Prey Preference of Lingcod {Ophiodon Elongatus), a Top Marine Predator

193 Abstract—Many highly exploited eco- Prey preference of lingcod systems are managed on the basis of single-species demograpbic informa- {Ophiodon elongatus), a top marine predator: tion. This management approach can exacerbate tensions among stakebold- implications for ecosystem-based ers with competing interests who in fisheries management turn rely on data witb notoriously bigh variance. In this case study, an application of diet and dive survey Craig A. Tinus data was used to describe the prey preference of lingcod (Ophiodon elon- Email address for contact autbor: [email protected] gatus) in a predictive framework on Oregon State University nearshore reefs off Oregon. The ling- Department of Fisberies and Wildlife cod is a large, fast-growing generalist 104 Nasb Hall predator of invertebrates and fishes. Corvallis, Oregon 97331-3803 In response to concerns that lingcod Present address: Oregon Department of Fisb and Wildlife may significantly reduce diminished Corvallis Researcb tab populations of rockfisbes (Sebastes 28655 Hwy 34 spp.), tbe diets of 375 lingcod on near- Corvallis, Oregon 97330 sbore reefs along the Oregon Coast were compared with estimates of relative prey availability from dive surveys. In contrast to tbe transient pelagic fisbes tbat comprised 46% of lingcod diet by number, rockfishes comprised at most 4.7% of prey items. Ecosystem-based fisheries manage- both useful and efficient as an exten- Rockfisbes were tbe most abundant ment (EBFM) has generated consider- sion of food web models to aid man- potential prey observed in dive sur- able interest over the last decade as agement of exploited stocks (Gaichas veys, yet tbey were the least preferred. a way of better managing depressed et al., 2010). In this study I used an Ecosystem-based fisheries manage- fisheries stocks (Pikitch et al., 2004; analysis of dive survey data with ment (EBFM) requires information Gaichas et al., 2010). This interest consumption data in a prey prefer- about primary tropbic relationships, has been in large part a reaction to ence model to better understand the as well as relative abundance and dis- the perceived failure of traditional likely effects of a rapidly increas- tribution data for multiple species. single-species fisheries management ing predator population on managed Tbis study shows tbat, at a minimum, to prevent the collapse of exploited prey. Consumption rates for gener- prédation relative to prey availability and ancillary populations in many alist consumers like lingcod (Ophi- must be considered before predator effects can be understood in a man- systems worldwide (Dulvy et al., 2003; odon elongatus Girard) may he either agement context. Hutchings and Baum, 2005; Myers positively or negatively correlated and Worm, 2005). One implication among different prey types, or they of EBFM is the capacity to forecast may be uncorrelated, and these ef- changes in managed populations in fects can be important in actively reaction to fluctuations in linked managed systems (Dill et al., 2003). predator and prey populations. This If spatially and temporally transient requires understanding what species prey species predominate in the diet of interest consume in a given tempo- of a resident predator, they may con- ral and spatial context. An additional stitute subsidies to the local preda- consideration is that many exploited tor population (Anderson and Polis, fishes are generalist consumers and 1998). When subsidies occur there shifts in densities and distributions may be a concomitant suppression of may produce complex top-down effects local prey species through apparent (Bruno and O'Connor, 2005). These competition among prey types with a are among numerous challenges in common predator (Holt, 1977; Chan- gathering the information required to eton and Bonsall, 2000). Especially in describe even a subset of primary tro- marine systems where trophic webs phic relationships in a dynamic system. may be poorly defined (Thompson Prey preference is the differential et al., 2007), initial consideration of Manuscript submitted 2 February 2011. consumption of some prey types over predator-prey relationships requires Manuscript accepted 28 November 2011. others given equal availability. It is dietary analysis (Heithaus et al., Fish. Bull. 110:193-204 (2012). considered a fixed behavioral char- 2008). Diets of targeted fishery spe- The views and opinions expressed acteristic and, as a way of forecast- cies provide necessary information or implied in this article are those of the ing prédation intensity on managed for understanding food web structure, author (or authors) and do not necessarily stocks, has received little attention. which is an important requirement reflect the position of the National Marine However, preference models may be for ecosystem-based fisheries science Fisheries Service, NOAA. 194 Fishery Bulletin 110(2) and management (Francis et al., 2007). However, in large (up to 152 cm total length [TL] and 59 kg) and addition to these basic trophic relationships, it is neces- fast growing. They are relatively site-attached, demer- sary to understand the context in which prey are being sal, generalist predators, found on shallow northeastern selected. The effects of prédation on both predator and Pacific rocky reefs. They roam across both rocky habitat prey populations change as prey densities vary. and soft-bottom over distances of at least hundreds of Although EBFM requires even more information than meters, yet they demonstrate a high degree of site fidel- traditional single-species management approaches, ity for time scales of at least weeks to months (Jagielo, managers, scientists, and stakeholders make use of 1990; Smith et al., 1990; Mathews, 1992; Yamanaka less certain information both in less accessible systems and Richards, 1993; Jagielo, 1999; Starr et al., 2004). and in those that are accessible but where temporal and Although lingcod population dynamics have been spatial scales far exceed the capacity to collect local studied from a fisheries perspective, very little is un- demographic data. For these reasons identifying specific derstood about how this predator affects the structure management triggers based on comprehensive and col- of fish populations and assemblages on rocky reefs. lectable information has been proposed (Samhouri et A previous study of diet and habitat associations of al., 2010) and the case made that uncertain data and demersal fishes on nearshore reefs along the Oregon imperfect advice must be embraced, as long as they are Coast revealed that 282 adult lingcod had consumed 27 appropriate data (Ludwig et al., 1993; Johannes, 1998; identifiable species of fish and invertebrates. Of those Frid et al., 2008). Challenges to the use of EBFM in- 134 prey items, no adult rockfishes were found and the clude "species conflicts," where management and stake- contribution to total biomass by all rockfish prey was holder interest in one target species may interfere with less than one percent (Steiner, 1979). However, no prior other species and often involve the assumed effects of lingcod studies have described diet in relation to prey large generalist predator(s) on recovering high value abundance. In order to assess differential selection, and prey species, sometimes in and out of marine protected thus characterize which prey types will most likely be areas. Examples of generalist predators involved in selected, there must be an estimate of prey availability management conflicts are groupers (Epinephelus spp. relative to consumption (Manley et al., 2002). The goal [Ault et al., 2006; Coleman and Koenig, 2010]), red of this study was to describe the diet of adult lingcod off snapper (Lutjanus campechanus [Wells et al., 2008; the coast of Oregon, to characterize relative patterns of Cowan et al., 2010]), cod (Gadus tnorhua [Link and consumption of transient and resident prey species by Garrison, 2002]), and striped bass {Morone saxatilis lingcod, and describe whether or not preference, defined [Paolisso, 2002; Walter et al., 2003]). as the differential consumption of one prey type over others in relation to availability, was evident. Specifi- Marine reserves are becoming more widely consid- cally, by using lingcod diet and prey abundance esti- ered as a management tool for protecting a portion of mates off the coast of Oregon, I addressed the following breeding populations as interest in EBFM increases. questions: 1) Do lingcod prefer particular prey species, However, in addition to providing a refuge from fishing and 2) do lingcod preferentially target rockfishes? The mortality, marine reserves can enhance local popula- answers to these questions were yes and no, respec- tions of large, resident, top-level predators (Martell tively. This information can be used to more effectively et al., 2000; McClanahan and Arthur, 2001). Among manage a reserve system where both predator and prey possible effects of a local increase in predator biomass populations are the focus of conservation efforts. is a decrease in a particular prey type (Graham et al., 2003). For example, this kind of interaction has been proposed for lingcod prédation on rockfishes (Sebastes spp.) within marine reserves (Beaudreau and Essing- Materials and methods ton, 2007; 2009) and both are major targets of commercial fisheries. Study area The following case study exemplifies necessary con- siderations for EBFM. Lingcod are targeted by both The nearshore zone off Oregon is generally exposed, has recreational and commercial

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