Publication Abstract

The stability of estimates of sustainabilities in MSUPA over four years of data from predator stomachs

J.C. Rice, N. Daan, J.G. Pope and H. Gislason

This work investigates how consistent predator preferences and prey vulnerabilities are over time, The multispecies VPA (MSVPA), as parameterized for the North Sea, provides estimates of suitabilities of each age of each prey for each age of each predator. MSVPA outputs parameterized with four years of stomach data allowed investigation of the stability of these suitabilities over time. The suitabilities were analysed with several linear models. One set of analyses investigated the total variance in suitabilities. The overall variance increased by about 20% when four years of data were included, compared with the variance in suitability based on a single year of data. Root mean square errors differed by less than 2% when the same linear models are fitted to the natural log of suitability from single-year and multi-year parameterizations. Other analyses were done treating each predator-year combination as a level of the factor predator. In most cases parameter estimates of the same predator in different years did not differ significantly. Predator-prey interaction terms showed some changes from year to year, but far fewer than expected by chance. Slopes of predator size preferences also did not change from year to year for cod or saithe, but did for whiting. Together these analyses indicate that predator preferences and prey vulnerabilities are stable over time when the effects of changing abundance and age structure are accounted for. This suggests that good multispecies models, parameter-ized with good field data, may be used to investigate predator-prey dynamics in multispecies management.

Reference:

J.C. Rice, N. Daan, J.G. Pope and H. Gislason, 1991. The stability of estimates of sustainabilities in MSUPA over four years of data from predator stomachs. ICES Marine Science Symposium, 193: 34-45.