DOI: 10.14466/cefasdatahub.13
title: Cefas Electronic Data Storage-Tag Database

description: This dataset has been extracted as part of an exercise to assemble "all" Cefas Temperature Data and publish it in a Data paper. It is one of 17 Cefas data sources assembled.

Electronic tags that record temperature and depth were attached to, or implanted into, cod caught in the southern North Sea between 1999 and 2009 (for methods see Neat et al., 2014). Data from tags that were returned from recaptured cod were downloaded and the depth time series was used to estimate daily geographic location.

Geolocation was done by matching the tidal and maximum depth data to known dates and locations as per the method described in Pedersen et al. (2007). Temperature data from each tag were binned into 10m depth intervals, and then averaged. The maximum depth in a bin was recorded and is used in the data provided. Temperature at the seabed is assumed to be the average of the temperatures sampled in the deepest 10m depth bin. Cod were at liberty to move at will, so the geographic and vertical sampling is not regularised to a grid or vertical stratification. The number of temperature records collected by cod on each day is also variable, since this depends on the number of cod remaining at liberty after release (i.e. those that were not recaptured by fishermen). The data describes the temperature data sampled by a total of 90 cod, and comprises temperature data collected on a total of 10,446 days.

Tags recorded data at a minimum interval of 72 times per day continuously throughout the time at liberty (11-541 days). Data are available for 9,600 days during the period 1999 to 2010.

The tags attached to, or implanted in, cod were of several types: Lotek 1200, 1400 and 2400, the Star-Oddi Centi and Milli, and the Cefas G5. All tags were calibrated by the manufacturer before deployment, and typically measure temperature to a precision of 0.03°C and an accuracy of at least 0.2°C. Temperature and depth are reported to 1dp.

Temperature data collected by the tags are assumed to be a precise measure of seawater temperature based on the calibration tests performed by tag manufacturers before the tags are deployed. There is no independent measure of temperature against which to assess sensor performance while the tags are deployed at sea. Unusual temperatures associated with sensor failure or data corruption were excluded from the dataset, as were data from the day of release or recapture, when spurious surface or air temperatures might be recorded to the tag memory. Daily temperature averages had standard deviations ranging from 0 to 6.8, with 2/3 <0.1. The high variation reflects the behaviour of the particular cod on the particular day.

The multiple sources are described in 17 separate metadata entries under the same Title, e.g. Seawater temperature records for the UK Shelf - 15 - RV Cefas Endeavour FerryBox Monitoring System. These data have been described in detail via the following publication. Morris, D. J., Pinnegar, J. K., Maxwell, D. L., Dye, S. R., Fernand, L. J., Flatman, S., Williams, O. J., and Rogers, S. I.: Over 10 million seawater temperature records for the United Kingdom Continental Shelf between 1880 and 2014 from 17 Cefas (United Kingdom government) marine data systems, Earth Syst. Sci. Data, 10, 27–51, https://doi.org/10.5194/essd-10-27-2018, 2018.