Bomb Dating and Age Estimates of Big Skate (Beringraja binoculata) and Longnose Skate (Raja rhina) Jacquelynne King, Fisheries and Oceans Canada David Ebert, Moss Landing Marine Laboratories Craig Kastelle, Alaska Fisheries Science Center Thomas Helser, Alaska Fisheries Science Center Christopher Gburski, Alaska Fisheries Science Center Gregor Cailliet, Moss Landing Marine Laboratories ABSTRACT MATERIALS AND METHODS RESULTS Age and growth curve estimates have been produced for big skate Bomb radiocarbon analyses Big skate (Beringraja binoculata [formerly Raja binoculata]) and longnose skate 1. Big skate (n=12) and longnose skate (n=33) vertebrae were collected • the estimated birth years ranged from 1965-1970 (Raja rhina) populations in the Gulf of Alaska, British Columbia and during the early 1980s off California. These fishes were estimated to • there were no low ∆14C values for big skate California. Age estimation for these two skate species relies on growth be alive during the atmospheric testing of atomic bombs which resulted Longnose skate band counts of sectioned vertebrae. However these studies have not in the rapid increase in oceanic radiocarbon (14C). • the ∆14C values for longnose skate overlapped with mid to top portion of the produced similar results for either species, highlighting the need for age 2. Vertebrae where thin (0.7-1.0 mm) sectioned and mounted on ∆14C reference curve for Petrale sole (Fig. 3) validation. Archived large specimens of big skate and longnose skate microscope slides. • these skate were not as old as originally estimated but there were early collected in 1980 and 1981 had minimum age estimates old enough to 3. Ages were estimated based on vertebral band counts (Fig. 2) and birth bomb signal specimens 14 suggest that radiocarbon ( C) signals from bomb testing conducted in the years assigned based on date of capture and age. 80 late-1960s could be used to establish dates of growth band formation (Fig. 4. The distances of INSIDE bands (first 3 grouping) and OUTSIDE bands 60 1). Accelerator mass spectrometry provided measures of Δ14C associated (last 3 grouping) along the corpus calcarea were measured (Fig. 2). 40 with a year of growth band formation based on skate age estimates. We • INSIDE = assumed pre-bomb signal (low 14C values) used Bayesian statistics to compare these values to reference Δ14C a • OUTSIDE = assumed post-bomb signal (high 14C values) C) 20 14 marine teleost otolith chronology produced that exists for California. 5. INSIDE and OUTSIDE bands were milled with a high-resolution micro- Δ 0 milling system (Carpenter Systems CM-2). Each band grouping had a -20 target of 5-15 mg per specimen. -40 Captured in 1981 at 22 years of age 14 14 6. Assays of C were be completed using an accelerator mass OUTSIDE bands are post-bomb signal HIGH Δ C values -60 spectrometry. ( Radiocarbon -80 Petrale sole Age estimation and vertebrae preparation method Longnose skate 7. Additional vertebrae of the same specimens were thin (0.3-0.4 mm) -100 Petrale pulse function Skate pulse function sectioned and mounted on microscope slides with 1-one section -120 unstained (as in Fig. 1) and 2-one section stained with the histological 1950 1955 1960 1965 1970 1975 1980 1985 stain Harris hematoxylin (Fig. 2). Deposition year 8. Bias and precision between readers were assessed with bias plots and Figure 3. ∆14C values for longnose skate (diamonds) compared to published reference the average percent error index (APE) respectively. curve for Petrale sole (circles). 14 Age validation • age estimates for longnose skate (∆ C deposition year) based on vertebral 9. We used Bayesian statistics to compare the values of 14C to published band counts appeared to be accurate (Fig. 4) Petrale sole reference ∆14C data to estimate time of band formation. • low inter-reader bias (Fig. 5) and improved precision (APE=5.99 versus 10.These Bayesian estimates of time of band formation were compared to APE=10.17 for stained) between readers were obtained for the unstained the two sets of age estimates (unstained and stained). vertebrae Born in 1959 INSIDE bands are pre-bomb signal LOW Δ14C values 15 10 Figure 1. Longnose skate vertebral thin section, aged at 22 years. This fish was captured in 1981, and estimated to have been born in 1959 before the nuclear bomb testing marine signal. The INSIDE bands should be pre-bomb signal and have low 5 Δ14C values. The OUTSIDE bands should be post-bomb signal and have elevated, high Δ14C values. This section is unstained. SELECTED REFERENCES Campana, S., L. Natanson, & S. Myklevoll. 2002. Bomb dating and age determination of large pelagic sharks. Can. Counts Band 2 Reader 0 J. Fish. Aquat. Sci. 59: 450-455. 0 5 10 15 Gburski, C., Gaichas, S.K. & Kimura, D.K. 2007. Age and growth of big skate (Raja binoculata) and longnose skate Figure 4. Bayesian posterior distribution of Reader 1 Band Counts estimated ages compared to ∆14C-derived (R. rhina) in the Gulf of Alaska. Environ. Biol. Fish. 80: 337-349. Figure 5. Inter-reader bias plot for Haltuch, M., Hamel, O., Piner, K., McDonald, P., Kastelle, C., & Field, J. 2013. A California Current bomb true ages (i.e. Bias). Distribution centered longnose skate for Reader 1 vs. Reader radiocarbon reference chronology and petrale sole (Eopsetta jordani) age validation. Can. J. Fish. Aquat. Sci. 70: around zero suggests age estimation 2, unstained (blue diamonds) and 22-31. accuracy. There is indication of a higher McFarlane, G.A. & King, J.R. 2006. Age and growth of big skate (Raja binoculata) and longnose skate (Raja rhina) in stained (orange squares). The diagonal probability to underestimate ages. British Columbia waters. Fish. Res. 78:169-178. line is equivalence line. Natanson, L.J., J.A. Sulikowski, J.R. Kneebone & P.C. Tsang. 2007. Age and growth estimates for the smooth skate, Malacoraja senta, in the Gulf of Maine. Environ Biol. Fish. 80:293-308. Zeiner, S.J. & Wolf, P.G. 1993. Growth characteristics and estimates of age at maturity of two species of skates (Raja CONCLUSIONS binoculata and Raja rhina) from Monterey Bay, California. In S. Branstetter (Editor) Conservation biology of • the archived big skate were born post-bomb signal and the age methodology elasmobranchs, pp. 87-99. US. Dept. Comm., NOAA Technical Report, NMFS 115. for big skate cannot be validated with this approach and samples ACKNOWLEDGEMENTS We would like to thank Sandra Zeiner and Patricia Wolfe for collecting the big and longnose skate vertebrae in Figure 2. The same specimen as in Figure 1, but this vertebral thin section is • can now refine the ageing criteria for longnose skate 1980-1981 to make this research possible with these historical samples and the North Pacific Research Board stained with Harris hematoxylin in an attempt to enhance band visibility. • the age methodology for longnose skate is now validated for funding and support (NPRB Project 1202). • the most suitable vertebrae preparation is unstained The recommendations and general content presented in this poster do not necessarily represent the views or official position of the Department of Commerce, the National Oceanic and Atmospheric Administration, or the National Marine Fisheries Service. .