Darkedge Midshipman Porichthys Analis (Batrachoidiformes: Batrachoididae), a Common Shrimp-Bycatch Fish from the Gulf of California
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Darkedge midshipman Porichthys analis (Batrachoidiformes: Batrachoididae), a common shrimp-bycatch fish from the Gulf of California Oscar A. González-Ochoa2, Juana López-Martínez1* & Norma Y. Hernández-Saavedra2 1. Centro de Investigaciones Biológicas del Noroeste, Unidad Sonora. Km. 2.35 Carretera a Las Tinajas, Col. Tinajas, Guaymas, Sonora, México. C.P. 85460; [email protected] 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; [email protected], [email protected] * Correspondence Received 30-IX-2011. Corrected 10-V-2012. Accepted 18-VI-2012. Abstract: 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 com- munity structure and function, together with their possible effect on commercial populations. With the aim of contributing to the knowledge of Darkedge Midshipman fish 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 coefficient indicated a moderate growth rate (K=0.5) with an estimated asymptotic length ofL∞=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 protected by its own bathymetric distribution and the off-shrimping season. This is the first study that considers population characteristics from this common but still unknown species. Rev. Biol. Trop. 60 (4): 1795-1805. Epub 2012 December 01. Key words: population biology, Porichthys analis, growth, mortality, recruitment. Shrimp fishing is important in the Gulf histories, seasonal variability, or growth rates of California (Sierra-Rodríguez et al. 2005), (González-Ochoa et al. 2009, Rábago-Quiroz but most shrimp bycatch species have low et al. 2008, 2011, López-Martínez et al. 2011, or null economic value and are normally dis- Morales-Azpeitia 2007). carded or underused (Kelleher 2005). Some Nowadays, species population characte- studies have described aspects on distribu- ristics, combined with community descriptors tion, taxonomy, or abundance of economi- to evaluate aquatic communities, are conside- cally important fish species reasonably well; red of outmost importance (Piet & Jennings nevertheless, we have not yet understood 2005, Rochet et al. 2005). Within this scheme, their functions in the ecosystems. In contrast, non-commercial species may function as pre- information on noncommercial species is still dators, prey, or competitors, affecting commu- scarce and some ignored, for example, life nity structure and influencing economically Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 60 (4): 1795-1805, December 2012 1795 important populations (Horn 1980). Models, Gonzaga at the peninsular shore (21°1’37’’- such as predation models, could be tested using 31°24’35’’ N and 105°16’06’’-114°22’51’’ W). size-based multispecies to explore community Sampling stations ranged from 10-70m in functions or to evaluate fishing effects (Rochet depth. Two sources of information were availa- et al. 2005). In addition, the proportion of ble: (1) A program of 10-onboard observers was noncommercial species has been suggested as implemented during the 2004-2005 shrimp- an indicator of fishing effects in marine com- fishing seasons, during which 20kg of bycatch munities (Trenkel & Rochet 2003). Besides, samples were taken from commercial trawling the population dynamics of various species is and were kept frozen until analysis. Authorized a useful element for community-based model bottom trawling nets were 37.5mm in mesh integration. Population parameters such as size at the cod-end and no less than 44.45mm growth, mortality, recruitment, and morphome- at the square. Sea turtle excluding devices were tric relationships, among others, are considered used in all nets. We took records from depth, key pieces of information (Petrakis & Stergiou trawling speed, crossed distance, and geogra- 1995, Froese 1998, Moutopouolos & Stergiou phical position for every trawl, among others. 2002, López-Martínez et al. 2011). The species P. analis was found in 91 samples Shrimp bycatch in the Gulf of California out of 2 439 (2). During the shrimp-spawning constitutes mainly fish (80%) and in a minor season, we obtained additional bycatch sam- proportion crustaceans and mollusks (López- ples from research surveys performed in July Martínez et al. 2010). The Darkedge Midshi- and August 2004 and 2005. For each trawling, pman fish Porichthys analis (Batrachoididae) we registered geographic starting and ending (Hubbs & Shults 1939) is one of the most position, initial and ending time, depth, speed, common species in shrimp bycatch (≅14%) sea surface and air temperature, among others (López-Martínez et al. 2010) and is practically (Herrera-Valdivia 2004). endemic in the Gulf of California region. This family comprises benthic and temperate to tro- Morphometric measurements: Once in pical species (Robertson & Allen 2002). P. ana- the laboratory, bycatch species were separated lis is one of the biggest species of the genera and identified (Fischer et al. 1995, Collet- and catalogued as a potential fishery resource te 1995) from each sample. The geographic (Collette 1995) lacking economic importan- origin of P. analis specimens was recorded ce. Additionally, Batrachoididae species have as well as total length (L), standard length often been used as experimental animals in (SL) (mm) (±1mm) and total weight (W) (g) biomedicine and evolutionary and ecophysio- (±0.1). Sex and sexual maturity were determi- logical research (Wang & Walsh 2000, Walsh ned according to a gonadal morphochromatic et al. 2004). However, practically nothing scale (Nikolsky 1963). is known about P. analis yet. Therefore, the main objective of this study was to contribute Population parameter estimation: Total to the knowledge of the species by estimating length-standard length (L-SL) relationship was some population characteristics obtained from determined by the least-squares method to fit shrimp trawl catches in the Gulf of California. a linear model L=a+bSL, and weight-standard length relationship (W-SL) to fit a potential b MATERIAL AND METHODS model W=aSL by non-linear estimation. We constructed monthly length frequency distri- Study area: The Northern side limits with butions (SL), and in using these, the von Ber- (- K (t - t0 ) the Southern end of the Biosphere Reserve of talanffy growth equation Lt=L∞(1-e ) the Upper Gulf of California and the Colorado was fitted, where Lt is standard length at age t, River Delta; to the South with Rio Fuerte, Sina- L∞ asymptotic length, K instantaneous growth loa at the continental shore; to Bahia San Luis rate, and t0 the theoretical age at zero length. 1796 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 60 (4): 1795-1805, December 2012 When fitting the von Bertalanffy equation, RESULTS an initial L value estimation was attempted ∞ A total of 1 725 P. analis were obtai- by the Powell-Wetherall method. With the L∞ value, Shepherd’s method (Sparre & Venema ned from commercial and research surveys. Spatial distribution of P. analis showed that 1998) was used to obtain an initial estimate it is present along the East coast, from the of K; the final growth parameter estimation upper Gulf of California to Sinaloa. Individual was made using ELEFAN I method. By using sizes ranged from 43-352mm (SL). The L-SL Pauly’s empirical equation, t was obtained as 0 relationship was described by the equation t =1x10[-0.3922- (0.2752LogL∞)-(1.038LogK)] (Sparre & 0 SL=0.9143L-4.8609 (Fig. 1). Given the close Venema 1998). correlation between both lengths, post-hoc Longevity was estimated as proposed by analyses were performed considering only SL. Taylor (1958) tmax=t0+3/K, where tmax is the The SL-W relationship was described by the longevity (yr) and other parameters as des- function W=0.000092SL3.0509 (Fig. 2). cribed above. Total mortality rate (Z) was Availability of organisms was restricted to estimated by the linearized length-conver- the shrimp-fishing season (September-March) ted catch curve (Sparre & Venema 1998) and research survey months (July-August).We Ln(Ni/∆t)=a+bti; where Ni is the number of used monthly length frequency distributions fish in length class i; ∆t is the time needed for shown in figure 3 to estimate the von Ber- the fish to grow through length class i; t is the talanffy growth parameters and adjusted the relative age corresponding to the mid-length of corresponding curve to the data. From our leng- class i;and b is an estimate of Z (sign changed). th distribution data, we identified at least four Natural mortality (M) was estimated using cohorts; only few larger size individuals appea- Pauly´s empirical equation LnM=-0.0152- red in July-September surveys. In L∞ estima- tion by the Powel-Wetherall method, we got 0.279LnL∞+0.6543LnK+0.463LnT, where T is the mean annual sea surface temperature an underestimation, so we used the maximum in the species habitat (ºC).