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.
Highlights
Ecosystem-based management (EBM) of marine resources is widely recognized as the step in achieving conservation and fishery objectives, while benefiting from lessons learned from the successes and failures of single-species fisheries management [1,2,3]
Predator requirements are formally considered in the management of Antarctic krill fisheries off South Georgia, such that body condition of krill predators can be used as an indicator to trigger reduction in fishery quotas [8]
A related management tool used by ICES is the Ecological Quality Objective, an example of which is that changes in sandeel (Ammodytes marinus) fishery management actions are triggered if breeding success of black-legged kittiwakes (Rissa tridactyla) falls below a predetermined threshold [9]
Summary
Ecosystem-based management (EBM) of marine resources is widely recognized as the step in achieving conservation and fishery objectives, while benefiting from lessons learned from the successes and failures of single-species fisheries management [1,2,3]. EBM includes incorporation of species interactions when setting conservation and fishery objectives [2,4]. For North Sea cod (Gadus morhua), the International Council for the Exploration of the Seas (ICES) has incorporated estimates of grey seal prey requirements to ensure that this predator is considered when setting fisheries quotas [9]. A related management tool used by ICES is the Ecological Quality Objective, an example of which is that changes in sandeel (Ammodytes marinus) fishery management actions are triggered if breeding success of black-legged kittiwakes (Rissa tridactyla) falls below a predetermined threshold [9]. An EBM approach could involve an explicit allocation of fishery quota for ecosystem or predator needs [10,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
