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Migration between fresh- and saltwater

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Pisces: Migration in freshwater

Migration in the freshwater - potamodromous species
Fish moving entirely within freshwater exhibit seasonal return movements to spawning areas, usually located upstream. Within rivers, this is called potamodromous. If feeding areas or spawning areas are located in lakes, this is called limnodromous. Besides bony fish (Osteichthyes), this migration pattern is observed in Cyclostomes (Lampreys: Petromyzodontidae) and even freshwater sting rays (Potamotrygonidae: Chondrychthyes) that migrate in the Amazon, the Mekong and the Niger river. Up to now, around 100 limno- and potamodromous species have been identified (see Table 4.9), but the scattered literature about migration in tropical river systems has not yet been evaluated. For example, in the middle Indus there seem to be "upstream migrations of three major carps Labeo rohita, Catla catla and Cirrhinus mrigala, the two carnivorous species Mystus aor and Mystus seenghala, the catfish Wallago attu and the snakehead Channa marulius. The large catfish Bagarius bagarius, a species that is widely distributed in the subcontinent, may also [...] move upstream" (Reeves & Smith 1997, p. 13). While this information needs careful examination, the disastrous impacts of dams on a great variety of highly productive tropical species is now a sad fact: major spawning areas of mahseers (Tor putitora and T. tor), holy carps in the eyes of Hindus, have been destroyed by dams in the upper reaches of rivers in the South Asian subcontinent (Nautiyal 1984, 1989).

The complexities of migration within the Mekong river were elucidated by an extensive field study in 1993 at Ban Hang Khone, an important fishing village on Khone Island just below the great waterfalls of the Mekong River at Lee Pee, southern Laos (Roberts 1993). Roberts identified three migratory periods, late January-February, May-July, and November-December. The study diagnosed a gradual decline of fisheries for all observed 93 species to about 20% of what it was in 1970. The endemic Mekong freshwater herring "pa mak pang" (Laotian shad: Tenualosa thibaudeaui), formerly one of the most abundant species, had almost disappeared, and is now red-listed as "Endangered" (Table 4.11). The decline is attributed to deterioration of flooded forest habitat, overfishing and destruction of spawning grounds by upstream dam construction. The Mekong river is also home to the only fish species listed in CMS Appendix I, the endangered giant catfish (Pangasius gigas, listed under Pangasianodon gigas). The Mekong river is still considered "a pristine river, free of dams and large-scale water diversion projects, and the water quality is generally good" (Hill & Hill 1995, p. 1). But in the light of huge development projects, co-ordinated by the Mekong River Commission, the authors conclude that "preservation and management of Mekong fish faunas will depend upon incorporating spatial information into decisions about [...] anthropogenic change" (l.c., p.1).

Probably the worst conservation status is observed among the sturgeons (Acipenseridae), which are actually driven to the brink of extinction by illegal fishing, habitat degradation and pollution. Following a proposal of the Federal Republic of Germany (1999), 6 potamodromous sturgeon species (Acipenseridae) have been added to CMS Appendix II, together with 18 anadromous sturgeons (see below). Further endangered potamodromous species are listed in Table 4.11. Research on the present conservation status is needed for the six additional species listed as "Data Deficient" (Table 4.12). In addition, it is necessary to keep in mind that dam construction can affect entire populations or whole species by irreversible blocking of upstream migration.

Tab. 4.11: Threatened diadromous and potamodromous fish, their CMS status and number of range states

Tab. 4.11: Bedrohte diadrome und potamodrome Fische mit CMS Status und
Anrainerstaaten

Class: Order	Family	Scientific name	Common name	RL 2000	Migration	Range states RL 2000	CMS
Actinopterygii:
Acipenseriformes	Acipenseridae	Acipenser baerii baerii	Siberian sturgeon	VU	anadromous	3	N.L.
		Acipenser brevirostrum	Shortnose sturgeon	VU	anadromous	2	N.L.
		Acipenser dabryanus	Yangtze Sturgeon	CR	anadromous	1	N.L.
		Acipenser fulvescens	Lake sturgeon	VU	potamodromous	2	App. II
		Acipenser gueldenstaedtii	Azov-Black Sea sturgeon	EN	anadromous	4	App. II
		Acipenser medirostris	Green sturgeon	VU	anadromous	3	App. II
		Acipenser mikadoi	Sakhalin sturgeon	EN	anadromous	3	App. II
		Acipenser naccarii	Adriatic sturgeon	VU	anadromous	6	App. II
		Acipenser nudiventris	Barbel sturgeon	CR	anadromous	2	App. II
		Acipenser oxyrinchus desotoi	Gulf sturgeon	VU	anadromous	2	N.L.
		Acipenser persicus	Persian sturgeon	VU	potamodromous	3	App. II
		Acipenser ruthenus	Sterlet sturgeon	VU	potamodromous	1	App. II (Pop)
		Acipenser schrenckii	Amur sturgeon	EN	anadromous	3	App. II
		Acipenser sinensis	Chinese sturgeon	EN	anadromous	1	App. II
		Acipenser stellatus	Sevruga	EN	anadromous	4	App. II
		Acipenser sturio	Baltic sturgeon	CR	anadromous	33	App. II
		Acipenser transmontanus	Columbia sturgeon	EN	anadromous	1	App. II
		Huso dauricus	Kaluga	EN	anadromous	3	App. II
		Pseudoscaphirhynchus fedtschenkoi	Syr Darya sturgeon	CR	potamodromous	3	App. II
		Pseudoscaphirhynchus hermanni	Dwarf sturgeon	CR	potamodromous	2	App. II
		Pseudoscaphirhynchus kaufmanni	Amu Darya shovelnose sturgeon	EN	potamodromous	3	App. II
	Polyodontidae	Polyodon spathula	Mississippi paddlefish	VU	potamodromous	2	N.L.
		Psephurus gladius	Chinese paddlefish	CR	potamodromous	1	N.L.
Clupeiformes	Clupeidae	Alosa alabamae	Alabama shad	EN	anadromous	1	N.L.
		Tenualosa thibaudeaui	Laotian shad	EN	potamodromous	4	N.L.
Cypriniformes	Cyprinidae	Barbus capensis	Clanwilliam yellowfish	VU	potamodromous	1	N.L.
		Labeo seeberi	Clanwilliam sandfish	CR	potamodromous	1	N.L.
Perciformes	Gobiidae	Lentipes whittenorum		VU	amphidromous	1	N.L.
		Sicyopus auxilimentus		VU	amphidromous		N.L.
		Stiphodon surrufus		VU	amphidromous		N.L.
	Terapontidae	Bidyanus bidyanus	Bidyan perch	VU	potamodromous	1	N.L.
Salmoniformes	Galaxiidae	Galaxias argenteus	Giant kokopu	VU	amphidromous	1	N.L.
		Galaxias johnstoni	Clarence galaxias	CR	catadromous	1	N.L.
		Galaxias postvectis	Shortjaw kokopu	VU	amphidromous	1	N.L.
	Osmeridae	Hypomesus transpacificus	Delta smelt	EN	anadromous	1	N.L.
	Retropinnidae	Prototroctes maraena	Australian grayling	VU	amphidromous	1	N.L.
	Salangidae	Neosalanx regani	Ariakehimeshirauo	VU	anadromous	1	N.L.
	Salmonidae	Coregonus huntsmani	Atlantic whitefish	VU	anadromous	2	N.L.
		Hucho hucho	Danube salmon	EN	potamodromous	13	N.L.
		Salvelinus confluentus	Bull trout	VU	anadromous	2	N.L.
Siluriformes	Pangasiidae	Pangasius gigas	Giant catfish	EN	potamodromous	6	App. I
Cephalaspidomorphi:
Petromyzontiformes	Petromyzontidae	Eudontomyzon hellenicus	Greek brook lamprey	VU	limnodromous	1	N.L.
		Mordacia praecox	Non-parasitic lamprey	VU	potamodromous	1	N.L.
Elasmobranchii:
Pristiformes	Pristidae	Pristis microdon	Great-tooth Sawfish	CR	amphidromous	5	N.L.
		Pristis perotteti	Largetooth Sawfish	CR	amphidromous	11	N.L.

• Migration between fresh- and saltwater

This document is part of the publication "Riede, K. (2001): The Global Register of Migratory Species � Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD (see copyright), orders: http://www.lv-h.de/bfn .