New depth record of Cherublemma emmelas, black brotula (Ophidiiformes: Ophidiidae) from the Gulf of California, Mexico

Nuevo registro de profundidad de Cherublemma emmelas, brótula negra (Ophidiiformes: Ophidiidae) en el golfo de California, México

Hugo Aguirre-Villaseñor^1* and Rosalina Castillo-Velázquez²

¹ Instituto Nacional de Pesca, Centro Regional de Investigación Pesquera, Mazatlán, Calzada Sábalo-Cerritos s/n, AP 1177, CP 82010, Sinaloa, México. *Correspondent: haguirre@ola.icmyl.unam.mx

Recibido: 18 enero 2010
Aceptado: 20 julio 2010

Abstract

Seven black brotulas Cherublemma emmelas inhabiting deep-sea soft bottom in the southeastern Gulf of California were collected using a benthic sledge during 2 oceanographic cruises (TALUD project) at a depth range of 905 to 1 010 m, a temperature range of 4.6 to 5.2°C, and hypoxic (0.13 to 0.20 ml/l) conditions. Until now, the presence of C. emmelas below 750 m had not been reported in the literature. This new record extends the known depth range of occurrence approximately 260 m deeper than the previously reported limit.

Key words: Cherublemma emmelas, Gulf of California, new record, maximum depth, hypoxic conditions.

Resumen

Palabras clave: Cherublemma emmelas, golfo de California, nuevo record, profundidad máxima, condiciones hipóxicas.

Cherublemma emmelas (Gilbert, 1890) is a bathydemersal species found in the tropical eastern Pacific from Baja California to northern Chile. Studies on its biology are scarce, and information available is mostly restricted to its taxonomy (Lea, 1995; Ambrose, 1996; Nielsen et al., 1999) and distribution (Castro-Aguirre and Balart, 1996; Sielfeld and Vargas, 1996; Pequeño 2000). Adults are found at depths between 70 and 750 m, juveniles are encountered at shallower depths (Lea, 1995), and larvae and prejuveniles are mesopelagic (Ambrose, 1996; Sielfeld and Vargas, 1996; Nielsen et al., 1999). Until now, the presence of C. emmelas below 750 m had not been reported in the literature. A single, deeper record (700-900 m) exists based on material deposited in the Ichthyological Collection of the California Academy of Sciences under vouchers CAS 40398 and CAS 54941.

The deep sea is typified by low temperature, extremely high hydraulic pressure, nonphotosynthetic light, and relatively low influx of utilizable organic material derived from primary production in surface waters (Morita, 1999). The vertical distribution of oxygen in the southeastern Gulf of California indicates the presence of 3 successive environments. The well-oxygenated epipelagic zone ranges from the surface to about 80-125 m, with oxygen concentrations 2 ml/l or greater. Deeper into the water column, a wide hypoxic (< 0.1 ml/l) to almost anoxic mesopelagic zone is found, extending roughly from 150-200 m to 600-800 m. The deep water benthic-demersal environment is almost anoxic in localities shallower than 600-800 m but oxygen content is higher in deeper localities; oxygen reaches values of 0.5-1.0 ml/l in the depth range of 800-1 300 m. In deeper water, there is a strong recovery of oxygen content, which progressively reaches values above 2.0 ml/l in depths greater than 2 000 m (Hendrickx, 2001; Zamorano et al., 2007). Epibenthic water temperature decreases regularly from 6.2°C at the shallowest station (approximately 700 m) to 2.0°C at the deepest station (approximately 2 100 m), at depths of 700-1 100 m temperature range was 3.6 to 6.2°C (Hendrickx, 2003; Mendez, 2007; Zamorano et al., 2007).

Specimens were collected aboard the R/V "El Puma" of the Universidad Nacional Autónoma de Mexico. The sampling device, a 2.35 m wide, 0.90 m high epibenthic sledge equipped with a collecting net of about 5.5 cm stretched mesh size, was operated at depths of 400 to 2 250 m in the Gulf of California. Every fishing operation lasted 30 min, at a ship speed of 2 knots. Sampling depth was estimated with an analogical Edo Western echo sounder. Temperature and oxygen concentrations were measured approximately 10 m above the bottom with a CTD. Specimens were fixed with a 4% formaldehyde sea water solution for at least 1 week, washed with tap water, preserved in 70% ethanol, and identified in the laboratory. The identification guide of Lea (1995) was used for identification.

A total of 6 females (TL, 100-182 mm) were caught on June 6^th, 2001 (TALUD VII, St. 18, 24º15'00"N, 108º17'06"W), at a depth range of 950-1 010 m. Only 1 male (TL, 210 mm) was caught on February 11^th, 2007 (TALUD X, St. 14, 27º44'03'N, 111º36'49''W), at a depth of 905-943 m. The temperature range at this sampling station was 4.6 to 5.2 °C (Table 1).

The vertical distribution of dissolved oxygen concentration (Fig. 1) indicated critical hypoxic conditions (< 0.1ml/l) at depths between 300 and 800 m, but oxygen content was slightly higher in deeper localities; oxygen concentration measured close to bottom reached values of 0.13-0.20 ml/l (moderate hypoxia < 0.5ml/l) at depth approximately of 933 and 1 000 m (TALUD VII St. 18 and TALUD X St. 14 respectively). In the southeastern Gulf of California, epibenthic dissolved oxygen concentration < 0.5ml/l always and occasionally < 0.1 ml/l limits the occurrence of macroinvertebrate species that cannot tolerate severe hypoxic conditions (Hendrickx 2001, 2003). However, for Cherublemma emmelas, this does not represent a barrier for dispersion from the mid-shelf into deeper waters (depth range 70 to 1 000 m).

Due to their rare occurrence and the lack of earlier systematic studies of deep-sea communities off the Pacific coast of Mexico, information related to occurrence of deep-water species is uncertain and a poor definition of bathymetric distributional limits exists. This new record extends the known bathymetric range by approximately 26 atm, in an area where hypoxic (0.13 to 0.20 ml/l) conditions prevailed. The updated information on C. emmelas distribution provided in this report will help in unraveling the rich deep-sea ichthyofaunal biodiversity of Mexico, which, at this point, is poorly understood.

We wish to thank M. Hendrickx, director of these projects, for his advice and for reviewing the manuscript. Thanks to C. Salas for editing this English-language text and her helpful comments, C. Ramirez for the facilitation of the bibliographic references and G. Ramirez for their help with editing the manuscript. The authors thank the academic staff, crew, and students who participated on the TALUD cruises aboard the R/V "El Puma". This study was supported by the CONACyT 31805-N and PAPIIT IN217306-3 projects.

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