CM 19971P:07

Diadromous Fish : Threats on Local and Global Scales (P)

Different kinds of diadromy: different kinds of conservation problems

RMMcDowall National Institute of Water and Atmospheric Research Christchurch

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INTERNATIONAL COUNCIL FOR THE EXPLORATION OF THE SEA

Annual Science Meeting, Baltimore, Maryland, USA, 25·30 September 1997 ..

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. Abstract , This paper presents a world-wide·review ofthe of diadromous fishes. In taxonomie and geographical terms, high levels of conservation threat are focussed particularly· on sturgeoris, family Aciperiseridae, and on western/ceritral Europe and the North Pacifie. The geographieal focus reflects largely the imperilled status of sturgeons rather than issues relating to spccies being diadromous. The paper also provides im interPretation of the threats to diadromousfishes, in terms of. \vhether theyare anadromous, catadromous or amphidromous. The significance of these· varied forms of diadromy strategy is discussed in relation to the, migration strategies thai adopt in mov'ing to und from fresh water. About half known diadromous fishes are catadromous or amphidromous. Their patterns of migration and the ways they. occupy river systems differ from those' of anadromous fishes, and these fishes therefore require parti,cular attention in providing for their conservation needs and in , mitigaiing the Cffects of river managemerit und modification.

Introduction '1 ,". • This paper addresses t\.vo distinct but interacting issues that relate to the conservation of diadromous fishes: . ' • Firstly it examines the broad spectrum of diadromous fishes to deiermine what species or .__ .groups of species are considered to be under conservation threat and \vhether there is any common feature about these species that might point to why they are threatenf~d. ' • Secondly,.it looks at the different life history strategies exhibited amongst'diadromous fishes, and points' to speeifie issues that need attention with relation to their conservation. " ,

In asense, what I am doing is 'Iooking at'a broad continuum of conservation, issues In· diadromous fishes from each oftwo opposirig ends of that contin~um, asking: . • What do diadromous species under eonservation threat tell us about conservation In diadromous species?and • What is there about diadrom'y in fishes that causes problems for their conservation? . In principle, it seems that diadromous fishes do have partieular eonservation probierris that necd to be ad~ressed (McDowall 1992), but what does this mean in practice?

Diadromous fishes In a broad review of diadrorriy, now aboui 10 years ~ld (McDowall 1988), I found that nearly 230 fish species were then recognised as diadromous. Subsequent discoveries and taxonomie e changes will have increased that .number a little, but not greatly-perhaps to 250 species, or probably less ihan 1.5% of all knO\vn fishes. Diadromy encompasses three distinet migratory . strategies, as defined by George Myers (1949) (see Fig. 1). Some\~hai less than half the known diadromous species (48%) are ariadromous, and a little more than a quarter each are c'atadromous and amphidromous. Changes in these numbers iri the, past deeade are likely to ' have most affected numbers of amphidromous species, particulafly as a result of 'the increasing recognition of the existerice of amphidromy among the sicydiine gobies (Parenti & Maciolek 1993). In addition to fishes~ there is a presently' undocumented number of diadromous shrimps (families Atyidae and Palaemonidae) and gastropod molluses (Family Neritidae) (Williams & Smith 1979; Resh et a1. 1990; Schneider & Lyons 1993), all of which are amphidromous. .. . .

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.. Fi~. ,I. Different kirids of diadromy . . . Thus, although diadromy is not exactly a major phenomenon in the world of aqu~tic life, nor is it a phenomenon to bc "dismissed" as of little importance-a significant number of species is diadromOlls; and same of these are biologically, histoi-ically, or economicaIiy important cr. interesting. This, cf course, explains \vhy there is aspecialist ICES eommittec on the subjeet, and why this meeting is being held. f •

. . . ~ . .' . This symposium's titl~ relales to extinciion in diadromOl.ls fishes, but cleady we need to view the subjeei a little more broadly than just extiriction, to eonsider both aetual and potential extinetions, of which the latter are the most: important. This brings us face to faee with diadromous species under some form of eonservatiOll thieat. . Conservation threat ean be examined at geographiealltaxonomie levels varyirig from: • • Species as awhole that are under threat, to: ,e Threatened sub-speCies, raees or evolutionarÜy significant linits (Waples 1995). ~ ..' 'Cleariy;: thc mueh discussed issue with regard to eonse'rvation ~f northem Pacific salmonids' . .(Nehlsen et aI. 1991; Baker et aI. 1996;' Huntington ei aL 1996; Slaney et aI. 1996), orings into eonsideration detailed questions of catchment-'adapted raees; whieh (imaginc' will be well-, addresse~ during this meeting.

Aware that pieniy of attention is likely to 'be given to problems at this level, I want to foeus at ' a broader seale. Onc major problem in trying to ~o this is that thc life histories and migratory status of many groups- espeCially clupeid shads, grey mullets, und diverse eleotrids and gobies-.are poody understood. Thus some species regärded as under threat by IDCN may be diadrcmous without this 'yet being reeognised. So, here is a 'critieal issue for managing the conservation : 0[· diadromous fishes:' To accurately identify what spedes' 'actually are 3 " • &

.. CriÜcally endangered: " ". • Common sturgeon, Acipenser sturio (eastern AtlanticlMediterranean, Balticto, Black Sea) (anadromous) • " . , : ,'. '.,' '., .. :.,r" , .. '" .,...... Endangered: ," , .' . Ship sturgeon, Acipenser nudiventris (Aral, Black, Azov and Caspian Seas) (anadromous) Stellate sturgeon, Acipeilser stel/atus (Caspian, Black; Azov and Aegean Seas) (uriudromous) , Persian sturgeon,Acipelzser persicus (Caspian and Black Seas) (anadromous) , . Russian sturgeon, Acipenser guldenstaedti (Caspian, Black arid Azöv Seas) (anadromous) Amuf sturgeon, Acipenser Scllrencki(Amur River, ,v'estern Pacific) (anadromous), , Chinese sturgeon, Acipen;er sinensii, (boreal ,western Pacific) (anadromous) .. Kaltiga, Huso dailricllS (boreal western Pacific) (anadromous). ' ... " .' Beluga, HliSO IzllSO (Caspian, Black, Azov and Adriatic Seas) (ariadromous)

Alabama shad, Alosa alabainae (Gulf ofMexico)(ariadromous) I ' •• ' :" Delta , H)1JOll;eslls.transpacijiclls (Pacific coast of North.America). (anadromous) . '. Vulnerable: Siberian sturgeon, Acipellser baieri (Siberian and Arctie Russia and Baltic) (a~adromous) . ' Shortnose sturgeon, Acipeiiser brevirostrlllii (western North Atlantie) (ailUdrorrious) . • Green sturgeon, Acipellser medirostris (borealfsub-Arctle Pacifie) (anadroinous) Sterlet, Acipenser rutlzellus (Baltic, Arctie Russiri, Caspian, Bluck, Azov Seas) (anarlromous)': ' Adriatie sturgeon, Acipd,lser llac~ari (Adriatie Sea) (anadromous) ',' , .' ...... • ..' • ,;, '. ..' . ;. .. '., ~ • , \. I Anakehlmeshirauo, Neosalanx regalli (Japan) (anadromous) , ', 11laraella (Australia) (amphidroinous) Giant kokopu, Gala:iias argentelis (New Zealand) (amphidromous) Shortjawed kokopu, Gaiaxias posivectis (New Zealarid) (amphidromous) 'Acadian ,yhÜefish, Coregolllls huntslliaizi (western AtIantic) (anadromous) cOliflll~lliliS Bull trout, Saillelillus (western r;iorth America) (anadromous?) , . " I ----:'------, Lemipes wlzittellOrll11l (Indonesia) (amphidromous?) ------, 'SiCYOPll~ axilli11lentlls (Philippiries) (amphidroino~s?) .----~--':.-:_-, sripilOdoll sllr~llfils (Philippincs) (amphidromous?) , : ' . . . " 4 Lower risk: ...... River lamprey, La11lpetrajlllviatilis (eastern Atlantic/Mediterranean) (anadromous), Atlantic sturgeon, Acipenser oxyr/zYllcllllS (v';estern AiIantic) (anadromous) . White sturgeon, Acipenser tra.,isl1iontall11S (eastern' Pacific) O'opu nopili, Sicydi1l11l sii11lpson~ (Hawaii) (amphidromous)

Data deficient: '. ------Mordacia lapicida (Chile) (anadromousf Allis shad, Alosa'alosa (eastern Atlantic) (anadromous) Twaite shad, Alosafallax (eastern Atlantic) (anadromous) . ------~--'Clllpeollella cliitivelltris (Caspian Sea) (anadrommis) Smelt, OS111erus eperlall11s (eastern Atlantic) (anadromous) Vendace, Coregollils alblIla (eastern Atlantic) (anadromous) :..------,-, Coregolllls lavaretlls (eastern Atlantic) (anadrom~us) Large boUom whitefish, CoregOllllS naSllS (boreal) (anadromous) Houtlng, Coregonlls ox)'rillclzis (eastern Atlantic) (anadromous) , ---:------, Stellodlls lellcichthys (boreal) (anadromous) : 9'opu, Eleotris sandwicensis,(Hawaii) (amphidromous) ..' • O'opu nakea, AwaOlIS sta11lillellS (Hawaii) (amphidromous) O'opu alamoo, Lelltipes concolor (Hawaii), (af!1phidromous) Redtailed goby, SiC)'OPllS halei (Sri Lanka) (amphidromous?) Lipstick goby, SiC)'oplisjanklaas! (Sri Lanka) (amphidromous?)

,. ~ . Some of the species listed above are uncertainly diadromous, particularly the sicydiine gobies which are included on the basis that most are thought to ~e amphidromous (Parenti and Maciolek 1993). ,~, ,

A significant number of species is in the "Data deficient" category. Data deficient can mean many things, varying from: ' • "There' is concern,' but we need. to know more to be more assured of the species' conservation status, etc.", to' ' '. , • "There is concern~ but we don't know enough to make a preliminary assessment".

And, presumably not listed are further species about whieh: • "We don't yet know enough to be concerned about what is known or to be concemed that • we don't know enough to be conce~.ed'~. .' . Again~ the sicydiine gobies' belong amongst such fishes, and I suspect thatthere are also other goby groups, as weil as some of the tropical shads. Grey mullets (Mugilidae) 'are another problem group. .

I· have had real difficulty getting information about thes~' fishes. Their taxonomies, distributions and life histories are poorly defined in many instances. In geographieal terms, we are looking partieularly at information deficiencies in the whole of Asia, from the Red Sea east to China, south to Indonesia und New Guinea,' and also smaIl; tropieal and subtropical . islands right around the globe. But, it seems'to me that life histories of even some of the lesser species of the Gulf of Mexico coastal streams, such as gobies, are poorly elucidated and more may be diadromous than are presently recognised (especially given the lack of recognition of

5 amphidromy by many North Ämerican fishery biologists (see McDowaiI 1997) - e.g. Nelson (1994) assigns galaxiids Hiat I consider amphidromous to ariadromy. . .

Also not given Iisting' by IUCN are the races and/or stocks of riorthern cool-temperate salmonids that are undcr serious threat (Nehlsen et a1. 1991; H~ntirigton et aL 1996; Bilker et a1. 1996; Slaney et a1. "996). There are very few groups ribout whieh we know as much as we .. do about saimonids, and here, in a way, the problem may be knO\virig so much· that the -problems are almost unmanageable. In part 'solving tnis question seems to have becom~ a question of knowing what is an evoluticinarily significant pop~lation or group of populations that requires special conservatiori attention (\Vaples 1995). Andit seerris to me that some complex, statutoi-yflegal questioris become implicated. :. .~ .

l" •. , ,I, ! . , I am far from sure that the IUCN listing gives a comprehensive or balanced .view. Not\vithstanding sedous efforts by IlJCN to develop rigorous, repeatable and defensible . criteria for ranking species, at two ends of the spectrum there are issues that need attention. . No-orie can provide for the protection of species whose status and ecology a.re unknown or

poorly known, and thc international rush for more attention' to biodiversity' is the only ' ..;1 solution. On the other hand, intensity of effort applied to understanding the conserVation: status of species, and die statutory foundations for prcividing protection, vary widely between • nations. The Australian Society for Fish Biology, for instance, has a very. vigorous and continual process of ev'aluation and re-evaluation (\Vager and Jackson 1993; Jackson. 1997), and you will find a large mimbef of species 'listed from Australia by IUCN (Baillie arid Groombridge 1996). This may reflect high vigilarice by Aus'tralian fish biologists as mud. as it does acomparatively high level of threatened species there. ' .•"

Different forms ofdiadromy and conservation status In terms of the differerit forms of diadromy, it is notable that no catadromous species have been listed oy IUCN. Pcrhaps marine spawning enhances recruitmerit that ouffers the impacts of teITestriaIly-based effects on catadromous species? However, tnere is, I know; local concern about recruitment of glass eels of the European eel (Al1g11illa a1lg11illa-f. Anguillidae) as a result of heavy exploitation in some parts of Europe (Moriarty 1986), as weIl as concern about local.declines of the American' eel (A~ rostrata) in some'parts of eastern North America. '

Otherwise it is largely anadromous arid amphidromous species t~at are causing concern.' • ., •. •I • Viewing the IUCN list taxonomieally (Table I, 2), anadromous sturgeoris are obviously in really serious peril - but not much more so than non-anadromous sturgeons (Birstein 1995; Birsteiri et al. 1997). Problems of their conservation seem likely to relate more' closely to'the demographie idiosyncnisies of being sturgeons than of beirig anadromous-.. such· as slow growth rates, high age rit first maturity, and heavy exploitatiori because they are good to eut: sec Birstein (1993) for:an eloquent plea for action on sturgeon coriservation (note that his evaluatiori of the conservation status of many eastern European sturgeons seems much more alrirrning than that of IUCN .lnd he \vrites from personal experience). However, Birstein (1993, 1995) points out'that non-fishery species are also sei'iously threatened, so that it is not just exploitatiori that is critieal. . , ',. .'

. . . \ The other family in trouble is Prototroctidae, with just two species (both amphidromous) ­ one species in New Zeaiand is extinctand the other in Australia is threatened. Reasons for 6

TABLE2 Fish families and geographical regions with threatened species.

Eastern North Caspian, Black, Western Atlantic and Boreal North Adriatic Seas, North Atlantic Mediterranean Pacific etc. Hawaii Other Total Source of "other"in listing Mordaciidae I 1 Chile Petromyzontidae 1 1 Acipenseridae 2 3 5 6 16 Clupeidae 1 2 1 4 Salmonidae 1 3 3 7 Osmeridae 1 1 2 Salangidae 1 1 Japan Galaxiidae 2 2 NewZealand Prototroctidae 2 2 New Zealand/Australia Gobiidae 3 5 8 Sri Lanka (2), Phillipines (2), \Indonesia Eleotridae 1 1 Total 4 10 9 7 4 11 45

8 e~tinction and decline in this family are p~~;i;'under~tood. Possibly' it .relates 'to a combination of thc erfeets of 4lnd trout introductions, hut this is speculative (McDowall 1990). It is too late for the extinct New Zealand species, und we are presently at' u loss to know how to reverse the process in 'the Australian species (but see Sources arid sinks, below)..

Viewing the list geographicaIly (Table 2), .it'. is dear' that the most senous. areas of cons~rvation concern are eastern Europe (Caspian, Black, Azov, Aral uridÄdriaticSeas) 'and the boreal North Pacifi~, but this emphasis lurgely is generatcd, once again, by the dire straits .of the sturgeons. Other diadromous fishes in North Amcrica an'd parts of Europe 'are also' iri serious trouble, and this is probably in line with high density. human populations, se'rious . estuarine habitat degradation, losses of access to critical habitats caused by impouridment, and heavy. exploitation that fish populations there have heen exposed to..

.~. The s~rioiJs state of the Hawaiian riverine fish' fauna isO an' ~nigrria. Four of HawaÜ;s five • species of indigenous fresh\vater fishes (all amphidromOlis gobioids) are listed as under some form of threat or are data deficient (Baillie arid Groombridge 1996), and concerris about their conservatlon have been discusscd at some length (Devick et al. i992; Fitzsimoris & Nishimoto 1995). These conservation concernsare, perhaps, more surprising than for species . in Europe~ given lower huma,ri populatiori densities and industrialisation .in Hawaii; but they are consistent with the generally iinperilled conservation status of the Hawaiian biota (Wagner & Funk 1995). High levels of impacts might be unexpected, given that there is apparently not such greut pressure on the Hawaiian freshwater' fish fauna from introduced predators or competitors as there is on the terrestrial fauna ofthese'islands.· . . -Thus, there appear to be few generalisations applicable to understanding the conservation status'of diadromous fishes that aredisiinct from those rehiting either to the fact thai they are' migratory within river systems (like many non-diadromous fishes), or that they are subjeci, to heavy exploitation und are impactedby habitat deterioration (like,other 'fresh\vater fishes).

. -... ~ The dryirig up of the Aral Sea (Birstein 1995) is the only instance I am aware of \vhere'a serious threat to any diadromous species' survival relates specifically to its marine life stages. • Otherwise, there prcsently seems to be no evidence forcoriservation issues, ether than possible overexploitation, during marine life stages of Pacific salmons ( Oncor/zync/ius) in the boreal North Pacific Ocean. This is a fisheries management issue. .

Differing life history strategies of diadromous fislu~s There are few obvious idiesyncrasies of explicitly diadromous life histories that expose diadromous fishes to threat. The distinctive feature' of diadromy, compared with migratory " , behaviour in other migratory fishes; is the regular, almost obligatory movement hetween marine amI fresh waters through esttiaries. Estuaries are habitats that have sufferedsevereIy us a result of human impacts, especially from frequent establishment of population centres und industdes around large river mouths throughout the, world. The' universal need for diadrömous species' to. pass through estuarie~' exposcs thein to the pervasi~e' effects of estmirine habitat degradation', as \vell as river mouth closure in some localities. Clearly, there are instances where habitat degradation in estuaries and the lower. reaches of rivers' has· 9 contributed to declines of riverine stocks of species in many parts of the world, e.g. Atlantic salmon, Salmo salar (f. Salmonidae) in the River Thames in England, and destruction of estuarine spawning gro~nds of inanga, Galaxias maclilallis (f. Galaxiidae), around the shores of many New Zealand river mouths where cities have developed. However, I ani unaware that this has explicitly affected any diadromous fishes to the exte~t that their survival is threatened.

The' migrations up stream by diadromous fishes:do expose them to risks, from impoundment, dewatered river reaches, and point source polluting discharges, but these are no different from the same effects on non-diadromous (potamodromous) riverine migratory species. However, it is likely that the' gn';at distances that somediadromous species migrate are at the upper extreme of migration distances, and that they are therefore more likely to be influenced than non-diadromous 'specie's on the grounds of simple probability. There are n':lmerous instimces all over the world of harmful' cffccts of impoundments on migratory fishes; including' , di~dromous species: ' '. ,. ~ Passage by diadromous fishes through physical bottlenecks, typically at the mouths of rivers, makes them very easy to harvest intensively and efficiently, and this exposes them to risk of • declinc:' Undoubtedly, the most extreme rase of this is the Tasmanian whitebait, Lovettia sealii (f. Aplochitonidae) which: although not regarded as threatened, underwent a very rapid and huge decline in the late t'940s and earl).- .1950s from which it has never recovered, despite closure of its fishery nearly 50 years aga (Fig. 2).' . .' ' . 500

450 :-

400

350

>< ' ...... Cl' 300

'150 •

'100

50

"1945 "1950 "1955 "1960 '1965 "1970 '1975 VEAR

Fig. 2. Catch i!" the Tasmanian whitebait (Lm'ettia sealii) fishery (from Fulton 1984)

In this instance, faHure of the 'populations to recover'after closure of the fishery may point to the coincidental effectsof both the beginning of intensive fishery exploitation and some' other . harmful habitat deterioration.

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\Vhen addressing coriservaiion and extinciion issues in diadromous fishes, there is,a criiical need to do so in the coritext '()f. the different types of migrritory'sti"ategies undertaken, by the wide diversiiy of diridromous fishes-atteniion to the coriservation needs of diridromous fishes must be given in an explicit awareness' that different ferrns of diadromy involve different migratory strrih~gies and behavioui-s by different life stages \vitl1 different migratory abilities.'

"Wheri l1e first introduced the term diacl,romy in;i949, George Mye~s als'o defined three sub­ c~tegories (Myers 1949) (see Fig. 1). Two of, these, anadromy and cat':ldr~my, were al ready , old and quite ,\Videly used terms, although theirusäge \vils, arid still ofteri is, co~fusing rind iriconsistent., However" the, third terin, amphidremy, was new. Anadromy rind catadromy contimie to be \videly used, but ampl1idromy has achieved less acceptilnce. This is not, in my , view, due to it beirig a less valid term ör less disdnct phenomenon. PrirtlY it is because it has becn misunderstood, ami' partiy because the distributions of amphidromous' fisl1es tend to' cOITelate negriÜvdy witl1 the distribution of ichthyologists rind biologists. This applies to the " extent that some workers discount the teml. aitogether, or des~ribe it as a deviant form of anridromy (BaIon & Bruiori 1994).' By contrast, the terrii is used routiriely by tl1e rather rarer bioiogists \vho work iri regions" oron g'roups of fishes, in \vhich amphidromy is a common ... phenomenon-'such as fishes of 'Japan, Hawaii, the southwestem PaCific (Australia und New • Zealand), aridlor \vl1o study sicydiine gobies, eleotrids and galaxiids (Nishimoto & Kuainoo 1991; Radtke.& Kirizie 1991; Parenti arid Madolek 1993; Fitisimons & Nishirrioto 1995; McDowaIl 1997; Pringle 1997). There is no doubt Hiat it is a useful and heurisiic term. " . , .,. '. . .-' . . , . . . ~...... • .. . , '• ~" ' . '• . ~, . • _.~ I • ,. Although commentators have suggesied that amphidromy is dosest io anadromy (BaIon and

Bruton 1994; Grass 1987) there are also I sirong ,similarities betw,:en, amphidroinyarid catadromy (Fig. 1). It is not my purpose here to further defend or further defirie amphidromy . (but sec McDowaIl 1997). Whrit I do want to emphasise are the 'differences between the three forms of diadromy, iri'the \vay the fish explolt freshwater habitats, and what this means for uriderstandirig rind triitigating conservatioI1lextinction problems. '.'

Biologists fa~iliar,with anadromy, as expres'sed iri' salmonids, osmerlds, dupeids" lampreys, and other groups" typicrilly erivisagc irivasiori of dvers from the sea by l~rge, adult, well­ maturcd individuals, often with their gonads weIl developed..Migration is lrirgelya process' of geiiing to the spa\vning grounds, often 10n'g distances upstrearri, as rapidly as possible to ' minimise mortalities and enei-gy expendiiure, arid to maximise availability of energy to invest in generatirig 'reproductive prouucts and to sustain spa\vning aciivity. This must be seen as a ' ,broad generalisation-for.which there ure exceptions: for example; ihere are sorrie species that spend unusuaIlylorig time periods during thCir upstream freshwater migration; such as spring migrating stocks of some autumn to wiriter spawning chinook salmon (Healey 1991). Moreover, the southem pouched lamprey (Geotria' allstralis, f. Geotfiidae), spends ~o long betweeri migrating from the sea and reaching sexual mriturity (about 14-16 months -,Potter et al. 1980; Glova 1995).that there 'are actualiy hvo breeding cohorts at different. stages of maturaiion (a year apart) simultaneously in river systems where it spriwns. Dut even though . preserit in fivers for long to short periods,' the upstrearri-rriigrating anädromous spawners are ' esseritially passive members of the freshwriter ecosystems that they enter for maturaiion, until

they do eve~tually spawn. .,' I, ' . .. . I~' general, th~ spa\vning sites of ariridromoiJs species repre~ent the species; upstrearri limits fn dver systems. After the young hatch there dcvelops atrajectory of downstream movement of ... t . 11 '. -

.' fccdirig'und growing ju~cnilcs that, ovcr periods ~f u fe\v weeks, to months, or evcn ycars, find theirwuy to sea. There are some stocks cf sockeye suhnon (Ollcorh)'llclllls 'llerka) in which thcre is an upstrcam migration from the spawning grounds into lakes (Burgner 1991), but these are exceptionaI. Dependirig on how rapidly the progeny of anadrorrious species make their way to sea; their presence in rivers rriay be highly variable seasonally, e.g. the young of pink and chum salrrion, 01lcorh)'llchus gorbuschil and O. keta, are present in fresh \vater for only day's or weeks' in the' early to mid sp'ring (Heard 1991; Salo 1991);' in other Pacific, 'salmons this phase may"last several wecks to rrionths overthe'spring and Sl.lInmer, but again there are very strong seasonal rilOdes in abundance arid distributiori (Burgrier 1991; Healey 1991; S~mdercock 1991): Alosid shads. mayaIso spend several 'months' in fresh water after hatching a~d before departing for the sea (reviewed in McDowall i988): Ho\~ever, the ne\viy hatched larvae 'of many anadromous species go straight tosea,'as' in Osmeridae, Salangidae, ~ the Australian' aplochitonid Lovettia seal;;, and New Zealand Retropinnldae (see McDo\vall 1988) ",."

.The processes of entry into fresh water, and, growth and maturation there by arriphidromous and catadromous species are very different from those iri anadromous species. In -both amphidromous and catadromous species, entry to i-ivers takes placc as small to well-gro\vn juveniles,'varying from about 15 to 75 mm in length, the upper extreme' being'anguillid glass • eels which are very slender, and so of very small mass. Migrating juveriiles of most species are less than 50 mm: long and many less thun 30'mm. Thüs both catadromous arid amphidromous species, at entry to fresh \Vater are very' smaJi and quite different from anadromous specics at migration. ' ." , . , At least iri New Zealand's amphidrom~iis species, what happens is that the small immigrant juveniles settle iri the low~r -reaches ofrivers, and over aperiod of' months or even years gradually make their way upstreain into habitats suitable for feeding, growth, a~d maturation. Distribution patterns for these species are thus anchored in the lower reaches of river systems and because thespecies are in almost all instances able to find suitable habitats no great distance upstremn, there is declining frequency -of occurrence and abundance with both increasing elevati~n and distance up stream. Fig 3 shows patterns of distribution for 12 rriostly - amphidromous and catadromous species in rivers of th6 'Vest Coast of the SouthIsland of Ne\v Zealand; the figure plots the percentage frequency of occiirrence of each species across intervals at 10m intervals of elevation, and so adjusts for differences in sainpling intensity at different e1evations. In' almost all species there is a greatest concentration at downstream, locations, highly varying' inland' penetratiön, but almost always -dedining ,frequency ~ of occurrence.' There is no hint of diadromous species having primarily inland ranges.

There is also evidence for changing age and' size. structure. of 'th6 popuiations of ainphidromous with distance. Lowcr down in river systems all age classes are jJresent; but .because upstrearri penetratiori takes time, the fish are older/larger by nie time they get further . up stream, and this is reflected in a changihg size and age distributions (Fig. 4). There are thus do\vristream-upstream trajectories of declining occurrence/abundance, and iricreasing'mean

. '. 12 , .

70 Retropfnna retTÖpinriä 70 Gaiciilas fasciatus 60 ... ,• • r 60 " 50 50 40 .4~ 30 30 , 20 20 10 . 10 0 , 0 ~"""~+J"""""'l'-""';-'--r-.,.....,r-r-r-...... -.--.- 70 GiJlaxias maculatus , 70 ,GobJomorphus hubbsi ~ ." 60 60 . E' 50 50 ~ , 40 40 ~ 30 30 " - CI) 20 20 ,-.t: 10 10 0 CU 0 o~"""~+J""""""""'H~~~",,--~~-.- CI) 70 a,.g~~teus 70 CU Galaxias . Gobiomorphus huttoni - 60 60 C 50 -CI) 50 CI) 40 40 ~ a. 30 30 , 20 20 • .~ 10 10 CI) ~,...., ~ ~~""--~~~..-. CI) 0 o ...... --'- ·Ü 70 CI) 70 Cheimarrlchthys ioiteri a. .GobiomorPhus cö'tidianus' 60 CI) • 60 50 .t: 50 0 40 ,40 ::E 30 30 20 == 20 CU' 10 10 -CI) 0..LJ~"""""'~"""~~~~~~"""~--'- CI) 0 ~ CI)- 70 Anguilla au'Stratis 70 , Gälax~äs brevipinnis 0 60 -CI) 50 C) CU 40 C 30 -CI) 20 0~. CI) 10 c.; 0 70 Galaxias pöstVectis 70 • 60 60.. 50 50 40 .- 40 30 . 30 20 20 10 10 oL1,....,...... ~""--~~ ....'-.II~~ ...... ~--'- 0 5 10 15 Elevation· Eh;;vation

Fi~. 3. OcciJrrence oe diad;omous fishes hi ,\rest COltst, South Islami, New ie~land rh'ers presented as 25 m eIevatiOll strahl to standai-dise occurrence aiainst varied samplin~ intensity 3t dilTerent elevations. ' ,

: 13 . ., and modal age and size. The process of entry into rivers and occupation of riverine habitats is perhaps best described as insinuation. Understanding these strategies of invasion is cruciai to' interpreting amphidrom'ous' and catadromous species' conservation needs.

Species differ in several parameters related to th~ir invasion of river syst~ms-in their swimming strength, cIimbing ability, and instinctive migratory drive. These differences result in species-characteristic patterns of occurrence. Those thai are weak migrators, as a result of either or both of weak swimming ability and low upstream migratory drive occur only at low elevations and distances from the sea. As one or both ofability and drive increase, so the' distribution spreads inland, but these species remain present at low elevations and distances' inland-thus they just ~ become more ~idespread. None of New Zealand's amphidromous species is abse'nt at low elevations distances and present only further inland (Fig. 3). These patterns do not apply to all amphidromous species,' e.g. the Hawaiian Lelltipes cOllcolor (f. Gobiidae-a species Iisted as data deficient by IUCN) has adistdbution that is primarily weIl inland and at high elevations and, apart from upstream migratory juvenile stages, is not found at low elevations (Devick et aI. 1992). It's pattern of distribution within Hawaiian river systems more cIosely resembles that of an anadromous species. •

•

Standard length (mm)

Fj~. 4. sizelfrequency distribution of populations of torrentfish, Cheimarrichthys fosten at different distances up stream from the sea in the Waikanae Rh'er, New Zealand (A. 2.8 km up stream; ß. 5.6 km; C. 10.6 km; D. 12 km)

However, the chief point that I want to make is that the rapid upstream movement by large, highly mobile, adult, anadromous fishes is not the only migratory pattern th'at needs consideration when reviewing conservation problems in diadromous fishes. 14 . \Ve need'also to take account of the way small upstrearri-moving juveniles of amphidromous and catadromous speCies migrate. '. Their ability. to . penetrate inland is based on quite, .distinctiveswimming skills. Typically, they are' climbers, especially those that move \vell inbnd, and,many of thern are capable of g~tting PaSt some formidable baITiers. The champion is perhaps Lentipes COllco[or, which Devick et al. (1992) reported above individual \vaterfalls more than 14Ö m high and above a cumulaiive hcight of sequential falls exceeding 600 m. However, this species is not alone in its climbing ability; other gobies, anguillid eels and some ' galaxiids are not far behind. \Vithout anything more thari a damp, exposed concrete dam-face,

.elvcrs get' over dams in NewZealand over 40 mhigh: I have found juvenile galaxiids a1:>ove I. falls that I estimate as 60 in high. ' ,,

Because of the different modes of' upstream perietration, the iechnology of fish passes fo~ rimphidromous and catadromous has, also, to be different. Thc very strongly developed rish',' pass technology for salrrioriids rind other larger jUmpers is often based on restirig pools arid carefully dcsigned low:-height ,haITiers that, fish can jurnp. These are of little or no use to ' , amphidromous and catadromous fishes, arid may be total baITiers for therri. They need fish . passes ihat facilitate climbing in contact wiih ri substnite iri the absence 'of ,powefful. flushing/turbulerit flaw's. Provided with a suitable fish pass, there is virtuaIiy no height that .: these riiTIazirig Httle fish cannat get past; they will seemingly keep on going until they rtin out of end·gy. Th'e beauty of this approach is that appropriaie,fish passes are, cheap, simple,erisy to install after a drim has been built, 'and require miriimal water flows. Wheri elvers and juvenile galaXiids were provided with a fish pass corilprising ~ hirge bottle-brush-type insert in . , a plastic pipe, they streamed up a' 75 in high . New Zeaiarid, dam in. such ntimbers' ihat ~eoxygenation ririd waste exc,reiions by fish weIl up the fi~h p~ss, suffocaied those lo\~er down..

To' deal \vith these rish, first there is a need to' recognise that they exist; and second io establish' a distinctive mind-set that accommodates their specific migrätory behaviours 'and abilities. '. , ; .

Sources and shits ' ,I ' fIoming' of spawnirig anadromous fishes back to natal sirea~s is a core idea in the ecology and behaviour of anadromous fishes, particulady in salrrionids; though it is also raised for other anadromous taxa (Jessop 1994; Dittinan and Quinn' 1996); fIowever, I know 'or rio serious discussion of the likelihood of homing in other forrris of diadromatis migrations. In • fact it is impossible in catadromous fish~s' ~ince the n,atal spawning rirea is at sea; juvenile catadromous fishes are thus enteririg rivers frorri which spawning adults havc, fOrrIterly deparied: Amangst amphidromous fishes, emigration frorri rivers is as ncwly hatched lrirvae, arid ihe prospect that they eari return to natal rivers on the. basis of memorised natal river characteristics seems somewhat far-fetched. .

The concept of populations' in highly. produ~tive'habitats ("sources") p;o~idin~ for recruitment 'into unproductive habitats ("sinks") has receritly beeri .emphasised (Pulliam 1988; Durining et al.. 1992) .as a' poteniially iinportant process for uridcrstanding ,community. and'limdscape . ecology. A mechanism of this sort was suggested as'anexplanatiori for the extinctiori" of the New Zealand grayling (McDowall' 1978, 1990), and has poientially .useful application to diadromous fishes. The process has the potential to set a species on a trajeetory to extinctiori if the drain on the source populations by the sink populations is 'sufficiently severe-especially if thc, productivity of recruits in sourcc populations is crratic and/or habitats of sourcc .' - 15 populations are under threat of degradation. In the ease of the southem graylings; possibly the , eontinuous.. drain on souree populations may have beenmore than ean be sustained. Furthermore, Hildrew (1996) has pointed out that the conservation status of a'species or community can only be evalun:ted properly if the balance bet\veen sources arid sinksis understood. In fact the' widespread distribution and local abundance of a species, that is , interpreted as favourabl~, may even disadvantage a'diadromous speci~s and conti-ibute to its ~ decline. ..' .t .

The concept of sources and sinks' in rClation to diadromous fish migrations, may, seem eounterintuitive in evolutionary/selective terms. However, dia'droinOlis fishes entering rivers are probably responding to environmental signals th~lt guide them into specific rivers, signals . . that correlate with the suitability of the upstream habitats - probably the geology, soils and vegetation through which the \vater flowing down stream passes and obtains its "character';. These sign~ls may increasingly be misleading as a result of human modification of catchments if the eritical signals remain present but the habitat up stream is de'graded. Impoundments of , river systems would be a classic example. . ' . .. , ' . ~" . . Thc question of landlocked stocks '. ., , .' , It is .weIl, known that in many diadromous., species, landlocked or freshwater-limited populations develop, most often in: lakes. This life history flexibility provides an opportunity to provide protection f~r populations by limiting tlleir passage needs and.. avoiding ~hem having to pass throtigh polluted waters Of piaces where exploitation' is heavy. However, it is really important to recognise that a landlocked population of a diadromous species represents . a seriously reduced form of the species, certainly behaviouraiIy and' probably geneticaIly. Attempts to provide for'the conservation needs of a species though protection Of landlocked stocks should thereföre be strenuously resisted, unless this is a last opportimity to-ensure a . species survival (McDo\'yaIl 1992). .

Conclusions '. ... I. Probably the most ci-itical issue for conservation ofdiadromous fishes is to leam which species ure diadromous arid to uriderstand their migration strategies; ... .' 2; Some diadromous,fishes are in serious conservation perit, particulafly Acipenseridae and Prototroctidae; . " 3. There is nothing specific about their being diadromous that coritributes significantly to that peril that is not also true of similar species that are migratory in fresh' water; , • 4. There is real concern abOlit the condition and habitat/water qu'ality in the lo\ver reaches or ,rivers in many parts of the world; :' ," , 5. Two distinct patterns of penetration of river systems must be given carerul consideraiion when attending to the migratory needs of diadromous fishes: '. • 'The rapid penetration of large, strong-swimming; 'adult ariadrorhous fishes, many of which can leap substantial barriers, and' .' . • The slow penetratiori by smalI' fishes' that move along or even within the substrate, and which can overcome incredible barriers oy ciimbing, as leng as some'simple eonsideration is given to thelr needs. .

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