National Library Bibliothèque nationale 1*1 of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395, rue Wellingtori Ottawa ON KIA ON4 OtfawaON K1AW Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant a la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sel1 reproduire, prêter, distribuer ou copies of this thesis in microfom, vendre des copies de cette thèse sous paper or electronic formats. la forme de microficbe/nlm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Impacts of Otter Trawling on Infaunal Bivalves Living in Sandy Bottom Habitats on the Grand Banks by %ent Gilkinson A thesis submitted to the School of Graduate Studies in partial fulfilment of the requirements for the degree of Doctor of Philosophy Department of BiologyRaculty of Science Mernorial University of Newfoundland St. JOhn' s, Newfoundland St. John's Newfoundland Abstract Otter trawling has been the prevalent method of ground fishg in Atlantic Canada Despite this, little is known about associated impacts to benthic habitat and cornmunities. This thesis examines the impacts of otter trawling on bivalves living in sand, a bottom type occurring widely over the Grand Banks. Bivalves are dominant membea of sandy bottoms on continental shelves and are good indicatoa of physical disturbance. Two broad categories of impacts to benthos from mobile fishing gear are direct harvest and incidental damage. Bivalves have low susceptibility to capture by groundfish otter trawls; trawl capture efficiency is on the order of 1O*? In order to investigate incidental impacts, a chree-year otter trawling expenment was conducted on a fine to medium sand bottom on the northeastem Grand Bank. Each year a total of 12 trawl passes were made dong the centre line of two 13 km by 200 m experimental comdors. Sampling was conducted inside experimentai and adjacent reference comdors with a 0.5 m' hydraulic grab. No significant effects of trawling were detected on bivalve populations in any year. Shallow burrowing species showed no significant changes in density or biomass and recruitment of juveniles 5 3 mm was apparent inside trawled comdors. The size structure of populations fiom trawled and reference areas were similar. Mean (2sd) percent major shell damage immediately afler trawling was Iow, ranging from 2.8 2 6.1% to 13.5 + 9.4%. Trawl doon are the most destructive gear component of otter trawls. A physical trawl door mode1 was towed through an artificial sand testbed, constructed to resemble an offshore seabed. Aithough bivalves within the scour path were displaced, levels of damage were low (c. 5%), similar to levels of damage from the combined effects of dl gear components recorded in the field experiment. The anomaly of disp lacement, accompanied by few instances of damage, is explained by sediment mechanics associated with scouring and size and life positiix of infaunal bivalves. Compared to naturai sediment-mediated distubances, otter trawling cm be manipulated over a wide range of Frequencies. Individual and population-level adaptive traits probably confer considerable stability to sandy bottom bivalve populations exposed to typical patterns of trawling activity on the Grand Banks. iii Acknowledgements 1 dedicate my thesis to my family. 1 cannot adequately express my gratitude to my wife Linda for her unwavering support, encouragement and patience. I thank my daughtea, Courtney and Kayla, for being so understanding about my many weekend absences. 1 apologize to my youngest for not picking a topic that involved sharks. 1 am forever grateful to my Mother and Father and Linda's parents for their constant support. 1 am indebted to Dr. Peter Schwinghamer for agreeing to supervise me and providing me with the opportunity to return to research and become involved in the Fishenes and Oceans fishing impact experiments. He was a constant source of encouragement and timely humour. His forced medical retirement in 1997 represented a great loss to our study team and to the field of benthic ecology. 1 am indebted to Dr. David Schneider for assuming the role of supervisor for me despite already having a full stable of graduate students. His door was always open and his advice and rapid tum-arounds of chapters were greatly appreciated. 1 am grateful to Dr. Ryan Phillips for providing guidance in the geophysical component of my thesis. 1 consider the trawl door mode1 experiment one of the highlights of my thesis work. It gave me the oppominity to 'muck about' in vast quantities of sand and 1 had the pleasure of working with a group of dedicated engineers and technicians at C-CORE including Mike Paulin, Shawn Hurley, Steve Smyth, Karl TufTand Don Cameron. Over the years there have been many people in the Groundfish Division, Fisheries and Oceans, St. John's, who have assisted me in various aspects of my research. 1 am grateful to al1 of them. 1 would like to thank Steve Walsh and Barry McCallum, Fisheries and Oceans, St. John's, for technical information on otter trawl gear. They gave me access to their extensive video library on otter trawling which proved invaluable. 1 thank David Kulka for providing me with bycatch data from the Fisheries and Oceans Observer Program. 1 thank my fellow study team rnembers at the Bedford Instihite of Oceanography. My ongoing association with these people is very iv rewarding. 1 am grateful to Patrick Woo, Kevin McIsaac and Cynthia Bourbonnais for their meticulous extraction of bivalves fiom the samples. My thesis benefited nom discussions with Pierre Pepin and Jens Prena. 1 would like to thank Janet Leawood, Fabian Hartery, Trevor Hoskins and Jonathan Walsh for their assistance in preparing the scour tank testbed. 1 am especially grateful to Mark Hawryluk for his companionship and assistance when we were laboratory roornmates. I thank Dr. Don Gordon, project leader for the DFO fishing impact experiments, for involving me in ongoing investigations into impacts of mobile fishing gear in Atlantic Canada. He generously agreed to review my thesis at a very busy time for him. Table of Contents Abstract .............................................................. ii Acknowledgements .....................................................iv List of Tables ..........................................................xi ListofFigures ......................................................... xv Chapter 1 Bac kground and Study Approach 1.1 Introduction ......................................................1 1.2 Mobile bottorn fishing gears: physical aspects of gear-seabed interaction .......................................................4 1.2.1 Dredges ..................................................$4 1.2.2 Bearn trawls ................................................6 1.2.3 Otter trawis .................................................8 1.3 Otter trawl technology in Atlantic Canada ............................ 11 1.3.1 Otterboards ..............................................11 1.3.2 Footgear .................................................. 12 1.3.3 Ground wires .............................................. 12 1.3.4 Net ...................................................... 12 1.4 History of investigations into environmental impacts of mobile bottom fishing gears ..................................................... 13 1.5 Environmental concerns associated with otter trawling in Atlantic Canada .... 15 1.6 Thesis topic ..................................................... 16 1.6.1 Bivalves as indicators of physical distutbance .................... 17 1.6.2 Thesis organization ......................................... 18 1.7 Literature cited ...................................................20 Chapter 2 Invertebrate Bycatch of Otter Trawls 2.1 Introduction .....................................................36 2.1.1 Purpose ofs~dy........................................... 37 2.2 Literature review ................................................. 37 2.3 Overview of spatial patterns of commercial otter trawling on the Grand Banks ............................................... 40 2.4 Otter trawl gear-seabed interaction ................................... 43 2.5 Swey trawl descriptions ........................................... 47 2.5.1 Engel 145 Hi-Lifi trawl ......................................48 2.5.2 Campelen 1800 trawl ........................................ 48 2.6 Trawling stations .................................................49 2.7 Quantification of bycatch ...........................................49 2.8 Grab sample collections ............................................50 2.9 Results and discussion .............................................50 2.9.1 Abundance and biomass of invertebrate bycatch ................... 50 2.9.1.1 Carnpelen .......................................... 50 2.9.1.2 Engel ..............................................51 2.9.2 Mollusc size fiequency distributions: Campelen 1800 ..............51 2.9.3 Factors determining the susceptibility