Spawning success7 July 2010
A habitat improvement project to promote lake sturgeon reproduction in the St Lawrence river has been an outstanding success. Dr Kevin McGrath from New York Power Authority explains why
In the late 1990s, the New York Power Authority (NYPA) embarked on what was to become one of the largest, most successful collaborative relicensing processes ever undertaken at a hydroelectric project, for a new 50-year federal operating licence at the St Lawrence-Franklin D. Roosevelt power project in northern New York.
One of the outcomes of the relicensing collaborative, which led to the issuance of a new project licence in October 2003, was the development of 11 habitat improvement projects (HIPs) for fish and wildlife in the vicinity of the 800MW generating facility. NYPA committed US$11M to fund the HIPs.
The improvement projects included establishing spawning beds in the St Lawrence river for an ancient fish – lake sturgeon – which is listed as a threatened species in New York and other states. The largest remnant population of lake sturgeon in New York resides in the St. Lawrence River in the vicinity of the St. Lawrence-FDR project. One of the more critical factors limiting the restoration of lake sturgeon has been the lack of quality spawning habitat.
In October 2007, NYPA constructed two spawning beds after a systematic site selection process supported by detailed study of the river characteristics and sturgeon activity.
The results have been outstanding. Large numbers of sturgeon were attracted to the area and high levels of successful reproduction occurred within the first season after the beds were in place. The success of the endeavour was even more apparent in 2009, the second season, with video observations showing nearly a fourfold increase in the use of the beds by spawning sturgeon.
The power authority intends to pursue the same deliberative approach in installing additional sturgeon spawning beds in the St. Lawrence-FDR project area over the next few years.
General project description
In undertaking the lake sturgeon spawning beds project, NYPA was mindful of the mixed results experienced by others in conducting measures to encourage lake sturgeon natural reproduction. Recognising the importance of undertaking a carefully thought out, data-based approach, NYPA worked closely with representatives of the New York State Department of Environmental Conservation (DEC), the US Fish and Wildlife Service (USFWS), New York Rivers United, the St. Regis Mohawk Tribe and other stakeholders in the siting and design of the new spawning beds.
The DEC, in trying to restore the remnant population in New York, put great value on achieving this through natural reproduction. Improving lake sturgeon spawning opportunities was identified in NYPA’s collaborative relicensing process as an unmet need, and became one of the habitat improvement projects incorporated in the new St. Lawrence-FDR project licence. NYPA agreed to install a total of six sturgeon spawning beds under this HIP.
NYPA wanted to have a high probability of long-term success for the new beds. It was agreed that a phased approach would be taken, so that lessons learned from the first phase could be incorporated into later phases. The first phase would involve the siting and installation of two beds, and, if successful, the successive beds would follow, adapting this successful model. NYPA agreed to initiate a rigorous research programme to identify the optimal site location and characteristics for the beds.
In 2004 and 2005, NYPA conducted a comprehensive survey of the St. Lawrence-FDR project impoundment – Lake St. Lawrence – using both underwater video cameras and gill netting to determine where sturgeon were active during the spawning season. These surveys also included characterisation of the riverbed’s structure and substrate. The studies found few signs of sturgeon activity until they reached the Iroquois control dam, part of the generating project, at the upper reaches of Lake St. Lawrence on the St. Lawrence river in the town of Waddington.
Near the control dam, NYPA’s contractors observed and gill netted several sturgeon. All were males and many were in spawning condition. Further surveys looked for sturgeon eggs in the near vicinity of the dam. None were found. NYPA concluded that although the few sturgeon in the vicinity of the dam appeared ready to spawn, there was no apparent egg laying activity where it was considering installing the beds. This meant there were opportunities to provide effective spawning habitat, just upstream and downstream of the dam, without impacting any existing spawning activity.
Having established a general site location, NYPA set out to understand the specific site characteristics that would optimise long-term success. Many factors figure into whether an area is attractive to sturgeon as a spawning bed and whether the bed will stay attractive in the long term. Many fish species are very selective about the characteristics of the bottom material where they lay their eggs (the ‘structure’). Lake sturgeon prefer coarse rocky material with open interstitial spaces between the rocks. These open areas, below the surface of the rocky material, provide a refuge from predators.
Sturgeon also seek areas with high flow velocities to ensure water circulates around the eggs, keeping the bed free of sediment while providing well-oxygenated water. As sturgeon are very powerful swimmers, they can remain stationary on the bed while releasing eggs with very little effort.
In the past, some similar projects have addressed site characteristics issues qualitatively, with limited success. The power authority decided to try to improve the likelihood of success by addressing each site characteristics factor quantitatively and analytically.
NYPA carefully reviewed the scientific literature for insight on the importance of spawning bed depth. Staff found conflicting reports but concluded that lake sturgeon can successfully spawn in deeper waters.
Another more difficult characteristic to understand was the effect of water flow velocities in the areas being considered for the new beds. The St. Lawrence river is very narrow around Iroquois dam, making for high velocity currents. The flow velocities were high enough that, given appropriate designs, they should result in limited sedimentation. Data on flows, particularly at the level of detail needed for these purposes, were not available, so NYPA initiated a study of the areas of interest using an acoustic Doppler current profiler that produced high quality data on flow rates throughout the water column and with great detail near the bottom. With this information, NYPA was able to determine general areas that had optimal flow characteristics.
NYPA also reviewed the scientific literature for information on the optimum physical characteristics of the spawning substrate. Again, the message was mixed, with some studies demonstrating smooth cobble as preferable, while other studies observed that broken stone was satisfactory. NYPA selected a relatively uniform size of coarse crushed gravel in large part because sturgeon had been observed using similar material for spawning further upstream near an industrial water intake. The uniform size was selected because stone of similar size provides the greatest amount of open interstitial space. Also, NYPA hired a marine engineering firm (Baird Associates of Ottawa, Ontario) to research the optimal form or shape of the bed that would prevent sedimentation and eventual clogging of the beds.
Assimilating the information on depth, substrate and velocity, the power authority decided upon two locations for spawning beds. One of the sites, upstream of Iroquois dam, had slightly lower velocities, while the site downstream of the dam had very high velocities. NYPA reasoned that the high velocities at the downstream site should help to keep it free of sedimentation while the upstream bed should provide the more optimum velocity characteristics for spawning.
Next, NYPA faced the challenge of constructing the beds and more particularly the placement of the coarse gravel on target in an area of high currents (0.8-1.5m/sec). After considering several options, NYPA hired a local construction firm (J.E. Sheehan Contracting Corp from Potsdam, NY) that identified a bottom-opening hopper barge as the most practical means to place the bed material evenly in the identified areas.
By using global positioning system equipment to precisely locate the sites, it was possible to deposit multiple loads of the material so it was well distributed in the area selected. NYPA’s contractor then built a heavy steel rake by welding metal ‘teeth’ onto a heavy steel I-beam that could be lowered from a work boat with a small crane and dragged along the bed to level the piles of gravel deposited from the barge hoppers. Divers were used to inspect the beds and identify areas that needed to be further leveled or required additional gravel.
Will they come?
With the bed material in place in the fall of 2007, the next step was to see if the sturgeon would be receptive. In other words, we built it – now will they come?
Come they did. In spring 2008, another NYPA consultant (Environnement Illimite of Montreal, Quebec) conducted video monitoring of the two beds to check for the presence of fish. Though hopeful, NYPA was prepared for several years of study to determine if the beds were successful in attracting fish, whether spawning was taking place, and whether larvae were being successfully hatched. It turned out that was over-preparation.
On the very first day of video monitoring, numerous sturgeon were observed on and near the beds. Continued monitoring showed that their numbers gradually increased and then dramatically so. This sharp peak was believed to be the result of the dynamic of the males gathering slowly and then the females arriving in greater numbers as conditions (water temperature, in particular) became optimal for spawning.
After the sturgeon were observed, egg traps were put out and quickly confirmed the presence of sturgeon eggs. After an appropriate incubation period, drift ichthyoplankton nets were put out and the sampling confirmed that larvae had successfully hatched. Production levels approached those found at very productive natural spawning beds. The beds had succeeded in their first year of use.
The second season, in 2009, video monitoring alone was conducted on the spawning beds. The same pattern was observed, with many sturgeon being observed on and near the beds prior to the optimum spawning temperature. Then, as the optimum temperature was reached, there was again a substantial increase of sturgeon on the spawning beds. Based upon semi-quantitative estimates, using video monitoring, it was estimated that the number of sturgeon on the beds had increased almost fourfold, compared to 2008, to approximately 1000. Further, the video monitoring demonstrated that the beds remained sediment free.
Given that no sturgeon were spawning at these specific sites prior to the installation of the beds, this demonstrates that the sturgeon spawning habitat was likely limited, and that the installation of the beds provided the needed substrate to allow the species to naturally reproduce, thus contributing to its restoration.
The experience with the new spawning beds has been a remarkable success. It was unexpected that the sturgeon would accept the beds so quickly and completely. NYPA and its relicensing collaborators have opened a new door for the recovery of the lake sturgeon.
Dr Kevin McGrath, manager, environmental studies and remediation, New York Power Authority
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