Aristaeomorpha foliácea), known as "moruno" in Brazil, and "gamba rosada" (Aristeus antennatus), a species similar to the Brazilian "alistado" (Aristeus antillensis), have been reported to concentrate at 700 m depth cióse to the borders of submarine canyons. Seasonal fluctuations in abundance have also been observed for both species; "gambero rosso" and "gamba rosada" are more productive in summer and winter-spring, respectively (Sarda, 2000). The highest catch rates of the "gambero rosso" shrimp were obtained off the coast of Algeria (around 12 kg hour-1 ), whereas "gamba rosada" shrimps were more productive on the coast of Tunisia (around 15 kg hour-1 ) (Sarda, 2000).

In other regions of the Mediterranean, catch rates have been considerably lower. In the NW Mediterranean, for example, a "gambero rosso" shrimp fishery was sustained for ten years (1991-2001) with catch rates oscillating between 4.55 kg hour-1 and 7.54 kg hour-1 (Carbonell & Azevedo, 2003). Off Brazil, deep-sea shrimp operations also concentrated around the 700 m isobath and catches included the "gambero rosso" exploited in the Mediterranean as well as the "alistado" (Aristeus antillensis) and "carabinero" (Aristaeopsis edwardsiana) shrimps also exploited off French Guiana. At least the "carabinero" and "moruno" shrimps showed seasonal concentrations in the main fishing areas and catch rates for all species ranged between 4.0 and 14.0 kg hour-1 , within the ranges reported for the aristeid fisheries above. Inter-estingly, scientific surveys conducted in 2004 in the northern extreme of the study area (northern sector) lead to the conclusión that these shrimps could not sustain economic exploitation on the basis of very similar catch rate levels obtained in most samplings (Costa et al., 2005). Whereas these levels are indeed remarkably lower than those generally sustained by coastal shrimps, the high market prices of aristeid shrimps allow a profitable commercial exploitation even in the long-term (more than 10 years) such as that observed in the Mediterranean fisheries (Carbonell & Azevedo, 2003).

Another similar pattern found between the Brazilian aristeid shrimp fishery and those sustained else-where in the world is the alternation of dominant species on the fishing grounds. Off the Brazilian slope, catches were generally dominated by the "carabinero" shrimp. As catch rates of this species decreased, pos-sibly as a consequence of heavy fishing, other species, usually the "moruno", tended to exhibit higher propor-tions and to replace the "carabinero" in the catches. In the Gulf of Lion (Mediterranean Sea), the same sce-nario was observed on fishing grounds where the disappearance of "moruno" shrimp resulted in the increase of "alistado" shrimp in catches (Campillo, 1994 fide Cau et al., 2002), although ecological aspects related to this pattern are unclear. But it is possible that the species composition in the catches reflects the natural dominance pattern of the three species in the depth stratum exploited by the trawlers, which, in turn, may be part of the potential outcome of a competition process in the slope areas. In this process, "carabinero" shrimps might have naturally predominated the fishing areas of Brazil, whereas "moruno" and "alistado" shrimps may have been limited to deeper or adjacent areas not exploited by the fishery. Because the "carabinero" attains larger sizes and matures later in life, the species may be better fit for survival and out-compete the others within the 700-800 m stratum. Fishing first removes the highly vulnerable "carabinero" shrimp, opening space on the fishing grounds for smaller and possibly faster-growing "moruno" to ex-pand their distribution. Studies conducted by Pezzuto & Dias (2007) revealed that the "moruno" shrimp has a continuous, year-round reproductive pattern, whereas the "carabinero" shrimp has defined, seasonal reproductive activity. Such distinct reproductive strategies may also provide evidence to support a pos-sible dominance oscillation. Although mostly hypothetical at this point, such an interpretation is partially supported by the results of trawling surveys conducted in the northern sector of the study area (Serejo et al., 2007), revealing discrete bathymetrically-defined crustacean assemblages on the slope. Aristeid shrimps, which occur in areas as deep as 1,800 m, seem to con centrate in the rather narrow 500-700 m depth stratum, as also reported in other areas of the world (Cartes & Sarda, 1992).

Despite the biological and ecological similarities of these resources, fishery regimes have usually been established following different structural and motiva-tional processes, including:

a) Long-term fisheries normally developed in com-bination with the seasonal availability of other demersal resources. In French Guiana, an aristeid fishery has been carried out for 20 years by a local fleet of small trawlers as a seasonal alternative to their main target, the coastal penaeid shrimp Far-fantepenaeus subtilis. Catches are concentrated between June and November, when the abundance of F. subtilis decreases on the shelf areas and that of the "carabinero" increases on the middle and lower slope (Guéguen, 1998). In the Mediterra-nean Sea, this fishery has existed for more than 60 years, conducted by regional fleets of trawlers generally smaller than those operating under the chartering program in Brazilian waters. Mediterranean trawlers concentrate on aristeid shrimp as long as their density is sustained over profitable levels, switching to other valuable resources otherwise (Maynou et al., 2003; Company et al., 2008).
b) Opportunistic exploitation as valuable bycatch components of multispecies trawling operations. In Portugal, small catches of aristeid shrimps are part of a multi-specific, crustacean slope fishery (Monteiro et al., 2001). Only in recent years has a directed fishery for aristeid shrimp been proposed due to its high market value and the overexploitation of traditional resources (Figueiredo et al., 2001).
c) Planned activities considering previously assessed local fishing potential. In Indonesian waters, a directed fishery for aristeid shrimp and other crustaceans only developed after stock assessment allowed for the definition of effort limits and maximum annual caches (Suman et al., 2006). On fishing grounds of the Ionian Sea, virginal populations of aristeid shrimps were intensely studied in order to subsidize the development of a directed fishery under precautionary effort limitations (Papaconstantinou & Kapiris, 2001, 2003).

None of the processes above can be directly related to the development of the Brazilian fishery for aristeid shrimps. In this case, the activity was induced by fishing authorities as a way of obtaining knowledge on stock distribution and availability, fishing and processing technology, and market opportunities (Pérez et al., 2003). This process, however, was not ruled by precaution or a previous delimitation of the stock potentiality but was mostly profit-oriented, fast, uncontrolled, and disorganized. Since its early days, an excessive number of large vessels were allowed to concentrate in very limited areas of the central slope, and the most productive grounds were fully swept (once to twice) in a very short time. The exploration of new sectors of the Brazilian slope were only initiated as catch rates of the "carabinero" shrimp dropped below profitable levels in the central sector. Such exploration, however, followed the same "clean-up" strategy and produced similar local density reductions in the northern and southern slope sectors. Pezzuto et al. (2006b) analyzed this fishery between October 2002 and August 2004, warning about the negative consequences of the kind of ishing regime promoted by the chartered fleet. They concluded that operating large chartered trawlers in very restricted areas of the slope was only justifiable as long as it complemented existing information on deep-sea shrimp concentrations with data from still unexplored areas. In that sense, the interruption of the entry of new vessels into the fishery was recom-mended, along with the establishment of a rotating harvesting strategy that would allow the effort to spread along the Brazilian EEZ. As demonstrated, however, the deep-sea shrimp fishery developed off Brazil after 2004 regardless of these recommenda-tions. In 2007, only two vessels were operating, a natural consequence of the major reduction of catch rates verified in most exploited fishing areas. Al-though producing timely estimates for a valuable and sustainable fishery development, this process rendered a biologically unsafe and unsustainable scenario and proved to be a dangerous strategy, particularly when directed at fragüe deep-sea resources. Whereas the fishing regime established for the aristeid shrimps off Brazil seems to be clearly incompatible with sustained activity, its continuity under any of the patterns de-scribed elsewhere in the world will depend on severe restrictions to the total effort and a complete plan for biomass restoration on most productive grounds.

ACKNOWLEDGEMENTS

The authors are thankful to the Brazilian Government (SEAP/PR/001/2003; SEAP/PR/078/2004; SEAP/PR/ 064/2005; SEAP/PR/027/2007), the team of fisheries observers, and the staff of "Grupo de Estados Pesqueiros" for making available information indispensable to this stady.

 

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Received: 4 Jun 2008; Accepted: 3 July 2009