UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Author: search.filters.author.Siskey, Matthew RyanSubject: search.filters.subject.Aquatic sciences

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    HISTORICAL EFFECTS OF FISHING ON AGE STRUCTURE AND STOCK MIXING IN NORTHWEST ATLANTIC BLUEFIN TUNA
    (2015) Siskey, Matthew Ryan; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Bluefin tuna support important fisheries in the Northwest Atlantic Ocean, which have declined in yield from intense, size-selective exploitation. Age structure, size-at-age, and stock composition were investigated as principal responses to exploitation, utilizing otolith microstructural and chemical analysis. To evaluate otoliths as ageing structures, annulus formation was compared to temperature-associated oscillations in otolith strontium:calcium. Evaluation of otolith stable isotope measures used in stock composition analyses indicated significant differences in δ18O measurements between laboratories, but not δ13C values. Comparisons of age structure, size-at-age, and stock composition over three periods (1974-1978, 1996-2002, 2009-2014) coinciding with the cycle of exploitation intensity suggest size-selective fishing caused (1) age truncation, where median age declined (14 to 6 years); (2) minor changes in size-at-age; and (3) fluctuating stock composition, with peak mixing in the 1990s (48% eastern stock contribution). Size-specific reductions in fishing mortality could contribute to recovery through more frequent production of strong year-classes.