Seamount benthic macrofauna off southern Tasmania: community structure and impacts of trawling

Published source details Koslow J., Gowlett-Holmes K., Lowry J., O'Hara T., Poore G. & Williams A. (2001) Seamount benthic macrofauna off southern Tasmania: community structure and impacts of trawling. Marine Ecology Progress Series, 213, 111-125.
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This study is summarised as evidence for the following.

	Action	Category
	Designate a Marine Protected Area and prohibit bottom trawling Action Link
	Cease or prohibit mobile fishing gears that catch bottom (demersal) species and are dragged across the seafloor Action Link

Designate a Marine Protected Area and prohibit bottom trawling

A replicated, site comparison study in 1997 of 14 seamounts south of Tasmania, South Pacific Ocean, Australia (Koslow et al. 2001) found that seamounts within a protected area closed to trawling tended to have different invertebrate community composition, more species and higher biomass of invertebrates, compared to shallow unprotected seamounts, but not compared to deep unprotected seamounts, after two years. Results were not tested for statistical significance. Invertebrate community composition appeared typically similar at protected seamounts and deep unprotected seamounts, but different to that of shallow unprotected seamounts (data presented as graphical analyses). Protected seamounts tended to have more invertebrate species (22 species/sample) and biomass (6 kg/sample) compared to shallow unprotected seamounts (9 species/sample; 1 kg/sample) and similar to deep unprotected seamounts (20 species/samples; 7 kg/sample). The low diversity and biomass at shallow unprotected were associated with the loss of coral substrate from intense trawling. In 1995, a protected area was established and closed to trawling. In 1997, invertebrates (including corals) (>25 mm) living on the seamounts inside (6 seamounts; 12 samples) and outside (8 seamounts; 22 samples) the protected area (peaks at approximately 660–1,700 m depths) were sampled using a dredge. Invertebrates were sorted into groups and weighed by groups. Shallow unprotected seamounts were heavily fished, but deep seamounts were only lightly fished.

(Summarised by: Anaëlle Lemasson)
Cease or prohibit mobile fishing gears that catch bottom (demersal) species and are dragged across the seafloor

A site comparison study in 1997 of 14 seamounts in the Indian Ocean, Tasmania (Koslow et al. 2001) reported that the number of fish species varied with historical levels of bottom trawling intensity but was also dependent on seamount depth. Data were not statistically tested. The total number of species of fish recorded/seamount was three for non-trawled seamounts, five for very lightly trawled (1–10 trawls), 12/for lightly trawled (11–100 trawls), seven for heavily trawled (101–1,000 trawls) and zero for very heavily trawled (>1,000 trawls) seamounts. In addition, the non-trawled and very lightly trawled seamounts were generally the deepest and therefore considered less likely to support high species richness. In January and February 1997, fish were sampled with longlines, traps and sleds across 14 seamounts off South Tasmania with peaks between 714–1,580 m depth (deployment numbers not given). The seamounts had been trawled at different fishing intensities and in 1995, a temporary protected area incorporating six seamounts with no or very low trawling was established in which the fishing industry agreed not to trawl for a 3-year period. Trawl samples were taken inside and outside the temporary protected area and across the different trawling intensities. Fishing intensity for the period 1988–1996 was obtained from fisher logbook records.

(Summarised by: Leo Clarke)