The simplest measure of population status is an estimate or index of the abundance at any given time. A series of estimates through time can be used to evaluate the population’s trend (i.e., increasing, declining, stable).
The most commonly used relative abundance index is based on catch per unit effort (CPUE), with catch in either weight or numbers of fish, and effort measures such as hooks, sets, or search time, depending on the fishing method. CPUE is usually standardized (a statistical modelling process) to adjust for factors not related to abundance.
Both target and bycatch populations are often monitored using longline CPUE. Fisheries scientists commonly fit dynamic population models to relative abundance indices.
See also ‘Bycatch Interaction Rates’.
- Etienne, M.-P., Obradovich, S., Yamanaka, L., and Mcallister, M. 2013. Extracting abundance indices from longline surveys: method to account for hook competition and unbaited hooks. arXiv preprint arXiv:1005.0892.
- NMFS. 2004. A Requirements Plan for Improving the Understanding of the Status of US Protected Marine Species. Report of the NOAA Fisheries National Task Force for Improving Marine Mammal and Turtle Stock Assessments. NOAA Technical Memorandum NMFS-F/SPO-63.