Repository logo
 

Taggart, Christopher T.

Permanent URI for this collectionhttps://hdl.handle.net/10222/22177

Browse

Recent Submissions

Now showing 1 - 8 of 8
  • ItemOpen Access
    Probability and mitigation of vessel encounters with North Atlantic right whales
    (Inter-Research, Nordbuente 23 Oldendorf/Luhe 21385 Germany, 2009-03) Vanderlaan, Angelia SM; Corbett, James J.; Green, Shannon L.; Callahan, John A.; Wang, Chengfeng; Kenney, Robert D.; Taggart, Christopher T.; Firestone, Jeremy
    Successful mitigation of vessel-whale encounters requires quantitative estimates of vessel strikes, how strike rates change over time, where strikes are most likely to occur, and options for minimizing strikes. In addressing these issues, we first demonstrate a 3- to 4-fold increase in the number of reported large whale-vessel strikes worldwide from the early 1970s to the early 2000s, corresponding to a 3-fold increase in the number of vessels in the world fleet that is paralleled by an increase in vessel tonnage and speed. Second, we estimate a 50% chance of 14 or more annual vessel-strike reports worldwide between 1999 and 2002. For North Atlantic right whales Eubalaena glacialis, we estimate a 60% chance of observing at least 1 right whale death from vessel strike. Adjusting for undetermined causes of death and unobserved deaths, we estimate a 10-fold increase (from 1 to 10) in the expected annual number of fatal ship strikes. Third, we evaluate the eastern United States geographic distribution of right whales and vessels to calculate relative probabilities of vessel-whale encounters among 3 major right whale habitats. We determine that the Southern Calving Ground poses the greatest threat of a vessel strike: 1.6- and 7-fold greater than in Cape Cod Bay and the Great South Channel, respectively. Finally, for the Great South Channel region we present a quantitatively determined vessel-traffic routing option that would achieve a 39% reduction in vessel-whale encounter probabilities. The methods employed in assessing encounter probabilities and vessel-routing options can be applied elsewhere to enhance the conservation of endangered and threatened species that suffer vessel-strike mortality.
  • ItemOpen Access
    Reducing the risk of lethal encounters: vessels and right whales in the Bay of Fundy and on the Scotian Shelf
    (2008) Vanderlaan, Angelia S. M.; Taggart, Christopher T.; Serdynska, Anna R.; Kenney, Robert D.; Brown, Moira W.
    The North Atlantic right whale Eubalaena glacialis is endangered, in part, due to vessel-strike mortality. We use vessel traffic and right whale survey data (similar to 3 nautical miles [n miles], similar to 5.6 km resolution) for the Bay of Fundy and on the Scotian Shelf (northwest Atlantic) to determine the relative risk of lethal vessel encounters by using 2 estimates: (1) the event-the relative probability of a vessel encountering a right whale, and (2) the consequence-the probability of a lethal injury arising from an encounter. For the Bay of Fundy region our estimates demonstrate that the relative risk of lethal collision could be reduced by 62 % by means of an amendment to the traffic separation scheme (TSS) that intersects a Right Whale Conservation Area. In the Roseway Basin region of the Scotian Shelf, the majority of vessels navigate outside of a Right Whale Conservation Area, although the highest relative risk is concentrated within the Conservation Area where fewer vessels navigate at greater speed. Here, our estimates demonstrate that a seasonal recommendatory area to be avoided (ATBA) could be designed to reduce the risk imposed by vessels upon right whales in the region. Our estimates contributed to the International Maritime Organisation (IMO) adoption of a TSS amendment in the Bay of Fundy and an ATBA on the Scotian Shelf. Thus, the goal of achieving the greatest reduction in the risk of lethal vessel-encounters with whales, balanced by some minimal disruption to vessel operations while maintaining safe navigation, can be achieved.
  • ItemOpen Access
    Absolute probability estimates of lethal vessel strikes to North Atlantic right whales in Roseway Basin, Scotian Shelf
    (2012-10) van der Hoop, Julie M.; Vanderlaan, Angelia S. M.; Taggart, Christopher T.
    Vessel strikes are the primary source of known mortality for the endangered North Atlantic right whale (Eubalaena glacialis). Multi-institutional efforts to reduce mortality associated with vessel strikes include vessel-routing amendments such as the International Maritime Organization voluntary "area to be avoided" (ATBA) in the Roseway Basin right whale feeding habitat on the southwestern Scotian Shelf. Though relative probabilities of lethal vessel strikes have been estimated and published, absolute probabilities remain unknown. We used a modeling approach to determine the regional effect of the ATBA, by estimating reductions in the expected number of lethal vessel strikes. This analysis differs from others in that it explicitly includes a spatiotemporal analysis of real-time transits of vessels through a population of simulated, swimming right whales. Combining automatic identification system (AIS) vessel navigation data and an observationally based whale movement model allowed us to determine the spatial and temporal intersection of vessels and whales, from which various probability estimates of lethal vessel strikes are derived. We estimate one lethal vessel strike every 0.775-2.07 years prior to ATBA implementation, consistent with and more constrained than previous estimates of every 2-16 years. Following implementation, a lethal vessel strike is expected every 41 years. When whale abundance is held constant across years, we estimate that voluntary vessel compliance with the ATBA results in an 82% reduction in the per capita rate of lethal strikes; very similar to a previously published estimate of 82% reduction in the relative risk of a lethal vessel strike. The models we developed can inform decision-making and policy design, based on their ability to provide absolute, population-corrected, time-varying estimates of lethal vessel strikes, and they are easily transported to other regions and situations.
  • ItemOpen Access
    Mixed-stock analysis of Atlantic cod near the Gulf of St. Lawrence based on microsatellite DNA
    (2000-08) Ruzzante, DE; Taggart, CT; Lang, S.; Cook, D.
    The collapse of various stock complexes of cod (Gadus morhua) in the northwest Atlantic has prompted a clarification of relationships among stock components. Here we examine the genetic composition of >2300 cod collected during 1994-1997 in the Gulf of St. Lawrence and its approaches to determine whether: (1) stock components can be genetically identified; (2) population structure is temporally stable; (3) components are always separated and, if not, where and when are they mixed; and (4) component contributions to mixtures can be estimated. We use polymorphism at six microsatellite DNA loci from cod collected on or near their spring and summer spawning grounds to examine structure and then employ maximum likelihood analyses to estimate contributions of each component to mixtures overwintering near the entrance to the Gulf. Estimates of genetic structure (F(ST) and R(ST)) reveal significant differences among cod populations during stock-separated periods, and the structure appears to be temporally stable. Multidimensional scaling analysis of estimates of genetic distance (D(A)) suggest that the structure results from differences among cod collected within the Gulf of St. Lawrence and those collected near the entrance to the Gulf on either side of the Laurentian Channel in the Cabot Strait, as well as among cod collected south of Newfoundland along the north side of the Channel. Weak genetic heterogeneity among seven regional mixed-stock collections during the overwintering period suggests that cod aggregations characteristically found in the overwintering region represent population mixtures that differ in the proportion of cod contributed to them by the various stock components, Maximum likelihood estimates indicate no significant temporal changes in component contributions to the mixed-stock samples between 1996 and 1997 when all of the winter mixed-stock samples were pooled. The combined contribution of cod from the southern and northern Gulf of St. Lawrence to the mixed-stock samples ranged between 46% and 71% (expected 64%), More precise estimates of contributions from these two regions are precluded by the weak genetic differentiation detected in our samples. The contribution by cod from the Cape Breton Island region was small and estimated at 3%. Contributions by cod from the eastern Scotian Shelf, southwest Newfoundland and south-central Newfoundland were in the range of 13-14%, 4%, and 8%, respectively. Contributions by inshore cod from Placentia and Fortune Bays in south Newfoundland were small to negligible (similar to 3% each). The results indicate that future management could be designed around the spatial and temporal scale of the stock structure identified during the stock-separated period and around the spatially varying contributions to the overwintering mixed-stock fishery.
  • ItemOpen Access
    Accelerometer tags: detecting and identifying activities in fish and the effect of sampling frequency
    (2013-04) Broell, Franziska; Noda, Takuji; Wright, Serena; Domenici, Paolo; Steffensen, John Fleng; Auclair, Jean-Pierre; Taggart, Christopher T.
    Monitoring and measuring the behaviour and movement of aquatic animals in the wild is typically challenging, though micro-accelerometer (archival or telemetry) tags now provide the means to remotely identify and quantify behavioural states and rates such as resting, swimming and migrating, and to estimate activity and energy budgets. Most studies use low-frequency (30 Hz) accelerometer sampling be used in similar laboratory and field studies. If battery and/or data storage is limited, we also recommend archiving the events via an on-board algorithm that determines the highest likelihood and subsequent archiving of the various event classes of interest.
  • ItemOpen Access
    Genomic islands of divergence and their consequences for the resolution of spatial structure in an exploited marine fish
    (2013-04) Bradbury, Ian R.; Hubert, Sophie; Higgins, Brent; Bowman, Sharen; Borza, Tudor; Paterson, Ian G.; Snelgrove, Paul V. R.; Morris, Corey J.; Gregory, Robert S.; Hardie, David; Hutchings, Jeffrey A.; Ruzzante, Daniel E.; Taggart, Christopher T.; Bentzen, Paul
    As populations diverge, genomic regions associated with adaptation display elevated differentiation. These genomic islands of adaptive divergence can inform conservation efforts in exploited species, by refining the delineation of management units, and providing genomic tools for more precise and effective population monitoring and the successful assignment of individuals and products. We explored heterogeneity in genomic divergence and its impact on the resolution of spatial population structure in exploited populations of Atlantic cod, Gadus morhua, using genome wide expressed sequence derived single nucleotide polymorphisms in 466 individuals sampled across the range. Outlier tests identified elevated divergence at 5.2% of SNPs, consistent with directional selection in one-third of linkage groups. Genomic regions of elevated divergence ranged in size from a single position to several cM. Structuring at neutral loci was associated with geographic features, whereas outlier SNPs revealed genetic discontinuities in both the eastern and western Atlantic. This fine-scale geographic differentiation enhanced assignment to region of origin, and through the identification of adaptive diversity, fundamentally changes how these populations should be conserved. This work demonstrates the utility of genome scans for adaptive divergence in the delineation of stock structure, the traceability of individuals and products, and ultimately a role for population genomics in fisheries conservation.
  • ItemOpen Access
    Lipid and gross energy content of North Atlantic right whale food, Calanus finmarchicus, in the Bay of Fundy
    (2007) Michaud, Josee; Taggart, Christopher T.
    We address spatial and temporal distribution of abundance, lipid and caloric content and water column energy density of the copepod Calanus finmarchicus, a major food source for the north Atlantic right whale (NARW) Eubalaena glacialis in a primary feeding habitat - Grand Manan Basin, Bay of Fundy. The focus is on the lipid-rich diapausing copepodite stage 5 (C5) that dominates the zooplankton community during the summer and autumn whale-feeding period. We show that from May through July 2002, monthly averages of depth-integrated zooplankton wet biomass ( 0.88, p < 0.05) to the abundance and quality (i.e. energy density) of food available in the habitat. Thus, a water column-integrated energy density of 3 kJ m(-3) appears to be a reasonable minimum estimate of that needed to define a right whale feeding habitat, though subject to spatial and temporal variation. Accordingly, inter-annual variation in the abundance and energy content of C5s will influence right whale feeding success and may influence arrival at and departure to and from, as well as seasonal residency in, primary feeding habitats. We suggest that prey field examinations and estimates of the type presented here should advance insights concerning the nature and location of other potential habitats as well as variation in right whale condition and reproductive capacity.
  • ItemOpen Access
    Spatial variation in right whale food, Calanus finmarchicus, in the Bay of Fundy
    (2011) Michaud, J.; Taggart, C. T.
    No abstract available.