2004 Ipswich River Herring Count by Ipswich River Watershed Association Kerry Mackin, Executive Director

Transcription

1 2004 Ipswich River Herring Count by Ipswich River Watershed Association Kerry Mackin, Executive Director Alewife (Alosa pseudoharengus) Blueback Herring (Alosa aestivalis) Illustrations Source: Kraft, C.E., D.M. Carlson, and S.C. Brown The On-line Fishes of New York State, Version 2.1. Department of Natural Resources, Cornell University, Ithaca, NY. Images: see Background

2 Since 1999, the Ipswich River Watershed Association (IRWA) has organized annual herring counts, which take place each spring at the fish ladder at the Ipswich Dam in downtown Ipswich. The purpose of the annual count is to document the conditions under which river herring (Alosa pseudoharengus or alewife, and Alosa aestivalis or blueback herring) migrate into the Ipswich River and their ability to utilize the fish ladder that was constructed at the Ipswich Dam in While the counts have not focused on accurate estimates of the numbers of returning herring, IRWA has developed an estimation method to compare returning populations for the six years that the count has now taken place, as explained further on page 3. IRWA s current fish count objectives are to: 1. Create public awareness and stewardship for the herring run. 2. Document the presence of the herring run and relate counts to temporal and environmental factors. 3. Produce reliable and comparable estimate of Ipswich River herring run passing at the dam. River herring River herring are very important to the ecology of coastal rivers such as the Ipswich River, and also to the marine fisheries, where they are an essential part of the food web. These herring are anadromous fishes; that is, they spawn and hatch in freshwater, migrate as juveniles out of their natal river to marine waters, where they grow to maturity over a period of several years, and then return to spawn in their watershed or origin. Alewife and blueback herring are closely related species which are similar biologically and function in a similar role in the ecosystem. One of the distinguishing characteristics between these species is that blueback herring typically spawn in flowing waters of the river channel, whereas alewife spawn in stiller waters, typically in ponds and lakes. Alewife tend to migrate and spawn earlier in cooler waters, typically beginning in mid-april in this region, whereas blueback herring tend to migrate several weeks later, typically from late April into early June. Historically the Ipswich River supported a robust population of alewife (Alosa pseudoharengus). For centuries, alewife was an economically important fish and helped to shape the culture of this region from pre-colonial times until the early 1800 s (Belding, 1921). Since then, a combination of factors has greatly diminished the population of herring in the Ipswich River. While colonial fish weirs were required to allow fish passage, larger dams constructed in the 1800 s obstructed the annual spawning run of river herring and other anadromous species. While the dams were later fitted with fish ladders to allow fish migration at the Ipswich and Willowdale Dams, the ladders proved ineffective. Other factors which have also impacted river herring populations include the transformation of historic alewife spawning lakes and ponds, such as Wenham Lake, into water supply reservoirs; and chronic low-flow and no-flow periods caused by water supply withdrawals and other flow alterations impair the herrings habitat and decimate juvenile and returning populations. As a result of these factors, the population of river herring was virtually extirpated. Herring Restoration Project Since about 1990, a broad coalition of governmental and non-governmental organizations has worked to restore the Ipswich River herring fishery. This effort began with habitat survey work documenting the presence of suitable spawning habitat for blueback herring in the mainstem of the river. Blueback herring were selected as the primary restoration species to avoid potential conflicts in trying to restore alewife to their natural habitats, which include ponds and lakes now managed as water supply reservoirs. The next priority was reconstruction of the Ipswich Dam s fish ladder, the first obstruction to fish passage located about 3 miles upstream of the river s mouth. Subsequently, the focus has been to restock the fishery by harvesting adult herring (primarily blueback herring, but including some alewife) migrating into the Charles River, which has a healthy herring population, and transporting them in specially outfitted trucks to the Ipswich River. Restocking with adult, spawning herring had taken place annually since the late 1990 s, but was temporarily discontinued in 2004 pending further evaluation of the restoration effort. Ipswich River Herring Count, 2004 Report 2

3 Notably, blueback herring have been observed spawning in the area downstream of the lowest dams in many rivers. This spawning takes place every year in the Ipswich, though assessments of this activity are currently beyond the scope of the Ipswich River fish count project. Fish Count Method and Results Annual counts of the spring herring run are used to determine if restoration efforts are beginning to establish a reproducing population in the Ipswich River. Trained volunteers perform counts in two successive five-minute intervals. The counts begin in early-mid April, and continue 1-2 months. In 2004, the Herring Count began on April 14 and continued until June 15, a total of 175 counts over 63 days, or about 2.78 counts per day. IRWA s count does not have coverage for every hour of every day; in fact, the total minutes counted over the course of the Herring Count was only about 3% of the time when fish would likely be migrating. In rivers with robust spawning runs, the two five-minute intervals per hour can reliably be used to estimate total numbers of returning herring. However, on the Ipswich River, the herring migration is very sporadic, making the count method less effective for population estimates, because there is little continuity for extrapolations on which the estimates are based. This factor, combined with a limited number of counts, means that there would be a large margin of error in any estimate of total numbers. Thus the Ipswich River counts are primarily intended to provide a sampling program to tell us if, when, and under what conditions herring are migrating up the Ipswich River. However, IRWA recognizes that the data present a basis to estimate returning populations, with the understanding that this estimate has a significant margin of error. We have evaluated the number of fish returning based the number of fish seen per count, and evaluated population based on the percent of time that counts actually took place, as a percentage of the total 15-hour day over the period of the count. Based on this method, we estimate that the returning population has varied from hundreds in , to a little over 2000 in The estimated population returning in 2003 was approximately 1000, and in 2004 it was 1782 based on this estimation method. Data from the fish count, are shown in Table Total number of fish Total number of counts Days of fish count average counts per day average fish per day of count average fish per count counts as percent of total time 3.1% 4.1% 3.2% 3.7% 8.2% 7.2% estimated fish (full period extrapolation) Table 1: Number of fish observed, counts, days and counts as a percent of total fish count, and estimated returning population, ; based on a 15-hour daily counting period. Table 1 indicates that in 2004, there were significantly fewer counts than in the years from The percent of time fish counting was occurring, as a percent of the total period of the fish count, was comparable in , but about half or less of the percent of total time for The counts took place over a shorter period than the later counts, but had more counts per day. Thus fish passing up the ladder in each day of the count were more likely to be observed, whereas in the later years it is more likely that a significant number of fish passed up the ladder without being observed, due to the less intensive coverage. This may suggest that there was an increase in the total number of fish migrating from , as compared to Ipswich River Herring Count, 2004 Report 3

4 2004 Herring Count Evaluation In 2004, 175 counts were conducted between April 14 and June 15, and 55 river herring were observed migrating up the fish ladder. Figure 1 shows the number of herring seen and the number of counts performed per day during the 2004 fish count. The graph indicates that most herring passed the fish ladder between mid-april and mid-may, with a definite peak from May 3-5th. Very few herring were seen after May 15 th. May 3 rd was the day when most fish were observed (14). Fish were observed during 5 of the 6 counts that day, ranging from 7 a.m. to 7 p.m. The next day, 8 fish were observed during 2 of the 4 counts that day; and the following day 6 fish were observed in 2 of 2 counts that day /14/2004 4/16/2004 4/18/2004 4/20/2004 4/22/2004 4/24/2004 4/26/2004 4/28/2004 4/30/2004 5/2/2004 5/4/2004 5/6/2004 5/8/2004 5/10/2004 5/12/2004 5/14/2004 5/16/2004 5/18/2004 5/20/2004 5/22/2004 5/24/2004 5/26/2004 5/28/2004 5/30/2004 6/1/2004 6/3/2004 6/5/2004 6/7/2004 6/9/2004 6/11/2004 6/13/2004 6/15/2004 Figure 1. Number of Herring Seen versus Number of Counts Taken Daily, Volunteer counts were not distributed evenly on a daily basis nor over the course of the count. The observation of fish migrating on the second day of the count suggests that some fish migration may have occurred prior to the onset of the count, and that beginning the count earlier in April may be advisable. Temperature is a factor in triggering the spawning runs (see below), and may be used in the future to determine the best time to begin the count. The variability in the number of counts per day (from zero to six) is not closely correlated with the variability in the number of fish observed (from zero to 14) in a single day. This suggests that higher fish numbers observed are due to more fish migrating on particular days, rather than because there were more counts done on that day. However, as noted below, the more counts that occur in a particular time period, generally the more fish are observed. IRWA has concluded that the sporadic nature of the herring run, combined with somewhat inconsistent coverage, results in a high likelihood that small pulses of migrating fish (which are typical on the Ipswich) would easily be missed. Different methods of counting are being considered to use for future counts to estimate the spawning population. fish counted number of counts Figure 2 shows the number of counts and number of fish seen during specific hours. Counts were performed throughout the day from 6 am to 9 pm (though this year, no counts actually occurred after the 7-8 pm hour). The majority of counts occurred between 9-10 am and in the afternoon and early evening. Approximately 9% of the herring were seen between 9-10 am (the same number as seen between 7-8 am despite many fewer counts at the earlier hour). 64% of fish seen were counted between the hours of 3 pm and 7 pm, which is also the period with the most counts: about 44%. For the Ipswich River Herring Count, 2004 Report 4

5 most part, the more counts that occurred in a time period, the more fish were observed. Similarly, the limited number of counts made from 2-3 pm likely restricted the number of fish seen ascending the ladder during that time period Total fish Total counts Figure 2: Number of counts and fish observed during each hour over the period of the count. Figure 3 below shows the percent of the total fish seen that were observed per hour over the course of the count, as compared to the percent of all the counts that occurred in each hour period. This indicates again that in general, the more counts that occurred during a particular hour, the more fish were seen. For the most part, hours with minimal coverage resulted in few or no fish observations. 30.0% 25.0% 20.0% 15.0% %fish %counts 10.0% 5.0% 0.0% Figure 3: Percent of total fish and percent of total counts per hour over the period of the count. Temperature: In 2004 Brad Chase of the Massachusetts Division of Marine Fisheries installed a temperature datalogger in the Ipswich River. Those data were used to determine what the water temperature was during the counts when fish were observed, as shown in Figure 4. Small numbers of herring were observed when water temperatures were 9 C 12 C. Most fishes were observed when temperatures were 14 C 20 C. No herring were observed in waters colder than 9 C nor warmer than 21 C. This generally corresponds to data obtained in other years. Ipswich River Herring Count, 2004 Report 5

6 Herring vs Temperature Herring counted <9C 9C-9.99C 10C-10.99C 11C-11.99C 12C-12.99C 13C-13.99C 14C-14.99C 15C-15.99C 16C-16.99C 17C-17.99C Temperature (Celsius) 18C-18.99C 19C-19.99C 20C-20.99C >21C herring Comparisons with other years: IRWA has now collected herring run data for 6 years. Our observations indicate that: The herring run typically begins between April 9-15 and peaks from the last few days of April through mid-may. Typically there are few fish observed after mid-may, though it is not unusual to observe some fish migrating during the last few days of May into early June. Herring have not been observed in any year of the count when water temperatures were below 8 C. The largest numbers have been observed when temperatures were between 14 C and 20C. IRWA has developed a method of estimating total fish passage during the counting period, using extrapolations based on the amount of time that fish are actually being counted as a percentage of the total time of the fish count. This method is primarily being used to allow IRWA to compare the years of the Ipswich River fish count, to help determine whether any population trends can be observed. Using this method, we estimate that the total number of herring passing up the ladder in 2004 was This represents an increase over the returning herring estimated in 2003 (approximately ) and is less than the estimated return for See Table 1 for herring count data and estimates. Conclusions A few general conclusions can be made based on the 2004 data and the data from the period. The fish ladder at the Ipswich Dam does function to allow fish passage, and there is some return of river herring each year. The highest numbers typically occur in late April to mid-may. In some years, there appears to be a small pulse of herring that occurs in early to mid April, followed by a larger pulse in early May. This may suggest that the earlier pulse consists of alewife and the later run may be dominated by blueback herring; however, further investigation is needed to test this assumption. The total number of fish observed returning has been less than 100 each year of the count. However, from , the count only provided coverage for about 3% of the total counting time during the migration period. This limited coverage, combined with the sporadic nature of the Ipswich River herring run, makes it difficult to estimate the spawning population. Different methods of extrapolation indicate that the total run in was in the hundreds, and that the returning population increased in Ipswich River Herring Count, 2004 Report 6

7 02, perhaps numbering herring. In 2003 the numbers dropped to less than half this estimate, and rebounded in Overall, the returning population appears to range from hundreds to low thousands, recognizing that the margin of error for these estimates is high. IRWA is currently working with the Massachusetts Division of Marine Fisheries and other NGO s to improve our understanding of the herring run in northeastern Massachusetts. In 2004, DMF installed a continuous temperature data logger at the Ipswich Dam. Consideration is being given to the use of other approaches to the count, including conducting intensive coverage for certain days of the herring run period, as well as automated counting methods. Another goal for the next year is to identify which species (alewife or blueback herring) is migrating at what time, to better assess the effectiveness of the restocking efforts and whether the herring observed may be remnants of the historical alewife fishery or fishes native to nearby drainages, such as the Parker River or Alewife Brook. IRWA and other organizations also wish to evaluate suitable approaches to improving fish passage, including dam removal, fish ladder improvements, bypass channels or rock ramps. IRWA is also committed to achieving flow augmentation during low-flow periods, which may improve survival rates of juvenile and outmigrating fishes in the summer and fall, and supports annual restocking events to maximize the potential rehabilitation of the Ipswich River s herring populations. Additional comments: The relatively small number of herring, the small pulses of fish that occur intermittently, and the gaps in coverage during the fish count make it difficult to reliably estimate the number of returning herring. They also make it difficult to recruit and continually engage volunteers. In 2004 a retaining wall just downstream of the fish ladder collapsed shortly before the fish count began, and work on a pedestrian footbridge was occurring during the count. Whether these factors had any effect on the herring run is unknown. Volunteers truly enjoy seeing herring, and usually begin the count with a high level of motivation. The first sighting of herring typically spurs an increase in counts. After the peak period in early May, counts taper off in regularity as the season progresses. Poor weather, poor visibility and other commitments sometimes affect the number of counts performed. The small numbers of fish, along with visibility problems at the counting area that tend to worsen from mid-may onward, make it difficult to continually interest the fish count volunteers. Typically the number of counts falls off after mid-may. Notably in 2004, Peg Lawrence of IRWA was successful in keeping the counting board relatively clean, which improved visibility markedly over the experience of when visibility was extremely poor from mid-may onward. Due to funding cuts and lack of staff, the 2004 Herring Count was organized by volunteers, primarily Kate Taylor. IRWA s Office Manager, Cathy Chadwick, handled much of the program coordination. Despite these limitations, there was a high number of volunteers (54) in 2004, for which IRWA is very grateful. In the future, we hope that a herring counting programs will become sustainable and will evolve to use video technology and become annual counts on the size of these herring runs. Acknowledgements: IRWA would like to thank all of its dedicated volunteers who made the 2004 Herring Count possible. This project would not have occurred in 2004, due to the lack of funding to support staff coordination of Ipswich River Herring Count, 2004 Report 7

8 the count. However, thanks to the efforts of Kate Taylor, Cathy Chadwick, Peg Lawrence and our volunteers, IRWA was able to collect data again in Thanks also to the individuals, businesses and organizations which sponsored the Ipswich River herring count: The Gaffney Foundation, Danvers Fish and Game Club, Ipswich Bay Striped Bass Fly Fishing Derby, Ipswich Shellfish Market, Robert V. Brophy and Benjamin B. Morrill. We appreciate the assistance of the Massachusetts Division of Marine Fisheries, Massachusetts Riverways Program, National Marine Fisheries Service, The Trustees of Reservations, Essex County Greenbelt Association and Massachusetts Audubon Society, which are part of the larger effort to restore the Ipswich River herring run. Finally, thanks to Brad Chase of the Massachusetts Division of Marine Fisheries, who installed a temperature data logger in the Ipswich River and advised IRWA regarding technical issues and data analysis, and to Rob Stevenson of the University of Massachusetts for his advice. For further information or to volunteer for future counts, please contact IRWA at irwainfo@ipswichriver.org, or download our volunteer application at Volunteers do not need any prior experience to participate. References Belding, D. L A report on the alewife fisheries of Massachusetts. Marine Fish. Ser. No. 1. Massachusetts Division of Fish and Game. 135 pp. Bigelow, H., and Schroeder, W. C Fishes of the Gulf of Maine. Fishery Bulletin of the Fish and Wildlife Service. Vol. 53, pp Washington, D.C. Field, G. W Alewife fishery of Massachusetts. Transactions of the American Fisheries Society 43: Lantagne, Daniele, and Kate Morkeski Freshwater Fish: A Guide to the Fishes of the Ipswich River. pp Kraft, C.E., D.M. Carlson, and S.C. Brown The On-line Fishes of New York State, Version 2.1. Department of Natural Resources, Cornell University, Ithaca, NY. Kerry Mackin, Executive Director Ipswich River Watershed Association 460 Boston Street, Topsfield, MA Mail: PO Box 576, Ipswich, MA This and other reports are available online at See the Biomonitoring section for the Herring Count reports. Ipswich River Herring Count, 2004 Report 8