 |
 |
|
|
To
produce a plan for the conservation and management of genetic resources
in European lobster fisheries taking into account natural population
diversity, extant industry practices, previous and current enhancement
activities, and the future potential for farming and or ranching
|
|
|
The
degree of differentiation seen in the European lobster is
compatible with all populations having been established from
a common refuge after the end of the last Ice Age, i.e. within
the past 15,000 years. There is no evidence of a separate
Mediterranean refuge. The low level of genetic differentiation
observed reflects the relatively short time since the populations
were established post-glacially (<3,000 generations) and not
a high level of gene flow. Overall the data suggest that the
European lobster comprises a large number of discrete populations
with very limited genetic exchange among them. Such an island
population structure is not surprising given low movement
after benthic settlement and several possible mechanisms that
prevent larval dispersal. Within populations, genetic change
(of essentially neutral alleles examined) has occurred to
a greater or lesser extent as a result of genetic drift. However,
with the exception of the examples noted above, most populations
are sufficiently large that the rate of frequency change effected
by drift is relatively low. Large in the genetic sense means
effective population sizes more than several thousand (i.e.
census population sizes >10,000) and does not imply large
from the standpoint of exploitation. With the possible exception
of the Aegean, there is no evidence for a metapopulation structure
in any of the areas of high sampling density, although the
existence of such a structure in other parts of the range,
where only a few samples were obtained, cannot be excluded.
The management importance of recognising an island population
structure is that, if over-harvesting occurs, the stock will
not be replenished by recruitment from elsewhere in a meaningful
time period. Thus European lobster management should be based
on local populations rather than on broader metapopulations
as recently favoured by fisheries ecologists. Delimitation
(i.e. what is the geographical extent) of a local stock is
not straightforward and needs to be based on a combination
of biological, hydrographical and genetic information.
|
|
|
 |
| Although
the overall level of genetic differentiation among European lobster populations
is low this does not mean that important inter-population adaptive genetic
differences are absent. Thus it is likely that lobsters living at the limits
of environmental tolerance for the species (e.g. northern Norway, Morocco,
Aegean) have adapted to some degree to local conditions as indicated by
differences in life history characteristics. Experimental breeding studies
indicate that significant fitness-related genetic differences occur even
between populations some 25km apart. The aim of this study was to look at
population structure and it is not possible to make conclusions about adaptive
differences among populations from differences in the essentially neutral
markers used. Even low levels of selection acting on an allele will result
in changes several orders of magnitude faster than neutral allele changes
by drift. Thus little or no detectable change may occur between two populations
for microsatellites but they may have different alleles at loci involved
in fitness traits. For example, no significant differences in microsatellite
frequencies were found between a reference sample of adults collected in
1991 prior to enhancement at Kvitsøy and fertilised eggs, of both ranched
and wild parents, collected in 2000. The fact that genetic change was not
detected for microsatellites, does not mean that functional gene changes
have not occurred due to ranching. Indeed the experimental comparison of
survival of wild and hatchery juveniles indicates that such changes have
taken place. In spite of the often-misleading information to the contrary,
molecular markers are of limited value in identifying conservation units
among allopatric postglacially-established populations since there is unlikely
to be a correlation between neutral and adaptive gene evolution. The main
use of such neutral markers is to identify reproductively isolated units,
inbreeding or outbreeding, phylogeographical relationships, and, most important
of all as far as microsatellites are concerned, parentage. |
|
| Further
detailed studies are required to determine the extent to which adaptive
differences occur among populations. In general it is not yet possible to
look directly at functional gene differences in natural populations. At
present this can only be done by experimental comparison of different families
and groups established under common environmental conditions from the embryo
stage, and using microsatellite profiling (as developed in this project)
for parentage identification. The European lobster is an ideal model species
for studying local adaptation. It occurs in a wide range of environmental
conditions and produces large numbers of offspring. Since it is relatively
easy to transport living females with attached fertilised eggs it is possible
to examine survival and other fitness traits of individuals from two populations
under reciprocal environmental conditions. Such movement is at best extremely
difficult for fish and many other marine organisms. It is also possible
to carry out experiments with lobsters under relatively natural conditions
making use of natural enclosures or lobster pounds as in this project. |
|
| Until
further experimental studies are undertaken, it is recommended that the
precautionary principle be applied to movements of lobsters for enhancement
purposes, with movements being confined to local areas. Certainly, northern
Norway and the Aegean should be protected from introductions. Where enhancement
is necessary due to low stock levels, local hatcheries should be established,
providing juveniles based on local stock, rather than larger 'centralised'
hatchery facilities. This use of local stocks is also preferred in order
to reduce disease risks. However, the low level of gene flow suggests that
lobster culture can be carried out in areas where native populations are
absent without adverse genetic impact. |
|
| Genetic
tagging should be considered to measure the success of all enhancement (ranching)
programmes as well as being applied to measure the success of V-notch female
release programmes, and other management schemes of hitherto un-quantified
benefit. If full life cycle culture of lobsters is undertaken there is considerable
scope for selective breeding. The recent improvements in aquaculture techniques
and the renewed interest in lobster enhancement and farming demonstrate
a growing potential for this. In that context, microsatellite markers in
parentage analysis for selective breeding of lobsters may represent one
of the most important factors for future economical success. |
V-notch on berried female |
|
|