Yellow Eel Fyke Net Survey 1987-2022

This dataset is used to examine a 35 year yellow eel survey to determine relative abundance trends while accounting for survey design, and important physical and operational covariates. Chains of ten, or sometimes 5, fyke nets were fished usually at fixed sites in four lakes on a catchment in the west of Ireland. Captured eels (10,474) were counted for each trap, and weight was recorded for each chain of nets (5,515 net nights fished). Surveys were carried out by Marine Institute staff, and in 2009 and 2010, in collaboration with Inland Fisheries Ireland. The survey was initiated in 1987 to establish a baseline for the eel stock in Burrishoole. The survey was continued as part of the core monitoring programme and has also been integrated into the National eel Monitoring Programme under the EU DCF. The data are in 3 sheets; Catch data for each net trap and chain of nets, eel measurement data, and survey net location and depth data. The summer fyke net is a passive method for capturing yellow eels. Summer fykes, so called as they operate best during warmer summer months, rely on eel activity and behaviour to become trapped and they are fished unbaited. Eels are not injured during capture and can be released alive. A summer fyke net consists of a pair of conical traps of mesh supported on rigid hoops, each trap fitted with two or more valves of netting and joined with leaders of net curtains, fished in contact with the bed of the lake or river (Moriarty, 1975). A double chamber fyke net consists of 3 funnels in each chamber and 40cm high leaders, with a mesh size of 17mm (half mesh) leader and first chamber, 14mm second chamber and 11mm codend. These nets were then joined end to end in chains, sometimes of five nets but more usually, of 10 nets. Each chain was usually deployed perpendicular to the shore at fixed locations, with the exception of 2009 and 2010 when chains of 5 fyke nets were deployed at random locations throughout the lake as part of the Irish Eel Monitoring programme. The fyke net has the following dimensions: 8m Leader, 3.4m trap = total fyke length of 15 m including end ties, so 5 nets cover 75m and 10 nets cover 150m, 7 stainless hoops (55, 50, 45, 40, 35, 30, 30cm), mesh netting No 5 and No. 6 codend. From 2014, otter guards consisting of a square rigid grid, creating four openings of 85mm were attached to the end of each of the first funnels and it is not thought that these significantly impact on either the catch number or size of eel being trapped. Otherwise net dimensions and mesh sizes remained constant throughout the survey time period. Standardised fyke nets have proven to be an effective survey tool for establishing changes in the dominant freshwater life history stage (yellow) of eels. Both stock relative abundance and biomass have changed markedly over long time periods. Important covariates included: year, day of year, depth, gradient, chain and trap number. There was a significant and often precipitous trend downwards in both number (CPUEn) and biomass (CPUEw), with yearly trends and between-chain variability significant for all locations and trap depth and gradient being important for some lakes.