CAFSAC
Advisory Document 80/5
Items from Invertebrates and Marine Plants Subcommittee Meeting
CAFSAC considered the deliberations of the Invertebrate and Marine Plants
Subcommittee and offers the following advice:
1. Bay of Fundy scallop stock assessment
In 1978 and 1979 landings from the Bay of Fundy scallop stock located
off Digby, N.S. were 483 and 442 MT respectively. These landings are well
above the long term average for the area. In these two years the fishery
exploited the highly abundant 1971 and 1972 year-classes. A resource
survey conducted in June 1979 demonstrated that the 1973, 1974, 1975 and
1976 year-classes are weak and considerably less abundant than the 1971
and 1972 year-classes. Landings can be expected to decline sharply as the
1971 and 1972 year-classes become depleted.
In 1979 the fishery was based on 7 to 8 year-old scallops (1971 and 1972
year classes) which yielded meat counts between 25-31 lb. Meat counts per
pound can be expected to increase as soon as landings begin to decline and
younger scallops are taken. Assessments indicate that yield per recruit at
present levels of F can be maximized for this stock by delaying age at first
capture to 8 years which would be equivalent to a meat count of 25/lb. If a
25/lb regulation were implemented for 1980 short-term losses would be minimal
since present exploitatior yields meat counts of 25-31/lb. and the younger age
groups would be protected from heavy exploitation. In the absence of such a
regulation the younger age groups will very likely be exploited. Yield per
2
recruit will be reduced by 55-60% if age at first capture is reduced to
3 years.
2. Cape Breton snow crab stock assessments
The Cape Breton snow crab fishery is divided into five inshore fishing
areas for management purposes.
Area 8 (Northwestern Cape Breton). This area was first exploited in
the late 1960's. Twenty-seven boats were licensed to fish this area in 1979.
Following peak landings of 1941 MT in 1978, a TAC of 1406 MT was set for 1979,
above the advised TAC for 1979 of 1189MT. The exploitation rate in 1979 was
estimated at between 55 and 62%. Estimates indicate a decline in commercial
biomass from 3016 MT in 1978 to 2239 MT in 1979. It was estimated that 1189 MT
was added to the commercial biomass from growth and recruitment during the initial
veeks of the 1978 season. This was the basis of the TAC advised for 1979. It was
estimated that 790 MT was added to the commercial biomass during the initial weeks
of the 1979 season, hence, the TAC advised for 1930 is 790 MT. It is also
suggested that consideration be given to delaying the opening of the fishing
season in this area to avoid the major period of molting thereby reducing the
proportion of soft-shelled crabs in the catches.
Area 9 (Southeastern Cape Breton). The fishery in this area began in 1977.
Landings increased with effort from 490 '1T in 1978 to 682 MT in 1979. Fifteen
licensed inshore boats and 10 with offshore permits fished in this area in 1979.
The exploitation rate on the grounds fished in 1979 was estimated at between
58 and 65%.
Area 10 (Northeastern Cape Breton). The Fishery in this area started in 1976.
The number of boats licensed to fish increased from 36 in 1978 to 48 in 1979,
however, landings decreased from 331 MT in 1978 to 289 MT in 1979. The exploitation
3
rate on the grounds fished in 1979 was estimated at between 62 and 71%.
Area 11 (Middle-eastern Cape Breton). The fishery in this area began
in 1977.
In 1979, 11 licensed inshore boats with 5 offshore permits
fished the area. Landings were 507 MT in 1979 and the exploitation rate
on the grounds fishes was estimated at 64%.
Area 12 (Southwestern Cape Breton). The fishery began in this area
in 1979 with 14 permits issued. Landings were 213 MT and the exploitation
rate on the grounds fished was estimated at 50%.
Area 13 (Southern Cape Breton). The fishery began in this area in 1979
with 8 permits issued. Landings were 27 MT and the exploitation rate on the
grounds fished was estimated at 39%.
It is not known to what extent the total commercial stocks in areas 9-13
were fished in 1979. The fisheries in these areas started quite recently and
very little biological or commercial information are now available. Until
sufficient data are available to adequately assess the stocks, it is advised
that fishing effort not be increased beyond the 1979 levels.
3. Assessment of Ascophyllum (rockweek) harvesting methods in southwestern
Nova Scotia.
In 1959 a pilot plant was established in southwestern Nova Scotia to
test the possibility of alginate extraction from fucoids. Within 2 years
the operation was harvesting 6,000 MT of Ascophyllum per year from Cape Sable
to Yarmouth. The plant became a commercial operation and during the first 10
years bought rockweed from fishermen who used scythes to harvest at low tide
and small seine nets to gather the floating rockweed. In 1968 the company
developed a mechanical harvesting method which by 1976 was used to harvest
80-90% of the crop. The remainder is harvested from small boats using cutter
rakes and from the beaches at low tide where the rockweed is cut with
scythes and loaded onto carts. In June 1978 a study was carried out to
4
assess the ecological effects of the mechanical and the cutter rake
harvesting methods.
The regenerative capacity of Ascophyllum is maximized when plants
are cropped to 30-40 cm in length. The study determined that the mechanical
harvesting method cut 22.1% of the plants to within 20 cm of the substrate and
had a mean cutting height of 35 cm. The cutter rake method cut 47% of the
plants to within 20 cm and its mean cutting height was 23 cm.
In addition,
due to poor cutting action, 16% ( by weight) of the cutter rake harvest
consisted of plants attached to holdfast tissue compared to 2% for that
harvested mechanically. When holdfasts are removed replacement of the
lost plants must be via germling settlement. The regenerative capacity
of an Ascophyllum population and its potential long-term yield are greatly
reduced when harvested with the cutter rake.
It is advised that the use of the cutter rake method of Ascophyllum
harvesting be eliminated and that hand harvesting using an effective
cutting method such as the scythe be restricted to areas where the
mechanical harvesting method cannot be used or is very inefficient.