Marine mammals' influence on ecosystem processes affecting fisheries in the Barents Sea is trivial
Peter J Corkeron
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Biol. Lett. (2009) 5, 204206
doi:10.1098/rsbl.2008.0628
Published online 6 January 2009
Marine mammals influence
on ecosystem processes
affecting fisheries in the
Barents Sea is trivial
Some interpretations of ecosystem-based fishery
management include culling marine mammals as
an integral component. The current Norwegian
policy on marine mammal management is one
example. Scientific support for this policy
includes the Scenario Barents Sea (SBS) models.
These modelled interactions between cod, Gadus
morhua, herring, Clupea harengus, capelin,
Mallotus villosus and northern minke whales,
Balaenoptera acutorostrata. Adding harp seals
Phoca groenlandica into this top-down modelling
approach resulted in unrealistic model outputs.
Another set of models of the Barents Sea fish
fisheries system focused on interactions within
and between the three fish populations, fisheries
and climate. These model key processes of the
system successfully. Continuing calls to support
the SBS models despite their failure suggest a
belief that marine mammal predation must be
a problem for fisheries. The best available
scientific evidence provides no justification for marine
mammal culls as a primary component of an
ecosystem-based approach to managing the
fisheries of the Barents Sea.
1. BACKGROUND
Managing the way that people impact the marine
environment requires understanding the ecological
processes being affected, including those driving fish
fisheries systems. There is a long-standing belief in
some quarters that consumption of fishes by marine
mammals must be a problem for commercial fisheries
(Lavigne 2003). Despite research suggesting that
marine mammal predation is a relatively trivial
issue (e.g. Trzcinski et al. 2006), some stakeholders
want ecosystem-based fishery management (EBFM,
Pikitch et al. 2004) to include culls of marine
mammals (e.g. Jones 2008).
Culling as part of EBFM is implemented in
Norways current policy on marine mammal
management (Corkeron 2006). It is also implicit in the St
Kitts & Nevis Declaration, drawn up by the
prowhaling bloc of the International Whaling
Commission in 2006 (Anonymous 2006).
Probably the strongest scientific argument for
culling comes from Norwegian research into marine
mammals diet and their role in the Barents Sea
ecosystem, which has been ongoing for over two
decades (e.g. Blix et al. 1995; Smout & Lindstrm
2007). This work includes the Scenario Barents
Sea Study (SBS) model (Schweder et al. 2000),
which indicated that more northern minke whales,
Balaenoptera acutorostrata, equate to less cod, Gadus
morhua, and herring, Clupea harengus. Results of this
model, and other aspects of the programme, were
used when developing Norways current policy on
marine mammal management ( Norwegian Ministry
of Fisheries and Coastal Affairs 2004).
2. MODELS OF THE BARENTS SEA SYSTEM
There are (or were) three major finfish fisheries in
the Barents Sea, for Northeast Arctic cod, juvenile
Norwegian spring-spawning herring and capelin,
Mallotus villosus (Hjermann et al. 2004a). Northeast
Arctic cod is the largest remaining cod population,
with a spawning stock biomass currently estimated at
over 600 000 ton (ICES 2008). Having recovered
from collapse in the 1960s ( Toresen & stevedt
2000), the Norwegian spring-spawning herring
population, at almost 12 000 000 ton (ICES 2007a), is the
largest fish stock in the eastern North Atlantic, and
the worlds largest herring stock. Cod and herring are
fished. In recent years, herring total allowable catches
(TACs) have been set at around those recommended
by ICES (2007a), but for cod, agreed TACs have
generally been higher than advised, and there is also
an illegal fishery estimated in the tens of thousands of
tonnes per year (ICES 2008). The capelin population
in the Barents Sea has gone through three crashes in
the past three decades. Since the first closure in 1987,
the capelin fishery has been open 8 years and closed
for 14 (ICES 2007b). A more detailed summary of
this system is available in Hjermann et al. (2004b)
There have been two main approaches used to
elucidate the processes driving the fishfisheries
system in the Barents Sea. One has focused on
interactions within and between the three fish
populations, fisheries and climate, primarily using statistical
models: time-series analysis and regressions of varying
sophistication (Hjermann et al. 2004a,b,c, 2007; Cury
et al. 2008). Data for most of these models were
available for the last two or three decades of last
century, and so coincide with the research on marine
mammal diet in the same area. These models
explained up to over 80 p (...truncated)