Newswise — AMHERST, Mass. – Though bonefish are one of the most
sought-after tropical sport fish in the world, drawing thousands of
anglers to Caribbean waters every season, until recently the only
information scientists had about their spawning habits were anecdotes
and fish tales.
Now, University of Massachusetts Amherst
researcher Andy Danylchuk and colleagues from several other institutions
know far more about bonefish spawning habits after using ultrasonic
transmitters to tag and track bonefish movements off Eleuthera in the
Bahamas. Their results appear in an early online issue of the journal
Marine Biology. Results should help focus habitat conservation efforts.
It has been estimated that 30 percent of anglers who visit the Bahamas to cast for bonefish come from New England.
What
Danylchuk and colleagues found by tagging these popular sport fish is
that bonefish gather in schools of over 1,000 at pre-spawning
aggregation sites for a few days twice a month from October to May,
primarily around the new and full moon. At dusk, these large schools
begin to move offshore to the edge of deep abyssal waters, over 1,000
feet deep, very unlike the shallow flats were anglers normally encounter
them. There, as night falls, the fish spawn under cover of darkness.
“This is the first time movement patterns of bonefish to deep water
have been formally described,” says Danylchuk, an expert on coastal fish
stocks, the impact of angling and how to protect ecosystems. Although
surprising, this movement to spawn in deeper water makes some sense, he
adds. “One possible benefit of bonefish migrating to offshore locations
to spawn is that it increases the dispersal of their fertilized eggs,
especially with the high tides that happen with the new and full moons.”
Danylchuk and colleagues tagged 30 bonefish over two years, 60
in all, following them along with a few individuals previously tagged,
from 2007 to 2009. Another first for this research team was observing
behaviors such as porpoising, that is groups of fish leaping part-way
out of the water as they travel along, they believe are likely
associated with bonefish courtship. Danylchuk was amazed to see these
usually bottom-hugging fish breaking the surface as they moved away from
their nearshore aggregation sites.
“This new understanding of
bonefish movement and spawning aggregations has significant implications
for their conservation,” he says, because it establishes that
pre-spawning aggregation sites identified in this study were located in
transition areas between shallow coastal habitats and deep oceanic
waters, the very same places that humans find desirable for marinas and
tourism development.
“Knowing that bonefish are not residents of
shallow flats alone means that pre-spawning aggregation sites and deeper
reef habitats also need to be protected to ensure sustainable bonefish
populations,” he says.
Danylchuk is familiar to many as a result
of several appearances on the ESPN2 network series, “Pirates of the
Flats.” This research was supported by the Bonefish and Tarpon Trust,
the Patagonia World Trout Initiative, the Cape Eleuthera Institute and a
number of private donors.
