Jeremy Tiemann
Illinois Natural History Survey
>I am an ecologist working for the Water Research Commission of South
>Africa at the University of Cape Town. We are currently planning a
>study of three endangered fish species in the Olifants River to the
>north of Cape Town in the Western Cape, South Africa. There is little
>expertise in South Africa for studying threatened fish species and it
>is difficult to know which questions can be answered using non-lethal
>techniques.
>
>The three species we are interested in occur in very low numbers as
>result of the introduction of exotic fish species and damming -
>the Clanwilliam yellowfish, Barbus capensis, the Clanwilliam
>sandfish and the sawfine. However, management strategies to conserve
>these fish urgently need to be developed. Extremely low numbers and
>threatened status of these species makes this a difficult job. I am
>interested to know how fisheries biologists in the US have gone about
>acquiring information on aspects of life history of fish which are
>rare. Failing this, I would appreciate it someone could refer me
>to any other people or publications which may be able to help in this
>regard
>
>First of all acquiring information on age-growth, age at
>maturity, fecundity, survival at all life stages and recruitment,
>require killing fish. I would need to sacrifice a minimum of 100 fish
>per species in several age classes. Firstly I am not sure the present
>populations could stand this kind of sampling pressure, and secondly,
>but more realistically, I don't think we could catch that many fish
>over the 3 year project.
>
>Secondy, the fish are so rare and mobile that mark-recapture has
>proved almost impossible - in the last year and a half I have had no
>recaptures. Estimates of absolute abundance would not therefore be
>possible using this technique. To give you an inidication of the
>densities - in 18 gillnet hours of sampling on the mainstem of the
>Olifants River we caught two fish. Smaller fish are more abundant in
>the tributaries, but large adult fish in the mainstem are almost
>impossible to find. We don't even know where they are spawning, or if
>they have spawned at all in the last ten years.
>
>Combined with this is that there are is no historical data on these
>species apart from anecdotal information which suggests that they were
>originally present in the river in their thousands and would
>regularly migrate up the river to spawn in riffles of the middle and
>upper reaches. The presence of the Clanwilliam dam now prevents this
>and recruitment by the remaining fish is being severely impacted by
>introduced largemouth and smallmouth bass populations (which are now
>very abundant in the river).
>
>Unless I am missing something, I am almost inclined to believe that
>studies should be laid aside in favour of a programme to eradicate
>bass and restore habitat.
>
>Regards
>Bruce Paxton
-- Jeremy Tiemann Illinois Natural History Survey Center for Biodiversity 607 E. Peabody Dr. Champaign, IL 61820 Phone: (217) 244-4594 Fax: (217) 333-4949 /----------------------------------------------------------------------------- /"Unless stated otherwise, comments made on this list do not necessarily / reflect the beliefs or goals of the North American Native Fishes / Association" / This is the discussion list of the North American Native Fishes Association / nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word / subscribe, unsubscribe, or help in the body (not subject) of an email to / nanfa-request_at_aquaria.net. For a digest version, send the command to / nanfa-digest-request_at_aquaria.net instead. / For more information about NANFA, visit our web page, http://www.nanfa.org </x-flowed>