Capelin samples from the September surveys

Geographical distribution of males and females at ages 2-4

Geographic distribution of samples

Bifrost is not an area distributed model. However, issues connected to geogaphical distribution are nevertheless important. Here, the geographical distribution of stock entities from the samples taken at the yearly September survey is presented. The Russian data are not in place for all years.

Within-sample distribution on age

For each sample the distribution at age and sex is shown in a pie chart pie. The sector for ages start at the left (hour 2100), as shown below.

Within-sample distribution on sex

The age distribution of females is shown on an outer pie. Overlayed on this is the distribution of males. If there are equal amounts of males and females, the radius of the inner pie will be half the radius of the outer pie.

Area integrated distributions

In addition to geographical distributions also area integrated distributions of the innermost growth zone and maturation is shown. These quantities have a bearing on the modelling approach in Bifrost and the line graphs presented provide food for thought concerning future developments of the model. The plot styles for different stock groups are:

Size of innermost growth zone

A small growth zone the first year may be indicative of late spawning. The late spawning component might be estimated by including terms in the likelihood for the age distribution of mature capelin in the main spawning period. If the later length at age is affected by the growth the first year, late spawning may have long term effects that may be necessary to address in the management models, not to mention the possibility of having different harvest strategies for late and early spawning capelin. In the growth zone vs. length plots, females are shown in red and males in blue.

Maturation

In the current (2013) maturation model for capelin in Bifrost it is assumed that the maturation is determined by length alone. The capelin in the September data data are determined to maturation degree following a visual scale. For females also a maturation scale based on gonadal development has been implemented. Here, only maturation in stage 2 or more mature is investigated.