CSIRO PUBLISHING www.publish.csiro.au/journals/mfr Marine and Freshwater Research, 23, 54, 483 488 Analysis of sportfishing catch rates of striped marlin (Tetrapturus audax) at Cabo San Lucas, Baja California Sur, Mexico, and their relation to sea surface temperature Sofía Ortega-García A,D, Alexander Klett-Traulsen B and German Ponce-Díaz C A Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional S/N, Apartado Postal 592, Colonia Playa Palo de Santa Rita, C.P. 23, La Paz, Baja California Sur, México. B Instituto Nacional de la Pesca, Centro Regional de Investigación Pesquera, La Paz, Carretera a Pichilingue Km 1, CP 232, La Paz, Baja California Sur, México. C Centro de Investigaciones Biológicas del Noroeste, S.C. Km 1 Carretera a San Juan de La Costa El Comitán, Apartado Postal 128, C.P. 23, La Paz, Baja California Sur, México. D Corresponding author. Email: sortega@ipn.mx Abstract. Cabo San Lucas, Baja California Sur, Mexico, is the main sportfishing location for striped marlin, with a mean annual catch rate of.6 fish per fishing trip. In the present study, the interannual and seasonal variation of sportfishing catch rates from 199 to 1999, and their relationship to mean monthly sea surface temperatures were analysed. Although interannual variation was not significant, the seasonal effect showed significant differences, with highest average catch rates in winter, and lowest catch rates in summer (.9 and.3 respectively). An interannual significant difference with a decreasing tendency was in length analysis. Significant length and weight differences were found between males and females. Among females, the heaviest fish were recorded during spring. A significant relationship between catch rate and sea surface temperature (r =.62) was found, but no significant changes of catch rates could be measured during the 1992 1993 and 1997 1998 El Niño Southern Oscillation events, in spite of an apparent catch rate increase during the spring of 1998. Highest catch rates were recorded at between 22 and 24 C. Introduction The striped marlin (Tetrapturus audax) is an epipelagic species distributed in tropical, subtropical and temperate waters of the Pacific and Indian Oceans. It is the most dominant and widely distributed of all billfish (Nakamura 1985). Striped marlin usually swim above the thermocline, and its total distribution in the western Pacific has been reported to be generally bounded by the 2 C and 25 C sea surface temperature (SST) isotherms (Howard and Ueyanagi 1965). In the eastern Pacific, this species has been harvested for several decades by longline and sportfishing fisheries, and also as bycatch of the tuna purse seine fishery (Squire and Au 199; IATTC 1999). Analysis of the longline logbook records from 1981 1987 and 1988 1992 showed that the south-western coast of Baja California Sur and the lower mouth of the Gulf of California are recorded as having the greatest catches of striped marlin. A seasonal fluctuation of the hook rates has been also reported, being greatest during the third and fourth quarters (Nakano and Bayliff 1992; Uosaki and Bayliff 1999). Cabo San Lucas, at the southern tip of the Baja Peninsula, is the most important sportfishing location on the Pacific coast of Mexico, and striped marlin account for about 8% of all billfish caught by the local recreational fishery (Klett et al. 1996). Cabo San Lucas lies in the middle of two 5 5 latitude by longitude blocks off southern Baja California Sur (B.C.S.), where the highest catch per unit effort in the Pacific has been reported (Squire and Au 199). Striped marlin spawning activity in this core area has also been reported (Gonzalez-Armas et al. 1999). In Mexico, this species is reserved for sportfishing within a range of 5 nautical miles from the national coastline. In 1987, a protection zone was established around Baja California Sur where commercial fishing was prohibited and, in 199, the permits for longliners that exclusively target billfish were cancelled, although a number of longliners with permits for shark and tuna catch, and recently for swordfish catch, have worked the area with a continuous incidental catch of billfish (Sosa-Nishizaki 1998; Santana-Hernandez 21). For this area, studies of marlin catch rates in sportfishing are scarce. Given that their use in the determination of the effect of fishing on the stock of fish could be used to evaluate fishing success relative to seasonal changes, specific types of fishing gear, or changes in gear, and effects of the environmental changes, their continuous analysis is important. CSIRO 23 1.171/MF1258 1323-165/3/4483
484 Marine and Freshwater Research S. Ortega-García et al. Table 1. Number of trips and striped marlin caught at Cabo San Lucas, B.C.S., during 199 1999 No. of trips No. of fish caught 199 13 589 7223 1991 19 417 11 747 1992 16 845 8641 1993 15 517 9171 1994 14 845 7942 1995 13 472 846 1996 15 315 1 451 1997 2 613 916 1998 23 51 19 638 1999 25 781 12 362 Fig. 1. Study area: A, zone reserved for sportfishing (5 nautical miles); B, billfish protection zone. B.C.S., Baja California Sur. The effect of the SST on the abundance and distribution of pelagic fish has been recognized in many studies. Particularly for striped marlin, it has been observed that its determination before or immediately after the start of good fishing might give some clues as to what thermal conditions may be contributing to successful striped marlin fishing (Squire 1974). Uda (1957) determined, from commercial longline catch data, that the optimum SST for this species ranged from 18.5 Cto 24 C. Talbot and Wares (1975) found that only 15 25% of the variation of striped marlin catch was related to SST off southern California. Squire (1985) found a high correlation between the average number of striped marlin caught and the occurrence of progressively warmer isotherms. Considering the economic importance that sportfishing has in this area (Ditton et al. 1996), and that striped marlin is the most important species in this fishery, we analysed catch rates of striped marlin and the effect that the SST has on these. Size and weight composition and sex data were also analysed. Materials and methods The information used in this study was obtained from the monitoring programme of the Centro Regional de Investigacion Pesquera at La Paz, B.C.S., and consists of a monthly compilation of catch and effort data from the operations of three sportfishing fleets of Cabo San Lucas, B.C.S. (Solmar, Pisces and Gaviotas fleets) that represent approximately 4% of the total operations in the area (Fig. 1). The catch was defined as the number of fish and the effort as number of trips. The total annual catch and number of trips during 199 1999 are shown in Table 1. The biological information was recorded during three consecutive days each month, for the extent of the study period. Eye fork length, weight and sex of 4521 landed striped marlin were recorded. Sea surface temperature records correspond to the Reynolds database (Reynolds and Smith 1994), from which the monthly average SST was estimated for four 1 1 latitude by longitude quadrants, defined by the coordinates: 22.5 N 19.5 W; 22.5 N 11.5 W; 22.5 W 11.5 W; 23.5 11.5 W. The average monthly and annual catch rates were estimated for the total period. CR = Ci Fi where CR is the average catch rate (monthly or annual), C i is the number of fish caught, and F i is the number of trips. Monthly average anomalies of catch rates and SST values were calculated using the equation: A ij = X ij X where ni=1 X ij X = n and A ij is the ith annual or monthly anomaly, X ij is the ith annual or monthly value, and X is the average value from 199 to 1999. Average of sex ratio, seasonal and annual average length, and weight data were estimated. Analysis of variance was used to determine if interannual and seasonal variation showed significant differences. Results Catch rates variability During the analysed period, the average catch rate of striped marlin recorded in Cabo San Lucas was.6 fish per trip. The maximum monthly average catch rate recorded during the analysed period was 2.3 fish per trip and the minimum was.5 fish per trip. Annual average catch rates are shown in Figure 2. Although interannual variability was observed for these values, with a minimum in 1992 (.42) and a maximum in 1998 (.81), the differences were not significant (F 3,11 = 1.1, P =.438). For the total period, significant seasonal differences (F 3,116 = 16.49, P =.1) were found in catch rates. The highest were recorded during winter and the lowest in summer, with.9 and.3 fish per fishing trip respectively (Fig. 3). Figure 4 shows the average monthly number of trips for the total period (199 1999), and it can be seen that they were similar throughout the year. Sea surface temperature relationship The lowest average monthly SST recorded during the 199 1999 period was 2.8 C, and the highest was 3.4 C, with
Sea surface temperature and striped marlin catch rates Marine and Freshwater Research 485 1.4 24 22 Catch rate (fish per trip) 1..8.6.4.2. 199 1991 1992 1993 Mean 1994 1995 1996 1997 1998 ± s.e. ± s.d. 1999 Number of trips 2 18 16 14 12 1 8 J F M A M J J A S O N D Month Mean ± s.e. ± s.d. Fig. 4. Monthly average number of trips made by sportfishing fleets in Cabo San Lucas, B.C.S., 199 1999. Fig. 2. Annual average catch rates of striped marlin in Cabo San Lucas, B.C.S., 199 1999. Catch rate (fish per trip) 1..8.6.4.2. Winter Mean Spring Summer Autumn Season ± s.e. ± s.d. Fig. 3. Average seasonal variation of striped marlin catch rates in Cabo San Lucas, B.C.S., 199 1999. the mean SST for the study period of 25 C. On average, the highest catch rates were recorded between 22 C and 24 C (December to June), with lower rates found during the higher SST values (July to November; Fig. 5). The correlation value between SST and the catch rate time series was.52 for original data and.62 for the smoothed series. Similar Sea surface temperature ( C) 29 27 25 23 21 J F M A M J J A S O N D Month SST Catch rate s.e.m. Fig. 5. Monthly average variation of striped marlin catch rates and sea surface temperature (SST) in Cabo San Lucas, B.C.S., 199 1999. behaviour can also be observed in Figure 6, where catch rates higher than.8 fish per trip were recorded at temperatures between 22 C and 24 C. This behaviour was similar throughout the period analysed, as shown in Figure 7. Biological data For the total period, the average eye fork length of striped marlin at Cabo San Lucas was 175 cm. Interannual length variation was significant (F 9,4757 = 41.17, P<.1), with a decreasing trend during 1992 1996 (Fig. 8). The minimum size (167 cm) was recorded during 1996 and the maximum (182 cm) in 1992. Significant length and weight differences were found between males and females (F 1,4487 = 65.8, P<.1 and F 1,4487 = 114.3, P<.1 respectively) (Table 2). Seasonal mean eye fork length and weight for males showed significant variation (F 3,2441 = 5.7, P<.7 and 1..8.6.4.2 Catch rate (fish per trip)
486 Marine and Freshwater Research S. Ortega-García et al. F 3,2441 = 39.5, P<.1 respectively). Among females, although no significant differences were found in length data, the average seasonal weights were significantly different (F 3,243 = 1.4, P<.1), with the heaviest fish recorded during spring. The weight frequency of male and females by season is shown in Figure 9, where one can note the lower number of fish during summer and that the few females recorded during this period were heavier than males. For all fish sampled, 2524 were males and 2122 females; the average sex ratio was 1 : 1.19. During all the years, more males were landed, but females were more frequent during the summer months (Figs 1 and 11). Discussion The average catch rate estimated during the analysed period in Cabo San Lucas was.6 fish per trip, a little higher than the.5 fish per trip recorded during 198 1986 by Squire and Au (199). The highest annual catch rate estimated in this study (.81 in 1998) has only been preceded by a similar historic value reported in 1971 by Squire and Au (199). A notable characteristic of 1998 was the presence of one of the strongest El Niños. Although no higher values have been Average catch rate 1..8.6.4.2 2 21 22 23 24 25 26 27 28 29 3 Sea surface temperature ( C) Fig. 6. Average catch rate by sea surface temperature in Cabo San Lucas, B.C.S., 199 1999. reported in other El Niño years in this area, Squire (1985) reported that warm years resulted in exponential increases in catch of striped marlin off southern California. The lowest annual catch rates were recorded in 1992 and 1997, during the first year of two El Niños (1992 1993 and 1997 1998). However, these differences were not statistically significant. Although observed catch rate trends reveal no apparent change in abundance of the exploited population, increases in effort efficiency or catchability by the Cabo fleets (e.g. increased experience of the fisherman, new technology) could potentially affect this conclusion. Further work directed at standardizing the catch rates and efficiency of the recreational fleet would shed light on this issue. It is important to do this because since 1995 the number of trips has increased substantially. The number of trips recorded in 1999 was almost 5% greater than in 1995. Average length (cm) 18 178 176 174 172 17 168 166 199 1991 1992 1993 1994 1995 1996 1997 1998 1999 Fig. 8. Annual average striped marlin eye fork length in Cabo San Lucas, B.C.S., 199 1999. Table 2. Mean weight, and the mean and range of eye fork length of striped marlin during 199 1999 Mean weight Mean eye fork Range of (kg) length (cm) eye fork length (cm) Males 51. 171.4 113 217 Females 54.7 174.4 127 23 Average catch rate 2. 1.5 1..5.5 1 199 1991 1992 1993 1994 1995 1996 1997 1998 1999 Catch rate (fish per trip) anomalies SST ( C) anomalies Fig. 7. Adjusted variation of striped marlin catch rates in relation to sea surface temperature (SST) in Cabo San Lucas, B.C.S., 199 1999.
Sea surface temperature and striped marlin catch rates Marine and Freshwater Research 487 3 Winter 3 Summer 25 25 2 15 1 5 2 15 1 5 15 25 35 45 55 65 75 85 95 15 15 25 35 45 55 65 75 85 95 15 3 25 2 15 1 5 Spring Autumn 3 25 15 25 35 45 55 65 75 85 95 15 15 25 35 45 55 65 75 85 95 15 Weight (kg) Weight (kg) 2 15 1 5 Males Females Males Females Fig. 9. Weight frequency by quarter for male and females striped marlin in Cabo San Lucas, B.C.S., 199 1999. 1 1 Percentage 8 6 4 2 199 1991 1992 1993 1994 Females 1995 1996 Males 1997 1998 1999 Fig. 1. Annual sex proportions of striped marlin in Cabo San Lucas, B.C.S., 199 1999. The decrease of catch rates during summer found in this study coincides with the presence of striped marlin reported by a longline fishery south of Cabo San Lucas and near Revillagigedo Islands during summer (Squire and Au 199; Nakano and Bayliff 1992; Santana-Hernandez 21) and with south and south-westward migratory movement from the southern tip of the Baja California peninsula, which has been reported by Squire (1987). However, the movement to the south must be in oceanic waters because the presence of this species was not recorded in sportfishing at Mazatlan, Sinaloa, during summer months (Beltran-Pimienta et al. 21). The results of the seasonal variation in catch rate values could also be related to increased SSTs. This suggests that striped marlin show a preference for temperate waters between 22 C and 24 C. Gonzalez-Armas et al. (1999) has reported the presence of striped marlin larvae from June to Percentage 8 6 4 2 J F M A M J J A S O N D Month Females Males Fig. 11. Average monthly variation of striped marlin sex proportions in Cabo San Lucas, B.C.S., 199 1999. November south to the mouth of the Gulf of California in temperatures between 27.8 C and 31.5 C. It is possible that females have to stay in warmer waters because of reproductive activity, such waters being more suitable for larvae survival. On average, length frequencies for the present study showed larger fish than those reported by Squire and Au (199), with a mode at 18 cm. Nevertheless, a decreasing trend observed from 1992 to 1996 reflects the need for closer monitoring of the species population behaviour. The recording of the heaviest fish during spring could be explained by reproductive activity during summer, which has been confirmed by the presence of larvae close to this area (Gonzalez-Armas et al. 1999). This also coincides with a greater proportion of females recorded during the summer months. In conclusion, although Mexico has taken conservation measures for striped marlin mainly inside of the core area
488 Marine and Freshwater Research S. Ortega-García et al. with the establishment of areas where commercial fishing is prohibited and sportfishing has maintained catch and release programmes, because of the migratory character of the species and the trends observed by us, catch monitoring is needed, including the incidental catch made by longliners fishing for swordfish or shark, the shark artisanal fishery and the tuna purse seine fishery. Information would be required to be recorded so that data could be incorporated into models through which the maximum sustainable yield could be estimated to allow improved management of the species. Acknowledgments The first author was supported by a COFAA (Comisión de Operación y Fomento de Actividades Académicas) fellowship. References Beltran-Pimienta, R., Klett-Traulsen, A., Ortega-Garcia, S., Bravo- Mendoza, F. G., and Campos A. J. T. (21). Captura de picudos y especies afines por las flotas deportivas de Mazatlán, Sin. y Los Cabos, B.C.S. durante el año 2. Boletín Informativo INP. CICIMAR. (Mazatlán Sin. México.) Ditton, R. B., Crimes, S. R., and Finkelstein, L. D. (1996). A Social and Economic Study of the Recreational Billfish Fishery in the Southern Baja Area of Mexico. Prepared for the Billfish Foundation in cooperation with the Los Cabos Sportfishing Association through a Research contact with the Texas A&M University. Gonzalez-Armas, R., Sosa-Nishizaki, O., Funes-Rodriguez, R., and Levy-Perez, V. A. (1999). Confirmation of the spawning area of the striped marlin, Tetrapturus audax, in the so-called core area of the eastern tropical Pacific off Mexico. Fisheries Oceanography 8, 238 42. Howard, J. K., and Ueyanagi, S. (1965). Distribution and RelativeAbundance of Billfishes (Istiophoridae) of the Pacific Ocean. Studies of Tropical Oceanography. Vol. 2. (University of Miami Institute of Marine Sciences: Miami, FL.) IATTC (1999). Annual Report of the Inter-American Tropical Tuna Commission, 1997. (IATTC: La Jolla, CA.) Klett, A., Ponce-Diaz, G., and Ortega-Garcia, S. (1996). Pesquería deportivo-recreativa. In Estudio del Potencial Pesquero y Acuícola de Baja California Sur. SEMARNAP-Gob. Del Estado de B.C.S.- FAO-UABCS-CIBNOR-CICIMAR-CETMAR. Vol. 2. (Eds V. M. Casas and D. Ponce.) pp. 389 418. Nakamura, I. (1985). FAO Species Catalogue, Vol. 5. Billfishes of the World: An Annotated and Illustrated Catalogue of Marlins, Sailfishes, Spearfishes and Swordfishes Know to Date. Fisheries Synopsis. No. 125. (FAO: Rome.) Nakano, H., and Bayliff, W. H. (1992). A review of the Japanese longline fishery for tunas and billfishes in the eastern Pacific ocean, 1981 1987. Inter-American Tropical Tuna Commission Bulletin 2, 187 355. Reynolds, R. W., and Smith, T. M. (1994). Improved global sea surface temperature analysis using optimum interpolation. Journal of Climate 7, 929 48. Santana-Hernandez, H. (21). Estructura de la comunidad de pelágicos mayores capturados con palangre en el Pacífico mexicano (1983 1996) y su relación con la temperatura supercicial del mar. PhD Thesis. (University of Colima, México.) Squire, J. L. Jr. (1974). Catch distribution and related sea surface temperature for striped marlin (Tetrapturus audax) caught off San Diego, California. NOAA Technical Report. NMFS. SSRF. 675, 188 93. Squire, J. L. Jr. (1985). Relationship of sea surface temperature isotherm patterns off northwestern Mexico to the catch of striped marlin, Tetrapturus audax, off Southern California. Marine Fisheries Review 47, 43 7. Squire, J. (1987). Striped marlin, Tetrapturus audax, migration patterns and rates in the northeast Pacific Ocean as determined by a cooperative tagging program: its relation to resources management. Marine Fisheries Review 49, 26 43. Squire, J., and Au, D. W. K. (199). Striped marlin in the northeast Pacific a case for local depletion and core area management. In Planning the Future of Billfishes, Research and Management in the 9s and Beyond. Proceedings of the Second International Billfish Symposium. Kailua-Kona, Hawaii, August 1 5, 1988. Part 2: Contributed Papers. (Ed. R. H. Stroud.) pp. 199 214. (NCMC: Savannah, GA.) Sosa-Nishizaki, O. (1998). Historical review of billfish management in the Mexican Pacific. Ciencias Marinas 24, 95 111. Talbot, G. B., and Wares, P. G. (1975). Fishery for Pacific billfish off southern California and Mexico, 193 69. Transactions ofamerican Fisheries Society, 14, 1 12. Uda, M. (1957). A consideration on the long years trend of the fisheries fluctuation in relation to sea conditions. Bulletin of Japanese Society of Scientific Fisheries 23, 368 72. Uosaki, K., and Bayliff, W. H. (1999). A review of Japanese longline fishery for tunas and billfishes in the eastern Pacific Ocean, 1988 1992. Inter-American Tropical Tuna Commission Bulletin 18, 421 82. Manuscript received 6 September 21; revised and accepted 14 January 23. http://www.publish.csiro.au/journals/mfr