North Sea Codwatch

 

This is an exciting new one year Fisheries Science Partnership (FSP) project monitoring the status in North Sea catches of the 2005 and 2006 year classes of cod (Gadus morhua) in 2007, and the 2006 and 2007 year classes of cod in January to March 2008, made by selected commercial vessels associated with the Eastern England Fish Producers Organisation Ltd (EEFPO). Cod in general (all ages) is also monitored.

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 of higher abundance than the recent low levels (about the size of the 1999 year class), especially in the central and northern North Sea (ICES, 2007). Industry indications, however, are that the 2005 year class is much stronger than the long-term historical average.

There have been also indications of relatively larger numbers of 0–group cod in the south eastern North Sea and Skagerrak in 2006 (2006 year class).

In addition to data on the 2005 year class, information collected on the 2006 and 2007 year classes and the general distribution of aggregations of cod (all ages) will enhance our understanding of the dynamics of North Sea cod. ACFM, Oct 2007.

Project rationale

Fishers on 12 EEFPO vessels are observing and recording, quantitatively where possible, the incidence, distribution and abundance of the 2005 and 2006 year classes (in 2007) and the 2006 and 2007 year classes (in 2008), and of cod in general, from commercial catches made between April 2007 and March 2008. These data (and relevant ancillary data such as fishing location, fishing effort and details of fishing gear, target species, etc.) 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 throughout the year. Only one has actually targeted cod during the project thus far, but even this effort has been interspersed with trips targeting sole (Solea solea) and periods of non-fishing related activity. Effectively, cod is now considered by industry partners to be a by-catch species.

Formal objectives

• To describe the fine-scale distribution and abundance in time and space of the 2005 year class as 2-year-olds in 2007.
• To describe the fine-scale distribution and abundance in time and space of the 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 2007 year class as 1-year-olds in 2008 (Jan-March).

• To better understand the spatial and temporal distribution of aggregations of cod (of all ages).

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

Vessel number 1	Port	Fishing gear	Areas fished	Species targeted
1	Fraserburgh	Twin rig trawl	Northern North Sea	Nephrops
2 2	Whitby	Gill-net	Central North Sea - inshore	Demersal spp
3	Whitby	Twin rig trawl	Central North Sea	Demersal spp Nephrops
4	Whitby	Twin rig trawl	Central North Sea	Demersal spp.
5 3	Whitby	Twin rig & single trawls	Central North Sea, Norway Sector	Demersal spp.
6 4	Whitby	Twin rig & single trawls	Central North Sea, Norway Sector	Demersal spp.
7	Scarborough	Pair trawl	Central North Sea	Demersal spp.
8	Scarborough	Pair trawl	Central North Sea	Demersal spp.
9	Scarborough	Twin rig trawl	Central North Sea	Demersal spp.
10 5	Grimsby	Anchor seine	Central North Sea	Demersal spp.
11	Grimsby	Gill-net	Southern North Sea	Cod, ling, pollack & sole
12	Grimsby	Twin-rig & single trawls	Central North Sea, Norway Sector	Demersal spp, Nephrops
13	Lowestoft	Long-line	Southern North Sea	Demersal spp

¹ The vessel number has been simplified to preserve confidentiality
² Only until 31 st August 2007
³ Only until 2nd June 2007
⁴ From 11 th August 2007
⁵ Only from 1 st July 2007

Trip logsheets

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

• Target species, gear type and dimensions (including mesh size) and quota allocation.
• Date, time, a single midpoint lat/long identifier for each tow/haul, target species, hours towed/soak-time.
• For each of the 4 objectives (2005 year class, 2006 year class, 2007 year class and all cod of all ages): a relative estimate of abundance using a 5-point scale (0 = zero, 1 = small numbers, 2 = moderate numbers, 3 = high numbers, 4 = very high numbers), and an estimate of the quantity (by weight and number) retained and discarded. Fishers were requested to estimate relative abundance using their previous historical knowledge of incoming year classes and of cod fishing in general (the average fishing experience of participating skippers is 30 years).

Fishers were 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 was made for potential differences in growth rate between different areas of the North Sea, but this was deemed appropriate in order to reduce the complexity of sampling by fishers moving in and out of different fishing areas. Fishers were provided with fish measuring boards and guidance was given in the sub-sampling of large or mixed catches. The distribution and collection of logsheets and the transfer of data onto Excel spreadsheets were carried out by the EEFPO. Fishers were encouraged also to record additional observations they considered relevant to the project.

Quality control

On receipt of logsheets, the EEFPO carried out initial quality checks of the data and resolved any queries directly with the fishers. The data were then captured on spreadsheets and forwarded to Cefas for analysis and graphic interpretation following protocols agreed between the two parties. Cefas 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 was made by Cefas for randomly selected months.

Calibration

Estimates by fishers of the numbers and weights of the 2005 and 2006 year classes and of all cod (all ages) in catches retained and discarded were 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, provides a reasonably robust indication of the accuracy and precision of sampling on Codwatch vessels.

Data storage, manipulation and graphical interpretation

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