Robert Cook, Paul Humphries, Ben Gawne, Helen Gigney, John

Robert Cook, Paul Humphries, Robert Cook, Paul Humphries, Ben Gawne, Helen Gigney, John Ben Gawne, Helen Gigney, John

Hawking, Daryl Nielsen, Garth Hawking, Daryl Nielsen, Garth Watson, Adam Richardson, Watson, Adam Richardson,

Luciano SerafiniLuciano Serafini

Natural Heritage TrustNatural Heritage Trust

Habitat patches

Habitat patches

Results from previous workResults from previous work

• Fish and shrimp larvae occur predominantly in slackwater habitats (Alison King’s PhD 2002 & Campaspe Flow Manipulation Project)

• Abundance of minute prey, refuge from current/predators

• Lowland River Project abundant microfauna• Slackwater habitats affected by irrigation

releases

Low flow recruitment Low flow recruitment hypothesishypothesis

• Some fish breed and recruit during warm, low flow period

• In backwaters and slow or still littoral habitats• Concentration of prey during declining flow• Epibenthos may be far more important than

pelagic prey (Observation)• Low flow period may enable development of this

prey source(Humphries, King and Koehn 1999)

An experiment

• Hypothesised:– that releases during the normally low flow

time may make conditions unfavourable for species which breed during this time and which utilise slackwater habitats as nurseries

• Experiment: to alter hydraulic conditions within slackwaters and measure response

Year 1 & 2 Year 1 & 2 -- AimsAims

• To determine the effect on fish and shrimp abundance and species composition– of an increase in the current speed through

slackwater habitats: thus ‘destroying’slackwaters

– of stopping the current through flowing habitats: thus ‘creating’ slackwaters

• To assess if the density of microinvertebratesand macroinvertebrates is affected by altered hydraulic conditions and may explain changes in fish and shrimp

• To assess if primary production and decomposition is affected by altered hydraulic conditions and may explain changes in fish, shrimp, micro and macroinvertebrates

Year 1 & 2 Year 1 & 2 –– Aims cont.Aims cont.

1. 1. ‘‘DestroyingDestroying’’slackwatersslackwaters 2. 2. ‘‘CreatingCreating’’ slackwatersslackwaters

Slackwater

Slackwater

Barrier ‘Destroyed’slackwater Barrier

‘Created’slackwater

Control slackwater Control flow

Destroying a slackwater

Creating a slackwater

Natural (control) flow

Natural (control) slackwater

Results: Current velocity

01234567

01234567

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Velocity (m s-1)

Freq

uenc

y

Destroyed s/waterDestroyed s/water

Control flowControl flow

Fauna flushed from Fauna flushed from slackwatersslackwaters

0

1

2

3

4

5

6

Experiment Control

Num

ber o

f fis

h df=6, t=1.92, p=0.05

Fish and shrimp species in Fish and shrimp species in samplessamples

• Fish–– Common carp, Common carp, CyprinusCyprinus carpiocarpio– Crimson-spotted rainbowfish, Melanotaenia fluviatilis– Carp gudgeons, Hypseleotris spp.–– Gambusia, Gambusia, Gambusia Gambusia holbrookiholbrooki– Australian smelt, Retropinna semoni

• Shrimp– Caridina mccullochi– Paratya australiensis– Macrobrachium australiense

0123456

0123456

1 2 3 4 5Sampling trip

Num

ber o

f fis

h

Total fishTotal fish

1. Control s/watervs

destroyed s/water(p<0.05)

2. Control flowvs

created s/water(p<0.01)

Control s/water

Destroyed s/water

Control flow

Created s/water

Fish species

Destro

yed

slack

water

Created

slack

water

Contro

lflo

w

Contro

lsla

ckwate

r

050

100150200250300 Gudgeon

Rainbow smelt redfinGambusiaCarp

CaridinaCaridina mccullochimccullochi

0.1

1

10

100

0.1

1

10

100

1 2 3 4 5

Log

num

ber o

f shr

imp

Sampling trip



2. Control flowvs


ParatyaParatya australiensisaustraliensis

0.1

1

10

100

0.1

1

10

100

1 2 3 4 5

Sampling trip

Log

num

ber o

f shr

imp



2. Control flowvs


Zooplankton Zooplankton –– year 1year 1

0

100

200

300

400

0

100

200

300

400

1 2 3 4 5

Den

sity

of z

oopl

ankt

on p

er L 1. Control s/water

vsdestroyed s/water

2. Control flowvs

created s/water

Sampling trip

Zooplankton – year 2

1 2 30

50100150200250 2. Control flow

vscreated s/water

Sampling trip

050

100150200250 1. Control s/water

vsdestroyed s/water

Primary Production

0123456

gCm

-2da

y-1

1. control s/watervs

destroyed s/water

0123456

2. control flowvs

created s/water

1 2 3Sampling trip

Macroinvertebrates

0100200300400


destroyed s/water

0100200300400

1 2Sampling trip

2. control flowvs

created s/water

All biota

Destroyed slackwater

Created slackwater

Control flow

Control slackwater

Stress: 0.16

Year 1 & 2 -summary • Fish are flushed from slackwaters by increased

flows• Fish and shrimp abundance greater in both

control and created slackwaters• Primary production not different between flow

types• Macroinvertebrate density higher in flow• Fish and shrimp abundance maynot be

explained by density of prey - conflicting• Hydraulic environment

shrimp macroinvertebratesconsumer microinvertebrates

fish & shrimplarvae

fish

birds

algae

macroinvertebratespredator

fish

prawn

macroinvertebratesconsumer

macroinvertebratespredator

algae

Habitat patch food websSlackwater Flow

Year 3 - Aims

• In progress• Succession - determine how rapidly the

function and biotic communities develop in slackwaters once state altered from flow to slack

• Assess how the function and biotic communities develop through time

Snag racks

The tanks

Summary

• The nature of slackwater areas altered by irrigation releases

• Distinct biotic communities exist in slackwaterand flowing habitats – food webs

• Hydraulic nature of a habitat appears to be driving habitat use– Primary production not different between habitats– Microfauna (larval fish food) – evidence conflicting

Summary – continued

• Slackwaters are important rearing habitat for fish and shrimp

• Fish are flushed from slackwaters by increased flow

• Altering the hydraulic nature of a habitat will alter the biotic communities– Destroy important rearing habitats– Loss of species which rely on slackwaters

Management implications

• Slackwater habitats need to be maintained over the late spring to early autumn period– Manipulate flow release strategies– Instream structures to create slackwater

areas

Management implications

• Information on how to manage flows -short and long term flow variations and seasonally:– maintain diversity of habitat patches– maintain river function– recruitment of fish and shrimp– maintain food web structure– maintain diversity

Management implications – cont.

• Rehabilitation - potential for in-steam structures to create slackwater patches when summer flows cannot be manipulated– improved fish and shrimp recruitment– maintain habitat diversity

Documents

Robert Cook, Paul Humphries, Ben Gawne, Helen Gigney, John