Due to their great ecological significance, mesopelagic fishes are attracting a wider audience
on account of the large biomass they represent. Data from the National Marine Fisheries
Service (NMFS) provided the opportunity to explore an unknown region of the North-West
Atlantic, adjacent to one of the most productive fisheries in the world. Acoustic data
collected during the cruise required the identification of acoustically distinct scattering types
to make inferences on the migrations, distributions and biomass of mesopelagic scattering
layers. Six scattering types were identified by the proposed method in our data and traces
their migrations and distributions in the top 200m of the water column. This method was
able to detect and trace the movements of three scattering types to 1000m depth, two of
which can be further subdivided. This process of identification enabled the development of
three physically-derived target-strength models adapted to traceable acoustic scattering
types for the analysis of biomass and length distribution to 1000m depth. The abundance
and distribution of acoustic targets varied closely in relation to varying physical
environments associated with a warm core ring in the New England continental Shelf break
region. The continental shelf break produces biomass density estimates that are twice as
high as the warm core ring and the surrounding continental slope waters are an order of
magnitude lower than either estimate. Biomass associated with distinct layers is assessed
and any benefits brought about by upwelling at the edge of the warm core ring are shown
not to result in higher abundance of deepwater species. Finally, asymmetric diurnal
migrations in shelf break waters contrasts markedly with the symmetry of migrating layers
within the warm ring, both in structure and density estimates, supporting a theory of
predatorial and nutritional constraints to migrating pelagic species.
Date of Award | Nov 2011 |
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Original language | English (US) |
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Awarding Institution | - Biological, Environmental Sciences and Engineering
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Supervisor | Stein Kaartvedt (Supervisor) |
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