Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Factors Affecting Harbour Porpoise Bycatch Occurrence In the Swedish Skagerrak and Kattegat Seas
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Biology Education Centre. Enheten för Miljöforskning och övervakning, Naturhistoriska Riksmuseet. (Anssi Laurila and Julia Carlström)
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
Abstract [en]

Incidental catch (bycatch) in fisheries is one of the major threats to marine mammal populations worldwide. The harbour porpoise (Phocoena phocoena, Linneaus 1758) is one of the most common cetaceans in northern Europe. Previous studies have reported high bycatch numbers of harbour porpoises in gillnet fishing operations in the North Sea and Skagerrak Sea. With the aim of disentangling the driving factors behind bycatch of harbour porpoises, I looked at the relationship between occurrence of harbour porpoise bycatch and properties of fishery and porpoise density. Parameters of fishing effort, gear characteristics and operations of 951 sets of strings of cod and pollack bottom set gillnets were collected by an on-board observer programme in the Swedish Skagerrak and Kattegat Seas during 1995-1997. Porpoise density data was generated from satellite tracking locations of 116 individuals from 1997 to 2016. Generalised linear models with binomial distribution were applied to identify the relationships between the occurrence of porpoise bycatch and seven explanatory variables extracted as soak time, string length, net height, mesh size, net bagginess, water depth and porpoise density. During the observer programme, a total of 21 porpoises were bycaught during 10,174 km*h of observed fishing effort. The total bycatch was estimated to be 2.6% of the population abundance at that time, i.e. above the maximum sustainable total anthropogenic removal (1.7%). Soak time, string length and water depth were identified to be positively related to bycatch occurrence. The findings provide guidance for bycatch mitigation measures in terms of adjusting fishing operations, improving gear and establishing separate management units. Modelling can be used to predict possible spatio-temporal high-risk hot spots for harbour porpoise as well as other marine-living species to optimise future monitoring efforts.

Place, publisher, year, edition, pages
2019.
Keywords [en]
Harbour porpoise, bycatch, incidental catch, fishery, marine mammal
National Category
Ecology
Identifiers
URN: urn:nbn:se:uu:diva-396236OAI: oai:DiVA.org:uu-396236DiVA, id: diva2:1367052
Educational program
Master Programme in Biology
Supervisors
Available from: 2019-11-07 Created: 2019-10-31 Last updated: 2019-11-07Bibliographically approved

Open Access in DiVA

fulltext(1301 kB)10 downloads
File information
File name FULLTEXT01.pdfFile size 1301 kBChecksum SHA-512
329ed6cbd96f005bef7726dfdc4484c9f8d7309f0d1ca2722ee5214593c58c824282a8b433243e40d13b8e7ff57ce34914182fe1877132de326cb6d4af4edfca
Type fulltextMimetype application/pdf

By organisation
Biology Education Centre
Ecology

Search outside of DiVA

GoogleGoogle Scholar
Total: 10 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

urn-nbn

Altmetric score

urn-nbn
Total: 120 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf