Falklands Conservation

Conserving and Managing the Falkland Islands Freshwater Fishes.

R.M. McDowall,
National Institute Water and Atmospheric Research, P.O. Box 8602, Christchurch, New Zealand

Introduction
The Falkland Islands have a sparse freshwater fish fauna, with only four accepted native species listed there. Only two of these are widely known around the islands: zebra trout, Aplochiton zebra, and Falklands minnow, Galaxias maculatus. The other two species, Galaxias platei and Geotria australis, are of uncertain status there. Some publications list more than are included here - but this result from confusion over the identity of different life stages, e.g. the name Galaxias attenuatus is sometimes listed (Stewart, 1973; Strange, 1992), but this name is junior synonym of G. maculatus (McDowall, 1971, 1972) - they are the same species.

In November 1999 a small New Zealand team surveyed 146 sites for freshwater fishes using various fishing techniques (electric fishing, seine, gill, dip, and fyke nets, and spotlighting at night). Prior to our 1999 visit, there had been no intensive survey of Falkland Islands freshwater fishes. This article outlines the results with particular reference to conservation and management issues.

Fish species present in Falkland Islands fresh waters
Our survey revealed only two native fish species in Falklands' fresh waters: the Falklands minnow and zebra trout. We collected neither Galaxias platei nor Geotria australis. In addition, the introduced brown trout, Salmo trutta was found. During our visit, some locals made reference to "rainbow trout". What is known worldwide as "rainbow trout", Oncorhynchus mykiss (long called Salmo gairdnerii - they are the same species), is not known to have been introduced to the Falklands, and it seems that what are sometimes called "rainbow trout" in the islands are in fact very brightly coloured brown trout.

The status of Galaxias platei and Geotria australis in the Falkland Islands
The failure to again record Galaxias platei in the Falklands (since its original description by Regan, 1905, as G. smithii), and our failure to find it in 1999, raises such questions as: Did the single original specimen come from the Falkland Islands? If so, does our failure to recollect it mean that it has disappeared? Or have the right habitats been explored? Little light can be cast on these questions. Regan (1905) noted that the fish he described came from "Sir A. Smith", who appears to have been the founding Director of the South African Museum (McDowall, 2000), and an authentic Falkland Islands origin of the fish is in doubt (McDowall, in press). It is of interest that comparisons showed that Regan's (1905) G. smithii is the same as the Patagonian G. platei (McDowall, 1971).

Gorham's (1977) record of Geotria australis, the pouched lamprey from the Falkland Islands has never been repeated or authenticated. Although Gorham took collections of fish back to Canada, there is no trace of a lamprey amongst Gorham's collection in the Canadian National Museum (C. Renaud, pers. comm.). Lampreys are distinctive animals, so that it seems unlikely that Gorham mistook some other fish for a lamprey. The pouched lamprey has very broad distribution in southern Australia, New Zealand, Chatham Islands, and South America (McDowall, 1990), and has been recorded from seas to the south of the Falklands (Permitin, 1967; Ivanova-Berg, 1968; Potter et al., 1979). This makes presence of lamprey at the Falkland Islands almost predictable. Perhaps it comes occasionally into Falklands streams, but we found none.

The place of diadromy in Falkland Island freshwater fish conservation
One feature important to conservation and management of Falkland Islands freshwater fishes is that both Falklands minnow and zebra trout are diadromous - this means that they migrate regularly between fresh waters and the sea (other well-known diadromous fishes are many trouts and salmons, lampreys, anguillid eels, and sturgeons - McDowall, 1988). Understanding these migrations is crucial to conserving and managing Falkland Islands freshwater fishes, as will be discussed below.

The Falklands minnow migrates to sea as freshly-hatched larvae c. 7 mm long, which then spend about 6 months there, before returning to fresh water as slender transparent juveniles c. 50 mm long - the return migrations of huge numbers of these juveniles support fisheries in New Zealand, Tasmania and Chile (McDowall, 1990), but the fish seems insufficiently abundant in Falkland Island streams to sustain a comparable fishery. The life history of zebra trout is not well understood, but post-larval zebra trout are known from Chilean seas, and juveniles (c. 50 mm long) were taken in several Falkland Island streams, during our survey, just upstream of the tidal zone. The life history of zebra trout appears to resemble that of Falklands minnow, with a marine larval and juvenile life. "Landlocked" populations of both Falklands minnow and zebra trout (whose entire life cycles are completed in fresh water - McDowall, 1988), are known in lakes, and were encountered in our survey. Thus, there is flexibility in the life histories of both species - they do not have to go to sea.

Perceived conservation status of Falkland Island freshwater fishes
The Falklands minnow is widespread (Fig. 1) and locally abundant, and there appears to be little reason for serious concern for its survival-even though there have been general statements of concern, for instance, that the minnow "has been supplanted in many [rivers]...by exotic species" (Strange, 1989). By contrast the zebra trout is widely regarded as seriously threatened (Stewart, 1973; Strange, 1989, 1992; Simpson, 1990, 1991; Lapsley, 1993; Oldfield, 1999). Anecdotal information has long suggested that this species' Falklands distribution is becoming greatly reduced, and there is legitimate concern about its survival. Many Falklanders report its disappearance from streams during their lifetimes, and as a result of these concerns the Falkland Islands Government recently invoked complete statutory protection for the species (Anon. 1999: Conservation of Wildlife and Nature Ordinance, 1999: The Falkland Islands Gazette, Supplement, Vol. 10 (18), 21 September 1999).

Brown trout in the Falkland Islands
Brown trout, Salmo trutta, were introduced to the Falklands several times, beginning in the 1940s. Imported stock originated variously in Chile, United States, England and Scotland 1948 (Stewart, 1973; Nolan, 1993). Brown trout can also be diadromous ("sea trout"), although non-migratory populations, and even non-migratory individuals in usually migratory populations routinely occur (McDowall, 1988). Life history characteristics of brown trout introduced to the Falklands, at least up to 1961, are unknown. Some commentators considered them to be from non-migratory stocks (Nolan, 1993; Lapsley, 1993). What ever their origins, brown trout in the Falklands rapidly became sea migratory, once introduced. Why they did so is unclear, but it is no surprise, as the species is highly adaptable, and the same has happened elsewhere (New Zealand - McDowall, 1990). The brown trout spawns in fresh water, where the juveniles spend several months feeding and growing before moving to sea. Life at sea may last for several years, and most feeding and growth take place there. Food in Falklands streams for predators like brown trout is sparse, and river-resident brown trout there are small (often < 0.5 kg weight and 200 mm length). The adults return to fresh water to spawn, after which they may go back to sea again to recover condition (before coming back to fresh water to spawn again in later years). In addition, sea-living brown trout may make irregular visits into river estuaries on a daily, or tidally-related pattern (McDowall, 1988), and it is probably these brown trout that are so favoured by anglers (Lapsley, 1993, 1999; Nolan, 1993; Wilson, 1997), with angler-caught fish up to 10 kg, probably based on growth at sea in the extensive semi-enclosed inlets around the islands (Fig. 1).

Brown trout are now very widespread. Our 1999 survey revealed them in most catchments sampled across the northern two thirds of West Falkland - except streams that flow into Philomel Harbour (we did not sample West Falkland south of Fox Bay). They are equally widespread across northern and central sectors of East Falkland (virtually all waters draining north of Choiseul Sound except Berkeley Sound, as well as at least one stream flowing from Lafonia into southern Choiseul Sound (but apparently not elsewhere on Lafonia - Fig. 1). Colonisation of northern Lafonia streams is recent according to John-Willy Jaffray.

Brown trout clearly have dispersed widely around the islands as an outcome of the sea-migratory (diadromous) life cycle they have adopted. They seem rapidly to have spread into many waters where no liberations were made (though past transfers are largely undocumented). Local attitudes include an interest in developing the trout fisheries, and as a result, there may be continuing transfers of stock into new waters What controls the range of brown trout, and how this distribution is changing with time, are unknown. Absence of brown trout from Philomel Harbour streams could be because the fish have not yet found the harbour's narrow entrance, (Fig. 1). If that is true, eventual trout invasion of Philomel Harbour seems inevitable. The streams there seem as suitable for brown trout as other streams and lakes on the islands. Absence of trout on most of Lafonia (Fig. 1) is unexplained, but again lack of suitable habitats seems an unlikely cause. Again it may be a question of when rather than if trout take spread there as well. Therefore, there seems no reason why brown trout should not, eventually, occupy the whole of the two main Falkland Islands, invading all waters accessible to fish migrating upstream from the sea.

Conservation issues related to migratory behaviours
The above details of life histories of Falklands minnow and zebra trout, and introduced brown trout, and in particular the existence of diadromous (sea) migrations, have crucial and sometimes quite complex implications for conserving and managing the native species, particularly for zebra trout.

Because of their migrations, it is important for Falkland Islands freshwater fishes to be able to move up- and downstream between the sea and their riverine habitats, through the river estuaries. There are few data on the penetration of rivers by Falklands minnow, but in New Zealand, this species mostly penetrates upstream only 10-20 km. However, that is a fair distance in many of the quite small Falkland river systems. No comparable figures exist for zebra trout. Thus Falklands minnow and zebra trout need both freedom of upstream access, and suitable habitats along the way. Conservation of these species, requires habitat conservation at the catchment scale as well as at the local scale - there is limited value in conserving rearing/adult habitat for these fish if they cannot reach these habitats owing to obstructions to migration.

The fact that these fish are present in the seas around the Falkland Islands, as juveniles, means that there is a stock of fish that can repopulate rivers should there be, for example, a fish kill in a river caused by either natural events (temporary stream blockage, river mouth closure) or human influences (pollution, etc.). This repopulation will occur naturally and rapidly, once factors causing perturbation abate, by immigration from the sea. However, zebra trout may now be so rare and localised that natural restoration of stocks may be in jeopardy.

Implications of introducing brown trout to the Falkland Islands
Harmful impacts on native fishes after introduction of brown trout are reported worldwide - in New Zealand, Australia, South Africa, and even North America where there were already diverse native salmonids in habitats where brown trout were introduced (McDowall, 1968, 1990; Townsend and Crowl, 1991; Jackson and Williams, 1980; Keam, 1994; Skelton, 1987, Lever, n.d.). There is a wide perception that, as elsewhere, introduction of brown trout has harmed native Falklands fish populations. As is typical of exotic fish introductions in most parts of the world, there were no reviews of likely impacts, nor evaluations of the impacts of Falklands introduction of brown trout - no 'before/after' or 'presence/absence' data for zebra trout/brown trout sites.

However, there is local acceptance of harm, leading to zebra trout being given total protection (discussed above). Stewart (1973), for instance, was "informed" that both zebra trout and Falklands minnow "have been supplanted in certain rivers" by brown trout. Simpson (1990) thought that "both species have been greatly affected". Although (in Clark et al., 1994) he later considered the minnow "not threatened by the introduced species", he repeated his concerns for zebra trout, which "soon disappears from a river system following the appearance of S. trutta". Lapsley (1993) wrote that though sea-trout fishing has been widely reported, "What is less well known...[is]... the effect the introduction of brown trout has had on the islands' indigenous freshwater species", and he commented on the "fragility of native species when confronted with comparable but more successful interlopers" [such as brown trout]...[the zebra trout] seems to have all but disappeared from virtually all of the waters in which the brown trout and sea-trout have become established".

The 1999 sampling confirmed the perception that zebra trout and brown trout tend to have mutually exclusive distributions in Falklands streams. With just two exceptions, zebra trout were present only where brown trout were absent - in streams draining into Philomel Harbour and on Lafonia (Fig. 1). Brown trout but no zebra trout were found at 42 of 146 of our sites, zebra trout but no brown trout at 17 sites. Exceptions were: 1) One zebra trout caught in Arrow Harbour Arroyo, southern Choiseul Sound (Fig. 1); brown trout were abundant, but may be new to this system; and 2) Zebra trout in House Creek, which drains into Port Howard (northeastern West Falkland - Fig. 1) where the stream has a few small brown trout (c. 150 mm), abundant Falklands minnows, and rare juvenile zebra trout just above tidal limits and then zebra trout present further upstream but an absence of brown trout. Overlap between zebra trout and brown trout in House Creek is slight, though the sea-migratory life stages of zebra trout must pass through the brown trout zone in the stream's lower reaches to reach upstream habitats. Why zebra trout and brown trout have nearly mutually-exclusive distributions is not known, but it could relate to predation, food competition, or competition for habitat. Data are needed on this question.

The conservation response
Commentators, both in press and in conversation, express the hope that survival of zebra trout in "refuges" yet to be invaded by brown trout provides the best hope for survival of this species in Falklands waters (Clark et al., 1994). This perspective, while understandable, is a cause for concern, for two reasons. 1) It remains possible that brown trout will eventually invade the apparent refuges, such as Philomel Harbour and Lafonia. It is over 130 years since brown trout were introduced to New Zealand and yet this species is still spreading; associated with that continuing spread is continuing decline extirpation of native species (McDowall, 1990). Refuges for zebra trout in the Falkland Islands seem, at best, a fragile and temporary respite from the species' extinction there. 2) Even if such areas as Philomel Harbour and Lafonia remain brown trout-free, because larvae of zebra trout apparently move to sea for early juvenile life, it is likely that the young of zebra trout will be spread around the islands, with many juveniles returning to brown trout-occupied streams, where they cannot survive. If this happens, and we are only postulating that it might, there ought to be concern about the long-term viability of all surviving breeding populations. Clark et al. (1994) referred to zebra trout of North Lake Sulivan (draining into Philomel Harbour), and noted that this lake is only narrowly separated from South Lake Sulivan, where brown trout are present. Breaching that barrier (as could happen when a proposed road is built) would give brown trout direct access to Lake Sulivan North and Port Philomel, threatening the zebra trout population there.

The role of landlocked populations
Both zebra trout and Falklands minnow form landlocked population, e.g. zebra trout in Red Pond (on Port Howard farm) which has no significant outlet, so the sea-migratory life stage is lacking. Moreover, brown trout cannot enter this small lake. Landlocked zebra trout populations, like that in Red Pond, are protected from effects of brown trout as long as the latter are excluded from the lakes, and this provides a "fall-back" conservation opportunity for zebra trout in the Falklands should the sea migratory populations be extirpated by brown trout (or other causes). While the Red Pond population is unquestionably of special value to the conservation of zebra trout, it must be viewed as a conservation "second best", in the sense that it does not represent the species' full genetic and behavioural diversity - it is certainly better than nothing.

Future action - zebra trout
Statutory protection for zebra trout (Conservation of Wildlife and Nature Ordinance, 1999 - discussed earlier: Anon. 1999) gives protection only from human interference such as fishing - it means only that human exploitation is not adding to the threat the species is under. However, if decline in zebra trout is related to habitat/ecosystem causes, statutory protection has reduced value. Urgent research is needed to clarify the species' life history and, specifically, determine when and where spawning, egg development and early growth occur, and the timing and life stages at which there are migrations;

Horse Paddock Pond, East Bay farm (West Falkland), has zebra trout that may be landlocked-though the pond does have a small outlet stream. Determining the migratory status of this population is important as a prelude to possible conservation action there; if the population is non-migratory, installation of barriers to invasions by brown trout, should they ever enter Philomel Harbour, would be a practicable and wise precautionary measure. It is urgent to better understand the complementary distributions of zebra trout and brown trout, especially: 1) more widely in Philomel Harbour; 2) in West Falkland south of Fox Bay; and 3) in Lafonia, especially eastern catchments draining into Choiseul Sound; 4) the west coast of Lafonia; 5) the many unstudied lakes and ponds.

Possibly the single most important zebra trout population is in North Sulivan Lake (Fig. 1); migratory behaviour by zebra trout makes it difficult to protect this population from invasion by brown trout, via the sea, since any measure preventing invasion by brown trout would probably exclude zebra trout. The status of this population should be determined - its distribution, abundance, and migratory status.

Data are needed to form a baseline for monitoring the spread of brown trout. While the 1999 survey greatly increased knowledge of fish faunas of Falklands' waters, this should be regarded as a foundation upon which to build, rather than a task completed. There remain numerous waters that were not sampled or which were inadequately sampled.

There needs to be education of the people of the Falkland Islands about the biodiversity significance of zebra trout; inclusion of zebra trout amongst threatened species featured on Falkland Islands postage stamps was a useful move in this direction; additional actions are needed on a continuing basis to give the fish 'iconic' status similar to that held by Johnny rook, steamer ducks, albatrosses, and penguins. It would be advisable to institute statutory prohibition on deliberate release of brown trout into any waters they do not already inhabit, and to seek support for this measure from managers of brown trout fisheries and groups interested in angling for brown trout.

Conservation issues for Falklands minnow
Unlike many other galaxiids, the Falklands minnow (known also in Australia, New Zealand and Chile/Argentina) seems able to survive co-occurrence with brown trout - even though there is some evidence for predation on minnows by trout in all areas of its broad distribution (McDowall, 1990). Minnow and brown trout do coexist in Falklands streams, though we found this to be true at only 11 of 146 sites. However, many sites where only brown trout were present may have been upstream beyond the inland penetration of minnows. Moreover, many sites that had minnows but no brown trout were outside the range of brown trout in the Falklands (isolated ponds, Philomel Harbour and Lafonia catchments). While we know of no claims that minnow suffer seriously from presence of trout, study of the relationships between the two species seems desirable. Even in other countries where the species co-occur (Australia, New Zealand, Chile, Argentina), little is known of their interactive ecology. Moreover, although we collected no quantitative data, it was our subjective impression that Falklands minnow were rarer at sites with brown trout, and that minnows there tended to be over-represented by larger size classes. This may indicate trout predation on small minnows.

Acknowledgements
The November 1999 survey of Falkland Islands freshwater fishes was funded substantially by National Geographic Society, Washington D.C., U.S.A. and the Shackleton Scholarship Fund, Falkland Islands; additional support was received from New Zealand's National Institute of Water and Atmospheric Research, Falkland Islands Government Department of Environment and Planning (Mr T. Eggeling), and Falklands Conservation (Ms R. Ingham and Dr. A. Clausen), Stanley, Falkland Islands. We also gratefully acknowledge unstinting support of people of the Falkland Islands, too numerous to mention here, and who provided accommodation, meals, vehicles, guidance around the landscape, information and encouragement. Claude Renaud, Canadian National Museum, Ottawa, provided information on the Gorham fish collections. This work was undertaken during the first author's tenure of a Royal Society of New Zealand James Cook Research Fellowship. Supportive colleagues on the visit were Richard Allibone, NIWA, and Lindsey Chadderton, Department of Conservation, both from Hamilton, New Zealand.

References
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Clark, R., Wilson, P., Simpson, N. and Nolan, R. 1994. Some recent earth science and ecological studies in the Falkland Islands. The Falkland Islands Journal 1994: 10-25.

Gorham, S. 1977. Notes on a collection of fishes from the Falkland Islands. The Falkland Islands Journal 1977: 43-52.

Ivanova-Berg, M.M. 1968. Discovery of the southern lamprey Geotria australis Gray in the Scotia Sea, near Georgia Island. Problems in Ichthyology 8: 138-141.

Jackson, P.D. and Williams, W.D. 1980. Effects of brown trout, Salmo trutta L., on the distribution of some native fishes in three areas of southern Victoria. Australian Journal of Marine and Freshwater Research 31: 61-67.

Keam, R. 1994. The impact of trout in Australian waters. Australian Trout Foundation, Victoria.

Lapsley, P. 1993. Alas, poor zebra. Salmon, Trout and Sea Trout, October 1993: 64-67.

Lapsley, P. 1999. One man's war. Falkland Islands Newsletter 75: 15.

Lever, C. n.d. Naturalized fishes of the world. Academic, London.

McDowall, R.M. 1968. Interactions of the native and alien faunas of New Zealand and the problem of fish introductions. Transactions of the American Fisheries Society 97: 1-11.

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McDowall, R.M. 1972. The species problem in freshwater fishes and the taxonomy of diadromous and lacustrine populations of Galaxias maculatus (Jenyns). Journal of the Royal Society of New Zealand 2: 325-367.

McDowall, R.M. 1988. Diadromy in fishes: migrations between freshwater and marine environments. Croom Helm, London.

McDowall, R.M. 1990. New Zealand freshwater fishes: a natural history and guide. Heinemann Reed, Auckland.

McDowall, R.M. 2000. Identity of the Smith of Galaxias smithii. The Falkland Islands Journal 7(4): 3-7.

McDowall, R.M. In press. Provenance and identify of Galaxias smithii Regan (1905) (Teleostei: Galaxiidae). Journal of Natural History

Nolan, C. 1993. The history of Falkland Islands trout. The Warrah: Newsletter of Falklands Conservation 4, 3 pp.

Oldfield, S. 1999. Biodiversity: the UK overseas territories. Joint Nature Conservation Committee, London.

Permitin, Y.E. 1977. Species composition and zoogeographical analysis of the bottom fish fauna of the Scotia Sea. Journal of Ichthyology 17: 710-726.

Potter, I.C,, Prince, P.A. and Croxall, J.P. 1979. Data on the adult marine and migratory phases in the life cycle of the southern hemisphere lamprey Geotria australis. Environmental Biology of Fishes 4: 65-69.

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Simpson, M.N. 1990. Freshwater ecology. Pp. 7-8 in The Cumbria and Lancashire Falklands expedition 1989. The Falklands Islands Journal 1990(5): 9

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Wilson, J. 1997. Sea trout and sea lions. Trout Fisherman, February, 104-107.

Figure 1. Geographic locations on Falkland Islands and distributions of fish species from 1999 survey.
A: Falklands minnow, Galaxias maculatus; B: Zebra trout, Aplochiton zebra; C: Brown trout, Salmo trutta
(numbers are sites sampled in October 1999; reverse-coloured numbers are sites from which each species was taken).

Reproduced from The Falkland Islands Journal 2001 (Vol. 7 Part 5) with kind permission of the Editor.

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