Controversy regarding the population status and rate of decline of large pelagic predators inferred from industrial fisheries catch and effort data was the primary motivation behind my PhD work. I chose to focus on three main question using the Japanese longline catch and effort data from 1950-2002.1) Given the complex temporal and spatial dynamics of fishing fleets and target species, how should Japanese longline catch and effort data be treated when used to develop abundance trends? 2) What do such trends indicate about stock productivity and trajectory given current exploitation levels? 3) How could fishing effort be distributed globally to limit fishing mortality on vulnerable species while maintaining viable industrial fisheries?

In addition to pursuing a PhD I have taught, since 2001, courses in the Fisheries Centre and Zoology department related to principles of applied ecology, theoretical population dynamics, modeling, and stock assessment. I also maintain a keen interest in exploring exploitation by humans as a selective force and the population level consequences of such selection.

Publications

Peer Reviewed

Ahrens, R.N.M. and Devlin, R.H. Submitted. Background-genotype effects on transgenes in populations: A growth-enhanced salmon simulation. Aquaculture.

Carruthers, T. R., McAllister, M.K. and Ahrens, R.N.M. In Press. Simulating spatial dynamics to evaluate methods of deriving abundance indices for tropical tunas. Can. J. Fish. Aquat. Sci. X:XX-XX

Jensen, O.P., S. Ortega-Garcia, S.J.D. Martell, R.N.M. Ahrens, M.L. Domeier, C.J. Walters, and J.F. Kitchell. In Press. Local management of a highly migratory species? The effects of longline closures and recreational catch-and-release for Baja California striped marlin fisheries. Progress in Oceanography. X:X-X.

Wittmer, H. U., Ahrens, R. N. M. and McLellan, B. N. 2010. Viability of mountain caribou in British Columbia, Canada:effects of habitat change and population density. Biological Conservation. 143(1):86-93.

Christensen, V., Walters, C.J., Ahrens, R., Alder, J., Buszowski, J., Christensen, L.B., Cheung, W.W.L., Dunne, J., Froese, R., Karpouzi, V., Kastner, K., Kearney, K., Lai, S., Lam, V., Palomares, M.L.D., Peters-Mason, A., Piroddi, C., Sarmiento, J.L., Steenbeek, J., Sumaila, R., Watson, R., Zeller, D. and Pauly, D. 2009. Database-driven models of the world’s large marine ecosystems. Ecological Modelling. 220: 1984-1996. PDF

Korman, J., Ahrens, R. N. M., Higgings, P. S. and Walters, C. J.. 2002. Effects of Observer Efficiency, Arrival Timing, and Survey Life on Uncertainty in Estimates of Escapement for Winter-Run Steelhead Trout (Oncorhynchus mykiss) Derived from Repeat Mark-Recapture Experiments. Can. J. Fish. Aquat. Sci. 59 :1116-1131. PDF

Book Chapters

Walters, C. J. and Ahrens, R. 2009. Oceans and Estuaries: Managing the Commons. In Principles of Ecosystem Stewardship. Resiliance-Based Natural Resource Management in a Changing World. Folke, C., Kofinas, G. P. and Capin, S., III eds. Springer New York.

Theses

Ahrens, R. N. M. 2010. A Global Analysis of Apparent Trends in Abundance and Recruitment of Large Tunas and Billfishes Inferred from Japanese Longline Catch and Effort Data. Ph.D. Thesis. University of British Columbia.

Ahrens, R. 1999. Heritable risk sensitive foraging in juvenile fish: potential implications for the dynamics of harvested populations. M. Sc. Thesis. University of British Columbia.

Reports

Ahrens, R. 2009. Middle (SG-2) and Lower (SG-1) Fraser River Sturgeon Monitoring Plan Guide. Prepared for British Columbia Conservation Federation. Surrey B.C. p.20.

Ahrens, R. N. M. 2006 Utility of the Steelhead Harvest Analysis in determining population trends and estimating escapement. Prepared for B.C. Ministry of Environment. Vancouver B.C. p. 48

Ahrens, R. N. M. 2005. The status of steelhead trout (Oncorhynchus mykiss) in British Columbia. Prepared for Pacific Fisheries Resource Conservation Council. Vancouver, B.C. p 384

Ahrens, R. N. M. 2003. Potential ecological consequences of introducing transgenes into wild coho populations. Prepared for Department of Fisheries and Oceans. West Vancouver, B.C.

Martell, S., Ahrens, R., Korman, J., Higgins, P. and Walters, C.. 2003. Evaluating alternative monitoring programs for estimating relative trends in recruitment.Prepared for B.C. Hydro. Power Supply and Environmental services. Burnaby,B.C.

Ahrens, R. and Korman, J.. 2002. What happened to the West Arm burbot stock in Kootenay Lake? Use of an age-structured population model to determine the possible causes for recruitment failure. Prepared for BC Ministry of Air,Land, and Water Protection. Nelson, B.C.

Korman, J. and Ahrens, R. 2001. Cheakamus River steelhead escapement estimation.Prepared for BC Hydro. Power Supply and Environmental services. Burnaby, B.C.

Korman, J. and Ahrens, R. 2000. Cheakamus River steelhead escapement estimation.Prepared for BC Hydro. Power Supply and Environmental services. Burnaby, B.C.