The IUCN/SSC Shark Specialist Group
Shark News 14: March 2002
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Lake Nicaragua revisited: conversations with a former sawfish fisherman
Matthew T. McDavitt
Diversity
In a series of articles spanning more than a decade, the late Dr. Thomas
Thorson chronicled the catastrophic decline of sawfish populations in Lake
Nicaragua. During his pioneering tagging study of bull shark movements
into the Rio San Juan-Lake Nicaragua system in 1966, he discovered that
largetooth sawfishes (Pristis perotteti) were remarkably abundant in the
lake. In 1970, the Nicaraguan government encouraged the development
of a targeted fishery to exploit the lake's rich elasmobranch resources. Two
companies and a processing plant were established in Granada, a town in
the northwest corner of the lake. By 1975, an estimated 60,000 - 100,000
sawfishes had been harvested (Thorson 1976). The meat was consumed
domestically and exported overseas; dried fins were marketed to the
lucrative Chinese shark-fin trade (Thorson 1982a).
By 1973, Dr. Thorson sounded the alarm that sawfish populations
were reaching critical levels, and that immediate action was required
to forestall the impending crash of the sawfish fishery (Thorson 1982a).
His recommendations went unheeded, and in the 1980's the industry
collapsed, and fishermen refused to target the now elusive sawfishes.
Faced with the reality that the once abundant sawfishes were now
functionally extirpated from the lake, the Nicaraguan government
instituted a temporary moratorium on targeted fishing for sawfishes
and sharks (Thorson 1982a). They hoped this would allow the sawfishes
time to replenish their stocks, beginning the slow process of reestablishing
healthy populations in the lake. Political upheaval in
Nicaragua during the 1980's precluded any reassessment studies of
sawfish populations in the lake. It remained unclear whether the ban
on targeting sawfishes had been effective. Had the sawfishes returned
to Lake Nicaragua?
A new survey
In the summer of 1998, I visited Lake Nicaragua to assist with a preliminary
survey of shark and sawfish populations initiated by Dr. William Raschi.
Guided by former shark fishermen who knew the best locations to find
these elasmobranchs, we set a series of longlines totalling 5,500 meters at
depths ranging from 2.4m - 37.8m. We had also planned to set a series of
gillnets, but our net vanished the first night it was set. No sharks or sawfishes
were caught during the brief survey. Conversations with local fishermen
confirmed that sawfish and shark populations have not recovered from the
devastating over-harvest two decades ago.
Interview on Ometepe
With the assistance of Alvaro Molina of the Estación Biológica de
Ometepe, I interviewed a fisherman who had participated in the
sawfish fishery. Eduardo entered the industry near the end of the
sawfish fishery; of particular interest are his assertions that he caught
substantial numbers of sawfishes during the 1980's, the decade when
the fishery collapsed and the temporary moratorium was eventually
enacted.
Q: What is your full name and occupation?
A: Eduardo Lanuza Diaz, fisherman.
Q: When did you become a professional shark fisherman?
A: In 1980, now I fish for tarpon (Tarpon atlanticus) and alligator
gar (Lepisosteus tropicus).
Q: How many sawfishes have you caught during your career?
A: During the 1980's I caught between 150 and 250 sawfishes
per week, fishing exclusively for sawfishes. There were three other
boats doing the same.
Q: Where in the lake can sawfishes be found today?
A: Between Ometepe Island (Maderas volcano side) and Zanate
Island, which is the deepest part of the lake.
Q: At what depth do you usually find sawfishes, and on what kind
of substrate?
A: 40 meters in depth, mostly on muddy bottoms.
Q: What type of gear do you use to catch sawfishes?
A: With gillnets laid out on the bottom of the lake.
Q: How many sawfishes are accidentally caught in your nets per
year now (1998)?
A: Between four and six sawfishes per year.
Q: Do you know anyone who has been injured catching sawfishes?
A: The animal can be very aggressive and has to be killed before
it can be handled. Sometimes they have to drag it to shore to kill it.
Injuries can occur when you drag it along the boat to kill it.
Q: If a sawfish gets caught in your nets, how do you kill it?
A: By hitting it on the head with a baseball bat type instrument.
Q: What do the sawfishes eat?
A: They eat small fishes at the bottom, the same kinds you caught
(cichlids). When sawfishes are in heat, they come to the surface to mate.
Q: Where can baby sawfishes be found in the lake?
A: In very shallow areas around Ometepe and Zanate Islands.
Q: How do you cure a sawfish snout?
A: Hang them from a tree to dry and the cut end is cured with salt.
Q: Do you think the ban on sawfish fishing has helped?
A: The population has not recovered from the overkill of the 1980's.
Conclusions
Lake Nicaragua is perhaps unique in the world. Nowhere else have
sawfishes been recorded in such densities (Thorson 1982a), the population
is even more remarkable because it exists in a lake. Dr. Raschi's brief
longline survey, in agreement with the opinions of local fisherman,
suggests that the government ban on targeted fishing for sawfishes and
sharks has been ineffective. While no longer subject to focused harvest,
sawfishes continue to be killed in gillnets set for other species. This
incidental capture has seemingly prevented any meaningful recovery of
elasmobranch populations in Lake Nicaragua. Unless substantial changes
are made to current fishing policy, it is doubtful that sawfishes will ever
return to their former abundance in the lake.
These observations are supported by examples of sawfish population
declines elsewhere in the world. Freshwater sawfishes (Pristis microdon) were
decimated in Lake Sentani, West Papua, Indonesia, by incidental gillnet capture
alone. In Florida, populations of smalltooth sawfish (Pristis pectinata) are just now
showing signs of slowing decline, only after gillnet fishing had been eliminated
from state waters for several decades (Colin Simpfendorfer, pers. comm.).
Sawfish populations are extremely sensitive to intensive gillnetting, regardless of
the species targeted. This factor must be considered carefully whenever habitat
is set aside for endangered sawfishes.
References
Thorson, T.B. 1976. Observations on the reproduction of the sawfish,
Pristis perotteti, in Lake Nicaragua, with recommendations for its
conservation. In: T.B. Thorson (ed.). Investigations of the
Ichthyofauna of Nicaraguan Lakes, pp. 641-650. Lincoln: School
of Life Sciences, University of Nebraska-Lincoln.
Thorson, T.B. 1980. La explotacion excesiva del pez sierra, Pristis
perotteti, en el Lago Nicaragua. ConCienca 7(1):11-13.
Thorson, T.B. 1982a. The impact of commercial exploitation on
sawfish and shark populations in Lake Nicaragua. Fisheries 7(2):2-
10.
Thorson, T.B. 1982b. Life history implications of a tagging study of
the sawfish, Pristis perotteti, in the Lake Nicaragua-Rio San Juan
system. Environmental Biology of Fishes 7(3):207-228.
Matthew McDavitt
6342 Hawthorne Terrace, Norcross, GA 30092, USA
Email: nokogiri@aol.com
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