NZ Southern Arrow Squid

Discussion in 'Physiology and Biology' started by Jean, Jan 27, 2004.

  1. Jean

    Jean Colossal Squid Supporter

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    Hi all,

    Before Christmas I had some requests to post my thesis onto Tonmo, well I've done some checking & apparently I'm not allowed to, something about the University owning the intellectual property rights or the copyright or something like that :( Sorry folks. What I can and have done is attached the abstract and if anyone wants me to, I can write a more comprehensive summary! (Although no guarantee's as to how long it will take me :lol: )

    Cheers

    J
     
  2. Jean

    Jean Colossal Squid Supporter

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    Darn....forgot the abstract :oops:!


    Abstract

    Nototodarus sloanii is an important component of the Southern Ocean fauna and is the basis of a large commercial fishery. Despite this there is still much to learn of the biological information about this species.
    Squid were collected (n=1020) by research vessel and by commercial jigger from 16 sites around the coast of New Zealand, a further small sample of juvenile squid was caught by light trap. Squid were immediately frozen and returned to the Portobello Marine Laboratory for analysis.

    Morphometric measurements were taken from both hard and soft tissues and were analyzed using Principle Components Analysis (PCA). There were problems with damage and plasticity of the soft tissue and thus they were not used in this part of the analysis. The hard tissues used were 5 measurements on each of the upper and lower beaks and 2 measurements on the gladius. PCA analysis suggested divisions in squid populations between shallow and deep water and between broad geographic locations (Canterbury, Otago, Catlins). These divisions were only apparent in the hard tissue measurements. They did not appear in age, dietary or reproductive differences.

    A sub sample of squid were aged using their statoliths (n= 281, 139 male and 142 female). No squid was found to be older than 206 days. All squid had begun the maturation process by 91-120 days and all were mature at 180 days. There were different growth rate for male and female squid. Females tended to be longer and heavier than males of a similar age.
    Back calculation from the date of capture showed that hatching was spread from August to February with a peak in late austral spring/ early summer. This indicates that N. sloanii spawns for most of the year. Growth rate for male squid differed depending on whether squid were hatched in the winter/spring or summer. Growth rates were more variable in the winter/spring hatched individuals and they attained larger size than summer hatched squid. This was not the case for female squid. Mean age for immature winter/spring hatched squid was significantly higher than for summer hatched squid. There was no difference in mean mantle length or body mass. There were no significant differences between mean age, mantle length or body mass for same gender mature squid regardless of hatch season. However mature female squid hatched in the winter/spring season were significantly longer than mature male squid hatched in winter/spring. No other differences were found.

    Validation experiments were run on juvenile squid caught in a light trap (n=7). Calcein marks were visible in 5 of the statoliths but they were incomplete and indistinct and the periodicity of the growth rings could not be validated.

    Gladius increments were examined and measured for 2 squid from each location (n=34). Individual growth curves were reconstructed for these specimens. No two curves were the same and there was a gender difference. Female squid had a shorter initial slow growth phase than male squid, indicating that growth varies considerably between individuals.

    A sub-sample of squid stomachs were retained for diet analysis (n=624, 299=female, 325= male). There were no significant differences between male and female prey ingested or numbers of otoliths found so all data was pooled. Nototodarus sloanii was found to prey on 16 species, of which 12 were identifiable teleost fish, 2 were crustaceans and 2 were cephalopods. Numerically, the euphausid krill, Nyctiphanes australis was the most important prey species, with the Lanternfish, Lampanyctodes hectorisi/i]and the Pearlside, Maurolicus muelleri as the next most important prey species.

    Most of the squid caught were immature stage 2 individuals. There was no significant difference between sites and so all data was pooled. GSI’s were calculated for male and female squid. These were low (7.12%± 0.3% for females and 1.9% ± 0.2% for males) suggesting that these squid are intermittent spawners. This is further supported by a histological examination which found germinal cells of different stages present in the same gonad. Histological examination was also used to validate the Lipinski maturity scale for use with this species, while some mis-identification occurred the scale is useful to place squid into the broad categories of immature, maturing or mature. Finer scale identification is not possible using this scale with this squid as maturation appears to be a continuum.
     
  3. um...

    um... Architeuthis Supporter

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    I don't know what the heck some of that meant (e.g. GSI?), but a lot of it sounded interesting. I, for one, would appreciate more details about pretty much everything mentioned in your abstract, Jean. :)
    :read:

    :notworth: to you and all of the other smarty-pantses who do this stuff.
     
  4. Jean

    Jean Colossal Squid Supporter

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    OK will do..............I'll even use English! I confess I just lifted that right out of my thesis file!

    GSI is a gonado-somatic index..........basically the relationship between reproductive tissue and everything else!

    J
     

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