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Statolith and gladius aging of the Southern Arrow Squid ( Nototodarus sloanii )

Statolith and gladius aging of the Southern Arrow Squid ( Nototodarus sloanii ). Jean F. McKinnon Department of Marine Science, University of Otago George D. Jackson Institute of Antarctic and Southern Ocean Studies, University of Tasmania. Photo by Kerry Perkins. Introduction.

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Statolith and gladius aging of the Southern Arrow Squid ( Nototodarus sloanii )

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  1. Statolith and gladius aging of the Southern Arrow Squid (Nototodarus sloanii) Jean F. McKinnon Department of Marine Science, University of Otago George D. Jackson Institute of Antarctic and Southern Ocean Studies, University of Tasmania. Photo by Kerry Perkins CIAC, Hobart, 2006

  2. Introduction • The statolith is the most commonly used structure for ageing, life history reconstruction and growth studies. However, the gladius has been investigated more recently as a tool for age and growth studies. CIAC, Hobart, 2006 Photo by Kerry Perkins

  3. Aims • To age N. sloanii using the statoliths. • To develop a technique to read the increments in the gladius. • To create individual growth curves from the gladius data. CIAC, Hobart, 2006

  4. Capture locations for squid • Squid were collected from south-eastern NZ during commercial jigging operations North Island West Coast Canterbury Otago A Catlins P South Snares N M H G E C South Island J O F Q B D L I K R CIAC, Hobart, 2006

  5. Statolith aging • Stage of maturity was noted for each squid • Statoliths were removed from the statocyst CIAC, Hobart, 2006

  6. Statolith aging • The right statolith was used as a matter of convention • The statolith was mounted on a microscope slide, ground on wet carborundum paper and polished with 0.05µm Alumina on felt • 281 statoliths were polished (139 male and 142 female) Photomicrograph by Jean McKinnon CIAC, Hobart, 2006

  7. Statolith aging • The increments in the dorsal dome of the polished statolith were counted using a camera lucida • To ensure accuracy the increments were counted three times for each statolith with a month between each count. Each count had to be within 10% of the average to be considered precise. Typical Camera Lucida drawing of a statolith (scale bar = 0.1mm) CIAC, Hobart, 2006

  8. Statolith aging results • Squid ranged in age from 29 days to 206 days old. • There was increase in size, (both mantle length and weight) with increasing age, but there was low correlation between age and either mantle length or weight • The log transformed slopes of the regressions for log age versus log mantle length were significantly different (p<0.05) for male and female squid. CIAC, Hobart, 2006

  9. Statolith aging Female r2= 0.491 r2= 0.377 Male r2= 0.2566 r2= 0.2565 CIAC, Hobart, 2006

  10. Statolith aging • There was considerable overlap when the range of ages was compared to stage of maturity (Table one). On average, however, the more mature the squid was the older it was. Table one. Maturity stage and age range for Nototodarus sloanii (Males and females combined CIAC, Hobart, 2006

  11. 5 25 25 25 25 25 12 Age at maturity Female 25 25 25 25 20 19 Male CIAC, Hobart, 2006

  12. Increment Validation Photograph by Kerry Perkins • Seven juvenile Nototodarus sloanii were caught in a light trap off the Portobello Marine Laboratory Jetty. • They were held in a 65L glass tank with flow through seawater and were fed live zooplankton. They were left to recover for twenty-four hours. • The squid were transferred to a 10L bucket containing calcein at a concentration of 0.5gcalcein/L seawater. They were left in the bucket for two hours. • After two hours, the animals were returned to the 65L holding tank. • The squid were checked several times a day and were fed zooplankton in excess once a day. CIAC, Hobart, 2006

  13. Validation • Calcein was present in the statoliths of five of the seven squid stained. • The calcein band was indistinct and incomplete. CIAC, Hobart, 2006 Photomicrograph by Jean McKinnon

  14. Validation Modal Analysis • A Modal analysis (Uozumi, 1998) was run on the data collected from three of the Catlins sites; Haldane 1, Haldane 2 and Haldane 3. CIAC, Hobart, 2006

  15. Validation Location of samples used for modal analysis North Island South Island D I K CIAC, Hobart, 2006

  16. Validation • A length composition graph was created for each sampling date wherelength-frequency interval was taken for every 10mm dorsal mantle length. • The age of the squid from this sub sample was regressed against sample date. CIAC, Hobart, 2006

  17. Validation • There was a gradual progression in the modes from 160mm DML to 220 mm DML between 22nd of January and 30th of January 1999. This suggests that the squid are from the same cohort. CIAC, Hobart, 2006

  18. Validation • The relationship between the number of increments and sampling date was linear The equation for the regression was y = 1.0503 x + 4.0206 (r2 = 0.08, n = 56) • The relationship was significant at the 5% level (ANOVA) The estimated value of the slope is very close to one, suggesting that the periodicity of the increments is daily CIAC, Hobart, 2006

  19. Gladius aging • The gladii were removed, dried under weight and stored in labeled tissue paper in tall glass jars. • 293 gladii were prepared for aging, by wiping the surface with mineral oil. • The increments were counted using a dissection microscope with an adjustable fibre optic light source. • Counting criteria were the same as for the statoliths. CIAC, Hobart, 2006

  20. Gladius aging • The measurements from the gladius were used to reconstruct growth curves from the oldest and youngest individual found at each sample location. • Only the increments from two individuals from each location were measured as it is an extremely time consuming procedure • Because growth was extremely variable, the curves were smoothed by calculating the running mean CIAC, Hobart, 2006

  21. Gladius aging • Gladius increments could be seen on the central rib and lateral plate. Increments Central rib Lateral plate Lateral rib Photomicrograph by Jean McKinnon CIAC, Hobart, 2006

  22. Gladius aging • The counts were very similar to those of the statolith from the same animal. male female r2=0.980 r2=0.997 Statolith versus gladius increment counts CIAC, Hobart, 2006

  23. Gladius aging • The growth curves showed a period of slow growth ranging from 20 to 70 days long then there may or may not be a period of faster growth followed by a period of rapid growth. • There was variation in this pattern which could not be attributed to location or hatch season. • Gender appears to be an important factor in the growth rate of the squid. • Female squid show growth curves with only a short period of slow growth, male squid have a longer period of slow growth. CIAC, Hobart, 2006

  24. Gladius aging Female growth curve • Curves are from squid from the same location, with similar hatch seasons and caught at the same time. Gladius increment growth (mm) Male growth curve Gladius increment number CIAC, Hobart, 2006

  25. Discussion • Previous research has found N. sloanii aged up to 270 days, this study 206 days old (mature at 6 months?). • May have an ontogenetic migration • Restricted sample period=> older animals not present? • Tropical squid often have life spans of less than one year and mature earlier than temperate species. • Jackson et al (2000), found that N. sloanii predominantly occur in warmer waters. • Southland current has subtropical characteristics. CIAC, Hobart, 2006

  26. Discussion • The direct validation of the periodicity of the squid statoliths using calcein was not a success, however modal analysis suggests daily periodicity of the growth increments. • The juvenile squid in this study did not survive longer than 48 hours. • The individual growth curves show that most squid have rapid growth, but that the degree of that growth is extremely plastic. • The growth curves reconstructed for N. sloanii are different to those reconstructed for most other squid species. Gender differences not seen. • This period of slow growth may be an example of the squid showing “cool” strategies with a slow growing period which eventually leads to a large size. CIAC, Hobart, 2006

  27. Discussion • Gladius growth increments have the potential to provide information on the growth of individual squid. • May be used as an environmental indicator? Squid growth may be readily influenced by both biological andenvironmental parameters. CIAC, Hobart, 2006

  28. Acknowledgements Supervisors/Thesis readers! Dr George Jackson, Dr Philip Mladenov Assoc. Prof. Mike Barker Squid Collectors Sea Resources Ltd., Wellington Master and Crew F. V. Fuji Maru 63 Dr Steve O’Shea , AUT Master and Crew R.V. Kaharoa Sandford South Island Ltd Otakou Fisheries Ltd Mr Peter Fullerton, Sea Lord Co. Ltd Master and Crew F.V. Meridien General Staff and Students of the Department of Marine Science and Portobello Marine Laboratory, Especially, Kerry Perkins, Bev Dickson, Karen Bonney and Daryl Coup Travel Funding New Zealand Marine Science Society; First overseas conference travel fund CIAC, Hobart, 2006

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