New Zealand Journal of Marine and Freshwater Research abstracts
The effects of spatial targeting of fishing effort on the distribution
of the Norway lobster, Nephrops norvegicus, on the Farn Deeps grounds,
northeast England
Michael C. Bell*
Jon M. Elson
Julian T Addison
The Centre for Environment, Fisheries &
Aquaculture Science
Pakefield Road, Lowestoft
Suffolk NR32 5DH
United Kingdom
email: j.t.addison@cefas.co.uk
*Present address: Goose Cottage, 4 Mobbs Cottages, Hall Lane,
Oulton, Lowestoft, Suffolk, NR33 0HT, United Kingdom.
Abstract Nephrops norvegicus is an essentially
sedentary species of lobster that forms the basis of valuable fisheries in
the northwest Atlantic and western Mediterranean. Fishers exploiting a sedentary
stock are likely to visit the most profitable (highest catch rate) areas
first. Such spatial targeting of fishing effort is likely to have important
consequences for stock monitoring and assessment. We used underwater television
surveys of Nephrops burrow densities on the Farn Deeps grounds, northeast
England, to describe changes in abundance and distribution between the beginning
and end of a winter fishing season. Above a threshold of c. 0.6 burrows m–2,
overwinter depletion increased with burrow density, consistent with fishing
effort being targeted at the highest densities. A simple simulation model
showed that this pattern of mortality is an expected consequence of spatially
targeted fishing behaviour. The model also predicted that there is decreased
spatial variability in density after fishing. An overall decrease in variability
was not evident from the survey data, but geostatistical analysis indicated
that there was “flattening” of the density profile along a north-south axis,
consistent with the dominant direction of commercial trawling. We concluded
that Nephrops fishers are able to find and exploit the highest densities
of their target species. A potential consequence is that catch per unit effort
(CPUE) data used to monitor trends in this stock potentially could mask declines
in stock abundance. CPUE might be more effective if analysed at finer spatial
scales, but this is not currently possible. In the absence of these fine
scale commercial data, fishery-independent surveys (e.g., underwater television)
are an important source of information on trends in stock abundance.
Keywords Nephrops norvegicus; Norway lobster;
spatial patterns; fishing; underwater television
M04054; Online publication date 29 July 2005 Received 27 February 2004;
accepted 6 December 2004
New Zealand Journal of Marine and Freshwater Research, 2005, Vol. 39:
1023–1037
0028-8330/05/3905-1023 © The Royal Society of New Zealand 2005
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