Does boat traffic cause displacement of fish in estuaries?
Estuaries are increasingly under threat from a variety of human impacts. Recreational and commercial boat traffic in urban areas may represent a significant disturbance to fish populations and have particularly adverse effects in spatially restricted systems such as estuaries. We examined the effects of passing boats on the abundance of different sized fish within the main navigation channel of an estuary using high resolution sonar (DIDSON). Both the smallest (100-300 mm) and largest (>501 mm) size classes had no change in their abundance following the passage of boats. However, a decrease in abundance of mid-sized fish (301-500 mm) occurred following the passage of boats. This displacement may be attributed to a number of factors including noise, bubbles and the rapidly approaching object of the boat itself. In highly urbanised estuarine systems, regular displacement by boat traffic has the potential to have major negative population level effects on fish assemblages.
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa. Electronic address: a.becker@saiab.ac.za.
Alistair
A
Becker
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa.
Alan K
AK
Whitfield
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa.
Paul D
PD
Cowley
Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen NO-7485, Trondheim, Norway.
Johanna
J
Järnegren
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa; Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen NO-7485, Trondheim, Norway.
Tor F
TF
Næsje
D000818:Animals; D017753:Ecosystem; D004784:Environmental Monitoring; D063366:Estuaries; D005399:Fishes / Q000502:physiology*; D011998:Recreation; D012767:Ships
Disturbance; Estuaries; South Africa; Urbanisation