Growth patterns and age validation from otolith ring deposition in New Zealand longfin eels Anguilla dieffenbachii recaptured after 10 years at large.

In 1998, 9500 juvenile New Zealand longfin eels Anguilla dieffenbachii (mean total length, LT , 42 cm) captured from the lower Clutha River were transferred upstream to Lake Hawea, a high-country oligotrophic lake in the same catchment where recruitment of juvenile eels has been prevented by hydroelectric dams since 1958. A total of 2010 of the transferred A. dieffenbachii were tagged with coded wire tags. Ten years later in 2008, the A. dieffenbachii population in Lake Hawea was sampled resulting in 399 recaptures (distinguishable by the presence of tags and by LT from the remnant resident population of large old A. dieffenbachii) of the 1998 transfers; 79 (19·2%) of the recaptured fish had tags compared with 21·3% at release, indicating good tag retention and low mortality due to tagging. All recaptured tagged A. dieffenbachii were female. Mean annual growth over the 10 years since release was 3·80 cm year(-1) for all recaptures and 3·65 cm year(-1) for tag recaptures, and both were significantly greater than the estimate of 2·38 cm year(-1) at release. After release, mean condition (K) increased significantly (P < 0·001) for all recaptures and tag recaptures. Annual length growth increment was linear. Tag recaptures showed significant increases in somatic growth rate post-transfer, and otoliths from the 2008 recaptured A. dieffenbachii were examined to see whether any similar enhanced growth after transfer was incorporated into the otolith structure that would serve as a date stamp. Measurement of otolith ring radii indicated that an increase in the radius occurred on most otoliths corresponding to the year after transfer. Because there was 9 years of completed growth following the observed growth inflection on the otoliths, this was strong evidence that opaque rings were formed annually.

Influence of boundary effects on minimum spanning tree features. A computer simulation.

OBJECTIVE: To assess the influence of boundary effects on quantitative data derived from the minimum spanning tree (MST). STUDY DESIGN: In a computer simulation, 10 patterns of points (resembling populations of nuclei in tumor tissue) were generated, ranging from completely regular to very irregular. This allowed for assessing the influence of boundary effects in populations with different degrees of disorder. A stepwise reduction of the size of the sampling window enabled the analysis of the influence of boundary effects at different sample sizes (from 1,024 down to 9 points). RESULTS: Both the mean and coefficient of variation of all features remained rather constant with decreasing sample size down to a sample size of 64 points per MST. CONCLUSION: Based on this model, it is concluded that boundary effects have only a minor influence on the outcome of MST features when the sample size is larger than 64 points.