Crustaceana 85 (6) 635-658 GROWTH, MATURITY, AND SIZE-AT-AGE VARIATION OF THE BIGHEADED SHRIMP HETEROCARPUS VICARIUS (DECAPODA, PANDALIDAE) IN THE EASTERN TROPICAL PACIFIC OFF COLOMBIA BY MILTON PEDRAZA-GARCÍA1,2,5),JAVIERA.DÍAZ-OCHOA3) and LUIS A. CUBILLOS2,4) 1) Programa de Doctorado en Ciencias Biológicas Mención Ecología, Pontificia Universidad Católica de Chile, Santiago, Chile 2) Laboratorio de Evaluación de Poblaciones Marinas (EPOMAR) 3) Facultad de Ciencias, Departamento de Ciencias y Recursos Naturales, Universidad de Magallanes, Casilla 113-D, Punta Arenas, Chile 4) Departamento de Oceanografía, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile ABSTRACT The bigheaded shrimp, Heterocarpus vicarius, is a commercially important species fished by bottom-trawling fleets in the Colombian Pacific. However, the life-history parameters necessary for a proper analysis of the population dynamics of this species remain unknown. This paper studies the growth, maturity, and size-at-age variations, of Heterocarpus vicarious, as well as observations on recruitment patterns. The Von Bertalanffy growth parameters were estimated by sex through modal progression analysis, which consisted of grouping cohorts into age classes. Growth parameters were similar for males and females, without significant differences (F = 3.23, p>0.05). The growth of both sexes is described by the following parameters: L∞ = 15.26 ± 1.93 cm total length (TL), −1 K = 0.594 ± 0.24 yr ,andt0 =−0.66 ± 0.31 yr. Size-at-age variability was due mainly to processes occurring before larval settlement, since the mean length of same-age individuals born during different reproductive events (intercohort) varied more than that of individuals born during the same reproductive event (intracohort). Length at 50% maturity was estimated at 11.72 cm TL for females, with 95% confidence intervals between 10.57 and 13.71 cm TL. The growth curve and the relatively advanced age at maturity estimated for H. vicarius in the study area suggest the species is very vulnerable to fishing exploitation. RESUMEN El camarón cabezudo Heterocarpus vicarius es un recurso económicamente importante de la costa Pacífica colombiana, capturado por una flota camaronera de arrastre de fondo; sin embargo, la información existente sobre parámetros de historia de vida y dinámica poblacional es escasa. Este trabajo contribuye al conocimiento de esta especie presentando información sobre crecimiento, 5) e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2012 DOI:10.1163/156854012X643924 636 M. PEDRAZA-GARCÍA, J. A. DÍAZ-OCHOA & L. A. CUBILLOS madurez, variación de la talla a la edad e inferencias sobre patrones de reclutamiento. Los parámetros de la función de crecimiento de Von Bertalanffy (FCVB) fueron estimados por sexo a través de un análisis de progresión modal, el cual incluyó un agrupamiento ordenando de cohortes dentro clases de edad. El crecimiento entre sexos no presentó diferencias significativas (F = 3,23, p>0,05), describiéndose por los siguientes parámetros: L∞ = 15,26 ± 1,93 cm de longitud total (LT), −1 K = 0,594 ± 0,24 año y t0 =−0,66 ± 0,31 años. La variabilidad de la talla a la edad fue principalmente ocasionada por procesos previos al asentamiento ocurridos en la población, dado que la longitud promedio de los individuos nacidos en diferentes eventos reproductivos (inter-cohortes) presento mayor variación que aquella registrada para los individuos nacidos en un mismo evento reproductivo (intra-cohortes). La longitud al 50% de madurez en hembras fue estimada en 11,72 cm LT, con un intervalo de confianza al 95% entre 10,57 y 13,71 cm LT. La curva de crecimiento y la edad relativamente avanzada de maduración estimadas para H. vicarius en el área de estudio, sugiere que esta especie puede ser especialmente sensible a niveles altos de explotación. INTRODUCTION Numerous shrimp species belonging to the family Pandalidae are exploited commercially world-wide (Wilder, 1977; Moffitt, 1983; Gooding, 1984; Crosnier, 1986, 1988; King, 1987; Hendrickx, 1990; Hendrickx et al., 1998). About 34 species have been identified as economically important around the world (Holthuis, 1980). Some of these reach large body sizes, among them Heterocarpus vicarius (Faxon, 1893), the northern nylon shrimp, which is known in Colombia as the bigheaded shrimp. This species is caught from the Gulf of California to Peru and is found in depths between 73 and 1400 m (Hendrickx, 1995). It is particularly important for fisheries in Costa Rica, Panama, and Colombia (Holthuis, 1980; Pedraza-García, 2000). Most studies report that given its wide distribution and abundance levels, H. vicarius is a promising fish resource, inhabiting depths greater than 200 m in the Eastern Tropical Pacific (Del Solar & Mistakides, 1971; Hendrickx & Wicksten, 1989; Hendrickx, 1995; Kameya et al., 1997). In the Colombian Pacific, H. vicarius is caught as part of the bycatch in a bottom-trawling fishery operating below 40 fathoms (72 m). The target species are the shrimp Farfantepenaeus californiensis (Holmes, 1900) (brown or choco- late shrimp), Farfantepenaeus brevirostris (Kingsley, 1878) (pink shrimp), and Solenocera agassizi Faxon, 1893 (cauliflower shrimp) (Rueda et al., 2004; Puentes et al., 2007). This fishery is considered fully exploited and the yields have great potential for international markets because exports attained 31 million dollars in 2005 (De la Pava & Mosquera, 2001; Samper, 2006). However, few studies have been carried out on this fishery and most of the information has been obtained from assessment surveys in the 1980s by the Colombian Natural Resources and Environment Institute (Instituto de Recursos Naturales y del Ambiente – INDER- ENA) and the Japanese International Cooperation Agency (JICA). The surveys VARIATIONS IN GROWTH OF HETEROCARPUS VICARIUS 637 showed promising yields for species such as Solenocera agasizzi and Heterocar- pus vicarius (cf. Squires, 1971; Rueda et al., 2004). In spite of the increasing pres- sure from fishing and its economic potential, information on the biology of H. vicarius is still limited. The literature available is mostly devoted to taxonomy, geographic and bathymetric distribution and habitat preferences (Méndez, 1981; Hendrickx, 1995). To our knowledge, the only information available for the ad- ministration of this fishery comprises a few reports on yields, density distribution, and description of the community structure (e.g., Kameya et al., 1997; Hendrickx et al., 1998; Puentes et al., 2007; Wehrtmann & Echeverría-Sáenz, 2007). Con- sequently, we do not know about key life-history aspects of the biology of Hete- rocarpus vicarius in the Colombian Pacific, even though this species is fully ex- ploited. The species probably exhibits slow growth rates and high natural mortality rates, a dangerous combination that could lead to the species collapsing under in- tense exploitation (King, 1987). The objective of this paper is to contribute basic knowledge on the biology of H. vicarius in the Colombian Pacific basin. To do this, we provide estimations of important life-history parameters. We estimated growth parameters, using length frequency data, length at 50% maturity, and re- cruitment periodicity of the species. We discuss some aspects related to environ- mental effects on variations in length-at-age with respect to recruitment to fishing grounds. MATERIAL AND METHODS Data sources Length frequency data were collected from the fishing fleet operating in the Colombian Pacific (6°80-1°42N) (fig. 1). Each length-frequency data set corre- sponds to monthly summaries of random samples obtained from the catches of the industrial trawling vessels of the Buenaventura deep-water shrimp fleet. Body size of specimens of Heterocarpus vicarius was measured as total length (TL), which was defined as the distance between the anterior edge of the maxillipeds and the tip of the telson. Each specimen was sexed, and the number of females in ovigerous condition was registered. The period of study covered 12 months in the 1995/1996 fishing season. Recruitment periodicity Recruitment periodicity was determined using a trigonometric regression model (Greybill, 1976: 310), in which the logarithm of mean monthly length was used as 638 M. PEDRAZA-GARCÍA, J. A. DÍAZ-OCHOA & L. A. CUBILLOS Fig. 1. Study area in the Eastern Tropical Pacific off Colombia (6°80 -1°42 N). the dependent variable: ln TL(ti) ∝ sin(2πF0(ti + H))+ V + εi (1) where TL(ti) is the mean size of individual i in month t, F0 = 2π/P0 is the fundamental frequency (P0 is the fundamental recruitment period), H is the horizontal phase shift (the horizontal displacement from the beginning of the cycle), V is the vertical phase shift (the vertical distance from zero for the mean response variable ln TL(ti)), and ∝ is a proportionality factor fixed during model fitting and equal to the difference between maximal(ln TL) and mean(ln TL).The model was fitted by non-linear least squares with the NONLIN module of SYSTAT software (Wilkinson, 1988). The number of recruitment events was computed from the ratio T/P0 (where T is the total number of months analysed). VARIATIONS IN GROWTH OF HETEROCARPUS VICARIUS 639 Cohort identification Mean length data were grouped by considering the number of recruitment events and the parameters P0 and H . It was assumed that: (i) the amount of monthly data within each group depended on the value of P0 (for instance, P0 = 6 means that the group contains six months of information), and (ii) the month when each group started to be dependent of the value of H (e.g., H = 2 means that the group begins in the third month). Cohort identification was accomplished using the mixed distribution analysis (Macdonald & Pitcher, 1979; Macdonald & Green, 1988) included in the MIX 3.0 software (Ichthus Data Systems, Ontario, Canada). The MIX algorithm assumes that a length-frequency data (LFD) set consists of n components (cohorts), each one representing a probability density function f(x), for which a normal distribution of length-at-age was assumed.