A fp7 Project: Management and Monitoring of Deep-sea Fisheries and Stocks wp2 – Template for Case Study Reports Case study 2 demersal deep-water mixed fishery Pascal Lorance, Ifremer, Nantes (coord.)
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- 4.3.3. Age determination materials and methods used.
- 4.3.4.Ages validation
- 4.3.5.Are the age data considered to be reliable
- 4.3.6.Age estimation workshops
- 4.3.7.Quality of biological data (quality, temporal and spatial extent, time series, availability, accessibility, flow)
4.3.Biological data for your stock4.3.1.4.3.1 Please complete the table below for each fleet/survey inserting in each cell the time series of data available, if quarterly (q) or annual (a), and if collected by observers (O), by market sampling (MS) or both (OMS). Please append all available time-series of quarterly and annual data.4.3.1 Please complete the table below for each fleet/survey inserting in each cell the time series of data available, if quarterly (q) or annual (a), and if collected by observers (O), by market sampling (MS) or both (OMS). Please append all available time-series of quarterly and annual data.
4.3.2.For the most recent assessment, how was total international catch data raised from fleets and what are the strengths and weakness of the current raising regime?French landings were extracted from logbook data. For roundnose grenadier, concerns were expressed over time about the reliability of the landings from international waters. In 2010, data of the Spanish fleet fishing in ICES division VIb and XIIb were provided. All data are not provided by statistical rectangle. Nevertheles, in ICESDivision Vb, VIa and Subarea VII the landings data are available for all fishing fleets.There is no major concern with the rasing regime. Conversion coefficients (between landed and live weight) may be a problem. This is a common concern for several species from the shelf as well as from the deep-water. This might require an specific review of how conversion coefficnet are applied over species, areas and fleets. 4.3.3. Age determination materials and methods used.Age data are available for roundnose grenadier. The most recent assessment was not age structure and age structure assessment may not be the best option for this species. Age estimation method was decribed in Lorance et al (2003). Further an intercalibration working group suggested a low level og agreement between readers. Age data were collected in the past for blue ling. Age estimation were resumed in 2009 under DCF, 750 blue ling otolith were read in 2009. The preparation of otoliths and age estimations methods followed the standard used for gadoid species. Although age reading of blue ling were abandoned in the early 1990s because they were considered poorly reliable, the otolith sections obtained with modern equipment seem quite straightforward to interpret (Figure 4.3.3). Note that fish are sampled from auction market were blue ling is landed gutted, therefore the sex of the individuals is unkown while there is a known sexuel dimorphism in this species (Ehrich and Reinsch 1985; Thomas 1987; Moguedet 1988).
Figure 4.3.3. Cross section of otoliths of blue ling. Left individual of 121 cm, 15 years; Right individual of 125 cm, 19 years. 4.3.4.Ages validationAge were validated for juvenile roundnose grenadier based upon the seasonal variation of the otoltih margin (Gordon and Swan 1996). Ages of blue ling were not validated but ages estimated from otoliths of 1–2 group blue ling corresponded well with assumed ages based on modes in the length frequency distributions from Icelandic groundfish surveys (Bergstad et al. 1998) and available growth parameters from different authors are fairly consistent (Ehrich and Reinsch 1985; Thomas 1987; Moguedet 1988; Magnussen 2007). Age estimation of black scabbardfish for the west of the British Isles are not available. Nevertheless, age estimation carried out further south on fish caught to the West of Portugal (ICES division IXa), in the canaries and Madeira suggest this sugest is short lived and fast growing. For this species age validation were carried out based upon the seasonal variation of the aspect of the otolith margin (see also CS 3c report). 4.3.5.Are the age data considered to be reliable?The growth increments observed on otolith have been validated as annual for some species and life stages. Where otoliths readings suggested high ages, this was confirmed by radiometric estimates (Andrews et al. 1999; Andrews et al. 2009). For roundnose grenadier age were considered poorly relaible based upon standard used from shelf species were a high 4.3.6.Age estimation workshopsFor roundnose grenadier, the exchange program followed by an intercalibration working group was done in 2007 (ICES 2007b). Altogether 66 sectioned otoliths were read on the slides and on images by 7 persons during the exchange program. All images were annotated. The overall agreement for sectioned otoliths agreement was low with 30.2 % (CV=10.4%). Similar level of aggrement between four otolith readers participating to the workshop was obtained by re-dearding 40 otoliths during the workshop. It was recommended that sectioning of otoliths should be used for the age determination of Roundnose grenadier. It is recognized that among readers random differences with respect to interpretations and age estimate errors will remain. The occurrence of such differences may only be reduced through frequent otolith exchanges and comparative readings.
In addition to this intercalibration, age in black scabbardfish were further validated for fish form the Canaries (Pajuelo et al. 2008). Nevertheless, for this species, alternative validation method would be useful. 4.3.7.Quality of biological data (quality, temporal and spatial extent, time series, availability, accessibility, flow)[a] impact on assessments and/or [b] affect your ability to provide timely fisheries advice to managers. Significant biological data have been accumulated for deep-water species. These are not given sufficient attention. Clearly the ranking of deep-water species by vulnerability carried out by ICES almost ten years ago should be revised as new data accumulated and deep-water species appears to be much more constrasted in terms of life history characteristics than previously thought. It is only in recent years that it was realised that black scabbardfish may live much less than 20 years, possibly 10-12 years only, i.e. less than most large commecial shelf demersal species. Age data for blue ling were not used in the past, while they probably convey valuable information on the stock status. Managers and stakeholders did not weel realized how much deep-water species are diversity. Their morphological, trophic and behavioural diversity was already stressed (Mauchline and Gordon 1985; Merrett and Haedrich 1997; Lorance and Trenkel 2006). This diversity seems to also applies to the essentiel live history parameters for the populations dynamics. Therefore, the different deep-water species exploited in this case study may sustain very different harvest rates and this has not been recognized so far.
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