SCRS/2007/025 Collect. Vol. Sci. Pap. ICCAT, 62(6): 1721-1738 (2008)

INTERACTION OF THE (PSEUDORCA CRASSIDENS) AND DEPREDATION ON THE SWORDFISH CATCHES OF THE SPANISH SURFACE LONGLINE FLEET IN THE ATLANTIC, INDIAN AND PACIFIC OCEANS

A. Ramos-Cartelle and J. Mejuto1

SUMMARY

On the basis of information provided by the fleet and by scientific observers during the 1992-2006 period, it was possible to identify the areas of interaction between the surface longline fishery and Pseudorca crassidens, the level of sporadic incidental by-catches of this cetacean and its depredation level carried out on the swordfish individuals caught by this fleet. In roughly 98% of the sets sampled by scientific observers, no depredation was detected on the swordfish longline catches and in only 2% there were signs evidencing this depredation. According to on-board scientific observations, the incidental catch rate of the false killer whale was estimated to be 1.464, 1.685 and 0.797 individuals per million hooks for the Atlantic, Indian and Pacific Oceans, respectively. The incidental mortality rate of the false killer whale was estimated 0.36 individuals per million hooks in the Atlantic and zero in the two other oceans. The intertropical band of the three oceans presented the greatest interaction with the swordfish fishery, reaching in some of the areas a mean impact affecting over 10% of the swordfish catch in number. On the basis of mean predation rates by region and quarter, the average number of swordfish estimated to have been depredated by the false killer whale in 2005 would range from 2999- 4804, 509-2706, 114-348 specimens, in the Atlantic, Indian and Pacific Oceans, respectively. These modest overall incidences compared with other fleets are probably due to fishing areas selected as well as the fleet’s effective practice of avoiding areas of interaction with the false killer whale. However, when attacks do occur, they can be devastating to the fishery interests of the vessel and may ruin their yields. Data from sets with HPUE>0 indicate that predation usually amounts to less than 5 swordfish per thousand hooks, although, it may sporadically reach or exceed 20 fish. Sets having HPR>0 indicate that, when attacks occur, depredation may affect a number of swordfish equivalent to 50% or more of the catch held on board and may even damage the catch in a proportion that is several times greater than the number of swordfish retained on board. For general purposes it was estimated that in 2005 Pseudorca crassidens carried out a mean overall depredation in the Spanish surface longline fleet of around 1.1-1.8%, 0.5-2.6%, 0.1-0.3% on the total number of swordfish caught in the Atlantic, Indian and Pacific Oceans, respectively.

RÉSUMÉ

D’après les informations soumises par la flottille et les observateurs scientifiques de 1992 à 2006, on a pu identifier les zones d’interaction entre la pêcherie palangrière de surface et la Pseudorca crassidens, le niveau de prises accidentelles sporadiques de ce cétacé ainsi que le niveau de déprédation causé par cette espèce sur les espadons capturés par cette flottille. Dans près de 98% des opérations échantillonnées par les observateurs scientifiques, aucune déprédation n’a été détectée sur les prises palangrières d’espadon et dans 2% des cas seulement cette déprédation était avérée. Selon les observations des scientifiques à bord, le taux de prise accidentel de cette fausse orque a été estimé à 1,464, 1,685 et 0,797 spécimens par million d’hameçons pour l’Océan Atlantique, l’Océan Indien et l’Océan Pacifique respectivement. Le taux de mortalité accidentel de la fausse orque a été estimé à 0,36 spécimens par million d’hameçons dans l’Atlantique et à zéro dans les deux autres océans. La bande intertropicale des trois océans présentait la plus grande interaction avec la pêcherie d’espadon, avec, dans certaines zones, un impact moyen affectant plus de 10% de la prise numérique d’espadon. Sur la base des taux moyens de prédation par région et trimestre, le nombre moyen d’espadon qui a été estimé comme ayant fait l’objet d’une déprédation par cette fausse orque en 2005 s’élèverait à 2.999-4.804, 509-2.706, 114-348 spécimens dans l’Océan Atlantique, l’Océan Indien et l’Océan Pacifique respectivement. Ces incidences globales modestes par rapport à celles d’autres flottilles sont probablement dues à certaines zones de pêche ainsi qu’à la pratique efficace de la flottille qui évite les zones d’interaction avec la fausse orque. Toutefois, lorsque des attaques se produisent, elles peuvent

1 Instituto Español de Oceanografía, P.O. Box. 130, 15080 A Coruña. Spain. 1721 être dévastatrices pour les intérêts halieutiques du navire et détruire ses productions. Les données d’opérations avec HPUE>0 indiquent que la prédation totalise généralement moins de 5 espadons par mille hameçons, même si elle peut parfois atteindre ou dépasser 20 poissons. Les opérations avec HPR>0 indiquent que lorsque des attaques se produisent, la déprédation pourrait affecter 50% ou plus de la prise d’espadon conservée à bord et même détruire la prise dans une proportion plusieurs fois supérieure au nombre d’espadons retenus à bord. On a généralement estimé que la Pseudorca crassidens a causé en 2005 une déprédation générale moyenne dans la flottille palangrière de surface espagnole de 1,1-1,8%, 0,5-2,6%, 0,1-0,3% environ sur le nombre total d’espadons capturés dans l’Océan Atlantique, l’Océan Indien et l’Océan Pacifique respectivement.

RESUMEN

Sobre la base de la información proporcionada por la flota y por los observadores científicos durante el periodo 1992-2006, ha sido posible identificar las zonas de interacción entre la pesquería palangrera de superficie y Pseudorca crassidens, el nivel de capturas fortuitas incidentales esporádicas de este cetáceo y su nivel de depredación en ejemplares de pez espada capturados por esta flota. En aproximadamente el 98% de las caladas de palangre muestreadas por los observadores científicos no se detectó depredación en las capturas de pez espada con palangre, y sólo en un 2% se observaron signos que evidenciaban esta depredación. Según las observaciones de los científicos embarcados, se estimó que la tasa de captura incidental de orca falsa (Pseudorca crassidens) ascendía a 1,464, 1,685 y 0,797 ejemplares por millón de anzuelos para los océanos Atlántico, Índico y Pacífico, respectivamente. La tasa de mortalidad incidental de orca falsa se estimó en 0,36 ejemplares por millón de anzuelos en el océano Atlántico y en cero en otros océanos. La franja intertropical de los tres océanos presentaba la mayor interacción con la pesquería de pez espada, alcanzando en algunas zonas un impacto medio que afectaba a más del 10% de la captura de pez espada en número. Sobre la base de las tasas medias de depredación por región y trimestre, el promedio de peces espada que se estima que han sido depredados por la falsa orca en 2005 oscilaría entre 2.999 y 4.804, 509 y 2.706, 114 y348 ejemplares para los océanos Atlántico, Índico y Pacífico, respectivamente. Estas incidencias globales, modestas en comparación con otras flotas, se deben probablemente a las zonas de pesca seleccionadas así como a la práctica efectiva de la flota de evitar las zonas de interacción con orcas falsas. Sin embargo, cuando se producen los ataques, éstos pueden ser devastadores para los intereses pesqueros de los buques y pueden arruinar su rendimiento. Los datos de las caladas con HPUE>0 indican que la depredación se sitúa en menos de 5 ejemplares de pez espalda por 1.000 anzuelos, aunque esporádicamente puede alcanzar o superar la cifra de 20 ejemplares. Los caladas de palangre con HPR>0 indican que, cuando se producen ataques, la depredación puede afectar a un número de peces espada equivalente al 50% o más de la captura retenida a bordo y podrían incluso dañar la captura en una proporción varias veces superior al número de peces espada retenidos a bordo. A efectos generales, se estimó que en 2005 la Pseudorca crassidens llevó a cabo una depredación global media en la flota palangrera de superficie española de aproximadamente el 1,1-1,8%; 0,5-2,6% y 0,1-0,3% del número total de peces espada capturados en los océanos Atlántico, Índico y Pacífico, respectivamente.

KEYWORDS

Pseudorca crassidens, false killer whale, swordfish, depredation, surface longline

1. Introduction

The false killer whale (Pseudorca crassidens), the only species of its genus, is one of the largest cetacean members of the Delphinidae family. While it might sometimes be confused with other cetacean having a similar morphology, such as the pygmy killer and melon-headed whales, and less commonly, pilot whales, fishermen seem to have no trouble identifying it and often see the damage it inflicts on their catches and bait. The shape of the head, dorsal fin, and flippers will be the best characters to use in distinguishing them2 (Baird, 2005). The taxonomic details are (Carwardine, 1995): Kingdom: Animalia. Phylum: Chordata. Class: Mammalia. Order: . Family: Delphinidae. Genus: Pseudorca, Reinhardt, 1862. Species: P. crassidens.

2 http://www.marinethemes.com/falsekiller.html 1722 The habitat of this species ranges from the tropical to temperate zones of both hemispheres. It appears to have a widespread distribution in temperate and tropical oceanic waters. However, unlike the killer whale (Orcinus orca), its distribution is preferably tropical, although it can often appear in subtropical and in some cases in temperate regions, particularly during certain seasons of the year. This species was reported in fairly shallow waters of the Atlantic, Indian and Pacific Oceans as well as in the Mediterranean Sea and Red Sea. It has not been widely studied despite its great abundance in all the oceans of the world. As an example of its broad- ranging geographic distribution, this species has been described in the Pacific Ocean from the Sea of Japan to New Zealand and between high latitudes in the Atlantic as well, from Scotland and the Grand Banks of Canada to Argentina. In the Indian Ocean its distribution is also extensive and its abundance may be even greater since this ocean lacks a North system similar to that of the other oceans and it contains vast areas with tropical-type environmental conditions. The observations provided in this document all agree with the idea that there is a wide distribution and great abundance of this cetacean in the tropical, subtropical and temperate regions of both hemispheres in the three oceans mentioned above.

As already reported3, this cetacean has a slender body with a dorsal fin that may be more than a foot high. One of the species’ distinguishing characteristics is a bend and bulge (usually called the "elbow") half-way along each of the flippers. The tips of the tail fin are pointed and the middle of the tail has a distinct notch. The false killer is uniformly coloured a dark grey to black. It grows to about 6 m long, may weigh 1,500 kg and lives for about 60 years. The false killer whale is a social , living in groups of 10-50 individuals. It is a fast and very active swimmer. It may breach or jump clear of the water and will often land on its side with a big splash. On other occasions the dive may be very graceful, leaving very little wake at all. It will readily approach boats and bow- and wake-ride. It may also emerge from the water head held high upwards and with the mouth open, revealing some of its 44 teeth.

False killer whales are reported4 as being very social marine hunting and sharing their food amongst the group. The groups of adult false killer whales can feed on tunas with a newborn calf, with birth folds evident on their flanks, joining in. During the feeding session one adult would hold the fish while others tore off strips of flesh. The sound of their feeding was like tearing apart strips of velcro2.

Although false killer whales eat primarily fish and cephalopods, they also have been known to attack small cetaceans and, on one occasion, even a humpback whale. Depending on the area, stomach contents included salmon, squids, sciaenid and carangid fishes, bonito, -fish, yellowfin tuna, mackerel, herring and smelt. In coastal areas of Chile the most important prey species were the oceanic and neritic-oceanic squids, Martialia hyadesi and Illex argentinus, followed by the neritic fish, Macruronus magellanicus.

There are reports4 that Pseudorca fed on and chased other in the eastern tropical Pacific during chase and backdown operations of tuna purse seine fishing. This habit has also been attributed to the pygmy killer whale (Feresa attenuata). The echolocation clicks appear to be the mechanism used by this species to locate its prey (Madsen et al., 2004).

Interaction between the false killer whale and human activities has been reported for centuries. This species has been hunted at least in some Caribbean areas (West Indies) Indonesia and Japan. It is well known for the enormous damage it inflicts on catches made by fishermen, especially tunas, swordfish and other species. In some communities this interaction has aroused sporadic bouts of wrath among fishermen towards this species in the geographic areas where it is concentrated temporarily. This may even lead to local mortalities of this cetacean.

Several studies have provided information on the interaction between fishery activities and marine mammals. However, most of them deal with this interaction from the standpoint of the mortality incurred by fishery activity on these stocks. Incidental captures of marine mammals including the false killer whale have been reported, especially by their interaction with gears such as gillnets and driftnets (Bearzi, 2002; Reeves et al., 2001).

However, use of oceanic longlines starting in the mid-1900s along with the associative behaviour of the false killer whale, have introduced a new kind of interaction between fishermen and this species. The false killer whale has learned to use bait and, in particular, the catches retained by the longlines, as a kind of larder full of easily accessible food. These cetaceans swim back and forth along the miles of gear set, eating the bait or the catch retained by the hooks, causing what might be considerable damage in some of the fishery operations of

3 http://it.wikipedia.org/wiki/Pseudorca_crassidens 4 http://www.cms.int/reports/small_cetaceans/data/P_crassidens.htm 1723 these commercial fleets. And they do this without running practically any risk at all of being harmed by the hooks. They chose their prey, selecting the species of greatest interest hanging from the branchline and wait for it to become debilitated or die on the hook before initiating their attack. These cetaceans are able to select the parts of the prey that will be most useful to them as an energy source, while avoiding the undesirable parts of the prey or those that may entail some risk owing to the location of the hook.

Recent studies have reported the concern expressed by some of the longline fleets over the extremely high interaction observed with the false killer whale, which has come to the point of jeopardizing the economic viability of some of these fisheries (Anon. 2007). The semi-industrial fleet of the Seychelles estimated that they suffered a loss of 24% (109 t) as compared to the catch taken in 1999, chiefly comprising swordfish and tropical tuna species (Bargain et al., 2000). Therefore, in addition to the above considerations, from a statistical and scientific point of view, this interaction adds to the uncertainty over the level of fish removals for the estimation of mortalities.

In an attempt to avoid or minimize this interaction, over the course of history fishermen have used different methods which do not appear to have been effective. Fishermen report than the false killer whale is able to recognize the sound of a vessel, and even if it changes fishing areas, the cetacean will follow it for days, severely hindering its fishing operations by feeding on the bait and catches. Recent technological developments have led to the possibility of using acoustic mechanisms aimed at reducing these interactions, although the effectiveness of these was questionable owing to the lack of reliable experiments conducted until now with the appropriate scientific supervision (Jeffereson, 1996).

The aim of this document is to assess the existing interaction between the false killer whale and the Spanish surface longline fishery targeting swordfish. Additionally, our purpose is to determine the magnitude of the possible incidental catches of the false killer whale and their rates due to fishing operations. On the other hand, to identify the distribution areas of this species, the predation rates observed in the different regions-areas and, for a recent year, to estimate the magnitude of the overall impact on the annual landed catches of the Spanish fleet as a whole.

2. Material and methods

Two sources of information have been used in this paper. A research project on swordfish longline fisheries started in 1992 incorporated among its protocols, data collection by the skippers of fishing vessels to record the presence of the false killer whale during their fishery activities, as well as the interaction of this species and the number of individuals or “heads” of swordfish attacked and depredated. The false killer whale usually leaves at least the head and viscera of the swordfish attacked on the hook, which means that estimations can be made as to the impact of this predation on the fishery activity. This information is extremely useful, however not all the skippers who supply fishery information provide details on the false killer whale attacks and the reliability of the data is not always consistent among skippers.

Another source of information comes from the scientific observers on board commercial fleets. Since 1993 scientific observers have been taking note of the interaction of the false killer in each set and recording the attacks and predation witnessed on the swordfish specimens caught with the longline or the number of “heads” attacked. In addition, they also record any sporadic incidental catches of the false killer whale, regardless of the cause (retained by a hook, tangled up the la main line, etc.). The estimations of incidental catch rate by ocean, interaction by region and potential impact on the fleet’s catches were calculated only from data provided by the scientific observers, since this source was considered to be more appropriate in terms of quality for these purposes.

The data recorded by on-board observers were classified according to 5x5 degree squares by region and quarter. A total of 8 regions were defined in the Atlantic and Indian oceans and 9 in the Pacific (Figure1). The data from all the years were combined. The incidental catch rate of the false killer whale (ICR) and their incidental mortality rates (IMR) were computed by relating the respective number of individuals captured to the fishing effort observed in each ocean, measured in thousands of hooks set:

ICR or IMR = # Pseudorca (alive and/or dead) / thousand hooks set

For descriptive purposes, the sets were combined and presented in graph-form in 5x5 degree squares, years combined, to estimate the percentage of swordfish caught that had been subject to depredation (heads attacked) as compared to the total catch obtained in each square (heads attacked+ retained on board).

1724

Two attack or incidence rates of the false killer whale by set were defined by relating the number of fishes or swordfish heads attacked and depredated to two variables:

a) The fishing effort or thousands of hooks in each set. Heads per unit of effort or HPUE, where HPUE = number of swordfish fed upon / thousands of hooks set.

b) The number of swordfish retained on board in each set. Heads per retention or HPR, where HPR = number of swordfish fed upon / number of swordfish retained on board.

Both rates were averaged by region and quarter using two different procedures. In the first, the data from each region was previously stratified by set, 5x5 degree square and quarter. The mean HPUE and HPR in each 5x5 degree square-quarter was weighted to the number of swordfish caught (retained+attacked) in the respective square to obtain a mean value by region and quarter. This first approach gives a different weight to the mean value of each 5x5 degree square-quarter according to the corresponding catch in number of swordfish. The second approach directly classified all the sets assigned according to their corresponding region and quarter, calculating their mean rates and respective 95% confidence intervals. This second approach does not consider the previous stratification of the information in 5x5 degree squares, which means that the average value by region-quarter is directly dependant on the spatial and temporal distribution of the observations within each region-quarter. The incidence rates of a region-quarter without observations available, but with data on the fishery activity of the fleet (Task II data), were replaced by the rates obtained in the closest region-quarter.

The mean incidence rates by region-quarter were later applied to the Task II data of year 2005 for each ocean belonging to the corresponding region-quarter, depending on the nominal effort exerted in each region-quarter, or according to the number of swordfish landed by region-quarter, respectively. Through these different approaches, it was possible to estimate the magnitude and total impact of the interaction of the false killer whale on all of the catches of the Spanish longline fleet in 2005, the most recent year for which data are available, in the Atlantic, Indian and Pacific.

3. Results

A total of 1,557 trips corresponding to 81,896 sets and 168,004 thousands of hooks were reported in the different oceans by the Spanish fleet between 1992 and 2005. In terms of fishing effort 86.4%, 6.2% and 7.3% corresponded to the regions of the Atlantic, Indian and Pacific oceans, respectively. Owing to the fact that the longline activity of the Spanish fleet in the Pacific and Indian oceans began more recently and is less intense, most of these observations come from the Atlantic.

A total of 140 trips corresponding to 8,249 sets and 13,427 thousands of hooks were sampled by scientific observers in the different oceans from 1993 to 2006. As regards the fishing effort observed for this purpose, 40.6%, 30.9% and 28.4% pertained to the regions of the Atlantic, Indian and Pacific oceans, respectively. Approximately 98% (range depending on the ocean 97.31% - 99.39%) of these observed sets did not exhibit any incidence or predation by the false killer whale on the swordfish catches and only around 2% (range depending on the ocean 0.61%-2.69%) of the observed sets reported attacks on swordfish.

The data collected by the scientific observers indicate that the total number of specimens of false killer whale incidentally trapped during the entire period observed amounted to 8, 7 and 3 individuals in the Atlantic, Indian and Pacific oceans, respectively. This would be equivalent to incidental catch rates (ICR) of 1.464, 1.685 and 0.787 individuals per million hooks set in each ocean. Most of these catches were due to the cetacean getting hooked by flippers or tangled up in the longlines. All of the specimens, with the exception of two captured in Atlantic region 2, were released alive. The resulting incidental mortality rate (IMR) in the Atlantic was 0.36 individuals per million hooks and zero in the other two oceans.

Figures 1 and 2 show the percentage of swordfish attacked by the false killer whale in relation to the total catch obtained in each 5x5 degree square (heads attacked +retained on board), for all the years and months combined and for each of the information sources used. The wealth of information from the reports submitted by the skippers of fishing vessels offers a broad geographic view on the distribution areas of this species and the varying probabilities of whether or not any interaction will occur, depending on the fishing zones. These data would suggest that interaction takes place in wide-ranging areas of all three oceans, predominantly within intertropical zones, and also extending to subtropical and even temperate zones, where the incidence percentages are more moderate. However, these accumulated data by 5x5 degree square do not identify mean interactions

1725 greater than 10% in any of the 5x5 degree squares and they would appear to underestimate interaction rates when compared with data from the observers.

Despite the fact that quantitatively less information is provided by scientific observers, it is more evenly distributed among oceans. It is also standardized in terms of gathering and reporting criteria and allows a more accurate identification of the areas of greatest interaction affecting the total catch. These data also suggest that the tropical band of the three oceans has the highest mean interaction rate, often with an impact on the total catches of over 4%, and this figure may even reach a maximum of 15.8% in some of these catches. Especially striking is the high predation rate observed in the North and NW areas of the intertropical band of the Indian Ocean, which might be able to explain the impact witnessed on some of the local fleets fishing in these areas.

Both sources of information coincided in identifying the areas located in the intertropical band as being those with the greatest interaction and most detrimental to this fleet. These zones coincide with the preferential distribution areas reported for this cetacean as they present the surface thermal conditions favoured by this species. However, most of the 5x5 degree squares show only a moderate or null interaction (Figure 3).

Tables 1 and 2 provide mean HPUE and HPR rates obtained by region and quarter related to the fishing effort exerted and to the number of heads retained on board for subsequent landing, respectively. In both cases it was possible to observe some regions-quarters without any known interaction, others with a moderate interaction and still others presented a high or very high interaction. Tables 3 and 4 show similar mean rates but the information has been stratified directly by region.

By applying the different rates obtained to the Task II data from 2005, it was possible to make a estimation of the number of heads or parts of swordfish that would be attacked by the false killer whale in relation to the total annual swordfish catch (retained+attacked). The mean number of heads attacked by the false killer whale in 2005 would be in the range of 2999-4804, 509-2706 and 114-348 individuals in the Atlantic, Indian and Pacific, respectively. If the upper limit of the 95%C.I. is taken into account, the number of heads could be even higher, reaching upper limit ranges of 5841-9284, 987-5764 and 276-693, for each of the above-mentioned oceans, respectively (Table 5). A comparison of the estimations obtained with different general procedures showed no apparent differences in their magnitude. The impact of whether or not the information was stratified into 5x5 degree squares would appear be less important in terms of estimating annual predation than the type of rate used (HPUE vs HPR), particularly in the Indian Ocean.

These seemingly low overall incidences would appear to be due to the fishing areas regularly selected by the Spanish fleet as well as the effective practices used by the skippers to escape and avoid interaction within areas. An analysis of data by set and region in those sets where it was verified that Pseudorca crassidens had attacked the catch, highlights the fact that, when an attack does occur, it can be devastating to the fishery interests of the vessel, and may even ruin the catch. In this sense, the HPUE>0 values show that the interaction per thousand hooks set is generally within a range of less than 5 fish per thousand hooks, although this interaction may occasionally increase to as many as 20 specimens attacked per thousand hooks. The HPR>0 values indicate that when an attack occurs, it may often affect 50% or more of the swordfish catch in numbers retained on board for commercial sets purposes. In some sets, predation might even damage the catches in a proportion as high as several times greater than the number of swordfish retained on board (Figure 4). However, we must bear in mind that depredation by this species affects the Spanish fleet in approximately 2%-3% of the sets analyzed.

The high HPR rate observed in some regions of the Indian and Pacific indicate that the magnitude of the annual impact on a fleet’s activity depends, to a large extent, on the fishing areas selected. Hence, the low predation values estimated for the Pacific in 2005 are merely a consequence of the traditional fishing areas selected by this fleet, until recently mainly located in the temperate zones of the SE Pacific which are affected by the cold Benguela current. In the Indian Ocean, by contrast, it is highly likely that annual predation was historically greater than our estimations here for 2005, since this fleet started fishing in the western Indian Ocean, which is the area where the highest interaction rates with Pseudorca crassidens were observed, and then subsequently expanded to central and eastern regions of the Indian Ocean, where these rates seems to be substantially lower.

On the basis of the estimations obtained for 2005 it may be concluded that in overall the Spanish surface longline fleet was moderately affected by Peudorca crassidens as a result of direct attacks and predation on swordfish catches on the longlines, suffering mean losses in 2005 of around 1.1-1.8%, 0.5-2.6% and 0.1-0.3% of its catch in number (retained+attacked), in the Atlantic, Indian and Pacific, respectively. However, this impact or predation might have been even greater in the past in some oceans such as the Atlantic and Indian and even now could reach higher proportions if the fleet wereto make an inappropriate selection of its fishing areas-seasons or

1726 if their avoidance strategies were to fail. This paper does not assess the negative repercussions that may be felt by the fleet on being forced to select fishing areas that may be less abundant in swordfish owing to the presence of the false killer whale in more favourable fishing grounds. Nor does this it deal with predation on other species caught, such as bycatch (tunas, sharks or their parts) which are also targeted for predation by this cetacean.

4. Acknoledgements The authors would like to give special thanks to Blanca García-Cortés for her dedicated and continuous work in coordinating the standard procedures, on-board observer programs and data bases that made this paper possible. We are also grateful to the many other people who have collaborated at different levels on this project to carry out this common effort started in 1992. Manuel Marín has been also a important figure in keeping the voluntary collaboration going with the longline fleet, with the more recent help of José Lorezo. We would also like to thank the staff of the IEO, I. Gonzalez, M. Quintans, A. Carroceda, F. González as well as the scientific observers, skippers and surface longline companies for their invaluable cooperation. This paper was done into the context of the research project SWOATL of the Instituto Español de Oceanografía (Spain).

Bibliography

ANON. 2007. Report of the workshop on the depredation in tuna longline fisheries in the Indian Ocean. Seychelles, 9-10 July, 2007. BAIRD, R.W. and A.M. Gorgone. 2005. False killer whale dorsal fin disfigurements as a possible indicator of the long-line fishery interaction in Hawaiian waters. Pacific Science. Vol. 59(4):593-601. BARGAIN, R.M, V, Lucas and T. Andrew. 2000. The Seychelles semi-industrial fishery. IOTC Proceeding no. 3: 164-168. BEARZI, G. 2002. Interaction between cetaceans and fisheries in the Mediterranean Sea. A report of the ACCOBAMS Interim Secretariat, February 2002. CARWARDINE, M. 1995. Whales, dolphins and porpoises (Spanish vers.). Dorling Kinsderley Limited, London. Ediciones Omega, S.A. Barcelona. JEFFERSON, T.A. and B.E. Curry. 1996. Acoustic methods of reducing or eliminating marine -fishery interactions: do they work? Ocean and Coastal Management, Vol. 31(1):41-70. MADSEN, P.T., I. Kerr and R. Payne. 2004. Echolocation clicks of the two free-ranging, oceanic delphinids with different food preferences: false killer whale Pseudorca crassidens and Risso´s dolphis Grampus griseus. Journal of Experimental Biology 2007:1811-1823. REEVES, R.R., Read A.J., and G. Notarbartolo di Sciara. 2001. Report of the workshop on interaction between dolphins and fisheries in the Mediterranean: Evaluation of mitigation alternatives. ICRAM. Roma, 4-5 May 2001.

1727 One of the false killer whale specimens (184 cm FL, female) that suffered incidental mortality in the Atlantic Ocean and details of its head and dorsal fin (photographs by Pedro Güemes, 1995).

1728 Table 1. Mean number of heads of swordfish per thousand hooks set (HPUE) depredated by Pseudorca crassidens, by region and quarter, in the Atlantic (AT), Indian (IN) and Pacific (PA) Oceans, as estimated from observers at sea during the 1993-2006 period. The number of swordfish caught in each 5ºx5º square was used as weighting factor for the mean calculations by regions-quarter. Shaded (blue) cells indicate data substituted from the closest region-quarter.

Quarter 1 2 3 4 AT01 AT02 0 0.03511 0.0969 0.13822 AT03 0 0 0 0 AT04 0.50189 0.4309 0.55551 0.30667 AT05 0.09773 0.52594 0.06633 0.01442 AT06 0.03155 0.26677 0.10463 AT07 0.11168 0.03507 0.24416 0.03195 AT08 0.11168 0.03507 0.24416 0

Quarter 1 2 3 4 IN01 0.14493 IN02 IN03 0.22698 0.29209 0 0.03927 IN04 0.90269 0.08287 0.73693 IN05 0.45601 0.41453 0 0.9738 IN06 0.03843 0.02341 0.13639 0.03879 IN07 0.01619 0 0 0 IN08 0 0.18354 0.17813 0.02273

Quarter 1 2 3 4 PA01 PA02 0 0 0.1317 0.02323 PA03 PA04 0 PA05 0 PA06 0.62156 0.14786 0.03453 0.21852 PA07 0 0 0 0 PA08 0.00628 0 0 0.00922 PA09 0.01714 0.02477 0.00406 0

1729 Table 2. Mean number of heads of swordfish per retention (HPR) depredated by Pseudorca crassidens, by region and quarter, in the Atlantic (AT), Indian (IN) and Pacific (PA) Oceans, as estimated from observers at sea during the 1993-2006 period. The number of swordfish caught in each 5ºx5º square was used as weighting factor for the mean calculations by regions-quarter. Shaded (blue) cells indicate data substituted from the closest region-quarter.

Quarter 1 2 3 4 AT01 AT02 0 0.0016318 0.0040074 0.0064734 AT03 0 0 0 0 AT04 0.056112 0.0575687 0.1066845 0.0461439 AT05 0.0087416 0.0525808 0.0083681 0.0016672 AT06 0.009926 0.0697022 0.0441505 AT07 0.0187461 0.0053542 0.036456 0.0050057 AT08 0.0187461 0.0053542 0.036456 0

Quarter 1 2 3 4 IN01 0 IN02 IN03 0.0574691 0.099641 0 0.0037696 IN04 0.0944536 0.0449309 0.1713519 IN05 0.0691466 0.0293096 0 0.2038426 IN06 0.0041449 0.0017014 0.0483571 0.0107405 IN07 0.0020835 0 0 0.0009756 IN08 0 0.0201094 0.0138733 0.0084474

Quarter 1 2 3 4 PA01 PA02 0 0 0.0283818 0.0204726 PA03 PA04 0 PA05 0 PA06 0.177458 0.0468648 0 0.0726356 PA07 0 0 0 0 PA08 0.000455 0 0 0.0011706 PA09 0.0021079 0.0011452 0.000243 0

1730 Table 3. Mean number of heads of swordfish per thousand hooks set (HPUE) depredated by Pseudorca crassidens, by region and quarter, in the Atlantic (AT), Indian (IN) and Pacific (PA) Oceans, as estimated from observers at sea during the 1993-2006 period. Observations by set-regions-quarter were used to obtain mean values and 95% confidence intervals (+/- CI). Shaded (blue) cells indicate data substituted from the closest region-quarter.

Quarter Quarter 1 2 3 4 1 2 3 4 AT01 IN01 0.1207729 CI CI 0.2367150 AT02 0 0.0507852 0.0947972 0.1358025 IN02 CI 0 0.0799400 0.1607009 0.1528834 CI AT03 0 0 0 0 IN03 0.2188768 0.2791281 0 0.0462963 CI 0 0 0 0 CI 0.2662516 0.3629002 0 0.0907407 AT04 0,4337734 0.3561854 0.5101739 0.3505291 IN04 0.9312826 0.1139212 0.7657596 CI 0,4051916 0.1678541 0.3145955 0.4930764 CI 0.3009827 0.1542933 0.3422884 AT05 0,1157407 0.3660104 0.0780702 0.0276179 IN05 0.4663031 0.4161967 0 1.0432436 CI 0,1065912 0.1898728 0.1222192 0.0406312 CI 0.1744878 0.3948490 0 0.4046435 AT06 0.022388877 0.2267074 0.0893524 IN06 0.0409063 0.0192790 0.1697531 0.0384420 CI 0.024700353 0.0885389 0.0724154 CI 0.0320842 0.0311220 0.1606988 0.0387421 AT07 0,1080088 0.0437315 0.2239057 0.0427815 IN07 0.0125805 0 0 0 CI 0,0899642 0.0309743 0.2116391 0.0516903 CI 0.0246578 0 0 0 AT08 0,1080088 0.0437315 0.2239057 0 IN08 0 0.1493195 0.1568298 0.0205694 CI 0,0899642 0.0309743 0.2116391 0 CI 0 0.2078122 0.1706836 0.0403159

Quarter 1 2 3 4

PA01 CI PA02 0 0 0.0829511 0.0187768 CI 0 0 0.1385501 0.0273897

PA03

CI PA04 0 CI 0 PA05 0

IC PA06 0.4390138 0.1550424 0.0490196 0.2167508 CI 0.6538785 0.0997450 0.0960784 0.2285936 PA07 0 0 0 0

CI 0 0 0 0

PA08 0.0049962 0 0 0.0127420 CI 0.0069164 0 0 0.0154982 PA09 0.0232288 0.0216431 0.0044640 0 CI 0.0455285 0.0179246 0.0087494 0

1731 Table 4. Mean number of heads of swordfish per retention (HPR) depredated by Pseudorca crassidens, by region and quarter, in the Atlantic (AT), Indian (IN) and Pacific (PA) Oceans, as estimated from observers at sea during the 1993-2006 period. Observations by set-regions-quarter were used to obtain mean values and confidence intervals (+/- 95% CI). Blue cells indicate data substituted from the closest region-quarter.

Quarter Quarter 1 2 3 4 1 2 3 4 AT01 IN01 0 CI CI 0 AT02 0 0.0023363 0.0039203 0.0069096 IN02 CI 0 0.0036260 0.0068497 0.0096815 CI AT03 0 0 0 0 IN03 0.0554167 0.1010875 0 0.0044444 CI 0 0 0 0 CI 0.0738249 0.1376964 0 0.0087111 AT04 0.0658565 0.0682662 0.1061600 0.0400000 IN04 0.0922555 0.0876623 0.1596752 CI 0.0581458 0.0368866 0.0689188 0.0784000 CI 0.0348801 0.1372246 0.1232035 AT05 0.0104500 0.0436001 0.0103704 0.0034469 IN05 0.0771890 0.0322673 0 0.2423546 CI 0.0103989 0.0178746 0.0196061 0.0054243 CI 0.0356139 0.0372328 0 0.1166122 AT06 0.0065515 0.0615111 0.0444431 IN06 0.0048988 0.0014013 0.0744891 0.0106450 CI 0.0085957 0.0365963 0.0379842 CI 0.0037442 0.0025225 0.0917372 0.0136410 AT07 0.0189881 0.0072205 0.0386516 0.0067033 IN07 0.0015298 0 0 0.0006178 CI 0.0189418 0.0060755 0.0414353 0.0088157 CI 0.0021154 0 0 0.0008657 AT08 0.0189881 0.0072205 0.0386516 0 IN08 0 0.0163597 0.0121585 0.0074993 CI 0.0189418 0.0060755 0.0414353 0 CI 0 0.0237909 0.0158044 0.0138514

Quarter 1 2 3 4

PA01

CI PA02 0 0 0.0244565 0.0159236 CI 0 0 0.0343536 0.0256977 PA03 CI

PA04 0

CI 0 PA05 0 CI PA06 0.1372549 0.0492778 0 0.0750331 CI 0.1841851 0.0360918 0 0.0936972

PA07 0 0 0 0 CI 0 0 0 0 PA08 0.0003659 0 0 0.0016785 CI 0.0005087 0 0 0.0017946 PA09 0.0028571 0.0010362 0.0002671 0 CI 0.0056000 0.0008237 0.0005235 0

1732 Table 5. Summary of the estimated mean number of depredated swordfish (#Heads) by Pseudorca crassidens in the Atlantic, Indian and Pacific oceans and their estimated rates using different methodologies. The rates included in this table were obtained as: Rate= #Heads / (#R + #Heads). These rates represent the proportion of swordfish depredated by Pseudorca crassidens in relation to the catch in number during 2005.

Ocean Rate Type 5ºx5º Task II data (1) # Heads Rate #Heads #Heads Weighted #R Llim (2). Ulim. AT HPR Yes 262002 4618 0.017322 - - AT HPR No 262002 4804 0.018001 1016 9284 AT HPUE Yes 262002 3142 0.011849 - - AT HPUE No 262002 2999 0.011319 583 5841 IN HPR Yes 102233 2257 0.021603 - - IN HPR No 102233 2706 0.025790 269 5764 IN HPUE Yes 102233 509 0.004954 - - IN HPUE No 102233 528 0.005142 121 987 PA HPR Yes 112098 348 0.003096 PA HPR No 112098 296 0.002635 2 693 PA HPUE Yes 112098 133 0.001186 - - PA HPUE No 112098 114 0.001020 2 276 (1): Number of swordfish retained on board during 2005 as estimated from Task II data (#R). (2): The lower limit (Llim.) should not be used because the negative Llim value obtained for a region-quarter was considered as zero incidence in the final estimations.

1733

Figure 1. Mean 5x5 degree values in percentage of heads attacked or swordfish depredated by Pseudorca crassidens in relation to the number of swordfish captured (attacked+retained), based on data from the skippers of the Spanish surface longline fleet for all the months and years combined from 1992 to 2005 and the definition of the regions into each ocean.

Figure 2. Mean values 5ºx5º in percentage of heads attacked, or swordfish depredated by Pseudorca crassidens in relation to the number of swordfish captured (attacked+retained), based on data from the on-board observers of the Spanish surface longline fleet for all the months and years combined from 1993 to 2006 and the definition of the regions into each ocean.

1734 100 100 AT AT 80 80

60 60

40 40 Freq. (%) Freq. Freq. (%) Freq.

20 20

0 0 0 0,01-2 % 2,01-4 % 4,01-6 % 6,01-10 % >10% 0 0,01-2 % 2,01-4 % 4,01-6 % 6,01-10 % >10% Range Range

100 100 IN IN 80 80

60 60

40 40 Freq. (%) Freq. Freq. (%) Freq.

20 20

0 0 0 0,01-2 % 2,01-4 % 4,01-6 % 6,01-10 % >10% 0 0,01-2 % 2,01-4 % 4,01-6 % 6,01-10 % >10% Range Range

100 100 PA PA 80 80

60 60

40 40 Freq. (%) Freq. Freq. (%) Freq.

20 20

0 0 0 0,01-2 % 2,01-4 % 4,01-6 % 6,01-10 % >10% 0 0,01-2 % 2,01-4 % 4,01-6 % 6,01-10 % >10% Range Range

Figure 3. Relative frequency of the number of 5x5 degree squares plotted in Figures 1 and 2 by percentage ranges of swordfish attacked in relation to the number caught (retained + attacked). The ranges are the same as plotted in Figures 1 and 2, for the Atlantic (AT), Indian (IN) and Pacific (PA) oceans and source of information. Figures on left: data from skippers 1992-2005 (see Figure 1). Figures on right: data from observers at sea 1993- 2006 (see Figure 2).

1735 20

15 HPUE

10

5

0 AT02 AT04 AT06 AT08 IN03 IN05 IN07 PA02 PA05 PA07 PA09 AT03 AT05 AT07 IN01 IN04 IN06 IN08 PA04 PA06 PA08 REGION

2.5

2.0

1.5 HPR

1.0

0.5

0.0 AT02 AT04 AT06 AT08 IN03 IN05 IN07 PA02 PA05 PA07 PA09 AT03 AT05 AT07 IN01 IN04 IN06 IN08 PA04 PA06 PA08 REGION

Figure 4. Box-plot of heads per unit of effort (HPUE) >0 and head per retention (HPR) > 0, by set and ocean- region.

1736

Figure 5. Some swordfish specimens caught with the surface longline gear that were later depredated by Pseudorca crassidens including one swordfish that showed signs of having been attacked but was not successfully depredated (lowest-right).

1737

Figure 6. Some specimens of Prionace glauca and Thunnus spp. caught with the surface longline gear that could be also depredated by Paseudorca crassidens. Prionace glauca is rarely preyed upon by this cetacean except in the ventral area, where it may feed on its liver. Shark attacks could be sometimes misinterpreted as Paseudorca crassidens depredation.

1738