Recent emphasis on linkages between essential fish habitat and fish stock productivity
has raised concerns about the management of fishing activities such as trawling, which
have the potential to impact fish habitat. Knowing specifically where and how
intensively trawl effort has occurred over time provides ecologists with the necessary
background for habitat impact and recovery studies, and provides fishery managers with
an assessment of how habitat conservation objectives are being met. The objectives of
this study were to (1) examine the extent to which the 2000 Pacific Fishery Management
Council footrope restriction has shifted and reduced trawl fishing effort on Oregon
fishing grounds, (2) to relate these changes in distribution to the benthic habitat type over
which they occur, and (3) to develop methods for enhancing fine-scale spatial review of
targeted fishing effort.
Density analysis of available trawl start locations provided a spatial and temporal
understanding of how fishing efforts increased and decreased in relation to habitat
distribution and fishery management actions between 1995 and 2002. Trawl effort
patterns exhibit significant inter-annual variability and patchy distribution. Areas of
increased fishing effort were still evident between years, despite an overall decline in
trawl tows across the time scale of this study. Tow end point locations for the years
1998-2001 were retrieved from manual logbooks for five reference sites located in the
proximity of rock habitat features. Trawl towlines were mapped from start to end point
and demonstrated a marked enhancement of fine-scale fishing effort resolution, with
increased ability to identify effort shifts over benthic habitat. Distinct spatial shifts in
fishing intensity (measured as km towed) away from rock habitat were evident at all
reference sites, with an average reduction of 86%. Some slight shifts into surrounding
unconsolidated sediments also occurred, indicating effort displacement as well as
reduction. Fishing intensity was calculated from commercial trawl and research trawl
survey towlines to achieve the most accurate assessment of fishing impacts and potential
habitat recovery areas. Research trawling intensity was less than 1% of commercial trawl
effort originating from the same sites. A brief comparison of Oregon vessel towlines and
California vessel towlines demonstrated similar targeted fishing patterns by both fleets,
except at one site.
Results indicate that the footrope restriction, in conjunction with associated landing
limits, was effective in protecting rocky habitats from trawl fishing impacts. Reference
areas were identified where essential fish habitat (EFH) recovery is likely occurring off
the coast of Oregon. Substantial regulatory changes continue in this fishery, with trip
limits and gear restrictions continuously adjusted. Continued monitoring and review of
spatial trawl data would assist in fishery management decision-making and assess
conservation objectives for depleted groundfish and associated habitats. Future research
should incorporate analysis of catch data and expand the review of trawl towlines for the
entire US West coast groundfish fishery. The trawl towline spatial analysis developed in
this work is a credible method for reviewing fishing effort at the scale of the fishery and
in relation to detailed habitat data. The research presented here provides an example of
how an interdisciplinary approach and critical assessment of data can work to resolve
marine management challenges. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32142 |
| Date | 13 April 2004 |
| Creators | Bellman, Marlene A. |
| Contributors | Heppell, Scott |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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