Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries

Marine mammals interact with commercial fisheries via competition for resources, depredation (feeding on fish caught in gear), entanglement, and bycatch in fishing gear. In New England, gray seals (Halichoerus grypus) and harbor seals (Phoca vitulina) are often taken as bycatch in sink-gillnet fishe...

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Main Author: Sirak, Laura N.
Format: Text
Language:unknown
Published: DUNE: DigitalUNE 2015
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Online Access:https://dune.une.edu/theses/120
https://dune.une.edu/cgi/viewcontent.cgi?article=1119&context=theses
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spelling ftunivnewengmai:oai:dune.une.edu:theses-1119 2023-05-15T16:33:09+02:00 Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries Sirak, Laura N. 2015-07-01T07:00:00Z application/pdf https://dune.une.edu/theses/120 https://dune.une.edu/cgi/viewcontent.cgi?article=1119&context=theses unknown DUNE: DigitalUNE https://dune.une.edu/theses/120 https://dune.une.edu/cgi/viewcontent.cgi?article=1119&context=theses © 2015 Laura N. Sirak All Theses And Dissertations Aquaculture and Fisheries Marine Biology text 2015 ftunivnewengmai 2022-01-22T20:14:43Z Marine mammals interact with commercial fisheries via competition for resources, depredation (feeding on fish caught in gear), entanglement, and bycatch in fishing gear. In New England, gray seals (Halichoerus grypus) and harbor seals (Phoca vitulina) are often taken as bycatch in sink-gillnet fisheries and are believed to depredate fish in gillnets. As seal populations increase, interactions with fisheries are also likely to increase, affecting both seal stocks and the New England fishing industry. This study aims to understand seal bycatch in the New England sink-gillnet fisheries by identifying the spatial and temporal trends in bycatch as well as the characteristics of seals that are taken most frequently as bycatch. Depredation is also a concern in the commercial fishing industry, however, there is some controversy among fishermen and scientists concerning the identification of the species responsible for depredation (e.g. seal vs. spiny dogfish (Squalus acanthias)). Therefore, a protocol for identifying seal and spiny dogfish depredation was developed and used to identify depredation in a small-scale study of the sink-gillnet fishery targeting skate. Data from the Northeast Fisheries Observer Program (NEFOP) from 2005 – 2013 were analyzed to assess seal bycatch in the Northeast sink-gillnet fishery. Male seals were taken significantly more frequently than females, with young of the year most commonly occurring as bycatch. Areas where seals were taken in New England shifted seasonally, generally following the annual life history of each seal species. Gray seal bycatch showed an increasing trend over the years of study, with highest bycatch occurring in the spring in areas closest to haul out sites: Muskeget and Monomoy Island, MA, USA. Harbor seal bycatch was much more variable between years, with highest bycatch occurring in the winter near major harbor seals haul out sites along the southern Maine coast and southeastern Massachusetts. This study was a crucial step to understanding the complexities of seal-fishery interactions in New England. In order to mitigate damage from depredation, it is important to know the source of the damage. Characteristics of seal and spiny dogfish bites were identified using foam imprints from jaws and bites by captive animals in the soft tissue of fish. Measurements from bite imprints and damaged fish were used to develop a protocol for identifying damage in the field. In general, dogfish bites were clean (flesh completely removed), circular in shape, and wider than long (bite ratio (bite length/bite width) < 0.6), whereas seal bites were ragged (flesh not completely removed, but partially torn from the bite), rectangular or trapezoidal in shape, and usually longer than wide or equal in length and width (bite ratio > 0.7). This protocol was used to identify damaged catch observed on a commercial gill-net fishing vessel targeting skate in New England waters June – August 2014. In this small-scale study, dogfish bites were identified as the damage source significantly more frequently than seal bites (Multifactor ANOVA: F df=2,66 = 9.306, p = 0.0003; Tukey HSD: p < 0.0001). This inexpensive, quick, and practical protocol can be used on a larger scale to further understand depredation by seals and dogfish throughout New England. Text harbor seal Phoca vitulina spiny dogfish Squalus acanthias University of New England: DUNE (DigitalUNE)
institution Open Polar
collection University of New England: DUNE (DigitalUNE)
op_collection_id ftunivnewengmai
language unknown
topic Aquaculture and Fisheries
Marine Biology
spellingShingle Aquaculture and Fisheries
Marine Biology
Sirak, Laura N.
Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries
topic_facet Aquaculture and Fisheries
Marine Biology
description Marine mammals interact with commercial fisheries via competition for resources, depredation (feeding on fish caught in gear), entanglement, and bycatch in fishing gear. In New England, gray seals (Halichoerus grypus) and harbor seals (Phoca vitulina) are often taken as bycatch in sink-gillnet fisheries and are believed to depredate fish in gillnets. As seal populations increase, interactions with fisheries are also likely to increase, affecting both seal stocks and the New England fishing industry. This study aims to understand seal bycatch in the New England sink-gillnet fisheries by identifying the spatial and temporal trends in bycatch as well as the characteristics of seals that are taken most frequently as bycatch. Depredation is also a concern in the commercial fishing industry, however, there is some controversy among fishermen and scientists concerning the identification of the species responsible for depredation (e.g. seal vs. spiny dogfish (Squalus acanthias)). Therefore, a protocol for identifying seal and spiny dogfish depredation was developed and used to identify depredation in a small-scale study of the sink-gillnet fishery targeting skate. Data from the Northeast Fisheries Observer Program (NEFOP) from 2005 – 2013 were analyzed to assess seal bycatch in the Northeast sink-gillnet fishery. Male seals were taken significantly more frequently than females, with young of the year most commonly occurring as bycatch. Areas where seals were taken in New England shifted seasonally, generally following the annual life history of each seal species. Gray seal bycatch showed an increasing trend over the years of study, with highest bycatch occurring in the spring in areas closest to haul out sites: Muskeget and Monomoy Island, MA, USA. Harbor seal bycatch was much more variable between years, with highest bycatch occurring in the winter near major harbor seals haul out sites along the southern Maine coast and southeastern Massachusetts. This study was a crucial step to understanding the complexities of seal-fishery interactions in New England. In order to mitigate damage from depredation, it is important to know the source of the damage. Characteristics of seal and spiny dogfish bites were identified using foam imprints from jaws and bites by captive animals in the soft tissue of fish. Measurements from bite imprints and damaged fish were used to develop a protocol for identifying damage in the field. In general, dogfish bites were clean (flesh completely removed), circular in shape, and wider than long (bite ratio (bite length/bite width) < 0.6), whereas seal bites were ragged (flesh not completely removed, but partially torn from the bite), rectangular or trapezoidal in shape, and usually longer than wide or equal in length and width (bite ratio > 0.7). This protocol was used to identify damaged catch observed on a commercial gill-net fishing vessel targeting skate in New England waters June – August 2014. In this small-scale study, dogfish bites were identified as the damage source significantly more frequently than seal bites (Multifactor ANOVA: F df=2,66 = 9.306, p = 0.0003; Tukey HSD: p < 0.0001). This inexpensive, quick, and practical protocol can be used on a larger scale to further understand depredation by seals and dogfish throughout New England.
format Text
author Sirak, Laura N.
author_facet Sirak, Laura N.
author_sort Sirak, Laura N.
title Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries
title_short Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries
title_full Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries
title_fullStr Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries
title_full_unstemmed Grey (Halichoerus Grypus) And Harbor Seal (Phoca Vitulina) Bycatch And Depredation In New England Sink-Gillnet Fisheries
title_sort grey (halichoerus grypus) and harbor seal (phoca vitulina) bycatch and depredation in new england sink-gillnet fisheries
publisher DUNE: DigitalUNE
publishDate 2015
url https://dune.une.edu/theses/120
https://dune.une.edu/cgi/viewcontent.cgi?article=1119&context=theses
genre harbor seal
Phoca vitulina
spiny dogfish
Squalus acanthias
genre_facet harbor seal
Phoca vitulina
spiny dogfish
Squalus acanthias
op_source All Theses And Dissertations
op_relation https://dune.une.edu/theses/120
https://dune.une.edu/cgi/viewcontent.cgi?article=1119&context=theses
op_rights © 2015 Laura N. Sirak
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