SCRS/2007/163 Collect. Vol. Sci. Pap. ICCAT, 62(2): 586-592 (2008)

“ASSOCIATED SCHOOL”: A NEW IN SOUTHERN BRAZIL – DESCRIPTION AND COMPARISON

F.A. Schroeder1 and J.P. Castello2

SUMMARY

A new tuna fishery is under development in southern Brazil, called “associated school”. It joins small- scale fishery techniques, such as hand line, and industrial techniques, such as school attractors (FAD - fish aggregating device). However, in this case, the boat itself works as an aggregating device, with being associated with it for long intervals. Such a technique provides good economic and physical safety, social and family contact for fishermen and low by-catch rates of species without commercial interest. Profitability is warranted by a yield focused on (Thunnus obesus Lowe, 1839), the Brazilian species with the greatest trade value, though focusing more on juveniles, which may represent a limitation on the development of the fishery. The study of the modality also contributes to the understanding of the associative behavior of tuna with floating objects.

RÉSUMÉ

Une nouvelle pêcherie de thonidés est en cours de développement au sud du Brésil : la pêcherie de « banc associé ». Elle regroupe des techniques de pêche à petite échelle, telles que la ligne de chalut à main, et des techniques industrielles, telles que les dispositifs de concentration du poisson (DCP). Toutefois, dans ce cas, le bateau en lui-même sert de DCP, les thonidés s’y concentrant pendant de longs moments. Cette technique assure une bonne sécurité économique et physique, des contacts sociaux et familiaux pour les pêcheurs et de faibles taux de prises accessoires d’espèces sans valeur commerciale. La rentabilité est assurée par une production centrée sur le thon obèse (Thunnus obesus Lowe, 1839), espèce brésilienne ayant la plus grande valeur commerciale, ciblant surtout les juvéniles, ce qui pourrait constituer une limite pour le développement de la pêcherie. L’étude de la modalité de pêche contribue également à nos connaissances du comportement associatif des thonidés avec les objets flottants.

RESUMEN

En el Sur de Brasil se está desarrollando una nueva pesquería de túnidos llamada “banco asociado”. En ella se unen técnicas de pesquerías de pequeña escala, como la línea de arrastre de mano, y técnicas industriales, como concentradores de bancos (DCP – dispositivo de concentración de peces). Sin embargo, en este caso, el buque en sí mismo funciona como un dispositivo de concentración, ya que los se asocian a él durante largos intervalos. Esta técnica proporciona una buena seguridad túnidos económica y física, contacto social y familiar a los pescadores y bajas tasas de captura fortuita de especies sin interés comercial. Los beneficios están asegurados gracias a un rendimiento centrado en el patudo (Thunnus obesus, Lowe, 1839), la especie brasileña de mayor valor comercial, aunque se centra más en los juveniles, lo que podría representar una limitación al desarrollo de la pesquería. El estudio de esta modalidad contribuye también a comprender el comportamiento de asociación de los túnidos con los objetos flotantes.

KEYWORDS

Fishery development, floating structures, attracting techniques, “associated school”

1 University of Rio Grande – FURG; Rio Grande – RS – Brazil; SEAP fellowship holder; [email protected] 2 University of Rio Grande – FURG; Rio Grande – RS – Brazil; [email protected]

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1. Introduction

Since the 1960s, fishermen have used FADs (Fish Attraction Devices) as a tool for tuna fishery (Sainsbury, 1996). Those attractors usually are buoys anchored at known positions, which increase accessibility and significantly reduce fuel consumption by boats (Sainsbury, 1996; Holland et al., 1998; Castro et al., 2002). However, since 2003, two skippers of the tuna fleet in southern Brazil – in search of cost-effective fishing procedures – have developed an alternative technique based on FADs, but using the boat itself as the aggregating device, and not anchored buoys. The present work describes such fishing modality.

2. Material and methods

A cruise was conducted with the commercial fleet boat “Ana Amaral I” (24-meter long, 13 crewmen, and 40 tons of hold) which operates along with a smaller boat “Stephanie Seif” (18-meter long, 9 crewmen, and 20 tons of hold). Both operate with pelagic longline, at times fishing through the technique described here. Between 25 May and 11 June 11 2006, tuna fishing was performed by using the alternative fishing technique we here call “associated school”.

Fishing operations took place along the mid-southern coast of Rio Grande do Sul state (southern Brazil), by the break of the continental shelf, in waters under the influence of the Sub-Tropical Convergence. Environmental conditions were recorded in the beginning and the end of fishing operations, by using the boat’s navigation equipment. Captured tuna were subjected to random fork length (FL) sampling with a 1 cm accuracy pachymeter, according to procedures recommended by ICCAT (Graham et al., 2006). In order to collect historical data and record the crewmen’s observations on the “associated school” fishery, interviews were held with the skipper and the crewmen during the second cruise.

3. Results and discussions

3.1 Description of fishing operations

The fishing strategy rests on the attractor principle, where the hull of the vessel itself plays such role, thus aggregating tuna fish near the boat. At first, it is necessary to find an attractor (a drifting buoy, possibly set loose by an oil platform) with fish aggregated to it, and then to convey the fish to the boat. This procedure is faster than waiting for the hull to work as an attractor, which would require a long period adrift at sea, and, according to the skipper, is less viable commercially.

Echo-sound recordings show that, after fish aggregate to the boat, a somewhat continuous recruiting takes place to the tuna school, as reported by Fréon & Misund (1999). Captured specimens are replaced through such feature, thus keeping the school at a stable or expanding size. It was reported by the crewmen that such recruiting only happened under the longer boat (24 m), whereas under the smaller boat (18 m), the school tended to decrease in size. Such finding may lead to speculation that the dimension of the hull (“attractor”) involved will directly mediate the size of the aggregated fish school.

The fishery takes place with both boats alternating, by “transfering” the school from one vessel to the other. Thus, while one boat continues fishing, the other is unloading at the port. Such alternation guarantees that the school will not disperse and remain available and vulnerable to fishing, even under adverse meteorological conditions.

Tuna fish caught in this trip originated from a drifting, 20-m3 buoy found in April 2006 near the break of the continental shelf (33º20’S; 50º33’W). It was then towed seawards, with the associated tuna “transferred” to the boat.

The “transfer” took place at night with the boat moving slowly (4 knots), with lights on and towing the buoy. When it was released and abandoned adrift, tuna fish kept following the boat, which then took on the attracting role, previously performed by the buoy. Likewise, it is possible to transfer the school from one boat to another. However, such operation is only effective during the night hours, which would increase the time at sea.

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After the experience acquired with this technique, the skippers enhanced the procedure, based on the position where the tuna followed the vessel (preferably the bow and the shadowy side), which may be performed at any time of the day. The maneuver consists in both vessels navigating in line on the same course, at low speed (4 knots), and at a few meters distance (2-5 m). The first boat “receives” the school from the one behind, as the trend is for the school to move to the bow of the first boat. The second one decreases its speed and stops. The first one, which has taken on the school, keeps moving and makes another passing by the dark side of the second, unmoving boat. The remainder of the school, still under the stopped boat, is “recruited” to the school under the moving boat. As referred by the crewmembers, tuna fish prefers to follow moving objects. Such feature was the rationale for the development and enhancement of the technique.

In this modality, fishing takes place at two well-established, short time intervals. The first one is by sunrise, and lasts about one hour. The second one is by sunset, and lasts about 40 minutes. That is, in both cases, the sun’s height on the horizon is low. There have been attempts at fishing outside those times, but yielding unexpressive catches. Work conducted by Klimley & Holloway (1996) on tagging shows that school approach is more intense between 02:00 and 09:00 hours and between 15:00 and 22:00 hours, which may explain the success at fishing during the schedule described.

At those fishing times, the boat kept a slow speed (4 knots), the waves always on the stern. The fish school is found to remain by the surface at this speed. At lower speeds, echo-sound recordings show a deepening of the school down to almost 100 meters when the boat is adrift, a fact also reported by Dagorn et al. (2001).

Eleven men composed the crew. Four of them operated hand lines and trawled at the boat’s stern. Two pairs operated rods, two men at each side of the boat. The supporting crewmen was formed by three fishermen, two of which took care of transferring pieces caught to deck hooks, and one was in charge of evisceration. At times, two trawling line fishermen would leave the stern and take on a rod, depending on the yield ratio between rod and trawling line.

The fishing rods made of bamboo and with no flexible parts, measured 2.7 meters. At the top end, a 40-cm #3 rope was tied, fitted with a swivel. A 5-m #3 rope and a 2-m #2.5 nylon line with a #12 or #13 hooks were attached to it. The artificial bait used was prepared aboard, by covering the hook with a withe rubber tube, leaving only the barb showing.

Pairs operated each rod. One crewman handles the rod, making undulating movements and making the hook jump around the water’s surface. The second one is in charge of the rope. Tuna is attracted by the hook’s movement and is hooked; the second pulls the rope bringing the fish near the boat. With the help of a gaff, it is taken from the water and to the deck.

At the stern trawling line, four crewmen worked a hand line each, made of a 20-25-m, #3 rope, a swivel, a 7-m, #2.0 nylon line, and a #12 or #13 hook. They kept the baits by the surface, at a 4-20 meters’ distance from the vessel. When nearer, the fisherman made movements shaking the line, thus making the ways of a live bait. Baits used were artificial ones, like those described for the rods, and natural ones, such as frozen sardines or flying fish and squids that, in an attempt to escape preying, ended up on board.

3.2 Species caught

The main catch was bigeye tuna (Thunnus obesus) with 537 individuals, 42 individuals of yellowfin (Thunnus albacares Bonnaterre, 1798), and one (Thunnus alalunga Bonnaterre, 1788). In addition, 10 dolphinfish (Coryphaena hippurus Linnaeus, 1758), 10 skipjacks (Katsuwonus pelamis Linnaeus, 1758), and 8 albatross (Thalassarche kelanophris Temminck, 1828) were also caught.

The sampled bigeye tunas varied in their fork length between 0.61 and 1.49 meters (Figure 1). Work by Fréon & Misund (1999) point to differences in a contrast between individual size in associated and non-associated schools. The length of skipjacks did not vary, but associated bigeye are usually smaller, and yellowfins are bigger.

Polymodal fork length distributions are common (Fréon & Misund, 1999), as the ones found in this cruise. The chart suggests that more than one school was associated to the FAD, as tuna form schools of individuals with similar length (Pitcher & Parrish, 1993).

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3.3 About the modality

Safety, both economic and physical, is an important factor in this technique, as once the school associates with the boat, there will be fish available to be caught for a long time. Therefore, the chance of the boat returning without fish to port is remote. However, it may be expected that, with an increase in activity/fleet, the finding of schools and the success of the fishery will both be made more difficult. According to crewmen, the physical safety is provided by a light work regime, with little chance of accidents.

Partnership is another important feature in this modality. As the fishery involves two boats and only one fish school, the crewmen spend a longer interval at land, usually 10 days aboard and 7 days at land. This feature provided greater contact with the family and the possibility of other side work.

The size of the tuna caught is a source of worry in this fishery. Only 25.8% of the tuna caught had fork length greater then 1.1 meter (corresponding to the first sexual maturation of bigeye tuna (Matsumoto & Miyabe, 2002)). Such fact means that the fishery focuses on sexually immature individuals.

Such feature is typical of FADs, where aggregated tuna are prevailing juveniles (Holland et al., 1998; Itano & Holland, 2000; Schaefer & Fuller, 2004). This situation calls for caution, for in case the technique spreads, it may compromise the sustainability of the fishery. However, Pauly (1997), Pauly et al. (2002), Maunder, (2002), and Beamish et al. (2006) underlined the importance of leaving the bigger females alive, due to their high capacity of producing eggs in number and viability (larger amount of yolk).

Still, if on one hand this fishery may impact the tuna population, it significantly decreases the involving other non commercial species. No turtle, ray, or shark were caught. The capture of albatross did not result in any death, all being released with good chances of survival.

The “associated school” fishery was followed between March and December 2006, period in which the school remained by the boats. It was interrupted when one of the boats had to part from the school, due to health problems in one crewman. As the yield was steady along the whole period (according to crewmen), this fishery may be speculated to be efficient both in the southern-Brazilian tuna season (May to October) as outside the best fishing time. Fréon & Misund (1999) state that, in average, the tuna-FAD association period approximately lasts 18 days. However, the school will revisit the place for many months, suggesting fidelity to the FAD. Such behavior may contribute to the maintenance of long fishing periods with good yield levels.

The practice of tuna fishing with the use of attractors (natural or artificial) is highly spread in the Indic , where it may represent up to 90% of the catch (Fréon & Misund, 1999). In the sub-equatorial tuna fishery in the East Atlantic, where natural and artificial attractors are less efficient, fishermen use small-size boats to act as attractors (Fréon & Misund, 1999).

3.4 Interviews with crewmen

The interviews held aboard during the cruise allowed for the crewmen to express their opinions about this new fishing modality, and to contrast it to longline. Most of the interviewees (82%) showed preference for working with the “associated school” fishery, which presents advantages such as the greater contact with their families provided by the alternation between boats. Another advantage pointed out is its financial security, as the fishery is guaranteed, since the fish does not need to be found, and the chance of a poor yield is lower.

Fishermen’s physical safety was also pointed out as an advantage, as the work is much “lighter” and less stressful for the fisherman. While in longline the work shift reaches up to 16 hours a day, in “associated school” it is only 3 hours a day. That is, physical weariness does not compromise fishermen’s safety. are also safer in “associated school”, the crewmen being guarded from severe accidents. The long idle period aboard was pointed out as a negative point as crewmen complained of boredom. Situations as such are unthinkable of in , given its intense work regime.

3.5 Attractors (FADs)

The reason for tuna fish to associate with floating objects is not very clear yet (Castro et al., 2002). It is known that tuna is less active when associated with floating objects, which may favor their capture (Fréon & Misund,

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1999). However, a few hypotheses regarding the role played by attractors have received credibility. Findings from the cruise seem to support some of those hypotheses.

Thus, the common finding of small schools that withdrew from the main one, moving away from the boat for feeding and then returning, would support the theory of a “meeting point” (Castro et al., 2002; Fréon & Misund, 1999; Fréon & Dagorn, 2000).

Other findings suggest that tuna fish associate to floating objects in order to find protection against predators (Rountree, 1989; Feigenbaum, 1989; Fréon & Misund, 1999). During the second cruise, the presence of an approximately 450-kg blue (Makaira nigricans Lacepède, 1802) was recorded. In that occasion, tuna behavior changed, with a portion of the school moving to deeper waters – about 100 m – and another moving very close to the vessel. The latter was mainly formed by small-sized individuals. It was not possible to identify the tuna species that approached the boat. The marlin, however, kept away, at about a 20-m distance from the boat.

Negative phototropism, pointed by Castro et al. (2002) as a possible reason for FAD efficiency, was also recorded aboard. Tuna fish were found to show an obvious preference for shadow, mainly following the boat along the opposite side to the sun. Such feature helps in the transferring maneuver of the school from one boat to another, contributing to the confirmation of this hypothesis.

This preference for shadowy places may also be explained as a protection from predators, as tuna fish were better camouflaged and able to keep their vision more accurate, as their pupils are more dilated under shadow. They may thus watch for possible predators that come near (Helfman, 1981).

Tuna’s vertical motion pattern, when associated with floating objects, was described by Dagorn et al. (2001), and also confirmed during the cruise. The relationship between the vessel’s speed and the depth at which tuna followed it is highly clear. The faster the boat navigated, the nearer the surface the school moved. As the boat decreased speed, the school would dive towards greater depths.

Based on such findings, it was determined by the vessel’s skipper that the optimum fishing speed is approximately 4 knots. At lower speeds, the tuna will withdraw from the surface, thus becoming less vulnerable to fishing gear. At greater speeds, fuel consumption also increases, thus heightening the production cost.

4. Conclusions

This fishing modality is a highly promising one, with ecological advantages over traditional longline fishery, particularly due to the absence of death through bycatch, the higher safety level, and the possibility of social contact for fishermen.

It also presents a good yield level and is directed to a highly commercially valuable species (bigeye tuna, in the Brazilian market), thus favoring the profitability of the modality.

In contrast to the traditional pelagic longline fishery, its disadvantages include the catching of juveniles, placing its sustainability at issue if practiced at large scale, and the need of finding an attractor with a previously formed school to begin activities. That is a rare event, which may limit fishing operations with the “associated school” technique, thus making it an “opportunistic” modality. However, in the present developmental stage, those weaknesses are not yet presented as limiting factors. Only two boats from the southern-Brazilian fleet perform “associated school” fishing. This technique is not disseminated as of yet, and may undergo adjustments that will minimize its disadvantages.

We suggest that the techniques employed for school maintenance and transfer also represent important tools for the study of tuna. Oceanographic fleet vessels could receive tuna schools and study them for long periods and under different oceanographic conditions. Finally, this description adequately illustrates the creative ability of skippers who are careful observers of fish behavior and nature of the sea. They have thus developed detailed and rich empirical knowledge for implementing new and effective forms of resource exploration.

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5. Acknowledgements

To skipper Celso Oliveira, who has been developing the “associated school” technique, and who has kindly offered his boat to conduct our research. To Leandro Bugoni, for his help aboard and his support in understanding this fishery model, and the academic Lígia de Abreu, for her support in developing the work.

6. Literature

BEAMISH, R.J., G.A. McFarlane, and A. Benson. 2006. Longevity . Prog Oceanog, 68: 289–302. CASTRO, J.J., J.A. Santiago and A.T. Santana-Ortega. 2002. Reviews in Fish Biology on - A General Theory on Fish Aggregation to Floting Objets: An Alternative to the Meeting Point Hypothesis. Rev Fish Biol. Fisheries 11: 255-277. DAGORN, L., E. Josse, and P. Bach. 2001. Association of (Thunnus albacares) with tracking vessels during ultrassonic telemetry experiments. Fishery Bull. 99: 40-48. FEIGENBAUM, D., A. Fridlander and M. Bushing. 1989. Determination of the feasibility of fish attracting devices for enhancing fisheries in Puerto Rico. Bull. Mar. Sci. 44(2): 950–959. FRÉON, P. and L. Dagorn. 2000. Review of fish associative behaviour: Toward a generalisation of the meeting point hypothesis. Rev. Fish Biol. Fisheries 10(2): 183–207. FRÉON, P. and O.A. Misund. 1999. Dynamics of behavior: Effects on Fisheries and Stock Assessment. Fishing New Books, London, 348 p. GRAHAM, M., A. Pilling, J.R. Cotter and J.D. Metcalfe. 2006. Data for assessment and research.: 1-133. In: ICCAT Field Manual. Accessible at http://www.iccat.es. /pubs_FieldManual.htm. HELFMAN, G.S. 1981. The advantage to fishes of hovering in shade. Copeia 2: 392-400. HOLLAND, K.N., P. Kleiber and S.M. Kajiura. 1998. Different residence Times of Bigeye Tuna, T. obesus, Found in Mixed Aggregations Over a Seamount. Fish. Bull. 97: 392-395. ITANO, D.G. and K.N. Holland. 2000. Movement and Vulnerability of Bigeye (Thunnus obesus) and Yellowfin (Thunnus albacares) in relation to FADs and Natural Aggregation Points. Aq. Liv. Res.13: 213-223. MATSUMOTO, T. and N. Miyabe. 2002. Report of Observer Program for Japanese Tuna Longline Fishery in the From August 2000 to July 2001. Collect. Vol. Sci. Pap. ICCAT, 54(5): 1741-1762. MAUNDER, M.N. 2002. The relationship between fishing methods, fisheries managemente and the estimation of maximum sustainable yield. Fish and Fisheries 3: 251-260. PAULY, D. 1997. Points of view. Putting back in places, Rev. Fish Biol. Fisheries 7: 125–127. PAULY, D., V. Christensen, S. Guénette, T. Pitcher, U.R. Sumaila, C. Walters, R. Watson and D. Zeller. 2002. Towards sustainability in world fisheries. Nature, 418: 689-695. PITCHER, T.J. and J.K. Parrisch. 1993. Functions of shoaling behavior in teleosts. p. 363-440. In Pitcher, T. J. Behavior of teleost fishes. Chapman and Hall, London, 715 p. ROUNTREE, R.A. 1989. Association of fishes with fish aggregation devices: Effects of structure size on fish abundance. Bull. Mar. Sci., 44(2): 60-72. SAINSBURY, J.C. 1996 Methods – An Introduction to Vessels and Gears. 3rd. edition. Fishing New Books, London, 359 p. SCHAEFER, K.M. and D.W. Fuller. 2004. Behavior of Bigeye (Thunnus obesus) and Skipjack (Katsuwonus pelamis) Tunas Within Aggregation Associated With Floating Objects in the Equatorial Eastern Pacific. Mar. Biol., 146: 781-792.

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Figure 1.Length frequency for bigeye tuna caught during cruise (n = 66; Mode= 0,94 m).

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