UC Santa Cruz

Many marine predator populations are commercially important and are threatened by human activities. As a result, many of these populations are heavily depleted, declining, or are recovering from past depletion. Recovery and management of threatened and exploited marine predators are complicated by life histories that 1) span international waters, 2) are dynamic in space and time, and 3) are hidden from direct observation. My goal with this dissertation was to attain a synthetic understanding of the implications of marine predator migratory life histories on the spatio-temporal dynamics of distribution, species overlap, and residency in Exclusive Economic Zones of countries. I analyzed an electronic tracking dataset provided by the Tagging of Pacific Predators program that contained location data for pinnipeds, seabirds, sharks, tuna, turtles, and whales. This dataset included 257,133 daily locations recorded from 1,679 individuals representing 18 species of pelagic predators electronically tracked in the Pacific Ocean during an eight-year period.

Many marine predators are broadly recognized as exceptional migrants but there has been little integration of traditional migratory theory with the study of their movements. In chapter one, I examined whether theoretical nonlinear models of migration developed for ungulates and based upon a fundamental statistic of random walk theory (net squared displacement) provide a useful framework for quantifying and predicting marine predator migratory behavior. I found that migration models fit species as ecologically dissimilar as moose and Pacific bluefin tuna suggesting that a unified approach to quantifying migration across taxa and biomes may be possible.

The potential utility of marine protected areas (MPAs) for pelagic conservation is debated, especially for wide-ranging species with large, dynamic area requirements. In chapter two I used kernel density analysis to determine the spatial and temporal extents of the distributions and core habitats of marine predators and quantified patterns of species overlap that could help guide management strategies. I found that spatial management measures may not need to be prohibitively large to include major core habitats of wide-ranging species---at least in reference to the size distribution of large extant MPAs. However, to account for seasonal variability in distribution, spatial measures may need to be dynamic, numerous, and/or embedded within strategic multi-scale zoning strategies. Seals, sharks, tuna, and turtles had high probabilities of overlap with black-footed albatross and sooty shearwaters. Spatial conservation efforts targeted at seabirds could help focus ecosystem management in this vast pelagic realm.

Integrated international efforts are required to effectively manage threatened and exploited populations of wide-ranging species. In chapter three I used generalized additive mixed-effects models to investigate non-linear daily trends in the probability of occurrence in Exclusive Economic Zones (EEZs) and in the high seas, and to account for the effects of tagging location, tagging date, track duration, and autocorrelated time-series data. Ninety-four percent of Pacific Ocean EEZs were visited. Land-breeding populations were estimated to spend 14-33% of their annual cycles within the waters of their breeding EEZs, and 53 to 76% of the year in the high seas. In contrast, most fish and shark populations were estimated to spend less than a quarter of their annual cycle in international waters. My results describe the suite of countries with shared management responsibility throughout the year for each species, and detail when this responsibility commences and concludes.