Prospects poor for North Sea cod
Based on an article first published in Fishing News, 8 October
1999
Dr John Casey from Cefas's Lowestoft
Laboratory outlines the preliminary results of the assessment of
North Sea fish stocks and on the management advice for
2000.
NFFO chairman Bob Casson lends a hand
mending a small tear in Cirolana's survey trawl during his
recent trip on the vessel.
Cefas' trawl survey of the North Sea has been carried out
annually during August/September for over 20 years. The results of
the survey provide a major input into the assessment of North Sea
stocks.
A total of 74 tows over all of the North Sea are fished each
year. After each tow, all fish are weighed and measured and a
sample of otoliths (ear stones) are taken to determine the age
compostion of the catch of the commercially important species.
The catch rates of each age-group of fish (numbers per tow), are
used to indicate the relative abundance at each fishing position
from one year to the next. This information is used by scientists
in stock assessment working groups in the International Council for
the Exploration of the Sea (ICES).
One of the principal uses of the catch rate data is to give an
index of the relative abundance of young fish (recruits) which will
become available to the fishery in the year following the survey.
This information is used by ICES to provide catch forecasts, which
form the basis of the advice on TACs.
Figure 1 shows the relative abundance of one year old cod from
the Cefas survey over the period 1995 to 1999. The data for 1999
are still provisional but are unlikely to change significantly
after they have been finalised. The black circles represent the
catch rates at each fishing position, and the same positions were
fished each year.
Figure 1. Relative abundance of one year old cod in the North
Sea from 1995 to 1999. Data are from Cefas's trawl survey carried
out onboard RV Cirolana during August/September each year.
The data for 1999 are provisional.
What is immediately obvious is that there were far more one year
old cod all over the North Sea in 1997 than in any of the other
years shown. These fish were spawned in 1996 and are referred to as
the 1996 year-class. They were two years old in 1998 and since most
of them were above the legal minimum landing size, they were
largely responsible for the good fishing on North Sea cod in that
year.
It is also apparent that the 1997 year-class as one year old
fish in 1998 was very poor. It is these fish which should form an
important part of the catch in 1999. However the fact that there
were relatively few of them even at age one in 1998 means that
there were even fewer of them in 1999 when aged two. This is one
reason why the industry has generally experienced a poor fishery
for cod this year.
The preliminary results from the recent survey indicate that the
1998 year-class is stronger than the 1997 year-class, but is still
poor.
Figure 2 shows the overall survey index for one year old cod
each year from 1978 to 1999. As for Figure 1, the index for 1999 is
still provisional. It is clear that in 1997, the number of one year
old cod in the North Sea (1996 year-class) was the highest since
1984.
Figure 2. Abundance index for one year old North Sea cod
from 1978 to 1999. Data are from Cefas's trawl survey carried out
aboard RV Cirolana during August/September each year. The
1999 value is provisional.
In contrast, the 1997 year-class as one year old fish was the
poorest on record. The 1998 year-class is also below average. The
1997 and 1998 year-classes will be three and two years old in the
year 2000, and it is these age groups which typically account for
the large majority of North Sea cod landings.
The relative scarcity of these age groups in the sea, will have
a direct impact on the catch forecasts calculated by ICES, and
hence on its management advice.
The data from the Cirolana survey will be combined with
results from similar scientific research surveys conducted by six
other countries that exploit North Sea fish stocks.
In addition, data from the commercial catches of North Sea
fishermen of all nationalities will be used to inform ICES of the
abundance of older fish.
These data will be analysed by the ICES Working Group on the
Assessment of Stocks in the North Sea and Skagerak, which will meet
from 11 to 20 October this year.
Advice on North Sea fish stocks for 2000 will be given by ICES'
Advisory Committee on Fisheries Management (ACFM) in November.
Bob Casson watching cod being sampled aboard Cirolana.
Data on length, weight and stage of maturity from individual fish
are electronically logged directly to Cefas's fishing survey
database.