Otoliths also known as ear stones are calciumcarbonate and protein structures found behind the head and beside the brain inteleost fish.
The function of ear stones are as the name suggests, they are usedfor hearing and balance in fish species (Popper et al, 2005). Annuli also knownas increments, form on the otolith itself and provides an age for the fish(Rezende and Ferreira, 2004). There are translucent and opaque annuli on theotolith in temperate areas which represent winter and summer growth respectively(Penttila, 1988). These annuli together equal one year of growth. Dailyincrements are also deposited on otoliths with an increment representing eachday of the year (Pannella, 1971).
This is very beneficial for researchersrecording larval stages of growth as these increments show the daily age of thelarvae (Brown and Wooden, 2007). Otoliths are the only way to record dailyincrements in the larval stages of growth or for species with short lifespans (Panfiliand Troadec, 2002). Other structures such as scales do not containdaily increments (Penttila, 1988). Daily increments can help estimate survivaland mortality rates of fish species earlier in their life cycle (Houde, 2008).Growth rate in fish is also proportional to growth in otoliths (Campana andThorrold, 2001).
After the onset of maturity somatic growth is reduced andtherefore so is otolith growth (Panfili and Troadec, 2002).Otoliths are a valuable resource for managing thecommercial fishing industry and for stock assessment where they are used to agefish species of commercial importance (Ono et al,2014). Otoliths can be used to determine a number of factors. Otolithage estimates are used to describe distribution of the stock. Using otoliths toage fish species can help determine how healthy the stock is in a certain areaand otoliths are essentially the basis for stock assessment (Cardin et al, 2014).For example if older fish are lost throughout an entire stock over a period oftime it may indicate over exploitation of the species as well as a loss ofdiversity.
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In some stocks age and size truncation have been related to lowerrecruitment, suggesting growth rate is an important factor in fish stockassessment (Stige et al, 2016). Age truncation increases the susceptibility ofcollapse of weakened fish stocks (Hixon et al, 2013). Age data can help to setquotas and minimum landing sizes for species, which is crucial for sustainable fishing.Otoliths are used in a number of ways to distinguish different stocks of thesame species (Begg et al, 2001).
For example, otolith increment width or otolithshape are often used to separate stocks (Burke et al, 2008). Analysing otolithelemental composition is another technique used to determine the differencesbetween stocks. Elemental composition reflects endogenous processes andexternal factors which relates to the fish species environment (Swan et al, 2006).
This is very useful when trying to discriminate between stocks. Otoliths can be used to recreate life histories andmovement of bony fish species (Elsdon et al, 2008). Hard structures such asotoliths are also important tools in recreating past climatic conditions andpredicting future environmental changes and variations (Smoli?ski and Mirny, 2017). Thesesources are currently underutilized for measuring and predicting environmentalresponses to changes in climatic conditions (Morrongiello et al, 2012). Thepresence of environmental factors that are influential on fish growth can be revealedthrough examining the width of otolith annuli (Smoli?skiand Mirny, 2017).
Otoliths are also usefulfor creating element profiles using environmental data, which can recreate pastenvironmental factors over decades and centennial periods (Izzo et al, 2016).Studies also showed that growth irregularities in otoliths mirrorirregularities in body size, which may benefit scientists studying species in areasof little data as otoliths patterns may help recreate life histories. (Blacket-al, 2013). Commercial species such as plaice, haddock and herringare valuable species for Ireland’s fishing industry. In the 2015, commerciallandings of Atlantic herring had a value of 8,351,982 euro and haddock landingshad a value of 6,416,707 euro (Conservation etal, 2017). In 2016 the seafood industry contributed 1.
1 billion euro in grossdomestic product (GDP) to the Irish economy, commercial species landed inIreland contributed 376 million euro to this figure (Anon, 2016). Conservationmanagement and sustainable fishing relies on the knowledge of spatial dispersalof species in relation to environmental factors (Lauria et al, 2011).Environmental factors such as temperature and salinity determine therelationship between species and its associated habitat. As well as determiningthe presence, survival rate, reproduction rate and the rate at which thespecies will grow (Lauria et al, 2011). If environmental conditions changesignificantly, species will inhabit areas with the most favourable resourcesfor survival. One of the main factors in the fluctuations of fish stocks areclimatic changes and unfavourable conditions which affects the productivity offish species (Rouyer et al, 2014).
Even small changes in fish growth can effectmortality, biomass and catch for the species (Rountrey et al, 2014). Studiesshow that fish species deemed to be insensitive to changes in climaticconditions and environmental factors may still face important changes in growthrate and body size that may have significant effects on productivity and thestock of fisheries (Rountrey et al, 2014). Environmental factors can contributeto the loss of biodiversity in the ocean ecosystem.
Otolith samples are collected by fisheries researchinstitutes all over the world. The marine institute in Ireland collectsotoliths from surveys such as the Irish ground fish survey (IGFS). Otoliths arenormally removed and collected from fish species caught on the surveys. Themarine institute mount some otolith samples, while other samples are leftunmounted and are archived.
Regardless of whether the otolith is mounted orunmounted all samples are archived. The archived samples may have accumulatedover many years from numerous surveys allowing for large collections to develop.This allows a broad range of data to be analysed. The archived samples are mainlycollected for age determination. However archived samples are also available forscientists addressing additional research questions.
Archived otoliths are often use to determine pastgrowth rates and can be used in climate change studies. For example historicotoliths can be compared to modern day otoliths to determine the difference inpast growth rates compared to modern growth rates (Bolle et al, 2004). DNA can also be extracted from archived otolith samples whichcan be combined with fish populations and niche models to determine different geneticpopulations of a species (Bonanomi et al, 2015). Archived otoliths can also be used to determine environmentalfactors that influence fish growth, as well as being used to determine rapidchanges in the ecosystem (Smoli?ski and Mirny, 2017). Data for environmental factors can be obtained throughthe continuous plankton recorder (CPR). The continuous plankton recorder hasbeen used since 1931 and is towed behind ships such as commercial ships tocollect plankton samples. Plankton distribution is a great indictor of changesin the marine environment, which is necessary for fisheries as well as forassessments of climatic change impacts (Batten and Burkill, 2010).
Sea surface temperature (SST) data can also be used todetermine the effects of environmental factors such as temperature change. Seasurface temperature is the skin temperature of the ocean surface water(Schluessel et al, 1987). Sea surface temperature data can be found on sitessuch as the North East Atlantic Real Time Sea Surface Temperature site which isa site published by the marine institute for data on the seas surroundingIreland such as the North East Atlantic.
The aims of this is study are 1) to compare plaice otolithsfrom the Celtic sea between the years 1990 to 2016 .2) to examine temporalchanges in growth rate and examine relationships between growth andenvironmental conditions. Otoliths compared from 1990 to 2016 will help todetermine the influence of environmental factors on the growth rates ofcommercially important species. Comparing otoliths will help determine if thereis a trend or pattern from 1990 to 2016 otoliths.
The age of the fish whencaught can also be compared to determine changes in growth rate. Otolithsamples will be received from the marine institute archived otolith collection.
