Vulnerability of Pacific salmon to invasion of northern pike (Esox lucius) in Southcentral Alaska

Abstract

The relentless role of invasive species in the extinction of native biota requires predictions of ecosystem vulnerability to inform proactive management strategies. The worldwide invasion and range expansion of predatory northern pike (Esox lucius) has been linked to the decline of native fishes and tools are needed to predict the vulnerability of habitats to invasion over broad geographic scales. To address this need, we coupled an intrinsic potential habitat modelling approach with a Bayesian network to evaluate the vulnerability of five culturally and economically vital species of Pacific salmon (Oncorhynchus spp.) to invasion by northern pike. This study was conducted along 22,875 stream km in the Southcentral region of Alaska, USA. Pink salmon (O. gorbuscha) were the most vulnerable species, with 15.2% (2,458 km) of their calculated extent identified as "highly" vulnerable, followed closely by chum salmon (O. keta, 14.8%; 2,557 km) and coho salmon (O. kisutch, 14.7%; 2,536 km). Moreover, all five Pacific salmon species were highly vulnerable in 1,001 stream km of shared habitat. This simple to implement, adaptable, and cost-effective framework will allow prioritizing habitats for early detection and monitoring of invading northern pike.

Fig 1. Map of Matanuska-Susitna basin, Southcentral Alaska, USA.

Stream reaches are represented as blue lines, sub-basin delineations as grey lines, barriers to fish passage as red triangles, major roads as black lines, significant lakes as grey polygons, and known pike-invaded lakes as yellow circles. The approximate location of the Alaska Range is shown in the inset as a black line.

Fig 2. Conceptual diagram depicting factors hypothesized to affect Pacific salmon vulnerability to invasion by northern pike in the Matanuska-Susitna basin (Southcentral Alaska, USA).

Shaded ovals represent input variables in the Bayesian network. See Table 1 for definitions of nodes and states within nodes.

Fig 3. Intrinsic Potential (IP) curves for northern pike for three attributes.

(a) gradient (%); (b) elevation (m); and (c) floodplain width (m).

Fig 4. Sum of stream reach habitat suitability (km) for northern pike and Pacific salmon in the Matanuska-Susitna basin, Alaska, USA.

Light grey represents low-potential, dark grey represents moderate-potential, and black represents high-potential habitat.

Fig 5. Vulnerability of Pacific salmon to invasion by northern pike for the Matanuska-Susitna basin (Southcentral, Alaska, USA).

Species-specific estimates shown in panels a–e and a composite “highly-vulnerable” estimate shown in panel f. Black lines represent sub-basins. Darker colors represent higher vulnerability with species-specific vulnerability shown in blues and the number of species identified as “high” vulnerability shown in oranges.