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COMMERCIAL AND RESEARCH LONGLINE CRUISE DURING 2002 AND 2003. Hirokazu Saito ... distribution verticale a été calculé à partir de huit spécimens.
SCRS/2005/042

Col. Vol. Sci. Pap. ICCAT, 59(1): 252-264 (2006)

USE OF POP-UP TAGS TO ESTIMATE VERTICAL DISTRIBUTION OF ATLANTIC BLUE MARLIN (MAKAIRA NIGRICANS) RELEASED FROM THE COMMERCIAL AND RESEARCH LONGLINE CRUISE DURING 2002 AND 2003 Hirokazu Saito and Kotaro Yokawa1 SUMMARY Current ICCAT assessments of Atlantic blue marlin (Makaira nigricans) are based on the estimation of relative abundance by using commercial longline CPUE data. There has been deployment in pop-up tags over the past few years to estimate the vertical distribution of fish for the appropriate calculation of relative abundance. Popup tags were attached on Atlantic blue marlin during longline research cruises of Japanese RV Shoyo-Maru and commercial longline cruises with observers. The vertical distribution pattern was calculated from eight individuals. We found that all fish spend the majority of time in the shallowest water layer, and dived deep if the bottom of the mixed layer depth was deep. Our results suggest that vertical distribution patterns for blue marlin are described by the bottom of mixed layer depth, even if area and season are different, and there are no clear relationships between fish size and depth distribution pattern. RÉSUMÉ Les évaluations actuellement menées par l’ICCAT sur le makaire bleu de l’Atlantique (Makaira nigricans) se fondent sur l’estimation de l’abondance relative en utilisant les données de la PCUE palangrière commerciale. Des marques pop-up ont été déployées au cours de ces quelques dernières années afin d’estimer la distribution verticale des poissons aux fins du calcul approprié de l’abondance relative. Des marques pop-up ont été apposées sur des makaires bleus lors des campagnes de pêche exploratoire à la palangre du RV Shoyo-Maru et des campagnes de pêche commerciale à la palangre avec des observateurs embarqués. Le schéma de distribution verticale a été calculé à partir de huit spécimens. Nous avons constaté que tous les poissons passent la majorité de leur temps dans la couche la moins profonde et plongeaient en eaux profondes si le fond de la couche mixte était situé en profondeur. Nos résultats suggèrent que les schémas de distribution verticale pour le makaire bleu sont décrits par le fond de la profondeur de la couche mixte, même si la zone et la saison diffèrent, et il n’existe pas de rapports clairement établis entre la taille du poisson et le schéma de distribution de la profondeur. RESUMEN Las actuales evaluaciones de ICCAT de aguja azul (Makaira nigricans) del Atlántico se basan en estimaciones de la abundancia relativa utilizando datos de CPUE de la pesquería de palangre comercial. Durante los últimos años se han colocado marcas pop-up para estimar la distribución vertical de los peces con el fin de realizar un buen cálculo de la abundancia relativa. Se colocaron marcas pop-up en ejemplares de aguja azul del Atlántico durante cruceros de investigación realizados en el palangrero japonés Shoyu-Maru y durante cruceros de palangreros comerciales con observadores a bordo. Se calculó el patrón de distribución vertical de ocho ejemplares. Descubrimos que estos ejemplares pasaban la mayor parte del tiempo en la capa de agua más superficial y se sumergían a mayor profundidad cuando el fondo de la capa de mezcla se hallaba a más profundidad. Nuestros resultados sugieren que los patrones de distribución vertical de la aguja azul están condicionados por la profundidad del fondo de la capa de mezcla, aunque la zona o temporada sean diferentes, y también sugieren que no existe una relación clara entre la talla de los peces y el patrón de distribución vertical.

KEY WORDS Atlantic blue marlin; Habitat; Mixed layer; Longline; Pop-up tag; Thermocline; Tropical Atlantic; Vertical distribution

1

National Research Institute of Far Seas Fisheries, 5-7-1 Orido, Shimizu, Japan 424-8633.

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1. Introduction Atlantic blue marlin, Makaira nigricans, is a common bycatch of tuna longline gear deployed for target species such as bigeye tuna. Estimations of abundance indices of Atlantic blue marlin caught by Japanese longliners with generalized liner model (GLM) have been facing with problems of obtaining unrealistic results about effect of gear configurations that is higher CPUE for deep setting operations than shallow setting operations. Hinton and Nakano (1996) developed a model to make direct estimation of the effective fishing effort on Pacific blue marlin using habitat information. This method applied on Atlantic blue marlin (Yokawa et al. 2001), but it was received a criticism for reliability of assumption about habitat preference of Atlantic blue marlin in the model, because it was estimated by the one from the Pacific blue marlin. In this study, we examined archival pop-up tag data for blue marlin caught in the tropical Atlantic during the scientific research cruise by R/V Shoyo-Maru (2,494GRT) (Saito et al. 2003), and the commercial longline cruise by Japanese longliner from September 2001 to January 2003 (Matsumoto et al. 2003, Matsumoto et al. 2004) to evaluate their vertical distribution pattern and to quantify the factors which seem to influence their habitat.

2. Materials and methods In this study, we stratified the data into four geographic areas (Area 1-4, Figure 1), because sea surface temperature was divided roughly into four areas. 2.1 Areas 1-3 In the period of August 30 to October 16, 2002, 27 longline operations were conducted by the Japanese RV Shoyo-Maru (2,494GRT) in the tropical Atlantic. Twelve Pop-up Archival Transmitting tags (PAT tag, Wildlife Computers Inc.) were deployed on blue marlins through the Shoyo-Maru research cruise, and six PAT tags successfully reported data (Table 1). PAT tags were programmed to take and store discrete depth, water temperature, and light intensity every minute. The sensors have rather good resolution (0.5m for depth, 0.05°C for water temperature) and wide ranges (0 to 1000m, -40°C to 60°C for water temperature, and depth down to 300m in clear water conditions for light intensity). The data of depth, water temperature and light intensity (used to estimate geolocation) were aggregated into 12 ranks which decided arbitrary using sea surface temperature and converted into a histogram by every 3, 4 or 6 hours. PAT tags also collect depth-temperature profile that contains the minimum and maximum temperatures recorded at each depth, and 6 further depths and their associated minimum and maximum temperatures that are dynamically chosen to be roughly equally spaced from the shallowest to the deepest depth. Two commercial vessels (161 longline operations) were monitored by on board observers from December 2001 to March 2002 in the tropical Atlantic (off Dakar (Area 3), off Abidjan or off Angola (Area 4)). Two PSATs (model PTT-100, Microwave Telemetry) were deployed on blue marlin by observers. The one tag Fish 24830 reported 30 days, but another one recorded very few data so that it was not used in this study. PSATs recorded ambient depth (into 5.38-m bins), light intensity and temperature (resolution +0.17°C). Table 1 shows Area, Fish ID, estimated body weight and summary of release and pop-up location for each individual. Duration of data collection ranged from 6 to 32 days. A metal dart (71mm long for the Shoyo-Maru cruise and 94mm long for the commercial longline cruise) was connected to the tag by a tether made by wire, polyethylene, and nylon, attaching the tag on the fish. As for the PAT tags, an auto severing device called RD1500 was fastened to the nylon part to the tether, and this device cuts the nylon line and releases the tag from the fish when it senses pressure, roughly corresponding to a depth of 1,500 m, thus preventing destruction by the water pressure. PSATs also have a similar fail-safe mechanism of release and data transmission if the tag approaches its depth limit (approximately 1,200 m). The major part of the tether covered the urethane pipe to prevent it from injuring the tagged fish. The metal dart was inserted by using a harpoon which is aimed at the side body of the dorsal fin, thus fixing the tag to the fish.

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The conditions of hooked blue marlin were checked carefully by researchers, crews and observers to confirm whether the species was good for tagging or not. Fish size was estimated by a veteran crew. The tagged fish were released by cutting the fishing line immediately after tag attachment. The tags detached from the fish, floated to the surface, and transmitted archived data to satellites in the Argos satellite system. Position information and sections of stored data were captured with each satellite pass, transmitted to a ground station, and ultimately to the authors by means of the Internet. Location data for PAT tags were analyzed by using the computer program offered by Wildlife Computers Inc. As for the PSATs, transmitted data was sent to the Microwave Telemetry and analyzed. As for the PAT tags, we classified depth bins into every 25m at the depths from 0m to 150m, and every 50m afterwards for the analysis. As for the PSATs, depth and temperature distributions were calculated based on 25 m and 1ºC bins, respectively. Of the PSATs, only temperature data recorded in 0:00 and 12:00 were used in this study, because water temperature recorded by PSATs except 0:00 and 12:00 can be biased from real observation value by a characteristic of a record system of the program of the tag if fish dived rapidly. The light intensity over time is used to estimate the geographical position of the tagged fish, but, it is known that geolocation by light intensity has severe inherent limits to accuracy (Metcalfe 2001). Although Kalman filter analysis (Sibert et al. 2003) was used to estimate the most probable track, it was not used in Areas 1-3 analyses because the daily location data of the tag was less. In this study, the water temperature data did not use for the Kalman filter analysis. CTD operations were conducted before or after longline operations in the research cruise of Shoyo-Maru. As for the commercial longline vessels, one vessel attached TDRs (SBT-500. Murayama Denki Ltd.) to the branch line to evaluate hook depth and hooking time of fish. In this study, we referred depth-temperature profiles collected by CTD and TDR. Sea surface temperature measured by a thermometer of ship was recorded when the fish was tagged (Table 1). 2.2 Area 4 One commercial vessels (86 longline operations) were monitored by observers from October 2002 to January 2003 in the tropical Atlantic (around off Angola and off Abidjan). Four PSATs were deployed on blue marlin by observers, by using same material and method of Areas 1-3. One PSAT popped-up successfully (Table 1). Fish 28837 was the only individual released in this area, but was able to get the longest record (58 days of data available for analyses). An estimate of a location using light intensity was successfully done by Kalman filter analysis. Because of elimination of data during transmissions of them, we were not able to estimate daily positions from January 19, 2003 to February 3, 2003. Depth and temperature distributions were aggregated into 10 m and 1ºC bins, respectively. There had no environmental data collections of CTD and TDR in the commercial longline vessel. 3. Results Area 1 (North off Brazil) Fish 8755 released north off Brazil moved in a northeast direction over ten days (Figure 1). Though the fish dived to 80 m, water temperature did not change largely (Figure 3). This fish spent vast majority (98%) of time at 0-25 m layer (Figure 4). Temperatures that the fish spent ranged narrow (27-29ºC, Figure 5). With referring to CTD data, this fish swam vast majority of time in the mixed layer (Figure 6). Fish 9111 moved in a southeast direction over 32 days. This fish dived mainly between 100 to 150 m (down to 14ºC). This fish spent 61% of time at 0-25 m layer, and mainly distributed in 0-125 m. The tag recorded a broader range of temperatures (14-29ºC) than that of Fish 8755, where released in the same area. With referring to CTD data, this fish dived into the thermocline (down to 160m, 40m below the bottom of mixed layer), down to 13ºC below the bottom of mixed layer temperature. 254

Fish 8758 moved in a southeast direction over 32 days. As for this fish, we could not get depth-temperature profile. Depth distribution of this fish ranged mainly in 0-200m, and had two modes at 0-25 m layer (62% of time) and 50-75 m (17% of time). This fish recorded deepest dive to the 300-1000 m bin. This fish spent 62% of time at depth shallower than 25 m, and recorded minimum temperature bin (9-14ºC) through this study. With referring to CTD data, the fish spent mainly in the surface mixed layer as well as Fish 8755 and 9111, although the fish sometimes dived deeply. Area 2 (East off Brazil) Fish 8752 released east off Brazil moved in a southsoutheast direction over eight days. Water temperature that the fish experienced did not change largely. Depth distribution of this fish ranged 0-125m, and had two modes at 0-25 m layer (88% of time) and 75-100 m (5% of time). This fish spent vast majority (99%) of time at temperature of 25ºC. With referring to CTD data, this fish swam vast majority of time in the mixed layer. Fish 8757 moved in a westnorthwest direction over 25 days. This fish dived mainly between 50 to 150 m. Temperature that the fish experienced ranged between 22 and 25ºC until the 17th days, and then changed between 17 and 22 ºC. This fish spent 71% of time at 0-25 m layer. This fish spent vast majority (97%) of time at temperature of 25ºC, and dived to the 17-21ºC bin, and also this fish dived into the thermocline (down to 140m, 50m below the bottom of mixed layer), down to 8ºC below the bottom of mixed layer temperature. Area 3 (Southwest off Dakar) Fish 9906 released southwest off Dakar moved in a southeast direction over 11 days. This fish dived within the range between 60 to 110 m (17-26ºC). Depth distribution of this fish ranged 0-125m, with two modes at 0-25 m layer (76% of time) and 50-100 m (21% of time). This fish spent 80% of time at temperature of 27ºC. With referring to CTD data, this fish dived into the thermocline (down to 110m, 50m below the bottom of mixed layer), within a range of 10ºC (-10ºC below the bottom of mixed layer). Fish 24830 released southwest off Dakar moved in a East-southeast direction over 31 days. This fish spent vast majority (96%) of time at 0-25 m layer. Temperature that the fish experienced mainly ranged between 25 and 27ºC. With referring to SBT-500 data, this fish dived into the thermocline (down to 40m, 20m below the bottom of mixed layer), within a range of 5ºC (-4ºC below the bottom of mixed layer). Area 4 (East off Angola) Fish 28837 released East off Angola moved to the east for first one week, and seemed to move clockwise direction after one week from release. According to the comparison with the Near Real-Time Geostrophic Velocity Viewer provided by Colorado Center for Astrodynamics Research, the direction of fish movement after one week from release was consistent with the direction of eddy. Sea surface temperature that fish experienced changed from 23ºC (4 January, 2003) to 28ºC (14 January 2003). Sea surface temperature that fish experienced became almost constant after January 14, 2003. Therefore we divided provided data into January 4 to January 14 (1st period) and January 15 to March 2, 2003 (2nd period). Depth and temperature distribution for Fish 28837 in each period are shown in Figure 8. As a result, this fish spent mainly in the sea surface layer through periods, and dived deeper to the 120 m (15ºC) in the 2nd period than that of 1st period (Figure 7). Depth-temperature profiles by blue marlin (Fish 28837) released in Area 4 also have the same vertical distribution pattern (Figure 9). As a total, this fish spent 92% of time at 0-25 m layer (Table 2). 4. Discussion In this study, blue marlin distributed majority of time in a mixed layer and also dived mainly down to 50 m below the bottom of mixed layer, down to 13ºC below the bottom of mixed layer temperature (Table 2). The frequency of dive to the thermocline ranged between 0 and 20%. Diving depth was deepest in Area 1 (the bottom of mixed layer was 120m) where deepest surface mixed layer was observed among four areas. For Fish 9906 and 24830 in Area 3, Fish 9906 released in August dived deeper than Fish 24830 released in March. There is a possibility that such difference may have occurred by the difference between deep (60m, Fish 9906) and shallow (30m, Fish 24830) mixed layer. 255

For Fish 28837 in Area 4, the tendency that depth and water temperature distribution pattern changed two weeks after release (Figure 9). This result may indicate that the fish move to the different water mass where have different depth-temperature profiles. It might be the cause of the stress after release, because this fish moved from low water temperature area to the high water temperature area after release. These results suggest that vertical distribution pattern for blue marlin is described by the depth of bottom of mixed layer depth, even if area and season are different. Our result support the hypotheses of Brill and Lutcavage (2001) that water temperature relative to mixed-layer temperature, rather than absolute temperature, that limits striped marlin vertical movements even if body weight was different. Goodyear et al. (2002) pointed out possibilities that there is no difference by age, sex, time of year and size. As for the fish size, we compared three individuals tagged in Area 1, which had different weight. For Fish 8758 (120 kg) and 9111 (70 kg), Fish 8758 dived deeper (150-200 m bin) than Fish 9111. Fish 8755 (200kg), which is heavier than Fish 8758 and 9111 spent majority of time (98%) in the 0-25m bin. Brill et al. (1993) suggests that water temperature relative to mixed-layer temperature, rather than absolute temperature, that limits striped marlin vertical movements even if body weight was different. Though the differences among individuals and fewness of a sample might have influenced, our results also showed that there are no clear relationships between fish weight and depth distribution pattern in a same area. Kerstetter et al. (2003) suggested that the possibility that blue marlin have a distinct bimodal depth preference. It is thought that Fish 9111 and 9906 had a distinct bimodal depth preference, spending their time in surface and below the surface mixed layer (Figure 4). As for Fish 8752 and 8758, two modes appeared for depth distribution. These modes were not appeared below the surface mixed layer but in the surface mixed layer. Other fish did not have a distinct bimodal preference. These results may suggest that blue marlin tends to have a bimodal depth preference, but two modes are not always made in surface waters and below the surface mixed layer. Acknowledgements We acknowledge the captain Tsukiyama and his crew of R/V Shoyo-Maru and three F/V for cooperation in the experiment. References BRILL, R.W., and M.E. Lutcavage. 2001. Understanding environmental influences on movements and depth distribution of tunas and billfishes can significantly improve population assessments, American Fishery Society Symposium, Vol 25, 179-198. BRILL, R.W., D. B. Holts, R. K. C. Chang, S. Sullivan, H. Dewar and F. G. Carey. 1993. Horizontal and vertical movements of striped marlin (Tetrapturus audax) near the Hawaiian Islands based on ultrasonic telemetry, with simultaneous measurements of ocean currents. Mar. Biol., 117, 567-574. COLORADO CENTER FOR ASTRODYNAMICS RESEARCH, Dept. of Aerospace Engineering Sciences, University of Colorado. 2005. Global Near Real-Time Altimeter Geostrophic Velocity Viewer. http://e450.colorado.edu/realtime/global_realtime/geovel.html. (Last access: January 7, 2005) HINTON, M.G., and H. Nakano. 1996. Standardizing catch and effort statistics using physiological, ecological, or behavioral constrains and environmental data, with an application to blue marlin (Makaira nigricans) catch and effort data from Japanese longline fisheries in the Pacific. IATTC Bull., 21(4): 171-200. KERSTETTER, D., W., B. E. Luckhurst, E. D. Prince and J. E. Graves. 2003. Use of pop-up satellite archival tags to demonstrate survival of blue marlin (Makaira nigricans) released from pelagic longline gear. Fish. Bull., 101:939-948. MATSUMOTO, T., H. Saito and N. Miyabe. 2003. Report of observer program for Japanese tuna longline fishery in the Atlantic Ocean from September 2001 to March 2002. Col. Vol. Sci. Pap. ICCAT, 55(4): 16791718.

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MATSUMOTO, T., H. Saito and N. Miyabe. 2004. Report of observer program for the Japanese tuna longline fishery in the Atlantic Ocean from September 2002 to January 2003. Col. Vol. Sci. Pap. ICCAT, 56(1): 254281. SAITO, H., Y. Takeuchi and K. Yokawa. 2004. Vertical distribution of Atlantic blue marlin obtained from popup archival tags in the tropical Atlantic Ocean. Col. Vol. Sci. Pap. ICCAT, 56(1):201-211. SIBERT, J. R., M. K. Musyl and R. W. Brill. 2003. Horizontal movements of bigeye tuna (Thunnus obesus) near Hawaii determined by Kalman filter analysis of archival tagging data. Fish. Oceanogr. 12:3, 141-151. YOKAWA, K., Y. Takeuchi, M. Okazaki, and Y. Uozumi. 2001. Standardizations of CPUE of blue marlin and white marlin caught by Japanese longliners in the Atlantic Ocean. Col. Vol. Sci. Pap. ICCAT, 53:345-355. Table 1. Area, Fish ID, estimated body weight and summary of deployment and pop-up location for each individual. Estimated Area *1 Fish ID

body weight

(kg)

1 1 1 2 2 3 3 4

8755 8758 9111 8752 8757 9906 24830 28837

200 120 70 180 150 140 80 150

Deployment

Pop-up date and location

Type

data

of tag*2 Date (UTC)

PAT PAT PAT PAT PAT PAT PSAT PSAT

Days of

Time Time (UTC) (Local)

Sea surface Latitude

Longitude

temperature

available Date

Latitude

Longitude

18-Oct-02 12-Nov-02 10-Nov-02 25-Sep-02 3-Oct-02 11-Sep-02 23-Apr-02 4-Mar-03

03°40'N 02°55'N 00°26'S 09°20'S 04°40'S 03°42'N 06°08'N 07°29'S

039°33'W 039°26'W 035°53'W 022°17'W 027°38'W 020°56'W 017°16'W 007°16'E

(°C)

8-Oct-02 22:37 19:37 03°25'N 040°29'W 10-Oct-02 0:33 21:33 03°32'N 040°23'W 8-Oct-02 1:27 22:27 04°10'N 041°03'W 17-Sep-02 0:06 22:06 08°24'S 021°57'W 8-Sep-02 22:10 20:10 07°50'S 021°12'W 31-Aug-02 19:42 18:42 05°40'N 022°36'W 23-Mar-02 1:08 1:08 08°00'N 021°36'W 4-Jan-03 2:00 2:00 10°51'S 002°47'E

27.7 27.7 27.7 25.3 25.2 27.6 26.9 -

for analyses

6 29 32 6 19 7 30 58

*1 Refer to Figure 1. *2 PAT: Pop-up Archival Transmitting tag (Wildlife computers), PSAT: Pop-up Satellite Archival Tag (Microwave Telemetry, Inc.)

Table 2. Characteristics of vertical distribution pattern for eight blue marlin and the mixed layer in each area. Area 1 Area 2 Area Fish ID 8755 8758 9111 8752 8757 Estimated body weight (kg) 200 120 70 180 150 Type of tag PAT PAT PAT PAT PAT Frequency in the 0 - 25 m layer (%) Maximum diving depth (m) Maximum temperature (ºC) Minimum temperature (ºC)

Area 3 9906 24830 80 140 PAT PSAT

Area 4 28837 150 PSAT

98 62 61 88 71 76 96 *1 * *1 *1 *1 *1 *2 75-100 300-1000 150-200 100-125 125-150 100-125 43 *1 *1 *1 *1 *1 *1 *3 28-29 28-29 28-29 25-26 25-26 28-29 27 *1 *1 *1 *1 *1 *1 *3 9-14 14-19 24-25 12-17 22-23 22 27-28

92 *2 118 *3 30 *3 16

120 90 50 The bottom of the mixed layer by CTD/TDR depth (m) 27 25 27 temperature (ºC) *1 Values of PAT tags show the obtained maximum / minimum depth and water temperature bins which decided arbitrary. *2 The depth data that recorded hourly by PSATs were used to obtain maximum depth. *3 Values of obtained water temperatures by PSATs that recorded in 0:00 and 12:00 were used, because a value of recorded water temperature by PSAT except 0:00 and 12:00 can be biased from real observation value by a characteristic of a record system of the program.

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Figure 1. Released and popped up point of pop-up tags attached to blue marlins. Each data was divided into four areas by using sea surface temperature and current information.

Figure 2. Estimated most probable track of blue marlin (Fish 28837). Each position was calculated by Kalman filter analysis.

258

0

30

Fish 8755, PAT

50

Area 1

Fish 8755, PAT

25

100

20

150

15

200

10

0

30

50

25

100

20 15

150

Fish 9111, PAT

Fish 9111, PAT

200

10 30

0

Fish 8752, PAT

Fish 8752, PAT 25

100

Depth (m)

Area 2

150 200 0 Fish 8757, PAT 50

100 150

Temperature (ºC)

50

20 15 10 30 Fish 8757, PAT 25 20 15

200

10

0

30 Fish 9906, PAT

Fish 9906, PAT 50

Area 3

25 20

100 Minimum depth Maximum depth

150 200

10

0

30

50

25 20

100 Fish 24830, PSAT Depth

150 200

Maximum temperature Minimum temperature

15

Fish 24830, PSAT Temperature

15 10

5

10

15

20

25

30

Days after release

5

10

15

20

25

Days after release

Figure 3. Profiles of diving depth (left panel) and temperature (right panel) recorded by pop-up tags attached to six blue marlins. For five PATs (top five panels), the minimum and maximum temperatures recorded at each depth in each time bin were used in this figure. A depth figure for PSAT (bottom panel, Fish 24830) include all record. A temperature figure for PSAT, data recorded in 0:00 and 12:00 were used, because a value of recorded water temperature by PSAT except 0:00 and 12:00 can be biased from real observation value by a characteristic of a record system of the program.

259

30

0-25 25-50 50-75 75-100 100-125 125-150 150-200 200-250 250-300 300-

Area 1 Fish 8755

0-25 25-50 50-75 75-100 100-125 125-150 150-200 200-250 250-300 300-

Area 1 Fish 8758

0-25 25-50 50-75 75-100 100-125 125-150 150-200 200-250 250-300 300-

Frequency (%)

Area 1 Fish 9111

0-25 25-50 50-75 75-100 100-125 125-150 150-200 200-250 250-300 300-

Area 2 Fish 8752

0-25 25-50 50-75 75-100 100-125 125-150 150-200 200-250 250-300 300-

Area 2 Fish 8757

0-25 25-50 50-75 75-100 100-125 125-150 150-200 200-250 250-300 300-

0

0-25 25-50 50-75 75-100 20 100-12540 125-150 150-200 Temperature 200-250 250-300 300-

Area 3 Fish 9906

60

80

100

(ºC)

Area 3 Fish 24830

Figure 4. Frequency histograms (±SE) for depth by pop-up tags attached to seven blue marlins released in the tropical Atlantic (Areas 1-3).

260

100 80

Area 1 Fish 8755

60 40 20 0 100 80

Area 1 Fish 8758

60 40 20 0 100 80

Area 1 Fish 9111

60 40 20 0 -9 100

Frequency (%)

80

9-14 14-19 19-23 23-24 24-25 25-26 26-27 27-28 28-29

Area 2 Fish 8752

60 40 20 0 100 80

Area 2 Fish 8757

60 40 20 0 12-17 17-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-60 100 80

Area 3 Fish 9906

60 40 20 0 8-13 13-18 18-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 100 80

Area 3 Fish 24830

60 40 20 0 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29

Temperature (ºC) Figure 5. Frequency histograms (±SE) for temperature by pop-up tags attached to seven blue marlins released in the tropical Atlantic (Areas 1-3). For Fish 28837 (upper panel), data recorded in 0:00 and 12:00 were used in this figure, because a value of recorded water temperature by PSAT except 0:00 and 12:00 can be biased from real observation value by a characteristic of a record system of the tag. 261

0

5

10

Temperature (ºC) 15 20

25

30

35

0

Depth (m)

50

100

150

200

Fish 8755 Fiah 9111 CTD data (8 Oct 2002)

250 Temperature (ºC) 0

5

10

15

20

25

30

35

0

Depth (m)

50

100

150 Fish 8752

200

Fish 8757 CTD data (8 Sep 2002)

250

Temperature (ºC) 0

5

10

15

20

25

30

35

0

Depth (m)

50

100

150

200

Fish 9906 CTD data (31Aug 2002)

250 Temperature (ºC) 0

5

10

15

20

25

30

35

0

Depth (m)

50

100

150

200

Fish 24830 TDR data (23 Mar 2002)

250

Figure 6. Depth-temperature plots by pop-up tags attached to six blue marlins and ones by CTD/TDR that collected in Areas 1-3.

262

Depth (m)

0 50 100 150

Temperature (ºC)

200 30 25 20 15 10

5

10

15

20

25

30

35

40

45

50

55

Days after release

Frequency (%)

29-30

28-29

27-28

26-27

25-26

24-25

100

23-24

80

22-23

60

21-22

40

20-21

20

19-20

0

15 Jan 2003 - 2 Mar 2003

18-19

15 Jan 2003 - 2 Mar 2003

70 60 50 40 30 20 10 0

17-18

0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120

4 Jan 2003 - 14 Jan 2003

16-17

4 Jan 2003 - 14 Jan 2003

70 60 50 40 30 20 10 0

15-16

0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120

Frequency (%)

Depth (m)

Figure 7. Profiles of diving depth (upper) and temperature (lower) recorded by pop-up tags attached to blue marlin (Fish 28837) released in the tropical Atlantic. As for temperature, data recorded in 0:00 and 12:00 were used in this figure, because a value of recorded water temperature by PSAT except 0:00 and 12:00 can be biased from real observation value by a characteristic of a record system of the tag.

Temperature (ºC)

Figure 8. Frequency histograms (±SE) for depth and temperature of blue marlin (Fish 28837) released in the tropical Atlantic. Depth and temperature data were divided into 4 January 2003-14 January 2003 and 15 January 2003-2 March 2003 by the period whether sea surface temperature elevated or not. As for temperature, data recorded in 0:00 and 12:00 were used in this figure, because a value of recorded water temperature by PSAT except 0:00 and 12:00 can be biased from real observation value by a characteristic of a record system of the program.

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Figure 9. Depth-temperature plots by blue marlin (Fish 28837) released in Area 4. As for temperature, data recorded in 0:00 and 12:00 were used in this figure, because a value of recorded water temperature by PSAT except 0:00 and 12:00 can be biased from real observation value by a characteristic of a record system of the program.

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