Brendan O'hea*, Graham JOHNSTON, Jonathan WHITE, and Leonie DRANSFELD
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ACTA ICHTHYOLOGICA ET PISCATORIA (2013) 43 (4): 285–291 DOI: 10.3750/AIP2013.43.4.04 LENGTH–WEIGHT RELATIONS FOR SEVEN GRENADIER SPECIES (ACTINOPTERYGII: GADIFORMES: MACROURIDAE) TO THE WEST OF IRELAND Brendan O’HEA *, Graham JOHNSTON, Jonathan WHITE, and Leonie DRANSFELD Marine Institute, Rinville, Oranmore, Co. Galway, Ireland O’Hea B., Johnston G., White J., Dransfeld L. 2013. Length–weight relations for seven grenadier species (Actinopterygii: Gadiformes: Macrouridae) to the west of Ireland. Acta Ichthyol. Piscat. 43 (4): 285–291 . Abstract . Length–weight regressions for seven grenadier species: Coryphaenoides rupestris Gunnerus, 1765, Trachyrincus murrayi Günther, 1887, Coelorinchus caelorhincus (Risso, 1810), Nezumia aequalis (Günther, 1878), Coryphaenoides mediterraneus (Giglioli, 1893), Coelorinchus labiatus (Köhler, 1896), and Coryphaenoides guentheri (Vaillant, 1888) are calculated from data collected on a series of deepwater surveys conducted by the Irish Marine Institute from 2006 to 2009, on the continental slope to the west and northwest of Ireland and the northern slope of the Porcupine Bank. The regression calculated for roundnose grenadier, C. rupestris , is com - pared with other regressions calculated for the species from different areas of its north Atlantic range. The diffi - culties associated with measuring many grenadier species, due to the fragility of their tails, are discussed. A rec - ommendation is made that pre-anal fin length should be accepted as the standard . Keywords: rattails , whiptails, deepwater survey, length–weight regression, northeast Atlantic, pre-anal fin length, regression comparison Grenadiers have a short, squat body, which leads into rupestris from this work with other regressions derived for a long whip-like tail. In many species the tail is very frag - different areas of the North Atlantic, and determines if any ile and can break easily. This creates difficulties when differences in length by location can be observed. Data measuring samples. Grenadier length measurements have used in these regressions were collected at different times been the subject of research since the 1960s. Much of this during the year. Where authors produced a number of work however has tended to focus on roundnose grenadier, regressions we selected the one corresponding closest to Coryphaenoides rupestris Gunnerus, 1765, and roughhead our work. Length–weight relations are compared with grenadier, Macrourus berglax Lacepède, 1801 (see Greenlandic data for Günther’s grenadier, Coryphaenoides Jørgensen 1996, Kelly et al. 1997, Danke 1987, guentheri (Vaillant, 1888), as is pre-anal fin length to total Magnusson 1987, Atkinson 1981, 1991, Savvatimsky 1994). length data for Murray’s grenadier, Trachyrincus murrayi Over the years, different length measurements have (Günther, 1887). been used in different countries and for different The Irish Marine Institute conducted a series of deep - Macrouridae species: total length (TL; Gordon 1978), head water fishing surveys aboard the R/V Celtic Explorer length (HL; measured from the tip of the snout to the pos - between 2006 and 2009, (ICES survey codes terior end of the operculum; Coggan et al. 1999, Swan et IDWS2006–2009). From 2006 to 2008 the surveys were al. 2003), pre-anus length (PA; from the tip of the snout to carried out in September, but moved to December in 2009. the front edge of the anus; Bergstad 1990, Kelly et The surveys concentrated on three areas of the continen - al. 1997), and pre-anal fin length (PAFL; from the tip of the tal slope to the west of Scotland and Ireland, and the snout to the base of the first anal fin ray (Jørgensen 1996) northern slope of the Porcupine Bank (Fig. 2). These areas (Fig. 1). The lengths were rounded to the nearest 0.5 cm. In are a subset of areas fished during a series of deepwater the cited sources, lengths have been measured either in surveys carried out by the Institute in the 1990s. Survey whole centimetres, half centimetres, or millimetres . methodology and sample collection protocols were based In this study data from the Irish deepwater surveys on those developed by the International Bottom Trawl 2006 to 2009 are used to derive length–weight relations for Survey (Anonymous 2012), and followed measurement 7 species of grenadier caught to the west of Ireland. It also protocols used by the Scottish Marine Laboratory which compares length–weight relations for Coryphaenoides were subsequently adopted by the Planning Group * Correspondence: Mr Brendan O’Hea, Fisheries Ecosystems Advisory Services, Marine Institute, Rinville, Oranmore, Co. Galway, Ireland, phone: +353 91 387200, fax: +353 91 387201, e-mail: brendan.ohea@marine.ie . 286 O’Hea et al. on North-East Atlantic Continental Slope Survey, urements of pre-anus length and pre-anal fin length were PGNEACS (Anonymous 2008). Fishing hauls were made made to the nearest millimetre below, and weight to the at depths of 500, 750, 1000, 1500, and 1800 m in each nearest 0.1 g. For two species with robust, unbroken, tails, area. Fishing tows were carried out along the contour of Coelorinchus caelorhincus (Risso, 1810), and the slope. Effective fishing time, from when the net set - Trachyrincus murrayi , measurements of total length were tled on the bottom to when it was hauled, was 2 h from also carried out. 2006 to 2008. In 2009, based on the recommendation of Linear regressions were carried out to derive a relation PGNEACS it was decided to reduce the fishing time to for pre-anal fin lengths to total lengths, 1 h (Anonymous 2009). Net and gear specifications can y = a + bx be found in Anonymous 2008. where: y = TL [cm], x = PAFL [cm], b = slope, and Fish catches were fully sorted, normally to species a = intercept. For lengths and weights regressions in the form level, and weighed. Each year full biological sampling, i.e., W = aL b length, weight, sex, maturity, and otolith collection was were: derived where W = weight [g], L = PAFL [cm], carried out on a number of target commercial species, b = slope, and a = intercept (Tables 1 and 2). Outliers in the including Coryphaenoides rupestris . For species where data were identified on the log transformed data by calcu - a large catch was made during a haul a random sub-sam - lating the distance measure “DFFITS”, which establishes ple of that catch was taken for length and weight measure - the predictive value of each data point by recalculating the ments. Length measurements were carried out on all other regression with each point omitted in relation to the origi - grenadier species. All grenadiers were measured from the nal regression function (Belsley et al . 1980). By comparing 2 tip of the snout to the pre-anal fin, measurements are against a critical value defined as p/n where p is the num - rounded to the nearest half centimetre below. The fish ber of parameters in the model and n is the number being measured are rounded to the measurement below of observations, outliers can be objectively identified their length (a grenadier of 5.9 cm would be recorded as and removed. 5.5 cm rather than 6.0 cm). Total weights were to the These outliers were then extracted from the dataset nearest gram. Length and weight data on some grenadier and the length weight relations were recalculated. Froese species were collected on an opportunistic basis, whenev - (2006) and Froese et al. (2011) recommend that the 95% er time allowed. confidence limits of the slope b, and the intercept a, as Random samples were also frozen for later measure - well as the sample size ( n) should be reported. These ments in the laboratory. For these samples length meas - results are presented in Table 3. Table 1 Length–weight relations for seven grenadier species (Actinopterygii: Macrouridae), including previously published data L–W parameters Species r2 L–W relation Area [reference] ab Coryphaenoides rupestris 0.478 2.687 0.988 PAFL–W Greenland [J] Coryphaenoides rupestris [♀] 0.239 2.872 0.991 PAFL–W Mid-Atlantic Ridge [D] Coryphaenoides rupestris [♂] 0.198 2.958 0.991 PAFL–W Mid-Atlantic Ridge [D] Coryphaenoides rupestris 0.732 2.587 PA–W Rockall Trough [K] Coryphaenoides rupestris 0.48 2.63 PA–W Skagerrak [B] Coryphaenoides rupestris 0.213 2.944 0.976 PAFL–W Rockall Trough [O’] Coryphaenoides rupestris 0.388 2.877 PAFL–W Iceland [M] Coryphaenoides guentheri 0.278 2.705 0.997 PAFL–W Greenland [J] Coryphaenoides guentheri 0.227 2.644 0.931 PAFL–W Rockall Trough [O’] Trachyrincus murrayi 0.132 2.583 0.824 PAFL–W Rockall Trough [O’] Coelorinchus caelorhincus 0.51 2.385 0.91 PAFL–W Rockall Trough [O’] Coelorinchus caelorhincus 0.001 2.42 0.87 PAFL–W Ionian Sea [L] Nezumia aequalis (fresh) 0.251 2.786 0.901 PAFL–W Rockall Trough [O’] Nezumia aequalis (frozen) 0.367 2.646 0.761 PAFL–W Rockall Trough [O’] Coryphaenoides mediterraneus 0.25 2.832 0.986 PAFL–W Rockall Trough [O’] Coelorinchus labiatus 0.072 2.873 0.969 PAFL–W Rockall Trough [O’] L = length (generalized), W = weight, a = slope, b = intercept, r2 = coefficient of determination; PA = pre-anus length, PAFL = pre-anal fin length; References: J = Jørgensen (1996), D = Danke (1987), K = Kelly et al. (1997), B = Bergstad (1990), O’ = this study, M = Magnusson (1987), L = Labropoulou and Papaconstantinou (2000). S Length–weight relations for seven grenadier species from west of Ireland 287 In total 91 835 grenadiers comprising ten species were intact tails. This was despite the fact that the fish brought caught over the time series. Length–weight relations were back to the laboratory were selected specifically as having calculated for seven grenadier species (Table 1). In addi - complete tails. For C. rupestris , an intact fish was defined tion PAFL to TL relations were calculated for the two as one where the tail terminated at a hair-like point.