Abstracts for Upcoming Conference on the Biology of Marine Mammals

Abstracts for Upcoming Conference on the Biology of Marine Mammals

Our lab has several abstracts accepted for presentation at the upcoming 19th Biennial Conference on the Biology of Marine Mammals. The conference is being held in Tampa, FL during November 28 to December 2, 2011. The theme of the conference is: “Cumulative effects of threats to marine mammals: Challenges to animals, scientists, and managers.” The following are the abstracts that have been accepted for poster or spoken presentations by Johnston Lab members and collaborators:

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Predators, ice and krill: Fine-scale ecological gradients in an enclosed embayment on the Western Antarctic Peninsula

Johnston, David W., A.S. Friedlaender, E.L Hazen and D.P. Nowacek

Sea ice is the dominant habit factor influencing the distribution, abundance and behavior of marine predators and their prey in the Antarctic ecosystem. The relationships amongst sea ice quantity and quality and marine predators have been explored at broad spatial scales, but few studies have attempted to explore them at fine scales (< 10km). It is at fine scales that many of the effects of climate change are playing out, as sea ice cover declines and marine predators react to changes in ice habitats and the distribution and availability of their primary prey, Antarctic krill. Here we present links between marine predators, krill and sea ice in an embayment on the Western Antarctic Peninsula during May, 2010. Vessel-based strip transects (counting pinnipeds and cetaceans) were conducted within Wilhelmina Bay, on transects along and across the axis of the bay, with synoptic ice cover estimation and EK60 echosounder prey surveys. These data revealed fine scale gradients in the presence of humpback whales, crabeater seals and Antarctic fur seals in relation to changes in sea ice cover and krill density. Contingency table analyses indicated that humpback whales were negatively correlated with increasing sea ice cover, and were excluded from deeper portions of the bay. Crabeater seals were found only in these deeper portions of the bay and Antarctic fur seals were found throughout, with greater numbers at mid to high ice concentrations. Multiple linear regressions of species counts and krill density in three portions of the water column revealed that only Antarctic fur seals were significantly correlated with krill in the upper water column. Humpback whales were most correlated with krill in the deeper portions of the water column, and crabeater seals negatively correlated with krill in near surface waters. These results shed light on the combinations of sea ice cover and prey presence that structure predator/prey relationships at fine scales. [/framed_box] [framed_box bgColor=”#d8ffdd” rounded=”true”]

Quantifying the efficacy of a spatio-temporal management intervention on human-dolphin interactions in Hawai’i

Tyne, Julian, David W. Johnston, Ken Pollock, Kim New, and Lars Bejder

Since the 1980’s, concerns have been raised about the extent of water-based tourism targeting spinner dolphins (Stenella longirostris) in their resting habitat off Big Island of Hawai’i. In 2010, spinner dolphins associated with the Big Island were defined as a unique stock and were also identified as one of the most vulnerable to anthropogenic disturbance. The National Oceanic and Atmospheric Administration is currently considering a management intervention to reduce the number and intensity of human-dolphin interactions by implement time-area closures in critical habitat. To measure the effectiveness of this mitigation approach a Before-After-Control-Impact (BACI) design is being employed to asses the local abundance, distribution and behaviour of spinner dolphins in four resting bays before and after the implementation of time-area closures. Systematic boat-based photographic identification surveys have been carried out continuously over the past year following Pollock’s Robust Design (Primary period: each month; Secondary Period: 2-4 consecutive days in each of the four bays). Of the 96 surveys undertaken over 850 hours, spinner dolphins were observed on 43 (45%) occasions with group sizes ranging from 6 to approximately 250 dolphins. Preliminary abundance estimates over five primary periods ranged between 205 (SE ± 18; 95% CI = 176 – 249) and 446 (SE ± 73; 95% CI=329 – 621) spinner dolphins frequenting the study area. The precision of these preliminary abundance estimates will be tested over the next 3 to 5 years of continued data collection. In addition, passive acoustic loggers have been deployed in each bay, recording 30 seconds every 4 minutes with data collected continuously. These acoustic data allow for cross-validation with photographic survey records, and the method of deployment will provide an index of the regularity of dolphin presence in each bay before and after the implementation of time-area closures.

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What is the resource, Resting Bays or Dolphins? Application of Common Pool Resource Theory to Spinner Dolphin (Stenella longirostris) Related Tourism on the Island of Hawai‘i

Heenehan, Heather, David W. Johnston, Xavier Basurto and Lars Bejder

Cetacean tourism is an expanding sector and has grown significantly in the past 15 years in the state of Hawai‘i.  On the Island of Hawai‘i one form of cetacean tourism depends heavily on spinner dolphins in  resting bays along the Kona coastline. Spinner dolphins move predictably into shallow bays for rest during the day and move offshore to feed at night.  In addition to swim-with and vessel-based spinner dolphin excursions, there are other users and user groups that depend on these bays for social, recreational and subsistence purposes including snorkel companies, fishermen, surfers, kayakers and spinner dolphins themselves.  Growing conflicts amongst these user groups are evident, and an integrated and comprehensive management approach is needed. For management purposes, these bays should be considered a common pool resource; it is difficult to exclude users from the resource and the resource exhibits high subtractability – meaning that one user’s use of the resource takes away the use of that resource from another user.  Previous examinations of this situation have identified spinner dolphins as the resource requiring management. This approach however, focuses on a single species and ignores other users that interact negatively with dolphins as a by-product of their activities. Here we argue that establishing the spinner dolphin resting bay as the common pool resource is more appropriate and far more useful. This method could be considered a true ecosystem-based approach that integrates the needs of all stakeholders and explicitly acknowledges the legal rights to the use of these habitats by spinner dolphins as established by the U.S. Marine Mammal Protection Act. This approach is also useful for assessing variability in the social construction of individual bays and can help inform the development and roll-out of one-rule-fits-all management schemes currently under consideration by management authorities.

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Abundance and movements of spinner dolphins off the main Hawaiian Islands

Hill, Marie C., Amanda L. Bradford, Kim R. Andrews, Robin W. Baird, Mark H. Deakos, Sabre D. Mahaffy, Aliza J. Milette, Erin M. Oleson, Jan Östman-Lind, Adam Pack, Susan H. Rickards, Suzanne Yin, and David W. Johnston.

Spinner dolphins in Hawaiian waters were recently redefined from one stock spanning the Hawaiian EEZ into six, including three within the main Hawaiian Islands (Ni‘ihau/Kaua‘i, O‘ahu /4-Islands, Hawai‘i Island). Photo-identification data, contributed to the Pacific Islands Photo-Identification Network, were used to calculate minimum abundance estimates for main island stocks and to analyze intra- and inter-island movements of individuals. The data include sightings from seven of the main islands (all except Moloka‘i) and span 2001-2009. The photographic catalog consists of 673 individuals, with island catalogs ranging from 11 to 215 individuals (median=49). Mark-recapture analyses produced six closed capture estimates of minimum seasonal abundance for leeward portions of Kaua‘i – 559 (CV=0.19) in Oct-Nov 2005; O‘ahu – 149 (CV=0.12) in Jun-Jul 2002 and 330 (CV=0.05) in Jul-Sep 2007; and Hawai‘i Island – 733 (CV=0.15) in May-Jul 2003, 260 (CV=0.20) in Jan-Mar 2005, and 190 (CV=0.15) in Jan-Mar 2006. Although negatively biased due to unmodeled survey effort variability and individual heterogeneity, the estimates suggest inter-island variation in abundance and seasonal variation in dolphin numbers along leeward coasts. Movement analyses quantified individual travel distances and rates at all islands and site fidelity (using standard distance deviations) and diffusion rates at O‘ahu and Hawai‘i Island. Findings indicate that 1) inter-island movements are infrequent, particularly between stocks; 2) observed travel distances and rates vary by island; 3) O‘ahu individuals exhibit higher site fidelity (lower mean standard distance deviations) than Hawai‘i Island individuals; and 4) diffusion rates differ between O‘ahu and Hawai‘i Island on daily timescales, but are less differentiated over timescales of weeks to years. Results from the movement analyses could be used to assess the potential for new stock divisions. Overall, this study demonstrates the value of using collaborative photo-identification data to explore the complex and variable population characteristics of spinner dolphins in the main Hawaiian Islands.

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An Analysis of an Environmental and Biological Factor Affecting Stranded and By-Caught Harp Seals (Pagophilus groenlandicus) in the Northwest Atlantic.

Kiester, Brianne, Kristina Cammen, Tom Schultz and David W. Johnston

We are currently witnessing significant climate changes in high latitude ecosystems including many areas of the Arctic. Many high latitude species, like harp seals (Pagophilus groenlandicus), will be affected by changing sea ice conditions, and their populations forced to adapt to changing habitats. The genetic makeup of the species, often measured as overall fitness and genetic diversity, will affect how quickly they can adapt to these changing climates. This study analyzed two factors that are likely to affect harp seals along the eastern coast of the United States: ice cover (environmental) and genetic fitness (biological). Ice cover assessments were conducted for the month of February in the Gulf of St. Lawrence whelping region from 1991-2010 using remote sensing data. Microsatellite makers were used to determine d2 as a proxy for fitness in stranded individuals and healthy (by-caught) animals. We found a strong negative correlation (r2=0.49) between ice cover in the Gulf of St. Lawerence and strandings, indicating that light ice conditions in harp seal whelping patches contribute to higher stranding rates of harp seals along the east coast of the U.S. We also found no significant difference in fitness (d²) between stranded and healthy harp seals, and that the overall fitness of the population is high. The results demonstrate that increases in stranded seals during light ice years are not the product of reduced fitness, and that changes in sea ice cover are having a greater affect on the population than differences in fitness. Any changes in either of these factors could have major implications for the population and its ability to adapt. Harp seals are an indicator species for changing high latitude ecosystems and it is important for managers to account for all factors affecting the species and understand how these factors affect them across the North Atlantic.

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Trends in sea ice cover across the North Atlantic: Implications for harp and hooded seals

Young, T J, David W. Johnston, Matthew T. Bowers, Ari S. Friedlaender and  David M. Lavigne.

Ongoing changes in ice conditions pose significant challenges for harp and hooded seals, which use sea ice as a platform on which to give birth and nurse their pups. It is known that sea ice dynamics in harp and hooded seal breeding locations are governed largely by the phase and amplitude of the North Atlantic Oscillation (NAO). In this study, we examined the coupled relationship between the NAO and satellite-derived measures of sea ice cover during February and March 1979 – 2011 in areas where harp and/or hooded seals traditionally reproduce. We confirmed a consistent positive correlation between the NAO Index and annual sea ice in the regions located in the Northwest Atlantic off eastern Canada. However, sea ice cover in the White Sea harp seal region between Norway and Russia was negatively correlated with the NAO, and the West Ice region off eastern Greenland showed a consistent decline across the entire time series that is indicative of longer-term climate change. A mixed effects linear regression analysis of sea ice cover in the same breeding regions revealed a significant annual decline in sea ice cover across the entire North Atlantic, regardless of regional NAO effects. These results indicate that both short-term and longer-term climate variability are affecting the breeding regions of harp and hooded seals. Management strategies for these and other ice-breeding seals should account for local climate effects and larger-scale climate trends. This is especially important for the West Ice stock of hooded seals, which has decreased in number by up to 90% over the last 50 years and was listed as “vulnerable” by the IUCN in 2008.

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