North Sea Codwatch

This is an exciting two-year Fisheries Science Partnership (FSP) project monitoring the status of North Sea catches of 1- and 2-year-old cod (Gadus morhua), which commenced in April 2007, made by selected commercial vessels associated with the Eastern England Fish Producers Organisation Ltd (EEFPO). Cod in general (all ages) and whiting (Merlangius merlangus) (all ages) are also monitored. From June 2008 the project is part funded by Yorkshire Forward.

Background

Recruitment of 1-year-old cod has varied considerably since the 1960s, but since 1998, average recruitment has been lower than at any other time. The 2005 year class is estimated to be one of the most abundant of recent below-average year classes (International Council for the Exploration of Sea (ICES), 2008). Industry indications, however, are that the 2005 year class is much stronger than the long-term historical average.

ICES has advised that it is necessary to reduce mortality especially on younger ages of cod, to allow more fish to reach maturity and to increase the probability of good recruitment. In the past five years, an average of 82% (84% in 2007) of the international landings in numbers consisted of juvenile cod aged 1-3. Because the fishery is at present so dependent on incoming year classes, fishing mortalities on these year classes are high, and just 12% of the 2-year-olds currently survive to maturity (compared with 22% in the early 1960s) (ICES, 2008).

The recruitment of the relatively more abundant 2005 year class to the fishery may have no beneficial effect on the stock if it is caught and heavily discarded. In 2006, the 2005 year class comprised 62% of the total catch by number, and in 2007 it comprised 55%. Discarding of this year class increased to 40% in 2007 and the propotion is expected to remain high in 2008. The last substantial year class to enter the fishery was the 1996 year class. That year class was a prominent feature in all surveys, was heavily exploited and discarded by the fishery at ages 1-5, and disappeared relatively quickly from the fishery with no benefit to long-term spawning stock biomass (SSB).

ICES has advised that recent measures to improve the survival of young cod such as the Scottish Credit Conservation Scheme, and the increased uptake of more selective gear in the North Sea and Skagerrak such as the Eliminator Trawl, should be encouraged.

French fishers have been reporting substantial discards of undersize cod in the eastern Channel (ICES Division VIId) in 2007 and early 2008. Relatively large numbers of the 2006 year class were first observed as 0-group fish in several surveys in the eastern Channel and southern North Sea. That year class was observed again in large numbers as age 1 fish in the French groundfish survey in the eastern Channel, and by French fishers targeting cuttlefish in the same area. This appears to be a localized phenomenon, because the 2006 year class is estimated to be poor in the North Sea, based on the IBTS Q1 and Q3 surveys.

In addition to data on 1- and 2-year-olds, information collected by Codwatch vessels on  the general distribution of aggregations of cod and whiting of all ages will enhance our understanding of the dynamics of these species in the North Sea.

Project rationale

Fishers on 12 EEFPO vessels are observing and recording, quantitatively where possible, the incidence, distribution and abundance of 1- and 2-year-old cod, and of cod of all ages, from commercial catches made between April 2007 and March 2009, and of whiting of all ages in catches from April 2008 to March 2009. These data (and relevant ancillary data such as fishing location, fishing effort and details of fishing gear, and target species.) are submitted to the EEFPO for collation prior to analysis and graphic evaluation by Cefas scientists and EEFPO representatives. Industry partners have commented that none of the vessels is pursuing a directed cod fishery continuously. At the start of the project only one vessel was actually targeting cod and currently (September 2008) none of the vessels are. Effectively, cod is now considered by industry partners to be a by-catch species. Many vessels have to discard cod due to lack of quota.

Formal objectives

• To describe the fine-scale distribution and abundance in time and space of the cod 2005 year class as 2-year-olds in 2007
• To describe the fine-scale distribution and abundance in time and space of the cod 2006 year class as 1-year-olds in 2007 and as 2-year-olds in 2008 (Jan-March).
• To describe the fine-scale distribution and abundance in time and space of the cod 2007 year class as 1-year-olds in 2008  and as 2-year-olds in 2009 (Jan-March).
• To describe the fine-scale distribution and abundance in time and space of the cod 2008 year class as 1-year-olds in 2009 (January-March). 
• To better understand the spatial and temporal distribution of cod and whiting of all ages (the latter from June 2008 to March 2009).

Selection of vessels

Twelve fishers with a track record of catching cod were selected by the EEFPO to maximise spatial coverage of the North Sea and to include a wide range of fishing gears and target species.

Summary of the characteristics of vessels participating in Codwatch

Trip logsheets

Trip logsheets designed and formatted by the EEFPO and Cefas are distributed to all fishers in the project. The logsheets include fields for:

For cod, fishers are provided with guidance by quarter on the expected upper and lower likely lengths of each year class, derived from previous sampling of retained and discarded catches of cod during recent fishing trips attended by observers in the central North Sea. No allowance is made for potential differences in growth rate between different areas of the North Sea, but this is deemed appropriate in order to reduce the complexity of sampling by fishers moving in and out of different fishing areas. Fishers are provided with fish measuring boards and provided guidance in the sub-sampling of large or mixed catches. The distribution and collection of logsheets and the transfer of data onto Excel spreadsheets are carried out by the EEFPO. Fishers are encouraged also to record additional observations they consider relevant to the project.

Quality control

On receipt of logsheets, the EEFPO carry out initial quality checks of the data and resolve any queries directly with the fishers. The data are then captured on spreadsheets and forwarded to Cefas for analysis and graphic interpretation following protocols agreed between the two parties. Cefas has provided software to check any large-scale errors in the recording of haul midpoint latitude and longitude. A final quality check on primary logsheet data is made by Cefas for selected months.

Calibration

Estimates by fishers of the numbers and weights of the 1- and 2-year-olds and of all cod and whiting (all ages) in catches retained and discarded will be compared with estimates of the same parameters derived from trips sampled under the Cefas Discard Observer Scheme. These trips are carried out on UK (England and Wales) vessels at random, so the number of 'Codwatch' trips sampled is likely to be small. Notwithstanding, available data, derived by length sampling and raising where necessary, and the application of age-length keys, provide an  indication of the accuracy and precision of sampling on Codwatch vessels.

Data storage, manipulation and graphical interpretation

All logbook data in spreadsheets are transferred electronically into a Microsoft Access database, and queries are used to manipulate data into a suitable format for graphic interpretation using software MapInfo.