Marine Institute

Sampling Nephrops larvae from the west of the Aran Islands for the first time on the RV Celtic Voyager

April 5, 2018

Scientists prepare for expedition sampling Nephrops larvae from the west of the Aran Islands carried out for the first time on the RV Celtic Voyager.  (Centre) Chief Scientist Ryan McGeady (Donegal), Marine Institute Cullen Fellow / NUIGalway  (LtoR) Darragh Furey,(Galway); Sophia Wasserman (Merryland, USA) IRC postgraduate scholar); Catherine Jordan (Mayo) Marine Institute Cullen Fellow / NUIGalway; Leigh Barnwall (Dublin). Photograph Cushla Dromgool-ReganA new survey sampling Nephrops larvae from the area west of the Aran Islands will be conducted for the first time, aboard the RV Celtic Voyager over the next two weeks (3rd to 16th of April 2018).

"Nephrops are more commonly known as Dublin Bay Prawn, Norway lobster or scampi, and are the most valuable demersal fishery in Ireland. 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," explained chief scientist Ryan McGeady, Marine Institute Cullen Fellow and NUI Galway PhD student

Despite its common name, 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 where 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, NUIGalway.

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 hyperspectral light measurements to assist in the validation efforts of Irish satellites. This will support a 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 Ryan McGeady (Donegal) Marine Institute Cullen Fellow / NUIGalway aboard the RV Celtic Voyager include Darragh Furey (Galway); Sophia Wasserman (Merryland, USA - IRC postgraduate scholar) Catherine Jordan (Mayo) Marine Institute Cullen Fellow / NUIGalway; Leigh Barnwall (Dublin). Dr Anne Marie Power of NUI Galway and Dr Colm Lordan of the Marine Institute will be 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.

Follow the blog from the survey here.

ENDS