International Workshop on
Tropical Snappers and Groupers:
A
Summary of Findings[1]
D. Pauly[2], F. Arreguín-Sánchez[3], J.L. Munro[4], and M.C. Balgos[5]
Abstract
This extended abstract
provides the participants of the Workshop on Aquaculture of Coral Fishes and
Sustainable Reef Fisheries held in Kota Kinabalu, Sabah, Malaysia on 4-8
December 1996, with the conclusions of the International Workshop on Tropical
Snappers and Groupers held in Campeche, Mexico on 26-29 October 1993, as a
reference for further discussion. Three
expert working groups were convened in the Mexico workshop to discuss the
status of knowledge and identify the priorities for further research on
population dynamics and ecology, fisheries management, and biology and
aquaculture. The following briefly
summarizes their findings.
Population
Dynamics and Ecology
Age determination techniques based on the examination
of skeletal structures are reliable in areas where seasonal temperature
fluctuations exceed 3-4oC, though validation continues to be
important. Further research is needed
in areas where seasonal temperature differences are slight.
For estimation of von Bertalanffy growth parameters
from size-at-age data, the use of non-linear fitting techniques is recommended
over the use of linearizing transformation.
For long-lived organisms such as groupers and snappers whose growth
curves are highly variable, estimation of growth parameters from
length-frequency data should be undertaken only when L/F data include those of
small, fast-growing specimens. Both
ELEFAN I and SLCA may be used in such cases.
Growth parameter estimates, particularly when based on
unvalidated ages or on length-frequency data should be compared with previous
estimates in the same or closely related species using the growth performance
index f'. Growth comparisons can also be done using
auximetric grids where growth parameters can be obtained from the FishBase
CD-ROM.
The standard techniques for estimation of total (Z)
and natural mortalities (M) can be applied to groupers and snappers, though
some methods may fail because of sex changes and other particular
behaviours. Emphasis should be given to
methods for improving the estimation of M in marine protected areas (MPA);
estimation of Z using length-converted catch curves which explicitly account
for seasonal growth oscillations and individual growth variation; environmental
effects on M and on cohort strength including stock dislocations that may
result from global climate changes; using variable (age-specific or
length-specific) estimates of M and/or estimates changing with environmental
forcing in models requiring inputs of neutral mortality; and interrelationships
between estimates of mortality and of catchability, which are strongly affected
by gregarious behaviour.
Though the reproductive strategies of groupers and
snappers (batch spawning, sex reversal, spawning aggregations) are reasonably
well known, further research is needed on the interrelationships among sex
reversal, formation of spawning aggregations and population dynamics, as well
as their impacts on the location of spawning aggregations and nursery
grounds. As a priority, two aspects
were mentioned: early life history in relation to habitat protection and the
effects of fishing on spawning aggregations.
Ecological, especially food web
considerations
Further research on trophic interaction should be
focused on:
·
food consumption
estimates (for individual fish and for age-structured populations);
·
quantitative food webs,
constructed using ECOPATH or other approaches suitable for describing the
trophic role of groupers and snappers; and
·
models of diet selection
including opportunistic feeding and prey switching.
The differential use of habitat space by early life
stage, juvenile and adult groupers and snappers are generally well documented,
as is the use of artificial reefs.
However, further research is required on:
·
distinguishing the
aggregative role from the habitat-enhancing role of artificial reefs;
·
economic aspects of
artificial reefs, especially their cost/benefit ratios;
·
potential effects of
habitat degradation and/or loss on stock size and structure; and
·
the fractal nature of
habitats, i.e., the availability of suitable crevices/holes for the successive
live-stages of cohorts, especially in groupers.
The
techniques for the general characterisation of stocks, a priority subject for
some regions, are well known. Further
research on stock identification must be addressed using molecular genetic and
allozyme techniques to provide the information necessary to manage mixed or
locally discrete stocks, and to avoid stock collapse and losses of genetic
diversity.
The following recommendations focus on fisheries
management issues specific to groupers and snappers:
·
Consider the distinct
growth/mortality schedules and mode of reproduction, population structure, and
the fact that most grouper and snapper fisheries are multispecies fisheries, in
developing fisheries management plans and policies concerning groupers and
snappers
·
Identify and quantify
sources of fishing mortality, including cryptic mortality due to the passage of
undersized fish through the cod-end of trawls and to the bycatch in
non-directed fisheries
·
Statistically validate
population parameters which have been estimated with restricted data sets
and/or with inappropriate models, particularly those which do not account for
the peculiar mode of reproduction of groupers
·
Define management
strategies specifically adapted to groupers and snappers, such as marine
protected areas, seasonally closed areas, fishing quotas, minimum size
regulations and maximum size limits
·
Incorporate risk
analysis and bioeconomic considerations in management advice, whenever possible
Biology and Aquaculture
Discussions within this working group placed
particular emphasis on the need to develop biotechnology for the following
aspects of production:
·
improvement of water
quality for larval culture (mainly an engineering problem);
·
larval nutrition:
studies of nutritional requirements of larval stages, finding smaller prey for
small-mouthed individuals, and development of formulated feeds; and
·
improvement of
broodstock management and technology for grow-out to market size.
·
description of larval
development; and
·
description and
experimental evaluation of processes controlling sexual differentiation.
·
developing techniques to
control or minimise environmental pollution resulting from aquaculture
enterprises;
·
increasing exchange of
information among East Asian, American and European aquaculture groups, notably
via translation of key documents; and
·
Discouraging aquaculture
of non-native species, and hence the required introductions of exotics.
·
Identifying proximate
causes of adult sex change at multiple levels of causation: behavioural,
genetic, neuroendocrine and hormonal, with emphasis on collaboration with
aquaculture environments; relating adult sex change to processes controlling
initial sexual differentiation in juveniles;
·
Evaluating hypotheses
concerning the function of spawning aggregations, including measurement, at
several scales, of physical oceanographic characteristics, rates of predation
on adults and eggs, down-current trajectories of eggs, and fertilisation rates
at aggregation sites;
·
Describing internal
structure of aggregations, including mating structure and sex ratio;
·
Identifying aggregation
sex ratios at which sperms may become limiting; measuring fertilisation rates
of eggs; changing numbers of sperm released by males, and oocyte atresia and
rejuvenilisation under different sex ratios;
·
Identifying which
species spawn in aggregations, with greater attention to snappers for which
this phenomenon is not as well documented as for groupers;
·
Choosing species
carefully for detailed studies to produce quick returns on research effort;
using most accessible species with the greatest potential of providing answers
to critical questions, including presently non-commercial species.
·
Resolving the issue of
whether fishing is to be banned from spawning aggregation sites at least at
spawning times.
·
Setting aside reserves,
both for conservation and as reference communities for comparison with impacted
populations.
·
Addressing the large
issue concerning what controls population size in unexploited populations:
rates of settlement, predation, food availability and substrate limitation, if
any;
·
Addressing the issues of
extent of population self-recruitment; the ability of larvae to swim against
residual currents and to control position over substrates; larval survivorship;
transport mechanisms from the pelagic phase to reef settlement areas; and
factors influencing the timing and location of settlement.
Life history strategies
·
evaluating consequences
of possible fishing selection for genetically large individuals on size
structure and genetic diversity of population.
Compare heavily fished with underfished stocks;
·
basic descriptions of
age and growth rates, onset of maturity, and degree of plasticity of time of
maturity and sex change.
·
evaluating predation
mortality of all life stages, including identification of predators and
predation rate, and evaluating feeding habits of different life history stages.
The
latest threat
One
issue that has become important since the Workshop was held is the live grouper
and snapper trade to Hongkong, Taiwan and China in which the use of sodium
cyanide has been emphasised. The major
threat, though, is overexploitation, with large areas of Southeast Asia and the
South Pacific being successively depleted a threat to which an adequate
response has yet to be found.
[1] ICLARM Contribution No.1382; adapted from a paper written by the same authors published in an ICLARM Conference Proceedings entitled “Biology, fisheries and culture of tropical groupers and snappers.”
[2] Also International Center for Living Aquatic Resources Management, MC P.O. Box 2631, 0718 Makati City, Philippines; e-mail: [email protected]
[3] Present address: Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional, A.P. 592, 23000 La Paz, Baja California Sur, Mexico; fax 52(112) 25322; tel. 52(112) 25344/25366; e-mail: [email protected]
[4] Also International Center for Living Aquatic Resources Management, MC P.O. Box 2631, 0718 Makati City, Philippines
[5] Also International Center for Living Aquatic Resources Management, MC P.O. Box 2631, 0718 Makati City, Philippines