Some current research topics

Improving estimates of fisheries bycatch and developing model-based decision tools for evaluating impacts of fisheries on non-target species


Fisheries bycatch has been linked to population declines of many long-lived, late-maturing marine wildlife species. However, bycatch can be difficult to estimate and only for relatively few species do we understand whether bycatch mortality is sustainable. Nevertheless, management organizations (such as the U.S. National Marine Fisheries Service) are charged with limiting impacts of fisheries on protected or non-target species such as marine mammals, sea turtles, and many sharks. But how do you set bycatch limits without knowing how much bycatch is too much? I am working on several projects related to this problem. A couple of examples include improving bycatch estimates for rare-event situations, developing reference point estimators to help identify sustainable levels of incidental mortality for sea turtles and improving estimates of population productivity rates that form the basis of many reference point estimators.

Vaquita conservation science

The vaquita porpoise of the upper Gulf of California is nearly extinct as animals die in illegal fishing nets.  As of autumn 2017, there maybe only be a dozen or few dozen animals left.  Several recent papers have documented this population collapse based on analysis of acoustic and visual survey data collected by colleagues at the Instituto Nacional de Ecología and SWFSC.  I participated in the 2015 international vaquita expedition, and as a member of the expert statistical panel for CIRVA (the International Committee for the Recovery of Vaquita), I have analyzed much of these recent survey data to help produce the recent estimates of population size and decline.

Image at left: Woodblock art of vaquita by Barbara Taylor.

Estimating population abundance and trends for cetaceans in the West Coast EEZ of the United States


​​Since the early 1990s, the Southwest Fisheries Science Center (SWFSC) has operated ship-based line-transect surveys to estimate abundance of cetacean species inhabiting waters off the west coast of the United States. Several factors make it difficult to estimate population size and infer trends from these estimates, most notably low precision of the estimates and variation in the proportion of a population that occurs within the survey area from year to year.  Deep-diving species (e.g., beaked whales) are particularly challenging to assess and required novel acoustic survey techniques.  I use Bayesian hierarchical trend models to address these issues and improve our inference about how cetacean numbers are varying from year to year. Current work involves exploring the use of different types of trend models and applying these to additional species in our waters, and also extending the methods traditionally used for visual survey data to acoustic datasets such as conducted from a recent PASCAL cruise.