By-catch from AFBI Irish Sea Nephrops Trawl Research Surveys 1994 - present

This dataset contains information on bycatch of non-target species from the AFBI Nephrops Trawl Research Survey series between 1994 – present from surveys carried out in the Irish Sea. The primary objectives of this research surveys series are:
• To study spatial variability in population structure and abundance of Nephrops and by-catch species.
• To obtain information on temporal trends of population structure of Nephrops.
• To study female maturity in Nephrops.
Between 1994 – 2010 the Research Survey was carried out on a bi-annual basis in the spring and autumn of each year. During each of these research surveys between 18 - 32 stations were primarily sampled using a nephrops otter trawl net; similar to that used in the commercial fishery. In addition, at select number of stations, various net types were used to sample for a comparison between nets. Each sampled station comprises a 3-mile trawling lane. Towing speed across the ground varies with tide and weather a target speed of 3 knots is aimed where possible.  
From 2010 – present, the research survey was carried out on an annual basis in summer of each year (July/August) whereby sampling occurred at c. 24 fixed stations.  
"This dataset contains a long-term time series (1994 – 2018) of bycatch data from the AFBI Nephrops Trawl research survey series carried out in the Irish Sea. It should be noted that the species of primary concern of this research survey was the Dublin Bay prawn (Nephrops norvegicus); and as such the survey design, sampling protocol and technical equipment were designed to maximise the recording of the target species. Over the course of the time series there has been adjustments to survey design, sampling protocol, survey staff and technical equipment in response to changing requirements and latest novel developments in survey equipment. Most notably was the change in Research Vessel from the R.V. Lough Foyle to the R.V. Corystes in 2005. At the end of each research survey individual cruise reports are composed by the Scientist in Charge of (S.I.C.) that provide a summary of the individual survey design, sampling protocol, survey staff and technical equipment and are available on request. 
The below protocol outlines a general overview of the sampling protocol of the research survey. A bespoke survey report outlined the specification.
From each towed station the total catch from the net is emptied into a 1 tonne fish hopper. If the catch is 100 kg or less the entire catch is sorted to species, for larger catches a stratified sampling scheme is applied whereby sampling effort is targeted to species of commercial interest. 
Dependent on the size of the catch, the catch is sorted into species and size categories at the hopper or for larger catches, unsorted baskets are sampled. The weights in each category of each species are recorded, as well as the weight of any unsorted catch. Greatest accuracy is required for commercial whitefish species for which indices of abundance of different age-classes are required for scientific stock assessments (cod, whiting, haddock and herring). For those species, take a sufficient number of fish at random from each category such that there are approximately 50 fish in the modal length class of the measured fish.  
Where there are several modes in the length frequency it may only be feasible to measure to about 30 in a mode. If there are several baskets of fish, take a sub-sample from each basket.
Sample-sizes for non-commercial species such as poor cod and sprat may be smaller, e.g. a total of 50-100 fish depending on the spread of length classes.
Record the weight of fish in the length frequency and enter it onto the length-frequency form together with all other relevant details, particularly the category number.
All fish are measured to the nearest cm below (pelagic fish, such as herring, sprat, mackerel, are measured to the 0.5 cm below), and are measured from the tip of the nose to the tip of the tail (total length).