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The Aquatic Exodus:
An Overview of Migratory Species in Jamaican Freshwater Systems
Prepared by
Ms. Kimberly John
Freshwater Conservation Specialist
The Nature Conservancy
&
Ms. Aisha Bailey
Volunteer - Freshwater Conservation
The Nature Conservancy
Introduction
Two mass migration events were recently reported in the Jamaican media (Daily
Observer, January 9th, 2006 and Jamaica Gleaner November 25th, 2005). Both involved
the natural migration of freshwater species from the sea to upstream areas in rivers.
Active migrations within river systems are not usually noticed or recorded by scientists
and locals in Jamaica (although they used to be a regular part of our rural culture).
Consequently, the migrations of freshwater gobies between November 2005 and
January 2006 sparked some temporary curiosity in the Jamaican public. What was not
publicly emphasised at the time was that these were not rare, unnatural or ominous
events. On the contrary the migration of many of Jamaica’s freshwater species from
upstream areas to the sea and vice versa is a regular natural occurrence and an
important facet of healthy, functional, aquatic ecosystems. This article aims to provide
general ecological information on migration in Jamaica’s rivers -a virtual aquatic
exodus- repeated over millennia across the island. This overview will hopefully provide
scientists and non-scientists
scientists alike with some insight into this fascinating aspect of
Jamaica’s natural history and set us thinking more critically about how our activities
impact freshwater ecosystems.
Figure 1: Front page of the Daily Observer, January 9th, 2005
2005- Spectators watch the upstream migration of
thousands of juvenile gobies ((Sicidium Plumieri) at the Yallahs fording.
Ecology of migration
Baker (1978), defined migration as the act of moving from one spatial unit to another. In
ecological studies many kinds of migrations are described; from accidental to nonnon
accidental, home range to navigational and latitudinal to altitudinal migrations. Seasonal
Se
migration -migration
migration that corresponds with changes in seasons
seasons- is the most common
interpretation of the term “migration”. Reproductive migration is a type of seasonal
migration in which animals move to other places or habitats in order to bear and/or
and/o raise
young. Relocation occurs generally in order to protect young from predators or other
environmental stresses or because the animal needs a different kind of habitat for that
particular life cycle stage. This article deals specifically with the reproductive migratory
patterns of Jamaican freshwater fauna.
Freshwater reproductive migration is classified based on the capacities of freshwater
species to cope with waters of varying salinities during specific stages in their life cycles
(McDowell 1988). Species that complete their entire life cycle within freshwater systems
(feeding and breeding grounds often being several kilometres apart) are known as
potadromous species. Of even greater significance to freshwater and evolutionary
ecology are those species whose life cycle takes place partly in freshwater and partly in
sea water. These are called diadromous species. Two groups are distinguished among
diadromous species. Anadromous species, for instance the well-known Atlantic salmon
(Salmo salar), reproduce in freshwater while the growing phase occurs in the sea.
Catadromous species, the American Eel (Anguilla rostrata) for example, migrates to
the sea for breeding and then migrate to freshwaters for growth and trophic purposes.
Jamaica’s Freshwater Migratory Fauna
This article is by no means an exhaustive survey of migratory species in Jamaican
rivers. However we will highlight some of the more prominent travellers in Jamaican
streams which have adapted to incorporate both freshwater and marine habitats into
their life cycles. Among these are fish such as mountain mullet, gobies and the
American Eel, and invertebrates for instance shrimp (janga) and the freshwater snail
locally called bussu.
Mullets
Figure 2: Young mountain mullet caught with hand
hand-held
held baskets while migrating upstream in Yallahs
River January 9th 2006. (K. John)
Agonostomus monticola (mountain mullet) is a ray-finned, perch-like
like fish from the family
Mugilidae (mullets). It is a pelagic fish that occurs in high
high-gradient
gradient freshwater streams in
neo-tropical
tropical regions such as Mexico, Central America and the West Indies. Mullets have
been recorded in the
e Swift, Buff Bay and Yallahs Rivers in Jamaica, although their
distribution is probably widespread. Aiken (1998) reports that Agonostomus monticola is
a relatively familiar species in Jamaican streams, but highlights the limited knowledge
regarding its biology
ology and ecology. Mountain mullets appear to be a catadromous
species migrating to the sea from freshwater to spawn. Several reports of mountain
mullets in other Caribbean rivers note the presence of spent individuals and the
absence of gravid females in the rivers coupled with the presence of larval forms in sea
with a simultaneous migration of spent individuals back to the rivers which suggest that
these mullets breed in sea water. It is postulated that the spawning period of the
mountain mullet coincides closely, but not always, with the rainy season.
Gobies
The upstream migration of Sicydium plumieri (Sirajo goby) (locally known as
‘suckstone’) in Great and Yallahs Rivers was recently captured in Jamaica’s print and
electronic media (figure 1) . Sicydium plumieri is a dermersal anadromous fish
belonging to the family Gobiidae (gobies), and subfamily Sicydiinae. They are
distributed mainly in the subtropical freshwaters of Central America and the West
Indies. S. plumieri post-larval migrations have been noted across the Caribbean. The
post-larvae are a local delicacy in Puerto Rico, Guadeloupe, Dominica and Martinique
where they are called “ceti” and in Jamaica where they are known as “fryers”.
Sicydium adults spawn in headwaters where females deposit their eggs on the
substratum under supporting structures such as boulders, stones and crevices or even
among vegetation. The eggs are attached to these structures with adhesive filaments.
These eggs are then fertilised by the male gobies which also protect them from
predation. After about two days the eggs hatch and the larvae drift downstream.
Spawning occurs in every month of the year but peaks during the rainy seasons when
the increased volumes of the river water carry the larvae downstream to the river mouth.
It is in these brackish or marine environments that the larval and post-larval stages
remain for one lunar month. At about the last quarter of the moon phase, post-larvae
appear along the sea shore as they approach the river mouth. The post-larvae then
metamorphose into juveniles.
Upon completing the juvenile stage the fish aggregate in large numbers and set out on
the journey back to the headwater regions of their ancestors. They normally move
inconspicuously below the water surface. However in areas where the channel is
constricted, - such as the Great River Dam or Yallahs Fording- massive shoals of these
young fish become visible as they congregate along the banks, walls and boulders.
These goby juveniles have specialized pelvic discs and tails that are used to climb
physical barriers, even outside of the water, in order to migrate upstream.
American Eel
The American Eel (Anguilla rostrata) is a catadromous fish, outstanding because of the
scale of its migration and the morphological and physiological changes that occur during
its life. A. rostrata is distributed across coastal areas and streams in the West Atlantic,
from Canada in the north to Trinidad in the south. It occurs in Jamaica, however its
specific distribution across the island is unknown (We have observed a child catching
an eel in upper Rio Grande with a simple hook and line). The eel’s life cycle begins with
spawning Sargasso Sea in the south-west Atlantic. Sexually mature eels migrate from
streams across their range for this annual mass spawning event between February and
April. It is assumed that adult eels die after spawning. The first stage in the life cycle,
called a leptocephalus, drifts and swims towards the continental shelf where it
metamorphoses into a “glass eel” because of its transparency.
Figure 3: Diagram of A. rostrata's
's life cycle. (taken from Communications Directorate
irectorate Fisheries and
Oceans Canada, 2000)
Upon reaching coastal areas, glass eels become pigmented and are known as
“elvers”. Many elvers swim upstream into rivers and streams in search of less crowded
or better quality habitat and replace eels that have already matured and left the river.
However, a proportion of the elvers remain in estuaries. Elvers mature into adults which
are called “yellow eels”. A. rostrata may remain in freshwater ecosystems for up to 15
years before sexual maturity and embar
embarking on the spawning migration.
Freshwater shrimp
Invertebrate freshwater species are also common migrants in Jamaican rivers. There
are several species of migratory shrimp in Jamaica (Hunte, 1978) usually belonging to
the Palaemonidae family. Macrobrach
Macrobrachium, commonly called Janga by locals, is one
migratory palaemonid genus which is relatively abundant in Jamaican rivers. These
organisms are generally subtropical and are very important for nutrition, recreation and
commerce throughout the Caribbean.
Figure 4: Macrobrachium spp in Rio Grande tributary. R. Love.
Macrobrachium spp. are anadromous spending most of their life cycle in freshwater
streams while larval stages reside temporarily in estuarine waters. Gravid females
remain in stream headwaters and release planktonic larvae which drift downstream to
estuarine regions. The larval stages remain planktonic for approximately 12 weeks after
which they begin to metamorphose into juveniles. The juveniles are benthic and migrate
upstream into freshwater. Hunte
nte (1980) and March et al (1998) noted that release and
hatching of eggs and larval drift occurred during the night so as to reduce the effects of
predation and hence decrease larval and juvenile mortality.
Bussu (Neritina punctulata)
The gastropod Neritina punctulata is yet another migratory invertebrate present in
Jamaican streams. These snails belong to the family Neritidae are quite abundant in
tropical regions such as Indo--Pacific
Pacific islands and the Caribbean. In the Caribbean
neritids have been found in Jamaica, Dominican Republic, Dominica, Costa Rica,
Guadeloupe, St. Lucia, St. Vincent and Martinique. In Jamaica N. punctulata has some
nutritional and economic value and is traditionally harvested in northern Blue Mountain
streams. However, its exploitation may be increasing with commercial harvesting in
support of events such as the annual Bussu Festival held in Portland parish.
N. punctulata has a similar anadromous migratory pattern to Sicydium and
Macrobrachium. The female snail lays her eggs in streams. The eggs hatch after 20-22
days and the planktonic larvae produced are carried to estuaries or the sea where they
develop into juveniles for approximately one year. These juveniles then migrate back to
the freshwater systems. Other observations also suggest that some neritids migrate
back to freshwater ecosystems as larvae, attach to substratum and then continue their
development. Several studies regarding the downstream and upstream migrations of
neritid snails have been conducted. However until recently mass or gregarious
migrations of snails have not been described. Schneider and Frost (1986) described the
mass upstream movement of juvenile neritids in a Costa Rican stream and it would be
interesting to investigate whether these kinds of migrations occur in Jamaican streams.
Conservation Implications of Aquatic Migration
Migratory aquatic species are highly dependent on the characteristics of the different
aquatic environments that support specific stages in their life cycle as well as the
ecological corridors that maintain connectivity between these habitats. In Jamaica, this
has implications for how we manage freshwater and marine ecosystems as well as the
estuarine areas in between.
The fact that there are important aquatic species utilising entire river systems and
estuaries highlights the need for a more holistic approach to the conservation of
freshwater ecosystems in Jamaica- beyond our attempts at controlling water pollution
and protecting upper watersheds. First and foremost we need information on the
distribution, ecology and status of migratory freshwater species. This remains a huge
data gap that can only be filled through focussed and systematic scientific research into
migratory aquatic species. We must also generate information on how activities that
have been shown to be detrimental to migratory species in other countries, such as
dams, affect our own fauna. However, Jamaica cannot wait for all the necessary
scientific information before taking conservation action. We can begin now, to manage
our freshwater ecosystems based on the available data and sound ecological principles.
For example, there is some evidence that dams and hydrologic stations are common
obstructions to migratory species in Caribbean rivers (Benstead et al 1999). Ideally we
should assess whether our old dams presently allow aquatic fauna to pass them on
their way upstream. However, at a minimum we should ensure that new dams and
fordings are constructed with passages and fish ladders. It appears that a significant
proportion of migrations that occur in Jamaican streams follow seasonal or even diel
(daily) patterns. Surely we can take this seasonality into consideration during sand
mining and river dredging. These seasonal patterns may also have implications for the
harvesting of freshwater biodiversity particularly in light of the increasing popularity of
“crayfish” (shrimp) and “bussu” festivals in Portland.
An interesting detail about migratory freshwater species that we have encountered is
the fact that all these species have evolved from families that are or were entirely
marine. Therefore the capacity of these populations to inhabit inland freshwater systems
and become entirely established is a fascinating evolutionary and biogeographical
phenomenon in the insular Caribbean. Hopefully in the future we will incorporate such
intriguing scientific information on aquatic migrations, and other ecological processes in
everyday affairs like collecting water, discarding waste-water, constructing dams and
diversions and harvesting freshwater animals for food and sport.
Acknowledgements:
We would like to thank Dr. Eric Hyslop of the Department of Life Sciences, University of
the West Indies, for the literature and information that formed the basis of this article
and particularly for his time in checking for accuracy. Thanks also to Dr. Karl Aiken of
the same department and to the many rural Jamaicans who have shared their
information on freshwater biodiversity over the years.
References
Aiken, K.A, (1998) Reproduction, diet and population structure of the
mountain mullet, Agonostomus monticola in Jamaica, West Indies.
Environ. Biol. Fishes 53:347-352, Netherlands.
Benstead, J.P., March, J. G., Pringle, C.M., Scatena, F.N. (1999) Effects of a
Low-Head Dam and Water Abstraction on Migratory Tropical Stream
Biota, Ecological Applications, Vol. 9, No. 2
Baker, R. Robin. 1978. The Evolutionary Ecology of Animal Migration.
Holmes & Meier Publishers, Inc. New York.
Bell, K. N. I. & Brown, J. A., 1995. Active salinity choice and enhanced
swimming endurance in 0 to 8-d-old larvae of diadromous gobies,
including Sicydium punctatum (Pisces), in Dominica, West Indies.
Marine Biology 121: 409-417.
Communications Directorate Fisheries and Oceans Canada (2000). Ottawa,
Ontario. www.dfo-mpo.gc.ca
Daily Observer, Front Page Caption, January 9,2006
Erdman, D.S., 1986. The Green Stream Goby, Sicydium plumieri, in
Puerto Rico. Tropical Fish Hobbyist, TFH Publication, New Jersey
Fievete. E. & Leguennec, B., 1998. Mass Migration of Sicydium spp.
(Gobiidae) in the Streams of Guadeloupe Island (French-West Indies)Implications for the Derivation Race of Small Hydroelectric PowerStations. Cybium 22: 293-296
Gross, M. R., Coleman, R. M., McDowall, R.M, 1988. Aquatic Productivity
and the Evolution of Diadromous Fish Migration.
Hepburn, Monique, “Migratory Eels Spark Renewed Interest”, Jamaica
Gleaner, November 25, 2005
Hunte, Wayne (1978) The distribution of freshwater shrimps (Atyidae and
Palaemonidae) in Jamaica
Society
. Zoological Journal of the Linnean
64 The Linnean Society of London.
Hunte, W., 1980. The Larval Development of the Shrimp. Caribbean
Journal of Science 15: 3-4
Keith, P., 2003. Biology and ecology of amphidromous Gobiidae of the
Indo-Pacific and the Caribbean Regions. Journal of Fish Biology 63: 831847
Larinier, M., 2000. Fish Migrations and Dams. World Commission on Dams
March J. G., J. P. Benstead, C. M. Pringle and F. N. Scatena, Migratory drift
of larval freshwater shrimps in two tropical streams, Puerto Rico. Freshwater
Biology 40: 261
Martin, T. R., 2004. Aspects of the Biology Neritina punctulata
(Gastropoda) in two Portland Rivers
Migration Basics. February, 2006. Online. Internet.
http://www.nps.gov/akso/ParkWise/Students/ReferenceLibrary/general/Migrati
onBasics.htm. National Park Service U.S. Department of the Interior
Pyron, M. & Covich, A.P., 2003. Migratory Patterns, Densities, and Growth
of Neritina punctulata Snails in Rio Espiritu Santo and Rio Mameyes,
Northeaster Puerto Rico. Caribbean Journal of Science Vol. 39, No. 3: 338347
Schneider, D. W. & Frost, T. M., 1986. Massive upstream migrations by a
tropical freshwater neritid snail. Hydrobiologia 137: 153-157
Contact Information
Name: Kimberly John
Email: [email protected]
&
Name: Aisha Bailey
Email: [email protected]
Mailing Address
The Nature Conservancy - Jamaica
Unit 5
32 Lady Musgrave Road
Kingston 5, Jamaica
(876) 978-0766