Estimates of annual food consumption/biomass ratio (Q/B) from the fish fauna of a mangrove estuary in North Brazil

To contribute to mass balanced trophic model parametrization, estimates of annual food consumption/biomass ratio (Q/B) were compiled for 37 selected fish species of the Curuçá Estuary in Northern Brazil using an empirical model. Samples were taken bimonthly between July 2003 and July 2004 in the main channel and intertidal creeks using an otter trawl and a fyke net, respectively. The aspect ratio of the caudal fin varied between 0.8 for Poecilia vivipara and 4.6 for Sciades herzbergii and the Q/B ranged from 2.3 for Epinephelus itajara to 67.3 for Cetengraulis edentulus. This study represents the first reference available on Q/B values of 29 fish species. This compilation of Q/B ratio presented here should be useful for construction of Ecopath models particularly in tropical conditions.


Introduction
One of the most important aspects of ecological studies lies in understanding the ecosystems through their trophic fluxes with regard to energy assimilation, transfer and dissipation (BAIRD; ULANOWICZ, 1993).During the last 50 years, indiscriminate fishing gear and unsustainable fishing practices have led to significant and steady decline in the mean trophic levels of fishery landings (PAULY et al., 2000).The global fishery collapse was observed over the last decades and its highly complex impacts on ecosystems have contributed to the substitution of the traditional single-species assessments for a more holistic approach: the "ecosystem-based management" (e.g.JENNINGS; POLUNIN, 1996;PAULY, 1998;CHARLES, 2001;JACKSON et al., 2001).
The Ecopath software (POLOVINA, 1984) has been widely used to describe trophic relationships in aquatic ecosystems on quantitative bases (PAULY et al., 2000).Information about feeding ecology and food consumption of the major functional groups of an ecosystem are necessary to construct mass and energy flow models (CHRISTENSEN;PAULY, 1993).Consumption is the intake of food by a species over a time period, expressed on an annual basis (CHRISTENSEN;PAULY, 1993).The food consumption per unit biomass (Q/B) indicates the number of times that a given population consumes its own weight per year (PAULY, 1986).
However, estimates of Q/B ratio are lacking for most tropical fish species.Therefore, this study compiled food-consumption estimates (Q/B) of 37 fish species caught in a macrotidal mangrove estuary in Northern Brazil, with the aim to contribute to mass-balanced trophic models construction in similar ecosystems.These species constitute up to 95 % in terms of both total catch weight and abundance in the studied area (GIARRIZZO; KRUMME, 2007;Macapá, v. 3, n. 2, p. 149-154, 2013 Estimates of annual food consumption/biomass ratio (Q/B) from the fish fauna of a mangrove estuary in North Brazil VILAR et al., 2013).This study represents the first reference available on Q/B for 29 fish species.

Material and Methods
Sampling was carried out in the estuary of the Curuçá River, Pará, North Brazil, located at the eastern tip of the mouth of the southern channel of the Amazon delta (Marajó Bay) (0° 10' S, 47° 50' W) (Fig. 1).The climate is hot and humid with mean annual rainfall of 2,526 mm (ANA, 2005; n = 16 years, range: 1,085 -3,647 mm).. Water temperature is constantly high with an average value of 26.7 °C.Salinity changes according to the season, being low during the rainy season, in the first half of the year and attaining values of marine water during the dry season.Like in the whole Northern Brazilian coast, the Curuçá estuary is fringed by mangrove forests composed of Rhizophora mangle L., Avicennia germinans (L.) and Laguncularia racemosa (L.).Tides in the region are characterized by a semi-diurnal pattern with a tidal range of 3 -4 m at neap tides and 4 -5 m at spring tides.
Samples were taken bimonthly between July 2003 and July 2004 at diurnal neap tides in the middle and upper estuary.To collect fishes from the main channel (3-7 m deep at low tide), 112 samples, distributed between eight sites (Figure 1), were taken with an otter trawl of 8.62 m width and 13 mm stretched mesh size (for details see VILAR et al., 2013).In addition, the intertidal fish fauna was collected using a fyke-net with 13 mm stretched mesh size placed at the mouth of four tidal creeks yielding a total of 28 samples (for details see GIARRIZZO et al., 2010).Q/B = 10 (7.964 -0.204 log w∞ -1.965T + 0.083A + 0.532h + 0.398d) where: Q/B is the annual food consumption/biomass ratio; W∞ is the asymptotic wet weight in g of the population calculated according to the relationship: W∞ = W max /0.86 (PAULY, 1984), where W max is the weight of maximum sizes fish caught (g); T is the mean habitat temperature expressed as 1,000/[T(°C) + 273.1];A is the aspect ratio of the population caudal fin, defined by the ratio: A = h 2 /S, where, h and S are the height and surface area of caudal fin, respectively; h and d represent the feeding type (h = 1 and d = 0 for herbivores; h = 0 and d = 1 for detritivores; h = 0 and d = 0 for carnivores).Macapá, v. 3, n. 2, p. 149-154, 2013 Estimates of annual food consumption/biomass ratio (Q/B) from the fish fauna of a mangrove estuary in North Brazil For each fish species, a random sub-sample of at least 50 fish was pooled to estimate the caudal fin aspect ratio.The software Scion Image was used to capture, display and analyze the drawings and subsequently measure with graphical interface, the height and the surface area of the caudal fins.
The Q/B ratios for those fish species that occurred exclusively as juveniles were estimated using the W max available in FishBase (FROESE; PAULY, 2013).When only the L max was available in FishBase, the W max was estimated using weight-length relationships according to Giarrizzo et al. (2006).

Results and discussion
A total of 1,877 specimens representing 37 species belonging to 21 families were analyzed (Table 1).The caudal fin aspect ratio values ranged from 0.8 for Poecilia vivipara (Bloch & Schneider, 1801) to 4.6 for Sciades herzbergii (Bloch, 1794).According to Palomares & Pauly (1989) fish species with a high swimming activity and consequently, high metabolic rates, frequently have caudal fins with higher A values, while sedentary fish, that presumably have a relatively lower food intake, are characterized by caudal fins with low values of A. For instance, S. herzbergii with an elongated body shape, short paired fins and a convex caudal fin is an active benthic feeder that needs high speed with quick acceleration to attack especially soft bottom preys.On the other hand, P. vivipara, a sedentary benthopelagic fish with a sub-cylindrical body shape and a round caudal fin, is a zooplanctivorous species that does not require much energy to feed.According to Isaac & Moura (1998) fish caudal fin shape is strongly related to swimming ability and metabolic needs.
Table 1.Estimates of the annual food consumption/biomass ratio (Q/B) of 37 fish species collected in mangrove estuary of the Curuçá River, Pará, North Brazil.For the fish species that occurred only as juveniles, the literature values of maximum total length (Lt max ) and maximum weight (W max ) of adults are indicated in parentheses.N: sample size; A: aspect ratio of the caudal fin; h and d: feeding type code according to Palomares & Pauly (1998).et al., 2006).Macapá, v. 3, n. 2, p. 149-154, 2013 Estimates of annual food consumption/biomass ratio (Q/B) from the fish fauna of a mangrove estuary in North Brazil The annual food consumption/biomass ratio (Q/B) of 37 fish species collected in the macrotidal mangrove estuary of the Curuçá River varied between 2.3 for Epinephelus itajara (Lichtenstein, 1822) to 67.3 for Cetengraulis edentulus (Cuvier, 1829).The proportion of plants in the diet directly influences the food consumption (GARCIA; DUARTE, 2002).Mean Q/B values (±SD) of herbivorous and carnivorous was 48.6 ± 13.3 (range: 32.1 -67.3), and 13.1 ± 5.6 (range: 2.3 -24.4), respectively.
The trophic level of fishes usually tends to reflect different energy requirements to obtain food.Detritivorous and planktivorous fish such as engraulids have a low energy intake and high Q/B ratios while ichthyophagous and benthophagous fish have high energy requirements and low Q/B ratios, for example species like E. itajara and Centropomus undecimalis (Bloch, 1792).Therefore, an inverse relationship was observed between the energy intake and its transformation in biomass.
Values of A, temperature, asymptotic wet weight and Q/B calculated according to the empirical model of Palomares & Pauly (1998), are shown in Table 2 to allow comparison of results with other studies.The observed differences among localities could be explained by a number of factors including temperature, environmental conditions and methods used to measure the height and surface area for the calculation of A.

Figure 1 .
Figure 1.Map of study location showing sampling sites.
Estimates of annual food consumption/biomass ratio (Q/B) from the fish fauna of a mangrove estuary in North Brazil Estimation of Wmax from literature value of Ltmax, using the weight-length relationship available for the same estuary (GIARRIZZO 8 Macapá, v. 3, n. 2, p. 149-154, 2013 *

Table 2 .
Annual food consumption/biomass ratio (Q/B) of species from the literature.Acknowledgements This work was funded by the Millennium Initiative Project Coastal Resources financed by the Ministry of Science and Technology of the Brazil and the project MADAM (Mangrove Dynamics and Management), a cooperation between the Center for Tropical Marine Ecology (ZMT), Bremen, Germany, and the