Compilation of alewife (Alosa pseudoharengus) trap net catch in Rat Cove, Otsego Lake,

Transcription

1 Compilation of alewife (Alosa pseudoharengus) trap net catch in Rat Cove, Otsego Lake, Michael S. Gray 1 and John R. Foster 2 INTRODUCTION Trap netting in the eulittoral area of Rat Cove began in 1989 (Foster, 1989) following the discovery of an alewife (Alosa pseudoharengus) in the stomach of a lake trout (Salvelinus namaycush) by Rufus J. Thayer on 15 May 1988 (Foster, 1989). Foster (1989) proposed that private citizens carried out the illegal introduction sometime in 1986 or Trap netting has continued annually to document alewife (and other littoral fish) population trends in order to determine the impact of the illegal introduction on the limnology of Otsego Lake. Alewives are believed to have caused significant impacts on the ecology of Otsego Lake (Harman et al., 22). The dramatic decline in the cisco (Coregonus artedii) and lake whitefish (Coregonus clupeaforms) populations are thought to be the result of competition for large zooplankters and predation on pelagic larvae and fry by the alewife (Harman et al., 1997). Alewives are efficient, size-selective predators of zooplankton; consequently, they have effectively changed the zooplankton community in Otsego Lake from a community dominated by relatively large cladocerans (e.g. Daphnia pulex) to one dominated by smaller cladocerans (e.g. Bosmina coregoni) and rotifers (Harman et al. 22; Warner, 1999). This shift to a community comprised of smaller zooplankton has likely led to reduced grazing capacity (compared to large zooplankton) and decreased size of algal cells (Harman et al., 22; Warner, 1999), which has led to drastically reduced transparency. Furthermore, there has been an increase in areal hypolimnetic oxygen demand, (Albright 22) due to the oxygen demand of bacteria decomposing the algae. This likely limits the volume of water suitable for lake trout survival in the summer (Harman et al., 22; Albright, 21). Therefore, while the introduction of the alewife has dramatically improved lake trout growth (Harman et al., 1997) (and possibly abundance) because of an increased available forage base (Harman et al., 22), the concurrent decline in late summer and fall hypolimnetic oxygen concentrations may negatively impact them in the future. Centrarchid fishes (except the bluegill [Lepomis machrochirus]) have exhibited slower growth rates following the alewife introduction (Gray, 2). The goal of this manuscript is to provide a compilation of available alewife trap net catch for The intent is not necessarily to provide a syntheses or interpretation of those data. Provided are year-to-year fluctuations in alewife abundance, whether due to the normal cyclical nature of their populations (Smith, 1985) or to attempts to manage that population. This contribution will provide other researchers with information that will be useful in ongoing studies, which examine Otsego Lake ecology/alewife interactions. These studies may include lake trout egg and fry survival 1 SUNY Oneonta biology MA candidate. Biological Field Station, Cooperstown, NY. 2 Adjunct Assoc. Prof., SUNY Oneonta; Prof. and Director, Fisheries and Aquaculture, SUNY College of Agriculture and Technology, Cobleskill.

2 (Tibbits, in prep), walleye (Steizostedion vitreum) growth and survival (Cornwellin prep.) and alewife population dynamics (Warner et al. 23.). METHODS A 1.2 m trap net with a 15.2 m lead was fished on the north side of Rat Cove (Figure 1.), Otsego Lake, New York during the summers of 1989, 199, 1991, 1992, 1993, 1996, 1997, 1999, 2, 21, and 22 according to Hubert (1996). Trap netting did not occur in 1994, 1995, and The 1999 sampling regiment was not as intensive as most years. Table 1 provides an overview of the number of trap sets, by month, for the years for which data are available. Figure 1. Otsego Lake, NY, showing Rat Cove, the site of trap netting in

3 Year June July August Total NA NA NA NA 1995 NA NA NA NA NA NA NA NA Totals Table 1. Number of trap days (24 hours sets), by month, in Rat Cove, Otsego Lake, Trap net sampling typically began in early June and ceased in the beginning to middle of August. The trap was typically set on Monday mornings and pulled to collect fish every 24 h until Friday, when the net was pulled from the water until Monday. Each fish was identified, measured to the nearest millimeter (TL; total length) using a measuring board and weighed to the nearest gram using a spring scale. Fish scales were collected in some years for age determinations. All fish were then released back into the water, with the exception of alewives from Alewives captured in were brought back to the Biological Field Station for more accurate weighing, measuring and additional data collection (e.g. aging via otolith). Alewife catch per unit effort (CPUE) is defined as number of alewives caught per 24 hour set. For weekly CPUE, the total alewife catch for the week was divided by the number of sample days (24 h sets) for that week. For monthly CPUE, the total number of alewives caught during the month was divided by the total number of sampling days for that month. Summertime CPUE was calculated by dividing the entire alewife catch for the summer by the total number of sample days for that year.

4 RESULTS Table 2 provides the mean catch per unit effort (CPUE; per 24 hr set) of alewives on a monthly basis for each year for which data are available. Figure 2 summarizes the mean CPUE over the entire summers for which data are available. Figure 3 presents the same data, but on a monthly basis. Figures 4 through 14 provide mean CPUE on a weekly basis for the summers of 1989, 199, 1991, 1992, 1993, 1996, 1997, 1999, 2, 21 and 22, respectively. For these figures: 1= days 1-7, 2= days 8-14, 3= days 15-21, 4= days 22-28, 5= days Because the CPUE for 1989 is significantly lower than other years, the y scale for that graph is 1.2 CPUE. For Figures 5 through 14, it is 35 CPUE. The number of sets, number of alewives caught and the catch per unit effort over the study period are given in Appendices A-L. Year June July August Total NA NA Mean Table 2. Mean catch per unit effort (CPUE; per 24 hr set) of alewives in Rat Cove, Otsego Lake, by month,

5 Year Figure 2. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rate Cove, Otsego Lake, by summer, Year Figure 3. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rate Cove, Otsego Lake, by month, Figure 4. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of 1989.

6 Figure 5. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of Figure 6. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of Figure 7. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of 1992.

7 Figure 8. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of Figure 9. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of Figure 1. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of 1997.

8 Figure 11. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of st- June 2nd- June 3rd- June 4th- June 5th- June 2nd- July 3rd- July 4th- July 1st- August 2nd- August 3rd- August Figure 12. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of Figure 13. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of 21.

9 Figure 14. Mean alewife Catch Per Unit Effort (CPUE; per 24 hr set) in Rat Cove, Otsego Lake, by week, during the summer of 22. DISCUSSION The data presented here illustrate the cyclical nature of alewife abundance (Figure 2). The data show that the highest catch rates were observed in 1991and Based on length at age data from Warner et al. (23), the length of the fish caught in 1997 (mean =118 mm) suggests they were members of the 1996 year class. Alewives from these year classes were large likely large enough to minimize recruitment of subsequent year classes via cannibalistic predation on larval alewives and fry. Subsequent declines in catch rates could be attributable to the dominant year-classes being themselves declining in abundance due to predation by piscivores. When that year class declined to the point of being unable to limit recruitment from subsequent year classes, a new strong class emerged. Given the above, one would expect a resurgence in alewife abundance in 23, following the 22 decline. However, recent attempts to re-establish walleye in Otsego Lake may avert that resurgence. Walleye were stocked in 2-22 with the primary goal of reestablishing that population. Concurrent with stocking efforts are monitoring strategies designed to evaluate declines in alewife abundance, due to predation by walleye, as well as to document any lake-wide trophic changes that might result from declining alewife abundance (Cornwell, 2). A stable, low alewife trap catch in ensuing years would imply that increased predation afforded by walleye is successfully managing alewife numbers. REFERENCES Albright, M.F. 21. Otsego Lake limnological monitoring, 21. In 34 th Ann. Rept. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Cornwell, M.D. In prep. M.A. thesis. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta.

10 Cornwell, M.D. 2. Monitoring trophic changes following the reintroduction of walleye (Stizostedion vitreum) to Otsego Lake: and executive summary. In 33 rd Ann. Rept. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Foster, J.R Introduction of the Alewife (Alosa pseudoharengus) into Otsego Lake. In 22 nd Ann. Rept. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Gray, M.S. 2. Comparative age and growth of centrarchid fishes in Otsego Lake following the introduction of alewives. In 33 rd Ann. Rept. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Harman, W.N., M.F. Albright and D.M. Warner. 22. Trophic changes in Otsego Lake, NY following the introduction of the alewife (Alosa Pseudoharengus). Lake and Reserv. Manage. 18(3) Harman, W.N., L.P. Sohacki, M.F. Albright, and D.L. Rosen The state of Otsego Lake, Occas. Pap. No. 3. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Hubert, W.A Passive Capture Techniques. Pages In B.R. Murphy and D.Q. Qillis, eds. Fisheries Techniques, 2 nd edition. American Fisheries Society, Bethesda, Maryland. O Gorman, R., and C. P. Schneider Dynamics of alewives in Lake Ontario following a mass mortality. Transactions of the American Fisheries Society 117: Rhodes, R. J., D. A. Webb, and T. S. McCormish Cannibalism by the adult alewife (Alosa pseudoharengus) in southern Lake Michigan. Proceedings of the conference Great Lakes Research 17: Smith, C.L The inland fishes of New York State. New York State Department of Environmental Conservation. Albany, NY. Tibbits, W. In prep. M.A. thesis. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Warner, D.M Alewives in Otsego Lake, NY: a comparison of their direct and indirect mechanisms of impact on transparency and chlorophyll a. Occas. Pap. No. 32. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Warner, D.M., M. D. Cornwell, W. Tibbets, and M. Gray. 23. Alewife abundance,growth, and mortality in Otsego Lake In 35 th Ann. Rep. SUNY Oneonta Biol.Fld. Sta., SUNY Oneonta.

11 117 Appendix I3 Number of trap sets, alewives caught. and alewife (PUE by week, IYli'J- Number of sets Number of Alewives CPUE I I 3 3 I 4th-july 4 5th-july 3 I Appendix C. Number of trap sets, alewives caught, and alewife (rue by week, 199. ''J'JU- Number of sets Number of Alewives CPUE I ]27 3l I Appendix D. Number of trap sets, alewives caught, and alewife (rue by week, ]991. ]99]- Number of sets Number of Alewives CPUE

12 118 Appendi~ E Number of trap sets, alewives caught. and alewife CPUE by week, 19l)2, IYY1- Number of sets Number of Alewives CPUE 2nd-J une I".J.J " th-J une I nd-J uly , 3 \32 44, 4th-july , st-Au,gust _,.J.J.J "''"''''' I Appendix F, Number of trap sets, alewives caught, and alewife CrUE by week, 1993.!lJlJ3 Number of sets Number of Alewives CPUE I 4 4, 4 3, , ,75 2nd-Julv , , , ,5 3 I,333 Appendix G, Number of trap sets, alewives caught, and alewife CrUE by week, 1996 IlJlJ6- Number of sets Number of Alewives CPUE 4 1 2, , , , , , 4 8 2, 4 3 7,5 5th-july 2 4 2,5 4, 3rd-Au.gust 2,

13 119 Appendix fl Number of trap sets.,de\vives c,lllgill and alewife ('PUr-: by week. lcjcj7 11)1)7- Number of sets Number of Alewives CPUE Ist-Julv Appendix l. Number of trap sets, alewives caught, and alewife CPUE by week, /1)1)1) - Number of sets Number of Alewives CPUE I I Appendix J. Number of trap sets, alewives caught, and alewife CPUE by week, 2. 2(J(J(J- Number of sets Number of Alewives CPUE 2 22 I th-july \

14 12 Appendix 1(. NUlllbel' of trap sets, alewives caught. 'lild alev.ife CI'l)E by week, 2 I. 2/- Number of sets N1I mber of Alewives CPUE I nd-J uly I.25 I. 4 I rd-Au.gust 3. Appendix L. Number of trap sets. alewives caught. and alewife CPUE by week, Number of sets Number of Alewives CPUE ~J.J~ I.25 4th-july