Life History and Ecological Correlates of Extinction Risk in European Freshwater Fishes1
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854 Life history and ecological correlates of extinction risk in European freshwater fishes1 John D. Reynolds, Thomas J. Webb, and Lorraine A. Hawkins Abstract: We used phylogenetically based comparative analyses to test for associations between extinction risk in European freshwater fishes and a variety of life history, ecological, and biogeographical traits. Based on the World Conservation Union classification scheme, a total of 47% of Europe’s 287 native species are classified as threatened with extinction. Threatened species are significantly smaller than less-threatened species in the same genera when anal- yses are restricted to fully freshwater species. This trend is reversed when anadromous genera are included. These comprise many large-bodied species in which fishing has often played a greater role in declines than in other taxa. Threatened species did not differ significantly in their habitats, although they tended to occupy a narrower variety of habitats biased toward streams and rivers. Threatened species occupy much narrower latitudinal ranges than close rela- tives that are less threatened, and they also have more southerly distributions where pressures on habitats are intense. This study suggests that links between life histories and threat status of freshwater fishes are not as clearcut as for ma- rine species. For fish restricted entirely to freshwater, small-bodied species are most at risk owing to their naturally small ranges, which may put them in a more precarious position when their habitats are impacted by humans. Résumé : Nous avons utilisé des analyses comparatives de nature phylogénitique pour évaluer chez les poissons d’eau douce d’Europe les associations entre le risque d’extinction et une variété de caractéristiques démographiques, écologi- ques et biogéographiques. D’après le schéma de classification de l’Union mondiale pour la nature, 47 % des 287 espè- ces indigènes de poissons d’Europe sont menacées d’extinction. Dans un même genre, les espèces menacées ont une taille significativement inférieure à celle des espèces moins menacées, lorsque l’analyse ne considère que les espèces franchement dulcicoles. La tendance est inversée si on inclut les genres anadromes; ceux-ci comprennent plusieurs espèces de grande taille corporelle, chez lesquelles la pêche a joué un rôle plus important dans le déclin que chez les autres taxons. Les espèces menacées ne diffèrent pas significativement par leurs habitats, bien qu’elles aient tendance à occuper une gamme plus étroite d’habitats, surtout concentrée dans les ruisseaux et les rivières. Les espèces menacées occupent des aires de répartition en latitude plus étroites que les espèces proches moins menacées et elles ont aussi des répartitions plus australes dans lesquelles les pressions sur les habitats sont intenses. Notre étude indique que les liens entre le cycle biologique et le statut de vulnérabilité de l’espèce ne sont pas aussi clairs que chez les espèces marines. Chez les poissons entièrement restreints aux eaux douces, les espèces de petite taille corporelle sont plus à risque à cause de leurs répartitions naturellement plus restreintes, ce qui peut les placer dans une situation plus précaire lorsque leurs habitats subissent l’impact des activités humaines. [Traduit par la Rédaction] Reynolds et al. 862 Introduction ened with extinction because the global assessments by the World Conservation Union (IUCN 2003) have considered Freshwater fish species face severe threats in many parts only approximately 5% of the 28 000 fish species that have of the world. The main problems include physical alteration been described. When analyses are restricted to the 20 coun- of habitats, introduction of alien species, pollution, and fish- tries for which assessments are most complete, 17% of fresh- ing (Miller et al. 1989; Leidy and Moyle 1998; Harrison and water fish species are considered threatened (IUCN 2003). Stiassny 1999). It is not yet possible to say with any confi- This new estimate matches the suggestion by Leidy and dence what percentage of the world’s fish species are threat- Moyle (1998) that more than 20% of species may be at risk Received 5 February 2004. Accepted 13 October 2004. Published on the NRC Research Press Web site at http://cjfas.nrc.ca on 10 May 2005. J17993 J.D. Reynolds.2 Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK. T.J. Webb. Environment Department, University of York, Heslington, York YO10 5DD, UK. L.A. Hawkins. Gatty Marine Laboratory School of Biology, University of St Andrews, Fyfe, KY16 8BL, Scotland. 1This article was part of a special symposium entitled Building on Beverton’s legacy: life history variation and fisheries management, which took place on 11–14 August 2003 in Québec, Quebec, during the 133rd annual meeting of the American Fisheries Society. 2Corresponding author (e-mail: [email protected]). Can. J. Fish. Aquat. Sci. 62: 854–862 (2005) doi: 10.1139/F05-066 © 2005 NRC Canada Reynolds et al. 855 of extinction. The comparable figures for birds and mam- common ancestors rather than as the result of independent mals are 12% and 24%, respectively (IUCN 2003). These evolutionary events. Caution is therefore required in any anal- assessments confirm the consensus that freshwater fishes are ysis that attempts to treat them as independent data points. facing severe threats globally (Bruton 1995; Harrison and In this study, we provide the first analyses of relationships Stiassny 1999; Duncan and Lockwood 2001). between threat status, life histories, and ecology of native The paucity of information about the status and ecology European fishes. The conservation status of nearly all of the of fishes, compared, for example, with information from the native species has been assessed in this region (Lelek 1980; world’s birds and mammals, has seriously hampered efforts Maitland 2000; IUCN 2003), and a reasonable amount of in- to assess conservation status and manage populations ac- formation is available concerning key life history traits and cordingly. Distributions and ecological requirements are of- habitat characteristics. Most of our analyses use methods ten poorly known, and population trends are rarely available that make explicit use of evolutionary relationships among (except for commercially important species). taxa. This method thereby yields comparisons that are more It may be possible to predict the conservation status of robust statistically than traditional cross-species comparisons. fishes by examining life history and ecological correlates of Furthermore, by comparing differences among species extinction risk (Reynolds et al. 2001a). There have been sev- within lineages, we control for many potentially spurious eral attempts to do this for marine species that are subject to differences that can arise when distantly related taxa are fisheries (Jennings et al. 1998; Rochet 2000; Dulvy and combined in cross-species analyses. Reynolds 2002). Most of these studies have found correla- tions between the extent of population decline under fishing Materials and methods pressure and one or more life history traits such as body size and age at maturity. These findings support theoretical pre- Taxonomic and geographic scope dictions that “fast” life histories, including associated traits We compiled a database of life histories, ecology, and such as rapid growth and maturity, should be related to the conservation status of native European freshwater fishes. ability of populations to withstand fisheries (Rochet 2000; The region corresponds to that used by Maitland (2000) bor- Reynolds et al. 2001b; Reynolds 2003). dered by the Arctic and Atlantic oceans and the Mediterra- It is more difficult to make predictions about links be- nean and Black seas and extending east to the Caucasus tween life histories and conservation status of freshwater Mountains, the Caspian Sea, and the Ural Mountains. We fishes. This is because unlike most commercially important considered all native fish species that spend a significant marine fishes where there is a single overriding threat (direct part of their life cycle in fresh water based on descriptions mortality by fisheries), freshwater fishes often face a greater by Maitland (2000). We include anadromous species but range of threats. The effects of this variety of threats on spe- analyse the data both with and without them. We exclude 29 cies with various types of life history cannot be predicted nonnative species as well as borderline cases involving fish easily (Duncan and Lockwood 2001). For example, if small- that primarily occupy marine habitats but also occasionally bodied species tend to occur in heavily impacted habitats, enter brackish waters or the lower reaches of waters that en- small size and associated fast life history traits would be cor- ter the sea. These criteria yield a total of 316 species for an related with extinction risk. This would reverse the predicted overall assessment of threat status. We then focus on 138 relationships between life histories and population status species that could be paired between close relatives that dif- compared with those found in marine species. Indeed, a fered in threat status (see below). study of freshwater fishes in Virginia found no overall asso- Our taxonomy follows Maitland (2000), which in turn fol- ciation between body size and vulnerability to extinction and lows Kottelat (1997), with a few exceptions such as a tendency of small-bodied minnows (Cyprinidae) to be more salmonids, where Maitland (2000) is much more conserva- extinction prone (Angermeier 1995). Parent and Schriml tive regarding species status. This taxonomy is still in a con- (1995) also found no overall association between body size siderable state of flux (Kottelat 1998). and risk status of fishes in the Great Lakes – St. Lawrence drainage of North America, although species with late ages Assessment of threatened status at maturity tended to be under greater threat. This study We used Maitland (2000) as the main source of informa- found relationships between risk of extinction and character- tion on threat status and compared summary statistics of per- istics of habitats.