Higher Aggregation of Key Prey Species Associated with Diet and Abundance of the Steller Sea Lion Eumetopias jubatus across the Aleutian Islands

Abstract

The Aleutian Islands ecosystem is a highly dynamic marine environment that supports commercially important fish species, such as Atka Mackerel Pleurogrammus monopterygius and Northern Rockfish Sebastes polyspinis, and several large marine mammals, including the Steller sea lion (SSL) Eumetopias jubatus. To protect SSL foraging behavior and prey, trawl exclusion zones (TEZs) were established around SSL rookeries and haulouts across the Aleutian Islands and are closed to bottom trawling. The Atka Mackerel fishery is concentrated at small, local patches (~37.04 km [~20 nautical miles]) across the Aleutian Islands, often near and adjacent to TEZs. Food web models and fishery stock assessments predict sufficient prey for both the fishery and foraging SSLs at the level of large management areas (each area is ~463 km [~250 nautical miles] longitudinally), but little is known about local fish distribution (~37.04 km) in proximity to SSL rookeries and haulouts. We used CPUE to examine the spatial distribution of two SSL prey species (Atka Mackerel and Northern Rockfish) and marine invertebrates (as a proxy for habitat quality) at large (across the Aleutian Islands) and small (~37.04‐km) scales. Although Atka Mackerel abundance estimates were similar across the Aleutian Islands, the density of Atka Mackerel differed. In the eastern Aleutian Islands, where SSL population trends have stabilized, Atka Mackerel aggregations were dense. In contrast, in the far western Aleutian Islands, where SSL populations are still in decline, Atka Mackerel distributions were diffuse and Northern Rockfish exhibited a greater density. Results indicated no significant difference in CPUE between areas open to fishing and closed areas (i.e., TEZs) at all study sites for Atka Mackerel and at all but one study site for Northern Rockfish, whereas invertebrate densities were significantly higher inside of TEZs at all study sites. We discuss how fish distributions across the Aleutian Islands may impact the success and behavior of foraging SSLs.

Investigating life‐history traits of Steller sea lions with multistate hidden Markov mark–recapture models: Age at weaning and body size effects

“…If so, later weaning may allow mothers time to teach foraging areas and skills, as suspected for Australian sea lions (Lowther & Goldsworthy, 2016 and references therein) and Odonocetes (reviewed by Matthews & Ferguson, 2015). Despite potential patterns, the complex relationships between habitat, diet, and sea lion life history remain largely unknown, including the importance to sea lion energetics of diet diversity (Fritz et al., 2019; Lander et al., 2009; Merrick et al., 1997), local variation in prey abundance (e.g., prey conditions for sea lions in northern Southeast Alaska are likely very favorable and are fueling high survival and population growth; Hastings et al., 2011; Mathews et al., 2011), and prey concentration (Rand et al., 2019; Winter et al., 2009), predictability (Baylis et al., 2012), and seasonality (Varpe, 2017). As yet, distinct regional differences in foraging effort or strategies have not been detected (Lander et al., 2020; Loughlin et al., 2003; Merrick & Loughlin, 1997; Pitcher et al., 2005; Raum‐Suryan et al., 2004; Rehberg et al., 2009).…”

Specific Gene Duplication and Loss of Cytochrome P450 in Families 1-3 in Carnivora (Mammalia, Laurasiatheria)

“…The following supporting information can be downloaded at: , Figure S1: Synteny of Pinniped CYP3As., Sequence files: CYP2C_protein.fas, CYP3A_protein.fas; Table S1: Sequence information of CYP2Cs; Table S2: Sequence information of CYP3As; Table S3: Food habitat of carnivoran [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , …”

Environmental drivers of demography and potential factors limiting the recovery of an endangered marine top predator

“…Sea lion genetics and diet composition also differ on either side of Samalga Pass, with diet in the eastern portion of the range being more diverse and dominated largely by walleye pollock ( Gadus chalcogrammus ) (O'Corry‐Crowe et al, 2006; Sinclair & Zeppelin, 2002; Sinclair et al, 2005). In contrast, to the west of Samalga Pass, deep and wide passes are supplied by colder nutrient‐rich waters of the Alaska Stream and are characterized by oceanic zooplankton, a lower diversity of potentially slower‐growing forage fish (Hunt & Stabeno, 2005), planktivorous seabirds, and a lower diversity sea lion diet dominated by less densely aggregated Atka mackerel ( Pleurogrammus monopterygius ) (Rand et al, 2019; Sinclair et al, 2005). These generalized patterns likely oversimplify the fine‐scale variability that occurs seasonally, interannually, and across island rookeries (Fadely et al, 2005; Mordy et al, 2005), particularly given the influence of mesoscale habitat features such as eddies (Lander et al, 2010, 2020; Miller et al, 2005) that influence the availability, abundance, and distribution of predators and their prey.…”