2016 Diadromous Migration Season on the Presumpscot A R E P O RT F R OM THE GMR I FIS HE R IE S E C O L OGY LAB ON CB AS S

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1 2016 Diadromous Migration Season on the Presumpscot A R E P O RT F R OM THE GMR I FIS HE R IE S E C O L OGY LAB ON CB AS S SEPTEMBER 2016

2 2016 Diadromous Migration Season on the Presumpscot 1 Beginning in 2013, GMRI began sampling the river herring spawning runs in the Presumpscot River as part of our Casco Bay Aquatic System Survey (CBASS). This year s survey revealed some surprises, including evidence of spawning smelt and notable numbers of shad and sturgeon. Starting in the last week of April of this year, we went to Presumpscot Falls (Figures 1 and 2) in Falmouth two to three days per week to look for diadromous fish at high tide (although some trips were made at low tide, out of curiosity) on their spawning migrations. Diadromous fish are defined by the fact that they migrate to fulfill their lifecycle; two more exact terms describe the direction of migrations, anadromous and catadromous. Anadromous fish are hatched in fresh water, and then migrate to the ocean, where they live as adults and only come back into fresh water to spawn. Although salmon are the iconic example of anadromy, lots of other fish species exhibit anadromous life histories. Catadromous fish spawn in the ocean but live in freshwater. Anadromous alewives (Alosa pseudoharengus) and other fish come up the Presumpscot River with the tide and the falls create a natural bottleneck during the migration, slowing the fish down and concentrating them. Only a few fish at a time are able to traverse the falls and schools of migrating fish, milling around trying to find their way upstream, can darken the water in such a concentration of life that it really must be seen to be appreciated. Every fish-eating predator benefits from this gathering of anadromous fish in coastal rivers. From harbor seals to herring gulls, striped bass to ospreys, and humans to raccoons, every animal gets in on the action during this impressive rite of spring. The passage of anadromous fish functions as a massive nutrient and energy vector, bringing marinederived nutrients into ecosystems up the river. Figure 1. This map shows the location of Presumpscot Falls, the head-of-tide of the Presumpscot River Estuary.

3 2016 Diadromous Migration Season on the Presumpscot 2 Figure 2. Presumpscot Falls is a popular area for recreational fishing. With the winter of being particularly warm, fishermen, managers, and scientists all anticipated a relatively early start to the 2016 alewife migration, although the Presumpscot run tends to start a little later than most in the state (Lew Flagg, formerly of DMR, personal communication). We typically see alewives at the falls starting around May 15th, although early reports of fish heading up Alewife Brook in Cape Elizabeth during the last week of April prompted us to start checking early this year. The cold spring we had and the suspected upwelling in the western Gulf of Maine (GMRI Ecosystem Modelling Lab) may have altered oceanographic conditions and resulted in a more typical timing of the spawning run. Although we did not catch any alewives at the falls until May 23rd, we saw a cormorant with an alewife in the river below the falls on April 25th. This seems to be typical in the system adult alewives will stage in the tidal estuary below the falls for weeks in the spring before the right combination of water temperature and discharge signal to the fish that it is

4 2016 Diadromous Migration Season on the Presumpscot 3 time to move upstream towards Highland Lake. This year was particularly interesting due to the lack of snowfall in the winter of , which meant there was no major spring runoff on the Presumpscot. Typically, when spring runoff subsides and temperatures rise, the fish start to move. The water temperature at Presumpscot Falls actually dropped during the first two weeks of May to 9.2 C from the unseasonable 10.8 C in the last week of April. The end of April also showed one dead adult rainbow smelt (Osemerus mordax) wedged in the rocks and the presence of smelt eggs adhered to the tidal rock faces near the falls (Figure 3). These were the first pieces of evidence encountered by the Gulf of Maine Research Institute of anadromous smelt and spawning activity in the Presumpscot Estuary. Figure 3. Rainbow smelt eggs adhered to rocky ledges on sides of the Presumpscot River.

5 2016 Diadromous Migration Season on the Presumpscot 4 The Presumpscot Estuary is a popular area in the spring for commercial elver harvesting. Elvers, also known as glass eels, are juvenile American eels (Anguilla rostrata) that are harvested with fyke nets and dip nets and exported for use in aquaculture. American eels are not anadromous but are instead catadromous that is, the adults live in freshwater and go out to sea to spawn. In the spring, elvers swim out of Sargasso Sea and migrate into freshwater systems up coastal streams and rivers. While we do not sample elvers as part of CBASS, we did encounter hundreds of elvers slithering up the wet ledges at the falls to continue their journey upstream in mid May (Figure 4). Much of the life history of American eels is still a mystery and we do not know the status of the population in the Presumpscot watershed. Figure 4. A juvenile American eel, or elver, captured at Presumpscot Falls.

6 2016 Diadromous Migration Season on the Presumpscot 5 We first encountered alewives at Presumpscot Falls making an effort to ascend on May 23rd, We sampled fish that day with a cast net, capturing our goal of 25 alewives (Figure 5). It seems to us that most of the alewives pass the falls in two or three days, with a few tides of major migration events sandwiched by a trickle of fish that can extend for weeks. On May 23rd, not only did we easily sample alewives at the base of the falls, but we also caught an adult American shad (Alosa sapidissima) with the cast net. This fish was presumably attempting to ascend the torrent to spawn upstream as it was a gravid female. Eventually, we did see a small school of dozens of shad in the water below the falls that morning but they evaded capture on this date. We encountered adult American shad a total of 4 times over the next few weeks attempting to ascend the falls, including on our last sampling day of June 13th, a full week after the alewife run had subsided. We determined where below the falls that the shad seemed to hold, and we did not sample that area, as shad were not the focus of our study and the holding area was treacherous for scientists and fishing nets to sample effectively. Both males and females in spawning condition were sampled below the falls, with lengths up to 51 cm and weights up to 1570 g. Additionally, no attempts at sampling were conducted above the head of tide due to permit limitations. Figure 5. Anadromous alewives sampled by Zach Whitener at Presumpscot Falls by cast net.

7 2016 Diadromous Migration Season on the Presumpscot 6 We had heard reports of adult shad in the Presumpscot, but this was the first time that we encountered any during our sampling. However, we have consistently captured juvenile American shad in the Presumpscot Estuary every summer during our seine sampling. Although we cannot determine if these fish were the product of a spawning population in the Presumpscot River, we do know that the area is suitable juvenile habitat. Blueback herring (Alosa aestivalis) were first captured in our sampling on June 8th and were the majority of migrating fish at the falls that week. By June 13th both species of river herring seemed to have finished their upstream migration and our sampling effort ceased. Shortnose sturgeon (Acipenser brevirostrum) have made a remarkable comeback in southern Maine with sightings common in estuaries in the region. This is the first year that we have seen sturgeon in the Presumpscot Estuary and in the month of July we saw them leaping from the water almost every time we brought our boat in the tidal basin between Route One and 295. Most activity seemed to be centered near the mouth of Scitterygusset Creek. Sturgeon are protected and we are not allowed to interact with them. This means that we do not have any data on the quantity of sturgeon utilizing the habitat or how typical this is, but it seems that their numbers have increased to the point of being commonplace. We do not know to which spawning population these fish belong, but it is believed that historically the Presumpscot River was a spawning area for shortnose sturgeon. The sampling described above is only a small part of our CBASS work. In addition to our work in the river, we conduct seine surveys of nearshore habitat and acoustic and jig surveys offshore. Over a ten-year period, CBASS will monitor and describe changes in this ecosystem, revealing potential linkages to changes in climate and oceanographic conditions, land use practices (e.g., fish passage), and other changes in the marine ecosystem (e.g., invasive species). This work will give us an unprecedented view of how a critical ecosystem functions and how it is changing essential information for fisheries and coastal resource management.