Ecology and Conservation of Large-Bodied Freshwater Catﬁ Sh: a Global Perspective

Ecology and Conservation of Large-Bodied Freshwater Catﬁ sh: A Global Perspective

ZEB S. HOGAN* Department of Natural Resources and Environmental Science, University of Nevada, Reno 1000 Valley Road, Reno, Nevada 89512, USA

Abstract.—The order Siluriformes includes some of the largest freshwater fi sh on Earth, including 5 of the world’s 10 largest obligate freshwater fi sh species. Large-bodied catfi sh occur predominantly in large lakes and rivers in North America, South America, Europe, Africa, and Asia. Throughout their range, catfi sh are an important component of commercial, subsistence, and recreational fi sheries. They can also have an important role in the ecosystem as top predators or as indicators of overfi shing. Despite their importance, relatively little attention has been given to the conservation status of large-bodied catfi sh. While certain species are considered endangered, other species have not been assessed, and no global study has been conducted to examine the threats they face or their conservation status. Multiple and combined threats from habitat degradation, dams, water withdrawals, pollution, and overexploitation have led to the decline of many catfi sh populations. In addition to these threats, large-bodied catfi sh face an additional set of conservation challenges, including shifting baselines, inadequate knowledge (including lack of taxonomic clarity), and a dearth of protected areas and species conservation plans for freshwater species. Despite these challenges, self-sustaining populations of large- bodied catfi sh still exist, most notably in free-fl owing rivers like the Amazon and the lower Mekong. Efforts to protect the ecological integrity of the Amazon and Mekong and other rivers where large-bodied catfi sh occur will benefi t thousands of species of freshwater fi sh and millions of people who rely on fi sh for their livelihoods and food security.

Introduction to-mature, high-value migratory species, catfi sh are particular vulnerable to multiple threats, including Freshwater fi sh biodiversity has come under increas- overexploitation, habitat degradation, and river frag- ing pressure from a rapidly growing human popu- mentation. This paper serves as a brief introduction lation (Dudgeon et al. 2006; Strayer and Dudgeon to the ecology of large-bodied catfi sh (order Siluri- 2010). Recent reviews suggest that 40% of North formes) and examines some of the broad issues sur- American freshwater fi sh and almost 50% of south- rounding their management and conservation. ern European freshwater fi sh are threatened (Kotte- lat and Freyhof 2007; Jelks et al. 2008). The situ- Data Sources ation for large-bodied freshwater fi sh may be even worse; several recent studies show that many species Data on fi sh size and distribution were taken from are classifi ed as imperiled (Hogan et al. 2004; Al- FishBase (Froese and Pauly 2010) and numerous lan et al. 2005; Dudgeon et al. 2006). Despite evi- other sources. FishBase is a dynamic, open-access dence that suggests large-bodied freshwater fi sh are database containing biological information on most disproportionately at risk of extinction (Olden et al. species of freshwater and marine fi sh, including 2007), the conservation status of the world’s largest body length data for more than 20,000 fi sh spe- catfi sh species is unclear. While certain species are cies. Data on conservation status are based primar- considered endangered, other species have not been ily on information from the International Union for assessed, and no global study has been conducted to the Conservation of Nature Red List of Threatened examine the threats they face or their conservation Species (IUCN 2010) as well as other sources. The status. As large-bodied, and often long-lived, slow- International Union for the Conservation of Nature Red List of Threatened Species (IUCN Red List) is a * Corresponding author: [email protected] widely accepted source for classifying conservation 39 40 HOGAN status. The general aim of IUCN Red List criteria than length. It is diffi cult to determine if reports are is to provide an explicit, objective framework for accurate; fi sh can be misidentifi ed, reported lengths classifi cation of species according to their extinction and weights exaggerated or estimated, or sizes based risk. Fish extinction risk is usually determined by on hearsay but recorded as fact. The uncertainty sur- examining trends in population size, extent of oc- rounding old and/or anecdotal records may be one currence, quality of habitat, and level of exploita- reason why the Mekong giant catfi sh Pangasian- tion. Even with data from the International Union odon gigas is considered by many to be the world’s for the Conservation of Nature (IUCN), information largest freshwater fi sh based on verifi ed catch of a on ecology and conservation status of freshwater 293-kg specimen in 2005 (Figure 1), even though fi sh is limited. Out of approximately 13,000 fresh- the wels Silurus glanis may be the longest by total water fi sh, only 4,000–5,000 (31–38%) have been length based on anecdotal data from Russia (Berg evaluated by IUCN. Similarly, out of approximately 1949; Stone 2007). 3,000 species of freshwater catfi sh, 827 (28%) have been assessed, and of those, 120 are listed as threat- Diversity and Distribution of ened (D. Allen, International Union for the Conser- Large-Bodied Catfi sh vation of Nature, personal communication). Because the IUCN Red List is constantly being updated and Catfi sh are among the largest of all obligate fresh- because Siluriformes have not been comprehen- water fi sh (Table 1). Five of Earth’s 10 largest fresh- sively assessed, IUCN data have been combined water fi sh are catfi sh. The top 20 largest catfi sh all with information from published literature, personal measure more than 1.5 m total length. These catfi sh experience, and unpublished data to provide a more occur predominantly in large lakes and rivers in complete picture of the global conservation status of North America, South America, Europe, Africa, and large-bodied catfi sh. Asia (Table 2). It should be noted that maximum sizes of fresh- The three largest catfi sh in North America are water fi sh are notoriously diffi cult to verify; for some the blue catfi sh Ictalurus furcatus, the fl athead cat- species, total length and weight of very large specifi sh Pylodictis olivaris, and the channel catfi sh I. mens were reported nearly 100 years ago (Holcik et punctatus. While all three are considered “big cats” al. 1988). In other cases, weight is reported rather and targeted as trophy fi sh by anglers, only the

FIGURE 1. The record breaking Mekong giant catﬁ sh caught in Thailand in 2005. The ﬁ sh weighed 293 kg. LARGE CATFISH CONSERVATION 41

TABLE 1. The world’s 10 largest obligate freshwater fi sh species. Maximum size is based on total length modi- fi ed from FishBase (Froese and Pauly 2010). Approximate maximum total length Species Common name Order (cm) Silurus glanis Wels Siluriformes 500 Arapaima gigas Arapaima Osteoglossiformes 450 S. soldatovi Soldatov’s catfi sh Siluriformes 400 Brachyplatystoma fi lamentosum Piraiba Siluriformes 360 Pangasius sanitwongsei Chao Phraya catfi sh Siluriformes 300 Pangasianodon gigas Mekong giant catfi sh Siluriformes 300 Catlocarpio siamensis Giant barb Cypriniformes 300 Tor putitora Mahseer Cypriniformes 275 Acipenser fulvescens Lake sturgeon Acipenseriformes 274 Electrophorus electricus Electric eel Gymnotiformes 250 blue catfi sh and fl athead catfi sh attain sizes greater catfi sh as large as 143 kg in the mid-1800s (Graham than 50 kg. The three species are widespread in the 1999), verifi ed records for fl athead catfi sh (56 kg) United States, and their biology and management is and blue catfi sh (59 kg) were both set in the past 20 treated in detail in many other articles in this book. years (and in the case of the blue catfi sh, the record One interesting detail is worth noting: while there was set in 2010). This may indicate that, at least in are anecdotal reports of catches of North American some areas, management for large size and longev-

TABLE 2. Size (total length) and continent of occurrence of the 20 largest catfi sh species on Earth. Data modi- fi ed from FishBase (Froese and Pauly 2010). Total length Species Common name (cm) Distribution Silurus glanis Wels 500 Europe/Asia S. soldatovi Soldatov’s catfi sh 400 Asia Brachyplatystoma fi lamentosum Piraiba 360 South America Pangasianodon gigas Mekong giant catfi sh 300 Asia Pangasius sanitwongsei Giant pangasius 250 Asia Wallago attu Wallago 240 Asia Bagarius yarrelli Goonch 200 Asia Brachyplatystoma rousseauxii Dorado 192 South America Silonia silondia Silond catfi sh 183 Asia Wallago leerii Tapah catfi sh 180 Asia Sperata aor Long-whiskered catfi sh 180 Asia Dinotopterus cunningtoni Singa catfi sh 175 Africa Clarias gariepinus Sharptooth catfi sh 170 Africa Pseudoplatystoma corruscans Spotted sorubim 166 South America Ictalurus furcatus Blue catfi sh 165 North America Hemibagrus maydelli Ponduga catfi sh 165 Asia Arius gigas Giant sea catfi sh 165 Africa Pylodictis olivaris Flathead catfi sh 155 North America Sperata seenghala Giant river catfi sh 150 Asia Sorubimichthys planiceps Firewood catfi sh 150 South America 42 HOGAN ity could be having the desired effect (Graham and Columbian-Peruvian border region are indicative of DeiSanti 1999; Mestl 1999). None of the large North other areas, the species could be listed as threatened. American catfi sh have been evaluated by IUCN. The dorado is a large-bodied, highly migratory Several large species of catfi sh occur in South catfi sh that was once fairly common in the Amazon. America, notably the piraiba, the dorado, and two It reportedly grows to at least 192 cm (Barthem and species of sorubim, the spotted sorubim and the fi re- Goulding 1997). Together with the smaller catfi sh, wood catfi sh (Figure 2). The piraiba, South Ameri- the piramutaba Brachyplatystoma vaillantti, the do- ca’s largest catfi sh, reportedly attains lengths in ex- rado is considered one of the most highly migratory cess of 3 m (Lundberg and Littmann 2003) and can fi sh species in the Amazon (Carolsfeld et al. 2003). weigh up to 200 kg (Boujard et al. 1997). It may make the longest migrations of any species The piraiba is a large, widespread, commercially of freshwater fi sh, a journey of more than 5,000 km important species (Barthem and Goulding 2007). (Barthem and Goulding 1997). The dorado migrates Found in the Amazon, Orinoco, and some rivers in from the lower Amazon to spawn in the Amazon the Guianas, the piraiba was long considered a single along the Brazilian-Columbian-Peruvian border species, but it may actually be two or more species (Barthem and Goulding 1997, 2007). Young fi sh are (Lundberg and Akama 2005; Barthem and Goulding carried downstream to the Amazon estuary, which is 2007). In the Amazon, Barthem and Goulding (2007) believed to be a nursery ground (Barthem and Gould- estimate an annual piraiba yield of approximately ing 2007). The dorado is targeted and, some argue, 5,500 metric tons. In the Brazilian-Columbian-Peru- overexploited (Carolsfeld et al. 2003) as part of a vian border region, it was once the most important major international fi shery. These fi sh are intensely fi sheries species by weight. Catch rates, however, harvested along their entire migration route. Young have declined over the past 20 years—from almost fi sh face heavy fi shing pressure in the Amazon estu- 4,000 metric tons in 1988 to less than 500 metric tons ary in Brazil, and adults are targeted in the Andean in the early 2000s. Based on these data, the species is foothill region of the Amazon basin. Overexploita- considered seriously overexploited in the region (Bar- tion could become a serious problem if catch lim- them and Goulding 2007). The species has not been its are not imposed (Barthem and Goulding 2007). assessed by IUCN, but if data from the Brazilian- Dams also represent a threat to this highly migratory

FIGURE 2. Piraiba and dorado. LARGE CATFISH CONSERVATION 43 species. If dams planned for the Rio Madeira block clined in some parts of its native range, it is thriv- spawning migrations, an entire stock of the species ing at certain sites outside of its native range, so could be wiped out (Barthem and Goulding 2007). much so that there is now an active debate about The species has been assessed by the IUCN as Least the effect of wels on native biodiversity (Benejam Concern because it is relatively common and wide- et al. 2007; Copp et al. 2009). Populations in the spread. Further monitoring is important, however, Ebro River in Spain, in particular, are considered given the species’ highly migratory nature, concern robust, although the invasion has not been studied over overexploitation, and new and growing threats in detail (Carol et al. 2007). The species has been posed by dams. categorized by the IUCN as Least Concern because The wels is one of the world’s largest fresh- it is relatively common and widespread. water fi sh and one of only two catfi sh species that Despite high freshwater fi sh diversity, Africa occur in Europe (Figure 3). It is native to much of is not home to any catfi sh species longer than 2 m eastern Europe (as far north as southern Sweden TL. Several species do grow over 150 cm, includ- and as far south as Greece and Turkey) as well as ing at least three catfi sh species in the family Clari- the North, Black, Baltic, Caspian, and Aral Sea idae: singa catfi sh, sharptooth catfi sh, and sampa basins (Kottelat and Freyhof 2007). Old reports of Heterobranchus longifi lis. Sharptooth catfi sh and very large fi sh come from Hungary (200–250 kg/3 sampa are both widespread species; sharptooth m total length [TL]), the Dnieper River (306 kg/5 catfi sh is a popular, and nearly pan-African, food m TL), the Volga River and Caspian Sea (300 kg), fi sh while sampa is the largest freshwater fi sh in and the Aral Sea basin (130 kg/2 m TL) (Copp et southern Africa. Singa catfi sh is endemic to Lake al. 2009). The wels is a popular sport fi sh and has Tanganyika where it is heavily exploited by fi sher- been introduced outside of its native range, most men. Sharptooth catfi sh and sampa have not been notably in the United Kingdom, Spain, Italy, and evaluated by IUCN while singa catfi sh is listed as Kazakhstan. While populations of wels have de- Near Threatened.

FIGURE 3. The wels. 44 HOGAN

Several of the world’s largest catfi sh are wide- cline of 42% (author’s unpublished data). The larg- spread throughout Asia; the wallago and the goonch est fi sh reported by Cambodian fi shers was an 80-kg both occur from Pakistan to Indonesia, the wels is specimen from 1990. Fishers also reported fi sh up found in western Asia, and the Soldatov’s catfi sh to 60 kg as recently as 2006 (author’s unpublished occurs in the Amur basin in Russia and China. The data). The IUCN lists wallago as Near Threatened. Mekong River is home to several species of large- The goonch is a large, predatory catfi sh that is bodied catfi sh, including the endemic Mekong giant widespread in Asia (Figure 5). In India, it occurs in catfi sh, the giant pangasius, as well as goonch, wal- the Indus, Ganges, and Brahmaputra River basins lago, the somewhat smaller river catfi sh Pangasian- (Froese and Pauly 2010). Based on available data, it odon hypophthalmus, and the highly migratory appears that populations of the goonch in the Indus “salmon” catfi sh Pangasius krempfi . and Ganges drainages have declined signifi cantly The wallago occurs in freshwaters from Paki- since 1980 (V. Badola, Otter Reserves, personal com- stan to Vietnam (Figure 4). It is a large, predatory munication). Likewise, Sheikh et al. (1997) reported catfi sh, attaining lengths of up to 2.4 m (Pethiyagoda that abundance of large-sized goonch has declined 1991). In India, the species is threatened by overhar- dramatically in certain sections of Brahmaputra. In vest, habitat degradation, and pollution (Mijkherjee the early 1980s, Sheikh et al. (1997) found goonch et al. 2002; Hossain et al. 2008). Due to these threats weighing up to 300 kg, but by the early 1990s, the and declining abundance, the species is considered size of fi sh had decreased signifi cantly due to in- endangered in India (Hossain et al. 2008; Sarkar creasing exploitation rates (Sheikh et al. 1997). Cap- et al. 2008). In the Cambodian Mekong, fi shers re- ture rates in the early 1990s were estimated at 10 ported a decline in abundance of 58% since 1980 times the capture rates of the early 1980s, resulting (author’s unpublished data). In Tonle Sap Lake, the in an increase in catch of juvenile fi sh (Sheikh et al. lower Mekong, and Kampong Cham areas, fi shers 1997). Goonch is found mainly in rapids of the main reported a decline of 71% since 1980, whereas in the Mekong River and its largest tributaries. It can attain Kratie and Stung Treng areas, fi shers reported a de- sizes greater than 2 m and 100 kg in the Mekong

FIGURE 4. The wallago. LARGE CATFISH CONSERVATION 45

FIGURE 5. The goonch.

River, but large adults are extremely rare. During 1 ant pangasius was a regular, though rare, catch in month of monitoring along an approximately 100- Chiang Khong, Thailand. In southern Laos, fi shers km stretch of the Mekong River in northern Thai- once used harpoons to catch giant pangasius and land (May 2006), the largest fi sh harvested by fi shers other large species. Fishers no longer use harpoons weighed 30 kg (author’s unpublished data). Goonch due to the disappearance of large fi sh (Roberts and is threatened by overharvest, habitat degradation, Baird 1995). The giant pangasius is vulnerable to and water extraction (Sheikh et al. 1997). IUCN lists overfi shing because of its large size and migratory goonch as Near Threatened. behavior. Large, spawning fi sh are taken from the Giant pangasius once occurred in the Chao Mekong River between Chiang Khong and Chiang Phraya River and its tributaries and the Mekong Riv- Saen, Thailand. Young fi sh are harvested for food er from Chiang Saen to Vietnam (Figure 6). Smith and aquaculture throughout the Mekong, particular- (1945) reports that capture of giant pangasius up to ly along the stretch of river from Nong Khai to the 3 m in length was relatively common prior to 1920. confl uence of the Mekong and Mun rivers (north- By 1945, the longest fi sh observed measured 2.5 m, east Thailand). Dams and disturbance of the fi sh’s and the average size of a fi sh reaching the Bang- spawning habitat may also represent a signifi cant, kok market was 40–60 cm. Giant pangasius is now though poorly understood, threat. Based on catch considered extirpated from the Chao Phraya River trends, the IUCN listed giant pangasius as Critically in Thailand. It still occurs in the Mekong, though Endangered in 2007. populations have decreased signifi cantly from his- Historically, Mekong giant catfi sh occurred toric levels (Hogan et al. 2009). Up until 1995, gi- throughout large rivers of the Mekong River basin 46 HOGAN

FIGURE 6. The giant pangasius. in Vietnam, Cambodia, Lao People’s Democratic kept in 1981 (author’s unpublished data). Mekong Republic (PDR), Thailand, and possibly Burma giant catfi sh was listed as Critically Endangered by and southwestern China (Figure 7). In Cambodia, the IUCN in 2003. the Mekong giant catfi sh moves out of the fl ooded habitats of Tonle Sap Lake at the end of the rainy Importance of Large-Bodied Catfi sh season (October–December). During the dry season (January–May), the species inhabits deep water Many large-bodied catfi sh are important fi sheries areas of the Mekong River. It is migratory, but the species. For example, in the Mekong River basin, extent of migrations is unknown. Little is known Mekong giant catfi sh, giant pangasius, and related about the spawning behavior of wild Mekong gi- species (catfi sh in the family Pangasiidae) are a ant catfi sh. There is strong evidence that the species dominant fi sh group, popular in aquaculture, and spawns in northern Thailand in June, but precise frequently the basis of local wild-capture fi sheries time and location of this spawning activity have not (Roberts and Vidthayanon 1991). Annual production been confi rmed. The Mekong giant catfi sh now ap- in Cambodia is estimated to be at least 10,000 metric pears limited to the Mekong River and its tributar- tons and in Vietnam is predicted to be an incredible ies in Cambodia, Lao PDR, and Thailand. Historical 1,000,0000 metric tons by 2010 (Lenormand 1996; reports indicate that the species was abundant in the Poulsen et al. 2008). Catfi sh represent 90% of all early 1900s. However, in the 1970s, local fi shers be- aquaculture and 20% of all inland capture fi sheries gan to report disappearance of the species. Current in Cambodia. They account for the majority of the population size is unknown, but a decline of more May to July harvest in southern Lao PDR and north- than 80% over the past 13 years can be estimated eastern Thailand (Mekong River Commission 1992). from past and current annual catch records (Hogan They are selectively caught as juveniles on a mas- et al. 2004). Fishing is a serious threat to Mekong sive scale (1–2 billion fi ngerlings per year) to supply giant catfi sh (Allan et al. 2005). Loss of migratory artisanal aquaculture needs. Including aquaculture routes through construction of dams (e.g., Pak Mun production from Vietnam, combined harvest from Dam in Thailand) may also have a negative effect the Mekong River is likely the largest catfi sh fi shery on fi sh abundance in the river (Hogan et al. 2004). in the world. Though not on quite the same scale, A 2.7-m, 293-kg Mekong giant catfi sh was captured catfi sh fi sheries are also very important in other re- by Thai fi shermen in 2005 (Stone 2007). According gions, especially North America, South America, to the Mekong Giant Catfi sh Fishermen’s Club, this and Africa. In North America, millions of pounds of was the largest catfi sh caught in the northern Thai wild ictalurid catfi sh were being harvested from the section of the Mekong since records started being Mississippi as early as 1894 (Carlander 1954). More LARGE CATFISH CONSERVATION 47

FIGURE 7. The Mekong giant catfi sh. recently, aquaculture production has surpassed pro- considered umbrella species because the protection duction from capture fi sheries, but recreational fi sh- of such species and their habitat also benefi ts many ing for trophy-sized catfi sh remains popular (Holley other species. In the Amazon, for example, Barthem et al. 2009). In South America, dorado, piramutaba, and Goulding (1997) write about a “profound and far and slobbering catfi sh Brachyplatystoma platyne- reaching predatory network” where large catfi sh are mum are targeted as part of a major international “beyond any doubt” the most abundant, wide-rang- fi shery. Barthem and Goulding (2007) estimate total ing predators. In fact, they dedicate an entire book Amazon River basin annual yield of Brachyplatys- to what they call the “catfi sh connection” (Barthem toma spp. at 30,000–40,000 metric tons. In some and Goulding 1997). Widespread and highly migra- areas, such as the Teotonio rapids on the upper Ma- tory catfi sh are thought to use an area of 2,500,000 deira River and the upstream areas like Leticia, Co- km2 and make the longest migrations of any fresh- lumbia, catches of large-bodied represent up to 90% water fi sh species in the world (Barthem and Gould- of the seasonal catch (Barthem and Goulding 2007). ing 1997). These highly migratory catfi sh create an In Africa, the large-bodied catfi sh such as sharptooth ecological link between the Amazon fl oodplain and catfi sh are important food fi sh. In Nigeria, where per the main river. Thus, management for an intact cat- capita consumption of fi sh is more than 7 kg/year fi sh connection would also benefi t other species over and catfi sh make up about 50% of total in-country a huge area. Likewise, in the Mekong River basin, production, sharptooth catfi sh is the most widely large-bodied Pangasiid catfi sh like the Mekong giant cultured species (Ponzoni and Nguyen 2008). catfi sh, giant pangasius, and related species are well Giant fi sh species, like large-bodied catfi sh, known for long-distance migrations, moving exten- can have an important role in the ecosystem as top sively between Vietnam, Cambodia, Lao PDR, and predators, as “umbrella” species, or as indicators Thailand (Hogan et al. 2007). Pangasiid catfi sh are of overfi shing. Large, migratory animals are often particularly vulnerable to threats from habitat degra- 48 HOGAN

dation and overexploitation because of their migra- Threats to Large-Bodied Catfi sh tory behavior, high economic value, requirements for specifi c water quality and fl ow, and complex life Fish and freshwater habitats are facing growing history dependent on the seasonal fl oods (Mekong threats from increased human use (Dudgeon et al. River Commission 1992; Roberts 1993; Hill and 2006). Multiple and combined threats from habitat Hill 1994). As such, protection of particularly vul- degradation, dams, water withdrawals, pollution, nerable species like pangasiid catfi sh can also pro- and overexploitation have lead to decline of popu- vide protection for many other aquatic species (Ho- lations of freshwater biodiversity at twice the rate gan et al. 2004). Pangasiid catfi sh also appear to be of terrestrial organisms (Dudgeon 2010; Strayer and an indicator of overfi shing; as fi shing pressure has Dudgeon 2010). Large-bodied catfi sh are vulnerable increased in the Mekong River basin, abundance of to many of these same stressors. In Asia, for exam- large-sized fi sh has declined (Baran and Myschowo- ple, gross pollution in the Ganges River and water da 2008). The largest species are among the most withdrawals in the Indus River threaten freshwater highly threatened (Table 3). fi sh like wallago and goonch (Hossain et al. 2008; In some cases, animals like large-bodied catfi sh Sarkar et al. 2008). Pollution, dams, and water with- also serve as charismatic fl agship species, galvaniz- drawals have also been blamed for the decline of gi- ing public and political support for cooperative ac- ant pangasius in the Chao Phraya River in Thailand tion to restore populations and protect habitat (Rabi- (Humphrey and Bain 1990; Roberts 1993; Hogan et nowitz 1995; Dillon and Wikramanayake 1997; al. 2004). In the Amazon River basin, large-bodied Caro and O’Doherty 1999). In border areas, such migratory catfi sh face an uncertain future due to the animals can stimulate transnational cooperation, planned Madeira hydroelectric complex. The Ma- which has led to policy formation and establishment deira complex, which will consist of four dams on a of international regulatory agencies (Dillon and main tributary of the Amazon, may block the spawn- Wikramanayake 1997; Lorenz et al. 2001). Success- ing migration dorado and other species (Barthem ful fl agship species are usually large, often endan- and Goulding 2007). Construction of dams will also gered, and sometimes migratory (Dietz et al. 1994; fl ood the town and rapids of Teotonio, a famous Dinerstein et al. 1997; Caro and O’Doherty 1999). fi shing spot for large, migratory catfi sh. Last, but Wide-ranging species can also make effective fl ag- certainly not least, overexploitation of large-bodied ships because they are known to a large number of freshwater fi sh, including catfi sh, is a serious threat. people in many countries (Butler 2000). For exam- Olden et al. (2007) found that commercial and sub- ple, the Mekong giant catfi sh is well known through- sistence fi shing are important drivers of extinction out the Mekong River basin (Kottelat and Whitten risk of large-bodied freshwater fi sh. The Mekong 1996; Hogan 1998). Thus, the species can be used giant catfi sh and giant pangasius are perhaps the to introduce transnational issues to local communi- two best documented examples of fi shing-related ties through outreach and education (Butler 2000). population decline. Overall catch of both species has Promoting community-level involvement in trans- declined steadily over the past several decades, and national cooperation reinforces international efforts populations are now thought to be at less than 10% at the local level (Agrawal 2000; Boer 2000). of historic levels.

TABLE 3. An example of the relationship between size and conservation status of catfi sh in the Mekong River basin. Total lengths come from Rainboth (1996) and are based on the maximum reported size of the species in recent times. Maximum size Species (cm) Conservation status References Mekong giant catfi sh 300 Critically endangered Rainboth (1996); Hogan et al. (2004) Chao Phraya catfi sh 250 Critically endangered Rainboth (1996); Hogan et al. (2009) Pangasianodon hypophthalmus 120 Declining/rare Roberts (1993); Rainboth (1996) Pangasius conchophilus 60 Common Roberts (1993); Rainboth (1996) Pangasius macronema 18 Common Roberts (1993); Rainboth (1996) LARGE CATFISH CONSERVATION 49

Conservation Challenges for a threatened category.” Lack of taxonomic clarity may also be an issue in South America where a The overarching and often interacting threats to fresh- new species of goliath catfi sh was recently described water biodiversity have been well documented (Ago- (Lundberg and Akama 2005), and taxonomy and stinho et al. 2005; Allan et al. 2005; Dudgeon 2010; population status of several large-bodied species Strayer and Dudgeon 2010). In addition to these is currently under discussion (Castello and Stewart threats, large-bodied catfi sh face an additional set 2010). of conservation challenges, that, though not unique Lack of protected areas and management plans to giant catfi sh, are signifi cant nonetheless. Those can also be an obstacle to conservation (Barletta et conservation challenges include shifting baselines, al. 2010). While terrestrial and marine protected areas inadequate knowledge (including lack of taxonomic are relatively common, freshwater protected areas, clarity), and a dearth of protected areas and species or even conservation plans for freshwater species, conservation plans for freshwater species. are rare (Abell et al. 2007; Suski and Cooke 2007). The idea of shifting baselines is not new, but Thus, in many cases, freshwater biodiversity does not it can be especially problematic for large, poorly receive the same level of protection as terrestrial and studied fi sh like the Mekong giant catfi sh, giant marine biodiversity, even though freshwater biodi- pangasius, river catfi shes, goonch, and goliath versity is more threatened. This is particularly prob- catfi shes of the Amazon. As these species become lematic for high value or highly migratory species, rarer, their importance, and in certain cases even especially those that cross international borders, since their presence, is rapidly forgotten (Humphries and these species are unlikely to be managed effectively Winemiller 2009). This is in large part due to lack without formal protection (Valbo-Jorgensen et al. of documentation of past abundance and a con- 2008). The large migratory catfi sh of the Mekong and stantly aging population of fi shermen. This leads Amazon rivers are cases in point; both Pangasiidae to a shifting perceptions of large fi sh abundance; and Pimelodidae are vulnerable to habitat degrada- decline of fi sh abundance is overlooked and society tion over a wide area, depend on critical habitats for does not recognize the need for, or importance of, survival, and are harvested as part of an international conservation. Until recently, this was certainly the fi shery. The situation has led to calls for species con- case for Mekong giant catfi sh and giant pangasius, servation plans, freshwater protected areas, basin- two species that, in the 1990s and early 2000s, qui- wide management (Hogan et al. 2004), and, in some etly drifted toward extinction (Sretthacheua 1995; cases, international treaties to protect these large, mi- Hogan 1998). gratory catfi sh (Barthem and Goulding 2007). Inadequate knowledge is a particular problem in tropical freshwater ecosystems where diversity is Conservation Opportunities highest (Dudgeon 2000, 2003). Many species remain to be discovered, and of those that have been discov- The Amazon and the Mekong rivers are hotspots ered and described, little information exists on their of large-bodied catfi sh biodiversity. Almost half of ecology or population status. For example, one of the world’s largest catfi sh species occur in one of the world’s largest fi sh, the giant freshwater sting- these two rivers, and both rivers are also home to the ray Himantura chaophraya, was only described in healthiest remaining populations of large-bodied cat- 1990, and since that time, no studies have been done fi sh on earth. In the Amazon, piraiba and dorado are on its biology or conservation status (Monkolprasit still abundant, and in the Mekong, smaller pangasiid and Roberts 1990; Stone 2007). Lack of taxonomic catfi sh remain relatively common. For larger endan- clarity can also be a serious obstacle to conserva- gered species like the Mekong giant catfi sh and giant tion because it is diffi cult to assess or protect a spe- pangasius, the Mekong River is a last refuge. cies when it is not properly identifi ed. The goonch, Perhaps more remarkably, neither the lower for example, is thought to be widespread through- Mekong nor Amazon mainstream has been dammed. out South and Southeast Asia, but the taxonomy of This is especially important because both the goliath the species is not well understood (IUCN 2010) and catfi shes of the Amazon, and the giant catfi sh of the some populations of the species have declined sig- Mekong, are migratory. Amazon species make some nifi cantly. This situation has lead to a call for goonch of the longest distance migrations of any species of to be “re-assessed following resolution of its taxo- freshwater fi sh, thousands of kilometers from the nomic uncertainty.” IUCN (2010) believes that “the mouth of the Amazon to the foothills of the Andes, subsequent species identifi ed may all then qualify to complete their spawning migrations. Likewise, 50 HOGAN several large-bodied catfi sh of the Mekong migrate ing the preparation of this manuscript. The author more than 1,000 km to spawn, moving upstream from also wishes to thank Tom Kwak, Paul Michaletz, Vietnam and Cambodia to Lao PDR and Thailand at and two anonymous reviewers for their helpful com- the beginning of the rainy season. Given these long ments. distance movements, and also the economic importance of most large-bodied catfi sh, they can be con- References sidered indicators of the overall health and integrity of the rivers where they occur (Hogan et al. 2004). Abell, R., J. D. Allan, and B. Lehner. 2007. Unlocking Sustainable development and fi shery harvest of the potential of protected areas for freshwaters. the Amazon and Mekong basins remains possible. Biological Conservation 134:48–63. Both river basins are incredibly productive; the Me- Agostinho, A. A., S. M. Thomaz, and L. C. Gomes. kong, for example, yields an estimated 2,000,000 met- 2005. Conservation of the biodiversity of Brazil’s inland waters. 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