Population Density, Growth and Reproduction of Arapaima in an Amazonian River-ﬂoodplain

Ecology of Freshwater Fish 2010: 19: 455–465 Ó 2010 John Wiley & Sons A/S Printed in Malaysia Æ All rights reserved ECOLOGY OF FRESHWATER FISH Population density, growth and reproduction of arapaima in an Amazonian river-floodplain Arantes CC, Castello L, Stewart DJ, Cetra M, Queiroz HL. Population C. C. Arantes1,3,†, L. Castello1,2,*, density, growth and reproduction of arapaima in an Amazonian D. J. Stewart2, M. Cetra4, river-floodplain. Ecology of Freshwater Fish 2010: 19: 455–465. Ó 2010 H. L. Queiroz1 John Wiley & Sons A ⁄ S 1Mamiraua´ Institute for Sustainable Develop- ment, Tefe´, Amazonas, Brazil, 2Department of Abstract – Compensatory density effects are key features of fish Environmental and Forest Biology, College of population dynamics that remain poorly understood in tropical river- Environmental Science and Forestry, State floodplains. We investigated possible compensatory growth and University of New York, Syracuse, New York, 3 reproductive processes for a river-floodplain population of Arapaima sp., USA, Departamento de Cieˆncias Exatas e Tec- nolo´gicas, Universidade Estadual de Santa Cruz, an extinction-prone fish species of South America. Body growth was Ilheús, Bahia, Brazil, 4Department of Ecology, studied through analysis of ring patterns on the scales, and size and age at Universidade Federal de Saõ Carlos, Campus sexual maturity was studied through analysis of female gonads. Growth Sorocaba, Saõ Paulo, Brazil and maturity were compared for unmanaged conditions with relatively low population density (in 1990s) versus managed conditions with markedly higher density (in 2005–2006); between 1999 and 2005–2006, abundance increased 7.3 fold. Results contradict theoretical expectations for slower growth and delayed reproduction at higher population density. Total lengths of arapaima at low population density were significantly shorter for age classes 1–5 compared with lengths of those age classes at high population density (ancova, P < 0.0001 for both slopes and intercepts). Key words: Brazil; management; osteoglossidae; size-at-age; size-at-first-maturity Total length at 50% maturity (L50) only declined about 4% with increasing density (e.g., 164 cm at low density vs. 157 cm at high density). Apparent C. C. Arantes, Instituto de Pesquisa Ambiental da faster growth at high density and only a slight change in size at maturity Amazoˆnia, Santare´m, Brazil; e-mail: carolinearan@ yahoo.com.br resulted in fishes spawning at an earlier age with high density conditions (age 3 vs. age 4–5). We hypothesise that these patterns reflect compliance Present addresses: *The Woods Hole Research with minimum size limits of catch during the high density (managed) Center, Falmouth, Massachusetts, USA, Instituto situation, where there was no harvest of immature fishes. Compliance with de Pesquisa Ambiental da Amazoˆnia, Santare´m, minimum size limits, thus, may have led to faster average body growth rate Brazil. and earlier reproduction, which has greatly promoted population recovery. Accepted for publication April 23, 2010 Vandermeer & Goldberg 2003). Compensatory density Introduction effects have been studied in many animal populations Compensatory density effects are key aspects of the worldwide (Bohlin et al. 2002; Schuller & Hansen dynamics of fish populations (Rose et al. 2001). They 2005; Simonovic & Nikolic 2007), but there are very promote growth of harvested populations, allowing the few studies in tropical river-floodplain fisheries. This populations to persist, and inhibit growth of nonhar- is problematic because, these fisheries are among the vested populations, preventing them from growing most overfished globally, and they occur in regions indefinitely (e.g., Schaefer 1954; Beverton & Holt with the least developed scientific and managerial 1957). These population-level effects stem from capacity (Allan et al. 2005). Information is needed to differential availability of resources per individual, help reverse this situation. leading to faster body growth in low population There have been few studies of density compensa- densities and slower growth in high densities, thus tory effects on body growth and reproduction in altering key life-history traits such as size-at-age and tropical river-floodplain fishes. Dudley (1974) studied size and age of first sexual maturity (Nicholson 1933; growth of three fish species in the Kafue River Taylor & Taylor 1977; Lorenzen & Enberg 2002; floodplain, Zambia, and found compensatory density doi: 10.1111/j.1600-0633.2010.00431.x 455 Arantes et al. effects on adults of only one species, Tilapia In the 1990s, Queiroz (2000) studied growth and Macrochir. Kapetsky (1974) also studied fishes of reproduction of arapaima when the population was the Kafue floodplain and found seasonal variations in overexploited and at relatively low population density growth of five fish species, but attributed those (average 4.45 ind.Ækm)2). In this study, we re-evaluate variations to the seasonal hydrologic cycle. Bayley those processes at a markedly higher density after (1988) evaluated the growth of 12 fish species in the population recovery (e.g., in 2005–2006 with about Amazon, and found weak evidence of compensatory 32.3 ind.Ækm)2); population density increased about density effects in only two. Studying these effects is 7.3 fold (Arantes et al. 2006; Castello et al. 2009). difficult, because of scarcity of time-series data Population abundance estimates stem from existing (Bayley & Petrere 1989). catch-per-unit-effort and direct census data collected Here, we investigate compensatory density effects during the study period and summarised in Castello for a population of the giant fish Arapaima sp.1 in a et al. (2009). The reported population increase has river-floodplain of the Amazon. Arapaima have been a been shown to be accurate and due to the key fishing resource in the Amazon (Verı´ssimo 1895) implementation in 1999 of a new management scheme but now are considered to be generally over-exploited for the arapaima based on compliance with minimum and even commercially extinct near urban centers size (150 cm), closed season (December–May), and (Castello & Stewart 2010). They are listed in the total catch limits (Castello et al. 2009). Because Appendix II of the Convention of International Trade smaller population increases in other fishes have of Endangered Species, which means they could caused density effects on body growth and reproduc- become threatened with extinction if trade and asso- tion (e.g., Muth & Wolfert 1986; Koslow et al. 1995), ciated harvests are not strictly regulated. All existing in this study we test the null hypothesis that this data show predominance of young in the catch largely increase in arapaima population neither reduced body because of widespread lack of compliance with size growth rates nor changed length or age-at-first-repro- and season management regulations (Martinelli & duction. Petrere 1999; Queiroz & Sardinha 1999). Community- based fishery management schemes can effectively Materials and methods conserve arapaima populations, and now they are the most used approach for arapaima conservation (Cas- Study area tello et al. 2009; McGrath et al. 2008). However, understanding of fish body growth, reproduction, and The study was developed in the Mamiraua´ Sustainable associated density effects is lacking, inhibiting man- Development Reserve, located in the middle of the agement and conservation initiatives. Solimo˜es River, Amazonas State, Brazil. The area is Fortunately, now it is possible to study density effects primarily varzea floodplain seasonally inundated by on an arapaima population at the Mamiraua´ Reserve, muddy or whitewaters that are rich in sediments and Brazil. Previous ecological studies have shown that nutrients. This floodplain is a complex mosaic of arapaima is piscivores (Sańchez 1969) and their life tropical rainforests, lakes, and canals that become cycle, like other river-floodplain fishes, is governed by broadly interconnected during seasonal floods (Irion flood pulses (Junk et al. 1989; Castello 2008a). When et al. 1997). The reserve was created to protect water levels are rising, they build nests and reproduce biodiversity through participative and sustainable along the margins of the forests (Castello 2008b), management of the natural resources, made with the guarding their offspring for about three months in the involvement of local communities, Mamiraua´ Institute flooded plains where there is much food and few and Brazilian governmental bodies (state and federal). predators. When water levels lower, they migrate to The studied arapaima population is managed by the the only remaining water bodies, the channels and community of Jaraua´, which controls an area encom- lakes. Here, arapaima are very vulnerable to harpoon- passing approximately 562 km2 with about 85 lakes and gillnet-specialist fishers because their obligate air- (about 2°50¢ S and 64°59¢¢ W). We refer to our study breathing behaviour makes them visible to the fishers area simply as Mamiraua´, but it is a small part of that every 5–15 min. much larger reserve. Fisheries management efforts at the Mamiraua´ Reserve have monitored abundance and aspects of Population density estimates body growth and reproduction over a 16-year period. Accurate estimates of population abundance of arapaima were made each year for 1999 through 2006, 1Taxonomic status of the studied population remains uncertain (Castello & Stewart 2010), so we use only the using the counting method of Castello (2004), which genus name. Our ongoing

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