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Revista de biología marina y oceanografía

versión On-line ISSN 0718-1957

Rev. biol. mar. oceanogr. vol.49 no.1 Valparaíso abr. 2014

http://dx.doi.org/10.4067/S0718-19572014000100016 

 

NOTA CIENTÍFICA

Length-weight relationships for 25 kelp forest-associated fishes of northern and central Chile

Relaciones de longitud-peso para 25 peces costeros asociados a macroalgas pardas del centro y norte de Chile

 

Alejandro Pérez-Matus1, Sergio A. Carrasco1 and Andrés Ospina-Alvarez2

1Subtidal Ecology Laboratory & Center for Marine Conservation, Estación Costera de Investigaciones Marinas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile. aperez@bio.puc.cl
2Centro de Conservación Marina & Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile


ABSTRACT

The present study reports length-weight relationships for 25 species of reef fishes associated with large brown macroalgae (i.e., Lessonia trabeculata and Macrocystis pyrifera) from the northern and central rocky coast of Chile (Southeast Pacific Coast; 18°-33°S). Weight scaled to length with an average power of 2.85, close to the expected value of 3, meaning that the relationship between length and weight is close to an isometric growth. No latitudinal (i.e., spatial) and temporal variations were observed on the growth coefficient of the fish species studied.

Key words: Rocky reefs, fish assemblages, distribution, allometric growth


INTRODUCTION

Size has a major impact on most features of fish biology. It is biologically more important than age, and can be constrained by ecological, behavioral and physiological factors (Wootton 1999). The understanding of size variation among species may have implications for diverse fields of fishery science, population and community dynamics (Santos et al. 2002). Length-weight relationships can be used to convert field-based estimates of lengths into weights, which can in turn be used to estimate growth rates of individuals (Taylor & Willis 1998) and biomasses of population and communities (Mora et al. 2011). When evaluated overtime, length and weight parameters can also be used to indicate changes in growth strategies associated with environmental disturbances, such as climate change, ocean acidification, disease, starvation, exploitation, among others (Csirke 1980).

Chilean temperate rocky reefs are dominated by large brown macroalgae (i.e., Lessonia trabeculata and Macrocystis pyrifera), with these canopy-forming species providing habitat for a number of fish species (Fig. 1) (Pérez-Matus et al. 2007, 2012). Nonetheless, basic biological information on most of these fish species is yet absent or unpublished. We aimed to provide the first L-W reference for 25 fish species inhabiting shallow subtidal reefs in northern and central Chile.

Figure 1. Map of the sampling and collection sites along with: A) interannual average night sea surface temperature from 5th July 2002 to 1st August 2013 which represent the temporal framework of the species collections (see methods for details) for each site. Nighttime Sea Surface Temperature (NSTT) data was acquired and extracted from the moderate resolution imaging spectroradiometer `MODIS AQUA L3' satellite data (incorporating standard atmospheric corrections)1 with a resolution of 1.2 km at high temporal frequency validated. B) pictures of representative species collected such as Cheilodactylus variegatus (bilagay) and Hemilutjanus macrophthalmos (apañao) (photo credit: A. Pérez-Matus)

Figura 1. Mapa de los sitios de muestreo y colecta de peces con: A) Promedio de la temperatura superficial del mar, registro nocturno, entre el 5 de julio de 2002 al 1 de agosto de 2013 representando la escala temporal de la colecta de especies (ver métodos para más detalles). La temperatura superficial del mar fue extraída de una imagen satelital de resolución moderada (1,2 km) del espectroradiómetro `MODIS AQUA L3' (incorporando correcciones atmosféricas)1 y validada en alta frecuencia temporal. B) Fotografías de especies de peces representativas tales como Cheilodactylus variegatus (bilagay) y Hemilutjanus macrophthalmos (apañao) (créditos: A. Pérez-Matus)

 

MATERIALS AND METHODS

Study area and sampling

The data reported herein were collected at 7 different sites along the northern and central Chilean coast (18°-33°S; Fig. 1) during austral summer and spring 2004-2005 (Rio Seco, Caleta Constitución, Caleta Angosta and Lagunillas) and in spring 2012-2013 (Lagunillas, Zapallar, and Punta de Tralca). Generally, sites were characterized as shallow subtidal rocky reefs (~15 m depth) dominated by the co-occurring large brown macroalgae L. trabeculata and M. pyrifera. Specimens were caught with different fishing gear such as gill nets (2.5 cm overture), spear gun (90 cm), hook and line and baited cages (60 x 80 cm and 60 cm height). All collections were performed during 10:00 to 16:00 h to minimize potential variability in the foraging behavior of the focal species. Most of the measurements of fish total length (L) and weight (W) were performed at fish's catch sites (see S1 supplementary data in Pérez-Matus et al. 2014). Total length was measured with an ichthyometer (i.e., 50 cm PVC tubes with a 5 cm aperture on top and a measuring tape on inner bottom to contain the fish during the measuring process) to the nearest 1 mm and fresh weights were measured using analytical balances with an accuracy of 1 g.

 

Data analysis

We used Huxley's (1932) power function, W = αLb, where L represents the total or fork length (cm) size, W the total weight (g), α the intercept (initial growth coefficient or condition factor) and b the slope (growth coefficient, i.e., fish relative growth rate), to express the scaling relationship of length-weight for the 25 fish species included in the model below. Length-weight allometry was quantified by deriving exponent a by regressing the natural logarithm of the length of each species against the natural logarithm of body mass and obtaining the slope.

Slopes were calculated using regression ordinary least squares (OLS) and the association degree between L and W was calculated by the determination coefficient r2. Additionally, 95% confidence limits of α intercept and b slope and the statistical significance level of r2 were estimated. All data management and analysis were performed using the R statistical software, version 3.0.0 (R Development Core Team 2012) with R base packages (see S2 supplementary data in Pérez-Matus et al. 2014). Regression ordinary least squares and testing for the different species regressions were computed using package `smatr', version 3.4 (Warton et al. 2012).

Equally, we tested the relationship of L-W discriminated by study sites to test if growth coefficient changed due to geographical (i.e., latitudinal) range. We spatially pooled the information since no statistical differences among slopes were detected among sites (P > 0.05), hence years (see above).

 

RESULTS AND DISCUSSION

A total of 760 individuals from 25 different species were collected in the present study, with length-weight equations applying to most teleost species commonly found on shallow subtidal reefs in northern and central Chile (Angel & Ojeda 2001, Pérez-Matus et al. 2007). L-W relationships, growth coefficients, and length-weight equations, along with different descriptive statistics for all species collected are presented in Table 1. Values of growth coefficient (b) ranged from 1.44 to 3.75, with a mean of 2.85 ± 0.48 (SD). The comparison between obtained values of t-test and the respective tabled critical values allowed for the determination of the b-values statistical significance, and their inclusion in the isometric range (b = 3) or allometric ranges (negative allometry: b < 3 or positive allometry: b > 3). The value of 2.85 was less than the rate of isometric growth of 3, meaning that on average, fishes associated to large brown macroalgae have a negative allometric growth; hence size (i.e., growth) was not proportional to weight. This differed to reef fishes from other temperate kelp forest systems as New Zealand, where growth has been shown to be nearly isometric (i.e., fish structure remains constant with growth; Taylor & Willis 1998).

Slopes of the length-weight regressions were not significant for the following species: Labrisomus philippii, Paralichthys adspersus, Nexilosus latifrons, Sebastes oculatus and Helcogrammoides chilensis, suggesting that these 2 variables were dependent to one another. In other words, data for these fish species did not spanned a reasonable size range to estimate α and b parameters (Table 1). Despite differences in cumulative sea surface temperature (see Fig. 1), the L-W relationship was constant. This is consistent with results from other systems such as the north Atlantic (Morato et al. 2001), suggesting that temperature primarily affects fish by altering their growth rates, not their weight at a given length.

Sexual dimorphism in length-weight relationships could occur in Semicossyphus darwini and Graus nigra, because of sequential hermaphroditism in the former and energy allocation hypothesis in the latter. We did not have sufficient males for S. darwini and no females for G. nigra. Nonetheless, Flores & Smith (2010) reported a slight sexual dimorphism in L-W relationship in G. nigra, with males having an isometric growth and females a negative allometric growth. Our estimates were similar to those reported by Flores & Smith (2010) for G. nigra, confirming the low variation in growth estimates among the species at different sites. Beside that study, no other source of information regarding length-weight relationships existed for kelp-forest associated fishes of northern-central Chile. This is relevant considering the fishing pressure that many of these populations are currently experiencing (Godoy et al. 2010).

 

ACKNOWLEDGMENTS

We thank Fabian Ramirez, Catalina Ruz (SUBELAB) and Francisco Díaz for assistance in the field. Fondecyt # 11110351 granted to APM provided funding for this research. We also thank the Marine Conservation Center, ICM - P10-033F, (funds from `Fondo de Innovación para la Competitividad, del Ministerio de Economía, Fomento y Turismo'). We would like to thank Dr. Richard Taylor and one anonymous referee for valuable comments on earlier draft.

 

NOTE

1<ftp://podaac.jpl.nasa.gov>, thermal IR SST, 4 km and 0.1°C resolution from MODIS databases

 

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Received 11 September 2013 and accepted 24 January 2014
Associate Editor: Mauricio Landaeta D.