Download Olaf Weyl, Rhodes University - Tulane University Biodiversity

Freshwater fish
research and conservation
in the Addo Elephant
National Park
Olaf Weyl et al.
Department of Ichthyology and Fisheries Science,
Rhodes University, South Africa
Graham Traas (MSc)
Henning Winker (PhD)
Ernst Swartz (SAIAB)
Olaf Weyl (PI)
Phillip Weyl (Hons)
Tony Booth (RU)
Bruce Ellender (MSc)
Jim Cambray (Albany Museum)
Tim Andrew (EFA)
Anton Bok (Fishways)
Mpho Ramoejane (MSc)
Addo Elephant National Park
•Proclaimed in 1931
•360 000 ha mega-park.
•120 000 ha marine reserve.
AENP-Goals
Conserve a representative sample of
Eastern Cape ecological patterns and
processes.
Manage the park to ensure the long term
persistence of biodiversity
Reduce external pressures
(inappropriate land use, illegal resource
use, impacts of invasion of alien biota)
Addo Elephant NP
 Includes 5 of South Africa's 7 biomes.
 One of the densest African elephant
populations on earth.
 Unique flightless dung beetle.
 Incorporates the largest coastal dune
field in the southern hemisphere.
 Big Seven, (elephant, rhino, lion, buffalo,
leopard, southern right whale and great
white shark).
 Protects the world's largest Cape gannet
breeding population on Bird Island.
Freshwater fish
 < 5% of South Africa’s rivers fall within
protected areas (Abell et. al., 2007)
 SAN-Parks funded research:
 Fish distribution and abundance.
 Determining critical conservation areas
 Not the global norm and exemplifies
South African recognition of freshwater
fish as conservation priorities.
East Cape redfin
Pseudobarbus afer
• IUCN listed (Endangered)
• Restricted to tributaries in
upper catchment areas.
• Preliminary results suggest
that maternal gene flow
among populations is not
uniform.
Goldie barb
Barbus pallidus
photo Roger Bills
• Addo Elephant NP
populations are likely to
be distinct from the
inland populations.
• Restricted to tributaries
in upper catchment
areas.
• Widespread but not
abundant
Chubbyhead barb
Barbus anoplus
• Recorded from one locality
in Addo.
• Mainstream species only
sampled in one locality.
• Reasons for decline
unknown but likely to
include competition with
and predation by alien
species.
photo Roger Bills
Moggel
Labeo umbratus
• Widespread includes
Orange River & east
flowing drainage.
• Widespread in Addo
Elephant NP.
• Mainstream species and
sampled in Sundays River
& Wit tributary.
Other
natives
• Gobies and
Anguillids are
widespread in
the park.
Indigenous species
Upper catchments of tributaries are key
conservation areas
Maintaining important catchment processes
and flow regimes in these areas is vital.
The Orange River
• Transfer of Orange River
water for irrigation since mid
1970’s
• Transformed the Sundays
River from a seasonal to a
perennial river.
• Flows governed by irrigation
demands.
Transferred Orange River fauna
Labeobarbus aeneus
Labeo capensis
Clarias gariepinus
Other imports of
unknown source
Mosquitofish
Common carp
Largemouth bass
Alien invasive fish
•Invasion is a downstream
process
•Upstream invasion
impeded by barriers.
Effects
• Evidence of Labeo umbratus X
Labeo capensis hybrids.
• C. gariepinus are very abundant
in the Sundays system.
– 80 anglers x 2 days fishing = 15
tons
– 100 kg per angler/day.
– Impact not quantified but small
barbs are now absent from Sundays
mainstream and Darlington Dam.
The Wit River (field trip site)
• Good example
• Typical upper catchment stream.
• Slagboom Dam has excluded Orange River
fish.
• Important site for L. umbratus to avoid
hybridisation.
• Dam was stocked with largemouth bass M.
salmoides by anglers.
• These have also invaded the river.
Invertebrates study site
Phil Weyl (Entomology student)
Sample site with no bass
Slagboom dam
2 biotopes sampled
Stones in current
marginal
vegetation/calm
pools
All invertebrates were sorted
and identified to family
Dendrogram of
Marginal vegetation:
the
cluster analysis
Largemouth
bass
absent
Stones in current:
Largemouth bass present
and absent
Marginal vegetation:
Largemouth bass
present
0
Physidae
Leptoceridae
Small
Ecnomidae
Hydropsychidae
Culicidae
Largemouth bass absent
Chironomidae
Medium
Psephenidae
40
Hydrophilidae
Largemouth bass present
Libellulidae
70
Coenagrionidae
p<0.05
Lestidae
50
otamonautidae
Gyrinidae
Dytiscidae
Nepidae
Belostomatidae
Notonectidae
Gerridae
Hydrometridae
n=9,
Aeshnidae
Gomphidae
Number of individuals
Marginal vegetation in calm pools
Mann-Whitney U-Test
Inconspicuous
Large/Conspicuous
60
30
20
10
Relative Fish abundance
3-pass depletion electrofishing in pools < 70cm deep
Downstream
P. afer density fish·m2
Upstream
P. afer density
Sampling site
Species
density
Other threats
• Water abstraction & alien vegetation.
• Connectivity between habitats altered.
• Predators especially effective when river flow is low.
• Genetic differences between P. afer populations
suggests that if we loose one population we cannot
replace it.
• Little understanding of competition between
indigenous and alien species.
Take home messages
• Main river is altered habitat and source
of invasion.
• Indigenous fish are threatened by alien
invasive fishes through predation,
competition & hybridization.
• Upper catchments of tributaries as key
conservation areas
– Maintaining important catchment processes and
flow regimes in these areas is vital (e.g. alien
vegetation removal).
– Stopping upstream invasion by alien invasive
fish is probably more important than ensuring
upstream migration of indigenous species.
The field trip
• 07:00 Departure from Grahamstown.
• 09:00 Meet me at Slagboom Dam
• Walk/drive to various sites on the river and meet
some of its inhabitants.
• I will show you various sites and point out
interesting features mentioned in the talk as we
walk up the system.
• Lunch somewhere along the river.
• 14:00 Addo main camp to see elephant,
warthogs, zebra and other mamals.
Things to remember
• Wear walking shoes the terrain is uneven.
• Bring binoculars if you have.
• Bring sunscreen, hat & a warm jacket (you now know the
Eastern Cape weather).
• Do not try to touch or attempt to feed any animals.
• Look out for snakes.
• Don’t collect any fish, we will be in a conservation area and
the fish populations are threatened.
• If you are unsure of anything, please ask.
Thank You!
Olaf Weyl, Department of Ichthyology and Fisheries
Science, Rhodes University, Grahamstown
6139,South Africa. [email protected]