Fisheries problems go deeper - March 11, 2009

arrowtooth blog.jpgDeep sea fish may be in worse trouble than we thought. A
study published this week shows that the impact of fishing extends far
deeper than previously shown.

Using a huge collection of data from scientific trawls dating back to 1977,
David Bailey, of the University of Glasgow, and colleagues found fish
abundance fell significantly at depths from 800 to 2,500 metres. The maximum
depth for commercial fishing is around 1,600 metres.

Bailey originally reported his findings at the 2008 Ocean Sciences Meeting
in Orlando, Florida. Now the research has been published in Proceedings
of the Royal Society B.

"What we think is happening is fish are getting impacted if they live any
part of their life within the fishing grounds," Bailey told Nature News
earlier this week. "As a result they're not living to spread out into their
normal range."

Declines of some species are spectacular. Roundnose grenadier
(Coryphaenoides rupestris), which are targeted by fishing boats, declined in
abundance by 41% between 1977 and 2002. Polyacanthonotus rissoanus, which
are not targeted, dropped 77%.

Jennifer Devine, a fisheries scientist with the middle depth fisheries and
acoustics group at New Zealand's National Institute of Water & Atmospheric
Research, told Nature:

That the impact of fishing is seen deeper than fisheries operate, as
suggested by this paper, is not surprising. Many studies, mostly
terrestrial, have shown that trouble at the edge of a species range presages
trouble over the entire range.

The work by Bailey et al. (2009) is exciting because they have data that
cover most of the depth distribution of several deep-sea species from a
moderately long time period; this is rare. Most data collected on deep-sea
fishes either encompasses only part of their distributional depth range or
are from relatively short time periods. This paper provides more evidence
that deep-sea fisheries may have wide-reaching effects and are difficult to
manage sustainably.