#MarineScience - A new survey sampling Nephrops larvae from the area west of the Aran Islands is currently being conducted for the first time aboard the RV Celtic Voyager.
“Nephrops are more commonly known as Dublin Bay prawn, Norway lobster or scampi, and are the most valuable demersal fishery in Ireland,” said Ryan McGeady, PhD candidate at NUI Galway and chief scientist on the two-week mission which began on Tuesday 3 April.
“The value of Nephrops of landings by Irish vessels was €60 million, the stocks around Ireland that the Marine Institute assess with the underwater TV surveys is more than €100 million.”
Nephrops are widely distributed in Irish waters, found in the Irish Sea, the Celtic Sea and off the West Coast of Ireland. They spend a great deal of time in their burrows found in areas of muddy sediment at the bottom of the ocean only coming out for food or mating purposes.
Unlike fish, Nephrops cannot be aged directly. Coupled with their complex biology and behaviour, stock assessment of Nephrops is notoriously difficult to assess.
Since 2002, the Marine Institute has been using underwater television surveys to independently estimate abundance, distribution and stock sizes on the Aran Grounds, Western Irish Sea and the Celtic Sea.
However, the primary focus of this survey is to collect data on the distribution of Nephrops larvae from two commercially important grounds, including off the West Coast and the Irish Sea.
Female Nephrops mature at three years of age, when they start to reproduce each year. After mating in early summer, they spawn in September, and carry eggs under their tails until they hatch in April or May. The Nephrops larvae develop in the plankton before settling to the seabed nearly two months later.
“The importance of this survey is that it is multi-disciplinary which allows us to use both oceanographic data and biological sampling to increase our knowledge on what influences larval distribution and retention on mud patches where the species lives,” Dr Colm Lordan of the Marine Institute said.
The data collected will be used to improve the accuracy of computer models that simulate the movement of Nephrop larvae in the ocean. The information gathered during the survey will also be used to validate or ‘ground-truth’ the model to ensure its accuracy.
“It is hoped that an improved model can be used to estimate the proportion of larvae surviving to adulthood each year. This will make it easier to estimate the health of the stock,” said Dr Anne Marie Power of NUI Galway.
Acoustic records of pelagic fish shoals will also be collected to compare with characteristics of the environment. Observations will be carried out to examine the effect of trawling on fish aggregations once gear has passed through.
Fish shoal sampling will contribute towards an IRC-funded project that will use models of mackerel collective behaviour to improve traditional fisheries assessments and provide a framework for using shoals as an indicator of population health.
Oceanographic data collection will feature hyper-spectral light measurements to assist in the validation efforts of Irish satellites. This will support a Marine Institute Cullen Fellow examining space-based observations of marine phytoplankton in Northeast Atlantic surface water masses and potential environmental monitoring applications.
The team of scientists supporting Cullen Fellow Ryan McGeady board the RV Celtic Voyager includes Darragh Furey (Galway); Sophia Wasserman (Maryland, USA; IRC postgraduate scholar); Catherine Jordan (Mayo; Marine Institute Cullen Fellow/ NUIGalway); and Leigh Barnwall (Dublin). Dr Anne Marie Power Dr Colm Lordan are providing base support for this research.
This research survey is carried out with the support of the Marine Institute, funded under the Marine Research Programme 2014-2020 by the Irish Government.
