Studies of the age, growth and shell increment patterns in the New Zealand cockle (Austrovenus stutchburyi)

ix, 155 leaves :ill., maps ; 30 cm. Includes bibliographical references. "April 1996." University of Otago department: Marine ScienceAustrovenus stutchburyi were collected (n=1100) from Papanui Inlet on the Otago Peninsula and half were marked using the fluorescent dye, calcein, and half were marked by exposing them to an abrupt decrease in temperature which thermally stressed the animals. A proportion of the cockles (n=660) were returned to cages in Papa.nui Inlet while the remainder (n=440) were maintained in tanks at the Portobello Marine Laboratory. Once a month, ten marked cockles from each treatment from each treatment from both Papanui Inlet and the Laboratory were collected and sacrificed by immersion in hot fresh water. The thermal stress method failed to leave a discernible mark in the shell and, therefore, these cockles were used for allometric measurement only. The cockles that had been treated with calcein were used for the growth analysis. These shells were cleaned, measured and internal increments examined using the thin section method. Under an ultraviolet light source, calcein was found to be incorporated as a green line in the shell. Measurements from the calcein line to the shell edge allowed a growth rate to be calculated. Thin sectioning of the shells revealed that there are two types of growth increment: larger macro-increments and smaller micro-increments. The calcein mark allowed the periodicity of these to be examined. The results indicate that the macro-increments found in the shell are annual in nature. Analysis of the periodicity of the micro-increments revealed that during the warm months of summer the periodicity of these increments is tidal. However, this periodicity breaks down over winter. In the summer months there was a relationship between the width of micro-increments and the spring/neap tidal cycle, with wider, more complex, micro-increments being laid down during spring tides and narrow, simple micro-increments being laid down during neap tides. Seasonality of growth was determined by examining the marginal increment on the shells and by comparing the actual growth of samples collected in summer and winter. The results support the hypothesis that Austrovenus siuichburui grows slowly in winter and faster in summer. There is also a slowing of allometric growth in summer that may be related to the physiological stress of gametogenesis and spawning. Cockles maintained in the laboratory showed little or no growth for the duration of this study. This may have been due to inadequate or inappropriate food

Aspects of the population biology of the southern arrow squid, Nototodarus sloanii, in southern New Zealand

Nototodarus sloanii is an important component of the Southern Ocean fauna, and the basis of a large commercial fishery. Despite this, much is unknown about the biology of this species. This study examines some aspects of the biology of N. sloanii. Stomach contents analysis identified no significant differences in diet between male and female squid. Sixteen putative species, including 12 identifiable teleosts, 2 crustaceans, and 2 cephalopods were identified in the diet of this species. The euphausid, Nyctiphanes australis was the most important prey item, Lanternfish, Lampanyctodes hectoris, and Pearlside, Maurolicus muelleri, were of secondary importance. Squid were aged using counts of statolith micro-increments and back-calculation from the date of capture showed that hatching occurred between August and February, with a peak in the austral winter/spring and another smaller peak in the austral summer. 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, although there was no significant difference in mean mantle length or body mass. No significant differences between mean age, mantle length, or body mass for same-gender mature squid, regardless of hatch season, were apparent. However, mature female squid hatched in the winter/spring season were significantly longer (ML) than mature male squid hatched in winter/spring. No squid was found to be older than 211 days. All squid had started to mature by 91-120 days old and all were fully mature at 180 days. Validation experiments run on juvenile squid using calcein markers were inconclusive, however the increments in the statoliths were very similar to those found in other validated species of ommastrephid squid, thus for the purposes of this study they were assumed to be of daily periodicity. Gladius increments identify a gender difference in growth rate, with female squid having a shorter initial slow growth phase than male squid. Gonadosomatic indices (GSIs) 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. Lack of mature individuals in this study means that these results are suggestive rather than definitive; more examination of the reproductive process of this squid is required. Histological examination was also used to validate the Lipinski maturity scale for use with this species, while some misidentification occurred the scale is useful to place squid into the broad categories of immature, maturing, or mature. New maturity scales were created for N. sloanii utilising these broad categories. Finer-scale identification is not possible using this scale, as maturation appears to be a continuous process. Morphometric measurements were taken from both hard and soft tissues and were analysed using non-metric multidimensional scaling and analysis of similarity. Divisions were only apparent in the hard structure measurements. They did not appear to be age, dietary or reproductive differences

Studies of the age, growth and shell increment patterns in the New Zealand cockle (Austrovenus stutchburyi)

ix, 155 leaves :ill., maps ; 30 cm. Includes bibliographical references. "April 1996." University of Otago department: Marine ScienceAustrovenus stutchburyi were collected (n=1100) from Papanui Inlet on the Otago Peninsula and half were marked using the fluorescent dye, calcein, and half were marked by exposing them to an abrupt decrease in temperature which thermally stressed the animals. A proportion of the cockles (n=660) were returned to cages in Papa.nui Inlet while the remainder (n=440) were maintained in tanks at the Portobello Marine Laboratory. Once a month, ten marked cockles from each treatment from each treatment from both Papanui Inlet and the Laboratory were collected and sacrificed by immersion in hot fresh water. The thermal stress method failed to leave a discernible mark in the shell and, therefore, these cockles were used for allometric measurement only. The cockles that had been treated with calcein were used for the growth analysis. These shells were cleaned, measured and internal increments examined using the thin section method. Under an ultraviolet light source, calcein was found to be incorporated as a green line in the shell. Measurements from the calcein line to the shell edge allowed a growth rate to be calculated. Thin sectioning of the shells revealed that there are two types of growth increment: larger macro-increments and smaller micro-increments. The calcein mark allowed the periodicity of these to be examined. The results indicate that the macro-increments found in the shell are annual in nature. Analysis of the periodicity of the micro-increments revealed that during the warm months of summer the periodicity of these increments is tidal. However, this periodicity breaks down over winter. In the summer months there was a relationship between the width of micro-increments and the spring/neap tidal cycle, with wider, more complex, micro-increments being laid down during spring tides and narrow, simple micro-increments being laid down during neap tides. Seasonality of growth was determined by examining the marginal increment on the shells and by comparing the actual growth of samples collected in summer and winter. The results support the hypothesis that Austrovenus siuichburui grows slowly in winter and faster in summer. There is also a slowing of allometric growth in summer that may be related to the physiological stress of gametogenesis and spawning. Cockles maintained in the laboratory showed little or no growth for the duration of this study. This may have been due to inadequate or inappropriate food