Preliminary observations on the biology and movements of porbeagle Lamna nasus around the British Isles

Preliminary data are presented from electronic tagging studies conducted in 2010–2012. To date, of the 21 tags released, data were received from 14 sharks, resulting in a total of 2062 days of data, with a further six tags still to be released and data recovered. Sharks showed shallow diving behaviour in shelf seas, and deeper diving over the continental slope. A complementary study investigating bycatch during commercial gillnet fishing operations detailed 18 trips with numbers from 1 to up to 10–50 dead and discarded porbeagle per trip. Discard observer programme data from CEFAS are also presented, with 45 records of porbeagle bycatch detailed by area, gear, sex and length. Although based on a small sample size, biological information is provided for length-weight conversion factors, including for total length (both caudal fin in a natural position, and flexed down), fork length and standard length with both total and gutted weight. Length-length conversion factors for relating total length and standard length to fork length are given. Data on liver, gonads and fin weights, as proportions of total weight, are summarised.