Andrew J. Read

The looming crisis: interactions between marine mammals and fisheries

Abstract Direct fisheries interactions pose a serious threat to the conservation of many populations and some species of marine mammals. The most acute problem is bycatch, unintended mortality in fishing gear, although this can transition into unregulated harvest under some circumstances. A growing issue in some fisheries is depredation, in which marine mammals remove captured fish from nets or lines. Depredation reduces the value of catch and may lead to a greater risk of entanglement and the potential for retaliatory measures taken by fishermen. The conservation threat caused by direct fisheries interactions is most dire for small populations of cetaceans and dugongs. Immediate action is needed to assess the magnitude of bycatch, particularly in many areas of Africa and Asia where little work has been conducted. New and innovative solutions to this problem are required that take account of the socioeconomic conditions experienced by fishermen and allow for efficient transfer of mitigation technology to fisheries of the developing world.

Acoustic alarms reduce porpoise mortality

The most serious danger to dolphins and porpoises around the world is the threat from various forms of gill-net fishing. One potential way to reduce the number of deaths of marine mammals is the use of active acoustic alarms to warn animals about the presence of nets. Until now, acoustic alarms have not been tested in field experiments with sufficient statistical power. Here we describe a field experiment showing that acoustic alarms are effective at reducing the number of deaths of harbour porpoises (Phocoena phocoena) in sink gill-nets.

Complexity and variation in loggerhead sea turtle life history

Juvenile loggerhead sea turtles spend more than a decade in the open ocean before returning to neritic waters to mature and reproduce. It has been assumed that this transition from an oceanic to neritic existence is a discrete ontogenetic niche shift. We tested this hypothesis by tracking the movements of large juveniles collected in a neritic foraging ground in North Carolina, USA. Our work shows that the shift from the oceanic to neritic waters is both complex and reversible; some individuals move back into coastal waters and then return to the open ocean for reasons that are still unclear, sometimes for multiple years. These findings have important consequences for efforts to protect these threatened marine reptiles from mortality in both coastal and open-ocean fisheries.

HARBOR PORPOISE AND FISHERIES: AN UNCERTAINTY ANALYSIS OF INCIDENTAL MORTALITY

The harbor porpoise (Phocoena phocoena) in the western North Atlantic is subject to mortality due to entanglement in gillnets. Such incidental mortality threatens a population if it is too large relative to the potential population growth rate. Critical values for incidental mortality have been established by the International Whaling Commission and the U.S. Marine Mammal Protection Act. As in many situations in conservation biology, use of these critical values depends on demographic calculations that are based on uncertain data. It is important to report not only estimates of demographic parameters, but also the uncertainty in those estimates. Here, we use a Monte Carlo approach to evaluate uncertainty in population size, incidental mortality, and population growth rate of harbor porpoise. To describe survival, we used model life tables derived from other mammals with similar life histories. By randomly sampling the space of model life tables and the distributions of estimated fertility and age at first reproduction, we produced a probability distribution that characterizes the uncertainty in the potential population growth rate. The median estimate for the potential annual rate of increase l is approximately 1.10. Combining this information with the uncertainty of incidental mortality and of population size, we estimate the prob- ability that the rate of incidental mortality exceeds the critical values established by the various management agencies; this probability ranges from 0.46 to 0.94. We conclude that recent incidental mortality rates are a threat to harbor porpoise populations. The methods developed here are applicable to other situations in which demographic analyses must be based on uncertain data.

Global patterns of marine mammal, seabird, and sea turtle bycatch reveal taxa-specific and cumulative megafauna hotspots

Significance Loss of megafauna, termed trophic downgrading, has been found to affect biotic interactions, disturbance regimes, species invasions, and nutrient cycling. One recognized cause in air-breathing marine megafauna is incidental capture or bycatch by fisheries. Characterizing megafauna bycatch patterns across large ocean regions is limited by data availability but essential to direct conservation and management resources. We use empirical data to identify the global distribution and magnitude of seabird, marine mammal, and sea turtle bycatch in three widely used fishing gears. We identify taxa-specific hotspots and find evidence of cumulative impacts. This analysis provides an unprecedented global assessment of the distribution and magnitude of air-breathing megafauna bycatch, highlighting its cumulative nature and the urgent need to build on existing mitigation successes. Recent research on ocean health has found large predator abundance to be a key element of ocean condition. Fisheries can impact large predator abundance directly through targeted capture and indirectly through incidental capture of nontarget species or bycatch. However, measures of the global nature of bycatch are lacking for air-breathing megafauna. We fill this knowledge gap and present a synoptic global assessment of the distribution and intensity of bycatch of seabirds, marine mammals, and sea turtles based on empirical data from the three most commonly used types of fishing gears worldwide. We identify taxa-specific hotspots of bycatch intensity and find evidence of cumulative impacts across fishing fleets and gears. This global map of bycatch illustrates where data are particularly scarce—in coastal and small-scale fisheries and ocean regions that support developed industrial fisheries and millions of small-scale fishers—and identifies fishing areas where, given the evidence of cumulative hotspots across gear and taxa, traditional species or gear-specific bycatch management and mitigation efforts may be necessary but not sufficient. Given the global distribution of bycatch and the mitigation success achieved by some fleets, the reduction of air-breathing megafauna bycatch is both an urgent and achievable conservation priority.

Saving the Vaquita: Immediate Action, Not More Data

∗Instituto Nacional de Ecolog ?a (INE), c/o CICESE, Km. 107 Carretera EnsenadaTijuana, Ensenada, BC 22860, Mexico †Instituto Nacional de Ecolog ?a (INE), c/o CICESE, Km. 107 Carretera EnsenadaTijuana, Ensenada, BC 22860, Mexico ‡Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92038, U.S.A. ∗∗Duke University Marine Laboratory, Nicholas School of the Environment, 135 Duke Marine Laboratory Road, Beaufort, NC 28516-9721, U.S.A. ††Okapi Wildlife Associates, 27 Chandler Lane, Hudson, Quebec JOP-1HO, Canada ‡‡National Zoological Park, Smithsonian Institution, P.O. Box 37012 MRC 5503, Washington, D.C. 20013-7012, U.S.A. §Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92038, U.S.A. This paper is posted at DigitalCommons@University of Nebraska Lincoln.

Fine-scale habitat modeling of a top marine predator: do prey data improve predictive capacity?

Predators and prey assort themselves relative to each other, the availability of resources and refuges, and the temporal and spatial scale of their interaction. Predictive models of predator distributions often rely on these relationships by incorporating data on environmental variability and prey availability to determine predator habitat selection patterns. This approach to predictive modeling holds true in marine systems where observations of predators are logistically difficult, emphasizing the need for accurate models. In this paper, we ask whether including prey distribution data in fine-scale predictive models of bottlenose dolphin (Tursiops truncatus) habitat selection in Florida Bay, Florida, U.S.A., improves predictive capacity. Environmental characteristics are often used as predictor variables in habitat models of top marine predators with the assumption that they act as proxies of prey distribution. We examine the validity of this assumption by comparing the response of dolphin distribution and fish catch rates to the same environmental variables. Next, the predictive capacities of four models, with and without prey distribution data, are tested to determine whether dolphin habitat selection can be predicted without recourse to describing the distribution of their prey. The final analysis determines the accuracy of predictive maps of dolphin distribution produced by modeling areas of high fish catch based on significant environmental characteristics. We use spatial analysis and independent data sets to train and test the models. Our results indicate that, due to high habitat heterogeneity and the spatial variability of prey patches, fine-scale models of dolphin habitat selection in coastal habitats will be more successful if environmental variables are used as predictor variables of predator distributions rather than relying on prey data as explanatory variables. However, predictive modeling of prey distribution as the response variable based on environmental variability did produce high predictive performance of dolphin habitat selection, particularly foraging habitat.

Changes in Blubber Distribution and Morphology Associated with Starvation in the Harbor Porpoise (Phocoena phocoena): Evidence for Regional Differences in Blubber Structure and Function

To examine patterns of blubber loss accompanying a decline in body condition, blubber thickness of juvenile harbor porpoises in normal/robust body condition ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Ontogenetic allometry and body composition of harbour porpoises (Phocoena phocoena, L.) from the western North Atlantic

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