Fishes population in Changuinola River are threatened

National Institute of Water and Atmospheric Research
PO Box 8602
New Zealand

13 February 2008

Dr .W. O. McLarney
Director, Stream Monitoring Program
Asociacion ANAI
San José
Costa Rica

Re: Listing of La Armistad World Heritage Site as a Site in Danger

You request my response to the assertion that “it is common knowledge” that the effects of impoundment “can be efficiently mitigated, guaranteeing the permanence” of diadromous species in the rivers of the region.

Based on my broad knowledge of diadromous fish, globally, and over more than 30 years of research on these fishes, the claim that the impacts of impoundment can be mitigated” is simply not credible. There are several reasons for this.

There has been substantial development of fish pass technology to assist the passage of large anadromous fishes like salmonids and shad, where there are major impoundments on river systems in both eastern and western North America, and also in Europe. However, firstly, it is well recognized that these fish passes are of only limited effectiveness, and intense effort has to be invested in facilitating passage by the fish, despite the expenditure of huge sums to design and construct fish passage facilities. In essence, they only work to a limited degree and much effort is invested in also facilitating passage by trucking of the fish past impoundments.

Secondly, and of much more importance, none of this technology is relevant to the passage of migrating amphidromous fishes which predominate in the rivers of Central America and the Caribbean. This is because the upstream migrating life stages of these fish are quite different from large, strong-swimming anadromous salmonids and shads. Amphidromous gobies, like those in the rivers of Central America, migrate upstream as small juveniles, usually less than 40 mm long; these lack powerful swimming and jumping abilities, and proven fish pass technology is inapplicable to the migration of these species. They achieve their upstream movement by climbing up wetted surfaces where dams impede migration. As far as I am aware, there is no seriously effective technology for assisting upstream passage by these fishes, and the assertion that the effects of impoundment can be efficiently mitigated is, to my knowledge, untrue.

Moreover, even if passage past impoundments can be achieved, which remains unproved and dubious, there remains the loss of very substantial distances of stream channel in which these fishes would customarily live as a result of the conversion of flowing river and stream channels, to near-stationary lake habitat so that the outcome of impoundment also generates the loss of substantial areas of aquatic habitat suitable for these fish species to inhabit.

I therefore suggest that ANAM, the Panamanian Natural Resources Authority is likely to be unable to provide an assurance of successful and efficient mitigation of the effects of impoundment on riverine fish faunas, and thereby meet its requirements for acceptable management or mitigation of environmental impacts.

R. M. McDowall
Fisheries Scientist (PhD, Harvard University; Fellow of the Royal Society of New Zealand)