Reconsidering residency: characterization and conservation implications of complex migratory patterns of shortnose sturgeon (Acispenser brevirostrum)

Abstract

Efforts to conserve endangered species usually involve attempts to define and manage threats at the appropriate scale of population processes. In some species that scale is localized; in others, dispersal and migration link demic units within larger metapopulations. Current conservation strategies for endangered shortnose sturgeon (Acipenser brevirostrum) assume the species is river resident, with little to no movement between rivers. However we have found that shortnose sturgeon travel more than 130 km through coastal waters between the largest rivers in Maine. Indeed, acoustic telemetry shows that shortnose sturgeon enter six out of the seven acoustically monitored rivers we have monitored, with over 70% of tagged individuals undertaking coastal migrations between river systems. Four migration patterns were identified for shortnose sturgeon inhabiting the Penobscot River, Maine: river resident (28%), spring coastal emigrant (24%), fall coastal emigrant (33%), and summer coastal emigrant (15%). No shortnose sturgeon classified as maturing female exhibited a resident pattern, indicating differential migration. Traditional river-specific assessment and management of shortnose sturgeon could be better characterized using a broader metapopulation scale, at least in the Gulf of Maine, that accounts for diverse migratory strategies and the importance of migratory corridors as critical habitat.

Atlantic Sturgeon Use of the Penobscot River and Marine Movements within and beyond the Gulf of Maine

“…The shorter nets were placed in locations where space was restricted. Sampling was conducted in the Penobscot estuary between rkm 7 and 46 for 0.2-23.8 h from May through November in 2006 and 2007 and between rkm 20 and 42 for 0.2-6.5 h from May through November in 2008 through 2013 (Fernandes et al 2010;Dionne et al 2013;Altenritter 2015). Catch per unit effort was calculated for each sampling year by dividing the total number of Atlantic Sturgeon caught by the total soak hours for all gillnetting for the season.…”

“…The area of the Penobscot River of interest for this study was the estuary and bay. We classified the upstream end of the estuary as the head of tide at rkm 46, as in Fernandes et al (2010), Dionne et al (2013), and Stich et al (2015). From 1833 until the summer of 2013, this was the upriver extent of Atlantic Sturgeon habitat due to the presence of the nowremoved Veazie Dam.…”

“…From 1833 until the summer of 2013, this was the upriver extent of Atlantic Sturgeon habitat due to the presence of the nowremoved Veazie Dam. Also consistent with Fernandes et al (2010) and Dionne et al (2013), the southernmost point of Verona Island was considered the downstream end of the estuary (rkm 0). Penobscot Bay extends from this point south, roughly 90 km ( Figure 1).…”

Research Tools to Investigate Movements, Migrations, and Life History of Sturgeons (Acipenseridae), with an Emphasis on Marine-Oriented Populations

“…River movement can be complex and include multi-step migrations [10] and include movement between and among rivers suggesting a meta-population structure [11]. Within a species, populations can differ on the timing of migrations into river systems, time spent within the river (holding), and the distance (upstream) from the marine environment where spawning occurs.…”

“…Natal homing fidelity is thought to be strong and thus in many cases rivers, or sections of a watershed between natural barriers, often define populations. On the other hand, metapopulations may also exist [11]. If individual populations differ in terms of abundance and reproductive capacity, researchers and fishery managers may want to minimize mortality of individuals from certain river systems while they are in marine environments.…”