Impacts of Fishing Gear on Marine Benthic Habitats

Document Sample
Impacts of Fishing Gear on Marine Benthic Habitats Powered By Docstoc
					Impacts of fishing on marine benthic habitats
Michel J. Kaiser1, Jeremy S. Collie2, Stephen J. Hall3, Simon Jennings4, Ian R. Poiner5
of Ocean Sciences, University of Wales-Bangor, Menai Bridge, Anglesey, LL59 5EY, UK School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882, USA 3Australian Institute for Marine Science, PMB 3, Townsville MC, Queensland 4810, Australia 4The Centre for Environment, Fisheries & Aquaculture Science, Lowestoft Laboratory, Lowestoft, NR33 0HT, UK 5CSIRO Division of Marine Research, PO Box 120, Cleveland, Queensland 4163, Australia
2Graduate 1School

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

Demersal fishing gears
Beam trawl rigged for clean ground

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

Scale of disturbance and recovery rate
10 y 5y 1y 1 mo
walrus fishing hurricanes bait digging fishing anoxia Ice scour hurricanes Hydraulic dredging grey whales

Recovery time

eider

rays 1 m² 100 m²

tidal currents

1 day

macrofauna 10 mm² 108 m²

Patch size
© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

The importance of Connell‟s intermediate disturbance hypothesis
High

Diversity

Climax community
Grossly stressed community Low

Disturbances frequent Soon after a disturbance Disturbance large

Infrequent Long after a disturbance Disturbance small

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

WHAT CAN WE LEARN FROM EXPERIMENTS?

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

Infaunal responses to fishing disturbance
No. spp No. indiv. Shannon‟s H

___________________________________

Stable sediment unfished 67±3*** fished 31±3 Mobile sediment unfished 29±5 ns fished 27±5

335±18** 196±32 59±11 ns 98±27

29±2*** 15±1 21±4 ns 16±3

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

META-ANALYSIS
GEAR
Intertidal Dredging Scallop Dredging Intertidal Raking Beam Trawling Otter Trawling -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6

HABITAT
Gravel Muddy Sand

Biogenic
Sand Mud -0.9 -0.8 -0.7

LOCALITY
Eastern Australia Northern Europe East North America New Zealand South Australia -1.5 -1.0 -0.8 0.0

CLASS
Anthozoa Malacostraca Ophiuroidea Holothuroidea Maxillopoda Polychaeta Gastropoda Echinoidea Bivalvia Desmospongia Asteroidea Oligochaeta -1.4 -1.2 -1.0 -0.8 -0.6 -0.4

RESPONSE

RESPONSE

School of Ocean Sciences, University of Wales-Bangor

THE RECOVERY TRAJECTORY OF DIFFERENT HABITATS

5
mud/sand

0

sand
-5 0 100 biogenic 500

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

Limaria hians nests previously undredged 3 *
Photograph: Jason Hall-Spencer
-2

* * *

* *

* *

*

test plot control * * * *

Number m

2

1

0

before

before

win95

win96

win97

sum94

sum95

sum96

0 Pre-dredge

1

2 3 Time after dredging (years)

sum97

win98

4

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

ENERGY SUBSIDIES
Fishing can also alter habitat by inducing population changes in „habitat engineering species‟

starfish catch numbers log (starfish catch numbers)

6 5 4 3 2 1 0 -1 -0.5 0 0.5 1

p < 0.005

Log proportion seabed swept/yr

log (proportion of seabed area swept by beam trawls per year)

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

TESTING PREDICTIONS AT A REALISTIC SCALE

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

Legend

Figure 1.

Plymouth Sound

Low fishing effort. LOW EFFORT Area 2 - No trawling permitted, Areas 5 & 8 - Pots only all year. Medium fishing effort. MEDIUM EFFORT Areas 4 & 7 - Seasonal trawling permitted between 15th January & 1st July. High fishing effort. HIGH EFFORT Areas 1, 3 & 6 - Trawling all year round.

1 Salcombe
Pots all year
50o 16’N

2
Pots all year

8
Trawling Jan - July

7 6
4o30’W

4

5

Towed gear all year

3

4o 00’W

School of Ocean Sciences, University of Wales-Bangor

Area 5, 4 and 3
Mean biomass of selected species Fishing effort Med High 121 2 12 7 3 259 14 0 3 1

Low Hydroids Dead men‟s fingers Dog cockle Sea potato Psammechinus 720 1606 10 32 85

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

Legend

Figure 1.

Plymouth Sound

Low fishing effort. LOW EFFORT Area 2 - No trawling permitted, Areas 5 & 8 - Pots only all year. Medium fishing effort. MEDIUM EFFORT Areas 4 & 7 - Seasonal trawling permitted between 15th January & 1st July. High fishing effort. HIGH EFFORT Areas 1, 3 & 6 - Trawling all year round.

1 Salcombe
Pots all year
50o 16’N

2
Pots all year

8
Trawling Jan - July

7 6
4o30’W

4

5

Towed gear all year

3

4o 00’W

School of Ocean Sciences, University of Wales-Bangor

Gear restriction management regimes help to conserve larger, emergent seabed fauna

100 90 80 70 60 50 40 30 20 10 0 1

biomass curve

100 90 80 70

100 90 80 70 60 50 40 30

abundance curve

60 50 40

30

Low fishing disturbance
10 100

20 10 0 1

intermediate fishing disturbance
10

20 10 0 1 10

high fishing disturbance
100

Species rank

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

CAN WE IMPLEMENT MANAGEMENT SYSTEMS THAT ARE USEFUL IN A CONSERVATION CONTEXT?

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

-76 42.5 41.2
Latitude

-74

Longitude -72 -70

-68

-66 42.5 41.2
Latitude

39.9 38.6
Fishing Time 1998

39.9 38.6

1998
Fishing 37.3 hours/nm^2 Time blue <2 green 2-9 36.0 yellow 9-44 -68 -66 red >44

37.3 36.0 -76

-74

-72 -70 Longitude

School of Ocean Sciences, University of Wales-Bangor

-76 42.5 41.2
Latitude

-74

Longitude -72 -70

-68

-66 42.5 41.2
Latitude

39.9 38.6
Fishing Time 1999

39.9 38.6

1999
Fishing Time 37.3 hours/nm^2 blue <2 green 2-9 yellow 9-44 36.0 -68 -66 red >44

37.3 36.0 -76

-74

-72 -70 Longitude

School of Ocean Sciences, University of Wales-Bangor

Effects of large-scale fishery closure off the eastern coast of the United States - secondary benefits for scallops
60 Outside closed area 50

Number per tow

Inside closed area

40 30 20 10 0 10 30 50 70 90 110 130 150 170 Shell height (mm)

© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor

Conclusions
Areas subject to fishing with towed bottom gear are dominated by lower biomass organisms and have less surface structure Areas exploited using pot gear have high biomass communities with greater surface relief It appears that with the application of common sense we can “have our cake and eat it” Areas closed to towed fishing gear can still be exploited while conserving the environment
© School of Ocean Sciences, British Crown Copyright 1998

University of Wales-Bangor


				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:56
posted:8/3/2008
language:English
pages:23