Revista de Biología Tropical ISSN: 0034-7744 [email protected] Universidad de Costa Rica Costa Rica Herrero-Pérezrul, M.D.; Reyes-Bonilla, H. Weight-Length relationship and relative condition of the holothurian Isostichopus fuscus at Espíritu Santo Island, Gulf of California, México Revista de Biología Tropical, vol. 56, núm. 3, diciembre, 2008, pp. 273-280 Universidad de Costa Rica San Pedro de Montes de Oca, Costa Rica Available in: http://www.redalyc.org/articulo.oa?id=44920273015 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Weight-Length relationship and relative condition of the holothurian Isostichopus fuscus at Espíritu Santo Island, Gulf of California, México M.D. Herrero-Pérezrul1 & H. Reyes-Bonilla2 1. Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, Ave. IPN S/n Col., Playa Palo de Santa Rita, CP. 23096, La Paz, B.C.S., México. Phone: +52(612)122-53-66. Fax: +52(612)122-53-22; [email protected]. 2. Departamento de Biología Marina, Universidad Autónoma de Baja California Sur, Apdo. Postal 19-B, CP 23080, La Paz, B.C.S., México. Received 11-IX-2007. Corrected 18-IV-2008. Accepted 17-IX-2008. Abstract: Holothurians were heavily exploited worldwide during the last decade. The high prices of the prod- uct prompted the opening of new fishing grounds in the west coast of American countries, such as México and Ecuador. In these countries, the target species is Isostichopus fuscus. There is good information regarding the reproductive biology, growth and abundance of this sea cucumber, however, more studies are still needed, espe- cially those which can supply information on the physiological condition of the individuals. The objective of this study was to estimate the relative condition of an exploited population of I. fuscus at Isla Espíritu Santo, in the southern Gulf of California, México. A total of 1 446 individuals were analyzed during 1996-1997. Length and weight were monitored each month. We calculated the weight-length relationship and the index of relative condition (Kn). The mean length and weight were 23.3+0.1 cm and 385.9+3.9 g respectively. The weight-length relationship showed that I. fuscus grew allometrically at the study site. The index of relative condition (Kn) had an average of 1.040 +0.027, and ranged from 0.123 to 2.816. There were no statistical differences in Kn along the year, although the highest values appeared from November to April. Kn presented a parabolic relationship with total length, and peaked at 21 cm length, the size of first maturity. This pattern may indicate that the condi- tion of individuals is slowly improving with age up to a point and then decreases gradually, a possible evidence of aging and the first indication of senescence in holothurians. Rev. Biol. Trop. 56 (Suppl. 3): 273-280. Epub 2009 January 05. Key words: Isostichopus fuscus, holothurians, weight-length relationship, relative condition, Gulf of California. Holothurians have been heavily fished and Shirley 1996, Herrero-Pérezrul et al. 1999, around the world, and reports of a decrease in Ramírez Soberón et al. 2001). I. fuscus is world catch have become common during the the most important commercial species in the last decade (Conand 2000, Hearn et al. 2005). eastern Pacific and has been so since the early In America this fishery is not traditional; never- nineties. After a few years of intense exploita- theless, the high price of the product prompted tion, the government of Mexico and Ecuador the opening of new fishing grounds in the west banned the fishery for many years (Anonymous coast of Alaska, Canada, the United States, 1994, Fajardo-León and Vélez Barajas 1996, México, and the Galapagos Islands, Ecuador. In Sonnenholzner 1997, Jenkins and Mulliken this region, the target species are Isostichopus 1999). At the end of the decade, strong social fuscus (Ludwig 1875), Parastichopus parvi- pressure lead to the reopening of the fishery, but mensis (H.L. Clark 1913) and P. californicus this time in the frame of a better legislation and (Stimpson 1857) (Heizer and Hobbs 1994, Zhou knowledge of the status of the populations. Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 56 (Suppl. 3): 273-280, December 2008 273 There is good information regarding the during 1996-1997. Individuals were collected reproductive biology, growth and abundance monthly on six shallow bays of the island (~10 of Isostichopus fuscus (Fajardo-León et al. m depth) where a total of 1 446 individuals 1995, Herrero-Pérezrul et al. 1999, Hamel et were measured and weighted. Length was al. 2003, Reyes-Bonilla and Herrero-Pérezrul registered in situ to the closest centimeter from 2003, Hearn et al. 2005), used to establish mouth to anus using flexible tapes (precision 1 basic management programs in México and mm), a procedure that avoided contraction of Ecuador, including total allowable catch (TAC), the holothurians. Each individual was collected reproductive ban (from June to September in in individual bags, transported to a boat, and México), and minimum weight and size of weighted with spring scales (precision + 5 g). capture. Notwithstanding, more studies are The organisms were then returned to the gen- still needed, especially those which can sup- eral area where they resided. ply information on the physiological condition With that information we estimated the of the individuals, as an indication of their weight-length relationship according to the fishing yield. The study of condition assumes general equation (Cone 1989): that heavier organisms of a given length are in b better physical condition, therefore, condition W = aL indices are used in fishery science as indicators where W = weight in g, L = body length in cm, of the weight-to-length relationship of a popu- a = the ordinate, b = the slope of the curve. lation or subgroup. The physiological state of Using the parameters of the equation and an animal is related to its evolutionary fitness, the observed data of weight and length, we thus health status would be an indicator of calculated the index of relative condition (Kn) reproductive success and of the ability to cope for each specimen (Anibeze 2000). This index with environmental factors (Cone 1989, Jones expresses how different is the weight of a given et al. 1999). One of the best ways to analyze individual from the expected value calculated this subject is to evaluate the relationship for the entire population. between weight and length of a given species, and the use of the relative condition index Kn = W/aLb Kn (Cone 1989). Relative condition relates individual weight to a standard population To describe the results we estimated the weight, which must be specified for a popula- monthly mean and standard error of Kn, as tion or region of interest (Murphy et al. 1991). well as the first and third percentile of the data Consequently, Kn is limited to comparisons of (Sokal and Rohlf 1995). It has been suggested individuals in a population of interest with a that regression-line-percentile is considered to standard population. be a proper technique when analyzing condi- Considering this background, the objective tion indices (Murphy et al. 1991). Finally, since of this study was to estimate the relative condi- data were normally distributed (Kolmogorov- tion of a population of I. fuscus at Isla Espíritu Smirnof, p>0.05) a one-way ANOVA (α = Santo, in the southern Gulf of California, 0.05) was used to detect differences in time of México, where the stock was under active the values of Kn. exploitation until 1994. RESULTS MATERIALS AND METHODS The sampled population of Isostichopus The population of I. fuscus of Isla Espíritu fuscus had a mean length of 23.3 ± 0.1 cm and Santo in the southern Gulf of California, weight of 385.9 ± 3.9 g, with minimum and México (24°35’55” N, 110°24’17” W; and maximum values of 5 and 40 cm, and 15 and 24°24’04” N, 110°19’13” W), was monitored 830 g, respectively. 274 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 56 (Suppl. 3): 273-280, December 2008 The weight-length relationship (Fig. 1) when the individuals are not in reproductive evidenced that the species grows allometri- activity, and low from June to October. cally, as it appears to be the general case in Kn presented a parabolic relationship with tropical holothurians (Table 1). total length (p<0.05; Fig. 3), which had its The index of relative condition (Kn) had highest point (1.0961) at 20 cm length. an overall average of 1.040 + 0.027 and ranged from 0.123 (lowest value found in June 1997) DISCUSSION to 2.816 (highest value in July 1997). No statistical differences were detected in the Kn According to Herrero-Pérezrul et al. (1999), values among months (F11, 1434 = 0.616, p = the maximum size of I. fuscus (estimated as the 0.817), although monthly mean was higher in asymptotic length Linf and weight Winf, from the September and August, 1996, and June and Bertalanffy growth equation) were 36.1 cm and July 1997. The tendencies of Kn are also clear 815.4 g, respectively. We found similar length in the plot of the third percentile of the data, values from other relevant commercial spe- which apparently depicts an annual oscillation cies for which information is available. It can (Fig. 2). be seen that the maximum length of I. fuscus The polynomial curve indicates that Kn is high, surpassed only by Stichopus japoni- attains its peak in winter and spring.