Publication Abstract

Prospects poor for North Sea cod

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.

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 on board 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.

NFFO chairman Bob Casson lends a hand mending a small tear in Cirolana’s survey trawl during his recent trip on the vessel.

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.

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 on board RV Cirolana during August/September each year. The data for 1999 are provisional.