Solange Brault

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.

RETROSPECTIVE ANALYSIS OF DEMOGRAPHIC RESPONSES TO ENVIRONMENTAL CHANGE: A LESSER SNOW GOOSE EXAMPLE

In general, analysis of population dynamics can proceed either prospectively or retrospectively. In the case of the former, asymptotic expectations are generally derived (analytically or numerically) from analysis of the potential effects of perturbation of the elements of the life table. However, the vital rates that are indicated by prospective analysis to contribute the most to projected growth rate are not necessarily those that have contributed to observed variation in growth rate over time. We used a retrospective analysis to analyze the life table responses of a population of long-lived herbivorous geese to a systematic reduction in food abundance within the traditional breeding colony. Typical of long-lived species, adult survival rate has been shown previously in a prospective perturbation analysis to have the largest potential impact on projected growth of the population. However, despite a significant long-term increase in adult survival over the course of the study, there has been a long-term decline in growth rates of the population inhabiting the traditional sampling areas, although absolute numbers of individuals in both populations increased over time. Retrospective assessment of the relative contributions of variation in underlying vital rates (adult and juvenile survival, in situ recruitment, emigration and immigration rates into the population) to projected growth showed that the long-term dynamics of the nesting population primarily reflected the combined effects of changes in postfledging juvenile survival, while changes in the postnesting population were most influenced by variation in juvenile survival and adult fidelity rate to the traditional brood-rearing areas. Decreases in both juvenile survival and fidelity reflect systematic reductions in food abundance over the course of the study. Our results confirm previous suggestions that philopatry to the brood-rearing areas may be a significantly more plastic trait than fidelity to nesting areas.

Distribution and Habitat Use of Antillean Manatees ( Trichechus manatus manatus ) in the Drowned Cayes Area of Belize, Central America

Belize, Central America, has long been recognized as a stronghold for Antillean manatees (Trichechus manatus manatus) in the Caribbean (O’Shea & Salisbury, 1991). The Drowned Cayes area, in particular, has been noted as an important habitat (Bengston & Magor, 1979; O’Shea & Salisbury, 1991; Auil, 1998, 2004; Morales-Vela et al., 2000). It is critical to evaluate habitat use and the relative importance of different habitat types within these cayes because this area is increasingly impacted by human activities (Auil, 1998). The two research objectives for this paper are (1) to document manatee distribution within the Drowned Cayes, Swallow Caye, and Gallows Reef, and (2) to examine habitat use patterns in order to identify habitat characteristics influencing the probability of sighting a manatee. Binary logistic regression was used to examine whether the probability of sighting a manatee varied in relation to several habitat variables. The probability of sighting a manatee across all points was 0.31 per scan (n = 795). Habitat category, seagrass category, and habitat category interaction with resting hole were the most important variables explaining the probability of sighting a manatee. The Drowned Cayes area clearly constitutes a manatee habitat area. Seagrass flats and cove habitats with resting holes were especially important habitat characteristics.

The importance of delineating networks by activity type in bottlenose dolphins (Tursiops truncatus) in Cedar Key, Florida.

Network analysis has proved to be a valuable tool for studying the behavioural patterns of complex social animals. Often such studies either do not distinguish between different behavioural states of the organisms or simply focus attention on a single behavioural state to the exclusion of all others. In either of these approaches it is impossible to ascertain how the behavioural patterns of individuals depend on the type of activity they are engaged in. Here we report on a network-based analysis of the behavioural associations in a population of bottlenose dolphins (Tursiops truncatus) in Cedar Key, Florida. We consider three distinct behavioural states—socializing, travelling and foraging—and analyse the association networks corresponding to each activity. Moreover, in constructing the different activity networks we do not simply record a spatial association between two individuals as being either present or absent, but rather quantify the degree of any association, thus allowing us to construct weighted networks describing each activity. The results of these weighted activity networks indicate that networks can reveal detailed patterns of bottlenose dolphins at the population level; dolphins socialize in large groups with preferential associations; travel in small groups with preferential associates; and spread out to forage in very small, weakly connected groups. There is some overlap in the socialize and travel networks but little overlap between the forage and other networks. This indicates that the social bonds maintained in other activities are less important as they forage on dispersed, solitary prey. The overall network, not sorted by activity, does not accurately represent any of these patterns.

2002 Aerial Surveys of Grey Seals in the Northeastern United States

In the past 20 years, grey seals have become established in coastal waters of the Northeastern United States. There are 3 sites where pupping and breeding occurs in January and February, 2 in Maine and 1 in Massachusetts. In 2002 we recorded a minimum of 1,040 pups born, primarily on Muskeget Island in Massachusetts. Pupping peaks in January on Muskeget Island but is significantly later on the 2 islands in Maine. A total of 3,326 grey seals (adults, juveniles and pups) were counted.

Long-term passive acoustic recordings track the changing distribution of North Atlantic right whales (Eubalaena glacialis) from 2004 to 2014

Given new distribution patterns of the endangered North Atlantic right whale (NARW; Eubalaena glacialis) population in recent years, an improved understanding of spatio-temporal movements are imperative for the conservation of this species. While so far visual data have provided most information on NARW movements, passive acoustic monitoring (PAM) was used in this study in order to better capture year-round NARW presence. This project used PAM data from 2004 to 2014 collected by 19 organizations throughout the western North Atlantic Ocean. Overall, data from 324 recorders (35,600 days) were processed and analyzed using a classification and detection system. Results highlight almost year-round habitat use of the western North Atlantic Ocean, with a decrease in detections in waters off Cape Hatteras, North Carolina in summer and fall. Data collected post 2010 showed an increased NARW presence in the mid-Atlantic region and a simultaneous decrease in the northern Gulf of Maine. In addition, NARWs were widely distributed across most regions throughout winter months. This study demonstrates that a large-scale analysis of PAM data provides significant value to understanding and tracking shifts in large whale movements over long time scales.