Shrimp fishery bycatch of the Gulf of California constitutes a wide variety of highly unknown fish, crustacean, and mollusk species with very low or null economic value, in contrast to those of commercial interest. However, there are no studies yet on the role of these low economic valued species have in the community structure and function, together with their possible effect on commercial populations. With the aim of ]]>
Porichthys analis, the most common waste species in this fishery, we estimated some population characteristics. For this purpose, we obtained shrimp-bycatch fish during the 2004-2005 fishing season and performed some research surveys. A total of 1 725 Darkedge Midshipman were captured from 350 bycatch samples. Individual size ranged from 43-352mm SL. The weight to standard length relationship was determined as W=0.000092SL3.0509. Von Bertalanffy’s growth ]]>
∞=352mm standard length, and a longevity of 6yr. Natural mortality was estimated as 0.97 and total mortality as 4.67. The recruitment pattern, as estimated by ELEFAN II, was extended over the year, peaking during spring and summer seasons. Sexual proportion of male:female was 1.65:1. Mature organisms appeared from August to March, and length at maturity was 157mm SL, which is larger than the mean size at capture 135mm SL. We concluded that the species is indirectly ]]>
Key words: population biology, Porichthys analis, growth, mortality, recruitment.
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Resumen
A diferencia de las especies de interés comercial, la historia de vida de los peces no comerciales es casi desconocida a pesar de su potencial importancia en la estructura y función de la comunidad. Para ]]>
Porcihchty sanalis. La fauna de acompañamiento de la pesquería del camarón en el Golfo de California está constituida por especies poco conocidas y de escaso valor comercial. Las especies de la familia Batrachoididae son frecuentemente utilizadas como animales experimentales, pero poco se sabe de P. analis. De esta manera a partir de la fauna de acompañamiento se recolectaron 1 725 organismos y se determinó la relación talla-peso ]]>
3.0509. Mediante ELEFAN I, se estimó un crecimiento moderado (K=0.5/año) con una longitud asintótica mayor que la observada reportada anteriormente (L∞=352mm SL) y una longevidad de 6 años. La mortalidad natural se estimó en M=0.97 la total en Z=4.67. El patrón de reclutamiento fue mayor durante primavera-verano. La proporción sexual M:F fue 1.65:1 y la talla media de primera madurez fue de 157mm SL mayor que la talla media de captura 135mm SL. Este es el primer reporte que considera las características poblacionales de esta especie ]]>
Palabras clave: biología poblacional, Porichthys analis, crecimiento, mortalidad, reclutamiento. Shrimp fishing is important in the Gulf of California (Sierra-Rodríguez et al. 2005), but most shrimp bycatch species have low or null economic value and are normally discarded or underused (Kelleher 2005). Some studies have described aspects on distribution, taxonomy, or abundance of economically important fish species reasonably well; nevertheless, we have not yet understood their functions in the ecosystems. In contrast, information on ]]>
Nowadays, species population characteristics, combined with community descriptors to evaluate ]]>
2002, López-Martínez et al. 2011).
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Shrimp bycatch in the Gulf of California constitutes mainly fish (80%) and in a minor proportion crustaceans and mollusks (López-Martínez et al. 2010). The Darkedge Midshipman fish Porichthys analis (Batrachoididae) (Hubbs & Shults 1939) is one of the most common species in shrimp bycatch (≅14%) (López-Martínez et al. 2010) and is practically endemic in the Gulf of California region. This family comprises benthic and temperate to tropical species (Robertson & Allen 2002).
P. analis is one of the biggest species of the genera and catalogued as a potential fishery resource (Collette 1995) lacking economic importance. Additionally, Batrachoididae species have often been used as experimental animals in biomedicine and evolutionary and ecophysiological research (Wang & Walsh 2000, Walsh et al. 2004). However, practically nothing is known about P. analis yet. Therefore, the main objective of this study ]]>
Material and Methods
Study area: The Northern side ]]>
P. analis was found in 91 samples out of 2 439 (2). During the shrimp-spawning season, we obtained additional bycatch samples from research surveys performed in July and August 2004 and 2005. For each trawling, we registered geographic starting and ending position, initial and ending time, depth, speed, sea surface and air temperature, among others ]]>
Morphometric measurements: Once in the laboratory, bycatch species were separated and identified (Fischer et al. 1995, Collette 1995) from each sample. The geographic origin of P. analis specimens was recorded as well as total length ]]>
Population parameter estimation: Total length-standard length (L-SL) relationship was determined by the least-squares method to fit a linear model L=a+bSL, and weight-standard ]]>
bby non-linear estimation. We constructed monthly length frequency distributions (SL), and in using these, the von Bertalanffy growth equation Lt=L∞(1-e (- K (t - t0 ) ) was fitted, where Lt is standard length at age t, L∞ asymptotic length, K instantaneous growth rate, and t0 the theoretical age at zero length. When fitting the von Bertalanffy equation, an initial L∞ value estimation was attempted by the Powell-Wetherall method. With the L∞ value, Shepherd’s method (Sparre & Venema 1998) was used to obtain an initial estimate of K; the final growth parameter estimation was made using ELEFAN I method. By using Pauly’s empirical equation, t0 was obtained as t0=1x10[-0.3922- (0.2752LogL∞)-(1.038LogK)] (Sparre & Venema 1998).
Longevity was estimated as proposed by Taylor (1958) tmax=t0+3/K, where tmax is the longevity (yr) and other parameters as described above. Total mortality rate (Z) was estimated by the linearized length-converted catch curve (Sparre & Venema 1998) Ln(Ni/∆t)=a+bti; where ]]>
Ni is the number of fish in length class i; ∆t is the time needed for the fish to grow through length class i; t is the relative age corresponding ]]>
i; and b is an estimate of Z (sign changed). Natural mortality (M) was estimated using Pauly´s empirical equation LnM=-0.0152-0.279LnL∞+0.6543LnK+0.463LnT, where T is the mean annual sea surface temperature in the species habitat (ºC). Fishing mortality rate (F) can be calculated by a difference of Z=M+F, and exploitation rate (E) was determined according to Jones (1984), E=Z/F (Sparre & Venema 1998).
Recruitment pattern was estimated by the ELEFAN II method. We also estimated both, length at first capture and length at sexual maturity using only all mature females (stages III-V). Organisms were grouped in 11mm length intervals and cumulated relative frequency calculated by interval. The nonlinear least-square fitting method, which is available in the FISHPARM suite (Prager et al. 1987), was used for fitting the logistic function P=1/ ]]>
-a(SL-SL50)), where P is the proportion of caught organisms or mature females in case of sexual maturity: SL50the standard length at which 50% of the population is caught (SLc50) or attains reproductive maturity (SLm50) according to the case.
Results
A total of 1 725 P. analis were obtained from commercial and research surveys. Spatial distribution of P. analis showed that it is present along the East coast, from the upper Gulf of California to Sinaloa. Individual sizes ranged from 43-352mm (SL). The L-SL relationship was ]]>
Fig. 1). Given the close correlation between both lengths, post-hoc analyses were performed considering only SL. The SL-W relationship was described by the function W=0.000092SL3.0509 (Fig. 2).
Availability of ]]>
figure 3 to estimate the von Bertalanffy growth parameters and adjusted the corresponding curve to the data. From our length distribution data, we identified at least four cohorts; only few larger size individuals appeared in July-September surveys. In L∞ estimation by the Powel-Wetherall method, ]]>
∞ seminal value in the K calculation by the Shepherd (1987) method. Both values were later used for the joint re-estimation by ELEFAN I, giving the adjusted growth equation SL=352(1-e (-0.5(t+0.31))).
We used these ]]>
Fig. 4); longevity was estimated in 6.31yr.Therecruitment pattern practically extended over the year and showed two peaks: one in February-May and another in July-October (Fig. 5).
Natural mortality M was 0.97 ]]>
The number of males exceeded the number of females and sexual proportion, M:F was 1.65:1 (X2α/2, 0.025,7=24.322, p<0.0000).
Mature organisms (stages II-IV) appeared from August to March, and frequencies were apparently higher from October to January (Fig. 6). Length at first capture was estimated considering cumulative frequency of all individuals. Adjusted sigmoid function was P=1/ (1+e -0.055(SL-135)), where length at first capture (SLc50) was 135mm SL (Fig. 7). We estimated ]]>
50) using SL records and considering cumulative frequency of mature females (stages III-V). The adjusted sigmoid curve function was P=1/ (1+e-0.051(SL-157)), so mean length at first maturity was attained at 157mm SL (Fig. 7). Both sizes (curves) were different when compared by Kolmogorov-Smirnov test (D0.05 = 0.1341), with length at capture being smaller than length at first sexual maturity (Sokal & Rohlf 1981).
Discussion
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Up to now, papers on P. analis have documented the sites where this species has been recorded. Our sampling comprised those areas from the Gulf of California where commercial trawling takes place, i.e. soft bottom between 9-80m in depth. Only few larger size individuals appeared in July-September surveys. Considered as a demersal benthic species from a visual inspection of body form, it may be inferred that the fish uses body-fin caudal transient locomotion. Species with this shape show low sustained cruise propulsion with sudden rapid acceleration (Webb 1984). Therefore, ]]>
The weight-length relationship showed an isometric growth, and despite the scarcity of larger sizes in our samples, it resulted similar to other studies. Pearl Spot Midshipman P. margaritatus showed values of a=0.0069, and b=3.19 (Ruiz-Ramírez et al. 1997), and Atlantic Midshipman
P. Porosissimus showed a=0.005 and b=3.148 (Vianna et al. 2000). Froese (2006) suggested that only a few individuals in the whole range size and throughout all seasons were enough to get representative results in this relationship.
A major number of larger organisms may lead to a decrement in K estimation. However, the observed maximum ]]>
Opsanustau showed an L∞=37.9cm and K=0.16; Gulf Toadfish O. beta L∞=30cm, K=0.22 (Serafy et al. 1997). The maximum observed size of Plainfin Midshipman P. notatus was 33cm attaining longevity of 7yr (Garrison & Miller 1982), which is very close to our P. analis ]]>
Considering the distribution area, the fishing mortality estimate in this work may also be lower than the one obtained because only a proportion (smaller sizes) of the population was caught by shrimp vessels. Moreover, the method used (length converted catch curve) considered death of organisms from the population were due to fishing throughout the time. This problem is showing the mortality evaluation in those species populations where we ]]>
From SL50 and using the inverse von Bertallanfy growth equation, age at maturity is 0.9yr (≅0.11months), which is earlier than Plainfin Midshipman P. notatus (3.5yr) ]]>
P. margaritatus shows a higher abundance at 60m during the warmest bottom water season and moves slightly to shallower waters during colder ]]>
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On the other hand, although an apparently higher frequency of Darkedge Midshipman fish P. analis mature organisms occurred during winter, the following must be considered: The spawning season in P. notatus occurs in springsummer (Garrison & Miller 1982), and in our study there were months without any samples (April to June). Shrimp off-season is from March to August when we had less represented samples from a few research surveys ]]>
Fig. 6) may have corresponded to the second spawning peak (although more accurate data might be obtained from reproductive biology during the shrimp closed season). The open shrimping season is usually from August-September to March-April each year, and then an associated ]]>
P. analis spawners, additional to the bathymetric and latitudinal distribution mentioned earlier.
Acknowledgments
We would like to ]]>
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*Correspondencia:Oscar A. González-Ochoa: Centro de Investigaciones Biológicas del Noroeste. Km. 1 Carretera a San Juan de La Costa “El Comitán”. Apdo. Postal 128, La Paz, B.C.S. 23097, México; ocibnor@yahoo.com.mx Juana López-Martínez: Centro de Investigaciones Biológicas del Noroeste, Unidad Sonora. Km. 2.35 Carretera a Las Tinajas, Col. Tinajas, Guaymas, Sonora, México. C.P. 85460; jlopez04@cibnor.mx Norma Y. Hernández-Saavedra: Centro de Investigaciones Biológicas del Noroeste. Km. 1 Carretera a San Juan de La Costa “El Comitán”. Apdo. Postal 128, La Paz, B.C.S. 23097, México; nhernan04@cibnor.mx 1. Centro de Investigaciones Biológicas del Noroeste, Unidad Sonora. Km. 2.35 Carretera a Las Tinajas, Col. Tinajas, Guaymas, Sonora, México. C.P. 85460; jlopez04@cibnor.mx 2. Centro de Investigaciones Biológicas del Noroeste. Km. 1 Carretera a San Juan de La Costa “El Comitán”. Apdo. Postal 128, La Paz, B.C.S. 23097, México; ocibnor@yahoo.com.mx, nhernan04@cibnor.mx ]]>
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