Shortnose and Atlantic sturgeon are found in the estuarine complex of the Sheepscot, Kennebec, and Androscoggin Rivers. The Kennebec and Androscoggin Rivers flow into Merrymeeting Bay, a large tidal freshwater bay which also receives inflow from several smaller drainages: the Eastern, Cathance, Abagadasset, and Muddy Rivers. The combined river systems exit Merrymeeting Bay through a narrow channel and flow approximately 20 miles to the Atlantic Ocean. This lower tidal segment is known as the "Kennebec River" The lower tidal section of the Kennebec connects with the Sheepscot River by means of the tidal Sasanoa River and several bays. This estuarine complex will be referred to as the "Kennebec River". The Kennebec River supports the largest population of shortnose sturgeon in the United States north of the Hudson River. It supports the only known reproducing population of Atlantic sturgeon in the United States north of the Hudson River.
The Maine Department of Marine Resources (MDMR) has conducted studies to determine the distribution and abundance of shortnose sturgeon in the estuarine complex of the Kennebec, Androscoggin, and Sheepscot Rivers (Squiers and Smith, 1979; Squiers et al, 1982). Additional studies were conducted to determine the timing of the spawning run and location of spawning areas in the tidal section of the Androscoggin River (Squiers, 1982; Squiers, 1983; Squiers et al, 1993). The estimated size of the adult population (>50cm TL) based on a tagging and recapture study performed from 1977 through 1981 was 7200, with a 95% C.I. of 5000 - 10,800 (Squiers et al, 1982). The average density of adult shortnose sturgeon/hectare of habitat in the estuarine complex of the Kennebec River was the second highest of any population studied through 1983 (Dadswell et al, 1984). During these early studies very few sub adult Atlantic sturgeon were captured indicating that only a remnant population of this sturgeon species existed in the Kennebec River.
Most recently MDMR has been conducting additional studies on shortnose sturgeon in the lower Kennebec River to delineate summer feeding grounds and over wintering area. These studies were conducted under contract with the Maine Department of Transportation to determine habitat use patterns in the immediate vicinity of the new Bath/Woolwich bridge. MDMR tracked shortnose sturgeon, which had been outfitted with sonic transmitters, from the fall of 1996 through early 1998. The transmitters were implanted internally in 15 shortnose sturgeon in the fall of 1996; an additional five shortnose sturgeon were tagged in 1997 to help determine if adult shortnose sturgeon over wintered in the Bath area, where a new bridge is being built. MDMR is also cooperating in an additional tracking study initiated in 1998 by Bath Iron Works (BIW) in the Bath region of the Kennebec River The major objective of this latter study, which is being conducted for BIW by Normandeau Associates, is to collect detailed information on the movements of both adult shortnose and sub adult Atlantic sturgeon in the vicinity of the BIW shipyard expansion. Both studies are providing valuable data on the feeding and over wintering areas for shortnose and Atlantic sturgeon. Preliminary assessment of the tracking data and earlier gill net studies indicates that the majority of shortnose sturgeon feed in the Bath region of the Kennebec from mid April through late November/early December and then migrate upriver to over winter in Merrymeeting Bay although a significant number remained in the Bath area in 1998/1999. In addition, the MDMR/Normandeau sampling efforts from 1996 through 1998 indicate that the Atlantic sturgeon population has increased significantly since the late 1970's.
The recently released Shortnose Sturgeon Recovery Plan (NOAA, 1998) identified several priorities necessary to facilitate recovery of shortnose sturgeon in the Kennebec River. These include updated information on population estimates, age structure, recruitment, growth rate, and reproductive success. Another priority task was to restore spawning and nursery habitat. This latter task will be accomplished with the removal of the Edwards dam in 1999. Priorities for Atlantic sturgeon recovery and management were established in Amendment 1 To The Interstate Fishery Management Plan For Atlantic Sturgeon (ASMFC, 1998). This management plan is essentially a recovery plan. The objectives include: 1) closing the fishery for at least 20 years; 2) reducing or eliminating bycatch; 3) determining and protecting spawning sites; and 4) reestablishing access to historical habitat. The removal of the Edwards dam will restore access of Atlantic sturgeon to their historical habitat in the Kennebec River.
The National Marine Fisheries Service (NMFS) has chosen to obtain updated population estimates and other population dynamics parameters for shortnose sturgeon in the Kennebec River in order to refine current management strategies to facilitate recovery or reclassify the population status, if warranted. The NMFS contract for the population estimate for shortnose sturgeon provides an opportunity for MDMR to collect additional valuable information on shortnose and Atlantic sturgeon by tagging all shortnose (up to 500) and Atlantic sturgeon captured. During the fall of 1998, MDMR tagged a total of 346 shortnose sturgeon. A total of 308 shortnose sturgeon were tagged with PIT tags (Avid 14mm microchip tags) and an additional 28 were tagged with Carlin tags. All shortnose sturgeon captured were scanned with an AVID Power Tracker II before and after tagging. The majority of shortnose sturgeon that were PIT tagged were dual tagged with Carlin tags. The PIT tags were inserted in the fleshy base of the dorsal fin on the right side; Carlin tags were attached by means of a stainless steel wire bridle inserted through the base of the dorsal fin.
The PIT tags that will be utilized should last the life of the fish which could be an additional 30 years or more. A shortnose sturgeon which was captured in 1998 had been tagged in 1982. Unfortunately, the pennants with the ID number on most of the tags that were applied from 1977 through 1983 have fallen off. The new PIT tags are injected into the musculature and the long-term retention in other studies has been excellent. All Atlantic sturgeon will be double tagged. They will be tagged with PIT tags and an external tag . The external tag will allow MDMR to collect information on the bycatch in commercial fisheries and to obtain information on their oceanic migratory movements.
Plans for 1999 include capturing a sufficient number of shortnose sturgeon in order to make a reliable population estimate and tagging an additional 500 shortnose sturgeon. Sampling efforts will be directed towards capturing shortnose sturgeon in the summer feeding areas which include Merrymeeting Bay, the Bath area of the Kennebec River , and the Sasanoa River from July through September. Tissue samples for genetic analysis have already been collected from adult shortnose on the spawning runs in the Androscoggin and Kennebec Rivers. Record numbers of shortnose sturgeon were captured on both river systems in early May. A total of 473 adult shortnose sturgeon were captured in an overnight set of two nets on the Androscoggin River and 134 were captured in an overnight set of one net on the Kennebec River. MDMR intends to implant sonic transmitters in an additional 17 to 20 shortnose sturgeon in order to learn more about behavior patterns of fish captured in different areas during the summer.