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Deployment of Satellite Tags on Swordfish using the California Harpoon
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2009, FY 2008,
FY 2007, FY 2006
The main objective of this PFRP project is to utilize the local California
harpoon fishing fleet in order to deploy satellite tags on approximately
30 swordfish. This project will help researchers determine whether tagging
onboard a harpoon fleet vessel is a viable platform for long-term deployment
of pop-up archival satellite tags. Project researchers will also field-test
two different dart designs and determine the contribution of the pin
to premature release. Data results from the tags will provide insight
into swordfish movements and habitat use and will further investigate
the potential for using environmental variables and dive patterns to
augment location estimates. If the method in this pilot effort proves
successful, the use of these techniques may be expanded both nationally
and internationally - e.g., off of South America and Japan, where there
are also harpoon fleets.
Swordfish support an economically important international fishery that
landed a record 85,000 metric tons (mt) in 1995, up from 59,000 mt in
1985 (Folsom et al. 1997). Many Pacific Rim countries host active swordfish
fisheries, including Chile, Japan, Australia, several of the north Pacific
Island nations, and the United States and Mexico (Carocci and Majkowski,
1996). While Pacific populations presently appear to be stable (Uosaki
1998, Hinton and Deriso 1998, M. Hinton pers. com.), it is critical
that effective management be implemented to ensure that the Pacific
swordfish populations are not over-exploited, as were the populations
in the Atlantic.
management, whether focused on single species or at the ecosystem level,
requires knowledge of stock structure. Efforts expended to date to define
swordfish stock structure in the Pacific have lead scientists to propose
that there may be from one to as many as four distinct stocks (Nakano
1998, DeMartini 1999, M. Hinton pers. com.). Unfortunately, lack of
scientific data still precludes determining with confidence, which proposed
model is most accurate. Research methodologies such as temporal and
spatial patterns in catch rates, genetic analysis, and conventional
tag and release studies, have failed to provide a complete understanding
of stock structure in the Pacific. Genetic data suggest some differentiation
around the Pacific basin, but it has not been possible to clearly distinguish
between a single and multi-stock structure (Reeb et al. 2000). Consequently,
developing a management plan or predicting Pacific-wide population trends
becomes considerably more complex. To provide the understanding of Pacific
swordfish stock structure necessary for effective management, additional
information is essential, and the demonstrated difficulties using traditional
techniques mandate a new approach.
pop-up satellite archival tags (PAT) provide an innovative tool for
examining the movement patterns and temperature and depth preferences
of many pelagic species (Block et al. 1999, Lutcavage et al. 2000, Arnold
and Dewar 2001, Boustany et al. 2001), studies conducted to date with
swordfish have returned disappointing results. In the first three studies,
fish were captured for tagging using longlines. Problems encountered
in these studies included the following (1) non-reporting by the satellite
tag, when the tag is deployed but never transmits, (2) fish mortality,
when it can be demonstrated using depth data that the fish died shortly
after release, and (3) premature release, when the satellite tag releases
from the fish prior to the programmed date (Sedberry and Loefer 2001,
Brill pers. com., Dewar unpublished data). Premature release and non-reporting
can both result from mortality. Sedberry and Loefer (2001) report that
52% of the tags deployed either released early or failed to report.
In the study conducted by Brill, the non-reporting rates ranged from
50-70% - half or more of the tags never transmitted information to a
satellite. Dewar (unpublished data) found that while all tags deployed
from a longliner reported, five out of eight swordfish died shortly
following release. These results indicate that a different approach
is necessary if the potential of PAT tags are to be realized in studies
of swordfish. Tagging swordfish from a longline vessel has proven ineffective
alternative to the use of longline vessels to deploy satellite tags
on Pacific swordfish is the harpoon fleet operating out of Southern
California. It is, with out doubt, the time on the longline and handling
that result in high mortality rates and also likely contribute to the
low reporting rates. The ability to harpoon swordfish diminishes the
level of stress associated with tagging efforts by eliminating the requirement
to catch and handle the fish During the harpooning event the fish are
at the surface and often listless, perhaps from spending long periods
in cool water, which thereby allows for the actual harpooning event
to be relatively controlled. An experienced harpooner can target a small
area on the fish for implanting the dart. The location of dart attachment
is critical for successful tag deployments. In 2002 and 2003, seven
satellite tags were secured to swordfish for short-term deployments
using a harpoon (Dewar unpublished data). The goal of this study was
to obtain high-resolution data on habitat utilization and the tags were
programmed to remain attached for only 6 to 8 weeks. Of the seven tags
deployed, two tags never reported, three tags released early, two of
which swam below 1500 m (triggering the release mechanism, the RD1500),
and the remaining two tags remained attached for the programmed time.
While this study indicates the potential for using the California harpoon
fleet to deploy satellite tags on swordfish, the sample size is small
and additional efforts are required to develop methods to maximize deployment
durations and minimize premature release.
The objectives of this project are four-fold:
First, by working with harpoon fishermen based out of southern
California project researchers will determine the potential for using
the harpoon fleet to deploy pop-up satellite tags for up to 10 months.
Efforts to date have shown some promise, however, the sample size is
currently too small to make any meaningful conclusions.
Second, in an effort to develop methods for long-term attachments,
two different dart types will be tested. The first design will be similar
to that used by harpooners but smaller and made from nylon. The second
dart to be used is the nylon dart developed by Pfleger Institute of
Third, the pop-up satellite archival tags will be used to begin
to examine reports that two stocks of swordfish mix off California in
the summer. Movements will be inferred from the release and pop-up points,
at a minimum. The behaviors and habitats encountered will be determined
from the temperature and depth data transmitted by the tags.
Fourth, because the diving behavior masks the light signals at
dawn and dusk used to estimate longitude and latitude we will examine
the potential for using hydrographic features to estimate locations
between tag and pop-up. The goal is to determine the rough geographic
regions rather than a highly accurate geolocation, which is unlikely.
In the summer and fall of 2004 -2006 project researchers will work with
the California harpoon fleet to deploy a total of 30 satellite tags
on swordfish off the coast of California, 6 in 2004 and 12 each in 2005
and 2006. Tags will be deployed for periods of 6 and 10 months using
two different dart types. If successful, this will provide a method
for future researchers to obtain critical information necessary for
the management of swordfish in the Pacific, information that has been
impossible to obtain using other methods.
Project researchers will use the PAT4 pop-up satellite archival tag
produced by Wildlife Computers of Seattle, WA. These tags are equipped
with a number of mechanisms to reduce non-reporting. The incorporation
of a RD1800 will sever the leader and release the tag if the fish swims
below 1800 m. In addition, a programmed "premature release software"
will initiate transmission if the tag releases early and floats to the
surface or the fish dies and sinks to the bottom that is shallower than
the release depth of the RD1800. The new RD1800, may reduce premature
release associated with deep diving behavior and increase deployment
durations for swordfish. An additional feature of the PAT4 will help
to identify the cause of premature release. The PAT4 determines if the
pin is still in place or broken when premature release is initiated,
which will help to determine what improvements are necessary.
The tags will be deployed using methods and equipment typically used
for harpooning swordfish in the waters off California. Deployments will
occur between July and November working with two harpoon fishermen,
Lance Reinhardt on the F.V. Leslie Anne and Leon Bundy on the F.V. Fin
Cat. Both fishermen have been harpooning for over 20 years and assisted
H. Dewar in PAT tag deployments in 2003. Working with only two fishermen
will reduce the variation in tag deployments.
Tags will be deployed using one of the following two dart types: (1)
a nylon dart recently designed at the Pfleger Institute of Environmental
Research. This dart was used successfully in previous deployments on
swordfish as well as other species such as white sharks and ocean sunfish.
To date, only 2 of 15 tags deployed using these darts has released prematurely
for reasons other than mortality or the fish traveling below the 1500
m release depth of the RD1500 (Dewar unpublished data). (2) The second
dart will incorporate the design of the swordfish irons used in harpooning.
However, this dart will be smaller and will be machined out of nylon
to reduce weight. The two darts will be distributed randomly among deployments
with half used for each of the 6 and 10 month deployments.
One of the main objectives of this project is to determine the potential
for using the California harpoon fleet to deploy satellite tags for
periods of 6 to 10 months. The success will be indicated by the incidence
of mortality, premature release, pin breakage, and non-reporting. Comparisons
of retention rates between the two dart types will indicate which is
better suited for long-term tag attachments.
For the data recovered from the tags, efforts will focus on integrating
the behavioral and environmental data to determine the influence of
physical features on behaviors. The behavioral data will include the
maximum and minimum depths and temperatures as well as the percentage
time spent in different temperature and depth increments. The environmental
data obtained from the tag will include thermal profiles, sea surface
temperature and occurrence of fronts as indicated by shifts in sea surface
temperature between measurement interval. Polovina has recently developed
analytical methods to describe a water columns thermal profile through
the duration of the tracks using temperature and depth data collected
by the PAT tags.
efforts using the behavioral and environmental data will explore the
potential for improving location estimates between tag deployment and
pop-up. The objective is not to obtain a precise latitude and longitude,
but to determine a general oceanographic region visited by the swordfish.
It should, for example, be possible to determine whether swordfish from
the eastern Pacific visit waters off Japan or move to the southern hemisphere.
The environmental information that will most likely prove useful includes
the thermal profile of the water column, the presence and characteristics
of fronts, and sea surface temperature.
for this 3-year project estimated to be available mid-2005.
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