Hidrobiológica 2008, 18 (3): 177-188

Population dynamics and spatial distribution of flatfish species in shrimp trawl bycatch in the Gulf of California

Dinámica poblacional y distribución espacial de los lenguados capturados incidentalmente en arrastres camaroneros en el Golfo de California

Carlos Hiram Rábago-Quiroz 1, Juana López-Martínez1, Eloisa Herrera-Valdivia1, Manuel O. Nevárez-Martínez2 y Jesús Rodríguez-Romero3

1Centro de Investigaciones Biológicas del Noroeste, Unidad Sonora, Campus Guaymas. Apdo. Postal 349, Guaymas, Sonora 85465, México 2Centro Regional de Investigación Pesquera Guaymas. Calle 20 Sur. Guaymas, Sonora. 85430, Mexico 3Centro de Investigaciones Biológicas del Noroeste, La Paz Baja California Sur. Apdo. Postal 128; La Paz, BCS 23090, México e-mail: [email protected]

Rábago-Quiroz C. H., J. López-Martínez, E. Herrera-Valdivia, M. O. Nevárez-Martínez y J. Rodríguez-Romero. 2008. Population dynamics and spatial distribution of flatfish species in shrimp trawl bycatch in the Gulf of California. Hidrobiológica 18 (3): 177-188.

Abstract By determining the specific composition, spatial distribution and population dynamics of flatfish species captured in shrimp trawls’ bycatch in the Gulf of California, this study aims to contribute to the knowledge of bycatch fish population which has thus far been of little interest. Samplings were taken from shrimp trawls’ in two fishing seasons (2002 and 2003) onboard shrimp fleets and also from two research cruises during closed shrimp season. The results showed 15 species of flatfish belonging to 5 families: Achiridae, Bothidae, Cynoglossidae, Pleuronectidae and Paralichthyidae. Paralichthyidae was the most abundant with 9 species. The range in sizes of these flatfish species varied in total length from 20 to 380 mm, with the most frequent sizes ranging from 60 to 180 mm and only a few species of the Paralichthys genera surpassing 250 mm in total length. The growth estimate parameter for the most abundant flatfish species varied according to the longevity of these species. More than 50 % of the organisms sampled were of small size, and the majority of these were captured before the sexual maturity which may have caused a potential effect on the population; however the consequences of this action on the population are unknown.

Key words: Bycatch, Gulf of California, flatfish, spatial distribution, population dynamics.

Resumen Con la determinación de la composición específica, distribución espacial y dinámica poblacional de las especies de lenguados capturadas incidentalmente por embarcaciones camaroneras en el Golfo de California, este estudio pretende contribuir al conocimiento en un nivel poblacional de especies capturadas incidentalmente, las cuales han sido de poco interés en las investigaciones. Se efectuaron muestreos de fauna de acompañamiento del camarón en dos temporadas de pesca (2002 y 2003) a bordo de barcos camaroneros y en dos cruceros de investigación durante la época de veda del camarón. Los resultados mostraron 15 especies de lenguados pertenecientes a cinco familias, siendo la familia Paralichthyidae la que presentó el mayor número de especies (9). El intervalo de tallas obtenido fue de 20 a 380 mm de longitud total, siendo las más frecuentes de 60 a 180 mm y sólo las especies del género Paralichthys rebasaron los 250 mm. Los parámetros de crecimiento estimados estuvieron de acuerdo a la longevidad de estas 178 Rábago-Quiroz., et al.

especies. Más del 50 % de los organismos fueron de tallas pequeñas y la mayoría fueron capturadas antes de su talla de primera madurez sexual, pudiendo tener potenciales efectos en las poblaciones; sin embargo las consecuencias de este hecho en las poblaciones son desconocidas.

Palabras clave: Captura incidental, Golfo de California, lenguados, distribución espacial, dinámica poblacional.

Introduction been made regarding species composition, distribution, relative abundance, or population dynamics of these flatfishes; they have In the international forefront, a transcendental issue in the man- only been mentioned in some researches about the shrimp trawl agement and conservation of exploited marine ecosystems is the bycatch (Grande-Vidal & Díaz-López, 1981; Van der Heiden, 1985; incidental capture of marine organisms by the main fisheries. Pérez-Mellado & Finley, 1985). For this reason, we investigated According to recent estimates of the FAO, the annual discard specific composition, spatial distribution, and population dynam- rate of all the worlds’ commercial fisheries is 8 %, which means ics of flatfish species captured in shrimp trawl bycatch in the Gulf a discard rate of 7.3 million tons per year with the highest rates of California, contributing to the knowledge of bycatch studies being found in those fisheries operating in shallow waters near at the population level of fish captured incidentally in the shrimp the coast (Kelleher, 2005). The shrimp trawl fisheries, tropical fisheries. shrimp fisheries in particular, are the greatest source of discard, accounting for 27.3 percent (1.86 million ton) of the estimated Material and Methods total discard in the world (Kelleher, 2005), with unknown conse- quences to the ecosystem and with discarded species that could We analyzed data on shrimp trawl bycatch from: a) samples be utilized as food source. obtained onboard two vessels of shrimp fleet from the Gulf of California (B/M “Maria Eugenia” and “Veronica” in March To date, there have been several international studies 2003, each covering different areas) (Fig. 1a); b) samples from pertaining to the shrimp trawl bycatch, which have focused on two research cruises in the Gulf of California during the closed bycatch volumes (Alverson et al., 1996; Kelleher, 2005), marine shrimp season onboard the vessels B/M “Delly IV” July-August megafauna (Julian & Beeson, 1998; Diamond et al., 2000), com- 2002 and B/O “BIP XI” July-August 2003 ( Fig. 1b). The capturing position of species especially these of economic value (Pikitch method for these samples was shrimp trawls which were con- et al., 1998; Galloway & Cole, 1999) and of measures which would ducted similarly to the commercial fishery system. The shrimp help to reduce the bycatch (Kenelly & Broadhurst, 1995; Macbeth fleet operated mainly in specific areas known as “caladeros”, et al., 2004; Chokesanguan, 2005), however little has been studied hence samplings were done in these areas. Samplings from about the overall bycatch population obtained through shrimp the research cruises were performed during the shrimp closed trawling. season according to series of stations (operated by the National The Gulf of California is one of the most mega-diverse regions Fisheries Institute of Mexico) for a specific trawling time (60 min in the world and it is the Mexican fishing region where most of the approximately) with the objective of covering the total distribu- commercial captures are obtained (Lluch-Cota et al., 2007), with a tion area of the shrimp species. total fishery production of 700,000 tons; of which approximately In both cases the following observations were recorded 9% correspond to the shrimp fishery (Anónimo, 2005 and 2006). during each shrimp trawl: depth and location of the trawling, This fishery is one of the most important in the Gulf of California trawl velocity, path distance and capture composition, the main because it is a source of income and employment for communities species captured, and the latitude and longitude at the begin- along the Gulf of California’s coast (López-Martínez et al., 2001). nings and end of each trawl. Once onboard the incidental cap- Despite the economic importance of this fishery, it is one which ture or bycatch was separated from the target species (shrimps contributes to the most bycatch, generating around 114,000 tons species), after which one sample of 20 kg approximately was of discarded fish per year (Bojorquez, 1998), with a total biomass obtained. estimated at (90 ± 45) × 103 tons (Madrid-Vera et al., 2007). Some researches on how to reduce this bycatch are currently underway In the laboratory, the samples were separated into general (García-Caudillo et al., 2000; Balmori et al., 2003). The majority of groups (fishes, crustaceans and mollusks). Flatfishes obtained the species in the shrimp trawl bycatch are species with little or from the samples were separated from the rest of fish species. no economic value (Van der Heiden, 1985; Pérez-Mellado & Finley, The flatfish species were identified using the Mexicans Marine 1985); however, there are some species that are appreciated com- Fishes Catalogue (INP, 1976), Eschmeyer & Herald (1983), Hensley mercially, including some species of flatfish. No research has yet (1995) and Robertson & Allen (2002).

Hidrobiológica Flatfish species in the shrimp bycatch 179

To obtain the spatial distribution of each flatfish species nate the sexual maturity of flatfish species; for this reasons a bib- captured, distribution maps were made using the capture depth, liographic search in different databases specialized (Fishbase, and the latitude and longitude from each trawl sampled. ITIS) in obtaining data for the sexual maturity of each species was carried out. The following measures from each organism were recorded: total length (LT), standard length, weigh, sex and sexual maturity The longevity of each flatfish species was obtained using (according to the Nikolski (1963) fish maturing scale). The length Pauly’s equation (1984): structures of the flatfish species were used to estimate annual t/= 3 K growth parameters through the seasonal von Bertalanffy growth max s equation of Pauly (1987):()−k () t−t0 − ()C / 2π ⋅ sin( 2π ⋅ (t−t ) Where K= growth coefficient (year-1), and tmax= longevity. Lt = L∞ [1−e ] ()−k ()t−t − ()C π ⋅ π ⋅ t−ts 0 / 2 sin( 2 ( ) Results Lt = L∞ [1−e ]

Where Lt= length at age t, L∞= asymptotic length, K= growth Sixty one shrimp trawls were sampled, 14 during 2002 and 47 coefficient (year-1), t0= length for the hypothetical age t=0. The during 2003, within different areas of the Gulf of California as is symbol ts and C are parameters that control seasonal growth shown in figure 1. oscillations over a period of one year. Species composition and spatial distribution. The more abun- The estimates of the growth parameters L∞ and K were dant groups found in the bycatch during this study were: fishes obtained by using an electronic length frequency analysis (78.6 to 97.4 %), crustaceans (1.7 to 10.9 %) and mollusks (0.02 to ELEFAN I (Gayanilo et al., 2005), using length-frequency data set 10.3 %). The flatfishes represented 9.09 % (4.92 to 11.6 %) of the of each species. The estimates of the third parameter, t0, were total bycatch (including fishes, crustaceans and mollusks). obtained from the empiric equation proposed by Pauly et al. (1984), which has the following equation: One thousand one hundred and ten flatfishes were ana- lyzed during this study. They belonged to five Families: Achiridae, []−0.3922−()0.2752 ⋅ log L∞ −()1.038k ⋅log Κ t = ⋅ Bothidae, Cynoglossidae, Pleuronectidae and Paralichthyidae. The 0 1 L∞ Paralichthyidae family represented the majority of species. There []−0.3922−()0.2752 ⋅ log L∞ −()1.038k ⋅log Κ Recruitment patterns from each flatfish species were were nine different Paralichthyidae species; two species each t = 1⋅L∞ obtained0 using ELEFAN II (Gayanilo et al., 2005). This method of Pleuronectidae and Cynoglossidae and one each of Achiridae reconstructs the recruitment pulses from a time series of length- and Bothidae (Table 1). frequency data to determine the number of pulses per year and the relative strength of each pulse. It was observed that the variation in abundance of differ- ent flatfish species captured was dependent of the sample area. Due to the fact that the majority of organisms analyzed Paralichthys woolmani (Jordan & Williams 1897), Citharichthys were small in size, there was insufficient information to determi- fragilis (Gilbert 1890), Achirus mazatlanus (Steindachner 1869),

31 ab Sonora Sonora L a t Kino bay Kino bay i 28 Guaymas bay Guaymas bay t Baja Baja u California California d Agiabampo bay Agiabampo bay e Gulf Sinaloa Gulf Sinaloa 25 of of N Pacific Pacific Ocean California Ocean California

22 117 114 111 108 105 Longitude W Figure 1a-b. a) Covered areas ( ) by two vessels of the shrimp trawl fleet of Sonora, Mexico during 2002 and 2003, b) Covered areas ( ) by two research cruises during the closed shrimp season (2002 and 2003).

Vol. 18 No. 3 • 2008 180 Rábago-Quiroz., et al.

Table 1. Flatfish species found in the shrimp trawl bycatch in the Gulf of California during 2002 and 2003.

Family Species Common Name Num. of org. analyzed* 1. Achiridae Achirus mazatlanus Mazatlan Sole 200

2. Bothidae Bothus constellatus Pacific eyed flounder 14

3. Cynoglossidae Symphurus fasciolaris Banded tongue-fish 4 Symphurus chabanaudi Chabanaud’s tongue-fish 88

4. Pleuronectidae Pleuronichthys verticalis Hornyhead turbot 1 Hypsopsetta guttulata Diamond turbot 2

5. Paralichthyidae Citharichthys gilberti Bigmouth sanddab 91 Citharichthys fragilis Gulf sanddab 214 Citharichthys xanthostigma Longfin sanddab 5 Etropus crossotus Fringed flounder 125 Etropus peruvianus Peruvian flounder 46 Hippoglossina stomata Bigmouth flounder 5 Paralichthys californicus California flounder 3 Paralichthys woolmani Speckled flounder 245 Syacium ovale Oval flounder 67 *Num. of org. analyzed = number of organisms analyzed.

Etropus crossotus (Jordan & Gilbert 1882), Citharichthys gilberti The growth parameters L∞, K and t0, obtained from the (Jenkins & Evermann 1889) Symphurus chabanaudi (Mahadeva most frequent and abundant flatfish species showed that & Munroe 1990), and Syacium ovale (Günther 1864) had a wider these species presented an accelerated growth, most common distributions in the Gulf of California (Fig. 2a-g). Other flatfish in species which have a short spawn cycles (Table 2). The species, such as; Pleuronichthys verticalis (Jordan & Gilbert growth curves of the most frequent and abundant flatfish spe- 1880), Paralichthys californicus (Ayres 1859), Hypsopsetta gut- cies are shown in figure 6. We observed that some species, like tulata (Girard 1856), and Hippoglossina stomata (Eigenmann & E. crossotus, S. ovale and C. fragilis, have an accelerate growth Eigenmann 1890) were only found in one or two trawl samples rate, reaching their maximum size in a short time due to their containing few organisms (Fig. 2h). short life cycle.

The range of depth where the majority of these flatfish were Analysis of the recruitment patterns of the most frequent captured was from 10 to 65 m (Fig. 3a-h). The most common cap- and abundant flatfish species analyzed showed one continuous ture depth was in the range of 10 to 40 m; however, we obtained period in the reproductive recruitment that spans from March to some organisms of P. woolmani and S. chabanaudi which were November (Fig. 7a-g). In species like A. mazatlanus, this recruit- captured up to a 64 m depth (Fig. 3a, 3f). ment period is shorter, going from February to July during which time the highest percentage is present (Fig. 7c). Only S. ovale Population dynamics of flatfish species. P. woolmani, C. fragilis, present two important recruitments periods: the first one of high A. mazatlanus, E. crossotus, C. gilberti, S. chabanaudi and S. intensity during April to August and the second one of lesser in- ovale (Günther 1864) were the most abundant flatfish species in tensity during September to November (Fig. 7g). this study, see figure 4. The majority of the flatfishes analyzed were small (20 ≥ Lt ≤ 380 mm total length) and the most frequent sizes ranged from 60 to 180 mm in total length (Fig. 5a-o). Discussion Due to the low abundance of Symphurus fasciolaris To the date, 29 flatfish species are the largest number of species (Gilbert 1892), Bothus constellatus (Jordan 1889), Pleuronichthys reported for incidental captures from shrimp trawls in the Gulf of verticalis, Paralichthys californicus, Hypsopsetta guttulata, California (Van der Heiden, 1985). This study found 15 flatfish spe- Citharichthys xanthostigma (Gilbert 1890), Etropus peruvianus cies, belonging to 5 families: Achiridae, Bothidae, Cynoglossidae, (Hildebrand 1946), and Hyppoglossina stomata in the samples, Pleuronectidae and Paralichthidae (these five flatfish’s families the population dynamic analysis was only made for: P. woolmani, have previously been reported for the Gulf of California); this Citharichthys fragilis, Achivrus mazatlanus, E. crossotus, C. gil- similar to finding by Grande-Vidal & Díaz-López (1981) and Pérez- berti, Syacium ovale and Symphurus chabanaudi. Mellado & Finley (1985), who found 4 flatfish families (Bothidae,

Hidrobiológica Flatfish species in the shrimp bycatch 181

Shrimp fleet Feb-Mar 2003 53 Shrimp fleet Feb-Mar 2003 61 35 40 65 33 Shrimp fleet Feb-Mar 2003 34 67 31 41 Shrimp fleet Feb-Mar 2003 24 29 Research cruise Jul-Agu 2003 Research cruise Jul-Agu 2003

9 13.1 18 42 22 21.4 13.1 26.9 24 21 22.3 25 11

12.7

a) Parahichthys woolmani b) Citharichthys fragilis

Shrimp fleet Feb-Mar 2003 Research cruise Jul-Agu 2003 37 Shrimp fleet Feb-Mar 2003 Shrimp fleet Feb-Mar 2003 34 67 25 27 Research cruise Jul-Agu 2003 Research cruise Jul-Agu 2003 11

25 9 9.1 13 11 13 18 22 21 18 24 21 23 22 38 36 38 11 9.1 14 13 18 20

c) Archirus mazatlanus d) Etropus crossotus

Shrimp fleet Feb-Mar 2003 Shrimp fleet Feb-Mar 2003 67 20 62 Shrimp fleet Feb-Mar 2003 42 37 Shrimp fleet Feb-Mar 2003 32 31 36 27 Research cruise Jul-Agu 2003 24 Research cruise Jul-Agu 2003

25 24 22 23 24 22 38 40 11

13

e) Citharichthys gilberti f) Symphurus chabanaudi

31 Shrimp fleet Feb-Mar 2003 h) Other flatfish species: 35 33 Shrimp fleet Feb-Mar 2003 26 Research cruise Jul-Agu 2003

28 42 18.2 21.9 E. peruvianus 9.1 B. constellatus H. stomata 25 C. xanthostigma S. fasciolaris P. californicus g) Syacium ovale H. guttulata P. verticalis 22 117 114 111 108 105

Figure 2a-h. Spatial distribution of the flatfish species in the shrimp trawls bycatch in the Gulf of California during 2002 and 2003. The numbers mean the depth in m wich the organisms were captured.

Vol. 18 No. 3 • 2008 182 Rábago-Quiroz., et al.

50 a) Paralichthys woolmani 40 b) Citharichthys fragilis

40 30

30 20 20

10 10

0 0

40 50 c) Achirus mazatlanus d) Etropus crossotus 40 30

30 20

% 20

10 10

0 0

70 e) Syacium ovale 70 f) Symphurus chabanaudi 60 60 Relative Frequency Frequency Relative 50 50 40 40 30 30 20 20 10 10 0 0

60 g) Syacium ovale 90 h) Other flatfish species 80 50 70 40 60 50 30 40 20 30 20 10 10 0 0 10 16 22 28 34 40 46 52 58 64 10 16 22 28 34 40 46 52 58 64 Depth (m)

Figure 3a-h. Histograms of the depth which were captured the different flatfish species in the shrimp trawl bycatch in the Gulf of California during 2002 and 2003.

Symphurus fasciolaris (0.4%) Citharichthys xanthostigma (0.5%) Paralichthys californicus (0.3%) Hippoglossina stomata (0.5%) Hypsopsetta guttulata (0.2%) Bothus constellatus (1%) (0.1%) Etropus peruvianus (4%) Pleuronichthys verticalis Syacium ovale (6%) Paralichtys woolmani (22%) Symphurus chabanaudi (8%)

Citharichthys gilberti (8%)

Etropus crossotus (11%) Citharichthys fragilis (20%) Achirus mazatlanus (18%) Figure 4. Abundance of the principal flatfishes in the shrimp trawls bycatch in the Gulf of California during 2002 and 2003.

Hidrobiológica Flatfish species in the shrimp bycatch 183

40 a) Paralichthys woolmani 40 b) Achirus mazatlanus 16 c) Citharichthys fragilis 35 35 14 30 30 12 25 Sexual 25 Sexual 10 20 maturation size 20 maturation size 8 Sexual 15 15 6 maturation size 10 10 4 5 5 2 0 0 0 40 80 120 160 200 240 280 320 360

35 25 d) Etropus crossotus e) Citharichthys gilberti 20 f) Symphurus chabanaudi 30 18 20 16 25 Sexual 14 15 maturation size 20 Sexual 12 10 Sexual 15 maturation size 10 8 maturation size 10 6 5 4 5 2 0 0 0

25 g) Syacium ovale 35 h) Etropus peruvianus 40 i) Bothus constellatus 20 30 35 25 30 Sexual 15 20 25 maturation size 20 10 15 15 10 5 10 5 5 Relative Frequency (%) Frequency Relative 0 0 0 45 j) Hippoglossina stomata 90 k) Citharichthys xanthostigma 60 l) Symphurus fasciolaris 40 80 50 35 70 30 60 40 25 50 30 20 40 15 30 20 10 20 10 5 10 0 0 0 m) Paralichthys californicus n) Hypsopsetta guttulata o) Pleuronichthys verticalis 70 100 100 90 90 60 80 80 50 70 70 60 40 60 50 50 30 40 40 20 30 30 20 20 10 10 10 0 0 0 40 60 80 100 120 140 160 180 200 40 60 80 100 120 140 160 180 200 40 60 80 100 120 140 160 180 200 Total Lenght (mm) Figure 5a-o. Size structures of flatfish species in the shrimp trawl bycatch in the Gulf of California during 2002 and 2003. For some species the first sexual maduration size is indicated.

Table 2. Growth parameters and longevity of the most abundant and frequents flatfish species in the shrimp trawl bycatch of the Gulf of California during 2002 and 2003.

Species L∞ K t0 Longevity Medium size (mm) (1/year) 3/K (annual) (total length mm) P. woolmani 388 1.0 –0.39 3.0 101.10 C. fragilis 210 0.92 –0.19 3.2 109.99 A. mazatlanus 200 1.2 –0.14 2.5 112.86 E. crossotus 170 1.6 –0.11 1.8 110.86 C. gilberti 200 1.2 –0.14 2.5 93.18 S. chabanaudi 220 0.71 –0.24 4.2 121.88 S. ovale 173 1.6 –0.11 1.8 105.43

Vol. 18 No. 3 • 2008 184 Rábago-Quiroz., et al.

40 25 a) P. woolmani b) C. fragilis 35 20 30 25 L = 38.8 (1–e –1.0 (t + 0.39) ) t 15 L = 21 (1–e –0.92 (t + 0.19) ) 20 t 15 10 10 5 5 0 0 0510 15 20 25 30 35 40 45 50 0510 15 20 25 30 35 40 45 50

20 20 c) A. mazatlanus d) E. crossotus 15 15 –1.2 (t + 0.147) –1.6 (t + 0.11) Lt = 20 (1–e ) Lt = 17 (1–e ) 10 10

5 5

0 0 0510 15 20 25 30 35 40 45 0510 15 20 25 30 35 40

20 25 e) C. gilberti f) S. chabanaudi

Total length (cm) length Total 20 15 –1.2 (t + 0.147) –0.71 (t + 0.24) Lt = 20 (1–e ) 15 Lt = 22 (1–e ) 10 10 5 5

0 0 0510 15 20 25 30 35 40 45 0102030405060

20 Age (months) g) S. ovale 15

–1.6 (t + 0.11) 10 Lt = 17.3 (1–e )

5

0 0510 15 20 25 30 35 40 Age (months) Figure 6a-g. Growth curves of the most abundant flatfish species in the shrimp trawl bycatch in the Gulf of California during 2002 and 2003.

Pleuronectidae, Achiridae and Paralichthidae) in the shrimp going from Central Baja California area and the central Gulf of trawls carried in the Gulf of California. California down to Peru (Hensley, 1995; Robertson & Allen, 2002). According to the latitudinal distribution of the flatfish spe- All the flatfish species found in this study were captured cies found in this study, all these species are endemic to the East within the reported depth distribution by Hensley (1995), and Pacific and are residents of this region (Hensley, 1995; Robertson Robertson & Allen (2002). The majority of flatfish species was & Allen, 2002). The majority of the species found in this study taken from 10 to 65 m, but the most common capture depth have a wide distribution ranging from Southern California to the was from 10 to 40 m. This does not mean that this is deepest Gulf of California down to Peru. According to Hensley (1995), and distribution levels for these species (Hensley, 1995; Robertson Robertson & Allen (2002), some species like C. fragilis have a dis- & Allen, 2002) since only the areas where the shrimp vessels tribution from California to Baja California and even to the middle normally trawl (5 to 65 m) were sampled. According to Petrakis of the Gulf of California. In this study C. fragilis was present in et al. (2002), the behavior and geographical distribution can be south of the Gulf of California, contrasting the reported distribu- important factors determining the volume and composition of tion. This is, in this work we report the amplification of the area some species captured, but the effects are dependent on the of distribution of C. fragilis. Another species found outside its captured species. This fact could determine species and size reported range was C. gilberti which was found in the north of the differences of the time and depth that the samples were taken. Gulf of California. This flatfish species normally has a distribution An example of these effects could be the migrations patterns of

Hidrobiológica Flatfish species in the shrimp bycatch 185

14 a) P. woolmani 16 b) C. fragilis 12 14 10 12 8 10 8 6 6 4 4 2 2 0 0

20 c) A. mazatlanus 16 d) E. crossotus 18 14 16 12 14 12 10 10 8 8 6 6 4 4 2

) 2 0 0

16 14 e) C. gilberti f) S. chabanaudi 12 14 12 Recruitment (% Recruitment 10 10 8 8 6 6 4 4 2 2 0 0 JanFeb MarApril MayJuneJulyAug Sep Oct NovDic 18 16 g) S. ovale Month 14 12 10 8 6 4 2 0 JanFeb MarApril MayJuneJulyAug Sep Oct NovDic Month Figure 7a-g. Recruitment patterns of the most abundant flatfish species in the shrimp trawl bycatch in the Gulf of California during 2002 and 2003.

some flatfish species, mainly of the genera Paralichthys, Etropus, 900 to 2500 mm in total length, and they are generally considered Achirus, which have a reproductive migration from deep waters of commercial value (Balart, 1996); meanwhile, other flatfish to the coastal areas (Balart, 1996; Reichert, 2000). For this rea- species captured in the shrimp trawls are generally species son, additional studies, increasing the sampling depth to other that are smaller than 250 mm with little or no commercial value areas in addition to where the shrimp fleets operate are needed (Hensley, 1995). to further understand the distribution and abundance of these The growth parameters obtained in this study for the most benthonic species and to gain enough information to evaluate the abundant and frequent flatfish species (Table 2), correspond with potential effects of fishing on the fish populations. the short longevity of these species (from 1.8 to 3.2 years) with the According to the length frequency diagrams of flatfish exception of P. woolmani which according to literature have a species (Fig. 5a-o), the majority of flatfish species were small greater longevity and which correspond with relatively low (ranging from 20 to 200 mm of total length), and only P. woolmani values of K (growth coefficient) and high values of L∞ (Hensley, surpassed the 250 (20-380) mm of total length (Fig. 5a). This is 1995; Reichert, 2000; Fishbase). When the growth parameters similar to findings from studies performed by Van der Heiden were estimated for P. woolmani (the most abundant flatfish spe- (1985) and Pérez-Mellado & Finley (1985), where they found out cies in this study), there was an absence of the largest sizes for that only the species of the Paralichthys genera surpassed 250 this species which caused an over-representation of the smallest mm in the shrimp trawl bycatch in the Gulf of California. The organisms, increasing the slope of the growth with no defined species of this genus habitually reach maximum size between limits for the asymptotic length and overestimating K. This type of

Vol. 18 No. 3 • 2008 186 Rábago-Quiroz., et al.

Table 3. Bibliographic searches about of maximums sizes, longevity and sexual maturation size of some flatfish species.

Species Maximum size (mm) Longevity Sexual maturation size Source (years) LT (mm) Paralichthys woolmani 800 5 – 10 325 Fishbase Citharichthys fragilis 220 1 - 2.5 125 Fishbase Achirus mazatlanus 210 1 - 2 140 Fishbase Etropus crossotus 200 1 - 2 92 Reichert (2000) Citharichthys gilberti 270 1 – 2 160 Fishbase Symphurus chabanaudi 250 2 – 3 157 Fishbase Syacium ovale 230 2 – 3 146 Fishbase

problems has also been documented for the blue shrimp (López- cation, biometry and data base conformation. Finally we thank to Martínez et al., 2005) and other fish species and perhaps is due Joaquin Magaña and Karen Link for improve the English text and to the these species have a reproductive migration from deep two anonymous referees. waters to coastal areas (Balart, 1996), causing changes in spe- cies and size availability. Another potentially influential factor is that the majority of the shrimp trawls were done at night, because References the shrimp fleet in the Gulf of California trawls primarily at night. Al v e r s o n , D. L., M. H. Fr e e b e r g , S. A. Mu r a w s k i , & J. G. Po p e . 1996. A global This could have affected the composition and length structure of assessment of fisheries bycatch and discards. Fisheries Technical the flatfish species in our samples since some flatfish species Paper 339 FAO. Rome, 233 p. can have diurnal habits. An ó n i m o . 2005. Anuario Estadístico de Pesca 2004. Secretaría de Analysis of recruitment for the most frequent flatfish spe- Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación. cies showed that the highest period of reproductive recruitment México, D.F. was from May to August (Fig. 7). This period occurs during the closed shrimp season, which is from March to September in An ó n i m o . 2006. Anuario Estadístico de Pesca 2005. Secretaría de the Gulf of California. During this time, the species captured Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación. incidentally can recuperate and the possible damage caused México, D.F. by the incidental capture of these species lessens. More than Ba l a r t , E. F. 1996. Pesquería de Lenguados. In: Casas-Valdez, M. y G. 50 % of the organisms sampled were of small sizes and the Ponce-Díaz (Eds.). Estudio del potencial pesquero y acuícola de majority of these were captured before sexual maturation (Table Baja California Sur. SEMARNAP, Gob. Edo. BCS, FAO, INP, UABCS, 3), this could potential have an effect on the population level. CIBNOR, CICIMAR, CETMAR. México, pp. 273-285. However, it is necessary to measure the level of abundances of each species within its entire total distribution and the area of Ba l m o r i -Ram í r e z . A., J. M. Ga r c í a -Ca u d i l l o , D. Ag u i l a r -Ram í r e z , J. R. To r r e s -Ji m é n e z y E. Mi r a n da -Mi e r. 2003. trawling of the shrimp fleet to estimate the real effect on these Evaluación de dispositivos excluidores de peces en redes de arrastre camaroneras del Golfo populations. de California, México. Reporte Técnico. INP, SAGARPA, CRIP Guaymas y Conservación Internacional A.C. 21 p.

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Hidrobiológica Flatfish species in the shrimp bycatch 187

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