Subject: Abstract from MSc thesis - Status of the Harbour Porpoise in UK (fwd)

Mike Williamson (
Tue, 19 Jan 1999 14:34:32 -0500 (EST)

---------- Forwarded message ----------
Date: Tue, 19 Jan 1999 11:23:11 GMT
Reply-To: Marine Mammals Research and Conservation Discussion
Subject: Abstract from MSc thesis - Status of the Harbour Porpoise in UK


The following is the abstract from an MSc thesis which may interest
some of you. Copies are available from
Depending on the number of requests, I may have to ask for a
contribution to cover photocopying costs.

Hughes, K. 1998. The Status of the Harbour Porpoise (Phocoena
phocoena) in UK waters. Masters thesis, University of Greenwich,
London. March, 1998.


The aim of this study was to review the status of the harbour porpoise
(Phocoena phocoena) in UK waters.

The introduction reveals the
characteristics and life history of this species, establishes its=92
present range and reviews the changes in distribution  that have
occurred over the past century. Throughout Europe, evidence shows that
the harbour porpoise has declined in certain areas: the Baltic, the
Channel and the southern North Sea. Within its global range, there are
areas in which it has become extinct, such as the Sea of Azov and
areas where it is in danger of extinction, for example the inner
Baltic. The human activities which have been associated with such
changes and declines in the abundance of the harbour porpoise are also
considered. In the past declining prey stocks were implicated with the
reduced number of harbour porpoises in the northern North Sea in the
1980s and, in the Baltic, extensive hunting during the first half of
the century probably initiated the decline in this region. Presently,
by-catch in commercial bottom-set gillnet fisheries poses the most
immediate threat to the UK harbour porpoise and long-term threats
continue from marine pollution and climate change. In view of past,
and continuing, declines in certain regions, it is important to
understand the population structure of the harbour porpoise,
especially for management purposes, and current information regarding
our present state of knowledge is detailed. Data from porpoise
mitochondrial DNA analysis supports the view of there being at least
two separate populations round the UK: one in western Britain/Ireland
and the other in the North Sea. Within these, the Celtic Sea and
southern North Sea may be distinct sub-populations.

The following chapter reviews the distribution and abundance of the
harbour porpoise in UK waters. The information presented is intended
to highlight the important regions for the harbour porpoise and to
note any seasonal movements. This section is also important as a
reference to areas and places referred to in subsequent chapters. It
is evident that the harbour porpoise is not evenly distributed around
the UK, with greatest concentrations occurring off the west coast of
Scotland, the northern Isles and the northern and central North Sea.
Seasonal movements occur with harbour porpoises moving into coastal
waters during late spring and early summer, possibly to benefit from
shelter during the breeding/calving period. In the North Sea, there
appear to be two main groups of porpoises centred in the Danish and
Scottish zones during the winter months and late Spring, after which
they disperse and there is a general movement of porpoises into
coastal waters of eastern Britain.

 Chapter 3 covers the threats to the harbour porpoise, including
fisheries interactions, chemical and acoustic pollution, other forms
of habitat degradation (e.g. coastal development) and climate change.
These threats affect the harbour porpoise throughout its range and
have been reviewed several times in the past. By-catch, in
particular, is detailed   incorporating recent information on the
levels of by-catch and methods of control. Evidence from observer
schemes established on commercial bottom-set gillnet fisheries shows
that at least 7,000 and 2,200 porpoises are taken annually in the
central North Sea and Celtic Sea respectively. Research into reducing
by-catch has largely focused on the design of active acoustic alarms
but although initial trials of such devices in the Danish cod
bottom-set gillnet fishery were successful, long-term reduction of
by-catch is likely to come from gear and fishery modifications. This
work strongly advocates the United States approach in their
development of =93Harbour Porpoise Take Reduction Teams=94 as one from
which the UK should learn and implement in some form.

Legislation and voluntary agreements which concern the protection of
the harbour porpoise, or its habitat, are discussed in Chapter 4. The
EC Habitats Directive and The Agreement on the Conservation of Small
Cetaceans in the Baltic And North Seas (ASCOBANS) are the most recent
legal regimes which appear to protect this species, in addition to
other small cetaceans. Their implementation and progress is
discussed, and a critique of their effectiveness in protecting the
porpoise and its habitat is given. ASCOBANS appears to provide the
best chances for the protection of the harbour porpoise because it
was designed specifically for cetaceans and addresses the full
complement of threats, some of which, such as noise disturbance, are
almost unique to cetaceans. The Habitats Directive requirement for
Special Areas of Conservation for species (Annex II) and habitats
(Annex I) has not been implemented in respect to the porpoise. Whilst
recognising there are problems in managing sites for wide ranging
marine species, there are sites which appear to fit the criteria of
the directive and should be seriously considered for designation. The
sites are namely south east Shetland and Strumble Head-Ramsey Sound.

The previous chapter determines that the lack of, or inaccuracy of,
data regarded the harbour porpoise has been noted as one of the main
reasons for the apparent complacency with which the UK Government has
implemented some aspects of European Law. Chapter 6 reviews the
methods used to survey and monitor harbour porpoise populations,
since the precision of these methods has a direct influence on that
of the data, and critiques both visual and acoustic techniques. The
most recent method for estimating absolute abundance was utilised
during the SCANS survey and is a further adaptation of the
=93Independent Observer=94 method using distance-sampling techniques.
Whilst the field methodology is fairly straightforward, the analyses
of the data are complex and hence this is not a technique available
to all of us. The development of new software in the UK, expected to
be ready for trial in 1999, should simplify the analyses
considerably. Until the SCANS survey, cetacean distribution was
documented as relative abundance, mainly as a result of the work by
the Sea Birds at Sea Team and the Sea Watch Foundation. The chapter
concludes with an outline of the roles of the methods in future
management of harbour porpoise populations. Whilst baseline
population estimates are essential to management, large scale surveys
are probably needed infrequently since the time to detect change in
cetacean populations is fairly long, unless the population is
changing rapidly. Power analysis can be utilised to estimate the
desired frequency of surveys . Relative abundance estimates are
available for all months of the year and provide more ecological
insights of the cetaceans by providing information, for example, on
seasonal movements and breeding periods. The acoustic technique is
useful for monitoring presence or absence of porpoises in an area,
but without sightings data taken simultaneously, it provides little
real information about relative densities since our knowledge of the
acoustic behaviour of wild porpoises is scarce.

 The final chapter draws conclusions on the status of this species,
what is being done to protect it, and how the future looks for this
species in UK waters. A list of research and action recommendations.
These are aimed at preventing further declines of the harbour
porpoise in the very near future and on a long-term basis by
safeguarding their habitats and minimising all threats in an attempt
to maintain and restore harbour porpoise populations in regions where
they were once known to flourish. Immediate measures are needed to
limit by-catch even if it means temporary closures of fisheries.
However, this should be avoided by trialing by-catch reduction
methods immediately and in the long-term establishing effective
HPTRTs and implementing a schedule of closed seasons/areas and gear
modifications. An international approach has to be taken in order to
limit pollution and climate change and the UK must meet all targets
set out under the various legal regimes.

 Research programs, utilising stranded animals and making direct
field observations, must continue to further our knowledge of this
species. However, whilst research is essential for successful
conservation, it is recognised that the harbour porpoise , like other
wide ranging cetaceans , is extremely difficult to study and, on this
basis, conservation measures should also be taken in light of the
=93Precautionary Principle=94.


Kelly Hughes (MSc(Res))
Natural Resources Management Dept.
Natural Resources Institute
Chatham Maritime
ME4 4TB.
TEL: 01634 883090.
FAX: 01634 883517