|
|
DUXBURY REEF:
2005 - 2007
Final
Report
In 2005 and 2006, we conducted a
collaborative research study in the heavily fished area off Bolinas, California
to gather information about species targeted in commercial and recreational
fisheries. Our goal in this project was to combine the resources of fishermen
and university scientists to learn more about populations of nearshore fishes
and provide information that will be useful for policy discussions regarding
marine protected areas (MPAs) in the region. We worked with charter boat skippers
and more than 200 anglers to catch, measure, tag, and release fishes to gain
information about the distribution, abundance, and movements of recreationally
targeted species.
Over 5,500 fish were tagged and released over the course of 31 sea days in 2005.
In 2006, we allocated 8 sea days to fishing in the same fishing locations and
depths in 2005, as well as in deeper water habitats. In areas where fishing
effort overlapped and depth range was similar between years, we found a significant
difference in species composition. However, these data are difficult to interpret
because the sample sizes were greatly different in each year. In 2007, we plan
to fish in these locations again to increase our sample size and continue to
look at interannual variation in species composition.
Tag-recapture data were recovered from fish caught in the recreational and commercial
fisheries. When fishermen recaptured a tagged fish, they would notify us with
the tag number and coordinates of recapture. 80% of recaptured fishes moved
less than 1 nm from their release location, and 95% were caught within 5 nm
of release location. This provides good evidence that the majority of species
we caught have relatively small home ranges. There were some notable exceptions,
however, to this pattern of relatively localized movements. Our data indicate
that there may be some interchange between the populations of black and yellowtail
rockfishes at Duxbury Reef area and those at the Farallon Islands. There were
also four black rockfish caught over 300 nm away; these fish may have been advected
northward by northerly currents caused by the frequent and strong storms we
experienced in the winter of 2005-2006.
We also collected length and maturity data from the fish we sampled. The mean
lengths of almost all species were below the corresponding lengths at 50% maturity
for their species. (Maturity is defined as the size at which 50% of the fish
at that size are mature). These data indicate much of the catch in the study
area was comprised of individuals that are immature. The mean lengths of most
species that were caught in this study, however, have not significantly changed
since about 1995, a pattern similar to that generated from CPFV fisheries in
other areas in Central California. These observations indicate that the current
population size and age structures of fished species may be in equilibrium with
the current rate of fishing, and that almost all fish are caught before they
reach the size at 50% maturity. Additional research is necessary to determine
whether the whether or not the current level of fishing is appropriate to maintain
the population size and age structure of a species in a long-term sustainable
manner.
This project proved to be a successful collaborative research endeavor involving
commercial passenger fishing vessels, recreational anglers, and university scientists.
All people involved contributed greatly to the collection of scientific information,
and information was shared among participants and to a broader audience via
web-based communications. Based on the high catch rates experienced in this
study, and that have continued over the past few decades, we believe the Bolinas
Bight is a productive location for nearshore rockfishes. We plan to continue
our work to collect more data on changes on interannual species composition
and further investigate some of our hypotheses about the age and size structure
of these populations.
Participants: Kristen Green (MLML),
Dr. Rick Starr (MLML), Roger Thomas, and volunteer anglers
Funding: Pacific States Marine Fisheries
Commission
|
Kristen Green holding
a tagged brown rockfish.
F/V Salty
Lady.
Volunteer anglers
hard at work fishing.
|
