Atlantic Polar Biome
155
that a small pelagic gadoid, the blue whiting (Micromesistius poutassou) that also abounds
in the Norwegian Sea, also has strikingly intermittent recruitment. In the final 30 years
of the last century, recruitment was usually of order 5–10 × 10
9 1-group fish each year
but peaked very much higher during four brief periods (1983–84 = 20 × 10
9 1990 =
22 × 10
9 1996 = 48 × 10
9 , and 2000 = 58 × 10
9 ), as reported recently by Skjoldal and
Saetre (2004).
So, it is perhaps in this very well studied province that we have as good a chance
as anywhere of finally unraveling the enigma of how variability in recruitment to fish
stocks is forced, and how it may be predicted. Even so, it is obvious that this is no simple
matter. A recent study of the relative influence of environment and size of the parent
stock on recruitment of cod, using a 60-year data set (1930–1990), suitable to support
age-based modeling, simply found that the effect of parent stock size on subsequent
recruitment is less clear the longer the time series that is examined. Unfortunately, as
Matishov et al. (2003) point out, even in well-studied regions such as the Barents Sea
it is very difficult to separate the natural dynamics from the consequences of many
decades of heavy industrial fishing. They emphasize that the biomass of each component
of what they call the “consortive” ecosystem (because many components depend on the
performance of a central species or group of species) is currently very different from the
pristine state, individual species and groups being reduced by 5–50% of pristine biomass.
Regional Benthic and Demersal Ecology
It is, of course, only in the shallow Barents Sea that significant benthic habitat exists
in this province, and here it must be significantly modified by decades of intensive
industrial trawling for demersal fish with heavy equipment. We must assume that, as in
the North Sea, the larger, long-lived lamellibranchs and echinoderms will have suffered
heavy damage. The pristine benthic ecosystem resembled that of BPLR and ARCT (see
earlier discussion) with a Venus fluctuosa community on sandy bottoms, and a Macoma
calcarea community down to 130 m where silt content is higher. An unusual bivalvepolychaete association (the Yoldia hyperborea community, sens. Thorson) also occurs in
the inner Barents Sea. There is some evidence of the effect of changing oceanographic
conditions in the progressive extension of Atlantic benthic species northward along the
shelf west of Spitzbergen between the 1930s and the 1950s.
Here, the benthic invertebrates support a fauna of demersal-feeding fish including
plaice (Pleuronectes platessa) and halibut (Reinhardtius hippoglossoides) and—another
human intervention—a burgeoning population of Kamchatka crabs (Paralithodes), introduced in 1932 and 1961 on Russian initiative; this population was estimated at 12.5
million crabs already by the year 2000 (Matishov et al., 2003). It is not credible that a population size of 15 million individuals is “acceptable for ecosystem stability” as is claimed:
such statistics cannot be computed, they must be obtained by experiments—irreversible,
in this case.
Synopsis
Case 1—Polar irradiance-mediated production peak. Z m undergoes deep winter mixing
until shallow thermal stratification is reimposed in April; Z eu is always shoaler than Z m
except for the 4 months when the pycnocline is illuminated (Fig. 9.5). Seasonal evolution
of P is symmetrical about a strong midsummer maximum, the vernal increase responding
to the light field more closely than to the initiation of shoaling of Z m . A change in the rate
of declining P occurs with autumnal deepening of Z m . Biomass accumulation in spring is
rapid (and varies strongly between years) and the subsequent decline after midsummer
is brief, because a major second period of accumulation occurs in the second half of the
year; this is highly variable between years. Renewal of accumulation in autumn and early
155
that a small pelagic gadoid, the blue whiting (Micromesistius poutassou) that also abounds
in the Norwegian Sea, also has strikingly intermittent recruitment. In the final 30 years
of the last century, recruitment was usually of order 5–10 × 10
9 1-group fish each year
but peaked very much higher during four brief periods (1983–84 = 20 × 10
9 1990 =
22 × 10
9 1996 = 48 × 10
9 , and 2000 = 58 × 10
9 ), as reported recently by Skjoldal and
Saetre (2004).
So, it is perhaps in this very well studied province that we have as good a chance
as anywhere of finally unraveling the enigma of how variability in recruitment to fish
stocks is forced, and how it may be predicted. Even so, it is obvious that this is no simple
matter. A recent study of the relative influence of environment and size of the parent
stock on recruitment of cod, using a 60-year data set (1930–1990), suitable to support
age-based modeling, simply found that the effect of parent stock size on subsequent
recruitment is less clear the longer the time series that is examined. Unfortunately, as
Matishov et al. (2003) point out, even in well-studied regions such as the Barents Sea
it is very difficult to separate the natural dynamics from the consequences of many
decades of heavy industrial fishing. They emphasize that the biomass of each component
of what they call the “consortive” ecosystem (because many components depend on the
performance of a central species or group of species) is currently very different from the
pristine state, individual species and groups being reduced by 5–50% of pristine biomass.
Regional Benthic and Demersal Ecology
It is, of course, only in the shallow Barents Sea that significant benthic habitat exists
in this province, and here it must be significantly modified by decades of intensive
industrial trawling for demersal fish with heavy equipment. We must assume that, as in
the North Sea, the larger, long-lived lamellibranchs and echinoderms will have suffered
heavy damage. The pristine benthic ecosystem resembled that of BPLR and ARCT (see
earlier discussion) with a Venus fluctuosa community on sandy bottoms, and a Macoma
calcarea community down to 130 m where silt content is higher. An unusual bivalvepolychaete association (the Yoldia hyperborea community, sens. Thorson) also occurs in
the inner Barents Sea. There is some evidence of the effect of changing oceanographic
conditions in the progressive extension of Atlantic benthic species northward along the
shelf west of Spitzbergen between the 1930s and the 1950s.
Here, the benthic invertebrates support a fauna of demersal-feeding fish including
plaice (Pleuronectes platessa) and halibut (Reinhardtius hippoglossoides) and—another
human intervention—a burgeoning population of Kamchatka crabs (Paralithodes), introduced in 1932 and 1961 on Russian initiative; this population was estimated at 12.5
million crabs already by the year 2000 (Matishov et al., 2003). It is not credible that a population size of 15 million individuals is “acceptable for ecosystem stability” as is claimed:
such statistics cannot be computed, they must be obtained by experiments—irreversible,
in this case.
Synopsis
Case 1—Polar irradiance-mediated production peak. Z m undergoes deep winter mixing
until shallow thermal stratification is reimposed in April; Z eu is always shoaler than Z m
except for the 4 months when the pycnocline is illuminated (Fig. 9.5). Seasonal evolution
of P is symmetrical about a strong midsummer maximum, the vernal increase responding
to the light field more closely than to the initiation of shoaling of Z m . A change in the rate
of declining P occurs with autumnal deepening of Z m . Biomass accumulation in spring is
rapid (and varies strongly between years) and the subsequent decline after midsummer
is brief, because a major second period of accumulation occurs in the second half of the
year; this is highly variable between years. Renewal of accumulation in autumn and early