Drift probabilities for Icelandic cod larvae

The climatological distribution of juvenile Icelandic cod is characterized by a negative spatial age gradient, with a fairly abrupt decrease in age near the northwest corner of Iceland, and a spatial abundance gradient with higher concentrations of 0-group fish inshore. Flowfields from a high-resolution circulation model developed for Icelandic waters were used to investigate larval drift from the various spawning grounds in Icelandic coastal waters to understand the distribution of 0-group fish. To present the results clearly, drift probability density functions (pdfs) are derived describing the probability of drifting from a given spawning ground to a given spatial region over a specified time interval. These pdfs are used to determine the spawning grounds most probably contributing to the observed age distribution. The observed spatial gradient in age is likely due to differences in the spawning location of larvae, with older larvae originating in spawning grounds in the southwest and younger larvae from farther north. In general, the contribution from the main spawning grounds in the southwest is predicted to decrease with clockwise distance from the source region. The pdf technique was also used to investigate drift from regions on the south coast of Iceland corresponding to known or possible subpopulation spawning grounds, to see whether these spawning areas are associated with distinct drift patterns. This technique is a useful way to present larval drift results and to facilitate comparison with real data.