Conservation Fisheries, Inc.
Newsletter #3
December 28, 2000
Tagging the rare boulder darter, Etheostoma wapiti
For quite a few years now, CFI has been
monitoring the status of the Endangered boulder darter, Etheostoma
wapiti. This rare darter is
only known recently from the lower Elk River in south-central
Tennessee and northern Alabama. Boulder darters are members of
the Etheostoma maculatum complex of darters. This group also includes the
coppercheek darter, E. aquali, known from the nearby Duck
and Buffalo rivers.
CFI has been participating in a captive propagation program for boulder darters for several years. Currently, propagated specimens are being used to augment the small boulder darter population now found in the Elk River. The captive propagation project has been conducted in concert with efforts to improve habitat in the Elk for these darters.
All members of the E. maculatum complex (as far as is known) cluster their eggs under slab rocks or in an angular crevice found between two rocks. The eggs are then guarded by the male until they hatch. Several females may contribute eggs to a single male's nest.
The Elk River is notably lacking in good spawning habitat for boulder darters. Most of the shoals are composed of pea-sized gravel with few of the larger-sized rocks suitable for boulder darters nest placement. For the past few years, the Tennessee Wildlife Resources Agency and the U.S. Fish and Wildlife Service, and other partners have been working to improve the situation by adding artificial and natural spawning substrate to portions of the Elk. One of our tasks has been to monitor the success of this endeavor.
The U.S. Fish & Wildlife Service asked us to mark the propagated boulder darters we release to augment the population. This would enable us to track their survivorship and movement in the river. We think we have found a great tool for doing this!
The ability to mark small,
non-game fishes with non-lethal, permanent, and readily
identifiable tags is a useful tool for the management of
captively propagated specimens destined for reintroduction
projects. This year, for the first time, we have experimented
with tagging various fish species using Visible Implant
Fluorescent Elastomer Tags produced by Northwest
Marine Technologies.
Northwest Marine kindly supplied us with sample kits to test
on our fishes. These are externally visible internal marks,
designed specifically for small fishes.
A small subset of fishes representing
several families was chosen to evaluate for tagging mortality and
retention. Fishes were injected with the Elastomer tags, a two
part, bio-compatible material that is injected just under the
skin of the fish. Elastomer material comes in a variety of
colors and fluoresces under a special blue light provided by the
company. This, coupled with the ability to mark fish in a variety
of body locations, offers numerous possibilities for
differentiating specific groups of fish.
Initially, fish to be marked were held in plastic shoebox
containers without anesthetization. Injections of the Elastomer
material were made using ultra-fine, 1/2cc, 29 gauge insulin
syringes. During later tagging efforts, fishes were anesthetized
using MS-222 at a rate of approximately 100 mg/l. Fishes were
recovered in another plastic shoebox containing well aerated
water from their aquarium system until we were confident they
were ready to be returned to their tanks.
In addition to the Elastomer tags, several subsets of fish
were tagged in a similar method using acrylic paints purchased at
a hobby shop. Other than the tagging material, handling was
essentially the same.
On 6/16/00, five boulder darters were tagged with the Elastomer material just under second dorsal fin. In addition to these, numerous other fish from several different fish families were tagged. We wanted to evaluate the safety and effectiveness of the tags, and document any groups of fishes that might be more sensitive to the treatment.
On 6/20/00, four mountain madtoms, Noturus eleutherus, and three boulder darters were tagged in a similar fashion using the acrylic paint. All fish from both treatments were monitored closely over the next couple of weeks. On 6/22, one of the mountain madtoms that had been tagged with the acrylic paint was found dead and on 6/26, one of the boulder darters tagged with the acrylic paint was found dead. At the end of one month, none of the fishes tagged with the Elastomer tags had died, and no additional losses were observed for the acrylic tagged fishes.
On 08/09 all remaining juvenile boulder darters were tagged
with red Elastomer tags. A total of 307 darters were tagged: 185
tagged on the left upper dorsal area (generally just below second
dorsal, sometimes near upper caudle peduncle); 122 tagged on the
right dorsal area. Most fish fell within a size range of 40-70 mm
TL.
On 08/21 these tagged boulder darters
were released into the Elk River. The first release was 183
darters into the Elk at Fayetteville, TN. These were tagged on
the left dorsal area, just beneath the second dorsal fin. A total
of 104 were released into the Elk at the I-65 bridge crossing.
These were tagged on the right dorsal area, just beneath the
second dorsal fin.
The I-65 site was revisited the following day. A total of 8 person-hours of snorkeling time was spent searching the area upstream of the bridge for boulder darters. Twelve were seen. Two of these were tagged individuals. Approximately 5.3 person-hours were spent beneath and just downstream from the interstate bridge. Four boulder darters, one of which was tagged, were seen at this locality.
On 09/18 both the Fayetteville and I-65 sites were revisited. At the Fayetteville site, four boulder darters were seen, all marked. At the I-65 site only the riffle above the bridge was sampled because of poor visibility conditions. However, in spite of bad surveying conditions, eight boulder darters were located. One was marked. Less than 1.5 person-hours were spent at each site.
Visible Implant Fluorescent Elastomer Tags have been shown to
be an effective method for tagging small, non-game fishes.
Mortality of tagged fishes was negligible. A cohort of
approximately 20 tagged boulder darters (tagged 08/09/00) has
been maintained at CFI to be incorporated as breeders in the
spring of 2001. As a result, we have been able to continue to
observe these specimens and follow the longevity and
effectiveness of these tags. At the time of this writing, there
has been no observed mortality and tags are still readily
visible. We will continue to monitor these fishes
indefinitely.
Although we had only a small sample of fishes marked with
acrylic tags, the mortality rate seemed to be distressingly high.
In addition, the marks were not as visible as the Elastomer tags
and these marks do not fluoresce under special lighting.
While searching for tagged fish in the Elk River, we were able
to clearly see the benefits of the fluorescent tags. When
illuminated with the blue underwater light, the marked fish were
readily identifiable, even in somewhat turbid waters. This
alleviated the necessity of capturing the fish to examine them
for marks. This would also enable observers with less experience
in identifying fishes to verify that they are indeed seeing the
target species.
Although we've observed fishes in the wild that we thought we had captively produced and stocked there, we've never before been able to document this without a doubt. Now, for the first time, we have the ability to observe captively produced boulder darters in their native habitat. It is encouraging to see that the captively produced individuals have integrated themselves into their surroundings and are behaving as would be expected of wild boulder darters.
Last year, several tons of slab-rock material was placed in
the Elk River at the I-65 bridge. This material was placed at
this site in hopes of improving habitat for this rare darter and
to provide potential spawning substrate. Despite difficult
working conditions (poor visibility), this year we observed more
boulder darters at this site than at any time in the past. The
vast majority of the individuals we observed were using the
imported rock. It is very encouraging to see so great an
improvement in numbers for a relatively small effort!
In the future, we hope to be able to use this marking technique, along with recapture (or observation of marked individuals) to allow for a better estimate of the numbers of boulder darters in selected areas in the Elk River. Marking these darters will also facilitate our ability to track movements of adult boulder darters in the Elk River. Captively produced individuals stocked in the future can be tagged with a different color, or on another area on their body. This may also enable us to determine longevity of wild boulder darters. All of this information will allow us to better manage the recovery of this rare darter.