title: Competing conservation objectives for predators and prey: estimating killer whale prey requirements for Chinook salmon.
abstract: Ecosystem-based management (EBM) of marine resources attempts to conserve interacting species. In contrast to single-species fisheries management, EBM aims to identify and resolve conflicting objectives for different species. Such a conflict may be emerging in the northeastern Pacific for southern resident killer whales (Orcinus orca) and their primary prey, Chinook salmon (Oncorhynchus tshawytscha). Both species have at-risk conservation status and transboundary (Canada-US) ranges. We modeled individual killer whale prey requirements from feeding and growth records of captive killer whales and morphometric data from historic live-capture fishery and whaling records worldwide. The models, combined with caloric value of salmon, and demographic and diet data for wild killer whales, allow us to predict salmon quantities needed to maintain and recover this killer whale population, which numbered 87 individuals in 2009. Our analyses provide new information on cost of lactation and new parameter estimates for other killer whale populations globally. Prey requirements of southern resident killer whales are difficult to reconcile with fisheries and conservation objectives for Chinook salmon, because the number of fish required is large relative to annual returns and fishery catches. For instance, a U.S. recovery goal (2.3% annual population growth of killer whales over 28 years) implies a 75% increase in energetic requirements. Reducing salmon fisheries may serve as a temporary mitigation measure to allow time for management actions to improve salmon productivity to take effect. As ecosystem-based fishery management becomes more prevalent, trade-offs between conservation objectives for predators and prey will become increasingly necessary. Our approach offers scenarios to compare relative influence of various sources of uncertainty on the resulting consumption estimates to prioritise future research efforts, and a general approach for assessing the extent of conflict between conservation objectives for threatened or protected wildlife where the interaction between affected species can be quantified.
authors.affiliation: University of Washington, Seattle, Washington, United States of America. rmcw@st-andrews.ac.uk
authors.forename: Rob
authors.initials: R
authors.lastname: Williams
authors.forename: Martin
authors.initials: M
authors.lastname: Krkošek
authors.forename: Erin
authors.initials: E
authors.lastname: Ashe
authors.forename: Trevor A
authors.initials: TA
authors.lastname: Branch
authors.forename: Steve
authors.initials: S
authors.lastname: Clark
authors.forename: Philip S
authors.initials: PS
authors.lastname: Hammond
authors.forename: Erich
authors.initials: E
authors.lastname: Hoyt
authors.forename: Dawn P
authors.initials: DP
authors.lastname: Noren
authors.forename: David
authors.initials: D
authors.lastname: Rosen
authors.forename: Arliss
authors.initials: A
authors.lastname: Winship
mesh_terms: D000818:Animals; D015233:Models, Statistical; D011235:Predatory Behavior / Q000502:physiology*; D012474:Salmon / Q000502:physiology*; D050685:Whale, Killer / Q000502:physiology*
references.citation: Science. 2007 Dec 14;318(5857):1772-5
references.pmid: 18079401
references.citation: Conserv Biol. 2006 Jun;20(3):617-9
references.pmid: 16909542
references.citation: PLoS One. 2010 May 27;5(5):e10761
references.pmid: 20523722
references.citation: Genome Res. 2010 Jul;20(7):908-16
references.pmid: 20413674
references.citation: Biol Lett. 2010 Feb 23;6(1):139-42
references.pmid: 19755531
references.citation: Science. 2004 Jul 16;305(5682):346-7
references.pmid: 15256658
references.citation: Conserv Biol. 2007 Jun;21(3):572-5
references.pmid: 17531035